environmental assessment of coastal sand mining using proposed criteria: a case of hai phong do thi thu huong 1, do gia khanh 2,3 , nguyen van thao 1 and tran dinh lan 1,3* 1 institute of marine environment and resources/vast 2 hai phong department of agriculture and rural development 3 graduate university of science and technology/vast corresponding author: tran dinh lan 1 institute of marine environment and resources/vast, hai phong, vietnam 3 graduate university of science and technology/vast, hanoi, vietnam email: lantd@imer.vast.vn a brief description of the novelty and importance of the findings coastal sand mining in hai phong port city causing serious environmental problems that were not quantitively assessed has threatened the sustainable development goals of the city. ten proposed criteria belonging to three sustainable development pillars were applied to evaluate quantitively the impacts of sand mining activities on the environment in the study area. study results show quantitively the negative environmental impact levels from moderate to high. high negative impacts occurred in the areas with economic activities, benthic biodiversity, and coastal ecosystems. moderate impacts were on other subjects and the whole study area. the study results support managers and planners in the sustainable development planning and management of the city with the biosphere reserve of cat ba and of the surrounding region, particularly the unesco ha long bay heritage site. declaration: there is no conflict of interest. informed consent: written consent was obtained from all participants prior to the study. contributorship: tran dinh lan conducted the study and wrote this paper. do thi thu huong developed and analyzed multi-criteria and maps. do gia khanh collected data and satistical analysis of socio-economic data. nguyen van thao analyzed physical and environmental data. acknowledgment. the authors gratefully acknowledge the support of the senior research fellow, vietnam academy of science and technology, code nvcc23.01/22-23. other issues: not applicable 55 sustainable marine structures | volume 04 | issue 02 | july 2022 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2022 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). doi: http://dx.doi.org/10.36956/sms.v4i2.669 *corresponding author: chandrasekaran srinivasan, madras institute of technology, india; email: drsekaran@iitm.ac.in editorial marine structures under special loads chandrasekaran srinivasan* madras institute of technology, india article info article history received: 15 august 2022 accepted: 25 august 2022 published online: 20 september 2022 environmental loads that act on marine structures are highly non-deterministic in general. estimating these loads is a basic requirement for their structural design, but their response is far beyond just counteracting the loads [1,2]. the marine environment poses more challenges starting from the choice of material, structural form, design methods, construction techniques, inspection methods, repair, and retrofitting. furthermore, strength degradation and service life decrement are complex to estimate as they pose a non-proportional response to age and material use. special loads such as fire, impact, blast, and loads that arise from marine growth need a special revisit. as the conventional design codes are silent about the recommendations for such special loads, design engineers satisfy the special requirements based on their domain expertise and experience. corrosion is one of the major threats to the structural members of the marine environment. x52 steel, one of the most-preferred candidates for steel members, also faces explicit challenges under this corrosive environment. functionally graded materials (fgm), one of the recent advancements in material science, is seen as an effective alternative to counteract the challenges imposed by the marine environment. but, due to the limited knowledge of fgm and its manufacturing techniques, marine engineers cannot take the way out of using conventional marine steel. apart from a very high-cost factor, relative disadvantages possessed by x52 steel in the marine environment are grossly ignored for want of no alternative. marine structures built for coastal protection should possess high reserve strength and long service life. not because they are strategically important, but because they cannot often be structurally intervened for repair. furthermore, repair of marine structures like jetties, dry docks, and breakwaters is generally carried out while they are in service. it is obvious that repairing structural members who face strength degradation is quite challenging 56 sustainable marine structures | volume 04 | issue 02 | july 2022 when they are in service [3]. capacity reduction without any incremental decrease in the encountered loads places marine structures under a special category of repair and retrofitting. invasive methods such as pressure grouting, crack filling with chemical admixtures, and waterproofing treatments are only cosmetic and shall not help restore the strength of structural members; but, even such methods of repair are directed by the chemical admixture manufacturers, which fall in the domain of non-engineering practices. inviting papers from academia, practicing engineers, and researchers addressing the above concerns aims to enlighten readers about robust design practices and repair techniques. we believe that the papers, though few, shall help the readers understand the focussed complexities faced by marine structures. on behalf of the journal’s editorial board, i sincerely thank the authors for contributing original papers to this journal. i shall expect a few more contributions from academia in the future. conflict of interest there is no conflict of interest. references [1] chandrasekaran, s., jain, a.k., shafiq, n., et al., 2021. design aids for offshore platforms under special loads, crc press, florida. pp. 280. [2] chandrasekaran, s., 2020. design of marine risers with functionally graded materials, woodhead publishing, elsevier. pp. 200. [3] liu, h.j., li, h.n., fu, x., 2021. wind-resistant performance and failure modes for a semi-submersible offshore platform during jacking closure. ocean engineering. doi: https://doi.org/10.1016/j.oceaneng.2021.110102 11 sustainable marine structures | volume 05 | issue 01 | march 2023 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2023 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). doi: http://dx.doi.org/10.36956/sms.v5i1.822 *corresponding author: eugen rusu, department of mechanical engineering, “dunarea de jos” university of galati, 800008, romania; email: erusu@ugal.ro editorial harvesting offshore renewable energy an important challenge for the european coastal environment eugen rusu* department of mechanical engineering, “dunarea de jos” university of galati, 800008, romania article info article history received: 1 march 2023 accepted: 6 march 2023 published online: 8 march 2023 in the last decades significant changes in the climate are noticed and it becomes obvious that these dynamics are strongly influenced by recent human development. from this perspective, there is an increasing concern regarding the possible evolution of the climate and various possible scenarios have been designed and analysed. thus, in 2014 the intergovernmental panel on climate change (ipcc) adopted the fifth assessment report, where the concept of representative concentration pathway (rcp) was introduced for climate modelling. this is a greenhouse gas concentration trajectory labelled after the expected values of the radiative forcing by the end of 2100. however, the last years’ climate developments showed that even the worst scenarios can be exceeded by reality, and various chain effects may occur having locally much more significant impacts than those indicated by the rcp scenarios. under such circumstances, it becomes obvious that the rcp approach should be completed somehow, and that is why a new and more complex concept has been defined in 2021, in the context of the sixth assessment report of ipcc. this is called the shared socioeconomic pathway (ssp) and provides a holistic picture of climate change in the general context of society development. a real race started for decarbonisation and to follow the green road in a more consistent way. almost threequarters of the greenhouse emissions are generated by the energy sector, while there is worldwide an increasing 12 sustainable marine structures | volume 05 | issue 01 | march 2023 energy demand [1]. from this perspective, it becomes clear for many responsible factors all over the world that rapid and effective measures have to be taken in replacing conventional energy sources based on fossil-fuelled with green energy. following this trend, the european union (eu) adopted 2019 the european green deal (egd), which draws the most significant directions to be taken by the eu for rapid and effective decarbonisation of the energy sector [2]. while the land is almost saturated as regards renewable energy extraction, there are large spaces in the marine environment and it is available a huge green energy potential. from this perspective, special attention is paid to offshore renewable energy (ore). while offshore energy is used to refer to all sources of energy that can be extracted from the ocean, including both renewable sources and fossil-based (for example gas and oil), ore refers only to the sources of renewable energy that can be extracted from the marine environment. this includes wind, waves, tides, currents, thermal and salinity gradients, floating solar panels and algae-based biofuels. ocean energy (oe) includes waves, tides and currents, and thermal and salinity. according to egd, very ambitious ore targets are established for 2050. this implies for offshore wind (ow) an installed capacity of 300 gw, a 25 times enhancement in relationship with 2021. the eu target for oe is 40 gw, and since the basis is quite low (13 mw), this means a more than 3000 times enhancement in relationship with 2021. such very challenging targets for a 30-year time window imply both large geographical extensions as well as significant technological advances. some considerations concerning the existent resources and the expected future renewable energy potential in the european coastal environment will be presented next, highlighting also the environmental and technological challenges that have to be faced in the harsh marine environment in the context of climate change. the northern seas of europe, the baltic and north seas, represent already reliable ore sources with almost 60 wind farms operating there. actually, the baltic sea is the pioneer in its relationship with offshore renewable energy extraction, since denmark installed there in 1991 the first offshore wind farm in the world. baltic sea has a significant wind power potential and the climate scenarios indicate a slight enhancement in the near future of the average wind energy. the most significant wind power potential is noticed in the north sea, where average wind power values higher than 1000 w/m2 are characteristic of large geographical spaces [3]. furthermore, the climate scenarios indicate that a significant enhancement of wind power is expected in the future with the tendency of the energy peak to move from the north-eastern to the northwestern side of the sea. a very resourceful marine area is represented by the western european coastal environment, where some tidal power plants are already operational and others are currently at the proposal stage together with power plants based on salinity gradients. in this western side of the continent, the iberian coastal environment represents a significant nearshore from the point of view of ore potential and of the resources’ complementary [4]. this includes wind, wave, tide, and offshore solar energy. an area with high unexploited potential from the ore point of view is represented by the mediterranean sea, where the first offshore wind farm project became operational in 2022. several studies [5] indicate hot spots, from the point of view of the wind energy potential, large geographical spaces from the mediterranean sea, such as the gulf of lion, the aegean sea and the southeast of the iberian nearshore, where average wind power densities higher than 800 w/m2 are characteristic. furthermore, the climate projections indicate that in these areas the average wind and solar power is not expected to decrease. as regards the black sea, its western side is more energetic and it has very similar characteristics to the mediterranean sea. although harvesting wind energy is based on mature technologies, there are still expected significant advances. the largest wind turbine in the world, with a rated power of 16 mw, is expected to become fully operational in 2026, and further on the race to the 20 mw wind turbines seems to face no significant obstacle. an emerging technology is related to floating solar panels, which are expected to have a very rapid development in the near future and this development will require significant challenges from the point of view of developing sustainable marine structures. conflict of interest there is no conflict of interest. references [1] ostergaard, p.a., duic, n., noorollahi, y., et al., 13 sustainable marine structures | volume 05 | issue 01 | march 2023 2020. sustainable development using renewable energy technology. renewable energy. 146, 2430-2437. [2] a european green deal, 2019. [internet] [cited 2022 sep 8]. available from: https://ec.europa.eu/info/ strategy/priorities-2019-2024/european-green-deal_ en. [3] rusu, e., 2022, assessment of the wind power dynamics in the north sea under climate change conditions. renewable energy. 196, 466-475. [4] onea, f., rusu, e., 2022. an evaluation of marine renewable energy resources complementarity in the portuguese nearshore. journal of marine science and engineering. 10, 1901. doi: https://doi.org/10.3390/jmse10121901 [5] rusu, e., rusu, l., 2019. evaluation of the wind power potential in the european nearshore of the mediterranean sea. e3s web of conferences. 103, 01003. 13 sustainable marine structures | volume 04 | issue 01 | january 2022 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2022 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). doi: http://dx.doi.org/10.36956/sms.v4i1.475 *corresponding author: erkan oterkus, peridynamics research centre, department of naval architecture, ocean and marine engineering, university of strathclyde, glasgow, united kingdom; email: erkan.oterkus@strath.ac.uk review applications of peridynamics in marine structures erkan oterkus* peridynamics research centre, department of naval architecture, ocean and marine engineering, university of strathclyde, glasgow, united kingdom article info article history received: 30 december 2021 accepted: 31 december 2021 published online: 10 january 2022 marine environment is a harsh and challenging environment for both operators and analysers due to extreme weather conditions. as a result of these conditions, marine structures are subjected to extreme and/or cyclic loadings. this will then lead to various different damage modes including corrosion and fatigue. such damage modes are major threats to the reliability and integrity of marine structures which can cause risk on human and environmental safety, and yield financial losses. moreover, climate change is a major concern which requires urgent attention. in order to minimize the negative effects of climate change, energy transition from utilisation of fossil fuels to greener energy solutions, such as offshore wind, should be adapted. there is currently a rapid progress on investment on green technologies especially offshore wind energy generation. another emerging area is hydrogen which is considered as the environmentally friendly fuel of the future. there are various ways to produce hydrogen which are classified as grey, blue and green hydrogen production. since co2 is also produced as part of the grey and blue hydrogen production, green hydrogen becomes the most environmentally friendly option. to produce green hydrogen, energy produced by offshore wind turbines can be utilised. a potential challenge of this approach is how to transport hydrogen to onshore. utilisation of offshore pipelines can be an economical option. in addition, if there is already an existing infrastructure available for oil & gas applications, this can be even much preferable option without any need to install a new pipeline system. however, this requires extra care since these pipelines were not originally designed to transport hydrogen. 14 sustainable marine structures | volume 04 | issue 01 | january 2022 hydrogen can cause embrittlement problem, known as hydrogen embrittlement, especially for metallic structures and can cause cracking for loads much smaller than the design loads. in order to minimize all the risks associated with the harsh marine environment and energy transition process, advanced computational methodologies should be utilised such as peridynamics as part of the analysis process. peridynamics [1-4] is a new computational methodology which is especially suitable for failure analysis of materials and structures. peridynamic equations are in the form of integro-differential equations and do not contain any spatial derivatives. therefore, these equations are always valid regardless of discontinuities such as cracks. definition of failure is pretty straightforward, and it is possible to analyse any number of cracks since cracks are not treated as special objects. there are many application areas for peridynamics to be utilised in maritime field. one potential area is to use peridynamics for the analysis of ice-structure interactions [5-8]. there is currently an interest to use northern sea route to ship products from far east to europe since this route is much shorter than the current route. however, icestructure interaction is a major concern since ships should be designed by considering potential impact of ice pieces on ship hull which can cause significant damage to the ship hull as in the titanic accident in the past. another important application of peridynamics is modelling the influence of underwater explosions on submarines or naval vessels. if an underwater explosion takes place, a shock wave is generated and this can cause significant damage to the structure. predicting damage due to shock loading, especially if the structure is made from composite material, is challenging. although composite materials have several advantages with respect to traditional metals, their failure behaviour is complex since different damage scenarios can occur including fibre breakage, matrix cracking, fibre-matrix splitting and delamination. peridynamics is capable of accurately predicting these failure modes in structures subjected to different loading conditions including shock loading [9-11]. another important application of peridynamics in marine structures is corrosion damage modelling. there are different corrosion mechanisms which can occur in structures due to material type, environment, and loading. one of the common corrosion damage mechanisms is pitting corrosion which creates localised damage in the structures. pitting corrosion damage areas can act as stress raisers and cracks can initiate and propagate from these locations. from modelling point of view, this requires multiphysics and multiscale analyses to simulate coupled diffusion and mechanical fields by considering the microstructure which can be done in a single peridynamic framework [12,13]. moreover, peridynamics can also simulate hydrogen embrittlement phenomenon as a stress corrosion cracking mechanism [14]. fatigue is also an important damage mode in marine structures. s-n curve and paris law are common approaches which are utilised for fatigue analysis of marine structures. fatigue damage is a complex process with three phases including fatigue initiation, fatigue crack propagation and final failure. s-n curve is capable to represent fatigue initiation and can provide fatigue life. however, it cannot predict how the fatigue damage evolves. paris law approach can predict how a fatigue crack can grow. however, it is not capable to predict fatigue initiation and final failure phases. as an alternative approach, peridynamics is capable of representing all three phases of fatigue damage [15-18] and can serve as a less conservative tool for the design and analysis of marine structures. finally, peridynamics can also be used for failure analysis of energy storage devices such as marine batteries [19] and fuel cells [20]. such devices will serve an important role to reduce carbon emissions in future ships and make significant contributions to reach net zero targets. as a final note, peridynamics, as a new and emerging computational methodology, can be a suitable and alternative computational tool for failure analysis of problems relevant to marine structures applications. references [1] silling, s.a., 2000. reformulation of elasticity theory for discontinuities and long-range forces. journal of the mechanics and physics of solids. 48(1), 175209. [2] silling, s.a., askari, e., 2005. a meshfree method based on the peridynamic model of solid mechanics. computers & structures. 83(17-18), 1526-1535. [3] silling, s.a., epton, m., weckner, o., xu, j., askari, e., 2007. peridynamic states and constitutive modeling. journal of elasticity. 88(2), 151-184. [4] madenci, e., oterkus, e., 2014. peridynamic theory and its applications. springer, new york, ny. [5] vazic, b., oterkus, e., oterkus, s., 2020. in-plane and out-of plane failure of an ice sheet using peridynamics. journal of mechanics. 36(2), 265-271. [6] lu, w., li, m., vazic, b., oterkus, s., oterkus, e., wang, q., 2020. peridynamic modelling of fracture in polycrystalline ice. journal of mechanics. 36(2), 223-234. [7] vazic, b., oterkus, e., oterkus, s., 2020. peridynam15 sustainable marine structures | volume 04 | issue 01 | january 2022 ic model for a mindlin plate resting on a winkler elastic foundation. journal of peridynamics and nonlocal modeling. pp. 1-10. [8] liu, m., wang, q., lu, w., 2017. peridynamic simulation of brittle-ice crushed by a vertical structure. international journal of naval architecture and ocean engineering. 9(2), 209-218. [9] diyaroglu, c., oterkus, e., madenci, e., rabczuk, t., siddiq, a., 2016. peridynamic modeling of composite laminates under explosive loading. composite structures. 144, 14-23. [10] oterkus, e., madenci, e., 2012. peridynamic analysis of fiber-reinforced composite materials. journal of mechanics of materials and structures. 7(1), 45-84. [11] kilic, b., agwai, a., madenci, e., 2009. peridynamic theory for progressive damage prediction in center-cracked composite laminates. composite structures. 90(2), 141-151. [12] de meo, d., oterkus, e., 2017. finite element implementation of a peridynamic pitting corrosion damage model. ocean engineering. 135, 76-83. [13] de meo, d., russo, l., oterkus, e., 2017. modeling of the onset, propagation, and interaction of multiple cracks generated from corrosion pits by using peridynamics. journal of engineering materials and technology. 139(4), 041001. [14] de meo, d., diyaroglu, c., zhu, n., oterkus, e., siddiq, m.a., 2016. modelling of stress-corrosion cracking by using peridynamics. international journal of hydrogen energy. 41(15), 6593-6609. [15] silling, s.a., askari, a., 2014. peridynamic model for fatigue cracking. sand2014-18590. albuquerque: sandia national laboratories. [16] hong, k., oterkus, s., oterkus, e., 2021. peridynamic analysis of fatigue crack growth in fillet welded joints. ocean engineering. 235, 109348. [17] nguyen, c.t., oterkus, s., oterkus, e., 2021. an energy-based peridynamic model for fatigue cracking. engineering fracture mechanics. 241, 107373. [18] zhu, n., kochan, c., oterkus, e., oterkus, s., 2021. fatigue analysis of polycrystalline materials using peridynamic theory with a novel crack tip detection algorithm. ocean engineering. 222, 108572. [19] wang, h., oterkus, e., oterkus, s., 2018. peridynamic modelling of fracture in marine lithium-ion batteries. ocean engineering. 151, 257-267. [20] wang, h., oterkus, e., celik, s., toros, s., 2017. thermomechanical analysis of porous solid oxide fuel cell by using peridynamics. aims energy. 5(4), 585-600. 1 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v1i2.28 sustainable marine structures http://ojs.nassg.org/index.php/sms article internal waves formation and propagation in the persian gulf seyed majid mosaddad* department of physics, shoushtar branch, islamic azad university, shoushtar, iran article info abstract article history received: 11 august 2020 accepted: 31 august 2020 published online: 31 october 2020 the persian gulf (pg), as a semi-enclosed water basin extends in [4757] e, [24-30] n, geographic domain. particularly, northern part of the pg shows more baroclinicity and turbulence because of the river inflow from the arvand, bottom and costal stresses. furthermore, wind stress has many effects rather than in mid deep domain of the pg. thermocline development in the pg is observed because of studying the data measured in the mt. mitchell cruise in 1992 by different models from winter to summer. the studied turbulence in the northern part of the pg is navigated from winter to summer due to the internal wave’s activity and stability intensified through water column. keywords: persian gulf (pg) thermocline internal waves turbulence 1. introduction internal waves play a major role in the formation of seawater stratification and are responsible for the main processes of ocean dynamics, such as energy transfer and mixing [8]. the surface layer is influenced by local wind forcing. the thermocline tries to re-stabilize itself after the cessation of dry season and oscillates for the rest of the year. a main source of turbulence energy is the internal wave field. some of internal wave energy derives from the transmission of wind energy through the surface mixed layer [1]. the measurement stations in the pg are presented in figure 1. figure 1. aero picture of the pg showing measurement stations in three measuring sections (northwestern, mid deep and near the strait of hurmoz) an important mechanism for exiting fields of internal *corresponding author: seyed majid mosaddad, department of physics, shoushtar branch, islamic azad university, shoushtar, iran email: mosaddad5@gmail.com 2 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 gravity waves (igw) in natural (ocean, the earth atmosphere) and artificial stratified media is their generation by sources of perturbation of various physical nature, i.e., of natural (moving typhoon, wind waves, flow past the ocean bottom relief imperfections, variations in the density and flow fields, leeward mountains) and anthropogenic) marine technological structures, collapse of the turbulent mixing region, underwater explosions( character [6]. as a result of variations of physical characteristics of pg water through column, and effects of climate on the water surface, internal waves happen and vary in water column of pg. therefore, study of the waves in the pg water column has an importance we concentrate in this paper including results of a research. 2. thermocline formation in the pg thermocline forms in the pg, and this is a seasonal phenomenon because of particularly temperature variation through water column in the pg. therefore, thermocline will be studied in this research according to data collected during mt. mitchel cruise in the pg, curves contours are drawn in figure 2 to figure 6. temperature, density and salinity are three useful physical properties of seawater to studying. naturally, the temperature of seawater is fixe at the surface by heat exchange with the atmosphere. temperature and density vertical variations in some stations in three measurement sections are as in the following profiles in the pg in winter and summer. figure 2. vertical variations of temperature and density in three measurement sections in the pg, winter and summer 1992 the atmospheric disturbance is set by an idealized pulse of cyclonic wind stress with a rankine vortex structure. strength, radius and duration of the forcing are varied. the effect upon wave generation of stratification with variable mixed-layer depth is also examined [9]. relying on the accuracy of the curves in figure 2, it could be stated that vertical gradient of temperature and density in the subsurface of the water column is very high in the summer but in winter, it is high only in the strait of hormuz because of water exchange in winter. in fact, it could be resulted that thermocline exists only in summer. overall, the temperature breaks in the subsurface layer through the water column because of wind stress, demonstrates the thermocline developed in the study area. in this regard, thermocline formation and its development are associated to some variations in internal waves, particularly in subsurface layer. in fact, thermocline development and its variation in space and time represent a turbulent flow, and thus propagation of internal waves through water environment. turbulence and internal waves propagate along the baroclinic pressure gradient in a vertical direction through the water column due to baroclinicity and tidal wind stress [10]. based on figure 2 comparing the curves, we could observe that thermocline does not form in winter, particularly in the strait of hormuz because of water exchange with the gulf of oman. however, it forms all over the pg through the water column, suggesting that thermocline develops from the strait of hormuz to the pg north from winter to summer. 3. results and discussion the point is that internal waves can create rather strong currents on the ocean surface. the flow is changed depending on the wave extension: its velocity is greater at the wave crest and wave trough, and is slower where thermocline oscillations are little [7]. internal waves in pg in summer differ from winter, due to differences of forcing and factors in summer and winter. internal waves breaking results in turbulence propagation during winter to summer [2]. arvand river inflow in northwestern of the pg helps to stratification, and then internal waves and turbulence can form there. of course, the gradient throughout density contours throughout the pg represents the existence of the internal waves due to thermocline formation, particularly in summer because of high intensity forcing. wind stress affects the pg surface in the following processes: (1) an atmospheric disturbance causes an internal wave. (2) turbulence is driven by internal waves shear. (3) vertical density fluxes are resulted from the mixing. doi: https://doi.org/10.36956/sms.v1i2.28 3 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 (4) a gravitational imbalance in the horizontal direction includes an intrusion. (5) high wave number internal waves are generated at the head of the intrusion. wind stress as a forcing generates an acceleration for water body in vertical and horizontal directions with its components due to shear induced on water [5]. thermocline forms in the open ocean and can be a seasonal phenomenon in the shallower part of the ocean or a permanent since it is seen in the deeper part of the open ocean. thermocline is a phenomenon which happens in the persian gulf., and it develops from winter to summer resulted of the numerical model (pom) in the pg[3]. formation of a shallow thermocline with upper mixing and displacements of the thermocline is associated with internal wave propagation, which plays an important role in turbulence generation. the stratification as an important factor influencing on local generation of internal waves in the coastal zones subjected to seasonal variability [4]. in this study, we have wanted to appoint internal waves dependence on thermocline development in the pg, and so will conclude internal waves and turbulence. as in the above profiles, there are fluctuations and variations along vertical t & d; therefore, it could be a crucial result of internal wave’s existence. thus, thermocline development often causes turbulence. we could express that turbulence happens in the pg, because of some forcing all over the pg, such as: tide, wind stress, river inflow. in the pg, baroclinic pressure happens in various stations as in the last profiles. buoyancy frequency (brunt vaisala) as following as baroclinicity and density gradients received by a code in fortran in some stations in regards to turbulence and internal wave’s existence are drawn against depth. figure 3 shows vertical variations of buoyancy frequency in two measurement sections. in fact, in most of the measurement stations, internal waves could form. figure 3. buoyancy frequency n (z) (* 0.01) in some important stations in summer and winter 1993, winter and summer 1992 i n f a c t , m o r e v a r i a t i o n s t h r o u g h t h e b u o y a n c y frequency happen in summer rather than in winter, because of more gradients in t and d. the buoyancy frequency is calculated as in the following: n (z) 2 = (-g/ρ) (δρ/δz) (1) where w, n (z), w and p (z) are vertical component of internal wave velocity, wave number velocity and mean density function in water column. depth mean variations for internal wave’s velocity (vertical component) profiles in the pg is received as in figures 4 and 5 in summer and winter with and without bottom stress. figure 4. mean tke through the pg during winter until summer figure 5. mean tke through the pg during winter until summer without bottom stress, winter and summer 1992 in figure 6, profiles of vertical component of internal wave velocity in some points of the pg in winter and summer 1993 depth (m) against velocity (m/s) are showing turbulence in summer because of thermocline develops from winter. doi: https://doi.org/10.36956/sms.v1i2.28 4 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 figure 6. internal wave’s velocity variations in some stations in the persian gulf in winter and summer, winter and summer 1992 as it could be seen, internal wave’s velocity variations in z direction are more in summer rather than in winter, because of thermocline fluctuations based on much density variations. 4. conclusion existence of stratification and development of thermocline in the pg is a crucial phenomenon. summer thermocline formation in the pg is a seasonal potential of turbulence, and internal wave’s creation would happen in the case study zone. thermocline formation is usually associated with internal waves as an important cause in turbulence. internal waves are able to provide and transmit the energy, which is essential for aquatic circulation and mixture. moreover, in coastal areas that charges in fluid temperature in water column causes diffusion of internal waves. it could be concluded that: (1) baroclinic pressure and stratification, cause turbulence throughout pg water column in summer. (2) in summer, turbulent behavior happens. the most effective factors on the behavior in the pg are tide, wind, evaporation and river inflow. (3) the existence of tides, northwestern winds and strong internal waves in pg results in high vertical component of internal wave’s velocity. (4) turbulence and internal waves due to baroclinic pressure because of density gradients exist in the pg water in summer. (5) vertical component of internal waves velocity has range of [-0.8, +0.8] with more fluctuations in summer. references [1] alford, m.h., pinkel, r. observations of overturning in the thermocline: the context of ocean. j. of physical oceanography, 2006, 30: 805-832. [2] bidokhti, a. a., ezam, m. the structure of the persian gulf outflow subjected to density variations. j. of ocean sci. discuss, 2008, 5: 135-161. [3] mosaddad, s. m., bidokhti, a. a., basirparsa, h. an observational and numerical modeling of thermocline development in the persian gulf. j. marine geodesy, 2012, 14. [4] mosaddad, s. m., bidokhti, a. a., basirparsa, h. development of summer thermocline in the persian gulf. j. of climate change: impacts and responses, mlbourn univ. press, 2009, 1(8). [5] onogi, k. j., tsutsui, h., koide, m., sakamoto, s., kobayashi, h., hatsushika, t., matsumoto, n., yamazaki, h., kamahori, k., takahashi, s., kadokura, k., wada, k., kato, r., oyama, t., ose, n., mannoji, n., taira, r. the jra-25 reanalysis. j. meteor. soc. japan, 2007, 85: 369-432. [6] bulatov v.v., vladimirov yu v. internal gravity waves from a moving source: modeling and asymptotics. journal of physics: conference series, 2019, 1268: 012013 doi: 10.1088/1742-6596/1268/1/012013 [7] miropol’skii yu. z., shishkina o.v. dynamics of internal gravity waves in the ocean. boston: kluwer academic publishers, 2001. [8] morozov, e.g. oceanic internal tides. observations, analysis and modeling. springer, 2018, 317. [9] voelker, g.s., myers, m., walter, b. r. southerland generation of oceanic internal gravity waves by a cyclonic surface stress disturbance. dynamics atm. ocean, 2019, 86: 16-133. [10] delphi, m., mosaddad, s. m. formation of summer thermocline in the persian gulf. int. j. environmental science and development, 2010, 1(5): 3. doi: https://doi.org/10.36956/sms.v1i2.28 35 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v2i2.330 sustainable marine structures http://ojs.nassg.org/index.php/sms article new method for building vector of diagnostic signs to classify technical states of marine diesel engine by torsional vibrations on shaft-line do duc luu1* cao duc hanh1 nguyen xuan tru2 1. vietnam maritime university, hai phong, vietnam 2. naval technical institute, hai phong, vietnam article info abstract article history received: 24 march 2021 accepted: 9 april 2021 published online: 15 april 2021 vector of diagnostic signs (vds) using torsional vibration (tv) signal on the main propulsion plant (mpp) is the vector of z maxima (or minima) values of the tv signal in accordance with the cylinder firing orders. the technical states of the marine diesel engine (mde) include r= z+1 classes and are presented in z-dimensional space coordinate of vds. the presentation of dk, k=1÷r using z diagnostic signs (vi, i=1÷z) is nonfigurative and quite complicated. this paper aims to develop a new method for converting vds from z-dimensional to 2-dimensional space (two-axes) based on the firing orders of the diesel cylinders, as an equivalent geometrical sign of the all diagnostic signs. the proposed model is useful for presenting a technical state dk in two-dimensional space (x, y) for better visualization. the paper verifies the simulation of the classification illustration of the 7–state classes for the mde 6s46mcc, installed on the motor vessel (mv) 34000dwt, using the new above mentioned method. the seven technical state classes (for 6-cylinder mde, z=6) are drawn separately and visually in the descartes. the received results are valuable to improve smart diagnostic system for analyzing normal/misfire states of cylinders in operation regimes. keywords: two-dimensional vector of diagnostic signs of torsional vibration signal new model of vds for misfiring diagnostics of mde vi s i o n d i a g n o s t i c s o f m d e b y t o r s i o n a l vibration signal 1. introduction the tv signal (tvs) contains much important information about the misfiring / normal working conditions of every cylinder in the multi-cylinder marine diesel engine (mde) [1]. the characteristics of the tvs identifying in time or frequency domains are used to estimate the technical states of the diagnostic object (do) and called diagnostic signs. in the works [1, 2, 4], the vds are formed from the maxima (va) or minima (vb) of the tvs correspondence with firing order of each cylinder. the size of the vds is equal to the number of cylinders in the do. the z-dimensional vds are used for classifying the technical states (normal / misfiring conditions) of every dme cylinder, in this case do is 6 cylinder mde type 6s46 mcc-7 of man-bw *corresponding author: do duc luu, vietnam maritime university, hai phong, vietnam; email: luudd@vimaru.edu.vn 36 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 manufactory. it’s hardly to illustrate every technical state dk, k=1÷r in z-dimensional space v= [v1…vz] of the vds (v=va or v=vb; va= [va1... vaz] or vb= [vb1... vbz]) because imagining mathematic models in the multi-dimensional space is quite complicated. in many cases, the illustration of dk (v1, v2 … vz) is divided in to a number of a pair of two-dimensional space (vi, vj); i ≠j, i=1÷z; j=1÷z [4]. to overcome the above-mentioned presentation inconvenience, the authors convert vds from z-dimensional to 2-dimensional space. from there, the diagnosis and identification processes could be solved in a more visualization way and easily applied in real-world diagnostic problems. 2. research method 2.1 modeling new two –dimensional vds from va or vb let us assume that the tv signals are simulated (or measured) in a working cycle of mde containing z cylinders. the signal normally has a number of samples, n=1024 or 2048. the signal is divided in to z parts, and every part has nc = [n/z] samples. in the part in accordance with firing order of every cylinder, we find the maximal and minimal values. we conduct the va and vb vector of the diagnostic signs from these values. the firing order of every cylinder is given in the mde technical documents, such as the 6s 46mcc shows the order [6]: 1-5-3-4-2-6. the parameter features (vam, vbm) of mth –cylinder are de-phased αm (degree) in accordance with the first cylinder (two-stroke diesel engine): α1=0; α5= 60 o; α3= 120 o; α4= 180 o; α2= 240 o; α6= 300 o or in radian: α1=0; α5= π/3; α3= 2π/3; α4= π; α2= 4π/3; α6= 5π/3. in generally, we conduct the de-phase vector of the working cylinders α: α = [0, α2…αz], (radian) (1) the new diagnostic vectors vn are calculated as follow: z z x i=1 i=1 vn = v(i)cos( (i) vn = v(i)sin( (i)); ) y α α∑ ∑ (2) where, v= [v (1), v (2) … v (z)], and v=va or v=vb. every class dk is written by two reference parameters: the mean vector µk and the covariance matrix kk in accordance with the two-dimensional vds vn= (vnx, vny), k=1÷r. illustration of the cylinder working conditions in the descartes (vnx,vny). the z –cylinder mde is classified into r =(z+1) technical classes dk as above mentioned for diagnostics of the normal or misfiring state of cylinder in accordance with the rules for classification and construction of sea-going ships [7]. the block scheme for building the new vds vn (vnx, vny) and illustrating the r states via the 2-dimensional space is shown in figure 1. figure 1. block scheme for building new vds in two-dimensional space vn(x, y) doe –design of experiments, cf –vector of the z firing coefficients, mde as a do; va, vb –vector of diagnostic signs (z elements of maxima or minima);vn –new vector of two equivalent elements in two-dimensional space (x,y) in measuring process, we supposed that the revolution n (rpm) and the load index (li) are fixed. however, the real measured signal has some random components and measuring errors. therefore, we conducted the measuring process ten repeated times with random noises, and the measurement device error is ±5%. this ±5% is bigger than almost thresholds of precise measuring devices in the market today [4]. the main controlling parameters of the technical states of all cylinders are firing coefficients, which are written in the form of vector cf = [cf (1)… cf (z)]. the real firing processes are random and for diagnostics model, we assume that firing coefficient cf (k) is varied with ±5% in accordance with the mean value. in the case of normal working, the cf = [0.9, 1.0], and with the misfiring state, cf = [0.0, 0.1]. for every cylinder there are three levels of one firing regime to be examined. the design of experiments has nn revolution regimes, for example nmean = 75 rpm, the ∆n=5%.75 =3.75. we would carry out the numerical experiments at nd = {71÷ 79} (rpm), for example at the nmean = 75 rpm, nd = 9 experiments. the design of experiments has r= (z+1) technical state classes. thus, we conduct ns = 3 z experiments for every revolution regime. for example, z=6, ns = 729. the total number of experiments of the doe is n=nd*ns. let us assume z =6, and we conduct each revolution 10 times (in accordance with the real measuring repeat times, nd =10), the total n is 10* 729 =7290 (experiments). after building database from the measured (simulated) tvs, the authors analyze tvs to find the va or vb, and doi: https://doi.org/10.36956/sms.v2i2.330 37 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 finally to draw the new vn-database for the r= (z+1) = 7 states. the vn–database is drawn visually in the two-dimensional (vnx, vny) axes, in accordance with equation (2). to diagnose the misfire of any cylinder in the multi-cylinder mde by classification methodology we have to make the new standard diagnostic characteristics and new diagnostic classifier using the new vector of diagnostic signs vn(x, y). 2.2 modeling standard characteristics of mde on the new vds vn(x,y) the technical states of mde are grouped in to r=z+1 classes, written with the symbol dk, k=1…r. every class has the called referenced (standard) characteristic to identify one with other [1]: (3) the covariance matrix kk is calculated. (4) 2.3 diagnostics classification of mde on the new vds vn(x,y) the current considered state dc is presented in the similar form with equation (3) in the following [1, 4]: (5) the solution of the diagnosis is finding minimum of mahalanobis distance dck from distance set: (6) the mahalanobis distance between two classes “c” and “k” is defined below. (7) where, kck – compound covariance matrix of the two matrixes kc and kk. 3. cases study: building the two-dimensional vds for diagnosing the 6s46 mcc the mde type 6s46 mcc is installed on the general cargo motor vessel with 34000 dwt (mv 34000 dwt). the tvs of the ship mpp are conducted and supposed to dnv (register) approve by hudong manufactory [6]. the method and software for automatic torsional vibration calculation (satvc) are developed at vietnam maritime university [0, 5] for this mpp on labview platform. the satvc has the features to automatically calculate one of the 7 normal/ misfiring states of the 6 cylinders with revolution regimes n= [0.4, 1.2] nmcr, where nmcr -maximal continuous rate (rpm) and in this case of mv 34000 dwt, nmcr =129 rpm. for diagnosing technical states normal / misfiring, the diagnostic revolution regimes have to be far from reso　　　　 (a)　　　　　　　　　　　　　　　　　　　　　　　(b) figure. 2 illustrating the seven classes of the mde 6s46mcc on mv 34000 dwt via new two-dimensional space (vnx, vny) in accordance with vds va (a) and vb (b) doi: https://doi.org/10.36956/sms.v2i2.330 38 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 nance revolution ranges of the torsional vibrations of the mpp because in the resonance or near–resonance revolutions the tvs are quite excited and too large. therefore we have to calculate the freedom tv for the mpp. table 1. freedom resonances of the mpp on the mv 34000 dwt the resonances of the first and second modes of the mpp on the mv 34000 dwt are also defined by the satvc, especially by the freedom torsional vibration module. the results of the freedom tvs are shown below[3,4]: n01=337.16 rpm; n02= 1436.02 rpm. the revolutions of the dme on the mv 34000 dwt at the interval [52, 155] rpm are resonances that are shown in table 1. the interval nd = [71, 80] is selected for diagnostic revolution regimes. the two-dimensional illustrations of the seven technical normal or misfiring conditions in cylinders of the do are shown in figure 2 using the simulation software which is developed in labview by authors. figure 2(a) shows that when using the maxima va of the tvs, the pairs of state classes: (d0 and d4), (d2 and d4), and (d6 and d2) couldn’t be separated fully in new two-dimensional vna (vnax, vnay). however, figure 2(b) shows that using the minima vb of the tvs, the pairs of state classes are very well separated in the new two-dimensional vnb (vnbx, vnby) 4. conclusions using the new method for building two-dimensional vds has the advantages in classifying r technical states of mde. the authors applied the new approach for diagnosing the technical sates in the two -axes descartes (vnx and vny) using the maxima and minima vds of the shaftline tvs. the results show that the minima vds produces the better classification performance than the maxima vds. references [1] do duc luu: dynamics and diagnostics of marine diesel engine by vibration technique. publisher “transport”, ha noi (2009). [2] do duc luu, et all (2020): regressive models for condition diagnosing marine diesel engine by torsional vibrations on propulsion shaft-line. international journal of modern physis b. issn 02179849. (5 pages). © world scientific publishing company. doi: https://doi.org/10.1142/s0217979220401268. [3] do duc luu and cao duc hanh (2021). automatic calculation of torsional vibrations on marine propulsion plant using marine two-stroke diesel engine: algorithms and software. journal of the institution of engineers (india): series c. issn 2250-0545 volume 102 number 1. pp. 51-58. https://doi.org/10.1007/s40032-020-00626-y. [4] do duc luu, cao duc hanh, et al. (2021): smart diagnostics for marine diesel engines using torsional vibrations signals on the ship propulsion shaft – line. naval engineer journal. issn: 00281425. march 2021| no 133-1. pp. 143-153 https:// w w w. i n g e n t a c o n n e c t . c o m / c o n t e n t o n e / a s n e / nej/2021/00000133/00000001/art00026. [5] luong cong nho, do duc luu, et al.: researching, building simulation of main propulsion plant and main switch-board on the marine cargo ship. national independent project on science and technology with id. dtdl.cn-14/15 carried out in vietnam maritime university, hai phong (2015 -2019). [6] hudong heavy machinery co. ltd: torsional vibration calculation report de 6s46mc–c7860 kw @ 129 r/min 34,000 dwt. pharung shipyard. dnv approved 2007. [7] russian maritime register of shipping, edit 2014: rules for classification and construction of sea-going ships. saint-petecbuarg, russian (2014). abbreviation list cf vector of firing coefficients do diagnostic object doe design of experiments dwt dead weigh tonnage mde marine diesel engine mpp main propulsion plant mv motor vessel satvc software for automatic torsional vibration calculation tv torsional vibration tvs torsional vibration signal vds vector of diagnostic signs vn new vector of two equivalent elements doi: https://doi.org/10.36956/sms.v2i2.330 13 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v2i2.301 sustainable marine structures http://ojs.nassg.org/index.php/sms article analysis of some elements and speciated compounds in fish found in the new calabar river of the niger delta area, nigeria ndubuisi kingsley owhonda* nigerian institute for oceanography and marine research, victoria island, lagos, nigeria article info abstract article history received: 21 december 2020 accepted: 11 january 2021 published online: 30 march 2021 the flesh of guinean and blackchin tilapia, and mullet found in choba river were collected for elemental studies of mercury, cadmium, lead, arsenic, nickel and speciated forms. analytical method of x-ray fluorescence (xrf) was used for the elemental studies while gas chromatographymass spectrometer (gc-ms) was used for the speciated forms. 4.3 mg/kg was the highest concentration of cadmium observed in blackchin tilapia. the three fish species all contained about 0.5 mg/kg of arsenic and 1 mg/ kg of mercury. 1.7 mg/kg of lead was detected in mullet while 7.3 mg/kg of nickel was detected in blackchin tilapia. organometallic compounds found were nickel tetracarbonyl, borane carbonyl in guinean tilapia, nickel tetracarbonyl, borane carbonyl and germanium(iv) pthalocyanine dichloride in blackchin tilapia and [µ-(ƞ6-benzene)] bis (ƞ5-2,4-cyclopentadien-yl) diµ-hydrodi-vanadium. borane carbonyl was found in mullet. keywords: arsenic mercury lead nickel cadmium speciated form guinean and blackchin tilapia mullet x-ray fluorescence gc-ms 1. introduction elements like mercury, arsenic, lead and cadmium are well-known to have major human health problems [1]. cadmium inhibits membrane-bound enzymes [2]. cadmium complexes with sulphydryl groups in the active sites of enzymes. research has shown that these complexes can hinder the formation of enzyme-substrate complex [3]. research has also shown that using dithiothreitol (dtt) for the treatment of cadmium toxicity is better than other methods since it serves as a chelator and also restores the sulphydryl groups [4]. it is well documented that people ingest arsenic and other toxic metals mainly through food such as poultry, rice, mushrooms and seafood [5,6,7,8]. mercury through microbe bio-transformation in fishes can form methylmercury (mehg). some researchers have reported that the accumulated form in fish are in many cases extremely high compared to the surrounding water [9]. mehg is known to be toxic and that it can also accumulate in the food chain [10]. mehg can be consumed through fish consumption. if mehg is found in animals it is usually in the organs like kidney, liver, nervous system and prenatal *corresponding author: ndubuisi kingsley owhonda, nigerian institute for oceanography and marine research, victoria island, lagos, nigeria; email: kingsleyndubuisiowhonda@gmail.com 14 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 life where it exhibits its toxicity [11]. high lead concentration can reduce aquatic population of mussel [12]. potato peel is prone to heavy metal accumulation [13]. thus, it should be removed before consumption. for a similar reason, this is why the amount of leafy vegetables eating in a day should be limited. the presence of high concentrations of nickel in animals can lead to retarded growth and development [14]. elements exists in various forms. while some these forms are toxic, others are not [15]. the essence of this work was to shed light on the concentrations of these toxic elements since people depend on this river for their source of fish and to also determine the speciated forms in these three fish species. the exact quantity of these toxic elements present in the fish consumed from rivers around the niger delta region is not well documented. this research work sheds light on this. 2. location, materials and methods 2.1 the study location the arrow in figure 1 shows the sampling site. this river is located between longitude 6o53.95e and latitude 4o53.78n [16]. it is in choba village. close to it is an extension of wilbros nigeria limited (wnl), an oil servicing company. figure 1. location of choba river 2.2 (a) sampling and the preparation of the sample for x-ray fluorescence table size fresh samples of the three fish species were taken from the river (figures 2,3,4). after cleaning, they were wrapped in an aluminum foil and then put into ice. finally, they were put in a black polyethylene bag and then all in a cooler to the laboratory for analyses. figure 2. guinean tilapia figure 3. blackchin tilapia figure 4. mullet 2.3 x-ray fluorescence analysis and quality control the concentrations of the elements were done with x-ray fluorescence spectrometer. this was done in accordance with the usepa 6200. the drying of the fresh fish samples was done in the oven and it was at 110°c and for twenty hours. the edible fleshy part of the fresh fish samples were reduced to lower than 2µm diameter through crushing. then, pulverized. they were further made into pellets, moved into a prolene foil that was already cleaned and then put into sample vial. they were then labelled doi: https://doi.org/10.36956/sms.v2i2.301 15 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 accordingly before arranging them in the sample tray. finally, they were taken to the compartment for sample in the x-ray fluorescence equipment (spectrox-labpro) for their elemental composition determination. through previously stored calibration and with a certified reference material the elemental concentrations of the samples were deduced. the source of excitation was x-ray tube (synchrotron). the matrix effect was corrected by the appropriate means. the sample was analyzed several times to check reproducibility. 2.3.1 gc-ms analysis this involved 2 stages. stage one was extraction while stage two was derivatization just before chromatographing. scales were removed first from fish using a ceramic knife as specified by iupac [17]. then the cutting of the edible part was done using the ceramic knife. mortar and pistol were used homogenizing. 2g of homogenized fish sample was collected and 5ml of 20% tmah was introduced to digest it. it was then taken to a water bath at the temperature of 60oc where it remained for 2 hours. at the end of the 2 hours ph was checked. it is important that the ph remains between 6-8. 3ml of 0.5m naddtc was added. 1.5ml of both toluene and benzene were then added. it was then agitated for 2hrs in a mechanical shaker. for the 2nd stage, a large balloon was filled with pure nitrogen gas. then, 5ml of the fish sample which was from the initial stage one was collected with a syringe. the air in the sample was then flushed with the nitrogen gas in the balloon and for several minutes. while the flushing was on, 3ml of n-bumgcl and 2ml thf were introduced. they were then agitated for 10 mins. in case of the presence of any excess grignard reagent, 10ml of 0.5m sulphuric acid was added to destroy it. two phases resulted which were then separated. gc-ms analysis was carried out on the organic phase. 3 results and discussion 3.1 results 3.1.1 x-ray fluorescence table 1 shows the concentrations of elements in the three fish species figure 5. concentration (mg/kg) of cadmium, arsenic, mercury, lead and nickel in the three fish species 3.1.2 gc-ms analysis chromatogram 44 figure 6: chromatogram of tilapia guineensis from choba river figure 6. chromatogram of tilapia guineensis from choba river table 1. x-ray fluorescence analysis result fish specie cd(mg/kg) as(mg/kg) hg(mg/kg) pb(mg/kg) ni(mg/kg) guinean tilapia (tilapia guineensis) 4.0 0.5 1.0 1.1 6.6 blackchin tilapia (sarotherodon melanotheron) 4.3 0.5 1.0 1.5 7.3 mullet (liza falcipinnis) 0.8 0.4 0.8 1.7 6.1 doi: https://doi.org/10.36956/sms.v2i2.301 16 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 49 figure 7: chromatogram of sarotherodon melanotheron from choba river figure 7. chromatogram of sarotherodon melanotheron from choba river 54 figure 8: chromatogram of mullet (liza falcipinnis) from choba river figure 8. chromatogram of mullet (liza falcipinnis) from choba river 3.2 discussion 3.2.1 cadmium the cadmium detected was 0.8-4.3mg/kg. cadmium is known to exerts toxic effect on kidney and body systems. thus, it has been classified as a carcinogen [18]. it is also known to accumulate in many organisms including crustaceans and molluscs. vegetables, cereals and starchy roots have shown lower concentrations [19]. safe amount of cadmium in a month is 25µg/kg body weight [19]. 3.2.2 arsenic the arsenic detected was 0.5mg/kg or less. the tolerable limit for arsenic in food is yet to be established [19,20]. thus, the quantity of these fish species consumed per day should be in moderation. 3.2.3 mercury for mercury, 1.0mg/kg or less was detected. mehg was not detected. research shows that mercury is toxic to humans no matter the form in which it is found [21]. it is even more so to the developing foetus in the uterus and its early life. this is because mercury damages the brain, the lungs and the kidney. 0.5-1mg/kg is recommended as safe limits [22]. 3.2.4 lead the lead detected was 1.1-1.7mg/kg. there is no known safe level [23]. table 2. speciated forms of elements detected in the three fish species type of fish compound detected retention time (minutes) amount (%) tilapia guineensis nickel tetracarbonyl 4.51 8.11x10-3 borane carbonyl 5.46 3.36 x10-4 sarotherodon melanotheron nickel tetracarbonyl 4.75 5.41 x10-1 borane carbonyl 6.69 3.07 x10-4 pthalocyaninedichloridegermanium 44.68 8.20 x10-3 mullet (liza falcipinnis) borane carbonyl 6.42 2.06 x10-4 [µ-(ƞ6-benzene)]bis(ƞ5-2,4-cyclopentadien-yl)di-µ-hydrodivanadium 34.74 1.55 x10-4 doi: https://doi.org/10.36956/sms.v2i2.301 17 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 3.2.5 nickel the nickel detected was 6.1-7.3mg/kg. 5-50µg of nickel is required per day. while 4.2µg of nickel per kg body weight in a day come from food [24] an upper limit of 1mg of nickel in a day for adults from all sources has been indicated [25]. nickel tetracarbonyl is an organonickel compound. it is the main carbonyl compound of nickel. it is a pale-yellow liquid with the formula ni(co)4 and is extremely poisonous. it is fatal if absorbed through the skin or even when inhaled [26]. the ld50 concentration is 3ppm. for humans, the fatal dose remains 30 ppm. this is because the halflife of ni(co)4 is just 40s and so, it can decompose very quickly in air [23]. as a result, it will not cause harm when ingested through fish consumption. 4. conclusions the results did show that the fish species contain toxic elements. it showed that the quantity of these toxic elements present depend on the type of fish and the river in which it is found. however, the result also suggests that their toxicity may well depend on the quantity of the fish consumed and the totality of all food sources that contain these toxic elements that are consumed daily. acknowledgement special thanks to fugro nigeria limited for the analysis of the many fish samples. references [1] hutton, m. (1987). human health concerns of lead, mercury, cadmium and arsenic. in chapter 6, book title “lead, mercury, cadmium and arsenic in the environment”. published by john wiley and sons limited. edited by hutchinson and meena, k.m, pp.5568. [2] toury, r., stelly, n., boissonneau, e. and dupuis, y. (1985). degenerate processes in skeletal muscle of cd-treated rats and cdzf inhibition of mitochondrial ca2+ transport. journal of toxicology and applied pharmacology, 77: 19-35. [3] vallee, b. and ulmer, d. (1972). biochemical effects of mercury, cadmium and lead. annual review of biochemistry, 41: 91-128. [4] cleland, w.w (1964). dithiothreitol, a new protective reagent for sh groups. biochemistry 3: 480-482. [5] jones, f.t. (2007). a broad view of arsenic. poultry science, 86: 2-14. [6] petroczi, a. and naughton, d.p. (2009). mercury, cadmium and lead contamination in seafood: a comparative study to evaluate the usefulness of target hazard quotients. food chemistry and toxicology 47: 298-302. [7] nepuscz, t., petroczi, a. and naughton, d.p. (2009). food alert patterns for metal contamination analyses in seafoods: longitudinal and geographical perspectives. environment international 35: 1030-1033. [8] smedley, p.l and kinniburgh, d.g (2002). a review of the source, behaviour and distribution of arsenic in natural waters. applied geochemistry 17: 517-568. [9] osman, a., wuertz, s., mekkawy, i., exner, h and kirschbaum, f. (2007): journal of environmental toxicology 22 (4): 375-389. [10] boudou, a. and ribeyre, f. (1997). mercury in the food web. accumulation and transfer mechanisms. metal ions in biological systems 34: 289-319. [11] clarkson, t.w. (1990). methylmercury. fundamental and applied toxicology. 16: 20-21. [12] ning, w.y., christopher, g., christopher, d.i., douglas, k., hardesty, t., may, t., augspurger, a.d., roberts, g., eric, g. and chris, m. (2010). sensitivity of early life stages of freshwater mussles (uniondae) to acute and chronic toxicity of lead, cadmium and zinc in water. journal of environmental toxicology and chemistry, 29 (9): 2053-2063. [13] yuangen, y., feili, l., xiangyang, b., li, s., taoze, l., zhisheng, j. and congqiang, l. (2011). lead, zinc and cadmium in vegetable/crops in a zinc smelting region and its potential human toxicity. bulletin of environmental contamination and toxicology, 87: 586-590. [14] abelardo, a.s., jose, l.d and jorge, h (2011). nickel toxicity in embryos and larvae of the south american toad. effects on cell differentiation, morphogenesis and oxygen consumption. journal of environmental toxicology and chemistry, 30 (5): 11461152. [15] who (2001). arsenic and arsenic compounds (environmental health criteria 224), 2nd ed. geneva: world health organization, international programme on chemical safety, p.18. [16] dienye, h.e and woke, g.n (2015). physico-chemical parameters of the upper and lower reach of the new calabar river, niger delta. journal of fisheries and lifestock production, 3 (4):1-4. [17] international union of pure and applied chemistry (iupac,1995). speciation of lead in environmental and biological samples. pure and applied chemistry, 67 (4):615-648. [18] international programme on chemical safety (2007). doi: https://doi.org/10.36956/sms.v2i2.301 18 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 cadmium, cadmium chloride, cadmium oxide, cadmium sulphide, cadmium acetate, cadmium sulphate. geneva, world health organization, pp.1075-1318. [19] who (world health organization) (2010). preventing disease through healthy environments. exposure to cadmium. a major public health concern. geneva, pp. 1-3. [20] fao/who (2010). summary and conclusions of the seventy-second meeting of the joint fao/who expert committee on food additives, rome, 16–25 february 2010. rome, food and agriculture organization of the united nations; geneva, world health organization (jecfa/72/sc, pp.1-10. [21] who (world health organization) (2007): preventing disease through healthy environments. exposure to mercury: a major public concern, pp. 1-4. [22] e u r o p e a n u n i o n c o m m i s s i o n c o m m i t t e e f o r regulating heavy metals directive 2001/22/ec, no.:466/2001, 2001, p.1-5. [23] stedman, d.h., hikade, d.d., pearson, r. and yalvac, e.d (1980). “nickel carbonyl: decomposition in air and related kinetics studies”. science 208 (4447):1029-1031. [24] european medicines agency (2007). preauthoriaation evaluation of medicines for human use, pp. 1-32. [25] racchelle beveridge (2008): department of medicine, university of montreal. lung cancer risk associated with occupational exposure to nickel, chromium (vi) and cadmium in two population-based studies in montreal, pp. 10-15. [26] board on environmental studies and toxicology (2008). “nickel carbonyl”: acute exposure guideline levels”. acute exposure guideline levels for selected airbone chemicals 6. national academics press, pp. 213-259. doi: https://doi.org/10.36956/sms.v2i2.301 11 sustainable marine structures | volume 04 | issue 02 | july 2022 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2022 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). doi: http://dx.doi.org/10.36956/sms.v4i2.505 *corresponding author: erkan oterkus, peridynamics research centre, department of naval architecture, ocean and marine engineering, university of strathclyde, glasgow, uk; email: erkan.oterkus@strath.ac.uk article structural integrity analysis of containers lost at sea using finite element method selda oterkus1 bingquan wang1 erkan oterkus1* yakubu kasimu galadima1 margot cocard1 stefanos mokas2 jami buckley2 callum mccullough3 dhruv boruah4 bob gilchrist4 1. peridynamics research centre, department of naval architecture, ocean and marine engineering, university of strathclyde, glasgow, uk 2. buckley yacht design ltd, new milton, uk 3. m subs limited, plymouth, uk 4. oceanways technologies ltd, london, uk article info abstract article history received: 07 march 2022 accepted: 15 april 2022 published online: 30 april 2022 unlike traditional transportation, container transportation is a relatively new logistics transportation mode. shipping containers lost at sea have raised safety concerns. in this study, finite element analysis of containers subjected to hydrostatic pressure, using commercial software ansys apdl was performed. a computer model that can reasonably predict the state of an iso cargo shipping container was developed. the von mises stress distribution of the container was determined and the yield strength was adopted as the failure criterion. numerical investigations showed that the conventional ship container cannot withstand hydrostatic pressure in deep water conditions. a strengthened container option was considered for the container to retain its structural integrity in water conditions. keywords: container finite element method structural integrity sea 1. introduction as a light steel structure, containers have many advantages in ocean transportation. container transportation reduces the number of manual loading and unloading, and handling in traditional transportation methods, which can avoid cargo damage, wet damage, and loss caused by human and natural factors. therefore, the shipping container transportation method has completely replaced the traditional shipping method and has become a new and highly efficient transportation method [1]. container transportation has revolutionized the transportation of goods by sea and has become the global standard for transportation of goods in the world today. http://dx.doi.org/10.36956/sms.v4i2.505 12 sustainable marine structures | volume 04 | issue 02 | july 2022 although containers simplify the transportation of large quantities of goods, many accidents still occur during transportation, causing a large number of containers to be lost during sea transportation. the world shipping council’s 2020 sea container lost report shows that an average of 1,382 containers are lost at sea each year [2]. according to “safety and shipping review” by allianz. although it is not uncommon for containers to be lost at sea, the risks of bad weather, improper stowage and strapping, and even the resulting environmental issues have caused people to pay additional attention to the issue of container loss [3]. containers are usually manufactured in factories, transported to the construction site, and assembled quickly [4]. due to the rapid increase in the use of freight containers for marine cargo and the development of special container ships, the safety of containerization in marine transport has been considered by international organization for standardization (iso). consequently, international convention for safe containers (csc) was introduced which aims to sustain a high level of safety of human life and facilitate international transport of containers by providing uniform international safety regulations [5]. there have been various studies available in the literature which considers the structural analysis of containers. giriunas et al. [6] have investigated the iso shipping container’s structural strength for non-shipping applications. antoniou and oterkus [7] proposed origami based design concepts which can improve the structural efficiency of a container by fem. an analytical, numerical, and experimental work on the in-plane stiffness of container buildings has been carried by zha and zuo [4]. they presented a feasible design and construction of the container. however, there is no study available in the literature which investigates the state of the containers lost at sea. the main goal of this study is to analyse structural integrity of the international organization for standardization (iso) shipping containers lost at sea. the construction standards of containers are presented. the structural response of shipping container subjected to underwater hydrostatic loading conditions is investigated. the von mises stress distribution on a container at various water depths is demonstrated. strengthened container option to withstand higher hydrostatic pressures is investigated. 2. methodology 2.1 finite element method in this study, a standard shipping container model was constructed and analysed by using finite element method. for numerical calculations, ansys, a commercial finite element software, was utilised. the container is subjected to hydrostatic pressure around all surfaces, which represents the state of the container lost at sea. the thickness of the side and top walls of the container is significantly smaller compared to its length and width. consequently, the container was discretized by shell elements in the finite element model. the thickness of the plates can be defined through the section property definition. the element type, shell181, used in this work is widely used to simulate shell structures with thin to medium thickness. as presented in figure 1, it is a four-node element with six degrees of freedom at each node which are translations in the x, y, and z directions, and rotations about the x, y, and z-axes. figure 1. shell181 geometry and its nodal degrees of freedom. 2.2 failure criterion in this study, the structural integrity of the container was examined by using the von mises yield criterion. it was assumed that if the von mises stress of the container subjected to hydrostatic loading is equal or greater than the yield limit of the construction material, then the container will damage. the stress state at a point can be defined by a 3×3 tensor for a three-dimensional model as (1) where , , are normal stresses and , , are shear stresses. von mises stress combines the stress components or principal stresses into equivalent stress. in terms of stress components given in equation (1), it can be calculated as [8] (2) 13 sustainable marine structures | volume 04 | issue 02 | july 2022 in terms of principal stresses, it can be expressed as [8] (3) in which , and are principal stresses. 3. container geometry model depending on the types of goods that their containers are carrying, iso and csc stipulate specifications related with structural strength, applicability, and application of shipping containers. according to the guidance based on iso, csc, and container manufacturer standards, the dimensions of the most common 20 ft container are shown in table 1 and figure 2. table 1. the geometrical dimensions of a 20 ft container length l width w height h 20 ft container 6090 mm 2440 mm 2590 mm figure 2. dimensions of a 20 ft shipping container. the container was designed and constructed for the transportation of general cargo on sea. the main components of the container in this work focused on the side walls, end walls and the roof of the container. the trapezium section sidewall is built with 9pcs 2.6 mm thick fully vertically continuous corrugated steel panels at the intermediate area and 2pcs 2.6 mm thick fully vertically continuous corrugated steel panels at both ends. the top to bottom view of the side wall is presented in figure 3. figure 3. top to bottom view of the side wall. the trapezium section end wall in figure 4 was constructed with 2.6 mm thick vertically corrugated steel panels, which are butt welded together to form one panel. figure 4. top to bottom view of the end wall. the roof was constructed by several die-stamp corrugated steel sheets with a certain upwards camber at the centre of each trough and corrugation while the floor of the container was constructed as a flat sheet. 4. numerical evaluation finite element software ansys mechanical apdl was performed for finite element analysis in this study. the considered container shown in figure 5 was constructed based on the geometry from table 1. the side walls are constructed based on the dimensions provided in figure 3 and figure 4, respectively. figure 5. the model geometry of the container. the container components are typically constructed with steel plate. the density , elastic modulus and poisson’s ratio of the model are specified as =7850 , , and . the material parameter and constitutive relationship of the container model varies depend on the material selected as three types of widely used metal material was considered in the construction. table 2 indicates material properties of these three material types including astm a283 carbon steel [9], spa-h steel [10] and hy-100 [11] steel. table 2. material parameters of container model material type yield strength ultimate strength astm a283 165 310 spa-h 457 572 hy-100 744 1062 14 sustainable marine structures | volume 04 | issue 02 | july 2022 the element size, element shape and mesh type of each component in the container model are specified in table 3. it is worth noting that to make sure that all components are connected to each other. it is important to merge coincident nodes after the mesh generation is completed, which can tie separate but coincident parts of the model together. the container model is considered in the occasions of falling and lost at sea during the operation caused by the unexpected sea state (figure 6). the container is subjected to hydrostatic pressure. defining the density of the seawater as =1025 , the state of the container was investigated at different water depths. the pressure values at different water depths are shown in table 4. the pressure loading is applied on all surfaces of the container model in the analysis. in finite element model, the hydrostatic pressure was considered as surface loads and applied on nodes. figure 6. schematic drawing of container lost at sea and associated hydrostatic pressure acting on it. the constrained displacements were applied as boundary conditions on the container model to prevent rigid body motion. in addition to hydrostatic pressure acted on all surfaces of the container components, the constrained displacements on the container surface were specified as table 3. the details of the finite element model of the container component side wall end wall top roof bottom floor mesh form element type shell 181 size 18 mm 18 mm 10 mm 14 mm mesh type structured structured structured structured thickness 2.6 mm 2.6 mm 3 mm 20 mm table 4. hydrostatic pressure at different water depths. depth (m) pressure (pa) 5 50276.25 15 150828.75 30 301657.5 50 502762.5 15 sustainable marine structures | volume 04 | issue 02 | july 2022 (4) (5) (6) (7) in which , and are the displacements in x, y and z directions, respectively. 5. results and discussion the von mises stress distribution on the container at considered depths is presented in figure 7. high von mises stresses can be observed in the middle of the sidewalls. moreover, a relatively high von mises stress distribution is shown on the edges of the container model. according to the failure criterion defined by the yield strength and considered construction materials in table 2, the maximum von mises stress observed on the container exceeds the yield strength at all water depths. therefore, the watertightness and structural integrity cannot be maintained after conventional shipping containers are lost at sea. based on the conclusion from the comparison, the container needs to be strengthened to withstand hydrostatic pressure. considering the containers are designed to be heavily loaded and stacked with other containers, it is not feasible to change the geometrical design of the container as this will cause the re-designed container incompatible with other containers operating in the market. however, the container strength can be improved by increasing the thickness of the sidewalls or alternative construction material. therefore, in the second case study, the container model components have been redesigned with a different thickness. the new thickness assigned to each component is shown in table 5. the second case has identical mesh configuration, loading conditions, and constrained displacements with the formal case. table 5. the thickness of re-designed container components component side wall end wall top roof bottom floor thickness 22 mm 22 mm 26 mm 30 mm figure 8 presents the distribution of von mises stress of the re-designed container. the comparison between maximum von mises stress at various depths and yield strength for selected materials is shown in figure 9. the maximum von mises stress of the container model is lower than the yield strength of all three materials considered in this study. thus, the new container design can retain the structural integrity of the container in deeper water conditions. table 6 compares the effect of thickness on the maximum von mises stress between the original and thickened container at different water depths. it can be observed that the thickened container significantly reduces the maximum von mises stress when subjected to the same hydrostatic pressure conditions as the conventional container. (a) (b) (c) (d) figure 7. von mises stress distribution on the container at (a) 5 m, (b) 15 m, (c) 30 m,(d) 50 m water depths. 16 sustainable marine structures | volume 04 | issue 02 | july 2022 (a) (b) (c) (d) figure 8. von mises stress distribution of re-designed container at (a) 5 m,(b) 15 m,(c) 30 m,(d) 50 m. figure 9. the comparison between maximum von-mises stress at various depths and yield strength. table 6. the effect of thickness on maximum von mises stress water depth original configuration thicker configuration stress reduction 5 m 2.79e9 pa 1.58e8 pa 94% 15 m 8.38e9 pa 4.75e8 pa 94% 30 m 1.68e10 pa 9.49e8 pa 94% 50 m 2.79e10 pa 1.59e9 pa 94% 17 sustainable marine structures | volume 04 | issue 02 | july 2022 6. summary and conclusions in this study, finite element analysis was conducted to investigate the structural behaviour of shipping containers lost at sea. three different construction materials were discussed for conventional size containers. von mises stress was employed as a failure criterion. the hydrostatic pressure was increased with the water depth. for containers constructed with traditional configuration, the container lost its structural integrity in shallow water very quickly. the increased thickness reduced the von mises stress and made the container to retain its structural integrity at a deeper water level. unpredictable weather conditions and low operational risk awareness could cause shipping containers to be lost at sea. increasing the thickness of the container sidewall will increase production costs, but if the structure is damaged when fell into the water, the consigned goods may spread out in the sea and float. floating containers and consignments could pose a risk of collision with small ocean-going vessels such as yachts and fishing boats. moreover, if the container contains dangerous goods that may cause risk to the ecological environment, it is even more important to maintain the structural integrity of the container when it falls into the water to prevent any type of pollution. as an alternative solution to traditional container shipping, commercial type cargo submarines can be utilised especially for short distances. acknowledgement this work was funded by uk department for transport and delivered in partnership with innovate uk. conflict of interest there is no conflict of interest. references [1] lee, c.y., song, d.p., 2017. ocean container transport in global supply chains: overview and research opportunities. transportation research part b: methodological. 95, 442-474. [2] the international institute of marine surveying (iims), 2020. world shipping council containers lost at sea 2020 report issued and shows a decrease. [online] available at: <https://www.iims.org.uk/ world-shipping-council-containers-lost-at-sea-2020report-issued-and-shows-a-decrease/> (accessed 29 december 2021). [3] allianz, 2021. safety and shipping review. an annual review of trends and developments in shipping losses and safety. [4] zha, x., zuo, y., 2016. theoretical and experimental studies on in-plane stiffness of integrated container structure. advances in mechanical engineering. 8(3), 1687814016637522. [5] csc, 1996. international convention for safe containers. [6] giriunas, k., sezen, h., dupaix, r.b., 2012. evaluation, modeling, and analysis of shipping container building structures. engineering structures. 43, 4857. [7] antoniou, k., oterkus, e., 2019. origami influence on container design. annals of limnology and oceanography. 4(1), 015-019. [8] timoshenko, s.p., goodier, j.n., 1951. theory of elasticity. [9] astm international, 2013. astm a283/a283m13-standard specification for low and intermediate tensile strength carbon steel plates. [10] akkaş, n., 2017. welding time effect on tensile-shear loading in resistance spot welding of spa-h weathering steel sheets used in railway vehicles. acta physica polonica a. 131(1), 52-54. [11] zarzour, j.f., konkol, p.j., dong, h., 1996. stressstrain characteristics of the heat-affected zone in an hy-100 weldment as determined by microindentation testing. materials characterization. 37(4), 195209. https://www.iims.org.uk/world-shipping-council-containers-lost-at-sea-2020-report-issued-and-shows-a-decrease/ https://www.iims.org.uk/world-shipping-council-containers-lost-at-sea-2020-report-issued-and-shows-a-decrease/ https://www.iims.org.uk/world-shipping-council-containers-lost-at-sea-2020-report-issued-and-shows-a-decrease/ analysis of wave added resistance and motion response of fishing boat sailing against waves 1wang jing, 2zhou yu 1(china institute of marine technology and economy beijing 100081) 2(jiangsu shipping college nantong jiangsu 226010) abstract：in order to accurately predict the on wave resistance and responses to hull motions of ships in actual sea conditions, the k-εmethod of rng model is adopted on the basis of the unsteady rans method. the two-formula turbulence model deals with viscous flow, the vof method captures the free surface, the velocity boundary method makes waves, the artificial damping method is used to eliminate waves, and the nested grid technology is used to deal with the motion response of ships on waves. combined with the 6-dof motion formula, a three-dimensional numerical wave cell for regular waves is established. for one example, taking a fishing boat sailing at a high speed, the increase of wave resistance and motion response at different wavelengths are analyzed, and the simulation results are compared with the content of strip theory in potential flow theory and the panel method to prove the reliability of cfd method in predicting ship motion. key words: cfd method; wave added resistance; motion response; numerical pool; numerical simulation 1.introduction in the actual navigation process, the ship will be affected by waves of different degrees and some movement phenomena, such as heave and pitch. these motions will not only increase the resistance of the ship and reduce the propulsion efficiency, but also affect the normal operation of the equipment on the ship and the working efficiency of the crew, and even cause the ship to capsize. therefore, accurate prediction of the motion performance of hull is very vital for ship design. therefore, the study of ship motion characteristics in waves has become current hot spots in academic research[1]. the traditional method of studying ship motion performance is based on potential flow theory and model test. the theory based on potential flow has been widely used for its convenience and rapidity. particularly in that initial design stage of a ship, in order to quickly obtain the motion performance of ships, it has been favored by ship designers. however, because there is a big error between the numerical simulation results and the theoretical calculation results, it is difficult to accurate prediction of nonlinear results such as the increase of ship motion amplitude, wave breaking and waves on the deck[2].therefore, it is very important to obtain more flow field information at the stage of ship detailed design. although the calculation results of the model experiment are accurate, due to a large number of manpower and costs, it cannot meet the requirements of the current fierce market competition for rapid acquisition of new ship types. in recent years, with the rapid development of computer technology and mathematical knowledge, using cfd technology to predict wave resistance and motion performance has become a reality. cfd method not only considers the viscous effect, but also fully considers the nonlinear effect, so it has been widely used. many research results have been published at home and abroad to predict wave resistance and motion performance using cfd.in foreign countries, for rans formula, it is solved by orihara and miyata[3] through the finite volume method, and used the overlapping grid technology to simulate and calculate the wave resistance and motion of container ships in regular waves; the numerical value of the dtmb5512 ship type large-amplitude motion is calculated and summarized by carrica and wilson[4] ,which is at medium and high speed, using the overlapping grid technology; tezdogan and kemal demirel[5] and others evaluated the resistance and motion of container ships at low speed following the waves using the unsteady rans method.in china, the cfd solver naoe-foam-sjtu independently developed by shen zhirong[6] team based on the open-source code openfoam can well predict the motion performance of ships and marine engineering, and has been verified by experiments. zhao invention[7] and others developed a cfd hydrodynamic performance calculation system for ships based on the rans method of overlapping grids, which can well simulate the resistance and response of ship motion; shi bowen[8] and others set up a three-dimensional numerical simulation wave-making water channel based on the viscosity principle. in this way, the performance of ship navigation in irregular waves is simulated. however, the resistance and response of different ship types moving on the waves are different. the fishing boat is a high-speed ship, and there are few detailed studies on wave resistance and motion response. based on the above conditions and experience, this paper numerically simulates the motion of fishing boats in waves in a six-degree-of-freedom regular wave numerical pool based on unsteady rans method, calculates the wave resistance and motion response, and verifies the reliability of this method by numerical calculation. the numerical calculation methods here include strip theory method and panel method. the research results of this paper can provide technical support for the design and optimization of similar ships. 2. basic theory of cfd the formulas followed in the calculation domain of the whole simulated pool are the continuity formula and n-s formula, and the turbulence model adopts the k method of rng ε.in the model, capture free liquid surface by multiphase flow model method. and the wave is generated at the given wave velocity at that border of the speed inlet, and factitious damping setting is added wave pool exit area for wave attenuation. 2.1 control formula [9] （1） （2） where: ux, uy, uz velocity components in x, y and z directions; t time; ρis the quality density of fluid; -reynolds mean velocity；-reynolds stress. 2.2turbulence model the turbulence model adopts the k method of rng ε.in the model, the turbulent energy formula and energy consumption formula are in the following form [10]: （3） （4）where:；, -the reciprocal of turbulence kinetic energy's effective prandtl number and turbulent dissipation rate; 2.3 free face snap under the condition of keeping the euler grid unchanged, the interface between the ship and the water surface is captured by free following of the hull surface, which is called vof method. it can be used to simulate the multi-flow model by finding the solution of the momentum formula and volume fractions of a fluid or fluids. in any control volume, the sum of the volume fractions of all phases must be 1. for the each qth phase, the formula is: （5） （6） where: a1 and a2-are the volume fractions of water and air respectively, and aq=0.5, which is the limiting surface between water and air; q=0 which represents that entire computing domain is water; q=1 which represents that th entire computing domain is air. 2.4 wave making and wave absorption this wave-making adopts the velocity boundary method, which makes waves by giving the wave velocity at the boundary of the velocity entrance[12]. compared with the physical test pool, it has high economic value, convenient operation, high calculation accuracy and slow attenuation.. at the same time, this method is easier to give a fixed the velocity of the vessel at the entrance boundary, which can avoid difficulties brought form moving the boundary, which is another advantage compared with the simulated physical method. the wave surface formula is: （7） the speed influences are as follows: （8） （9） where: a is wave amplitude. k=2 π/ λ determine, which is called wave number. ω 0 natural frequency of wave,. ωe can be calculated by formula:ωe＝ ω0+ku, which is called the frequency of a wave as measured by its relative velocity and wavelength.this equation shows that ωe varies with the change of the velocity of the vessel u. the expression of artificial damping coefficient μ is as follows: （10） where: xf ≤ x ≤ xa (f and a are the two endpoints of the resistance region in the x direction, separately); zd ≤ z ≤ zu (d and u are the bottom along the y direction and the intersection of water and air separately); α is the damping control parameter. 2.5 dof equation of motion when establishing the ship motion formula, two reference coordinate systems are established. one is the fixed coordinate system ooxoyozo, which is fixed on the earth; the other is the ship moving coordinate system gxyz, which is fixed on the ship[13]. the origin of the moving coordinate system is located at the center of gravity g of the ship, where gx, gy and gz are the intersection lines of the longitudinal section, the transverse section and the horizontal liquid level passing through the center of gravity g, respectively, and the downward direction of the z axis is positive. （11） （12） where, ω is the angular velocity, b is the ship's moment, f is the additional force, u is the ship's speed, k is the moment of momentum, and m is the sum moment. 3. example the wave resistance and body responses of high-speed fishing boats sailing in waves are calculated. figure 1 shows the fishing boat’s geometric model. and the main dimensions and hull form parameters are shown in table 1. fig1. geometric model of the fishing vessel table 1. the fishing vessel’s main dimensions and hull form parameters parameter full-scale ship model unit length between perpendiculars（lpp） 34.5 4.8 m draft（d） 2.5 0.35 m moulded width（b） 7.6 1.06 m square coefficient（cb） 0.597 0.597 displacement (△) 425 1.45 t wet surface area（s） 324 6.27 m2 design speed 35 13 kn 3.1 calculation domain and boundary conditions according to the symmetry of the hull, it can be assumed that the flow field is also symmetrical in the numerical simulation, and the symmetry plane is the x-z plane. considering the parameters such as wavelength, period and wave height of simulated linear waves, taking half of the hull as the calculation domain can effectively improve the calculation speed. taking the calculation range of 4.5l×2.0l×2.5l (where l is the captain and the unit is m) as the whole calculation domain, that is, the numerical simulation research object. the distance between the bow and the pool entrance is l, and the simulated water depth is 1.5l. the specific dimensions are shown in figure 2. the upper part of the computational domain is air and the lower part is water. (a) (b) fig2. calculation domain and boundary conditions the boundary setting of velocity inlet is applied to the front surface, upper surface and lower surface of numerical simulation wave pool respectively, and the inflow velocity is added to the boundary of the front surface, which is the velocity of the vessel. attach the pressure outlet parameter to the rear surface. attach a rigid surface (wall) parameter to the surface of the boat. finally, the calculation domain is set to be symmetric on the boundary of the middle longitudinal profile and its opposite sides. 3.2 meshing meshing is an essential part of the numerical simulation process. if you change the density and form of the grid, it will change the overall simulation time and the judgment of the results. therefore, only by grasping the effect of the grid can you control the accuracy and reliability of the calculation results. in this paper, the embedded grid technology is applied in the commercial software star-ccm+, and static and dynamic grids are established. as to better analyze the ship's trajectory and sway on waves. among them, static grids sparsely drawn, and dynamic grids can be densely drawn with encrypted grids. overlap and background grid junction should be excessive according to a constant ratio. interface between air and water must be no less than 80 grilles in the wavelength distance and no less than 20 gratings in the peak to trough range. considering the machine configuration and simulation time, the total number of grids finally determined is 1.85 million. figure 3 shows the grid near the free surface. as can be seen from the figure, the closer to the hull, the more dense the grid, and the farther away from the hull, the more sparse the grid. figure 4 shows the size and shape of the hull surface grid. and grid encryption is needed at the bow and stern. fig3. grid division of free surface and longitudinal section fig4. hull grid division 3.3 grid independence check mesh number has a great impact on the calculation results. the number of grids is too large, which wastes computing resources, is too small, and the results are inaccurate. as a result, it is essential to find a number of grids appropriately. in this paper, five types of grids are calculated respectively, and the calculation grid with less influence on the calculation results due to the increase of grid is obtained. future calculations are based on this grid. the calculation results are shown in figure 5. fig 5. grid independence 3.4 calculation conditions of wave drag increase this paper mainly simulates the motion law of fishing boats under different wavelength length ratio and different wave steepness. take the wavelength to length ratio:λ/ l=0.75,λ/ l=1.00,λ/ l=1.25,λ/ l=0.50,λ/ l=7.75,λ/ l=2.00; and wave steepness: 0.0175, 0.035, 0.0775, 0.0875 as the calculation conditions. the volume fraction of fishing boats is shown in figure 5. fig5. volume fraction of the fishing vessel 4. analysis of simulation results figure 6 shows the relationship between the shear stresses received by the fishing boat hull over a period of time. it can be seen from the figure that the hull shear stress will change continuously with the wave peak and its steepness, especially the bow will bear huge shear stress in 1/4-1/2 cycle, because the bow is located at the wave peak position at this time, and there will be phenomena such as burying the bow or wave on the deck. (a)t/te=0.00 (b)t/te=0.25 (c)t/te=0.50 (d)t/te=0.75 fig 6. change of hull shear stress over a period of time (fn=0.28, λ/ l=1.0) figure 7 shows the change relationship of the free surface of the hull over a period of time. it can be seen from the figure that the change of draught at the bow and both sides of the hull can clearly show severe heave movements and pitch movements. in addition, waves appeared on the deck. the severe pitching motion may cause the bulbous nose to constantly enter and exit the water surface, resulting in a loud bang on the head, which will worsen the seakeeping of the ship. (a)t/te=0.00 (b)t/te=0.25 (c)t/te=0.50 (d)t/te=0.75 fig7. waveform of interface between water and air in one cycle (fn=0.28, λ/ l=1.0) figure 8, figure 9 and figure 10 are the comparison of the cfd simulation results of the heave, pitch transfer function and wave resistance coefficient of fishing vessels using the slice theory and the panel method respectively. it can be seen from the figure that the calculation curve trend of the three methods is basically the same, and they can well predict the relationship between heave, pitch and wave resistance with the increase of wavelength-to-length ratio. the accuracy of the cfd calculation method has been confirmed by engineering practice, so the cfd simulation results should still prevail in the absence of test values. in addition, the heaving and pitching relationships of the fishing vessel under different wave steepness are also studied. as can be seen from the figure 11, the heave of the ship increases slowly and gradually with the increase of wave steepness. in contrast, the pitching of a ship increases rapidly and gradually with the steep waves. fig8.the heave transfer coefficient fig 9. the pitch transfer function fig 10. wave resistance coefficient fig 11. the heaving and pitching values of the fishing vessel under different wave steepness 5. conclusion based on the cfd method, the commercial cfd software star-ccm+is used to study the resistance and motion response of high-speed fishing boats in waves. the first order stokes wave numerical flume is established to simulate the wave resistance, heave and pitch motion response of fishing vessels under the condition of wavelength length ratio of 0.75 to 2.25. the shape of the kelvin free surface wave system is reproduced, and the relationship and reason of the change of the hull surface shear stress are analyzed. finally, the results of cfd numerical simulation are compared with those of strip theory and panel method, which shows that the cfd method has advantages in simulating ship motion and resistance. reference [1]zakerdoost.h,ghassemi.h,ghiasi.m.ship hull form optimization by evolutionary algorithm in order to diminish the drag[j]. j marine sci,appl.2013.(12):170-179. [2]serani a. hybrid global/local optimization methods in simulation-based shape design [d]. universit`a degli studi roma tre,2016. [3] zhao feng, li shengzhong, yang lei. review of research progress in ship form optimization design based on cfd [j]. ship mechanics，2010, 14 (7):812 -821. [3]orihara h, miyata h. evaluation of added resistance in regular incident waves by computational fluid dynamics motion simulation using an overlapping grid system[j]. journal of marine science and technology, 2003, 8(2): 47-60. [4]carrica p m, wulson r v, noack r w et al. ship motions using single-phase level set with dynamic overset grids[j]. computers and fluids, 2007,36(9): 1415-1433. [5]tezdogan t, demirel y k, kellett p et al.full-scale unsteady rans cfd simulations of ship behaviour and performance in head seas due to slow steaming[j].ocean engineering,2015,97: 186 -206. [6]shen zhi-rong , ye hai-xuan, wan de-cheng.urans simulations of ship motion responses in long-crest irregular waves[j].journal of hydrodynamics, 2014,26(3):436-446. [7] zhao invention, gao chengjun, xia qiong. application of overlapping grids in ship cfd [j]. ship mechanics，2011. 15(5): 332-341. [8] shi bowen, liu zhengjiang, wu ming. numerical simulation of top wave motion in irregular waves of ship model [j]. ship mechanics，2014，18（8）：906-915. [9]lin p, liu p l f. a numerical study of breaking waves in the surf zone[j]. journal of fluid mechanics, 1998,24(3):239-264. [10]sheng-long zhang,bao-ji zhang,tahsin tezdoganle-ping xu,yu-yang lai . computational fluid dynamics based hull form optimization using approximation method, engineering applications of computational fluid mechanics,2017,12(3): 1-8. [11]masoudian m，pinho ft，kim k，et al. a rans model for heat transfer reduction in viscoelastic turbulent flow[j]. international journal of heat & mass transfer. 2016， 100：332-346. [12]claus, d., simonsen, j.f. and otzen, s.j.. efd and cfd for kcs heaving and pitching in regular head waves. journal of marine science and technology,2013,18:435–459. [13]sheng-long zhang,bao-ji zhang,tahsin tezdoganle-ping xu,yu-yang lai.research on bulbous bow optimization based on the improved pso algorithm, china ocean engineering, 2017,(33)4: 487494. [14]maki a, umeda n, renilson m, et al. analytical formulae for predicting the surf-riding threshold for a ship in following seas[j]. journal of marine science and technology, 2010, 15(3): 218-229 i u ' ' j i u u r () () [()] i keffkbm ijj ku kk ggy txxx r r amre ¶ ¶¶¶ +-=+-¶¶¶¶ 2 132 () () [()]() i effkb ijj u cgcgcr txxxkk eeee re reeee amr ¶ ¶¶¶ +-=+-¶¶¶¶ 2 eff k c m mmr e =+ k a e a 0 ) ( ) ( ) ( = ¶ ¶ + ¶ ¶ + ¶ ¶ + ¶ ¶ z wa y va x ua t a q q q q å = + = ñ + ¶ ¶ n p qp pq q q q q q m m s v t q 1 . . ) ( 1 * r r a a a ) cos( t kx =a e w h u t kx e u=a e kz + ) cos( 0 w w ) sin( 0 t kx e w=a e kz w w l p w / 2 0 g = 2 £ (,)()() f d afdu xx zz xz xxzz ma = -f b = ´ w + dt db m b u k = ´ + ´ w + dt dk () () () 0 y x z u u u txyz r r r r ¶ ¶ ¶ ¶ +++= ¶¶¶¶ i j j i j j i i j i j i f x u u x x u x p x u u t u r r m r r + ¶ ¶ ¶ ¶ ¶ + ¶ ¶ = ¶ ¶ + ¶ ¶ ' ' 2 35 sustainable marine structures | volume 04 | issue 01 | january 2022 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2022 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). *corresponding author: chandrasekaran, s., department of ocean engineering., iit madras, chennai, india; email: drsekaran@iitma.c.in doi: http://dx.doi.org/10.36956/sms.v4i1.490 short communication functionally graded material and its application to marine structures chandrasekaran, s.1* hari, s.2 1. department of ocean engineering., iit madras, chennai, india 2. school of petroleum technology, pandit deendayal petroleum university, gandhinagar, india article info abstract article history received: 14 february 2022 accepted: 21 february 2022 published online: 28 february 2022 marine structures are exposed to harsh weather conditions, demanding special pre-requisites in design and functional perspectives. under dynamic loads of larger magnitude, the material-centric design procedure alone is not feasible to ensure the safe disbursement of loads. the compliant offshore structures resist loads primarily by their geometric novelty, and hence their design is form-dominant and no more strength (material) dominant. large displacements in the rigid body modes in the horizontal plane under lateral loads require their construction material to possess enough ductility to absorb this energy. steel is one of the most competitive materials for marine structures as it offers good ductility, but corrosion in the marine environment is a major concern. it undergoes strength and functional degradations and therefore requires serious investigation. in the present study, functionally graded material (fgm) is proposed to substitute for steel in marine applications. the method of fabricating fgm and assessing its mechanical and durability properties are discussed. results show that fgm possesses strength and durability properties at par with the conventionally used x52 steel for marine risers. the presented study will be a major initiative towards future research in exploring competent materials which will be strong and sustainable in the marine environment. keywords: marine structures functionally graded materials marine riser offshore structures form-dominant design 1. form-dominant design approach offshore structures are intended to perform oil and gas exploration under the marine environment while facing many challenges in extreme load combinations, sustainability against the corrosive environment, and a quick return on investment (roi) [1,2]. the exploration activities towards ultradeep water and arctic regions induced a paradigm shift in their design procedures [3]. advances in technology and industry maturity make deepwater oil and gas exploration an attractive investment. furthermore, wind and wave energy have become the recent focus and pivotal points of attraction for green energy harvest. environmental loads that arise from mailto:drsekaran@iitma.c.in http://dx.doi.org/10.36956/sms.v4i1.490 36 sustainable marine structures | volume 04 | issue 01 | january 2022 waves, wind, and current become more severe in ultradeepwater. offshore engineers are increasingly deploying compliant systems that are permitted to undergo large displacements. for example, exploratory and production drilling has become more comprehensive with the recent developments in the design of semi-submersibles [4]. effective design methods, based on the postulated failure analyses help arrive at the safer and sustainable design of platforms for extreme ocean conditions. the natural periods and damping ratios for the semi-submersible at 1500 m and 2000 m water depths, with and without a submerged buoy, are obtained from free-oscillation tests; results are shown in table [5]. it is seen that considerable periods in the surge, sway indicate higher flexibility about the horizontal plane. in contrast, small periods in roll, pitch, and heave show that they are stiff in the vertical plane. by this compliant approach in the design, natural periods in sway and yaw are found to be increased, along with a significant increase in the damping ratios for the surge, pitch, and yaw in the presence of a submerged buoy. it is interesting to note that a semi-submersible platform is usually characterized by possessing free modes, indicating that the natural periods in all degrees of freedom are above the wave periods [6]. postulated failure analysis for compliant platforms helps investigate the failure modes under extreme conditions to assess their survivability. surge response is significantly higher in the case of postulated failure of mooring lines. addition of buoy at an appropriate location in the mooring help to reduce the response of mooring lines [4]. surge response, which is the controlling factor for design is significant in the absence of submerged buoys. compliant offshore platforms are designed to resist lateral loads from waves, current and wind by their innovative geometric form. see, for example, tension leg platform (tlp), spar, triceratops, and semi-submersibles. out of the six degrees of freedom exercised by the rigid body motion of these platforms, two translational and one rotational degree, namely surge, sway, and yaw, are very flexible, exhibiting considerable periods. it makes the platform flexible in the horizontal plane and enables it to resist the lateral loads by undergoing large displacements. the remaining degrees of freedom, namely heave (translational in z-axis) and roll and pitch (rotational), exhibit very stiff behaviour and make the platform rigid in the vertical plane. such hybrid motion characteristics are salient features of compliant platforms. let us consider a tlp, whose conceptual figure is shown in figure 1; a figure of neptune tlp shown by the side gives an idea of various structural components. it consists of vertical columns and pontoons designed as tubular members to enhance buoyancy. as the design concept conforms to the fact that buoyancy shall exceed the weight of the platform, it is position-restrained by tethers, which are under axial pretension to balance the excessive buoyant force. as a result, motion on the vertical plane such as heave, pitch and roll are restrained while it allows large displacements along with surge, sway and yaw degrees-of-freedom. table 1. dynamic characteristics of moored semisubmersible [5] description surge sway heave roll pitch yaw without buoy 1500 m water depth tn (s) 209 165 21 24 25 49 ζ (%) 6.15 6.92 2.47 2.97 0.93 6.51 2000 m water depth tn (s) 193 184 25 25 25 54 ζ (%) 5.84 6.38 4.15 4.75 1.91 7.98 with buoy 1500 m water depth tn (s) 195 183 21 23 24 54 ζ (%) 6.56 6.77 1.20 1.44 1.32 10.36 2000 m water depth tn (s) 213 199 21 23 24 53 ζ (%) 6.87 6.21 1.45 1.06 0.83 4.61 as seen in figure 2 [7], which illustrates the tlp mechanics, a strong coupling is seen between surge (offset) and heave (set down) motion. large displacements along surge invoke a supportive resistance from heave motion, which helps to encounter the lateral loads. this formdominance characteristic makes their design unique, imparting a design shift from material strength-dominant to form-dominant. in addition, the horizontal components of the increased tension in the tethers help the platform return to its equilibrium position under the presence of loads. it is referred to as recentering, and geometric stability is imposed by the recentering ability taught in the design. another classic example is the triceratops, shown in figure 3 [7]. offshore triceratops is a new generation of offshore platforms that are intended for use in ultradeep waters. the deck of the platform is supported by the buoyant legs, which are, in turn, anchored to the seabed using pre-tensioned tethers. ball joints are placed between the deck and the buoyant legs (please, see figure 3), which partially isolate the deck from the buoyant legs and help counteract the lateral loads and moments [8]. these ball joints transfer only the translations from the legs to the deck and vice-versa; they restrain the moment’s transfer and thus partially isolate the deck from the buoyant legs. such design methods are often referred to as form-dominant design, which forms the basis for most of the compliant offshore structures. large displacements of such compliant structures demand a ductile material to absorb these motions without 37 sustainable marine structures | volume 04 | issue 01 | january 2022 any strength degradation [1,2]. although steel is recognised as the most suitable material, it corrodes in the marine environment. hence, in addition to the desired strength requirements, materials for marine structures should also possess desirable functional requirements for their sustainability in the marine environment. a few of them are namely corrosion-resistance, anti-biofouling, and nontoxic. no single material can meet all such challenges of functionally and structurally excellent. furthermore, even if such materials are manufactured, they cannot be used to construct marine structures unless the design codes of practices recommend them. therefore, the current trend is to address the design by strength considerations and fulfil others using chemical or biological treatments. as a result, the sustainability of marine structures encounters a bi-fold problem: one concerning strength degradation and the other is the functional degradation under ageing. this challenge faced by the marine structures during their service life needs to be addressed to make them sustainable and functional. 2. functionally graded material functionally graded materials (fgm) are useful in the defence, aerospace, and medical field; recent attempts are made to assess their use in the marine environment [9]. process industries where pipelines are subjected to corrosion under chlorides and sulphides, many mechanical components and appurtenances are replaced with fgm [10]. fgm is a novel material manufactured by functionallygrading two metal components, which are chosen based on strength and corrosion resistance. manufacturing a) conceptual figure b) neptune tlp [3] figure 1. offshore tension leg platform figure 2. tlp mechanics figure 3. offshore triceratops 38 sustainable marine structures | volume 04 | issue 01 | january 2022 such materials is a big challenge as the manufacturing process shall impose significant challenges in achieving the desired properties of fgm [11]. in the manufacturing process of fgm, materials of desired characteristics are chosen, and their geometric compositions (not the metallurgical composition), in terms of thickness and number of layers, are varied continuously across the cross-section. thus, the composition and microstructure are altered along the cross-section to generate the desired property gradient. it is intended to utilise completely the mechanical, metallurgical and structural properties of the original materials while forming the fgm [12]. the wire arc additive manufacturing method (waam) enables the metallurgical composition of user-defined materials by a step-wise addition [13]. the component metals are deposited in layers in wires, while an electric arc is used as the heat source. metallic wires are advanced using a secondary wire-feeder at the desired speed. a high-pulse current is supplied to form an arc between the electrode wires and the substrate, resulting in the melting of the filler tip of these advancing wires. a stainless-steel substrate is used to deposit the materials, while a highpower source is used for the deposition process. figure 4 shows various components of the waam unit, namely the cold metal transfer (cmt) torch, the substrate and the cnc machine integrated with the torch. the deposition parameters for the waam process are based on the constituent materials and the appropriate fillers. marine risers are subjected to severe corrosion in the presence of hydrogen sulphide and chlorides. further, stress corrosion is accelerated due to the high-pressure and high-temperature conditions [14]. hence, marine risers are a classic example of structural members under stress concentration and corrosion. x-52 steel is a common candidate for marine risers. in the present study, x-52 carbon-manganese steel is graded with duplex stainless steel to manufacture fgm on the lab scale. the chosen materials are code compliant for marine structures [15,16]. while duplex stainless steel possesses a higher corrosion resistance in acidic conditions, x-52 steel is a good strength contributor. as discussed in the earlier section, materials for fgm are chosen based on the functional requirements, namely strength and corrosion resistance. figure 5 shows the cross-section of the riser under investigation, where the inner layer of 3 mm is duplex stainless steel, and the rest of 14 mm is carbon manganese steel. the sizing of the riser is as per the existing riser of auger tlp [17]. x-ray computed tomography test on the fgm build confirmed that it is free from porosity and micro-cracks. fgm build, extracted from the manufactured specimen, is shown in figure 6, where the optical markers are made to assess the longitudinal and lateral strain during the tension test. it is important to note that loading is applied parallel to the interface of the materials to observe its behaviour at the critical interface (please see, figure 7). figure 4. waam unit used to manufacture fgm. figure 5. cross-section of riser under investigation figure 6. fgm build extracted from the specimen. the tension tests are carried out on the fgm specimens at a strain rate of 1x10-3 s-1. the ultimate strength of fgm samples is about 600 mpa, while the yield strength is about 400 mpa, with the modulus of elasticity computed as 213 gpa. compared with x-52 steel, one can observe a significant increase in the ultimate and yield strength with a very high ductility ratio. results are summarised in table 2. as seen in figure 9, the fractured sample confirms that the failure is not along with the interface of the constituent metals but similar to structural grade steel. 39 sustainable marine structures | volume 04 | issue 01 | january 2022 a) load direction b) loaded specimen c) fractured specimen figure 7. tension test at the interface of the constituent metals, an elemental line energy dispersive x-ray analysis (edx) is carried out to determine the chromium variation along with the interface. figure 9 shows the edx image, which verifies that the chromium content in duplex stainless steel is about 22% at 35 microns from the interface, and it is closer to the duplex stainless steel side. it offers corrosion resistance to fgm. x-ray diffraction analysis (xrd) resulted in an output confirming a prominent peak of (cr 0.1, fe 1.9) indicating the presence of chromium oxide at the interface regions. a) longitudinal direction b) lateral direction figure 8. stress-strain relationship of fgm table 2. mechanical properties of fgm builds material/parameters x52marine riser steel fgm youngs modulus (gpa) 210 209.66 ± 4.48 yield strength (mpa) 358 390.66 ± 12.23 ultimate strength (mpa) 453 587.66 ±12.76 strength ratio 1.265 1.50 ± 0.02 ductility ratio 32.207 45.47 ± 0.82 tensile toughness (j/m3) 104.92 120.50 ± 2.84 poisson`s ratio 0.3 0.30 ± 0.07 % elongation 21 22.31± 0.11 variation in micro-hardness along the build is assessed using the vickers hardness test. figure 10 shows the result, which confirms that hardness is in the range of (307-320) at the interface. a pitting corrosion test showed about twelve times more corrosion in x52 steel than the proposed fgm. 40 sustainable marine structures | volume 04 | issue 01 | january 2022 figure 9. edx image at the interface of fgm mould figure 10. micro-hardness variation in fgm build 3. conclusions materials for the construction of marine structures should complement the form-dominance criteria and the strength and functional requirements to sustain the ocean environment hazards. while the design procedures are shifted to a form-centric approach, properties in materials need to be upgraded in parallel. the presented study illustrated the fabrication of fgm and its application to marine structures.more details can be seen in the detailed studies carried out by the authors [10,12]. it is seen that fgm possesses a higher yield and ultimate strength in comparison to the steel currently deployed for marine construction. in addition, it also offers excellent corrosion resistance, which was not satisfactory in the former. significant enhancement in ductility guarantees i t s c o m p l e m e n t a r y s u p p o r t t o l a rg e d i s p l a c e m e n t characteristics of compliant marine structures. rigorous s t u d i e s o n s i m i l a r l i n e s w o u l d s u ff i c e a s t r o n g e r inclination for the design codes to recommend fgm as a structural material shortly. references [1] chandrasekaran, s., arvind kr. jain, nasir shafiq, m., et al., 2021. design aids for offshore platforms under special loads, crc press, florida. pp. 280, isbn: 9781032136844. [2] chandrasekaran, s., nagavinothini, r., 2020, offshore compliant platforms: analysis, design and experimental studies, wiley, u.k, isbn: 978-1-11966977-7. [3] chandrasekaran, s., 2019. advanced steel design of structures, crc press, florida, isbn: 978-036-723290-0. [4] chandrasekaran, s., 2020. offshore semi-submersible platform engineering, crc press, florida. pp. 240, isbn: 978-0367673307. [5] chandrasekaran, s., syed azeem uddin, 2020. dynamic analysis of semi-submersible under postulated failure of restraining system with the buoy, intl. j. of steel structures. 21(1), 118-131. [6] dnv-rp-f205, 2010. global performance analysis of deepwater floating structures. [7] chandrasekaran, s., nagavinothini, r., 2020. parametric studies on the impact response of offshore triceratops in ultra-deep waters, structure and infrastructure engineering. 16(7), 1002-1018. [8] chandrasekaran, s., nagavinothini, r., 2020. offshore triceratops under impact forces in ultra-deep arctic waters, int. j. of steel structures. 20(2), 464479. [9] albino, j.c.r., almeida, c.a., menezes, i.f.m., et al., 2018. co-rotational 3d beam element for nonlinear dynamic analysis of risers manufactured with functionally graded materials (fgm), engineering structures. 173, 283-299. [10] chandrasekaran, s., 2020. design of marine risers with functionally graded materials, woodhead publishing, elsevier. pp. 200, isbn: 978-0128235379. [11] chen, x., li, j., cheng, x., et al., 2017. microstructure and mechanical properties of the austenitic stainless steel 316l fabricated by gas metal arc additive manufacturing, mat. sc. and engg.,: a. 703, 567577. [12] chandrasekaran, s., hari, s., murugaiyan, a., 2020. wire arc additive manufacturing of functionally graded material for marine risers, j. mat. sc., & engg. a. 792, 139530. [13] martina, f., mehnen, j., williams, s.w., et al., 2012. investigation of the benefits of plasma deposition for the additive layer manufacture of ti–6al–4v, j. mat. 41 sustainable marine structures | volume 04 | issue 01 | january 2022 processing tech. 212(6), 13. [14] shen, y., jukes, p., 2015. technical challenges of unbonded flexible risers in hpht and deep-water operations, proc. of twenty-fifth int. offshore and polar engg. conf., june 21-26, hawaii, usa. [15] dnv, g., 2018. dnvgl-rp-f112 duplex stainless steel – design against hydrogen-induced stress cracking, dnv gl, 1-44. [16] dnv, g., 2012. dnv-os-f101 submarine pipeline systems, oslo: dnv gl, 1-367. [17] phifer, e.h., kopp, f., swanson, r.c., et al., 1994. design and installation of auger steel catenary risers, proc. of offshore technology conference, 2-5 may, houston. 19 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v2i2.308 sustainable marine structures http://ojs.nassg.org/index.php/sms article spatio-temporal variability of dinoflagellates in different salinity regimes in the coast of rakhine khin khin gyi1 wint thuzar nwe1 zin zin zaw2 khin khin san3 1.department of marine science, mawlamyine university, mon state, mawlamyine, 12012, myanmar 2.department of marine science, pathein university, ayeyarwady division, pathein, 10014, myanmar 3.department of marine science, sittway university, rakhine state, sittway 07011, myanmar article info abstract article history received: 3 january 2021 accepted: 5 february 2021 published online: 30 march 2021 regarding the spatial and seasonal variations of dinoflagellates in different salinities regimes, prorocentrum rostratum showed a strong correlation with high salinity (≥ 29 ppt.). however, p. micans had a negative correlation with salinity. in dinophysoids, dinophysis caudata showed a wide salinity tolerance than other species in the group. d. miles, ornithocercus magnificus, o. steinii, and o. thumii showed a strong correlation with salinity. in gonyaulacoids, ceratium furca, c. fusus, c. horridum, c. trichoceros, c. tripos, gonyaulax polygramma, g. spinifera, and pyrophacus magnificus showed a strong correlation with salinity. in peridinoids, protoperidinium depressum, p. oblongum, p. oceanicum, p. pyreforme, and podolampus palmipes showed a strong correlation with salinity. in gymnodinoid and noctilucoid, gyrodinium estuariale and n. scintillans showed a strong correlation with salinity. keywords: dinoflagellates salinity seasonal spatial 1. introduction dinoflagellates are important components of the phytoplankton in the near-shore and continental shelf environments [1]. along with diatoms, over half of dinoflagellates are photosynthetic [2,3,4]. their ecology and biology have permitted them to be among the most successful aquatic protists, capable of surviving in different conditions of resource availability [5,6]. they are one of the major groups of primary producers that constitute the basic source of energy in aquatic food webs [7,8]. because of the annual variability in species composition of dinoflagellates, these species are regularly monitored in many developed countries. in myanmar, however, has not yet set effective monitoring programs, though there are reports of some bloom events that had been occurred in the coastal area. since the south-west monsoon (swm) is the main source of climatic variations subjected to make changes in the physicochemical parameters which in turn affecting dinoflagellate community structure in the water column [9,10]. thus, observations on salinity and species occurrence of dinoflagellates were made monthly during three consecutive periods 2012, 2013, and 2014. 2. materials and methods 2.1 environmental parameters of the study area the rakhine coast experiences intense rainfall during *corresponding author: khin khin gyi, department of marine science, mawlamyine university, mawlamyine city, mon state, myanmar; email: khinkhin.marinescience@gmail.com 20 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 the monsoon months of june-september causing variations in salinity ranges. during the summer season (februarymay), salinity was higher (32-34 ppt.) in all stations, and the lowest salinity range, 21-23 ppt. is in the rainy season, (june-september). 2.2 sampling sites and sample collection a total of eight sampling sites were set along the rakhine coast. sampling sites were plotted at wetthe (wte) (n17º 08´ 34.474”, e94º 27´51.226”) as station-1; magyi tidal creek (upper) (mgu) as station-2; magyi tidal creek (lower) (mgl) as station-3; magyi coastal area (mgc) as station-4; kyauk-maung-nama (kmn) as station-5; phoe-kala island (pki) as station-6; ngwe-saung (nsg) as station-7 and chithu island (cti) near ngwesaung beach (n16º 49´6.243”, e94º 23´8.757”) as station-8, respectively. among the stations, stations 2, 3, and 7 are in and near the tidal creek; stations 1, 5, and 8 are in the open coastal areas and stations 4 and 6 are at the mouth of the tidal creek. figure 1. sample collection sites at rakhine coastal waters. the sample collection was made by scooping a known volume of surface water using a basket and sieved with a 20 µm mesh phytoplankton net. then transferred the water sample to the plastic bottles and immediately fixed it with formalin (final concentration 1%). while collecting the samples, water salinity was measured in-situ with a refractometer. triplicate analysis of 1 ml sub-sample was taken from the samples and count with the sedgwick-rafter chamber. pearson’s correlation coefficient was performed to analyze the relationship between dinoflagellate species and the salinity. 3. results and discussion 3.1 seasonal variations of salinity at station 1, wte, the highest salinity occurred in late summer, march-april, and the range was 34 ppt. in 2012; 33 ppt. in 2013 and 32-33 ppt. in 2014. during the monsoon period, july to september, salinity reaches its minimum values, 25-26 ppt. in 2012; 23-24 ppt. in 2013 and 23-25 ppt. in 2014. mean salinities were 29.6±3.1 in 2012; 28.25±3.65 in 2013 and 28.5±2.87 in 2014. at station 2, mgu, the highest salinity occurred in late summer, march-april, and the value was the same 30 ppt. in three successive years, 2012, 2013, and 2014. station 2 has highly fluctuated with terrestrial runoff. during the monsoon period, july to september, salinity reaches its minimum values, 13-16 ppt. in 2012; 13-19 ppt. in 2013 and 13-18 ppt. in 2014. mean salinities were 22.92±5.79 in 2012; 23±5.24 in 2013 and 22.75±5.48 in 2014. at station 3, mgu, the highest salinity occurred in late summer, march-april, and the values were 29-32 ppt. in 2012; 32 ppt. in 2013 and 2014. during the monsoon period, july to september, salinity reaches its minimum values, 25-24 ppt. in 2012, 2013 and 24-25 ppt. in 2014. mean salinities were 27.92±2.84 in 2012; 28.2±2.91 in 2013 and 28.2±3.1 in 2014. at station 4, mgc, the highest salinity occurred in late summer, march-april, and the values were 33-34 ppt. in three successive years, 2012, 2013, and 2014. during the monsoon period, july to september, salinity reaches its minimum values, 25-26 ppt. in 2012, 22-24 ppt. in 2013 and 23-25 ppt. in 2014. mean salinities were 25.50±5.77 in 2012; 26.25±5.00 in 2013 and 23.93±6.24 in 2014. at station 5, kmn, the highest salinity occurred in late summer, march-april, and the values were 29-32 ppt. in 2012; 32 ppt. in 2013 and 2014. during the monsoon period, july to september, salinity reaches its minimum values, 18-21 ppt. in 2012, 24-22 ppt. in 2013 and 2524 ppt. in 2014. mean salinities were 26.7±5.68 in 2012; 27.83±3.98 in 2013 and 28.08±3.04 ppt.in 2014. at station 6, pki, the highest salinity occurred in late summer, march-april, and the values were 34 ppt. in 2012; 2013 and 2014. during the monsoon period, july to september, salinity reaches its minimum values, 26-24 ppt. in 2012, 26-23 ppt. in 2013 and 26-25 ppt. in 2014. doi: https://doi.org/10.36956/sms.v2i2.308 21 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 mean salinities were 29±3.81 in 2012; 29±3.51 in 2013 and 29.58±3.55 ppt.in 2014. at station 7, nsg, the highest salinity occurred in late summer, march-april, and the values were 32-33 ppt. in 2012; 33-34 ppt. in 2013 and 34 ppt. in 2014. during the monsoon period, july to september, salinity reaches its minimum values, 26-25 ppt. in 2012, 2013 and 2827 ppt. in 2014. mean salinities were 29±3.19 in 2012; 29.33±3.22 in 2013 and 30.58±2.63 ppt.in 2014. at station 8, cti, the highest salinity occurred in late summer, march-april, and the values were 32-33 ppt. in 2012; 33-32 ppt. in 2013 and 32-33 ppt. in 2014. during the monsoon period, july to september, salinity reaches its minimum values, 27-26 ppt. in 2012, 26-25 ppt. in 2013 and 24-25 ppt. in 2014. mean salinities were 29.42±2.6 in 2012; 29.17±3.02 in 2013 and 28.58±3.55 ppt in 2014. in the present study, the mean salinities of the study period, 2012-2014, were 29 ppt., 27 ppt., 28 ppt., 30.3 ppt., 30.1 ppt., 29 ppt., 30 ppt., and 29 ppt. at stations 1, 2, 3, 4, 5, 6, 7 and 8 respectively. salinity distributions in all sampling stations vary from month to month within seasons (table 1). the mean salinity of the whole study area was 29±2.83, and the mean salinity at the sampling stations was 29±1.2 part per thousand. figure 2. mean salinity at sampling stations of the study areas during 2012-2014. 3.2 spatio-temporal variations of dinoflagellates prorocentroids cell density varied from 1500 to 1780 cells l-1 during the study period. the cell density of dinophysoids varied from 810 to 1590 cells l-1 during the summer and post-monsoon periods. two genera such as dinophysis and ornithocercus were mainly composed in the dinophysoid group which occupied 40% and 60%, respectively. gonyaulacoids was the largest and dominant group in the study area, and the cell density ranged from 540 to 1770 cells l-1. a total of six genera were occupied in the table 1. mean salinity of the study area during 2012-2014. no. months wte mgu mgl mgc kmn pki nsg cti mean sd 1. jan 30.7 28.7 29.7 32 32.3 32 31.7 32 31.1 1.2 2. feb 31.7 29.3 30 33.3 33 33 33 32.7 32 1.4 3. mar 33 30 32 34 33.7 34 33.7 32.3 32.8 1.3 4. apr 33.3 30 32 33.7 33 33.7 33.7 31.7 32.6 1.2 5. may 30.3 27.7 29.7 31.7 31.3 31 30.7 29.7 30.3 1.2 6. jun 27.7 26 27.3 30 29.3 28.7 28.7 27.7 28.2 1.2 7. jul 24.7 24 24.7 27.3 27.7 26 26.7 25.7 25.8 1.2 8. aug 23.3 23.3 22.7 26 26 23 24.3 23.3 24 1.2 9. sep 25 24.7 24.3 27.3 27 24 25.7 25.3 25.4 1.1 10. oct 27 25.7 26.3 28.3 28 26.3 27.7 27.7 27.1 0.9 11. nov 28.7 26.7 28.3 29.7 29 28.3 29.7 29.7 28.8 1.0 12. dec 30 27.7 30 30.7 30.7 30.3 30.3 31 30.1 1.0 mean 29 27 28 30.3 30.1 29 30 29 29 1.2 sd 3.2 2.2 2.9 2.6 2.5 3.6 3.0 3.0 2.8 0.2 doi: https://doi.org/10.36956/sms.v2i2.308 22 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 gonyaulacoids group, ceratium 65%, gonyaulax 10%, pyrocystis 10%, alaxandrium 5%, spiraulax 5%, and pyrophacus 5%, respectively. the peridinoids cell density ranged from 800 to 1440 cells l-1, in which protoperidinium composed 57%, podolampus 28.6%, and peridinium 14.3%, respectively. the gymnodinoids and noctilucoids group had the lowest cell density ranged from 90 to 112 cells l-1. in the study area, the cell density was normally higher during summer and post-monsoon periods when the salinity was ≥29 ppt. 3.3 statistical analysis multiple correspondence analyses were made for the correlation coefficient of species and salinity changes. salinity changes may vary from one station to another. in table 2, p. rostratum showed a strong correlation with high salinity, 29-31 ppt. p. micans showed no correlation with salinity. p. gracile, p. lima, p. micans, and p. rostratum species were not found in station 2 where salinity is low. high cell densities were found normally at salinity, 30-31 ppt. in february-march. table 2. correlation coefficients of prorocentroids and salinity. no. prorocentroids 2012 2013 2014 1. prorocentrum gracile± 0.14 0.67 0.60 2. p.lima± 0.16 0.79 0.19 3. p.micans0.02 0.34 0.45 4. p.rostratum++ 0.72 0.68 1 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated table 3. correlation coefficients of dinophysoids and salinity. no. dinophysoids 2012 2013 2014 1. dinophysis caudata± 0.83 0.41 0.86 2. d. miles++ 0.80 0.74 0.79 3. ornithocercus magnificus++ 0.55 0.72 0.84 4. o.steinii++ 0.74 0.71 0.99 5. o.thumii++ 0.9 0.75 0.57 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated in the dinophysoids group, o. thumii species showed low salinity, 23-25 ppt. tolerant than other species in the group. d. miles, o. magnificus, o. steinii, and o. thumii showed a strong correlation with a wide salinity range, 23-34 ppt. o. steinii cannot tolerate low salinity than o. magnificus species. d. caudata cannot be found in low salinity of less than 22 ppt. (table 3). the gonyaulacoids, the largest and dominant group in the study area, and among them nine species show a strong correlation with a wide range of salinity. they were ceratium dens, c. furca, c. fusus, c. horridum, c. trichoceros, c. tripos, gonyaulax polygramma, and g. spinifera, respectively. g. polygramma was found in low salinity, 23 ppt. (table 4). table 4. correlation coefficients of gonyaulacoids and salinity. no. gonyaulacoids 2012 2013 2014 1. alexandrium concavum± 0.24 0.65 0.05 2. ceratium breve0.02 0.34 0.45 3. c. dens++ 0.72 0.68 0.67 4. c. extensum± 0.48 0.41 0.76 5. c. furca++ 0.70 0.92 0.79 6. c. fusus++ 0.65 0.50 0.78 7. c.horridum++ 0.67 0.71 0.66 8. c.inflatum± 0.48 0.75 0.66 9. c.lineatum0.25 0.49 0.19 10. c.porrectum± 0.27 0.39 0.53 11. c.macroceros± 0.53 0.36 1 12. c.schmidtii± 0.42 0.61 0.69 13. c. trichoceros++ 0.71 0.60 0.93 14. c. tripos++ 0.89 0.75 0.51 15. gonyaulax polygramma++ 0.65 0.71 0.74 16. g.spinifera++ 0.76 1.0 0.50 17. spiraulax kofoidii0.44 0.47 0.19 18. pyrocystis lunula± 0.08 0.45 0.07 19. pyrophacus magnificus++ 0.53 0.53 0.67 20. p.steinii± 0.48 0.40 0.65 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated doi: https://doi.org/10.36956/sms.v2i2.308 23 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 in the peridinoid group, all the members of protoperidinium show a strong correlation with salinity. some peridinium were assigned to the genus protoperidinium in some systematic studies. in this study, this species shows less correlation with salinity. the cell density of protoperidinium may vary with salinity changes. cell density will increase when the salinity increases in the water column. (table 5). table 5. correlation coefficients of peridinoid and salinity. no. peridinoid 2012 2013 2014 1. protoperidinium depressum++ 0.85 0.62 0.93 2. p. oblongum++ 0.57 0.53 0.92 3. p.oceanicum++ 0.51 0.69 0.99 4. p.pyreforme++ 0.64 0.71 0.62 5. peridinium pentagonum0.24 0.65 -0.04 6. podolampas elegans± 0.39 0.47 0.77 7. p.palmipes++ 0.74 0.72 0.93 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated in the gymnodinoids and noctilucoids group, all species show a strong correlation with salinity. the abundance of gymnodinoids and noctilucoids was lower than that of other morphospecies groups throughout the study period. distinct temporal and spatial variations in dinoflagellate cell densities were clear. cell density changes may associate with the salinity concentration. (table 6). table 6. correlation coefficients of gymnodinoids and noctilucoids and salinity. no. gymnodinoids and noctilucoids 2012 2013 2014 1. gyrodinium estuariale++ 0.74 0.72 0.93 2. noctiluca scintillans++ 0.88 0.64 0.61 (++) = strongly correlated, (±) = more or less correlated, (-) = less correlated in the prorocentroid morphospecies group, p. rostratum shows a strong correlation with salinity while p. micans shows less correlation with salinity. p. gracile and p. lima show more or less correlation with salinity. in the dinophysoid group, d. caudata shows less correlation with salinity during the study period, 2012-2014. the other species in the group show a strong correlation with salinity. in the gonyaulacoid group, c. dens, c. furca, c. fusus, c. horridum, c. trichoceros, c. tripos, g. polygramma, g. spinifera, and pyrophacus magnificus show strongly correlated with salinity during the study period. alexandrium concavum, c. extensum, c. inflatum, c. porrectum, c. macroceros, c. schmidtii, pyrocystis lunula, and pyrophacus steinii show more or less correlated with salinity. c. breve, c. lineatum, and spiraulax kofoidii show less correlation with salinity. in the peridinoid group, protoperidinium depressum, p. oblongum, p. oceanicum, p. pyreforme, and podolampas palmipes show a strong correlation with salinity during the study period. peridinium pentagonum, and p. elegans show more or less correlation with salinity. in gymnodinoid and noctilucoid group, g. estuariale and n. sintillans show a strong correlation with salinity during the study period. 4. conclusions in terms of dinoflagellates distribution which was based on different salinity regimes, the gonyaulacoid species, ceratium comprises 65% and stands first in the dinoflagellate community. in the dinophysoid group, ornithocercus takes 60% in species composition. moreover, in the peridinoid group, protoperidinium takes 57% in species composition of it. in the study areas, 52.6% of dinoflagellates are strongly correlated with salinity while 13.2% shows less in correlation with salinity. braaurd (1961) suggested that some dinoflagellate species such as ceratium spp., peridinium spp. and prorocentrum spp. reproduced more actively at the lower salinities. thus, changing salinity in nearshore areas might influence the dinoflagellate species composition. acknowledgment the authors are indebted to dr. aung myat kyaw sein, rector, and dr. san san aye, pro-rector of mawlamyine university, for their support in preparing this research work. we are thankful to dr. san tha tun, professor and head of the department of marine science, mawlamyine university, for providing the use of departmental facilities. many thanks are especially to dr. khin maung cho, pro-rector (retired), mawlamyine university, for his kind suggestions in preparing the manuscript. also, permission for this work from the department of higher education, the ministry of education, and for facilities of the department of marine science, mawlamyine university doi: https://doi.org/10.36956/sms.v2i2.308 24 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 is most appreciated. references [1] sahu, g., mohanty, a.k., samantara, m.k., satpathy, k.k., “seasonality in the distribution of dinoflagellates with special reference to harmful algal species in tropical coastal environment, bay of bengal”, environmental monitoring and assessment, springer international publishing switzerland, 2014, 186: 6627-6644. [2] gaines, g., elbrächter, m., “heterotrophic nutrition. in: taylor, f.j.r. (ed.) the biology of dinoflagellates”, botanical monograph,1987, 21: 224-268. [3] butterfield, e.r., howe, c.j., nisbet, r.e., “an analysis of dinoflagellate metabolism using est data”, protist, 2013, 164: 218-236. [4] janouškovec, j., gavelis, g.s., burki. f., et al., “major transitions in dinoflagellate evolution unveiled by phylotranscriptomics”, proceedings of the national academy of sciences, 2016, 114: e171–e180. [5] aishao, l., stoecker, d.k., coats, d.w., “spatial and temporal aspects of gyrodinium galatheanum in chesapeake bay: distribution and mixotrophy”, journal of plankton research, 2000, 22: 2105-2124. [6] smayda, t.j., reynolds, c.s., “strategies of marine dinoflagellate survival and some rules of assembly”, journal of sea research, 2003, 49: 95-106. [7] hackett, j.d., anderson, d.m., erdner, d.l., bhattacharya d., “dinoflagellates: a remarkable evolutionary experiment”, american journal of botany, 2004, 91: 1523-1534. [8] hamdan, n.a., hassan, m.s.a., noor, n.m., hamid, s.a., bunnori, n.m., “dinoflagellates: ecological approaches and spatial distributions in malaysia waters”, journal of oceanography and marine research, 2017, 5(3): 164, 10.4172/2572-3103.1000164. [9] d’costa, p.m., anil, a.c., patil, j.s., hegde, s., d’silva, m.s., chourasia, m., “dinoflagellates in a mesotrophic, tropical environment influenced by monsoon, estuarine”, coastal and shelf science, 2008, 77(1): 77-90. [10] sahu, g., mohanty, a.k., samantara, m.k., satpathy, k.k., “seasonality in the distribution of dinoflagellates with special reference to harmful algal species in tropical coastal environment, bay of bengal”, environmental monitoring and assessment, 2014, 186(10): 6627-6644. doi: https://doi.org/10.36956/sms.v2i2.308 35 sustainable marine structures | volume 01 | issue 01 | january 2019 sustainable marine structures http://ojs.nassg.org/index.php/sms distributed under creative commons license 4.0 doi: *corresponding author: surendran sankunny, department of ocean engineering, indian institute of technology madras, chennai, india 600036 email: sur@iitm.ac.in. abstract moonpools are openings right through the hull from continuous deck to bottom of the ship, allowing equipment or mini-submarines to be put into the water at a location on the vessel with minimum ship motion. open moonpools in a drillship are causing additional resistance when the ship is in forward speed. it was shown that the water inside the moonpool started to oscillate at forward speed. the water mass in the moonpool is subjected to sloshing and piston modes. the vertical motion is piston mode and the longitudinal one is called as sloshing mode. this water particle motion inside the moonpool is mainly depended on the geometry, moonpool depth, and encountered wave frequency. out of this, moonpool geometry is one of the key factors for the performance of the moonpool. the varying cross-section geometry is one of the practically possible and economically feasible solutions to reduce the oscillation to a considerable level is attempted in this paper. also the resistance caused by the moonpool and the free surface generated around the hull is investigated with the use of computer simulation. article info article history: received: 26 december 2018 accepted: 7 january 2019 published: 18 january 2019 keywords: moonpool free surface elevation water motion article influence of moonpool on the total resistance of a drillship by the effect of water motions inside the moonpool sivabalan ponnappan surendran sankunny* department of ocean engineering, indian institute of technology madras, chennai, india. 1. introduction a moonpool is meant for access to underwater part from onboard ship. it is located mostly at the midship region of the drillship for under water operations either in square or rectangular in shape.in drillship, these openings are used for supply the raiser and other drilling equipment through it.this drillship moonpool is mainly subjected to two types of motions of water mass inside the column namely, piston mode and sloshing mode. the piston mode is a type of water particle motion where the water particles can be seen as a “plug” which oscillates in the vertical direction. in sloshing mode the movement of water plugs in the horizontal direction and makes a standing wave effect on the side wall of the moonpool. this piston and sloshing mode play a major role in vessel's surge and heave motion while the drill ship in operation/transit and its lead to a larger quantity of green water on the weather deck. in the case of rectangular moonpool the dominating mode is sloshing where as in square moonpool the piston mode of oscillation is the dominant one. because of this water motion inside the moonpool the drillship regular activities may be affected. also this water motion is the reason for a large quantity of sea water can enter on to the continuous deck of the vessel. if this quantity of water added with the green water at the deck because of the waves then the net effect 36 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: may be cause critical situation of the vessel. also this water entry leads to the down time period of the drillship, because the crew members working on the drillship feel instability over the deck. therefore this entry of water to the deck should be minimized to better performance of the drillship.this water motion inside the moonpool also increases the drillship resistance, when the ship is in transit condition. the moonpool opening can be close during the transit by hatch cover, but any failure happened in the operation of the hatch cover leads to stop the drillship operation. this may cause major economic loss to the company, therefore most of the transit the drillship hatch cover in open condition. in regular moonpool geometry the water motion inside the moonpool when the drillship in operation mode is a considerable level, it further increases when the ship is in transit condition. this led to a number of studies in changing the moonpool geometry. some of the studies are discussed here. moonpool hydrodynamics and the mathematical model formulated for relative water motion inside the moonpool. in both the numerical and experimental study the influence of the damping mechanism was also evaluated [1]. the numerical simulation of the free surface flow around the vlcc hull form with the use of potential flow code and viscous flow finite volume code and compared the same with the available results. the geometry of the moonpool is one of the important parameter in the case of the formation of vortices[2]. the experimental research conducted on the behaviour of the water column oscillations in different shapes of moonpool and its effects on the vessel motion. the author observed that the flow inside the moonpool mainly depended on the shape of the moonpool [3]. the flow inside the moonpool is like turbulent in nature, also the aft end of the drillship. to simulate the free surface around the hull a suitable model considered as explicit algebraic stress model (easm) by gatski and speziale [4]. the water motion inside the moonpool will cause the resonance when it is at a critical level. the different levels of experiments conducted in moonpool with different motion minimizing attachments to reduce the free surface elevation inside the moonpool. the authors also attempted with a varying cross section of moonpool along the depth of the ship to reduce the water motions[5]. the experimental and numerical study of resistance and flow field was carried out in kvlcc2 hull. the easm and sst turbulence model were used in a numerical study. the results of both the model have good agreement with the experimental study. also, the detected outputs from turbulence models in resistance, sinkage, trim, and the free surface are found to be good[6]. the overall resistance of a ship can be divided into two as wave resistance and viscous resistance[7]. out of these two resistance part, the drillship with moonpool does not affect the wave resistance, but it affects the viscous pressure resistance due to pressure imbalance generated by the moonpool. the theoretical formulas derived for both the piston mode and sloshing mode natural frequency of moonpool in two dimensional and three-dimensional cases using linearized potential flow theory. in this study, the author formulated the free surface shape for both the piston and sloshing mode[8]. moonpool resonant oscillations are initiated by vortices that start at the upstream bottom end of the moonpool when the drillship in forward speed condition. the model test on moonpool of the drillship with different length to breadth ratio and studied the correlation between the shape of moonpool and increase of resistance. the authors arrived at the variation of free surface elevation inside moonpool according to the ratio of draft to moonpool breadth [9]. the present study mainly on the changing the moonpool geometry by introducing cut-out angles in moonpool and the performance is compared with the zero cut-out angle moonpool. the cut-out moonpools are otherwise called the varying cross-section moonpool because its area gradually decreases from bottom to top. this decrement decreases the water motion inside the moonpool to a considerable level both in operation and transit mode of the drillship. the performance of the cut-out moonpools is comparatively good than the zero cut-out angle moonpool. in this study, two different cut-out moonpools (20 degrees and 30 degrees) are used for the computer simulations for the study of free surface and the resistance. 2. moonpool modeling the computer simulation is done by the use of shipflow package for different froude numbers and different draft of the drillship. the total resistance coefficient, free surface around the hull, trim and sinkage are found from the computer simulation. the body plan of the drillship and the main particulars of drillship are given in figure 1 and table 1 respectively. a full-length drillship is used for the computer simulation. figure 1. body plan 37 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: all the iteration the same hull is used with different moonpool configurations. all the rectangular, 20-degree cut-out moonpool and 30-degree cut-out moonpool are placed at the midship area of the hull. clear views of cut-out moonpools and rectangular moonpool are given in figure 2. table 1. principal dimensions of the ship specification value length (loa) (m) 292 length(lbp) (m) 280 breadth (m) 50 draft (m) 16.5 depth (m) 25.48 displacement (ton) 1,94,156 in cut-out moonpool case the cut-out is given in the aft end of the moonpool and the other end (forward end) is simply a vertical wall. this cut-out angle gradually decreases the cross-sectional area of the moonpool from bottom to top and the moonpool like a varying cross-section moonpool. figure 2.(a) drillship hull with a rectangular moonpool figure 2.(b) drillship hull with 20-degree cut-out moonpool figure 2.(c) drillship hull with 30-degree cut-out moonpool 3. computer simulation 3.1 shipflow theory in the present study, shipflow package is used for the computational study. the features of the shipflow cfd code has discussed here. in this, the solver solves the flow problem in a zonal approach. in an overall view, it divides the object into three zones with three different solution approaches. zone 1 uses the potential flow solver with rankine source panel method. in the potential flow method, the shipflow code can be run in both linear and non-linear mode. it solves the forward portion of the ship hull. 2 2 2 2 2 2 2 0 (1)x y z φ φ φ φ ∂ ∂ ∂ ∇ = + + = ∂ ∂ ∂ (1) in zone 2 in shipflow, the boundary layer is computed using a momentum-integral method. it is based on streamlines, which are automatically traced from the potential-flow solution. in zone 3 the governing equations are the reynolds-averaged navier-stokes (rans) equations, obtained by averaging the time-dependent navier-stokes equations over the entire length and time scales of the turbulent fluctuations. it solves the aft end of the ship hull by turbulent flow solver. ( ) ( ) 0 (2)i i u t x ρ ρ ∂ ∂ + = ∂ ∂ (2) ( ) ( ) ' '( ) 2 [ ( ] (3) 3 i i j i i j i i ji l ij j j i l u u u t x p u u x x uu u x x x x ρ ρ ρ µ δ ∂ ∂ + = ∂ ∂ ∂ ∂ − + − + ∂ ∂ ∂∂ ∂∂ + − ∂ ∂ ∂ ∂ (3) shipflow software consists of a number of compact modules like xmesh, xpan, xbound, and xgrid, each briefly discussed here. xmesh is the mesh generator that creates panels for the hull and the free surface for the potential flow solver, xpan. in the present study totally 7529 panels are generated for the potential flow study. xpan is the potential flow solver. it solves the potential flow around the bodies based on a panel method and using the mesh generated by xmesh. xpan can compute the wave resistance, wave pattern, pressure contours, and sinkage/trim. the result from xpan is stored in a database file required to run the xbound module. xbound is the module that deals with the turbulent boundary layer but is also capable of computing the laminar boundary layer. bound creates a database file required to execute xchap. xgrid creates the grid used in viscous computations in xchap. with xgrid it is possible to create grids for ship or submarine hulls. 38 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: xchap is a module that solves reynolds averaged navier-stokes equations using one of several available turbulence models (easm, k-ω bsl, k-ω sst). the explicit algebraic stress model (easm) used in the turbulent flow analysis. the total resistance can be computed by combining the results from xpan, xbound, and xchap. in the present study the free surface elevation inside the moonpool, the total resistance act on the drillship and the free surface around the hull are simulated for different froude numbers in all different moonpool configurations. 3.2 free surface wave eevation the free surface wave elevation inside the moonpool may be any one of the following condition. i) during transit condition in the drilling location, ii) wave heading during stationary condition. the oscillations inside the moonpool initiated during forward speed condition by vortices, formed at the leading end of the moonpool. because of the flow separation of the shear layer at the bottom of the hull nearby forward end of the moonpool. these oscillations increase the resistance also the deck wetness. in the case of cut-out moonpool the free surface elevation considerably controlled when it is compared with the rectangular moonpool. the oscillations inside the moonpool are suppressed by the tapered wall of the moonpool. in rectangular moonpool this oscillation like a standing wave on the side walls. the effect of the oscillations inside the moonpool creates noise and pressure on the structure. the amplitude of the free surface elevation mainly depends on the speed of the drillship and geometry when the ship is in forward speed condition. the pressure acting on the moonpool wall is directly proportional to the forward speed. this pressure drops when the velocity increases, this is due to the free surface oscillating frequency and the shear layer oscillating frequency. the free surface elevation from the computer simulation for the froude number of 0.0393 is given in figure 3.this is given along the center line of the hull along the length of the vessel. the simulation done for various froude numbers (0.0196, 0.0393, 0.0589, 0.0785, 0.0982, 0.118, 0.137, and 0.157) with the vessel maximum loaded draft. the free surface elevation increases once the velocity increases as shown in figure 3(a). the maximum elevation is at the aft end of the vessel. the rectangular moonpool effect in the hull when it compared with the without moonpool hull is given in figure 3(b). it have the maximum elevation as compared with the cut-out moonpool is given in figure 3(c).in cut-out moonpools, the effect of the free surface has smaller difference as shown in figure 3(d) . from figure 3 it is clearly mentioned that the cut-out moonpools are comparatively good in the reduction of free surface elevation by suppressing the water particle movement and act as a damper. figure 3(a). free surface elevation in the bare hull figure 3(b). free surface elevation in the rectangular moonpool figure 3(c). free surface elevation in 20-degree cut-out moonpool 39 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: figure 3(d). free surface elevation in 30-degree cut-out moonpool 3.3 pressure on the hull the pressure distribution over the bow part of the drillship from xpan at froude number 0.0393 is given in figure 4.the pressure distribution is given in the form of pressure coefficient, it can be found panel wise. this pressure distribution over the hull is used for the calculation of wave resistance. the total pressure acting along the hull is directly proportional to the wetted surface area, velocity, and density of salt water. the pressure coefficient is simulated using the panel method. the pressure distribution over the hull is used to find the critical regions. high fluctuation of pressure along the waterline represents the wave crest and the trough. the drillship has higher block coefficient like tanker vessel, the wave making resistance/ wave breaking resistance have a higher value near the forward shoulder part of the vessel. that can be found by pressure integration of over the hull. figure 4. pressure distribution over the bulbous bow 3.4 free surface around the hull the free surface around the drillship hull without moonpool and 20-degree cut-out moonpool at froude number 0.0393 is given in figure 5(a) and 5(b) respectively. figure 5(a). free surface around a bare hull figure 5(b). free surface around the drillship hull with 20-degree cut-out moonpool 3.5 total resistance the total resistance coefficient (ct) from the simulation is the combination of wave resistance coefficient (cw), viscous resistance coefficient (cv). in the viscous part; frictional resistance coefficient (cf) and viscous pressure resistance coefficient (cpv) are counted. this viscous part is added with the wave resistance part and the total resistance coefficient is evaluated. cv = cf + cpv ct = cv + cw 20.5 t t r c svρ = (4) the total resistance (rt) of the vessels is directly proportional to the wetted surface area, the speed of the vessel and density. the total resistance of the drillship against different froude number is plotted in figure 6. 4. conclusions the total resistance of the drillship and the effect of free surface with different selected moonpool configurations are discussed in this paper. the computer simulation conducted for different froude numbers in the loaded draft of the drillship. the xchap simulation runs up to 40 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: 5000 iterations for convergence results. the moonpool with cut-out angles is good in controlling the free surface elevation inside the moonpool as compared with the rectangular moonpool. when the moonpool is open to the sea there is an increase in the resistance of ship when it is in forward speed condition. the moonpool with cutout angle gives the resistance in between the rectangular moonpool and hull without moonpool. from the cfd simulation, it is understood that the hull with moonpool geometry disturb the flow at the bottom of the hull and increases the resistance of the ship. this increment in resistance will increase the fuel consumption of the drillship in transit. nomenclature: φ flow potential υ kinematic viscosity (m-2 s-1) ρ density of water (kg m-3) p pressure (n m-2) fn froude number v speed (m s-1) s wetted surface area (m-2) µ dynamic viscosity (n s m-2) x position along the length of the vessel author contributions: sivabalan p. he has done this work for his ph d. the works consisted of experimental and numerical simulations using package programmes. surendran s. the work discussed in the paper was done under the guidance of the second author. conflict of interests: there is no conflict of interest with any agencies/institutes or persons. references [ 1 ] aalbers ab, the water motions in a moonpool. journal of ocean engineering 1984, 11(6):557-579. [ 2 ] ahmed y, guedes soares c, simulation of free surface flow around a vlcc hull using viscous and potential flow methods. journal of ocean engineering 2009, 36, 691696. [ 3 ] fukuda k., behavior of water in vertical well with bottom opening of ship and its effects on ship-motion. journal of the society of naval architects of japan, 1977, 141, 107122. [ 4 ] gatski tb, speziale cg, on explicit algebraic stress models for complex turbulent flows. journal of fluid mechanics 1993, 254, 59-78. [ 5 ] guilhem gaillarde, anke cotteleer, water motion in moonpools empirical and theoretical approach. maritime research institute. netherlands, 2005. [ 6 ] guo bj, deng gb ,steen s, verification and validation of numerical calculation of ship resistance and flow field of a larger tanker. journal of ships and offshore structures, 2013, 8, 3-14. [ 7 ] larsson l.,raven hc, the principles of naval architecture series ship resistance and flow, the society of naval architects and marine engineers, 2010. [ 8 ] molin b, on the piston and sloshing modes in moonpools. journal of fluid mechanics 2001, 430, 27-50. [ 9 ] rianvantveer, tholen hj, 'added resistance of moonpools in calm water', proceedings of the asme twenty seventh international conference on offshore mechanics and arctic engineering, 2008. figure 6. total resistance 41 sustainable marine structures | volume 01 | issue 01 | january 2019 sustainable marine structures http://ojs.nassg.org/index.php/sms distributed under creative commons license 4.0 doi: *corresponding author: s surendran, department of ocean engineering, indian institute of technology madras, chennai, india; emial: sur@iitm.ac.in abstract wind energy is considered one of the most promising alternative energy sources against the conventional fossil fuels. however, the deployment of these structures in deep-water for better power production is considered as a complex task. this also has raised the issue regarding selection of appropriate support structures for various sea conditions by considering environmental impact and carbon footprint. this paper considers a jacket like support structure as a case study for an intermediate water depth (50m). the jacket is considered to be located in north of dutch sea, and 100-extreme wave is applied as load condition. here, the presented methodology provides an insight towards environmental/social impact made by the optimized designs in comparison with reference design. article info article history: received: 26 december 2018 accepted: 7 january 2019 published: 18 january 2019 keywords: wind turbine support structure sustainable design optimization multi criteria decision making non-linear based design article a practical decision making on design of fixed offshore wind turbine support structure considering socio-economic impact m vishnu surendran sankunny* department of ocean engineering, indian institute of technology madras, chennai, india 1. introduction fixed offshore structures are one of the most com-monly used offshore structures for intermediate water depths compared to monopile. these are technically feasible and economically viable in design but are complex to design in nature. this possess many challenges in designing and execution of the project. moreover, offshore structures are designed to resist extreme wave loading but can succumb to collapse damage due to failure of multiple components members. one major challenges faced by industry is cost effective design of structures under extreme and normal environmental conditions. for a reliable and cost effective design under extreme loads, a non-liner static structural analysis always been a significant aspect. computer aided structural optimization can assist in designing economical structure under various constraints like fatigue. hence, optimization of structure has to fatigue and extreme loads under the target life. chew et al.[1] has considered gradient based optimization and reported the importance of buckling and fatigue load constraints over the design variables. gentils et al.[2] integrated genetic algorithm (ga) and fea (finite element analysis) to optimize support structure under various constraints. the paper also reported the advantage of using meta-heuristic methods as compared to gradient based optimization. gomes[3] has studied the truss optimization using particle swarm optimization (pso)[4] based on the reported the well behavior of the algorithm. in most cases, api and iso codes are used to design structures under elastic and component based design[5,6]. however, nizamani[7] suggested the advantage of system based design considering structure as a whole component. 42 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: the stress re-distribution between the members can result in extended load capacity towards plastic stage based design [8]. hence the approach proposed by ueda et. al [9] is used in this paper by using a finite element based code, usfos[10]. in 2007, as per major world leaders a 20% share of energy from renewable sources by 2020, by making individual targets for all eu member states [11]. the uk targets to acquire 15% of its final energy intake from renewable sources by 2020 and to decrease co2 emissions by a minimum of 26% by 2020 and 60% by 2050 [11] and also having the best geographically varied wind resources in europe [12]. so, it is also worth considering the social impact made by a wind energy project at various stages from manufacturing, installation and decommission stages. lozano-minguez et al.[12] investigated regarding the influence of environmental factors like carbon foot, noise, and vibration, water turbidity, etc. the authors also proposed the advantage of using topis (technique for order preference by similarity to ideal solution) method as multi criteria decision making tool. from the above literature review, the authors understand the importance of considering socio-economic impact on decision making of offshore structural designs. hence, this paper aims to provide an analytical methodology for the selection of the most preferable fixed jacket like support structure for a typical 5 mw wind turbine in 50 m water depth. in this analysis; engineering, economics, and environmental assessment will be considered to balance the socio-economic activities of the sustainable energy sector. figure 1 below provides sketch of offshore wind turbine (owt) support structure under environmental loads and the methodology followed is given below table 1. figure 1. jacket model table 1. methodology step 1 selection of site, loading condition and structure step 2 evaluating optimal designs under constraints step 3 evaluate social impact for each design step 4 topis method 2. methodology 2.1 step 1: case study a fixed jacket structure was proposed by vorpahl et al.[13] was designed to support an offshore wind turbine of 5 mw capacity. the height of the jacket structure is 66m and is placed at a water depth of 50m. the location to be installed is considered as the north of dutch sea. the structure consists of 56 nodes and 104 beams of steel tubular cross section and used in this paper to perform structural optimization. the jacket structure is modelled using usfos as shown below figure 1. the tubular members of the jacket are categorized into six groups to utilize them for the structural optimization, and the cross sectional details of the groups are given table 2. also, the structure can work with stand loads even if one member is failed under yield conditions and the force redistribution happens to other members. this is indicated by factor referred as reserve strength ratio (rsr) and considers the nonlinear static capacity of the structure [14]. ultimate collapse load rsr design load = (1) table 2. jacket reference design (continued) design variable description diameter (mm) thickness (mm) group 1dark blue leg 1200 50 group 2red brace 800 20 group 3yellow brace 800 20 group 4-green brace 800 20 group 5-cyan brace 800 20 group 6-blue brace 800 20 the jacket material properties are given in table 3. 2.1.1 hydrodynamic loading the wave environment used is based on statistical wave description. table 4 gives the significant wave height and the hydrodynamic forces acting on the tubular members are calculated using morison's equation [15]. as per equation (2), the relationship between wave height and return period was formulated as: ,3 ( ) 0.6127 ln( ) 7.042s hrs returnh t x= ⋅ + (2) 43 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: from the 100-year return period significant wave height, extreme design wave is calculated by the following relationship (16): he = 1.86hs (3) for the given location, the shallow water depth allows the use of 1.86 as the factor and the loading condition shown below. table 4. wave data parameter [unit] description value hs,100 [m] significant wave height in 100 year return period 9.90 he,100 [m] extreme wave height in 100 year return period 18.41 v100 [m/s] mean wind speed in 100 year return period 44.50 u100 [m/s] current speed in 100 year return period 1.20 a typical analysis for the considered reference case and given wave leading is shown below figure 2. the load displacement curve indicates the maximum load factor or rsr. here the rsr is evaluated as 3.6 and is over conservative as compared to minimum prescribed values of 1.58 and 1.85 provided by api and iso respectively. however, there seems to be lack of knowledge on target rsr values for various site and loading conditions. also, considering target values from code based methodology for offshore oil and gas structures for wind energy system may not be feasible approach. this demands multi criteria based decision making methodology in conjunction with optimization of structures to evaluate target load factor. figure 2. typical load deflection curve for reference case 2.2 step 2: integrated usfos-matlab optimization in the present study, the evolutionary approach based particle swarm optimization (pso) algorithm proposed by kennedy and eberhart is considered[17]. perez[18] and gomes[3] reported the robustness of pso algorithm for truss optimization. initially, the design variable and objective functions are defined. fitness values for each design is evaluated by integrating finite element structural analysis with pso algorithm developed in matlab (figure 3). (a) problem formulation the optimization problem for minimizing structural weight with design variables, subject to sizing and ultimate collapse load factor as constraints, can be formulated as follows. the optimization problem can be formulated as given below: minimize jacket mass: ( ) 1 ( ) en n n n i f x a x lρ = = ∑ (4) subjected to: (varied from1.6 to 3.2)trsr rsr≥ l ux x x≤ ≤ rsr is the collapse load factor for given wave load. here x represents the vector of jacket member dimensions namely, diameter and thickness; a is the vector of cross section area, l represents the length of each member, ne represents the total number of members. this is a simplified representation of the cost function and other cost components that are incurred in the design life cycle of support structures, excluding manufacturing, installation and maintenance costs. (b) sizing constraints sizing constraints define the lower and upper bounds of table 3. jacket properties property description material used steel elastic modulus 2.1 × 105 mpa poisson's modulus 0.3 yield strength 345 mpa density 7850 kg/m3 dead load 350 ton x joints 16 k joints 24 t/y joints 16 height 66 m mass 608 ton 44 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: design variables as well as the geometrical relationships among the variables. they can be expressed as 1 min maxg b b b= ≤ ≤ here bmin and bmax are the lower and upper bounds of the design variables as shown in below table 5. table 5. design bounds member type (group) diameter bound (mm) thickness bound (mm) legs (1) (600,1400) (30,60) braces(2,3,4,5,6) (400,800) (10,30) figure 3. integrated usfos-matlab optimization framework the results for the optimsation are shown in table 6 for various target rsr values. table 6. optimal design vs. rsr mass (ton) rsr 285 1.6 324 1.8 365 2.0 398 2.2 430 2.4 447 2.6 480 2.8 525 3.0 538 3.2 2.3 step 3: economic and environmental impact assessment (eeia) this section will describe about the various environmental and social impact made by installation of jacket structure. this mainly includes the following factors: (a) carbon footprint the equivalent amount of carbon di oxide (co2) can be expressed as following: 2 2 4270 24.5 1.4co e n o ch co= × + × + × (5) for steel structures, the emission unit per kg of total weight is 0.07, 0.04 and 0.93 g for n2o, ch4 and co respectively (b) noise and vibration as the machinery used is the same and the duration of the work will not vary significantly, it can be assumed that the choice of foundation will not affect the impact. (c) electromagnetic fields however, it is not yet known whether the fish will suffer any consequences caused by this interaction. the choice of foundation will not, therefore, be considered as affecting the impact. (d) impact on birds the choice of foundation will not affect the impact on birds. (e) net present value this parameter will convert the total cost of the service life of the structure to present value. 2.4 step 4: multi criteria based decision making (topis) as given in publicly available literature by lozano-minguez et al. [12], the basic steps of multi criteria based decision making algorithm is given below. for more information, the readers are advised to refer the above paper. (a) formulate initial design matrix (b) normalized design matrix (c) construct weighing matrix from experts (d) weighted normalized decision matrix (e) derived pis and nis (f ) evaluate relative closeness of each solution (g) ranking the solution analysis of attributes for finding the optimal design from possible nine alternative designs, nine criteria has been considered as follows (table 7). table 7. description of attributes sl. no attribute negative/ positive value significance 1 artificial reefs positive higher the better 2 certification positive 1if certified0.5if not certified 3 co2e negative lower the better 4 depth compatibility negative 1 for depth < 40 m 5 durability positive 5 for jacket and 4 for monopile 6 life cycle cost negative capex + opex 7 reserve strength ratio (rsr) positive higher the better 8 water turbidity negative 2356 for jacket and 1530 for monopile 45 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: the weights as shown in table 8 used for the study influence the decision approaching and has been taken from experience of experts from cranfield offshore renewable energy group[12]. table 8. weight factor for each attribute attribute 1 2 3 4 5 6 7 8 expert weight 0.65 0.65 0.91 0.91 1.00 1.00 0.83 0.74 3. results and discussion for the nine design combination corresponding to jacket based support structure, only the attribute 3, 6 and 7 are variables with no change for remaining. for evaluating the life cycle cost excluding risk expenditure, the capital cost (capex) is evaluated considering 1000 € per ton as material cost and manufacturing cost as 400% of material cost. for evaluating operational cost (opex), it is considered as 10% of the capex. however, a present worth factor should be considered to take care of the economic parameters during the life span of 20 years. (1 ) 1 / (1 ) ls w ls d p ls d d + − = + (6) below is tabulated results of lcc and rsr for each design index (table 9). table 9. lcc vs. rsr for each optimal design design index lcc (106 euro) rsr 1 2.92 1.6 2 3.13 1.8 3 3.34 2.0 4 3.45 2.2 5 3.62 2.4 6 3.75 2.6 7 3.90 2.8 8 4.10 3.0 9 4.21 3.2 (a) based on the attributes (1-8), the initial decision matrix is given below table 10 table 10. initial design matrix (continued) 1 2 3 4 5 6 7 8 8787 1 6036 1 5 2.92 1.6 2356 8787 1 6863 1 5 3.13 1.8 2356 8787 1 7730 1 5 3.34 2.0 2356 8787 1 8492 1 5 3.45 2.2 2356 8787 1 9107 1 5 3.62 2.4 2356 8787 1 9465 1 5 3.75 2.6 2356 8787 1 10166 1 5 3.90 2.8 2356 8787 1 11200 1 5 4.10 3.0 2356 8787 1 11395 1 5 4.21 3.2 2356 (b) the normalized decision matrix is as follows (table 11). table 11. normalized design matrix 1 2 3 4 5 6 7 8 0.58 0.58 0.22 0.58 0.58 0.26 0.21 0.58 0.58 0.58 0.25 0.58 0.58 0.28 0.24 0.58 0.58 0.58 0.28 0.58 0.58 0.30 0.27 0.58 0.58 0.58 0.30 0.58 0.58 0.31 0.29 0.58 0.58 0.58 0.33 0.58 0.58 0.33 0.32 0.58 0.58 0.58 0.34 0.58 0.58 0.34 0.35 0.58 0.58 0.58 0.37 0.58 0.58 0.35 0.38 0.58 0.58 0.58 0.40 0.58 0.58 0.37 0.40 0.58 0.58 0.58 0.41 0.58 0.58 0.38 0.43 0.58 (c) the average normalized weight matrix is given in table 8 (d) and the weighted normalized matrix is obtained is given as table 12 table 12. weighted normalized design matrix 1 2 3 4 5 6 7 8 0.38 0.38 0.20 0.53 0.58 0.26 0.17 0.43 0.38 0.38 0.23 0.53 0.58 0.28 0.20 0.43 0.38 0.38 0.25 0.53 0.58 0.30 0.22 0.43 0.38 0.38 0.27 0.53 0.58 0.31 0.24 0.43 0.38 0.38 0.30 0.53 0.58 0.33 0.27 0.43 0.38 0.38 0.31 0.53 0.58 0.34 0.29 0.43 0.38 0.38 0.34 0.53 0.58 0.35 0.32 0.43 0.38 0.38 0.36 0.53 0.58 0.37 0.33 0.43 0.38 0.38 0.37 0.53 0.58 0.38 0.36 0.43 (f) the positive and negative ideal solution (pis and nis) as given in table 13. table 13. pis and nis matrix 1 2 3 4 5 6 7 8 0.38 0.38 0.20 0.53 0.58 0.26 0.36 0.43 0.38 0.38 0.37 0.53 0.58 0.38 0.17 0.43 after evaluating the decision matrix using topis method, design index four was found to be best option (0.69). the selected index has reserve strength ratio of 2.2 with mass of 398 ton. the rsr value is found to be well above the minimum prescribed value of 1.58 and 1.85 as per api and iso studies respectively. 46 sustainable marine structures | volume 01 | issue 01 | january 2019 distributed under creative commons license 4.0 doi: 4. conclusion the study provides a multi criteria based decision making methodology for design of offshore structures. this methodology not only considers technical feasibility, but social and economic factors for selection of optimal design. the optimal design provides technically safe and sustainable design. further, this methodology can be extended to design of floating structures for deep water also. a sensitivity study can also be performed for change is water depth and environmental conditions. author contributions: the first author mr. vishnu murali (ph.d. scholar) has developed the methodology for design of offshore structures considering sustainability. his work includes scripting in matlab and fe analysis is usfos. he has also integrated usfos-matlab for seamless working of optimization methodology. the second author prof. surendran sankunny has provided the necessary inspiration and motivation for the work. he has contributed significantly to the research work in detailed correction and providing technical support for numerical analysis. conflict of interest: no conflict of interest was reported by the authors. acknowledgments: the first author greatly acknowledge the research grant from the ministry of human resources development, government of india. the authors also want to thank dr. tore holmas of www.usfos.no for his support that improved the quality of the paper. references [ 1 ] chew k-h, tai k, ng eyk, muskulus m. analytical gradient-based optimization of offshore wind turbine substructures under fatigue and extreme loads. mar struct. 2016, 47, 23–41. [ 2 ] gentils t, wang l, kolios a. integrated structural optimisation of offshore wind turbine support structures based on finite element analysis and genetic algorithm. appl energy. elsevier ltd; 2017, 199, 187–204. available from: http://dx.doi.org/10.1016/j.apenergy.2017.05.009. [ 3 ] gomes hm. truss optimization with dynamic constraints using a particle swarm algorithm. expert syst appl. elsevier ltd; 2011;38(1):957–68. available from: http://dx.doi. org/10.1016/j.eswa.2010.07.086. [ 4 ] coello c a c, pulido gt, lechuga ms. handling multiple objectives with particle swarm optimization. evol comput ieee trans. 2004, 8(3), 256–79. [ 5 ] api. recommended practice for planning, designing and constructing fixed offshore platforms — working stress design. api recomm pract [internet]. 2007, 24–wsd, 242. [ 6 ] international organization for standards (iso). petroleum and natural gas industries — fixed steel offshore structures. iso 19902. 2007, 2007, 638. 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[13] vorpahl f, popko w, kaufer d. description of a basic model of the “upwind reference jacket” for code comparison in the oc4 project under iea wind annex xxx. fraunhofer inst wind. 2011, 1(february), 1–14. [14] montes-iturrizaga r, heredia-zavoni e, vargas-rodríguez f, faber mh, straub d, de dios de la o j. risk based structural integrity management of marine platforms using bayesian probabilistic nets. j offshore mech arct eng . 2009, 131(1), 11602. [15] abdel raheem se. nonlinear behaviour of steel fixed offshore platform under environmental loads. ships offshore struct. taylor & francis; 2016, 11(1), 1–15. available from: http://dx.doi.org/10.1080/17445302.2014.954301. [16] wei k, myers at. directional effects on the reliability of nonaxisymmetric support structures for offshore wind turbines under extreme wind and wave loadings. eng struct. elsevier ltd; 2016, 106:68–79. available from: http://dx.doi.org/10.1016/j.engstruct.2015.10.016. [17] kennedy j, eberhart r. particle swarm optimization. 1995,1942–8. [18] perez re, behdinan k. particle swarm approach for structural design optimization. comput struct. 2007, 85(19– 20), 1579–88. 12 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v1i2.116 sustainable marine structures http://ojs.nassg.org/index.php/sms article moisture absorption and diffusion of a carbon composite structure bing wang* school of mechanical engineering & automation, fuzhou university, fuzhou 350108, china article info abstract article history received: 9 september 2020 accepted: 21 september 2020 published online: 31 october 2020 composite materials are lightweight structures and have been wildly used in marine applications. a carbon composite structure usually absorbs moisture while in-service, which can significantly affect its properties, and detriments the overall performance. we perform a detailed study on moisture absorption and diffusion of a carbon fibre reinforced vinyl ester resin composite system. composite samples are immersed directly in four different solutions at a temperature of 37±0.5 ℃ for 1444h. the moisture diffusion is analysed through the fickian diffusion model; the diffusion parameters are subsequently determined from the gravimetric data. the moisture absorption and interaction with the composite constituents are then discussed. these indicate the fundamentals of the moisture absorption and diffusion within the carbon composite structure. keywords: composite moisture absorption degradation fickian diffusion 1. introduction composite materials are superior in terms of specific strength, modulus and product efficiency. there are increasing interest in their applications to aerospace, automotive, medical, as well as sustainable marine structures [1]. one disadvantage is that their properties are susceptible to aggressive environments and subjected to change while in-service [2]. moisture absorption is one of the triggering factors that can significantly affect the material performance [3]. i t i s k n o w n t h a t a c a r b o n c o m p o s i t e s t r u c t u r e typically absorbs moisture in a humid environment and at elevated temperatures. this has been studied by various research groups by exposing the composites in different aggressive environments, such as water, sea water, low and high temperatures, and coupled with different loads [3-6]. the reinforcements include nature fibres, such as hemp fibre [7], jute fibre [8], sugar palm fibre [9], bamboo cellulose fibre [10], as well as synthetic fibres, e.g. graphite fibre [11], glass fibre [12,13], carbon fibre [14,15], and hybrid braided fibres [16]. among these, the commonly used matrices are epoxy resins and unsaturated polyester resins. vinyl ester resin (ver) is a bisphenol-d rived polymer, which offers better resistance to moisture absorption and hydrolytic attack than polyester [17]; carbon fiber (cf) has a high degree of corrosion resist compatibility [2]. thus, carbon fibre reinforced vinyl ester resin (cf/ver) composite has great potential in sustainable marine structures. in this paper, we studied the fundamentals of moisture absorption and diffusion in a cf/ver composite system. section 2 introduces the principles of the fickian diffusion model; section 3 shows the detailed experimental *corresponding author: bing wang, school of mechanical engineering & automation, fuzhou university, fuzhou 350108, china; email: b.wang@fzu.edu.cn 13 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 procedures; section 4 presents the results and discussion; and section 5 concludes the study. 2. fickian diffusion model generally, moisture absorption and diffusion of a polymer-matrix composite can be described by fick’s second law of diffusion [18,19], where the moisture content initially increases linearly with the square root of time and then gradually slows down until it reaches the effective moisture equilibrium, see figure 1. for a material that follows the fick’s law as in eqn 1 is also named as a single-phase fickian material. 2 2z c c d t z ∂ ∂ = ∂ ∂ (1) where: c is the specimen moisture concentration, g/mm3; t is time, s; c t ∂ ∂ is time rate of change in moisture concentration, g/ (mm3·s); dz is fickian moisture diffusivity constant, mm 2/s; z is through-the-thickness direction, mm. the single-phase fickian diffusion model as shown in figure 1 can be established using eqns 2-9 [20]. to predict the moisture content, the equilibrium content mm and the fickian moisture diffusivity constant dz are essential [21,22]. they both can be calculated from gravimetric data, and follow: (2) where: h is the thickness of the specimens, mm; m m i s t h e e q u i l i b r i u m m o i s t u r e c o n t e n t o f t h e specimens, %; mx, my is the moisture content of any time interval tx, ty in the linear portion of the curve mi versus t 1/2, %. figure 1. single-phase fickian diffusion model moisture absorption rate, k, is the slope of the linear part of the curve: ) / ( )y x y xk m m t t=（ (3) thereby: (4) the moisture content in a material at a given moisture exposure level is: ( ) ( ), b m bm t t m g m m= + − (5) where: t is temperature, °c; m(t,t) is moisture content as a function of time and temperature, %; mb is baseline moisture content, %; mm is moisture equilibrium content, %; h is thickness of material, mm; g is moisture absorption function and follows: ( ) ( ) 2 2 2 22 0 exp 2 1 8 1 2 1 z j d t j h g j π π ∞ =   − +     = − + ∑ (6) approximately: 0.75 21 exp 7.3 zd tg h    = − −       (7) to r e a c h a g i v e n m o i s t u r e c o n t e n t a t a f i x e d temperature and moisture exposure level, the time can be predicted as follows: ( ) 4/3 2 1 ln 1 7.3 b z m b m t mh t d m m  − − = −   −    (8) regardless the ambient moisture exposure level, the time necessary for a completely oven-dried specimen to get 99.9% of moisture equilibrium at a given temperature is: ( ) 2 max 0.93 z h t t d = (9) 3. experimental 3.1 sample preparation the matrix used in this research is vinyl ester resin and its chemical structure is shown in figure 2; the reinforcement is carbon fibre t300-1k purchased from toray, japan. ch2 ch oh o c ch3 ch3 o ch ch2ch2 ch2 n cooc ch3 ch2 oh coo c ch3 ch2 figure 2. chemical structure of the vinyl eater resin used in this research to produce a composite sample, resin, hardener and crosslinker were thoroughly mixed at room temperature, doi: https://doi.org/10.36956/sms.v1i2.116 14 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 the carbon fibre was then put into the mixture to ensure sufficient impregnation. the impregnated fibres were placed following [0°/+45°/-45°/90°]s, and locked inside a mould. the whole mould was then subjected to a curing process of 90 ℃ /2h+110 ℃ /2h+130 ℃ /2h+150 ℃ /2h. after mould releasing, the composite specimens were cut into designated sizes and subjected to aseptic processing as detailed below. the specimens were rinsed in distilled water under ultrasonic cleaning for 15 minutes. the naturally dried samples were exposed to ultraviolet (uv) light for 30 min, and scrubbed with anhydrous ethanol; then oven-dried and weighted separately as w0, which was used as reference for water absorption experimenting, using an electronic balance with an accuracy of 0.1mg. the specimens were then stored in sterilized jars ready for testing. 3.2 moisture absorption and degradation the moisture absorption and degradation studies were carried out in four solutions with different ph: (i) distilled water (dtw); (ii) hydrogen peroxide solution (hps); (iii) fenton’s reagent (ftr); (iv) phosphate buffered saline (pbs). the dtw was prepared following iso 3696 and gb/t 16886.13; hps was prepared using 3% h2o2 (in volume fraction) from lircon, shandong, china; ftr contained 100 μmol/l feso4 and 3% h2o2 (in volume fraction); pbs was prepared from distilled water and contains: nacl 140 mmol/l, na2hpo4 8.1 mmol/l, kh2po4 1.5 mmol/l, and kcl 3 mmol/l. experimental procedure follows below: firstly, solutions were stored in different sterilised jars with previously processed composite samples. here, the volume ratio of the specimens and the test solution is at least 1:10 (gb/t 16886.13), and the specimens must be completely immersed in the liquid. the jars were then placed into a constant temperature water bath which had previously reached the specified steady-state of 37±0.5℃ , and the water level must be higher than that in the jars. after the designated period, each specimen was taken out and rinsed with distilled water for at least three times, surface moistures were wiped out entirely with dry and clean filter paper. the specimen was weighed immediately to the required precision and recorded as wi, along with total elapsed time and the time interval since previous measuring, then put the sample back into the jar. each sample should not be out of the jar for more than 5 min per reading (astm d5229). the sample weight was monitored until effective moisture equilibrium was reached. since h2o2 in hps and ftr would become invalid after a certain time, both solutions were changed every week. the moisture content (mi) of specimens at different time intervals could be calculated by the weight difference from eqn 10: 0 0 100%ii w w m w = × (10) after been immersed in different solutions for 1444 h (two months), one specimen from each solution was cleaned following the same procedures as above, and then oven-dried until it reached the specified dry steadystate. the oven-dried weight was recorded as wd, and the weight change (mc) is calculated using: 0 0 100%dc w w m w = × (11) the value of ph in each solution was also monitored using a precision ph meter every week; surfaces of the immersed composite specimens were also examined using a scanning electron microscope (sem) su-1500 produced by hitachi to detect any interfacial debonding. 4. results and discussion 4.1 fickian diffusion the moisture content mi versus the square root of time t is plotted together with the fickian diffusion model in figure 3. it is clear that the experimental data well fits the fickian model except the one in ftr. this is because ftr has stronger oxidation effect for its well-known classical reaction between fe2+ and h2o2 [23] than the other three mediums. the composite sample undergoes severe corrosion during the same time interval, causing more gaps and voids inside the specimens, which in turn leads to heavier moisture absorption. figure 3. moisture absorption and diffusion curve of composite specimens, curves are fitted by using the fickian model doi: https://doi.org/10.36956/sms.v1i2.116 15 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 t h r e e p a r a m e t e r s o f m o i s t u r e a b s o r p t i o n w e r e computed from gravimetric data using eqns 3, 4, and 10, resulting data are shown in table 1. the value of dz in tdw is the lowest, which indicts that the moisture diffusion is the slowest. this attributes to the lowest osmotic pressure in pure water which can accelerate the diffusion of moisture compared to the other three solutions. the value of mm in both hps and ftr are relatively low, which is caused by the corrosion of the specimens as seen from the sem micrographs in section 4.4. table 1. parameters of moisture absorption in different solutions coefficients solutions tdw hps ftr pbs mm (%) 1.65 1.20 1.23 1.59 k (s-1/2) 2.46×10-5 2.50×10-5 2.32×10-5 3.05×10-5 dz (mm 2/s) 3.91×10-6 7.69×10-6 6.34×10-6 6.49×10-6 tmax(37℃ ) (h) 594.60 302.29 366.65 238.76 max (37 )t ℃ (h 1/2) 24.38 17.39 19.15 15.45 the time when mi reached 99.9% of its moisture equilibrium is determined from eqn 9, and shown in table 1. the predictions show good agreement with experiments shown in figure 3. therefore, it is concluded that the single-phase fickian diffusion model can properly predict the moisture diffusion of the cf/ver composite. 4.2 moisture absorption and interaction when composite specimens are immersed in a liquid medium, there are two main actions between water molecules and composite microstructures: (1) physical diffusion; (2) chemical degradation. physically, the moisture absorption of composite is mainly the diffusion of water molecules. water go through the defects in the matrix and interface such as holes, cracks to penetrate into the composite at first. this leads to the swelling of matrix and molecular chain relaxations, causing changes in residual stresses within the composite which may further result in the formation of micro-cracks [24]. all these can speed up the moisture absorptions. in a polymer matrix, there is a distribution of micro-porous at molecular level, and water molecules can easily get into the internal of cross-linked resin. these absorptions can destruct the hydrogen bonds between original macromolecular chains, weaken the crosslinking strength and decrease the wear resistances. thus, the existence of micro-porous facilitates the convection which also accelerates the absorption of water. the water molecules continue to spread into the composite interfaces, and initiate serious effects such as further swelling of the matrix and the generation of internal stresses. these can cause significant damage such as interface debonding and delamination, crack propagation, and so on, further increase the moisture content within a composite. meanwhile, carbon fibre is a hydrophilic material, water molecules can easily form hydrogen bonds with the carbon fibre. thereby, they undermine the combinations of the fibre and matrix, which decreases the interfacial strength and gradually lead to the failure of the interfaces. furthermore, the dissolution and penetration of water soluble substances can generate the osmotic pressure within the composite which also can accelerate the diffusion of water molecules. (a) formation of hydrogen bonds (b) formation of secondary crosslinking figure 4. model of potential secondary crosslinking between water molecules and a polymeric matrix material the chemical degradation effect is mainly through the chemical reactions between water molecules interior the composite and some elements within the matrix. water molecules connect with macromolecular chains can react with the hydrophilic groups to undermine the original composition of the composite, further lead to the irreversible changes in material properties. thus, if there are chemical groups such as ester which can easily degraded under the action of water molecules, the material would lose weight in the humid environment. also, water doi: https://doi.org/10.36956/sms.v1i2.116 16 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 molecules are polar molecules, which may be combined with hydrophilic groups within the matrix or fibres to form hydrogen bonds or other new bonds, or even lead to secondary cross-linking between molecular chains. zhou and lucas [25] established a model to describe this new bonding between water and epoxy network as illustrated in figure 4, which has similarity with the moisture absorption within our cf/ver composite structure. 4.3 degradation analysis the varieties of ph over two months are plotted in figure 5. there is a rapid change of ph in the tdw in the first week, and then becomes stabilised. the ph varieties are all very small in other three solutions, and there is almost the same trend of ph between hps and ftr. the overall changes of ph in different solutions are shown in table 2, with a maximum value of 1.42. it is noted that the secure ph value change for medical material leaching solution is no more than 1.5 [26], thus the cf/ver composite can be preliminarily determined to be safe. figure 5. the value of ph in different solutions over two months table 2. the changes of ph in different solutions in two months the value of ph tdw hps ftr pbs minimum 6.18 2.59 2.50 7.14 maximum 7.60 2.99 2.90 7.47 changed 1.42 0.40 0.40 0.33 the weight changes after immersed for 1444 h (i.e. two months) are determined from eqn 11 and show in table 3. the mc has increased by 0.35% in pure water, indicating that water molecules are combined with hydrophilic groups to form the hydrogen bonds, or the secondary crosslinking occurred between molecular chains as discussed in section 4.2. for hps and ftr, the composite samples loss weight giving negative mc, and ftr has the strongest corrosive effect to the cf/ver composite. the weight of the specimens that immersed in pbs are almost unchanged. table 3. weight changes after immersed in different solutions for 1444 h tdw hps ftr pbs mc (%) +0.35% － 0.61% － 2.69% +0.03% 4.4 surface debonding micrographics of the composite sample surfaces before and after immersed in different solutions are shown in figure 6. as it can be seen from the original composite, the adhesion of the matrix and fibres are good, fibres were tightly wrapped by the matrix. after immersed for five weeks, the composite interface remains to be good in tdw and pbs, which indicates that the degradation of cf/ver composite in such solutions are very small. this correlates with the few changes of ph as in figure 5. however, corrosions of composite interfaces in hps and ftr are quite obvious, leaving smooth fibre surfaces exposed to the acidic solutions, which is detrimental to the composite properties. (a) original sample (b) in tdw bath (c) in hps bath (d) in ftr bath doi: https://doi.org/10.36956/sms.v1i2.116 17 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 (e) in pbs bath figure 6. sem micrographs of composite samples before and after immersed in different solutions for five weeks 5. conclusions we performed detailed experimental and analytical studies on moisture absorption and diffusion of a carbon fibre reinforced vinyl ester resin composite system. composite samples were immersed in four different solutions at a temperature of 37±0.5 ℃ for 1444h. moisture absorption curves of cf/ver composite in different solutions are obtained and the diffusion processes basically follow the single-phase fickian diffusion model. the diffusion coefficients are then determined from the gravimetric data. the moisture diffusion in pure water is the lowest due to its low osmotic pressure; the changes in ph falls within a safe rang; and cf/ver system has very good corrosion resistance in salted water. these infer the fundamentals of the moisture diffusion within the carbon composite structures, and facilitate their applications in marine engineering. declaration of interests the authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. acknowledgments the author would like to acknowledge the fuzhou university for providing the start-up research funding for minjiang scholar distinguished professor scheme in fujian province, china. financial support from the national natural science foundation of china (52005108) is also appreciated. references [1] pedersen pt. marine structures: future trends and the role of universities. engineering, 2015, 1: 131-8. 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[24] roy s, xu w. modeling of diffusion in the presence of damage in polymer matrix composites. int j solids struct., 2001, 38: 115-26. [25] zhou j, lucas jp. hygrothermal effects of epoxy resin. part i: the nature of water in epoxy. polymer (guildf), 1999, 40: 5505-12. [26] wan c. biological properties and biocompatibility evaluation of biomaterials. sichuan university press: chengdu, 2008. doi: https://doi.org/10.36956/sms.v1i2.116 1 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 doi: http://dx.doi.org/10.36956/sms.v3i1.354 sustainable marine structures http://ojs.nassg.org/index.php/sms/index article analyzing potential water harvesting from atmosphere in near coastal area ida bagus mandhara brasika1,2*　putra bagus panji pamungkas2 1. department of marine sciences, universitas udayana, jl. raya kampus unud, jimbaran, kuta selatan, badung, bali, 80361, indonesia 2. center of remote sensing and ocean science (cresos), universitas udayana, jl. p.b. sudirman, denpasar, bali, 80234, indonesia article info abstract article history received: 26 april 2021 accepted: 18 may 2021 published online: 30 may 2021 water is a basic need. however there are many near coastal regions which have very limited access to fresh water. the water in area close to coastal is mainly affected by ocean, indirectly by weather/climate conditions and directly from seawater intrusion. while abundant fresh water is actually available in the atmosphere in the form of moisture. recent technology, such as atmospheric water generator (awg), is a possible solution to gain water from our atmosphere. however, comprehensive study is needed to understand the potential water harvesting in our atmosphere. here, we examine the water availability in the atmosphere based on several parameters like temperature and humidity. the data are collected from observation using ws1040 automatic weather station in a year of 2020 with a half-hour interval. then, we calculate the availability of water content during each season, especially in dry conditions. we also simulate the water harvesting to fulfil daily basic need of fresh water. the atmospheric parameters have shown a monsoonal pattern. water content decrease in atmosphere during the dry season but the water deficit occurs after the dry season. although water harvesting able to supply daily freshwater need, it is not recommended to be a single source as it requires massive water storage and high-efficient awg. keywords: water scarcity intrusion water vapor density atmospheric water generator 　 *corresponding author: ida bagus mandhara brasika, department of marine sciences & center of remote sensing and ocean science (cresos), universitas udayana, jl. raya kampus unud, jimbaran, kuta selatan, badung, bali, 80361, indonesia; email: mandharabrasika@unud.ac.id 1. introduction water scarcity or drought is a growing issue in many regions. there is no standard for drought definition [1], but in general drought is the dry condition longer than normal and causes the availability of water below the need [2]. there are more than 4.3 billion people or 71% of the global population living under conditions of moderate to severe water scarcity at least 1 month of the year [3]. the report from the world economic forum stated that water crises as the largest global risk in terms of potential impact [4]. the water scarcity might be caused by the high demand or limited access of water. in the case of bali, the water crisis is dominantly caused by the conflict of different user groups [5]. the factor of growing tourism has a significant role. however, some areas like karangasem (east bali) have limited ac2 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 cess to water [6] due to their geographical condition. due to several research, 260 of 400 rivers in bali had run dry and the largest lake had dropped 3.5 metres [7]. the climate has worsened the condition. some climate variability like el nino southern oscillation (enso) has a significant role. indonesia precipitation is strongly correlated with enso variations in the pacific basin [8]. there are 43 drought events in indonesia during 1884-1998, only 6 of them are not correlated with el nino [9]. meteorological role is more common in bali during moderate and strong el nino [10]. rainfall pattern in bali is categorized as the monsoonal season which has the driest and longest dry season in indonesia, compared to other types of season. the minimum mean of rainfall might reach 100 mm/month with the driest months between july and september [11]. el nino has a significant impact on dry conditions in bali, mainly between june-october [12]. el nino modoki (tripole mode of el nino) has decreased rainfall in bali for 8-16% [13]. bali is a relatively small island which most of their population lives near the coastal area. the near coastal region with a high population has been threatened by saltwater intrusion. this characteristic can be found in south bali such as denpasar, kuta, jimbaran and others. for example in jimbaran (our observation station located) has several coastal close by and the closest one is less than 3 km away. the salt groundwater in this region is mainly caused by seawater and hydrogeochemical influence [14]. in other similar near coastal region with a high population like semarang city, salt water intrusion affects 3,44 km region from coastline [15]. however, this region might change over time depending on several factors such as aquifer withdrawal, hydraulic properties and the confining unit of coastal area [16]. there are many solutions offered to combat this water crisis. some like rainwater harvesting, greywater reuse and solar desalination [17,18,19]. other potential solution is harvesting the water directly from the atmosphere as our air contains lots of water. on land surface, satellite can detect the amount of water in our air is about 3,42 g/cm2, with standard deviation 1.82 g/cm2 [20]. however, we need tools to collect the water from the atmosphere, it is known as atmospheric water generator (awg). awg has a similar principle with refrigerator and air conditioner which is cooling through evaporation [21]. but before developing awg, we have to understand our weather condition. how much the real water content in our area. when is the optimum condition for water harvesting. in this research we observe several atmospheric parameters. then calculate water availability. lastly it is simulated to model the potential of water harvesting to fulfil daily water needs. 2. data and method 2.1 atmospheric observation using ws1040 in this research we observe the atmospheric condition in our station at the faculty of marine science and fisheries, udayana university. the observation utilizes automatic weather station (aws) as a data collector. the aws is ws-1040 which is produced by shenzen tiankan electronic technology co., ltd. ws-1040 is a series of wireless weather station with solar power and pc link. this can be seen in figure 1 [22]. figure 1. installation of ws1040 weather station on udayana university with this equipment, we can observe several atmospheric parameters such as temperature, humidity, pressure, wind speed, wind direction and rainfall in 30 minutes timestep. the ws-1040 is placed in the open-air area with a radius of minimum 30 meters to the closest building. this is to reduce the bias of data caused by the effect of building or other possible disturbance such as trees, animals and humans. figure 2 shows the location of the weather station. it is located in the open area of faculty marine sciences and fisheries, udayana university. the closest coast is less than 3 km away and there are many beaches in the radius 5 km. thus, the potential of seawater intrusion is high and atmospheric condition is mainly affected by ocean. figure 2. location of weather station: faculty of marine sciences and fisheries, udayana university doi: http://dx.doi.org/10.36956/sms.v3i1.354 3 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 the observation was started in november 2019. however, the data that will be used in this research is from 01 january 2020 to 31 december 2021. we only focus on 3 parameters, station pressure (mbar), ambient temperature (c) and relative humidity (%). as they are considered in optimization design of atmospheric water generator [23,24,25]. the daily, monthly and seasonally pattern of these atmospheric parameters will be observed to gain a general understanding of the condition in our station. for the season, we divide it into 2 season, dry and rainy. this is due to the classification of indonesia’s rainy season. bali is located in the area with monsoonal season [11]. dry season is in april-september, while the rainy season is october-march. 2.2 water content at atmosphere to measure the amount of water in the air, we calculate it from several atmospheric parameter such as temperature and relative humidity. from research by [26], the absolute humidity is calculated as below: ρv = e m r t a w × k ea and es is given by: e rh ea s= × es = ×0.611 exp( )c t b t + × where: ρv is absolute humidity or vapor pressure (g/ m3), ea is vapor pressure (kpa), es is saturation vapor pressure (kpa), mw is molecular weight of water (g/mol) equal to 18.02 g/mol, r is universal gas constant (j/ mol k) equal to 8.31 j/mol k. t is temperature in celcius (oc) while tk is in kelvin (ok). rh is relative humidity (%). b and c both are constant, b = 17.502 and c = 240.97 for liquid. 2.3 model of water surplus/ deficit by calculating the amount of water content in the atmosphere, we can address fluctuation of potential water harvesting. however, this information is insufficient to explain the possibility of water harvesting from the atmosphere to fulfil the daily water need. we have to consider the minimum need and optimum need of water per person. we model this condition by fitting the gap between water harvesting and water need in daily time-series. the surplus and deficit of water can be seen on our model. we simulate the extra water of each day being stored in water storage. so, the surplus/deficit water is calculated based on cumulative sum. the surplus day is when the cumulative sum is positive (above 0) and the deficit is negative (below 0). in this model we assume there is 100% efficiency and 10.000 m3 of air is processed in a day. the sum of surplus and deficit is also calculated to evaluate the annual condition. this can address the strategy of water storage. 3. result and discussion 3.1 atmosphere variability a. daily and monthly atmosphere variability first, we want to understand the general variability of several atmosphere parameters during our observation time. figure 3 shows the daily and monthly timeseries of temperature, humidity and absolute pressure in 2020 at the faculty of marine sciences and fisheries campus using weather station ws1040. the daily mean illustrates clearly the oscillation of its variability. the monthly timeseries can show the general condition but fail to detect the detail. for example, humidity between october-december is low in monthly average but if we see the daily average it increases in general. this is because during this month the humidity is more unstable which causes more significant changes day by day. doi: http://dx.doi.org/10.36956/sms.v3i1.354 4 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 figure 3. daily and monthly timeseries of temperature, humidity and absolute pressure from 01 january 2020 to 31 december 2020 temperature has two peaks in april and november, with the lowest point in august. in general during the dry season (april-september), the temperature is dominantly low. compared with the dry season, it has higher unstable monthly temperature. this is very clear when november mean temperature reaches more than 29oc, then it drastically drops to less than 27,5 oc in december. for humidity, it starts to decrease in april (dry season) and remains low until december. so, it is generally low humidity during the dry season. the absolute pressure has an opposite pattern. it is dominantly high during the dry season between april-september. however, these three patterns have shown the similarity of unstable conditions between october-december. it is clear when we compare daily average and monthly average. while the monthly average is going down, the daily average is generally increasing. b. day-night mean during rainy season to get a deeper understanding of when is the optimum time to generate water from the atmosphere. here we compare the day-night mean of atmosphere parameters in the rainy and dry season with a 30 minutes interval. we calculate the mean of parameter at the same time during a season. for example, the mean temperature at 7 a.m. in the morning in each day during the rainy season. the dry season will be discussed in the next section. day-night mean in the rainy season (october-march) can be seen in figure 4 as below: figure 4. day-night mean variability of temperature, humidity and absolute pressure during rainy season general day-night variability is clearly shown for all parameters in the rainy season. temperature and humidity have an opposite pattern. while temperatures increase between 08.00 to 14.00, humidity decreases exactly at the same time. then temperature decreases from 14.00 to 19.00 and humidity increases. at night (19.00-08.00), both temperature and humidity day-night mean are constant. the absolute pressure is oscillating the peak around 09.00 and 23.00, the lowest point around 16.00. c. day-night mean during dry season figure 5 shows day-night mean during the dry season between october-march. in general there are no significant differences between the rainy season and dry season. the cycle of increasing and decreasing temperature appears between 07.00-19.00. while the humidity shows the opposite pattern with temperature. figure 5. day-night mean variability of temperature, humidity and absolute pressure during dry season doi: http://dx.doi.org/10.36956/sms.v3i1.354 5 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 there are slight differences in the ranges. for example, in dry seasons humidity might occur less than 40%. temperature, humidity and absolute pressure are also more unstable in the dry season compared with the rainy season. there is a typical stable time for the parameter. temperature and humidity are relatively stable from 09.00 to 10.00. the absolute pressure is more stable around 12.00. 3.2 optimum water generation by calculating absolute humidity, we get the amount of water in every cubic of air in the atmosphere. although not all 100% water content can be extracted into fresh water due to the limitation of technology, we can still understand its potential by analysing the variation of absolute humidity. here figure 6 simulates the daily mean of water content of every 10.000 m3 air for each month. as water is a daily need, we need water availability on a daily basis. here we plot daily mean of water content, based on absolute humidity calculation, in figure 6. figure 6. daily mean of absolute humidity here we can see the detailed daily water content. although the monthly mean is high, it does not mean that the water is available in the very high concentration every day. for example, between january and march the water content is changing drastically day-by-day. the highest reaches almost 150 litres per day, while the lowest is less than 25 litres per day. in the dry season, the variation of water content is lower. it is constant around 20-50 litres per day. to collect water from the atmosphere, awg (atmospheric water generator) is the tool. there are many types of awg. however, the efficiency of water generation is mainly caused by 3 factors, temperature, humidity and flow rate. for example, awg with a thermoelectric cooling method able to produce 11-25 gram/hour [27]. the water generation increases with humidity and air flow rate, optimum in 90% rh and 30 m3/h flow rate [28]. 3.3 daily fresh water simulation to fulfil their fundamental water need, humans require about 50 litres of water per person per day, although in humid climates humans can survive with 10 to 20 litres per person per day [29]. in figure 7, we illustrate the gap between daily water need (50 litres/day/person) and daily water supply/availability. we assume there is water storage which is able to store all surplus water in previous days. so we can understand the surplus (positive) and the deficit (negative) of water on a daily basis. figure 7. water surplus/deficit simulation between january and may, the water supply is higher than water demand. the excess water can be stored in water storage. the minimum capacity of water storage needed is 2.000 litres which is seen from the peak of the graph. then in the period may-november, the water supply decreases below the daily fundamental water need. this caused a drop in water storage until the water deficit in september-november. the water deficit is not in the dry season, but months after the dry season. in total, we can extract 14.528 litres of water in a year if we process 10.000 m3 of air every day and gain 100% efficiency. unfortunately, it is not enough to fulfil water needs of a person in a year, as it still deficit around 871 litres of water. 4. conclusions our atmosphere observation with ws1040 automatic weather station has shown the variability of several parameters in our location. the data with intervals 30 minutes provide detailed observation. temperature is more stable during the dry season from april to september which increases periodically every month. while in the rainy season, the unstable condition might be caused by some disturbance such as heavy rain or strong wind. the humidity has the opposite general pattern with temperature during the dry season. however in the rainy season, both temperature and humidity are generally high. these two parameters are utilized to calculate the water content in atmosphere. between january and may is the highest water content in the atmosphere. the daily water content in november-may fluctuates heavily in the day to day basis, while in other months it is consistently low. doi: http://dx.doi.org/10.36956/sms.v3i1.354 6 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 the water harvesting potential might reach as high as 100 litres per day. our model shows that harvesting 100% water from 10.000 m3 air per day is not sufficient to fulfil a person’s fundamental daily water need (50 litres/person/day) between september and november. in the other months, we need water storage with a minimum capacity of 2.000 litres to save the water surplus. however, with this simulation, humans in the near coastal region of south bali are able to survive by harvesting water from the atmosphere although not all of their fundamental daily water needs are fulfilled. the use of water harvesting methods as a single source of water is not recommended. references [1] j. dracup, "drought monitoring," stochastic hydrology and hydraulics 5, pp. 261-266, 1991. [2] r. nagarajan, "drought assesment," springer, dordecht-netherlands, 2009. [3] m. m. mekonnen and a. y. hoekstra, "four billion people facing severe water scarcity," science advance, 2016. [4] world economic forum, "global risks," world economic forum, geneva, 2015. [5] s. straus, "water conflicts among different user groups in south bali, indonesia," human ecology, pp. 69-79, 2011. [6] g. a. bawantu, i. g. b. s. dharma and n. n. pujianiki, "potensi air permukaan daerah aliran sungai unda untuk memenuhi kebutuhan air domestik dan non domestik di kabupaten karangasem," jurnal spektran, pp. 38-49, 2018. [7] l. samsura, "aljazeera.com," 1 12 2019. [onl i n e ] . av a i l a b l e : h t t p s : / / w w w. a l j a z e e r a . c o m / news/2019/12/1/bali-the-tropical-indonesian-islandthat-is-running-out-of-water. [8] hendon, "indonesian rainfall variability: impacts of enso and local air-sea interaction," journal of climate, pp. 1775-1790, 2003. [9] b. irawan, "multilevel impact assesment and coping strategies againts el nino: case of food crops in indonesia," working papers 32714, united nations centre for allevation of poverty through secondary crops development in asia and the pacific (capsa), p. 105pp, 2003. [10] a. m. setiawan, w.-s. lee and j. rhee, "spatio-temporal characteristics of indonesian drought related to el nino events and its predictability using multi-model ensemble," international journal of climatology, 2017. [11] e. aldrian and r. d. susanto, "identification of three dominant rainfall regions within indonesia and their relationship to sea surface temperature," international journal of climatology, pp. 1435-1452, 2003. [12] i. w. nuarsa, i. w. s. adnyana and a. r. as-syakur, "pemetaan daerah rawan kekeringan di bali-nusa tenggara dan hubungannya dengan enso menggunakan aplikasi data penginderaan jauh," jurnal bumi lestari, pp. 20-30, 2015. [13] i. b. m. brasika, "ensemble model of precipitation change over indonesia caused by el nino modoki," journal of marine research and technology, pp. 7781, 2021. [14] m. bahar, r. mezbaul and m. salim, "hydrochemical characteristics and quality assessment of shallow groundwater in a coastal area of southwest bangladesh," environment earth science, pp. 1065-1073, 2010. [15] n. rahmawati, j.-f. vuillaume and i. l. s. purnama, "sea intrusion in coastal and lowland areas of semarang city," journal of hydrology, pp. 146-159, 2013. [16] k. rotzoll, d. s. oki and a. i. el-kadi, "changes of freshwater-lens thickness in basaltic island aquifers overlain by thick coastal sediments," hydrogeology journal, pp. 1425-1436, 2010. [17] i. n. norken, i. k. suputra, i. b. n. purbawijaya and i. b. p. adnyana, "rainwater harvesting for drinking water in bali: indonesia," engineering and technology quarterly reviews, 2019. [18] a. khatun and m. amin, "greywater reuse: a sustainable solution for water crisis in dhaka, bangladesh," in 4th annual paper meet and 1st civil engineering congress, dhaka, 2011. [19] s. gorjian and b. ghobadian, "solar desalination: a sustainable solution to water crisis in iran," renewable and sustainable energy reviews, pp. 571-584, 2015. [20] n. c. grody, "remote sensing of atmospheic water content from satellites using microwave radiometry," transactions on antennas and propagation, p. 24, 1976. [21] a. tripathi, s. tushar, s. pal, s. lodh, s. tiwari and p. r. desai, "atmospheric water generator," international journal of enhanced research in science, technology and engineering, 2016. [22] dongguan meteorology electronic technology co., ltd., "meteorologyhk.com," 20 02 2021. [online]. available: http://www.meteorologyhk.com/en/displayproduct.html?id=2855714227421508#. [23] s. suryaningsih and o. nurhilal, "optimal design of an atmospheric water generator (awg) based doi: http://dx.doi.org/10.36956/sms.v3i1.354 7 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 on thermo-electric cooler (tec) for drought in rural area," in aip conference proceeding, bandung, 2016. [24] k. pontious, b. weidner, n. guerin, a. dates, o. pierrakos and k. altaii, "design of an atmospheric water generator: harvesting water out of thin air," in ieee xplore, charlottesville, 2016. [25] t. anbarasu and s. pavithra, "vapour compression regrigeration system generating fresh water from humidity in the air," in seiscon, chennai, 2011. [26] c. campbell, "environmental biophysics," 19 december 2019. [online]. available: https://www. environmentalbiophysics.org/chalk-talk-how-to-calculate-absolute-humidity/. [27] s. liu, w. he, d. hu, s. lv, d. chen, x. wu, f. xu and s. li, "experimental analysis of a portable atmospheric water generator by thermoelectric cooling method," in 9th international conference on applied energy, cardiff, 2017. [28] w. he, p. yu, z. hu, s. lv, m. qin and c. yu, "experimental study and performance analysis of a portable atmospheric water generator," energies, p. 73, 2019. [29] p. h. gleick, "basic water requirements for human activities: meeting basic needs," water international, pp. 83-92, 2009. doi: http://dx.doi.org/10.36956/sms.v3i1.354 5 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v1i2.94 sustainable marine structures http://ojs.nassg.org/index.php/sms article biochemical composition and anticancer effect of different seaweed species (in-vitro and in-vivo studies) t.h. ranahewa1* a. d. premarathna1 r.m.k.k. wijesundara1 v. wijewardana1,4 a. p. jayasooriya2,3 r.p.v.j. rajapakse1* 1. department of veterinary pathobiology, faculty of veterinary medicine and animal science, university of peradeniya, peradeniya, sri lanka 2. department of basic veterinary sciences, faculty of veterinary medicine and animal science, university of peradeniya, peradeniya, sri lanka 3. department of basic veterinary sciences, faculty of medical sciences, university of west indies, trinidad and tobago, west indies 4. department of atomic energy agency (iaea) vienna, austria article info abstract article history received: 1 september 2020 accepted: 13 october 2020 published online: 31 october 2020 seaweed is an enormous resource comprised with natural bioactive compounds with several therapeutic effects including anticancer activity. in this context, the biochemical composition of seaweed plays a major role. many biochemical compounds isolated from seaweed, fractions of seaweed and crude extracts has revealed ability of seaweed to fight against several cancer types. in this contrast seaweed extracts inhibit cancer cell growth and proliferation by inducing apoptosis and by inhibiting metastasis activity. in this review, biochemical and anticancer properties of seaweeds are discussed and this will provide the basic information to develop a novel chemotherapeutic drug to challenge the cancers. keywords: seaweed biochemical bioactive anticancer apoptosis *corresponding author: t.h. ranahewa, department of veterinary pathobiology, faculty of veterinary medicine and animal science, university of peradeniya, peradeniya, sri lanka; email: thakshila77harshi@gmail.com; r.p.v.j. rajapakse, department of veterinary pathobiology, faculty of veterinary medicine and animal science, university of peradeniya, peradeniya, sri lanka; email: jayanthar@pdn.ac.lk 6 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 1. introduction ca n c e r i s a d r e a d f u l d i s e a s e c a u s e s d u e t o uncontrolled cell proliferation and migration [17,26]. among all human cancer types, lung cancer and colorectal cancer are the major cancers found in male whereas breast cancer, cervical cancer and lung cancer are considered as the common cancers found in female [1,40]. although chemotherapy and radiotherapy treatments are practiced to cure cancers, the survival rate is still low and many side effects are also reported [23]. due to the continuing of failure of the availability of effective chemo-preventive agents for cancers, therapeutic agents from biological resources are being experimented to control this malignant disease [8,11,18]. seaweeds are marine macro algae, found in intertidal and sub-tidal zones and classified based on their pigmentation and chemical composition as chlorophyta (green algae), rhodophyta (red algae) and phaeophyta (brown algae) [6,23]. laminaria sp., fucus sp., ascophyllum sp., porphyra sp., ulva sp., sargassum sp. and gracilaria sp. are some of the examples for the famous edible seaweed species that comprise with many bioactive compounds coming under the groups of polysaccharides, proteins, lipids, minerals and vitamins [14,1]. moreover, due the availability of theses bioactive compounds many seaweed species account for promising health promoting effects such as antibacterial, antiviral, anti-inflammatory, antiulcer and anticancer activities [1,13,33,41]. therefore some secondary metabolites in seaweeds are extracted and incorporated into several products such as foods, medicines and cosmetics [5]. recently, seaweeds are increasingly being considered as a source with effective anticancer agents that are able to lower the risk of cancer [1,17,26]. in this context, investigation of anticancer drugs with less or no side effects has become an interesting topic in novel research field [37,43]. 2. biochemical composition of seaweeds there are two types of biochemical substances present in seaweeds as high molecular materials and low molecular materials. high molecular materials such as dietary fibres are not absorbed into the human body whereas low molecular materials are absorbed directly [14]. though seaweeds comprise with several biochemical compounds including carbohydrates, proteins, lipids, vitamins, polyphenols, free amino acids and minerals [7,14,24] the composition varies based on the geographical location, seasonal variation and water temperature [14,24]. s e a w e e d s c o n t a i n 2 0 % 7 6 % ( d r y w e i g h t ) o f polysaccharides as structural and storage compounds. cellulose, starch, hemicellulose, fucoidan, alginic acids, sulfated fucans, alginate and laminarin are the polysaccharides which are mainly present in the seaweeds that provide strength and flexibility to the cell wall [5,13,14]. out of three seaweed types red seaweeds consist with the highest protein content which accounts for 30%-40% of dry weight whereas brown seaweeds contain 15% and green seaweeds contain 30% of dry weight [34]. many essential amino acids, such as glycine, alanine, arginine and glutamic acids are present in seaweeds. however, the lipid content of seaweeds is comparatively low (1%-5% of dry weight) and it contains a high proportion of essential fatty acids and poly unsaturated fatty acids such as ω-3 and ω-6 [30]. vitamin b, c, a and d are the most common vitamins present in the seaweeds. in general, seaweeds accounts for 36% (dry weight) of minerals including, potassium, sodium, magnesium, calcium, sulfur, chlorine, phosphorus, iron, zinc, iodine, copper and some other trace metals [34]. several studies reported that there are severel types of secondary metabolities with therapeutic effect are present in seaweeds (table 1) table 1. secondary metabolites in seaweeds family seaweed species secondary metabolites reference pheophyta fucus vesiculosus fucus evanescens ascophyllum nodosum undaria pinnatifida sargassum thunbergii ecklonia cava fucoidan [3,13,16, 20,32,39,45] laminaria sp. laminarin [13,31] sargassum heterophyllum laminaria ochotensis hijikia fusiformis undaria pinnatifida ectocarpus siliculosus fucoxanthin [2, 25, 38] chlorophyta nitella hookeri ulva fasciata flavonoids [31] laurencia glandulifera dactylone [10] 3. anticancer effect of seaweeds uncontrolled cell growth and proliferation is the main reason for cancer formation. chemo-preventive agents extracted from natural resources have got the attention due to the ability to suppress cancer cell formation with lesser or no side effects with compared to available chemotherapeutic agents [20]. basically, cell death can be caused by any chemotherapeutic agent through the cell doi: https://doi.org/10.36956/sms.v1i2.94 7 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 cycle arrest by targeting necrotic pathway or apoptotic pathway of respective cells [23,26]. bioactive compounds are able to induce apoptosis in cancer cells, this is one of the key mechanisms in cancer therapy because apoptosis is a kind of programmed cell death which can kill only the targeting cancer cells without causing damage to normal surrounding cells [2,40]. in this context, cell death is evoked through intrinsic mitochondrial pathway or extrinsic death receptor pathway [23,40]. several studies have proven that seaweed constitute many novel bioactive compounds with anticancer effect and able to induce apoptosis in several types of cancer cells [1,3,9,13,35,37]. anticancer effect of methanolic extract of caulerpa r a c e m o s a m e n t i o n e d w a s e x a m i n e d a g a i n s t h l 60 (human promyelocytic leukemia) cell line and a remarkable cell growth inhibition was reported by lakmal, et al., 2014 [21] in dose dependent manner with compared to normal cell line; vero (monkey kidney cell line). apoptotic body formation and dna damage of treated hl-60 cancer cells were obsereved under fluorescent microscopy and flow cytometric analysis was also showed dose dependent sub-g1 dna accumulation in hl-60 cell line. aqueous and methanolic extract kappaphycus striatum has showed cell growth inhibition activity against hela (cervical adenocarcinoma) cell line and this study explains that the molecular weight, monosaccharide sequence, bond formation and charge of molecules are the characteristics of bioactive compounds present in seaweed extracts which support seaweeds to act as an anticancer agent [22]. zandi, et al., 2010 [42] has found that the aqueous extract of sargassum oligocystum shows cytotoxic activity on k562 (human chronic myelogenous leukemia) and human daudi (burkitt lymphoma) cell lines in dose dependet manner. moreover by another study zandi, et al., 2010 [43] expalins that the aqueous extract of gracilaria corticata filtered with whatman paper no.1 filter paper showed more pormising cell growth inhibition results on jurkat and molt-4 (human lymphoblast) cell lines and they emphasis that filtration is the one of the best methods of sterilising the seaweed extarcts since some of the bioactive compounds in seaweeds are heat sensitive. mcf 7 (human breast adenocarcinoma) cell line treated with aqueous extracts of different seaweed species such as gracillaria corticata, ulva fasiata, chaetomorpha antennina showed growth inhibitory effect and morphological observation such as cell shrinkage and cell shape changes related to apoptotic induction were also observed [4]. m e t h a n o l i c e x t r a c t o f s a rg a s s u m m u t i c u m h a s showed antiproliferative activity by inducing apoptosis in mcf-7 (human breast adenocarcinoma) cell line. electron microscopic images with membrane blebbing, apoptotic body formation and microvilli reduction, the morphological changes of treated cells stained with hoechst 33342 and flow cytometric analysis indicating the accumulation of treated cells at sub-g1 phase provide evidence on inducing apoptosis by methanolic extract of sargassum muticum [28]. mcf-7 (human breast cancer cell line) and hepg2 (human liver cancer cell line) treated with methanolic extracts of enteromorpha antenna, gracilaria corticata and enteromorpha linza has shown cytotoxic activity with compared to normal vero cell line (monkey kidney cell line) [29]. gomes, et al., 2015 [12] found the methanolic extracts of dictyota c i l l i o l a t a a n d d i c t y o t a m e n s t r u a l i s s h o w s d o s e dependent and time-dependent antiprolifertive effect on hela (human cervical cancer cell line). nuclear morphology changes such as formation of apoptotic bodies and chromatin condensation in the cells stained with 4, 6-diamidino-2-phenylindole (dapi) staining was observed under fluorescent microscope. it is reported that percentage of annexin-positive (annexin v-fitc+/ pi−) cells flow was increased and it is a sign of early apoptosis process of cells. further the results highlighted that the methanolic extracts of dictyota cilliolata inhibits the growth of hela cells by blocking the cell cycle at the s phase whereas dictyota menstrualis shows apoptotic induction without inducing cell cycle arrest. caspase 3 and caspase 9 activation empahasis that intrinsic apoptotic induction occurs by the seaweed extracts in the cancer cells. ethanol extract of ulva fasciata has showed growth inhibition due to apoptosis induction hct 116 (human colon cancer) through mitochondrial pathway by increasing cell at sub-g1 phase and activation of caspase 3 and caspase 9 [36]. fractions of polysaccharides; sp-3-1 and sp-32 extracted from sargassum pallidum were treated on hepg2 (human hepatoma), a549 (human lung cancer) and mgc-803 (human gastric cancer) cell lines and evaluated by mtt assay. sp-3 fraction with the highest sulfate content exhibited higher antitumor activity against all tested cancer cell lines. further, this study states structure, glycosidic linkages and sequence of monosaccharaides effects on the function of the extracted polysaccharides [41]. anticancer effect of a sterol fraction of porphyra dentata was evaluated against 4t1 breast cancer cell line and pronounced in dose dependent and time dependent cell proliferation inhibition of was resulted in the treated 4t1 cells and percentage of apoptotic-necrotic cells increased was also increased due to the results of pi and annexin v dual staining [19]. liu et al. (2016) [23] evaluted the anticancer effect of a doi: https://doi.org/10.36956/sms.v1i2.94 8 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 novel sulfated polysaccharides (sps), extracted from sargassum integerrimum against a549 (human lung cancer) cell line. cell growth inhibition was resulted due to necrosis or apoptosis the treated and control cells were stained using hoechst 33258 staining and morphological changes were observed. comparatively, typical apoptotic cell characteristics such as cell shrinkage, cell bubbling, fragment shape nucleus and nuclear shrinkage were observed in the sps treated cells. flow cytometric analysis using annexin v-fitc/pi double staining and jc-1 staining also confirms that the growth inhibition is due to apoptosis induction and further due to loss of mitochondrial membrane potential. moreover, antiapoptotic and pro-apoptotic protein markers expression were also tested using western blotting. according to the results, the expression level of p53; tumor suppressor protein was increased and bcl-2; anti-apoptotic protein expression was down regulated whereas bax; proapoptotic gene expression was decreased. several studies have found that fucoidan extracted from different seaweed species as natural bioactive compound with anticancer effect (table 2). fucoidan is a type of sulphated polysaccharide mainly present in brown seaweeds. there are many studies to evident the induction of apoptosis in human colon cancer cell lines such as hct-15, widr, hct116 and ht-29 by fucoidan [16,17,20]. moreover hct-15 cells treated with fucoidan inhibited the growth of colon cancer cell lines in dose dependent manner through apoptosis induction. the treated cells have been visualized with condensed and fragmented nucleus and bcl-2 expression was down regulated whereas bax, pro-caspase 3 and 9 expressions were up regulated by the fucoidan treated cells there for it proves that this growth inhibition is due to apoptosis induction table 2. anticancer activity of different seaweed extracts extract type seaweed species cancer cell type in-vitro analysis references mtt assay morphological chances cell cycle arrest gene expression methanoic caulerpa racemosa hl-60 (human promyelocytic leukemia) + + + [21] sargassum muticum mcf-7 (human breast adenocarcinoma) + + + [28] enteromorpha antenna enteromorpha linza mcf-7 (human breast cancer cell line) hepg2 (human liver cancer cell line) + [29] gracilaria corticata mcf-7 (human breast cancer cell line) hepg2 (human liver cancer cell line) + [29] dictyota cilliolata dictyota menstrualis hela (human cervical cancer cell line) + + + caspase 3 caspase 9 [12] aqueous sargassum oligocystum k562 (human chronic myelogenous leukemia) daudi (human burkitt lymphoma) + [43] gracilaria corticata jurkat (human lymphoblast) molt-4 (human lymphoblast) mcf-7 (human breast adenocarcinoma) + [4,42] ulva fasiata mcf-7 (human breast adenocarcinoma) + [4] chaetomorpha antennina mcf-7 (human breast adenocarcinoma) + [4] ethanol ulva fasciata hct 116 (human colon cancer) + + + caspase 3 caspase 9 [36] doi: https://doi.org/10.36956/sms.v1i2.94 9 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 in the colon cancer cell lines by fucoidan [16]. further, hct116 and ht-29, human colon cancer cell lines treated with fucoidan (5-20 µg/ml concentrations) have also showed remarkable dose dependent and time dependent cell growth inhibition and any significant cytotoxic effect was not reported on fhc (human normal colon epithelial) cell line. this growth inhibition was also due to apoptosis induction via activation of caspase 3, 7, 8 and 9 [20]. table 3. anticancer activity of bioactive compounds isolated from seaweeds bioactive compound seaweed species used to extract fucoidan cancer cell type reference fucoidan fucus vesiculosus hct-15 (human colon carcinoma cells) [16] ht-29 (human colon adenocarcinoma) hct116 (human colon adenocarcinoma) [20] sargassum sp. turbinaria sp. padina sp. widr (human colon adenocarcinoma) mcf-7 (human breast adenocarcinoma) [17] sargassum oligocystum daudi (burkitt lymphoma cells) k562 (human chronic myelogenous) [42] caulerpa racemosa hl-60 (human promyelocytic leukemia cell line) [21] laminarin laminaria digitata ht-29 (human colon adenocarcinoma) [31] fucaxanthin laminaria japonica ej-1(human bladder cancers) [44] undaria pinnatifida hl-60 (human promyelocytic leukemia cell line) [15] laminarin is another bioacive compound present in seaweeds examined for anticancer properties. laminarin extracted from laminaria digitata has shown anticancer effects against ht-29 colon cancer cell. laminarin showed an activity against ht-29 cell line in a dosedependent manner. accumulation of sub-g1 and g2-m during the flow cytometric analysis and inhibition of phosphorylation and erbb2 expression reveals that laminarin induces apoptosis through erbb signaling pathway [31]. anticancer effect of fucoxanthin extracted from laminaria japonica was tested against ej-1(human bladder cancers) cancer cell line and observed time and dose dependent cell viability reduction. cell morpholgical changes observed by contrastand fluorescence microscope and activetion of caspase-3 reveals that this cell viability reduction is due to apoptosis induction [44]. fucoxanthin extracted from undaria pinnatifida inhbited hl-60 (human promyelocytic leukemia) cell line proliferation due to apoptosis induction. the results such as dna fragmentation resuted from agarose gel electrophoresis a n d s a n d w i c h e l i s a t e s t s p r o v e t h e a c t i v i t y o f fucoxanthin against leukemia cancer cell line [15]. further, not only in-vitro studies but also in-vivo studies provide the evidance of anticancer activity of seaweeds. in this contrast, llc (lewis lung carcinoma) cells were transplanted in c57bl/6 mice and treatments (fucoidan and cyclophosphamide) were started after nine days of transplantation. it is recorded that fucoidan shows and atiancer and antimetastatic activity when the drug is used combined with cyclophosphamide [4]. abirami & kowsalya, 2012 [1] investigated anticancer effect of ulva fasciata using albino mice (in-vivo). dal (dalton’s ascites lymphoma) cells were transplanted in swiss albino mice and treated with methanolic extract and aqueous extracts of ulva fasciata once daily for 14 days. the parameters such as hematological parameters, lipid profile, liver function tests, body weight, cancer cell counts were examined and methanolic and aqueous exracts of ulva fasciata showed in-vivo anticancer effect against dal cancer type. further mammary cancer induced female rats were treated with eucheuma cottonii extract (150 and 300 mg/kg of body weight) for four weeks. the tumor was reduced by e. cottonii extract and inhibition rate showed dose-dependent variation [27]. 4. conclusion the therapeutic effect of seaweeds was explored due the presence of novel bioactive compounds. in this context anticancer effect of seaweed plays a major role by inducing apoptosis through intrinsic and extrinsic pathways [12,20]. seaweed are comprised with many secondary metabolities and some of them have been isolated and further studies are reqiuired for isolation of other theraeutic compounds from seaweeds since the most of them show cytotoxic activity against cancre cells and not in normal cells. thus further studies will open the gate to reveal new chemotherapeutic agents which are able to fight against cancers while having no or less impact on normal cells. references [1] abirami, r.g., kowsalya, s. anticancer activity of methanolic and aqueous extracts of ulva fasciata in albino mice. international journal of pharmacy and pharmaceutical sciences, 2012, 4(2): 681-684. 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[37] wijesekara, i., pangestuti, r., kim, s. biological activities and potential health benefits of sulfated polysaccharidesderived from marine algae. carbohydrate polymers, 2011, 84: 14-21. [38] yan, x., chuda, y., suzuki, m., nagata, t. fucoxanthin as the major antioxidant in hijikia fusiformis, a common edible seaweed. 2011, 63: 605-607. [39] yang, l. et al. fucoidan derived from undaria pinnatifada induces apoptosis in human hepatocellular carcinoma smmc 7721 cells via the ros mediated mitochondrial pathway. 2013, 11: 1961-1976. [40] yaoxian, w. et al. emodin induces apoptosis of human cervical cancer hela cells via intrinsic mitochondrial and extrinsic death receptor pathway. cancer cell international, 2013, 13(71). [41] ye, h., zhou, c., liu, j., zeng, x. purification, antitumor and antioxidant activities in vitro of polysaccharides from the brown seaweed sargassum pallidum. food chemistry, 2008: 428-432. [42] zandi, k. et al. anticancer activity of sargassum oligocystum water extract against human cancer cell lines. european review for medical and pharmacological sciences, 2010 14: 669-73. [43] zandi, k. et al. in vitro antitumor activity of gracilaria corticata (a red alga) against jurkat and molt-4 human cancer cell lines. african journal of biotechnology, 2010, 9(40): 6787-90. [44] zhang, z. et al. potential chemoprevention effect of dietary fucoxanthin on urinary bladder cancer ej-1 cell line. oncology reports, 2008, 20: 1099-1103. [45] zhuang, c., itoh, h., mizuno, t., ito, h. antitumor active fucoidan from the brown seaweed, umitoranoo (sargassum thunbergii). 2014, 22(41). doi: https://doi.org/10.36956/sms.v1i2.94 29 sustainable marine structures | volume 04 | issue 01 | january 2022 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2022 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). *corresponding author: bipu hu, department of chemistry and biology, college of science, national university of defense technology, changsha, 410073, china; email: 1508422574@qq.com doi: http://dx.doi.org/10.36956/sms.v4i1.438 article effects of antifouling technology application on marine ecological environment liangcheng liu1 ge wang2 junyi song1 bipu hu1* 1. department of chemistry and biology, college of science, national university of defense technology, changsha, 410073, china 2. institute of special services, naval research academy, beijing, 102442, china article info abstract article history received: 08 september 2021 accepted: 10 january 2022 published online: 25 january 2022 resolving the contradiction between marine economic development and marine ecological environment protection has become an unavoidable and sharp problem. the uncontrolled use of marine antifouling technology will bring uncontrollable and even irreversible damage to the marine biosphere, which will lead to ecological disaster and threaten the survival of human beings. therefore, it is an urgent task to find antifouling technology with lower environmental toxicity under the premise of considering economy. more attention should be paid to the long-term impact of mature and new technologies on the marine ecological environment. this paper introduces the development status of antifouling technology, its influence on marine ecological environment and puts forward the design strategy of comprehensive biological fouling prevention and control technology. keywords: biological contamination antifouling technology marine ecological environment the risk assessment 1. introduction with the increasing frequency of human marine activities and the construction of large-scale marine projects, marine fouling organisms will seriously threaten the safe and stable operation of marine facilities and cause greater economic losses. humans have tried to explore marine antifouling technology by means of poisoning, coercion, avoidance, stripping and cleaning. at present, there is no antifouling technology that has the advantages of low cost, high efficiency, persistence, broad spectrum and environmental friendliness. developing more green antifouling technology has become the world consensus. the importance of marine environmental protection is self-evident, and the marine environmental pollution caused by economic development is increasingly prom30 sustainable marine structures | volume 04 | issue 01 | january 2022 inent. the maritime environment protection committee (mepc) of the international maritime organization (imo) has been committed to energy conservation and emission reduction of ships, improving the international convention for the prevention of pollution from ships and other conventions [1]. on march 3, 2011, china submitted its accession to the international convention on the control of harmful anti-fouling systems on ships to the international maritime organization and took effect on june 7, 2011 [2]. in building a modern legal system for marine ecological and environmental protection, china has revised the marine environmental protection law four times, and issued more than 100 supporting regulations, departmental rules and local legislation. the widespread use of antifouling technology is one of the marine pollution sources that can not be ignored, and its impact on the marine ecological environment has attracted more and more attention of policy makers and scientific research institutions. 2. application status of antifouling technology 2.1 harm of fouling of marine organisms fouling of marine organisms mainly involves the formation of organic membranes by adsorption of organic molecules on the substrate, and the formation of biofilm by attachment reproduction of microorganisms [3]. then, spores of algae, small fouling animals and larva of large benthic fouling organisms will attach and grow, and eventually form a large number of stable biological communities. in the development process of biological fouling from the early, middle and late stages, there is the phenomenon of attachment succession in the fouling community. in the end, micro and large fouling organisms usually form the fouling together, and it is often manifested as the aggregation and attachment phenomenon of some dominant fouling organisms, such as barnacles and mussels. however, in the actual environment, the formation process and apparent phenomena of defilement biomes are very complex and diverse, which are affected by various factors such as environment and competition between species, and are complicated with environmental conditions such as sea area, season, temperature and surface characteristics of materials [4]. the fouling of marine organisms mainly involves the formation of organic membranes by absorbing organic molecules on the substrate, and then the biofilm is formed by the attachment and reproduction of microorganisms. then the spores of algae, small fouling animals and larva of large benthic fouling organisms will attach and grow, and eventually form a large number of stable biological communities. in the development process of biological fouling from the early, middle and late stages, there is the phenomenon of attachment succession in the fouling community. in the end, micro and large fouling organisms usually form the fouling together, and it is often manifested as the aggregation and attachment phenomenon of some dominant fouling organisms, such as barnacles and mussels. however, in the actual environment, the formation process and appearance of defilement community are very complex and diverse, which are affected by various factors such as environment and competition between species, and have complex relationship with environmental conditions such as sea area, season, temperature and surface characteristics of materials. barnacles, mussels, worms and other representatives of large marine fouling organisms have both can secrete powerful underwater adhesion glue and the characteristics of calcium have hard shell, able to withstand high speed water erosion, the population is dominant in the community, the harm to marine underwater installations, the largest is the main factors of ship sailing resistance increase [5]. therefore, it has become the main research object in the field of marine pollution prevention. the most critical link for the occurrence of biological fouling is that larvae or algal spores are easy to attach themselves to underwater fixed facilities or anchored ships with relatively smooth water flow [6]. biological fouling will increase the ship’s sailing resistance, the most serious can increase the shaft power 84%, and accelerate the shell corrosion; the flow of seawater is reduced by blocking the seawater pipeline; blocking aquaculture cage mesh and production reduction; signal and transmission failures affecting underwater detection equipment. in freshwater basins, the main fouling organism is the limnoperna fortunei [7], which is the most harmful to water transport projects, water conservancy projects and inland river navigation. 2.2 principles of marine antifouling technology according to the scientific principle of antifouling technology, it is classified and introduced [8]. physics-based antifouling technology has little impact on the environment, but it has great limitations in use and high energy consumption. once physical conditions cannot be maintained, biological fouling will occur immediately. mechanical removal refers to the removal of fouling organisms attached by underwater dynamic machinery instead of divers. marine static facilities need continuous use. cleaning before the ship docks can prevent biological invasion, and cleaning before leaving the port can timely prevent the development of early fouling and reduce treatment costs. increasing flow rates and creating turbulence both work by creating a flow environment that adheres to the surface of the substrate and 31 sustainable marine structures | volume 04 | issue 01 | january 2022 makes it difficult for the plankton larvae to attach; increasing the surface temperature of the attached substrate will cause the larva to escape, and the fouling organisms will die and fall off at the temperature that can not survive. the reduction of oxygen concentration is mainly aimed at the use of closed pipes. when oxygen concentration is lower than a certain value, the larva will lose its motor ability and cannot attach, and will cause the death of the attached contaminated organisms. ultrasonic vibration makes it difficult for plankton larvae to attach and causes the shedding of early fouling organisms through the high-frequency vibration attached to the substrate [9]. uv antifouling refers to the direct exposure of diode radiation or the embedding of the diode on the substrate of the high permeability uv coating. uv radiation will cause dna, rna and protein denaturation, so that the fouling organisms lose their attachment ability or die [10]. antifouling technology based on chemical principle has environmental toxicity, mainly divided into direct release antifouling agent and antifouling coating. the former is the early use of heavy metal ions or highly toxic pesticides as antifouling agents to kill a large range of contaminated organisms, and has been banned [11]. the latter has the advantages of high efficiency, broad spectrum, durability and low cost, and is the main antifouling technology means at present. antifouling coating can be divided into biodegradable coating, fouling release coating (frc) and self-polishing coating (spc) according to the technical principle. biodegradable coatings are mainly polyester polymer materials which can be degraded by biology and environment. the continuous degradation makes the contaminated organisms lose the binding site and desorption, but the service life is short because of continuous degradation. fouling desorption coating is a kind of polymer material represented by silicone and fluoropolymer, which is difficult for fouling organisms to attach and easy to desorption due to its low surface energy and low modulus. however, its service life is limited by mechanical strength and underwater adhesion between substrate. the cations in seawater can be replaced by antifouling agent after hydrolyzing the polyacrylate silane ester resin base material in the self-polishing coating, so that the antifouling agent is released slowly, but the porosity will gradually increase. humans have tried to screen antifouling agents by extracting antifouling active substances from marine animals, plants and microorganisms in large quantities, but high production cost, difficult grafting and easy degradation are the biggest limiting factors. the antifouling technology based on biological principle mainly adopts biological suppression to limit the fouling of organisms by predation of natural enemies. this approach remains in the theoretical stage, because changing the stable abundance of organisms in the ecosystem or introducing alien species may cause secondary ecological disasters, and it is difficult to limit the activity range of the removal organisms, and the effect is slow. the removal organisms themselves are also affected by environmental changes. bionical anti-fouling technology in recent years become a hot research topic, human through material micro-nano structure design and simulation of lotus leaf [12], salvinia natans all, sea anemones, shark, fur animals, andrias and so on antifouling mechanism [13], the structure has the characteristics of low surface energy, low modulus, in subsequent studies found creatures and antifouling secretion metabolic stop loss of anti-fouling ability of structure, such technologies therefore need to address issues such as the high cost of manufacturing materials and the simulation of dynamic life processes. 3. environmental effects of marine antifouling 3.1 current situation of marine pollution due to its huge volume and strong self-purification capacity, the ocean is regarded as a “sea containing all kinds of pollution” by human beings. ocean warming, acidification and accumulation of toxic substances are the most significant characteristics of its pollution [14], and the pollution of the upper coastal waters and tidal flats is the most serious. direct economic losses mainly come from the reduction of aquaculture and fishing [15]. the exploitation and utilization of fossil fuels leads to the overload emission of greenhouse gases such as carbon dioxide, methane and nitrous oxide [16], which is the basic cause of global climate warming and ocean warming. ocean warming will bring global ecological problems such as glacier melting and release of ancient viruses, land area shrinking due to sea level rise, irreversible degradation of coral reefs and other ecosystems [17]. excessive fossil fuel use releases acidic gases such as carbon dioxide, sulfur dioxide and nitrogen oxides, which dissolve in water, causing ocean acidification and hindering the growth of calcareous skeletal shells of organisms such as crustaceans, coelenterates and mollusks. toxic substances accumulate in water due to their stable chemical properties and most of them can be enriched in organisms, such as heavy metal ions, radioactive substances and microplastics, etc. oil pollution will cause large-scale death of plankton and decrease of dissolved oxygen in water [18]. therefore, marine pollution will bring about the compression of human living space and the destruction of food supply chain and other problems that threaten human existence. marine underwater facilities are one of the main sources of pollution. nuclear power plants and nuclear-pow32 sustainable marine structures | volume 04 | issue 01 | january 2022 ered vessels will cause radioactive pollution [19]. oil exploitation, transportation and ship navigation will produce oil pollution. there are also industrial emissions of heat sources, ship navigation noise and other physical pollution and solid and liquid waste pollution. 3.2 effects of antifouling coating active substances on marine environment the polyester polymer materials in biodegradable coating are degraded into esters with low toxicity in water without forming residues [20]. it is worth mentioning that artificial synthesis of bacterial toxin butenolide extracted from fusarium can block the fouling of biological attachment signal pathway rather than poison to achieve antifouling effect. the antifouling effect of the defiled-desorption coating depends on the physical properties of its material surface [21]. it does not release toxic substances. after the expiration of its life, the coating is scraped off for harmless treatment. the most harmful component to the marine ecological environment is the antifouling agent in the antifouling agent release coating [8]. most antifouling agents are used in combination with cuprous oxide and organic biocides. copper ions exist stably in free state in seawater and are difficult to be mineralized and precipitated. they accumulate in the environment and are enriched in the biological food chain. long-term use will threaten the breeding of marine organisms and human food safety. pyridinthione (pt) in the biocide will degrade to pyridine 1-ox-2-sulfonic acid with low toxicity in a short time [22], and the isothiazolinone derivative (dcoit) can be rapidly oxidized and degraded to low toxicity in water, and finally converted to non-toxic substances without residue [23]. irgarol 1051 (2-methyl sulfur-4-tert-butylamino-6-cyclopropyl amino-s-triazine) degrades slowly in water but is easy to photolysis [24]. it is most toxic to marine plants and has little effect on animals and bacteria. antifouling agent release of antifouling paint in the base material and auxiliary materials of the pollution is small, the base material component polyacrylate silane ester resin, the main chain fracture hydrolyzed into low toxicity acrylate single molecule and is slowly degraded, will not remain as microplastics; xylene in excipients is a class 3 carcinogen, which can degrade slowly in water and volatilize photodecomposition easily. it is not a persistent pollutant. n-butanol has a stronger paralyzing effect than ethanol, and it is not the main pollutant. 3.3 impact of other antifouling technologies on the marine environment physical antifouling has no residual harm, no environmental toxicity for fouling organisms, but the need for high energy consumption to maintain physical conditions may produce greater secondary pollution. high temperature antifouling requires a heat source to maintain the temperature of the base surface. therefore, the continuous release of heat will increase the water temperature near the facility, causing the temperature stress effect on the surrounding aquatic organisms, and may affect the facility itself or the operator due to heat conduction. because ultrasonic vibration can be widely spread in water, it may cause neurotic disorder of ultrasonic sensitive marine organisms such as dolphin, grouper, black bass and drum shrimp. although there is no residual harm, the radiation area is wide, and it will also affect the precision instrument components and operators of facilities. ultraviolet radiation causes nearby plankton die and biological exposed skin burns, a wide range of radiation attenuation in the water and won’t cause pollution and no residue, but the extensive use of diode produces electronic garbage disposal costs and maintenance costs of circuit may be higher, so only apply to small underwater detection equipment. in chemical antifouling, electrolysis of seawater produces hypochlorite ions and chlorine gas [25], which can directly kill plankton microorganisms, destroy the mucus on the body surface of fish and lead to electrolyte metabolism disorder in the body. although non-toxic chloride ions can be rapidly converted, the electrochemical corrosion of the substrate will be accelerated, and energy consumption is also high. analog enzymes, although they consume no energy, remain in the conceptual stage and are not discussed here. bionic antifouling materials mostly do not release toxic substances, but the leakage of silicone oil from the porous structure will also cause oil pollution. 4. management of the use of marine antifouling technology 4.1 risk assessment of marine antifouling technology because the pollutants produced by immersion of antifouling coating have the characteristics of long halflife, accumulation and enrichment, strong toxicity and uncontrollable, the vast majority of laws and standards restricting the use of antifouling technology in the world are formulated for antifouling coating. the united states enacted the toxic substances control act (tsca) in 1976; in 2006, the european union issued the registration, evaluation, authorisation and restriction of chemicals (reach), and in 2012, a new biocide regulation bpr-biocidal products regulation replaced the original biocide directive bpd-biocidal products directive. in 33 sustainable marine structures | volume 04 | issue 01 | january 2022 2017, china also issued national standards such as risk assessment method for marine environment of antifouling active substances used in ship antifouling bottom systems and risk assessment method for marine environment of ship antifouling bottom systems using antifouling active substances. the risk assessment procedure of antifouling coatings is firstly to screen substances [26], quantify the release rate and establish exposure scene model to obtain the predicted environmental concentration (pec) to complete the exposure assessment. then collect hazardous information for toxicity assessment and obtain environmental effect threshold (pnec) to complete the risk assessment; finally, all the information is integrated to carry out risk characterization to obtain risk entropy and form a risk assessment report. in recent years, the regulatory procedures for risk assessment and control of antifouling coatings have been basically and increasingly improved. the problem that needs to be solved is to perfect the model database of each sea area exposure scenario and construct various functional laboratory microcosmic models. in addition, the impact of other antifouling technologies on the marine ecological environment, especially precious and endangered species, should also be included in the evaluation scope. 4.2 design strategy of marine antifouling technology the biggest factor limiting new environmentally friendly antifouling technologies is cost control, and copper-containing antifouling paints are still dominant in the short term. it should be noted that the environmental toxicity of copper is much lower than tbt and other organotin antifouling agents, but the minimum effective permeability is more than 10 times of the latter. the cumulative effect of long-term use is uncontrollable and irreversible, which is obviously not a long-term solution. the afs has banned organotin since 2008, and this year, the 76th session of the international maritime o rg a n i z a t i o n ’s m a r i n e e n v i r o n m e n t a l p r o t e c t i o n committee (mepc) adopted the afs amendment. use of cybutryne (2-tert-butamino-4-cyclopropyl-6methanethio-1,3, 5-triazine) in antifouling bottom systems will be prohibited from 1 january 2023. the leaching rate of copper ion is limited by the technical requirements for environmental marking products antifouling paints for ships formulated by the ministry of environmental protection of china. all over the world, the regulation of existing antifouling agents and the access of new antifouling agents will only become more stringent, and it is necessary to continue to look for antifouling agents with lower environmental and biological toxicity. low cost bionic degradable antifouling agent and antifouling coating with dynamic surface matching use, forming multi-mechanism long-term static antifouling is an important direction of antifouling coating development. the ultimate goal of antifouling is to achieve zero emissions only through physical structure and material surface properties. but in the real sense of the present environment-friendly antifouling technology has a variety of congenital defects, we can develop antifouling strategies through the macro level. to establish a database of the changing rules and characteristics of the fouling community in different seasons and sea areas, and to formulate a comprehensive anti-fouling strategy according to the dominant fouling organisms. on the premise of meeting the discharge standards, the pollutants discharged into the ocean are screened as antifouling agents, and local enrichment and discharge are carried out in antifouling parts to achieve antifouling effect, and the pollutants are reused. comprehensive anti-pollution technology strategy should be considered in an overall way to find a balance between economic cost and risk management, so as to achieve lower overall toxicity and less consumption of pollutants produced by anti-pollution. 5. conclusions a large number of species extinction, seabed desertification, abnormal climate change, deterioration of coastal water quality, frequent fishing disasters have rung the alarm bell for human beings. let us realize that it is urgent to solve the irreversible pollution problem, and we should comprehensively reduce the pollution caused by marine pollution prevention from multiple dimensions such as technological research and development, rational use, legal supervision and so on. oceans connect all continents. only by making joint efforts to protect and sustainably utilize oceans and marine resources can we maintain our common “blue granary” and “blue medicine storehouse”. this is the only way for human civilization to continue to grow and flourish. references [1] aldo, ch., 2019. the imo initial strategy for the reduction of ghgs from international shipping: a commentary(article). international journal of marine and coastal law. 3, 482-512. [2] hassan, c.a.s.h., 2016. the impact of implementing the international convention on the control of harmful anti-fouling systems in ships (afs convention) on the marine environment. shipbuilding and ocean engineering. 1, 57-63. 34 sustainable marine structures | volume 04 | issue 01 | january 2022 [3] culver, c.s.a.b., johnson, l.t.c., page, h.m.b., et al., 2019. integrated pest management for fouling organisms on boat hulls. north american journal of fisheries management. [4] dürr, s.p.w.d., wahl, m., 2004. isolated and combined impacts of blue mussels (mytilus edulis) and barnacles (balanus improvisus) on structure and diversity of a fouling community. journal of experimental marine biology and ecology. 2, 181-195. [5] farkas, a., degiuli, n., martić, i., 2020. the impact of biofouling on the propeller performance. ocean engineering. 108376. [6] liang, ch., strickland, j., ye, z.h., et al., 2019. biochemistry of barnacle adhesion: an updated review(review). frontiers in marine science. [7] wei, l., xu, m.zh., zhang, j.h., et al., 2020. survival and attachment of biofouling freshwater mussel (limnoperna fortunei) to environmental conditions: potential implications in its invasion, infection and biofouling control. limnology. 2, 245-255. [8] tian, l., yin, y., bing, w., et al., 2021. antifouling technology trends in marine environmental protection. j bionic eng. 18(2), 239-263. [9] salta, m., goodes, l.r., maas, b.j., 2018. bubbles versus biofilms: a novel method for the removal of marine biofilms attached on antifouling coatings using an ultrasonically activated water stream(article). surface topography: metrology and properties. 3, 1-18. [10] ryan, e., turkmen, s., scopus preview benson, s.d., 2020. an investigation into the application and practical use of (uv) ultraviolet light technology for marine antifouling(article). ocean engineering. 107690. [11] amara, i., miled, w., slama, r.b., et al., 2018. antifouling processes and toxicity effects of antifouling paints on marine environment. a review. environmental toxicology & pharmacology. 115-130. [12] carve, m., scardino, a., shimeta, j., 2019. effects of surface texture and interrelated properties on marine biofouling: a systematic review. biofouling. 35(6), 597-617. [13] tian, l., yin, y., bing, w., et al., 2021. antifouling technology trends in marine environmental protection. j bionic eng. 18(2), 239-263. [14] dobretsov, s., coutinho, r., rittschof, d., et al., 2019. the oceans are changing: impact of ocean warming and acidification on biofouling communities. biofouling. 35(5), 585-595. [15] yigit, u., ergun, s., bulut, m., et al., 2017. bio-economic efficiency of copper alloy mesh technology in offshore cage systems for sustainable aquaculture. indian journal of geo-marine sciences. 10, 20172024. [16] man, l., feng, k.sh., zheng, h., et al., 2021. supply chain effects of china’s fast growing marine economy on greenhouse gas emissions. environmental research letters. 5, 54061. [17] bradley, d.e., andersson, a.j., cyronak, t., 2014. benthic coral reef calcium carbonate dissolution in an acidifying ocean. nature climate change. 11, 969-976. [18] jin, ch.h., xu, y.p., 2021. risk analysis and emergency response to marine oil spill environmental pollution. iop conference series: earth and environmental science. 12070. [19] m-navarrete, j., espinosa, g., i-golzarri, j., et al., 2014. marine sediments as a radioactive pollution repository in the world. journal of radioanalytical and nuclear chemistry. 299(1). [20] ma, ch.f., zhang, w.p., zhang, zhang, g.zh., et al., 2017. biodegradable polymers; studies in the area of biodegradable polymers reported from hong kong university of science and technology (environmentally friendly antifouling coatings based on biodegradable polymer and natural antifoulant). journal of engineering. [21] hu, p., xie, q.y., ma, ch.f., et al., 2020. silicone-based fouling-release coatings for marine antifouling. langmuir : the acs journal of surfaces and colloids. 36(9). [22] zhi, y.s., jung, j.h., jang, m., et al., 2019. zinc pyrithione (znpt) as an antifouling biocide in the marine environment—a literature review of its toxicity, environmental fates, and analytical methods. water, air, & soil pollution: an international journal of environmental pollution. 230(4). [23] heloísa, b.g.a., da-silveira-guerreiro, juliana, z.s., 2021. molecular and biochemical effects of the antifouling dcoit in the mussel perna perna. comparative biochemistry and physiology, part c. 239. [24] zhang, a.q., zhou, g.j., lam, m.h.w., et al., 2019. toxicities of the degraded mixture of irgarol 1051 to marine organisms. chemosphere. 565-573. [25] gaw, sh.l., sarkar, s., nir, s., et al., 2017 electrochemical approach for effective antifouling and antimicrobial surfaces(article). acs applied materials and interfaces. 31, 26503-26509. [26] karina-lotz-soares-a, c., sergiane-caldas-barbosa, c., ednei-gilberto-primel, c., et al., 2021. analytical methods for antifouling booster biocides determination in environmental matrices: a review. trends in environmental analytical chemistry. e108. 25 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v2i2.329 sustainable marine structures http://ojs.nassg.org/index.php/sms article makran coastal zoning for the construction of new marine areas based on hydrological and hydraulic characteristics using satellite data and spatial analysis hossein khanzadi1* karim akbari vakilabadi1 ramin almasi2 1. department of marine faculty, imam khomeini maritime university, nowshahr, iran 2. m.sc. of civil engineering, tabriz university of technology, tabriz, iran article info abstract article history received: 5 march 2021 accepted: 31 march 2021 published online: 31 march 2021 on one hand, the diversity of activities and on the other hand, the conflicts between beneficiaries necessitate the efficient management and supervision of coastal areas. accordingly, monitoring and evaluation of such areas can be considered as a critical factor in the national development and directorship of the sources. with regard to this fact, remote sourcing technologies with use of analytical operations of geographic information systems (gis), will be remarkably advantageous. iran’s south-eastern makran coasts are geopolitically and economically, of importance due to their strategic characteristics but have been neglected and their development and transit infrastructure are significantly beyond the international standards. therefore, in this paper, with regard to the importance of developing makran coasts, a multi-criterion decision analysis (mcda) method was applied to identify and prioritize the intended criteria and parameters of zoning, in order to establish new maritime zones. the major scope of this study is to employ the satellite data, remote sensing methods, and regional statistics obtained from jask synoptic station and investigate the region’s status in terms of topography, rainfall rate and temperature changes to reach to a comprehensive monitoring and zoning of the coastal line and to provide a pervasive local data base via use of gis and mcda, which will be implemented to construct the coastal regions. in this article, while explaining the steps of coastal monitoring, its main objectives are also explained and the necessary procedures for doing so are presented. then, the general steps of marine climate identification and study of marine parameters are stated and the final achievements of the coastal monitoring process are determined. in the following, considering that this article focuses on the monitoring of makran beaches, the method of work in the mentioned region will be described and its specific differences and complexities will be discussed in detail. also, the impact of such projects on future research results will be discussed. keywords: makran coasts multi-criterion decision analysis zoning local data base *corresponding author: hossein khanzadi, department of marine faculty, imam khomeini maritime university, nowshahr, iran; email: hk.patriot6@gmail.com 26 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 1. introduction makran beaches as one of the most important aquatic habitats in the country have been strategically neglected due to the lack of a comprehensive and integrated management approach in recent years. in order to manage the strategic area of makran, the use of satellite data and spatial analysis provides us with valuable information for a comprehensive monitoring. however, the spatial information of many of the world’s aquatic habitats is considered to be one of the main unknowns in the study of water resources. for reasons such as high costs and lack of necessary equipment, makran beaches lack accurate information on spatial changes, which is one of the main limitations of this study. the effects and natural phenomena of the earth’s surface are changing rapidly, and these changes are remarkable throughout human life [1]. one important point is that these changes can be carefully reviewed so that natural and human factors recognize these changes; therefore, coastal areas, the lake interior, lake fluctuations and other important parameters are considered as ecological environments [2]. in this context, monitoring and evaluating such areas can be considered as an important issue in national development and water resource management. with the advancement of marine science and technology and stakeholder engagement, it is possible to solve the problems [3]. marine and coastal studies provide decision makers with plenty of information to manage coastlines. existing regional management plans for regional sustainable development in coastal areas do not provide the intended purpose for the construction of new offshore areas[5]. to ensure the sustainable development of offshore areas, the conservation of coastal resources is a requirement[6]. it is not clear to the departments and developers of the new maritime areas which areas can be used for offshore projects, mfz method can be used to clarify many issues[7]. thus, over the past few decades, the use of measuring technology to detect such changes over time has attracted the attention of various researchers [8]. understanding natural potential, including the climate of each region as the basis for human activities, forms the basis of environmental planning. earth warming research provides an important insight into the response to terrestrial ecosystems [9]. lack of knowledge of the sub-regions of the regions, causes the economic and agricultural planning fail. for this reason, the importance and necessity of identifying homogeneous climatic regions has long been of concern to geographers and climatologists, and has led to the development of diverse climatological methods such as sylaninov, hansen, coupon, de martonne, embereger, etc. makran coast in the southeast of iran is of geopolitical, geostrategic and geo-economic importance due to its strategic location and characteristics. the existence of a free trade-economic zone in chabahar, the existence of suitable beaches, land and proper shelter along the coast, the existence of excellent platforms for transit and shipping, the presence of small bays (banks), the presence of coasts with adequate defense capabilities, the proximity to free waters and the proper operational depth oman sea, the presence of naval areas of the army, the existence of the necessary conditions for the expansion of military units and the adaptation of the military area by political divisions are part of the capabilities of the region, but over the past decades, due to more focus on gulf ports and beaches, these capabilities have not been used. makran’s lanes are not only the most developed iranian seaboard, but also on the basis of development indicators, this axis is among the most rebellious areas in iran. however, the future development of the country, especially in the middle east, depends to a large extent on the geographical and coastal situation of the oman sea. considering the above, fertilizing the capabilities of these important beaches will increase iran’s geopolitical weight in the region and even in the world. zoning is an appropriate tool for guiding the use of sustainable regions, and its growing effectiveness is undeniable among scholars [10]. zoning is an approach that can provide a good prospect for researchers to explore different areas for human activities [11]. it shows the zoning of marine activities in different regional scales [12]. marine spatial planning (msp) is increasingly considered an effective tool that can resolve conflicts among various human uses as well as the conflicts between human uses and the marine environment. many countries such as australia, united kingdom, germany, belgium, and united states have already initiated or implemented msp. in china, marine functional zoning (mfz) has developed independently since it was first proposed by the chinese government in 1988 [14]. in marine protected areas (mpas), zoning schemes can help balance multiple resource uses. literature on ocean zoning design methods points out the need for analytical tools that guarantee stakeholder involvement and that address the unique spatial characteristics of the sea, especially under multiple jurisdictions [15]. to showcase the contribution of mfz as a practical approach for xiamen integrated coastal management (icm) [16], the five dimensions of integration in icm are applied as an analysis framework. firstly, through compiling of the historical data and documents of the sea uses and marine environments, and socioeconomic status as well, the key drivers of initiating mfz in the 1990s is summarized doi: https://doi.org/10.36956/sms.v2i2.329 27 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 as increasing but incompatible and even conflicting sea uses, degrading marine environments due to negative effects of intensified human activities, and the lack of coordinating mechanism which has worsened the use-use and use-environment conflicts. secondly, the technical guidelines and adaptive evolvement of xiamen mfz is introduced, and the achievements of xiamen mfz are explored. based on the above analysis, the relationships of mfz and icm is looked into the dimensions of legislation, coordinating mechanism, scientific and technical support, integrated law enforcement and public participation; and how mfz contributes to icm in integration of dimensions of intergovernmental, inter-sectoral, land and sea, science and management, and multiple disciplinary is analyzed in-depth [16]. by collecting thin sections, the sediments of the area are studied and their types are determined. finally, combining these two sources of information, potentially suitable and unsuitable areas for the construction and development of jetties, ports and fuelling jetties are determined. it was shown that factors such as fluctuations in the sea level, tectonic processes, climatic atmosphere, hydraulic processes, especially tidal currents, human interference, and construction activities in the jetties and these coastal regions are the most destructive and constructive forces at work in the coastal regions [17]. the morphology of six adjacent major catchments draining the onshore makran accretionary wedge in southeast iran and southwest pakistan was studied to examine how the channel pattern and the length profiles may reflect the recent and active growth of the wedge. qualitative field surveys were combined with the quantitative analysis of channel steepness and concavity measured from digital elevation models. these profiles were compared with modelled profiles using a stream power approach assuming homogeneously uplifting, uniform rock substratum. results show a distinct difference between the studied western and eastern catchments [18]. the present study aims to classify the climatic and zoning of makran coastlines, taking into account parameters such as coastline changes in order to achieve a comprehensive location database for the construction of maritime areas and optimal utilization of the functions of the region. table1. monthly raining data from jask station geographical location: jask station average monthly rainfall(mm) average monthly rainfall(mm) 8 2016 2 2012 7.47 2008 3.33 2004 1.37 2000 10 2017 8.63 2013 7.56 2009 7.87 2005 6.04 2001 12.86 2014 5.11 2010 14.74 2006 2.73 2002 11 2015 2.62 2011 15.09 2007 1.43 2003 table2. monthly temperature data from jask station geographical location: jask station average monthly temperature(oc) average monthly temperature(oc) 27 2016 27.36 2012 26.87 2008 27.96 2004 27.76 2000 26.86 2017 26.85 2013 27.6 2009 27.36 2005 27.86 2001 26.89 2014 27.73 2010 27.3 2006 27.8 2002 26.1 2015 24.34 2011 27.46 2007 27.74 2003 doi: https://doi.org/10.36956/sms.v2i2.329 28 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 2. methods and material the studied area in this research is the makran coast in southwest of iran. makran is approximately consisted of sistan and balouchestan and part of south coast of hormozgan in iran. 2.1 determination of the studied area’s climate as it is pointed out, climate is one of the most effective phenomena of human life and recognition natural potentials i.e. regional climate is the basis of environmental planning. hydraulic and hydrological characteristics are different in varied naval regions [13]. so in this study to determine the regional climate, required data of temperature and raining are prepared from synoptic station in the port of jask (tables 1 & 2). average data of raining and temperature are derived from using interpolation and then using climate determination methods de martonne and embereger, the climate of studied region is determined. in de martonne method determination of climate type is based on yearly raining amount and temperature. in embereger method which is more sensitive than de martonne, besides using monthly raining amount, the coldest and hottest temperature of the month is used to determine the climate conditions. 2.2 check the topography and tilt status of the area a closer examination of the amount of precipitation and temperature and the subsequent mapping of the makran coastal strips requires a knowledge of the topographic conditions of the area, because the precipitation varies with the variations in rainfall, and the type of climate in the study area can change. if the altitude changes are taken into account in the estimation of moisture and heat regimes, soil moisture and heat regimes in different regions will be very diverse. in order to investigate the topography status of the present study, we use the gis techniques to estimate the required maps using the raster and wactar data. for this purpose, a 38-meter digital map taken from the aster satellite has been used. also, for plotting consistent maps, necessary regression equations were determined using the mean annual rainfall and temperature data, and by making a series of calculations in the arcgis software, a digital elevation map prepared from the area in a 90-pixel, was used. 2.3 area zoning of coastal areas using climatic data in this study, climatic parameters of precipitation and temperature as the selected indicators for assessing the status of the region from the point of view of precipitation and temperature variations for the port of jask station and 17 years of climate data from the synoptic station have been used. to do this, first, using spss software and kolmogorov-smirnov statistical test, the rainfall and temperature distribution data were analyzed. after examining the results, the least amount of data was extracted on each scale during the statistical period and its coverage maps in each scale during the statistical period, the arc map is drawn. then, after the calculations, the results of the various interpolation methods of idw and kriging with a weighing power of one to five were evaluated. also, for a better and more accurate assessment of coastline changes, using the modis satellite data from 2006 to 2016, the coastline of makran has been reviewed. 3. results and discussion 3.1 determining the type of climate in the study area in order to calculate the embereger relationship, the three following parameters are needed: average temperature of the coldest and warmest month of the year, and the mean precipitation (in millimeters). despite the mentioned parameters, the relationship was calculated and based on table 3, the climate of the study area was determined. according to the calculations performed to determine the climatic condition of the embereger method, it was found that the port of jask and the coastline are dry to semi-arid zones. of course, the beach strips are more volatile than the area, and there is no barrier to building offshore areas. secondary method, which is a more convenient way to determine the type of climate in most regions of the country, uses the annual average of rainfall and temperature in the area for this purpose. using the calculations done by the method of the de martonne, the area has a dry to semi-arid state. the corresponding coastal strip has high evaporation due to extreme temperature fluctuations and precipitation and proximity to the equator. table 4 shows the results of calculations of the de martonne method based on jask’s synoptic station. table 3. embereger formula calculation and regional climate determination climate typeresults dryq<28 hot8>m>5.1 doi: https://doi.org/10.36956/sms.v2i2.329 29 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 table 4. de martonne formula calculation and regional climate determination climate typeresults dryi<10 3.2 review the process of precipitation and temperature changes in order to better match and to better characterize the result obtained from the relations between embereger and de martonne, the diagram of precipitation and temperature variations in the region and the coastal strip is drawn up (figures 1 and 2). according to the precipitation fluctuation chart, in this coastal strip the range of precipitation variation between 5 and 12 mm is very common. on the other hand, by examining the temperature changes, the 17-year average for this port was 26 degrees. this amount of temperature is very important during the year from the examination of rainfall conditions and situation in the area. as this temperature shows that in the area and coastline the evaporation phenomenon is common in most of the year, and this evaporation is unavailable due to the lack of a coherent source such as a mountain that can enter the region’s hydrological cycle again with cooling. this low rainfall it can also be concluded from the sea currents and the climatic conditions that cause rainfall in the coastal regions; therefore, it can be concluded from embereger and de martonne ‘s relations that the climate of the region is dry. it should also be noted that during the period from 2000 to 2007, temperatures were high, but this temperature dropped by 2 degrees in 2017. of course, these climatic conditions can have an impact on coastal factors, so that many projects in the coastal areas do not have much progress. figure 1. raining changes in jask plot 3.3 check the topography and tilt of the area considering the conditions studied in the temperature variation and precipitation of the coastal strip, it is necessary that the area be considered in terms of topographical features and other effective factors considering the strategic nature of the jask area, especially the makran coast. in figure 3, the map of the area and the coastal strip is specified. according to the map, you can see the role of temperature and precipitation in the region. coastal areas are up to kilometers without mountains and highlands, which can be attributed to precipitation shortages in the region and high temperatures. however, according to the map, the existence of plains and coastal areas with a slope of less than 9 percent, as well as the existence of gorgeous rivers and natural attractions in the region provide a great opportunity to build tourist and recreational areas along the makran coastline. figure 2. temperature changes in jask plot figure 3. regional topology and slope plot figure 4. 3d view from region doi: https://doi.org/10.36956/sms.v2i2.329 30 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 further, arc hydro software has been used to more accurately assess the status of the area, the existing rivers, and follow up of surface water behaviors on the route. figure 4 shows the image obtained from this software. using the gis software and measurement tool, it is also possible to predict the status of the region and the coastline using hydrological and climatic data. for this purpose, arc hydro, one of the options available in the arcgis software, has been used based on the digital map of the area, the status of the arctic and the rivers. this software, which has been shown in figure 5, has a high ability to determine and assess the physiological characteristics of the region. in this picture, the coastal strip has the proper features for implementing many economic projects in the region. for more accurate evaluation of temperature and precipitation fluctuations in the area and coastal strip, consistent maps and homogeneous maps were provided with topographic maps, data obtained from the jask port’s synoptic station, and made by a series of calculations in arcgis software (figures 6 and 7). according to the regional map of the area, there is a higher rainfall in the central parts of the port of jask and there is no shortage of factors in the coastal areas to avoid evaporation, but the amount of precipitation is lower than other areas. in the entire coastal zone of makran, this issue is clearly visible. according to the coherent map, the coastal strip has a higher temperature than the central and upland areas of the port of jask. this state of affairs treats the situation in the region to a large extent, as the high temperature conditions associated with humidity disrupt many activities in the region. figure 5. forecasted model using hydrological and climatic derived from arcgis figure 6. co-raining plot of jask figure 7. co-temperature plot of jask 4.3 coastal zoning using climatic data in this study, climatic parameters of rainfall and temperature have been used as indicators for determining the status of the region. to do this, we first used the kolmogorov-smirnov test to investigate the rainfall distribution data and temperature of the area, and the results are presented in tables 5 to 7. considering the significant level (p) of more than 0.05 (for rainfall data equal to 0.13 and for temperature data equal to 0.093), data from rainfall and temperature have a good level of coastline level; therefore, rainfall and temperature data are normal and a parametric test can be applied to these data. after reviewing the output results, the least amount of data was extracted on each scale during the statistical period and its coverage maps were plotted in arc map for each scale during the statistical period. after calculating, the results of various interpolation methods for idw and kriging with a weighing power of one to five were evaluated. among interpolation methods, the two-dimensional weighted photo-idw method with the least power for rainfall parameters and temperature the error value of the rmse and mape and mbe errors are much more than other zoning methods. the lowest rmse estimate for each of the indices with respect to the potentials is 0.22 and 0.4 respectively. hence, this method is the most appropriate method for zoning the status of water resources in the makran region and the doi: https://doi.org/10.36956/sms.v2i2.329 31 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 coastal strip. the rainfall and temperature zone maps were also prepared in the coastal zone by precipitation and temperature data (figures 8 to 11). investigation of the maps shows that the coastline has the least rainfall distribution and the highest dispersion in the highlands of the port of jask but according to the temperature zoning map, in the coastal areas, the highest amount of dispersion and the lowest temperature in the highlands. coastal areas, such as high temperatures and high evapotranspiration, are in a state of inferiority, so that many projects are not in this situation. table 5. result of kolmogorov-smirnov test for raining data using software spss one-sample kolmogorov-smirnov test v1 n 17 normal parametersa,b mean 7.42145061728395e0 std. deviation 4.186981284660888e0 most extreme differences absolute 0.113 positive 0.113 negative -0.081 kolmogorov-smirnov z 0.481 asymp. sig. (2-tailed) 0.975 a. test distribution is normal. b. calculated from data. table 6. result of kolmogorov-smirnov test for temperature data using software spss one-sample kolmogorov-smirnov test v1 n 17 normal parametersa,b mean 2.72981372549020e1 std. deviation 0.485733938643530 most extreme differences absolute 0.149 positive 0.093 negative -0.149 kolmogorov-smirnov z 0.613 asymp. sig. (2-tailed) 0.847 a. test distribution is normal. b. calculated from data. table 7. kolmogorov-smirnov test table for raining and temperature parameter kolmogorov-smirnov nsiq raining170.975 temp170.847 figure 8. regional temperature plot for jask and makron coast using idw method figure 9. regional temperature plot for jask and makron coast using kriging method figure 10. regional raining plot for jask and makron coast using idw method doi: https://doi.org/10.36956/sms.v2i2.329 32 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 figure 11. regional raining plot for jask and makron coast using kriging method 3.5 changes in lines of the makran coast in this study, the changes in the makran coastline were reviewed using modis satellite data between 2006 and 2016. in figure 12, the accuracy of the measured data can be seen in the extent and evolution of the oman sea in the coastal strip of makran. in figure 13, coastline changes were monitored for three consecutive years between 2014 and 2016. assessing the amount of seafront progress or resettlement can certainly be important in making decisions for the construction of residential and commercial areas. figure 12. changes in coastal lines during 2006 till 2017 figure 13. changes in makran coast during 2014 till 2016 4. conclusions the climate of the studied area was determined by embereger and de martonne methods and 17 years of climatic data obtained from the synoptic station of port of jask. according to the calculations carried out with the parameters of the warmest and coldest months of the year, it was found that the port of jask is arid to semi-arid. the process of rainfall and temperature changes also indicates that in most days of the year, the phenomenon of evaporation is common in the region and coastal strip, and this evaporation is due to the lack of a coherent source such as mountains and suitable flows to create an outdated hydrological cycle and this low rainfall can also be deduced from sea currents and climatic conditions that cause rainfall in coastal areas. of course, the beach strips are more volatile than the area, and it should not be difficult to construct sea areas according to the conditions. considering the geographical conditions, scoring and determining the relevant criteria, the central part to the east of the makran coast has a high value from the point of view of the creation of maritime conditions. this area is also suitable for hydraulic topography. in order to more accurately assess the precipitation and temperature conditions, the region was also examined for topographic properties. the obtained maps indicate that the coastal areas have the lowest tilt and topography that is very flat and smooth, up to kilometers without mountains and highlands, but, according to the map, the existence of plain and coastal areas with a slope of less than nine percent as well as the presence of rainy rivers and natural attractions in the region, it has provided very good conditions for the construction of new sea areas along the makren coastline. with the possession of topographic maps and data on temperature and precipitation, we developed consistency maps. according to the regional map of the area, there is a higher rainfall in the central parts of the port of jask and there is no limiting factor in coastal areas as a way of preventing the evaporation from wasting. the amount of precipitation is lower than other areas. according to the coherent map, the coastal strip has a higher temperature than the central and upland areas of the port of jask. this state of affairs treats the situation in the region to a large extent, as the high temperature conditions associated with humidity disrupt many activities in the region. according to the topographical and hydrological conditions of the makran coast, the zoning of the coastal areas is favorable and suitable so the geographical and natural parameters are effective in determining the status of the coast and zoning. in this study, regional distribution of coastal areas was performed using spss software and kolmogorov-smirnov test to analyze doi: https://doi.org/10.36956/sms.v2i2.329 33 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 rainfall and temperature data of the region. the results showed that the data from rainfall and temperature have a good significance at the coastal level, so the rainfall and temperature data are normal and the parametric test can be applied to these data. after calculating the results of various interpolation methods for idw and kriging with a weighing power of one to five, it was found that the weight difference method (idw) with a power of two for rainfall and temperature parameters had the lowest rmse error and mape and mbe errors compared to other methods are zoning. rainfall and temperature zone maps were also prepared in the coastal zone by rainfall and temperature data. investigation of the maps shows that the coastline has the least rainfall distribution and the highest dispersion in the highlands of the port of jask but according to the temperature zoning map, in the coastal areas, the highest amount of dispersion and the lowest temperature in the highlands. coastal areas, such as high temperatures and high evapotranspiration, are in a state of inferiority, so that many projects are not in this situation. valuing and determining the appropriate points for the expansion of the marine areas, according to the views of the relevant experts in the field of marine science, can be an appropriate option. multi-criteria methods can also provide good and precise results by prioritizing and weighting different parameters. ultimately, the development of the makran coast, despite some restrictions, is a national, regional and even international imperative. development of basic facilities and expansion of commercial and recreational infrastructure can lead to national development in addition to improving the situation in the south-east region of iran. therefore, identifying and studying factors affecting the region’s situation can be important in many aspects. references [1] macleod & congalton, 1998, analysis of barrier shoreline change in louisiana from 1853 to 1989. atlas of shoreline changes in louisiana from, 36-97. [2] jensen, 1996. shoreline change along, remote sensing, 3(7): 1516-1534. [3] zafar ullah, wen wu, peifang guo, jing yu, a study on the development of marine functional zoning in china and its guiding principles for pakistan ocean & coastal management, volume 144, 15 july 2017, pages 40-50. [4] pravin d. kunte, nitesh jauhari, utkarsh mehrotra, mahender kotha, alexandre s. gagnon, multi-hazards coastal vulnerability assessment of goa, india, using geospatial techniques ocean & coastal management, volume 95, july 2014, pages 264-281 [5] wang chunye, pan delu, zoning of hangzhou bay ecological red line using gis-based multi-criteria decision analysis ocean & coastal management, volume 139, april 2017, pages 42-50 [6] lien-kwei chien, wen-chien tseng, chih-hsin chang, chih-hsiang hsu, a study of ocean zoning and sustainable management by gis in taiwan ocean & coastal management, volume 69, december 2012, pages 35-49 [7] ling ou, wei xu, qi yue, chang l. ma, yue e. dong, offshore wind zoning in china: method and experience ocean & coastal management, volume 151, 1 january 2018, pages 99-10 [8] donny & singh, 1989, shoreline changes along the rosetta-nile promontory: monitoring with satellite observations, marine geology, 99(1): 67-77. [9] gleissy mary amaral dino alves dos santos, alexandre rosa dos santos, luciano josé quintão teixeira, sérgio henriques saraiva, rodrigo scherer, gis applied to agriclimatological zoning and agrotoxin residue monitoring in tomatoes: a case study in espírito santo state, brazil journal of environmental management, volume 166, 15 january 2016, pages 429-439 [10] gonzalo hernán camba sans, sebastián aguiar, maría vallejos, josé maría paruelo, assessing the effectiveness of a land zoning policy in the dry chaco. the case of santiago del estero, argentina land use policy, volume 70, january 2018, pages 313-321 [11] zhiming zhang, ruth sherman, zijiang yang, ruidong wu, xiaokun ou, integrating a participatory process with a gis-based multi-criteria decision analysis for protected area zoning in china journal for nature conservation, volume 21, issue 4, august 2013, pages 225-240 [12] suzanne j. boyes, michael elliott, shona m. thomson, stephen atkins, paul gilliland, a proposed multiple-use zoning scheme for the irish sea.: an interpretation of current legislation through the use of gis-based zoning approaches and effectiveness for the protection of nature conservation interests marine policy, volume 31, issue 3, may 2007, pages 287298 [13] muhammad atiq ur rehman tariq, nick van de giesen, floods and flood management in pakistan physics and chemistry of the earth, parts a/b/c, volumes 47-48, 2012, pages 11-20 [14] qinhua f., ran z., luoping z., huasheng h., marine functional zoning in china: experience and prospects, journal coastal management volume 39, 2011 issue 6, 2011 pages 656-667 [15] michelle e. p., zoning design for cross-border madoi: https://doi.org/10.36956/sms.v2i2.329 34 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 rine protected areas: the red sea marine peace park case study, ocean & coastal management 2007, 499–522 [16] qinhua f., deqiang m., liyu z., shouqin z., marine functional zoning: a practical approach for integrated coastal management (icm) in xiamen, ocean & coastal management, 2018 [17] ahrari roudi m., moussavi-harami r., lak r., mahboubi a., motamed a., sedimentology-environmental assessment of the makran coastal region of iran., journal of applied geology autumn 2011, vol. 7, no. 4. [18] haghipour n., jean-pierre b., geomorphological analysis of the drainage system on the growing makran accretionary wedge., geomorphology, volume 209, 15 march 2014, pages 111-132 doi: https://doi.org/10.36956/sms.v2i2.329 1 sustainable marine structures | volume 04 | issue 02 | july 2022 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2022 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). *corresponding author: chungkuk jin, department of ocean engineering, texas a&m university, texas, the united states; email: jinch999@tamu.edu doi: http://dx.doi.org/10.36956/sms.v4i2.492 article comparison of potential theory and morison equation for deformable horizontal cylinders chungkuk jin* department of ocean engineering, texas a&m university, texas, the united states article info abstract article history received: 18 february 2022 accepted: 10 march 2022 published online: 30 march 2022 this study investigates the hydro-elastic behaviors of fully submerged horizontal cylinders in different regular waves. two methods were proposed and compared in this study. the first method was based on potential theory in frequency domain and the discrete-module-beam (dmb) method, which discretizes a floating elastic structure into a sufficient number of rigid bodies while simultaneously representing the elastic behavior from beam elements with euler-bernoulli beam and saint-venant torsion. moreover, the morison method in time domain was employed; this method estimates wave forces from the semi-empirical morison equation, and the elastic behavior is embodied by massless axial, bending, and torsional springs. various parametric studies on cylinder diameter, submergence depth, and wave direction were conducted. wave forces, dry/wet mode shapes/natural frequencies, and dynamic motions are presented and analyzed. keywords: wave force discrete-module-beam method potential theory morison equation horizontal cylinder 1. introduction underwater cylindrical structures have been suggested for various reasons. many of them lie on the seabed, and typical examples include submarine pipelines that transport water, oil, and natural gas, submarine cables for electricity transmission, and immersed tunnels for public transportation. even if these structures have accumulated engineering practices, several critical limitations still exist. these structures are susceptible to seismic activities [1,2]; the seabed should be even for installation; scours, the removal of sediment around the pipeline, can occur and are critical for vibration and fatigue damage associated with seabed movement [3]. also, the deepwater application is very challenging for submarine pipelines and cables due to not only high hydrostatic pressure and temperature difference but also high costs associated with a longer length and additional intervention work for the seabed [4]. submerged floating structures have been proposed as novel alternatives to the above structures, and representative examples are submerged floating pipelines and submerged floating tunnels. these structures float at a submergence depth and keep their location with mooring 2 sustainable marine structures | volume 04 | issue 02 | july 2022 systems if needed. they have several advantages: (1) they can be safe from wave and seismic actions by properly selecting design parameters, (2) the deepwater application is much more straightforward without considerable hydrostatic pressure and temperature difference, as in the deepwater location, and (3) structural health monitoring is much easier [4-9]. their considerable dynamic and structural behavior and the resulting large mooring tension are still considered severe under various environmental conditions such as waves, currents, earthquakes, and tsunamis. many studies adopted the morison equation [10] for force estimation of the horizontal cylinder [11-13] due to low computational cost. however, the morison equation has limitations in that wavelength should be more than five times the characteristic length ( / 0.2d l ≤ where d is cylinder diameter and l is wavelength), and the radiation effect is neglected. in addition, when the structure is close to free surface, the free-surface effect can be substantial, which results in a considerable variation of the scattering wave force compared with the deeply submerged structure cases [14]. the resulting mooring tension can also be different to a great extent. in this regard, validation work of the morison equation for fully submerged floating structures is essential with respect to different diameters, submergence depths, and wave directions. several papers discussed the validity of the morison equation by comparing it with theory-based approaches. typically, the inertia coefficient mc is fixed at 2 according to the slender body assumption and can vary for the non-slender body. for example, chakrabarti and tam [15] estimated the effective inertia coefficient for the morison equation for bottom-mounted surface-piecing vertical cylinder and proved that the effective inertia coefficient significantly decreases as /d l increases. chung [16] stated that when an object is close to free surface, the inertia coefficient can be a function of frequency, and radiation damping can be empirically added. in other words, its validity may be weakened when the free-surface effect exists to a great degree. chang et al. [17] showed that the morison equation reasonably estimates wave force up to second order for the hinged vertical cylinder at small wave steepness. however, they also mentioned that the morison equation underestimates the peak wave force and overestimates trough wave forces at high wave steepness. varying inertia coefficients along the submergence depth are proposed as in ref. [18]. regarding horizontal cylinders, li et al. [19] conducted experimental studies for inline responses for a submerged horizontal cylinder and showed that the inertia coefficient is not changing significantly with respect to the keulegan-carpenter number as opposed to vertical cylinders. chen et al. [20] compared the morison equation with cfd simulation and showed that the morison equation underestimates the wave force on a partially submerged horizontal cylinder by up to 50% relative errors. this study compared the potential theory with the morison equation for fully-submerged horizontal cylinders. both ends were fixed with the fixed-fixed boundary condition in which there are no displacements and angles at both ends. the multibody-based hydro-elasticity method with the potential theory in frequency domain—referred to as the discrete-module-beam (dmb) method—was compared with the lumped mass method with morison equation—referred to as the morison method. the froude-krylov, scattering wave, and radiation damping forces in the dmb method were compared with the inertia force of the morison equation in the morison method. dry/wet natural frequencies/mode shapes and horizontal/vertical motions/forces were systematically presented and analyzed. 2. theory and formulation two different approaches were selected to evaluate dynamic behaviors and wave forces for a fully submerged horizontal cylinder. the first method was the dmb method, in which wave forces are estimated by 3-dimensional (3d) potential theory in frequency domain and euler-bernoulli beam and saint-venant torsion are employed for representing elastic behaviors. the second method is the morison method, in which the morison equation estimates wave forces with representative added mass and inertia coefficients in time domain while beam elements are modeled by the lumped mass method with massless axial, bending, and torsional springs. the theory and formulation of the two methods are explained in this section. detailed formulations regarding the two methods and their validations can be found in refs [12,21,22]. 2.1 discrete-module-beam method in frequency domain the dmb method is based on 3d potential theory for the multibody in frequency domain; a large deformable structure consists of m rigid bodies and 1m − connecting beams [23,24], as shown in figure 1. the dmb method uses the right-handed cartesian coordinate system. figure 1. dmb method [25]. 3 sustainable marine structures | volume 04 | issue 02 | july 2022 laplace equation is governing equation for the potential theory when fluid is incompressible, irrotational, and inviscid as: 2 0 i te ωϕ − ∇ φ = φ = (1) where φ is the total time-dependent velocity potential, which can be decomposed into the total time-independent velocity potential ϕ and the time-dependent term i te ω− based on the assumption of harmonic excitation with wave angular frequency ω and time t . ϕ can further be decomposed into diffraction and radiation components with the incident, scattered, and radiation potentials iϕ , sϕ , and ( )m rϕ as: ( ) ( ) ( ) ( ) 1 6 1 m m i s r m m m m jr jr j i ϕ ϕ ϕ ϕ ϕ ω ξ ϕ = = = + + = − ∑ ∑ (2) where m represents the mth rigid body and ( )mjξ is six degrees of freedom (6dof) displacements of the mth rigid body, i.e., surge, sway, heave, roll, pitch, and yaw motions. first-order iϕ can be written as: ( ) ( )cos sincosh cosh ik x yw i k z higa e kh θ θϕ ω ++= (3) where wa is the amplitude of an incident wave, k is the wavenumber, h is water depth, θ is the wave direction, and g is the gravity acceleration. moreover, sϕ and ( )mrϕ can be obtained by considering the following boundary conditions on the free surface fs , bottom bs , body ( )1, 2, ... ,ks k m= , and far-field s∞ as: ( ) ( ) ( ) ( ) ( ) 2 0 on 0 0 on on , on 0, lim 0 on f b s i k m m jr j kk r g s z z s z h z s n n n k m s n k m r ik s r ω ϕ ϕ ϕ φ ϕ ϕ × × × ∞ →∞ ∂  − + = = ∂  ∂ = = − ∂ ∂ ∂ = − ∂ ∂ ∂ = =  ∂ ≠ ∂  − = ∂  (4) where r is the radial distance from the origin. ϕ × can be sϕ or ( )m jrϕ . ( )mjn is the inward unit normal vector for the j th dof on the m th body surface with respect to the bodyfixed coordinate system. sϕ and ( )m jrϕ are obtained by the 3d boundary element method. each body’s coordinate center is its center of gravity. the wave excitation force that is the sum of the froude-krylov and scattered wave forces for the j th dof on the m th rigid body in the body-fixed coordinate system is given in equation (5): ( ) ( ) ( ) m m m i s jjw s f i n dsρω ϕ ϕ= +∫∫ (5) the radiation force for the j th dof on the m th rigid body induced by the k th dof of the n th rigid body in the body-fixed coordinate system is given in equation (6): ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 2 2 m m mn mn n mn n n n jr jkr jk k jk k k kr m s f a i b ds n ϕ ω ξ ω ξ ρω ξ ϕ ∂ = + = ∂∫∫ (6) where ( )mnjka and ( ) mn jkb denote the added mass and radiation damping coefficients of the j th dof of the m th rigid body induced by the k th dof of the n th rigid body. in addition, the hydrostatic restoring force of the m th rigid body for the j th dof is given in equation (7): ( ) ( ) ( ) ( )( ) ( )53 4 m m m m m m m m jjh s f g y x n dsρ ξ ξ ξ= − + −∫∫ (7) after the hydrodynamic forces and coefficients have been introduced, the equation of motion for m rigid bodies can be written with the mass, added mass, radiation damping, hydrostatic restoring coefficient matrices, m , a , b , and k , and wave-excitation-force vector wf as: ( )( ) ( )( ) ( ) ( )e wω ω ω+ + + + + =rm a ξ b b ξ k k ξ f  (8) where upper dot means time derivative and rb is the structural damping matrix. in equation (8), the external stiffness matrix ek is introduced to consider the elastic behavior of a deformable floating structure. ek is constructed with euler-bernoulli beam and saint-venant’s torsion theory for 1m − beam elements. the 12 by 12 sub-stiffness matrix ek for the e th beam element in the local coordinate system is given in equation (9): 3 3 2 2 3 2 3 3 2 3 2 2 . 12 0 12 0 0 0 0 0 6 4 0 0 0 6 4 0 0 0 0 0 0 0 0 0 12 6 12 0 0 0 0 0 12 6 12 0 0 0 0 0 0 0 0 0 0 0 0 0 0 6 2 6 4 0 0 0 0 0 0 0 c e z e y e x e y y e e z z e e e c c e e z z z e e e y y y e e e x x e e y y y e e e ea symm l ei l ei l gi l ei ei l l ei ei l l ea ea l l ei ei ei l l l ei ei ei l l l gi gi l l ei ei ei ei l l l − = − − − − − − k 2 2 6 2 6 4 0 0 0 0 0 0 0 0 y e z z z z e e e e l ei ei ei ei l l l l                                                                    −   (9) where e and g are young’s and shear moduli, ca is the cross-sectional area, el is the element length, and xi , yi , and zi are the torsional, vertical, and lateral second moments of area about x, y, and z axes, respectively. ek can be expressed for 1m − beam elements with the 6 by 6 sub-stiffness matrices of ek as: 4 sustainable marine structures | volume 04 | issue 02 | july 2022 (11) (12) 1 1 ( 21) ( 22) (11) (12) 1 1 2 2 ( 21) ( 22) (11) 2 2 3 ( 22) 1 ( ) ( ) ( ) ( ) 0 0 0 0 0 0 0 0 e m ii ij e e e ji jj e e −     +   = +          =     k k k k k k k k k k k k k k k k          (10) 2.2 morison method in time domain the morison method was also modeled in time domain [26]. in this method, a deformable floating structure consists of finite elements with nodes and segments. key physical properties are included in the nodes while segments present structure’s deformability with massless axial, bending, and torsional springs. the morison equation evaluates the hydrodynamic forces for a moving body at its instantaneous node position. the computational time of this method is lower than the frequency-domain dmb method since this method is dependent on the morison equation for wave-force estimation. it is worth utilizing this method if accurate global performance estimation is possible with a cheaper computational cost. the equation of motion for a deformable floating structure in time domain can be expressed as: ( )1 2 n n n n n n a m dc c c aρ + + = + = − ∆ + ∆ + − − r s m m mx b x k x f w f x η η x η x       (11) where sk are the structural stiffness matrix, mf is the hydrodynamic force vector based on the morison equation, w is the wet-weight vector (i.e., buoyancy minus dry weight), ac , mc , and dc are the added mass, inertia, and drag coefficients, ∆ and a are the displaced mass and drag area, ρ is the seawater density, η and η 4 are the velocity and acceleration vectors of fluid particles, and n denotes the normal direction. structural deformability is represented by ks with axial, bending, and torsional springs. the drag term of the morison equation, i.e., 3rd term in equation (11), was neglected since the keulegan-carpenter number of the presented problem is low (inertia dominant). 3. case description figure 2 shows the configuration of a concrete hollow cylinder. its density and young’s modulus were 2300 kg/m3 and 30 gpa. the length of the concrete cylinder was fixed at 500 m, whereas various diameters of 10 m–20 m, submergence depths of 20 m–60 m, and wave directions of 30°–90° were selected as design parameters. in this study, the cylinder’s buoyancy-weight ratio was set at 1.0, which means its buoyancy is the same as its dry weight. then, the inner diameter and axial, bending, and torsional stiffness were reversely estimated based on the given buoyancy-weight ratio. the fixed-fixed boundary condition at both ends was designed; in other words, displacements and angles at both ends do not change. water depth was fixed at 100 m. 4. results and discussions 4.1 wave force the wave excitation force wf in potential theory is often correlated with the inertia force term if in the morison equation, i.e., 2nd term in equation (11). if is with the inertia coefficient ( )1m ac c= + , and 1 and ac are associated with contributions from the froude-krylov force and scattered wave force. the validity of the morison equation is then assessed by comparing wf and if . figures 3–4 show the comparison of horizontal/vertical wf and if (wave force per unit length). wave direction was fixed at 90° figure 2. configuration of a cylinder with fixed-fixed boundary condition (d denotes diameter; sd stands for submergence depth). 5 sustainable marine structures | volume 04 | issue 02 | july 2022 with respect to the positive x-axis, and if was calculated from the fixed body. at a low submergence depth of 20 m, which is close to free surface, trends and magnitudes of wf are somewhat different from those of if , as shown in figure 3(a) and (c). the morison model tends to overestimate the wave force at high frequencies of 0.7 rad/s or more. however, wf and if are very close at higher submergence depths, regardless of the wave frequency range, as shown in figure 3(b) and (d), which means that the morson method can estimate the wave force accurately for deeply submerged cylinders even if the cylinder diameter is large. moreover, the higher the submergence depth, the lower the importance of high-frequency wave forces since the wave kinematics decreases with submergence depth as a function of ( )cosh k z h+ for intermediate water and kze for deep water. as shown in figure 4, the difference between the two forces is significantly reduced at a small diameter of 10 m even if the submergence depth is 20 m. the previous results show that the morison equation accurately estimates the wave inertia force at the large submergence depth and small cylinder diameter. it is well known that the morison equation has a limitation, i.e., / 0.2d l ≤ . at the given water depth of 100 m and a cylinder diameter of 20 m, the wave frequency should be less than around 0.8 rad/s to be included in this condition. the scattered wave force scf is mainly associated with this limitation since the scattered wave force has a tendency to be important as the wave frequency increases. figure 5 shows the comparison of the froude-krylov force fkf and scf in the dmb method with half of if in the morison method ( )0.5 i = mff f that corresponds to fkf in the dmb method. wave kinematics for the morison equation is estimated at the geometric center, while that for fkf is based on the cylinder surface. at the given cylinder diameters, regardless of submergence depths, mff is similar to fkf , which means that kinematics estimation at the geometric center in the morison method is still valid for this horizontal cylinder at the given frequency range. then, as noticed in figure 5(a), scf induces the difference between wf and if only when submergence depth is low. in this case, the existence of free surface influences the calculation of scf . no free-surface effect is detected when the submergence depth is 60 m due to a large distance between free surface and the cylinder. (a) (b) (c) (d) figure 3. comparison of horizontal/vertical wf and if at a diameter of 20 m and different submergence depths. (a) (b) figure 4. comparison of horizontal/vertical wf and if at a diameter of 10 m and a submergence depth of 20 m. 6 sustainable marine structures | volume 04 | issue 02 | july 2022 4.2 modal analysis next, modal analysis was conducted, and dry/wet mode shapes/natural frequencies were obtained. wet mode shapes and natural frequencies require the added mass and hydrostatic restoring coefficient matrices. in the morison equation, ac is typically selected as 1 based on previous practices for the slender body [27]. however, the added mass is frequency-dependent, and wet mode shapes and natural frequencies can be changed. tables 1-2 give dry and wet natural frequencies at different diameters and submergence depths. morison and dmb models calculate similar dry natural frequencies with a maximum difference of 0.3%. note that elements number for dmb and morison methods for this example are 22 and 50, respectively. since the morison method is based on the lumped mass method, more elements are generally required than the high-order beambased dmb method. twenty-two finite elements in the dmb method are sufficient to represent the elastic behavior. for the wet mode, while both approaches are well matched at a small diameter of 10 m or a large submergence depth of 60 m, the large difference is observed when diameter and submergence depth are both 20 m. in this case, free surface plays some roles in the modification of wet natural frequencies by changing added mass. the maximum difference is increased to be 5.0%. in this regard, when a cylinder is large and close to free surface, special care should be made to evaluate wet natural frequencies. figure 6 shows the representative wet mode shapes of two methods at the diameter and submergence depth of 20 m. even if there is a maximum difference of 5% in wet natural frequencies, there is no noticeable difference in the wet mode shape up to 3rd mode. (a) (b) figure 5. comparison of fkf , scf , and mff at different diameters and submergence depths. table 1. dry natural frequencies at different diameters. d(m) direction mode# morison (rad/s) dmb (rad/s) difference (%) 20 horizontal 1 2.01 2.01 0.0 2 5.51 5.51 -0.1 3 10.73 10.73 -0.3 vertical 1 2.01 2.01 0.0 2 5.51 5.51 -0.1 3 10.73 10.73 -0.3 10 horizontal 1 1.01 1.01 -0.3 2 2.77 2.76 -0.2 3 5.40 5.38 -0.3 vertical 1 1.01 1.01 -0.3 2 2.77 2.76 -0.2 3 5.40 5.38 -0.3 7 sustainable marine structures | volume 04 | issue 02 | july 2022 4.3 global behavior in previous sections, there were two distinct differences between the dmb and morison methods; at the diameter and submergence depth of 20 m, the existence of free surface changes the scattered wave force and added mass, which results in differences in total wave force and wet natural frequencies. in this section, global behaviors are further checked at different wave directions. the structural damping matrix based on rayleigh damping rb was added to deal with unrealistic resonant motions at natural frequencies. this study assumes a representative damping ratio of 5% for concrete structures at the fundamental horizontal and vertical natural frequencies. figure 7 shows the amplitude envelopes of horizontal and vertical displacements at the diameter and submergence depth of 0.2 m and wave direction of 90°. it turns out that the lowest mode shape is dominant for the given frequency range. in other words, the lowest horizontal and vertical natural frequencies for the dmb method are around 1.50 rad/s and 1.49 rad/s, and thus the lowest natural frequency is dominant for the given frequency range of 0.3 rad/s–1.3 rad/s. since the morison method overestimates the wave force at the high-frequency region, highly overestimated motions are seen, especially when wave frequency is close to the fundamental natural frequency. table 2. wet natural frequencies at different diameters and submergence depths. d(m) sd(m) direction mode# morison (rad/s) dmb (rad/s) difference (%) 20 20 horizontal 1 1.42 1.50 5.0 2 3.91 4.04 3.4 3 7.62 7.88 3.4 vertical 1 1.42 1.49 4.9 2 3.91 4.06 3.7 3 7.62 7.94 4.1 20 60 horizontal 1 1.42 1.42 0.1 2 3.91 3.93 0.5 3 7.62 7.70 1.1 vertical 1 1.42 1.42 -0.3 2 3.91 3.91 0.2 3 7.62 7.68 0.8 10 20 horizontal 1 0.71 0.72 0.3 2 1.96 1.98 1.0 3 3.82 3.86 1.0 vertical 1 0.71 0.72 0.3 2 1.96 1.98 0.9 3 3.82 3.85 0.7 (a) (b) figure 6. wet mode shapes at the diameter and submergence depth of 20 m. 8 sustainable marine structures | volume 04 | issue 02 | july 2022 since the center has the most considerable movement related to the fixed-fixed boundary condition at both ends, results at the mid-length are presented in the later section. figure 8 shows the horizontal and vertical motions at the diameter of 20 m, different submergence depths of 20 m and 60 m, and wave direction of 90°. again, the motion trend coincides with wave force. overevaluated motions by the morison method at the submergence depth of 20 m are observed, particularly in the high-frequency region. since fundamental wet natural frequency for the morison method is lower than that for the dmb method, resonant induced motion associated with high wave force is detected for the morison method. on the other hand, the morison method accurately estimates displacements for deeply submerged cylinders for the given frequency range since wet natural frequencies and wave forces between the two approaches coincide. finally, figure 9 shows the horizontal and vertical motions at the diameter and submergence depth of 20 m and different wave directions of 30° and 60°. as wave direction is not perpendicular to the cylinder, there is an arrival time lag of input waves along the length, which can induce a phase cancellation effect where wave force in the different locations can be canceled out. the phase cancellation effect can be dominant in the high-frequency region. in this example, the lower the wave direction, the smaller the high-frequency motions. as shown in figure 3, the dmb model estimates the higher wave excitation force for the range of 0.3 rad/s–0.7 rad/s; thus, the dmb model tends to produce higher motion than the morison method for the given wave directions. also, the magnitude of motions at the mid-length tends to decrease as the wave direction decreases. (a) (b) figure 7. amplitude envelopes of horizontal (a) and vertical (b) displacements (diameter of 0.2 m; submergence depth of 0.2 m; wave direction of 90°). (a) (b) figure 8. amplitude of displacements at the mid-length and submergence depths of 20 m (a) and 60 m (b) (diameter of 0.2 m; wave direction of 90°). (a) (b) figure 9. amplitude of displacements at the mid-length and wave directions of 30° (a) and 60 ° (b) (diameter of 0.2 m; submergence depth of 0.2 m). 9 sustainable marine structures | volume 04 | issue 02 | july 2022 5. conclusions this study focuses on the hydro-elastic behaviors of a fully submerged horizontal cylinder in regular waves. the frequency-domain discrete-module-beam (dmb) method was developed; a continuous elastic floating structure is discretized into a certain number of rigid bodies while structural flexibility is modeled by beam elements with euler-bernoulli beam and saint-venant torsion; the hydrodynamic coefficients and wave forces were obtained from 3d potential theory. the time-domain morison method was also employed; the morison equation estimates wave forces and elastic behaviors are represented by massless axial, bending, and torsional springs. various parametric studies on the cylinder diameter, submergence depth, and wave direction were conducted, and wave forces, dry/wet mode shapes/natural frequencies, and dynamic motions were analyzed. the results derived from this study are as follows: (1) the presence of free surface tends to change the scattered wave force in the dmb model; the larger the diameter and the smaller the submergence depth, the greater the change in the scattered wave force. the overestimation of wave force in the high-frequency region is observed in the morison model. (2) consideration of frequency-dependent added mass in the dmb method slightly changes the wet natural frequencies, whereas wet mode shapes of the two approaches are almost the same. (3) the difference of wave forces and wet natural frequencies results in significant changes in the overall magnitudes of the dynamic motions. in this example, the morison model tends to significantly overestimate dynamic motions around the fundamental wet natural frequency. (4) dynamics motions decrease with decreased wave direction, and high-frequency motion is reduced mainly due to the arrival time lag of incoming waves along the length, which induces phase cancellation of wave force. conflict of interest author declares that there is no conflict of interest. references [1] anastasopoulos, i., gerolymos, n., drosos, v., et al., 2007. nonlinear response of deep immersed tunnel to strong seismic shaking. journal of geotechnical and geoenvironmental engineering. 133(9), 1067-1090. 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[27] faltinsen, o., 1993 sea loads on ships and offshore structures. london, uk: cambridge university press. 16 sustainable marine structures | volume 04 | issue 01 | january 2022 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2022 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). 1. introduction the passive fire protection (pfp) coating system is widely used in offshore topside structures to protect structures from hydrocarbon fires in both oil and gas industries. in particular, epoxy intumescent passive fire protection material has been used for the past 30 years. when a fire breaks out, the epoxy intumescent coating thickness increases and the coefficient of heat conduction of the coating decreases thereby slowing down heat transfer. the reduction in heat transfer prevents the protected structure from experiencing elevated temperatures from the fire. epoxy passive fire protection materials are expensive and construction takes a lot of time and money. the weight is not negligible either. in order to solve these problems, various studies were conducted on the efficient application of passive fire protection and analytical techniques and procedures were developed for optimal design. amongst these, kim et al. [1,2] performed nonlinear finite element analysis to analyse floating production storage and offloading (fpso) topside structures subjected to *corresponding author: erkan oterkus, university of strathclyde, glasgow, uk; email: erkan.oterkus@strath.ac.uk doi: http://dx.doi.org/10.36956/sms.v4i1.476 article thermal and structural behaviour of offshore structures with passive fire protection sangchan jo erkan oterkus* university of strathclyde, glasgow, uk article info abstract article history received: 30 december 2021 accepted: 7 january 2022 published online: 30 january 2022 in offshore structures, hydrocarbon fires cause the structure to loose its rigidity rapidly and this leads to structural integrity and stability problems. the passive fire protection (pfp) system slows the transfer rate of fire heat and helps to prevent the collapse of structures and human losses. the vital design factors are decided in the detailed design stage. the determined design thickness must be accurately applied in the fabrication yard. however, there are many cases that the pfp is overused because of various reasons. this excessive application of the pfp is an unavoidable problem. several studies have been conducted on the efficient application and optimal design of the pfp. however, the strength of the pfp has not been considered. in addition, research studies on the correlation between the thickness of the pfp and the structural behaviour are not widely available. therefore, this study attempts to analyse the thermal and mechanical effects of the pfp on the structure when it is applied to the structural member. in particular, it is intended to determine the change in the behaviour of the structural member as the thickness of the pfp increases. keywords: passive fire protection thermal structural beam finite element method 17 sustainable marine structures | volume 04 | issue 01 | january 2022 fire load. friebe et al. [3] presented different case studies to demonstrate the effect of different applications of pfp on collapse time of an fpso module structure. sari et al. [4] used a risk-based method and compared against a conventional pfp optimisation method based on api rp 2fb and concluded that a risk-based approach can provide significant reduction of required pfp material. lim et al. [5] presented a pfp material selection and optimisation process to reduce the impact of fire by considering different pfp material thicknesses. they indicated that cementituous material and cellular glass showed better fire prorection performance. garaniya et al. [6] proposed a methodology to assess the effectiveness of passive fire protection by using fire dynamics simulator. paik et al. [7,8] performed full-scale fire testing to investigate the collapse of steel stiffened plate structures subjected to lateral patch loading with and without passive fire protection. in another study, ryu et al. [9] presented new computational models to study fire-induced progressive collapse behaviour of steel stiffened plate structures with and without pfp. they developed transient thermal elastic-plastic large-deformation finite element models for this purpose. the pfp coating system is designed based on fire risk analysis of the offshore structure. the effect of fire is assessed through sophisticated fire load assessments and cfd-based fire simulations. based on these, the duration of each structural member’s exposure to high temperatures can be calculated. depending on its duration, the type and thickness of passive fire protection coating for each area are designed. ambient conditions, materials, and structural composition of each structural member are also considered in the passive fire protection design. however, there is one big issue in the application of passive fire protection; it is often applied more excessively than the design requirement. this is due to the geometric shape of the structural members, the surrounding fittings, and the skill of the workers. for example, about 20 to 30 mm of pfp is installed in the angle type beam to which 11 mm of pfp should be applied. it is one of the inevitable problems in the structural production process. this kind of thick passive fire protection causes unexpected interference with surrounding outfittings. in addition to that, the weight increase of the structure cannot be ignored due to its vast area of coverage. significant additional cost of materials should also be considered. therefore, it is essential to determine the effect of the thick pfp itself on the structure. moreover, it is important to investigate whether the pfp attached to steel has a positive effect on the thermal and mechanical behaviour of the steel structural members. to the best of authors’ knowledge, the effect of pfp material properties on structural behaviour was not taken into account in earlier studies. hence, this study aims to evaluate how the application of passive fire protection affects the thermal and mechanical behaviour of structural members. the effect of the change in the thickness of passive fire protection on the structure is examined. possible positive effects besides the original function of the pfp applied to offshore structures are considered. for structural members with passive fire protection, finite element analysis is conducted for each condition before and during a fire. 2. passive fire protection systems when a fire occurs and the temperature reaches 260470 ºc, the young’s modulus of the steel is reduced by 40% [11]. in the case of a fire caused by flammable gas or liquid, it takes less than one second for the structure to reach this temperature. this can cause collapse of the structure. the passive fire protection (pfp) is one of the means used to prevent the premature destruction of steel structures in the event of a fire. the proper amount level of pfp is determined by the following factors: the size of the individual elements of the steel structure, the size of the member section, and the purpose of use. this study considers the characteristics of epoxy pfp materials based on the chartek 7 product, which is a widely used product in the offshore industry. the ingredients, which cause fire protection, are very similar across a broad spectrum of products [10]. 2.1 material characteristics of epoxy pfp in the event of a fire, epoxy pfp material swells or intumesces. a layer of durable insulated char slows the rate of temperature rise on the steel substrates. the pfp materials protect the steel structure from reaching the critical core temperature within a certain period of time. the critical core temperature is the temperature at which the steel begins to loose its load capacity and it depends on the grade of the steel and the internal load requirements [12]. the pfp material is generally highly impervious to water ingress. it can also provide additional anti-corrosion features for the iron. adhesion and strength are effectively improved by using flexible mesh together. it is tough, durable and resistant to impact and vibration damage. it does not require much maintenance [13]. table 1 shows the material characteristics of chartek 7 which is a representative product of passive fire protection materials. the density of 1.0 t/m3 is much smaller than normal cement of 2.8 t/m3 and similar to that of rubber of 18 sustainable marine structures | volume 04 | issue 01 | january 2022 0.93 t/m3. the thermal conductivity of 0.213 w/m°c is superior to the concrete of 0.92 w/m°c and as small as the thermal conductivity of the wood of 0.2 w/m°c. the thermal properties such as the thermal conductivity and specific heat can be found in detail in section 3. table 1. material characteristics of epoxy pfp property value units density 1000 kg/m3 thermal conductivity 0.213 (1.45) w/m°c (btu·in/hr ft2°f) coefficient of thermal expansion 68×10–6 (38×10–6) cm/cm°c (in/in°f) specific heat 1.17 (0.28) j/g°c (btu/lb°f) moisture absorption 3.3% non topcoated 1.4% top-coated flame spread 25.0 smoke generation 130.9 toxicity index 1.3 hardness typically 70 impact strength / inch of notch 0.69 (0.10) j/cm (ft·lb/inch) 2.2 mechanical properties of epoxy pfp table 2 indicates the mechanical properties of chartek 7. its lap shear strength is 10 mpa and compressive strength is above 18 mpa. it is flexible and not affected by the deflection of the steel substrate for pre-erection applications. this material has a fully fire rated capability such as h-rated and j-rated for offshore platform applications [13]. table 2. mechanical properties of epoxy pfp property value units spray applied density 1000 (62.4) kg/m3(lb/ft3) tensile strength 12.8 (1850) mpa (psi) tensile modulus 1786 (259,000) mpa (psi) compressive strength 18.6 (2700) mpa (psi) compressive modulus 1172 (170,000) mpa (psi) flexural strength 22.8 (3300) mpa (psi) flexural modulus 1586 (230,000) mpa (psi) lap shear strength 10.0 (1450) mpa (psi) 3. methodology primary and secondary members are subjected to passive fire protection because they can possibly be affected by fire loads in offshore topside structures. as mentioned earlier, pfp’s main purpose is to help the structural member maintaining its function even at extreme temperatures of the rapidly rising hydrocarbon fire. the type and thickness of the passive fire protection system suitable for each component are finally determined in the process of the detailed design phase. its thickness is usually determined from a minimum of about 3 mm to a maximum of about 18 mm. it is possible that it can be applied thicker in some different cases. this study considers three types of pfp systems. based on these, 44 case studies are considered to examine the thermal and mechanical characteristics of structural members with the pfp as the thickness of passive fire protection increases. the first analysis study explores the temperature distribution and thermal characteristics under different pfp coverage and thermal load conditions. this is done through transient analysis by applying the standard hydrocarbon fire curve. the second study is to perform linear static structural analysis for structural members with pfp in the absence of fire. in the third study, the behaviour of the pfp-applied structural members under both thermal and structural loads during the outbreak of fire is investigated. finally, time-dependent thermal loads are applied to the columns subjected to compression in order to examine deformation and buckling characteristics. 3.1 selection of target structures structures as shown in figure 1 were considered to determine the application of passive fire protection and its impact on the behaviour of the structural members. the structural steel i-section beam is mainly used as a primary structural member to support various decks, gratings, pipes, and equipment in offshore platforms. numerical analysis is carried out by dividing the state into no fire (i.e., no thermal load) and under fire conditions as: a. the i-beam supports the steel deck as a primary structure. the underside of the steel deck is directly subjected to the heat of the fire. therefore, the underside is covered with pfp. the top face of the i-beam is not covered with the pfp since it does not directly contact with fire heat. b . t h e i b e a m s u p p o r t s s t e e l g r a t i n g ( o r l a rg e equipment) as a primary structure. the i-beam does not have the pfp on the upper surface. in the event of a fire, the heat affects directly to all sides of the i-beam. c. as a primary structure, the i-beam acts as a column. thus, the compression force is applied to the top of the i-beam. passive fire protection applies to all aspects. the thermal load from the fire is also applied to all sides of the i-beam. 3.2 definition of analysis conditions as given in table 3, the analysis cases are set in groups of three and 44 different cases are considered. transient 19 sustainable marine structures | volume 04 | issue 01 | january 2022 thermal and structural analyses were performed using ansys, a commercially available finite element analysis software [14]. the temperature distribution obtained as a result of heat transfer analysis was used as an input for the structural analysis. group a uses the plane element type to accurately identify the thermal distribution and characteristics of the i-beam section for hydrocarbon fire. transient thermal analysis was performed with 200 time steps. group b is a setting to identify the structural behaviour of the pfpapplied beam with the data obtained by thermal analysis. this coupled analysis was performed on the pfp-applied beams with six types of pfp thickness. group c aims to examine the buckling behaviour of the columns subjected to compression. the vertical displacement caused by the compressive force can also be calculated. the buckling analysis considers “prestress effects” in the structural analysis process of a beam subjected to compressive force. then, the characteristics of buckling can be evaluated by performing “eigen buckling” analysis. (a) i-beam supporting the steel deck (b) i-beam supporting the grating (or large equipment) (c) i-beam as a column figure 1. i-beam frame with pfp 20 sustainable marine structures | volume 04 | issue 01 | january 2022 table 3. cases of the numerical analysis group no. pfp thickness (mm) structural load thermal load numerical analysis boundary condition type element a th3-00 0 not applicable standard hydrocarbon fire transient/ thermal plane55 not applicable th3-01 1 th3-03 3 th3-06 6 th3-10 10 th3-15 15 th4-00 0 not applicable standard hydrocarbon fire transient/ thermal plane55 not applicable th4-01 1 th4-03 3 th4-06 6 th4-10 10 th4-15 15 b nfs-00 0 30 kpa not applicable static structure solid185 fixed at both ends nfs-01 1 nfs-03 3 nfs-06 6 nfs-10 10 nfs-15 15 df3-00 0 30 kpa standard hydrocarbon fire transient/ structural thermal coupled solid70 solid185 fixed at both ends df3-01 1 df3-03 3 df3-06 6 df3-10 10 df3-15 15 df4-00 0 30 kpa standard hydrocarbon fire transient/ structural thermal coupled solid70 solid185 fixed at both ends df4-01 1 df4-03 3 df4-06 6 df4-10 10 df4-15 15 c nfb-00 0 compression load 350 mpa not applicable static structure solid185 one end fixed other free nfb-01 1 nfb-03 3 nfb-06 6 nfb-10 10 nfb-15 15 dfb-00 0 compression load 350 mpa standard hydrocarbon fire transient/ structural thermal coupled solid70 solid185 one end fixed other free dfb-01 1 dfb-02 2 dfb-03 3 dfb-04 4 dfb-06 6 dfb-10 10 dfb-15 15 21 sustainable marine structures | volume 04 | issue 01 | january 2022 3.3 application of structural and thermal loading, and boundary conditions figure 2 shows the dimensions, structural loads, thermal loads, and boundary conditions based on the model demonstrated in figure 1. in figures 2 (a) and (b), 30 kpa of uniformly distributed load is applied to the upper surface of the i-beam over the entire length. the two ends of the member are assumed to be fully fixed. in case of figure 2 (a), the fire heat on the top surface of the i-beam section is not taken into account in the numerical calculation. figure 2 (b) is the setting in which fire heat is applied to all sides. the numerical analysis was performed by considering the symmetry condition. for figure 2(c), a compressive load of 350 mpa was applied to one side of the cantilever beam. the other side is fully fixed. the size of the member section used for all analyses is 200×100×10 (mm). the temperature by the standard hydrocarbon fire curve, indicated in figure 3, was applied for 200 minutes under the conditions of each structural model [15]. (a) i-beam with no fire on the top surface (df3 analysis cases) (b) i-beam with fire on all sides (df4 analysis cases) (c) i-beam as a column with fire on all sides (dfb analysis cases) figure 2. configurations of the steel member for analysis figure 3. standard hydrocarbon fire curve figures 4 and 5 show the finite element models for the coupled analysis which are based on figure 2. first, the solid70 elements were used for the transient thermal analysis and then solid185 was utilized for the structural calculation. figure 4. finite element models for df3 and df4 analysis cases figure 5. finite element model for dfb analysis cases 3.4 material properties to examine the behaviour of the offshore structure 22 sustainable marine structures | volume 04 | issue 01 | january 2022 subjected to fire heat load, the dependency of materials on the temperature change must be defined [2]. in this study, specific heat, thermal conductivity, and elastic modulus values of each material were used for the numerical analysis. 3.4.1 properties of steel the variation of specific heat (ca, j/kg⋅k) of steel with temperature is given below and is represented in figure 6 (a) as [11] 1 3 2 6 3for 20 c 600 c; 425 7.73 10 1.69 10 2.22 10a a a a acθ θ θ θ − − −≤ ≤ = + × − × + ×o o 1 3 2 6 3for 20 c 600 c; 425 7.73 10 1.69 10 2.22 10a a a a acθ θ θ θ − − −≤ ≤ = + × − × + ×o o (1a) 13002 for 600 c 735 c; 666 738a a a cθ θ ≤ ≤ = + − o o (1b) 17820 for 735 c 900 c; 545 731a a a cθ θ ≤ ≤ = + − o o (1c) for 900 c 1200 c; 650a acθ≤ ≤ = o o (1d) where, θa is the steel temperature [°c]. the variation of the thermal conductivity of steel (λa, w/m⋅k) with temperature is given below and is shown in figure 6 (b) as [11] 2for 20 c 800 c; 54 3.33 10a a aθ λ θ −≤ ≤ = − ×o o (2a) for 800 c 1200 c; 27.3a aθ λ≤ ≤ = o o (2b) (a) specific heat (b) thermal conductivity of steel figure 6. variation of steel properties with temperature the change in young’s modulus of steel is shown in [11]. the modulus of elasticity of the steel does not change until the temperature reaches 100 °c, but it starts to decrease after that temperature. it is shown that it decreases by 40% at 500 °c and decreases by more than 90% at 800 °c. 3.4.2 properties of the pfp material the specific heat of the epoxy type pfp material changes depending on the temperature as shown in figure 7(a) [16]. this value decreases linearly as the temperature increases to around 1300 °c. above 1300 °c, the rise of the temperature has no impact on the value. figure 7(b) shows the change in thermal conductivity with increase in temperature of the pfp material. the thermal conductivity rapidly decreases at 150 °c. the change in both density and elastic modulus with the increase in temperature of the pfp material was not considered in numerical analysis due to the lack of information. (a) specific heat (b) thermal conductivity figure 7. variation of properties of the epoxy type pfp material with temperature 4. numerical results 4.1 analysis group a generally, the conditions of fire protection for offshore structures are mainly applied for 60 minutes and 120 23 sustainable marine structures | volume 04 | issue 01 | january 2022 minutes. therefore, figure 8 shows the temperature distribution results of the i-beam section after 60 minutes of fire. looking at the results of the th3 cases, it can be seen that as the thickness of the pfp increases, temperature change in the beam section decreases significantly. in particular, when the pfp thickness is 15 mm, the heat of the fire hardly reaches the steel. hence, it is determined that the pfp is completely slowing the heat transfer. this trend can also be seen in the interpretation of th4 cases on the top surface of the i-beam section without the pfp. the temperature rises rapidly. from the height of 100 mm to 200 mm of the section, it shows a constant temperature distribution due to the effect of the pfp. (a) th3 analysis cases (b) th4 analysis cases figure 8. temperature distribution in the i-beam section after 60 minutes of fire figure 9 shows the temperature change over time at the midpoint of the i-beam. by comparing the two graphs when the pfp is not applied and when 1 mm thick pfp material is applied to the steel, it can be seen that the application of the pfp causes a significant delay in heat transfer even at very small thickness of pfp. furthermore, it is confirmed that the rate of temperature change over time gradually decreases as the pfp becomes thicker. in cases where the applied pfp is over 6 mm thick, the temperature increase over time is not much larger than the fire temperature. in particular, in the cases of th3, the temperature does not exceed 100°c even at 200 minutes. the temperature tends to stay at an almost constant value. on the other hand, in th4 cases, the rate of the temperature change with time is relatively large. since 100 °c is the starting point of the change in the elastic modulus of the steel, this result is important. (a) th3 analysis cases (b) th4 analysis cases figure 9. change in temperature over time (center point of i-beam) based on the results above, the temperature of the steel was analysed 60 and 120 minutes after the fire occurred. as mentioned earlier, in the fire protection design for offshore structures, the conditions of 60 and 120 minutes defence time are the critical design criteria. figure 10 shows the temperature difference between the th3 and th4 analyses at the same pfp thickness after 60 and 120 minutes of fire. the average difference at 60 minutes is less than 10 °c. after 120 minutes, the difference is about 40 °c. if the structural member should be protected from the fire heat up to 60 minutes, the behaviour of the condition of the i-beam is not that dangerous even if the pfp is not applied on the top surface of it. it can also be seen that the thicker the layer of the pfp is, the smaller the difference is. this result is very meaningful for the following reason. in terms of heat transfer under the design conditions of h60 or j60 fire rated, it can be seen that it is not important whether pfp is applied or not to the flange side of the i-beam section even when heat is applied to the steel from all directions. 24 sustainable marine structures | volume 04 | issue 01 | january 2022 figure 10. temperature difference between th3 case and th4 case after 60/120 minutes of fire figure 11 shows the relationship between the temperature after 200 minutes of fire and the pfp thickness at the center point of the i-beam. it can be seen in figure 11 that in both cases of th3 and th4, the temperature of the steel decreases as the pfp thickness increases. as the pfp thickness increases, the temperature change rate becomes smaller. therefore, if the pfp is applied thicker than the appropriate thickness (which is judged to be 6 mm in this study), it is confirmed that increase of the pfp thickness does not significantly affect the reduction of the heat transfer. figure11. change in temperature with increase in pfp thickness (center point of i-beam) 4.2 analysis group b regarding the behaviour of the pfp-applied beam during normal fire-free conditions, figure 12 shows the change in vertical displacement at the center of the beam. when the pfp is applied, it appears that the deformation is increased by its weight. if self-weight is not taken into account, the application of a thicker pfp reduces the deformation of the beam. therefore, the application of the pfp can increase the strength of the beam, but its weight causes the deflection of the beam. figure 13 shows the change in the vertical displacement value depending on the thickness of the pfp after 200 minutes of fire. in the range of 0 to 1 mm, the pfp layer plays a significant role regarding vertical displacement. there is a big difference between if the pfp layer exists or not. even 1mm of the pfp material significantly lowers the heat conduction. although the displacement at the midpoint of the beam decreases in proportion to the increase in the pfp thickness, the reduction rate is not large. the main reason is that the pfp’s own weight has a great influence on the beam behaviour. if the effect of self-weight of the pfp is limited, the increase in the thickness of the pfp layer can be interpreted in the sense that it reduces the deformation and increases the stiffness of the beam. (a) self-weight is not considered (b) self-weight is considered figure 12. beam deflection change in case of no fire 25 sustainable marine structures | volume 04 | issue 01 | january 2022 figure 13. comparison of the vertical displacement results after 200 minutes of fire (self-weight is considered) figure 14 shows the change in displacement over time. here, it can be seen that the deflection of the beam is significantly reduced by applying the pfp. also, the displacement tends to slightly increase as the pfp thickness increases. this is due to the self-weight of the pfp, as described above. in the case of df3 analysis, the time-displacement is linear in most analysis cases because the pfp protects the beam from the thermal loads. in the analysis of df4, the heat is transferred directly from the top of the i-beam where the pfp is not applied, so the deflection has a non-linear characteristic. in particular, looking at the df4 analysis case, it can be seen that the rate of the time-displacement change increases at the point for about 100 minutes. the slope of the graph increases. after this point, the rate of the displacement change starts to increase and doubles at the end. (a) df3 analysis cases (b) self-weight is considered figure 14. time-displacement curve by pfp thickness during fire (center of i-beam) 4.3 analysis group c when the pfp was applied to a column subjected to axial compressive force, the deformation behaviour and buckling load of the column structural member were examined. this type of structure is commonly used in real offshore structures. as shown in figure 15, it is confirmed that the temperature of the steel does not exceed 100 °c since the pfp thickness is over 6 mm. figure 16(a) shows the magnitude of displacement due to a compressive force according to the thickness of the pfp. in a fire-free situation (nfb), there is little change in deformation depending on the thickness of the pfp. however, the role of the pfp is obvious in the event of fire and heat. when the thickness of the pfp is less than 6 mm, the thickness of the pfp has a positive effect on the deformation of the beam. from the point where the pfp is 6 mm thick or more, the displacement is very similar to the case when there is no thermal load. similar trends can be seen in the blf (buckling load factor) values in figure 16(b). the blf is an index for evaluating the strength against the buckling of structures under compression. this coefficient is defined as the relative ratio of the critical load causing buckling divided by the compressive force exerted on the real object. in other words, a large buckling load factor indicates that the object is safe from buckling. the blf value is significantly improved due to the application of the pfp. when a 6 mm thick pfp layer is applied to the beam, the buckling critical load increases by about 60 times compared to the case when there is no pfp layer. for the pfp 6 mm thickness case, it shows a very similar value of the blf value in case of no thermal load. in addition, as more pfps are applied, it can be seen that the blf value gradually increases. it can be seen that the pfp layer contributes to the increase in stability against buckling. figure 15. temperature by pfp thickness in dfb analysis (after 200 minutes) 26 sustainable marine structures | volume 04 | issue 01 | january 2022 (a) displacement (b) blf value figure 16. displacement and blf for each pfp thickness (self-weight is considered) figure 17 shows the amount of compression displacement over time. the effect of applying the pfp to the four sides of the i-beam can be clearly seen by comparing dfb-00 and dfb-01. even a very small amount of the pfp has a clear effect on reducing the heat transfer. in addition, as the pfp is applied thicker, the amount of heat transmitted to the steel is getting smaller. therefore, there is no significant change in displacement. figure 17. displacement change by compression over time by changing pfp thickness here, it can also be seen that when the thickness is greater than a particular thickness, the effect of the increase in the amount of pfp on the deformation of the beam is reduced. the particular thickness value in this study can be determined as 6 mm and a larger amount of pfp than 6mm can be considered as overused. however, it is clear that even though the amount of reduction in deformation is small compared to the amount of the increased pfp, it contributes to the reduction in the deformation of the structural member. 5. discussions various types of numerical analysis cases were considered for the pfp-applied beam. the research findings offer a new perspective on designing pfp for offshore structures. according to the current study, the following points can be emphasized: 1) large number of research studies have been conducted on the efficient use of the pfp and the optimized design of the pfp-applied structures. however, the strength of the pfp itself has not been considered. in this study, the structural behavior of the pfp-applied beam was analysed using the pfp tensile strength value. this is the beginning of a new perspective in the field of the pfp research. the structural members which were analysed in this study is an i-beam. it is the most widely used primary member in offshore structures. numerical analysis of 44 cases was considered by combining the pfp application condition, application thickness, and fire load application condition for this beam. coupled analysis was performed to simulate the actual structural member situation and includes thermal and structural analyses. firstly, the thermal analysis was performed by inputting the time-dependent standard hydrocarbon fire temperature and the result was used for structural analysis. the temperature changes for 200 minutes and the structural behavior of the beam were analysed. when performing the thermal analysis, the quality of the analysis result was improved by considering the temperature dependent properties such as specific heat and thermal conductivity. in structural analysis, the relationship between the safety of buckling and the application of the pfp layer was analysed by using the blf value. 2) this study offers a new perspective. efforts were made to find the positive effects of the pfp material which has no function on structures unless a fire breaks out. this attempt can contribute to the cost reduction of offshore 27 sustainable marine structures | volume 04 | issue 01 | january 2022 structures fabrication. the pfp is very widely applied to structures and it is often overused. if the technical data on the structural rigidity is inputted in the structural design, the effect of reducing the size of structural members can be expected. in addition, it would be possible to solve the problem of the excessive pfp application in the field. this study is the first step towards those goals. 3) this study considered the inclusion of the temperature-dependent material properties as much as possible. however, there is lack of information about temperature-dependency of some of the pfp properties such as the density and elastic modulus. for more accurate simulation of the pfp and beam behavior during a fire, studies on these two properties are definitely needed. 4) a mesh made by steel or fiber is one of the components of the pfp system. however, since the information on the mesh properties is not clear, the effect of it was not considered in this study. it will be necessary to study the mechanical properties of the mesh and include it in numerical analysis and experiments in the future. 6. conclusions pfp is widely used to help maintaining the integrity and stability of offshore structures for a certain period from hydrocarbon fires. in this study, the thermal and structural behaviour of pfp-applied beams before and during the fire was analysed using ansys. the research findings can be summarised as: 1) from the results of heat transfer analysis, it was confirmed that in all cases, the application of pfp, even for a very small amount, significantly delayed the rate of heat transfer from the fire to the steel. the thicker the pfp, the greater reduction of the heat transfer takes place. however, when the thickness of pfp is greater than a certain value (6 mm), the effectiveness decreases. 2) a condition in which the pfp was not applied on the top surface of the i-beam was considered. coupled analysis was performed on the cases where fire heat was directly transmitted to the top surface (df4 analysis cases) and the case where it was not (df3 analysis cases). as the thickness of the pfp increases, the deformation of the steel caused by heat decreases, but there is no significant change in the vertical displacement of the beam. looking at the df4 cases’ results of the displacement of the i-beam over time, the rate of the displacement change increased by about 2 times after about 100 minutes. 3) the buckling analysis was performed on the pfpapplied column structure. it was confirmed that both the displacement and the blf value caused by the compressive force were sufficiently improved until the pfp reached a certain thickness. in particular, when the pfp layer is applied to the i-beam, the critical buckling load is improved by about 60 times compared to the case without the pfp layer. however, after reaching a certain thickness, the amount of thermal load had little impact on both the displacement and the blf value. this is related to the point when the temperature of the steel remains below 100 °c when the pfp is thicker than 6 mm. 4) this study will contribute to other further studies on the application of pfp as providing a new perspective to study structural analysis of pfp and beam composite. acknowledgement this research is supported by pnu korea-uk global program in offshore engineering(n0001288) funded by the ministry of trade, industry and energy. references [1] kim, j.h., kim, c.k., islam, m.s., park, s.i., paik, j.k., 2013. a study on methods for fire load application with passive fire protection effects. ocean engineering. 70, 177-187. doi: https://doi.org/10.1016/j.oceaneng.2013.05.017 [2] kim, j.h., lee, d.h., ha, y.c., kim, b.j., seo, j.k., paik, j.k., 2014. methods for nonlinear structural response analysis of offshore structures with passive fire protection under fires. journal of ocean engineering and technology. 28(4), 294-305. doi: https://doi.org/10.5574/ksoe.2014.28.4.294 [3] friebe, m., jang, b.s., jim, y., 2014. a parametric study on the use of passive fire protection in fpso topside module. international journal of naval architecture and ocean engineering. 6(4), 826-839. doi: https://doi.org/10.2478/ijnaoe-2013-0216 [4] sari, a., ramana, e., dara, s., azimov, u., march 2016. passive fire protection pfp optimization in offshore topsides structure. in offshore technology conference asia. offshore technology conference. [5] lim, j.w., baalisampang, t., garaniya, v., abbassi, r., khan, f., ji, j., 2019. numerical analysis of performances of passive fire protections in processing facilities. journal of loss prevention in the process industries. 62, 103970. doi: https://doi.org/10.1016/j.jlp.2019.103970 [6] garaniya, v., lim, j.w., baalisampang, t., abbassi, r., 2020. numerical assessment of passive fire protection in an oil and gas storage facility. in advances in industrial safety. springer, singapore. pp. 1-21. [7] kee paik, j., ryu, m.g., he, k., lee, d.h., lee, s.y., park, d.k., thomas, g., 2020. full-scale fire testing 28 sustainable marine structures | volume 04 | issue 01 | january 2022 to collapse of steel stiffened plate structures under lateral patch loading (part 1)–without passive fire protection. ships and offshore structures. pp.1-16. doi: https://doi.org/10.1080/17445302.2020.1764705 [8] paik, j.k., ryu, m.g., he, k., lee, d.h., lee, s.y., park, d.k., thomas, g., 2020. full-scale fire testing to collapse of steel stiffened plate structures under lateral patch loading (part 2)–with passive fire protection. ships and offshore structures. pp.1-12. doi: https://doi.org/10.1080/17445302.2020.1764706 [9] ryu, m.g., he, k., lee, d.h., park, s.i., thomas, g., paik, j.k., 2020. finite element modeling for the progressive collapse analysis of steel stiffened-plate structures in fires. thin-walled structures. pp.107262. doi: https://doi.org/10.1016/j.tws.2020.107262 [10] wade, r., march 2011. a review of the robustness of epoxy passive fire protection (pfp) to offshore environments. corrosion 2011, houston, usa. pp. 13-17. [11] european standard bs en 1993-1-2:2005, 2010. eurocode 3. design of steel structures general rules part 1-2 structural fire design. [12] international paint, 2014. chartek trusted epoxy passive fire protection. https://www.perge.cz/data/blob/ product-application_pdf-20190630122600-8941chartek-trusted-epoxy-passive-fire-protection.pdf [13] international paint, 2010. chartek7 fireproofing. http://www.pfpsystems.com/assets/uploads/c7brochure0407001.pdf [14] ansys, 2014. ansys mechanical apdl element references. ansys inc. [15] european committee for standardization (cen), 2007. eurocode 1: actions on structures – part 1-2: general actions – actions on structures exposed to fire. en 1991-1-2. [16] kim, m., kim, g., oh, m., june 2017. optimized fire protection for offshore topside structure with 3-sides pfp application. in the 27th international ocean and polar engineering conference, san francisco, usa. pp. 25-30. 46 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v2i1.311 sustainable marine structures http://ojs.nassg.org/index.php/sms article an in-depth analysis for optimal cable tray support span sung wuk jung erkan oterkus* university of strathclyde, united kingdom article info abstract article history received: 7 january 2021 accepted: 29 january 2021 published online: 31 january 2021 nowadays, it is crucial to reduce the cost of the overall project so that the competitiveness of offshore oil and gas without compromising on quality or safety can be achieved. this study investigates how to define the longest cable tray support span considering constructability in order to reduce the number of supports which is a chief cost of a cable tray system. this study presents not only material and geometry frequently used for cable tray but also the formula to estimate the maximum cable load which can be installed within cable tray. to verify the longest span without increasing the crosssection of cable tray, finite element modelling approach was employed based on ansys and comparisons were made between numerical analysis and simplified hand calculation. the constructability for the longer span obtained from finite element analysis has been validated in view of manual handling of the cable tray. it is shown that the optimal span suggested in this paper can lead to a better economic benefit without degrading the constructability. for instance, as the span is longer, the cost of material as well as construction manpower can be saved. it is also expected that this approach will contribute to enhance the competitiveness of offshore oil and gas. keywords: cable tray system finite element method ansys oil and gas offshore 1. introduction global oil and gas markets have faced a significant change with dramatic rise in the us production of shale oil and gas. us shale oil production has increased from approximately 0.4 million barrels a day in 2007 to more than 4 million barrels a day in 2014 [1]. as a result, it has incurred the sharp decline in the global price of oil after 2014 and the investment of offshore oil and gas had been significantly dropped due to relatively high production unit price. in order to recover the offshore oil and gas market, there is effort to reduce the general cost level of offshore oil and gas projects without compromising on quality or safety. for instance, offshore standardization joint industry project (jip) was established with various participants such as hhi, dsme, bv, abs, dnv-gl, chevron, technipfmc and others to reduce cost and increase predictability in international offshore epc projects by using standardized materials, design and procedures for construction and commissioning in 2015 [2]. a cable tray system is used to support the insulated electrical cable used for power distribution, control and communication in the electrical wiring. cable tray system has various shapes and sizes in the market. in the design of a cable tray, the most significant cost driver is the cost of the supports. the number of structural steel supports needed in cable tray installation is mainly determined by the support span. typically, 3m is the maximum support *corresponding author: erkan oterkus, university of strathclyde, united kingdom; email: erkan.oterkus@strath.ac.uk 47 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v2i1.311 span employed in offshore oil and gas. however, total installed cost for cable tray can be lower if a longer span than industrial practice is utilized in offshore industry. the simplest way to achieve the longer span is to enhance the cross-section of cable tray. recently, there were several trials to employ the longer span with thicker cable tray in offshore industry to reduce the overall cost. despite the cost savings, there are also the negative points caused by the heavier cable tray at longer span. for instance, if the weight of cable tray remarkably increases at longer span, it will cause difficulty in cable tray handling and installation. it is the main reason that more than 3m span length is not generally applied to offshore industry. although 3 meter is the commonly employed support span for cable ladder horizontal run in offshore oil and gas industry, it is required to study whether longer span can be utilized without degrading the constructability. to achieve it, first, the maximum cable weight allowed by cable ladder space needs to be defined then the longest span which can meet both nema ve 1and iec 61537 under the largest load condition shall be evaluated in the view of constructability. there are several standards to give suggestion for the critical bending moment of the elastic lateral torsional buckling (ltb). however, their formulas are hard to apply to find the failure load of the cable ladder. in all equations of critical bending moment, the unbraced length of the beam is important variable to determine the mcr. however, it is difficult to clearly define the unbraced length of the beam in cable ladder structure because the rung structures of cable ladder partially restrain the lateral displacement of the side rail as indicated in figure 1. figure 1. partial lateral restraint of cable ladder [13] through finite element analysis to verify the effect of rung at bucking, it has been recognized that the shorter interval between rungs has greater eigen buckling factor (see table 1). table 1. the effect of rung interval length for ltb span between support interval of rung eigen bucking factor total span: 3.6m load over span: 6755n 300mm (total rung qty: 12ea) 1.2 total span: 3.6m load over span: 6755n 600mm (total rung qty: 6ea) 0.5 in addition, the latest version of eurocode 3 does not specify the method to calculate the elastic critical bending moment for the ltb of beams. the old version of eurocode 3 named env 1993-1: 1992 had the 3-factor formula incorporated though, and the formula is now found in ncci [3]. however, ncci states the expression of mcr only for uniform straight members that the cross section is symmetric around the minor axis. for cases not covered by ncci, critical moment may be determined by a buckling analysis of the beam provided that the calculation accounts for all the parameters liable to affect the value of mcr : (1) geometry of the cross-section (2) warping rigidity (3) position of the transverse loading with regard to the shear centre (4) restraint conditions therefore, it is very complicated and difficult work to check the lateral torsional buckling of cable ladder structure indicated in figure 1 via hand calculation. so, by using numerical methods for the elastic buckling solution, the elastic buckling analysis of the cable ladder needs to be performed to find the failure load of cable ladder as well as the optimal span. there are various studies in the literature for the analysis of cable trays. amongst these, kalupa [4] presented guidelines to be used in the design of cable tray systems particularly for electrical industry. desmond and dermitzakis [5] provided effective-length factors for the buckling of cable-tray supports used at nuclear power facilities. reigles et. al. [6] presented a review of test data and conclusions to develop a design methodology for the seismic qualification of safety-related cable tray support systems. masoni et. al. [7] performed shaking-table tests on full-scale three dimensional cable tray systems. in another study, huang et. al. [8] performed shaking table tests to investigate the seismic performance and damping ratio of cable tray systems in nuclear power systems. huang and mosalam [9] developed a finite element model of the cable tray for time history analysis under the effect of selected ground motions. in this study, how much span can be longer than off48 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 shore practice without increasing the cross-section of cable tray is investigated. the geometry including thickness and material which are the most often used for cable tray is described for finite element analysis (fea) and hand calculation to verify the optimal span. it also provides a method to estimate the maximum cable weight which can be installed in a cable tray. in addition, it suggests how to determine the longest span via fea considering constructability. finally, it presents the positive impacts induced by the optimal span which is obtained from this study. 2. methodology to define optimal cable tray support span, this research will conduct quantitative analysis for cable tray buckling and deflection at the maximum cable load. the approach adopted is described as below: step 1: to define the material property and geometry for the cable tray. step 2: to define the criteria to determine the optimal span step 3: to calculate the maximum cable load step 4: to conduct finite element analysis step 5: to conduct simplified hand calculation. step 6: to do the verification of result. 2.1 step 1: define material property and geometry stainless steel ansi 316l (en 1.4404) ladder type is selected for this study because it is the most frequently used in offshore oil and gas industry. the mechanical properties for en 1.4404 from british standard european norm is indicated in table 2. table 2. the mechanical property of en 1.4404 [10-12] mechanical property value poisson’s ratio 0.3 elastic modulus (gpa) 200 yield strength (mpa) proof strength 240 tensile strength (mpa) 520~670 in general, i beam profile can carry more load than c channel beam profile. therefore, c channel beam shape is selected for side rail of cable ladder in order to define the longest span allowed in worst condition. figure 2 and table 3 provides information about the product, oe 150 of oglaend system [13] which is one of well-known channel type products. table 3. the data for geometry geometry data value side rail height (mm) 150 thickness of side rail (mm) 1.5 rung length (mm) 900 moment of inertia ixx for the side rail (mm4) 933,170 figure 2. channel type side rail [13] 2.2 step 2: define criteria to determine the optimal span there are two kinds of load test methods to verify optimal support span. one is the destruction load test at simple beam and the other is the deflection load test at continuous beam. the optimal support span shall meet both load test criteria at the greatest cable load which is defined in step 3. 2.2.1. nema ve-1 destruction load test figure 3 shows the nema ve 1 safe rated load test (destruction load test) at simple span. in this load test, both ends of straight section shall be supported directly on a 65mm diameter round steel bar or heavy wall steel tube fastened to a rigid base. then, the load which is 1.5 times (safety factor) of the maximum cable weight defined in step 3 distributed uniformly along the span. in this study, the span increases with interval of 300mm until it causes the collapse [14]. figure 3. safe rated load test with simple span according to nema ve-1 doi: https://doi.org/10.36956/sms.v2i1.311 49 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 2.2.2 iec 61537 deflection load test the other method is the safety working load (deflection load) test on multiple span based on iec 61537. the test shall be conducted with the samples consisting of two or more cable ladder lengths over multiple support span given in figure 4. cable ladders shall be placed on fixed, rigid supports which shall be horizontal and level with a width of 45mm±5mm. the ladders shall not be fixed to the supports unless a fixing method is declared by the manufacturer in which case this fixing method shall be used [15]. the load, 1.7 times (safety factor) of the maximum cable load, shall be uniformly distributed on end span, intermediate span and cantilever and each support and splicing(joint) shall be positioned according to figure 4. the vertical deflection at mid-span shall be measured at the points near the side rails and its result shall be less than 1/100 of span without collapsing in order to meet the iec criteria but buckling and deformation of the cable ladders is permissible. the span increases with interval of 300mm until the collapse is caused or the vertical deflection is more than 1/100 of span. figure 4. deflection load test with multiple span according to iec 61537 type test ii in addition, transverse deflection (rung sagging) is not considered in this study as it is theoretically not affected by support spacing space. thus, transverse displacement is not discussed here. 2.3 step 3: calculate maximum cable load national electrical code (nec) states the high voltage power cables shall be installed in a single layer with certain distance between two cables. however, control and communication cables which has no heat generation problem can be stacked together in several layers as long as the sum of the cross-sectional areas of all cables does not exceed 50% of fill area of the ladder [16]. figure 5 shows the ladder fully filled with control cables versus the ladder fully filled with high voltage cables. as indicated in figure 5, the cross section of cable ladder can be more occupied with the cables when it is fully filled with control cables. therefore, the largest cable weight can be estimated based on the case that the sum of control cables cross section equals to 50% of fill area of the cable ladder. following is formula to calculate the maximum cable load depending on ladder cross section. the largest cable load per one-meter ladder is max.cable load(kg/m)=n×m (1) where (2) and δh is effective height (mm) = h hr, h is side rail height (mm), hr is rung height (25mm), w is ladder width (mm), a is cable cross section (mm2), n is maximum cable quantity within ladder cross section, and m is cable weight per meter (kg/m). once the maximum cable weight is calculated, the greatest total load can be obtained by adding the ladder unit weight to max. cable unit load as max.load(n/mm)=max.cable load per mm(n/mm)+cable ladder weight(n/mm) 2.4 step 4: conduct finite element analysis finite element analysis (fea) to find the optimal tray support span is performed by using the commercial software, ansys mechanical ansys parametric design language (apdl) product launcher 2019 r1. the figures 6 and 7 show the flow diagram for nema ve 1test and iec 61537 test. figure 5. the comparison for cable fill allowance doi: https://doi.org/10.36956/sms.v2i1.311 50 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 2.4.1 build the fea model ansys shell elements, “shell 181”, which is a fournode element with six degrees of freedom at each node, was selected to analyze the stability and the displacement of the ladder when the largest cable load was placed. figure 8 indicates the direction of the coordinate system. modeling for cable ladder was performed based on material property and geometry data shown in table 2, table 3, and figure 2. for meshing, free mesh is used for this study. on top of that, the splicing modeling is not considered for iec 61537 deflection test because the bending moment at the position of splicing is as small as negligible when it has been placed on 1/4 of span. figure 6. nema-test flow diagram figure 7. iec-test flow diagram doi: https://doi.org/10.36956/sms.v2i1.311 51 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 2.4.2 apply boundary conditions and loads the boundary conditions for the round steel bar supports are shown in figure 9. the midpoints of both webs are restrained in x, y and z direction on the first support and only in y direction on other supports. however, there is no restraint of rotation in all direction. the unit load is applied to the elements on the top of rung. since a rung is spaced in every 300mm, the value of pressure on elements is (4) where unit load = (maximum cable unit load + ladder unit weight) × safety factor (5) and rung area is 900mm × 41.7mm=37,530mm2, iec safety factor = 170%, and nema safety factor= 150%. 2.4.3 perform the analysis of deflection and stress the elastic static analysis is conducted to verify whethfigure 8. directions for the coordinate system figure 9. boundary condition for supports doi: https://doi.org/10.36956/sms.v2i1.311 52 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 er the vertical deflection and von-mises stress at mid-span do not exceed the criteria in table 4 when the greatest cable load is placed. table 4. the criteria of deflection and stress test type max. deflection at side rail. max stress (yield stress) nema destruction load test na, only record for comparison <240 mpa iec deflection load test <1/100 of span without collapse <240 mpa the maximum vertical deflection at mid-span shall be measured at the points near the side. in other words, the rung sagging displacement (transverse sagging) should be excluded in the calculation of the vertical displacement. for accurate measurement of displacement and stress, those values need to be obtained by using “path operation”. figure 10 shows the path of measuring point in ansys. figure 10. path for measuring stress and deflection table 5 indicates the coordinate of location for “define path” in order to measure the max. stress and max. displacement at mid-span. 2.4.4 conduct eigenvalue buckling analysis eigenvalue buckling analysis estimates the theoretical buckling strength of an ideal elastic structure. it predicts the structural eigenvalues for the given conditions such as load and constraints. if the eigenvalue under the largest load condition is less than 1, the cable ladder will collapse at the placed load. so, when the result is less than 1, the span of support shall be reduced to avoid the buckling of side rail [17]. 2.5 step 5: conduct simplified hand calculation the maximum vertical sagging displacement and the greatest bending stress at middle of span can be estimated based on following simplified formula. assumption: (1) the material is linear elastic (2) the side rail is prismatic, which means that cross-section remains constant throughout its length. maximum vertical deflection for simple span in figure 11 is (6) with (7) where e is elastic modulus (n/mm2), i is moment of inertia of side rail (mm4), l is support span (mm), x is distance from pin support, w is load per unit length (n/ mm), and δmax is maximum deflection (mm). table 5. the coordinate of location for “define path” test code span (mm) location #1 location #2 x(mm) y(mm) z(mm) x(mm) y(mm) z(mm) nema ve1 3000 1500 0 0 1500 147 0 nema ve1 3300 1650 0 0 1650 147 0 nema ve1 3600 1800 0 0 1800 147 0 nema ve1 3900 1950 0 0 1950 147 0 nema ve1 4200 2100 0 0 2100 147 0 iec 61537 3900 4875[1] 0 0 4875[1] 147 0 note: [1] middle position of intermediate span in multiple span test. doi: https://doi.org/10.36956/sms.v2i1.311 53 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 figure 11. simple beam with udl when cable ladders are installed across several supports with udl as figure 12, the maximum sagging displacement is (8) where e is modulus of elasticity (n/mm2), i is moment of inertia of side rail (mm4), w is load per unit length(n/ mm), l is support span (mm), δmax is maximum deflection (mm), and e and i are constant. figure 12. continuous simply supported beam with overhanging maximum bending stress at middle of span is (9) with (10) (11) where m is bending moment at the middle of span (n∙mm), l is support span (mm), w is load per unit length(n/mm), i is moment of inertia of side rail (mm4), y is vertical distance away from the neutral axis(mm), and σmax is maximum bending stress at the middle of span (n/ mm2). figure 13 shows the bending moment diagram for the continuous span of iec 61537. bending moment for each position indicated in figure 13 can be calculated as (12) (13) (14) (15) (16) (17) where w is load per unit l ength(n/mm) and l is intermediate span length (mm). m2 distance from left of beam m1 m3 m4 m5 m6 figure 13. bending moment diagram for iec 61537 test 2.6 step 6: the validation of the result the validation of the result is performed in two ways; one is to compare the result of fea and the result of hand calculation and the other is to verify the constructability for the greatest span obtained from fea. the comparison is made for the deflection and bending stress. if the difference between two outputs is too large to be neglectable, the errors shall be corrected until the gaps reach the acceptable range or a justification for the errors shall be addressed. in addition, it is required to be validated whether the weight of cable ladder is suitable to handle and install at site when the longest span in fea is applied. in current practice, the cable ladder is manually handled and installed by maximum of two workers. therefore, the maximum weight of cable ladder shall be less than two times of the maximum recommended weight for manual lifting defined in national institute for occupational safety and health (niosh). in other words, if the ladder weight is more than 46.26kg, more manpower may be required to handle and install the cable ladder at new span. 23.13kg×number of worker(2 persons)≥the weight of cable ladder 46.26kg≥the weight of cable laddder where 23.13kg is the maximum recommended weight for manual lifting without injuries in ideal condition [18]. 3. results 3.1 maximum load table 6 shows the result of the maximum load calculation. for the finite element analysis and the hand calculation, the safety factor defined in each standard shall be multiplied with the sum of cable weight & ladder weight. in this study, only data for width 900mm is considered because nema ve-1 states the test shall be conducted with the greatest width [14]. doi: https://doi.org/10.36956/sms.v2i1.311 54 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 3.2 finite element analysis numerical analysis has been carried out for both nema ve-1 destruction load test and iec 61537 deflection load test. 3.2.1 nema ve-1 destruction load test by using formula (4), the test pressure distributed on the top of each rung has been calculated as the figure 14 shows the largest vertical deflection (vertical sagging of side rail) which is measured at midspan. it significantly increases as span increases. figure 14. maximum vertical deflection for simple span figure 15 is the trend for von-mises stress as span increases. although the longer the span is, the larger the von-mises stress is, the maximum von-mises stress at the mid-span did not reach the yield stress of material up to 3.9m span. figure 15. max. von-mises stress for simple span based on the stress contour in figures 16, the largest stress was observed at boundary condition location position of support, but it was neglectable because of the minor area. other than the stress at boundary condition location, the greatest bending stress was induced on top flange of side rail at mid-span where the largest vertical displacement took place. figure 16. von-mises stress contour for nema destruction test with 3.6m span table 6. the summary of maximum load width of ladder [mm] max. cable weight (a) [n/mm] ladder weight (b) [n/mm] max. load(c) (a)+(b) [n/mm] nema test (c)*1.5[1] [n/mm] iec test (c)*1.7[2] [n/mm] 300 0.430 0.057 0.487 0.730 0.828 450 0.645 0.062 0.707 1.060 1.202 600 0.860 0.068 0.928 1.392 1.577 750 1.075 0.073 1.148 1.722 1.951 900 1.290 0.078 1.369 2.053 2.327 notes: [1] nema safety factor: 150% [2] iec safety factor: 170% doi: https://doi.org/10.36956/sms.v2i1.311 55 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 figure 17 shows the result for eigenvalue buckling analysis when 0.0164 n/mm2 is uniformly distributed on the top of rung. as a result, the elastic critical bending moment reached between 3.6m span and 3.9m span because eigenvalue buckling factor in this region became less than 1. therefore, it concludes that the largest span of nema test simulation is about 3.6m. figure 17. eigenvalue buckling factor for simple span 3.2.2 iec 61537 deflection load test the pressure for each rung for deflection load test is: the finite element analysis for iec 61537 load test was performed only at the longest span (3.6m) which met nema ve-1. figure 18 is stress contour for multi-span (iec 61537) condition. as for simple span (nema ve-1 load test), the greatest stress was found at the boundary condition of the support and it is neglectable due to the minor area near hole. other than the stress at support position, the maximum bending stress occurred on the top flange of side rail at middle of intermediate span where the largest vertical displacement was observed. figure 18. von-mises stress contour for iec deflection test with 3.6m span figure 19 is deformed shape of buckling for iec test. eigen buckling factor is 2.16 which is almost 2 times of eigen buckling factor in simple span load test. figure 19. deformed shape of buckling for iec deflection test with 3.6m span table 7 is comparison of results between nema load test (simple span) and iec load test (multiple span). all outcomes of the multiple span are much more positive than that of simple span. table 7. simple span versus multi-span at 3.6m span value nema-simple span (a) iec-multi span (b) criteria (a)/(b) max. deflection at mid-span (mm) 12.6 2.9 ≤39[1] 4.34 max. bending stress at mid-span (n/mm2) 129.4 51.0 ≤240[2] 2.54 eigenvalue buckling factor 1.10 2.16 ≥1 0.51 notes: [1] 1/100 of 3600mm [2] yield stress of material in summary, 3.6m is the maximum span which doesn’t reach critical bending moment for buckling, yield stress and 1/100 of deflection. 3.3 simplified hand calculation the simplified hand calculation has been carried out up to the longest span (3.6m) which doesn’t reach buckling in numerical analysis. figures 20 and 21 show the results for the maximum deflection and bending stress at the mid-span. as a result, the vertical deflections of the cable ladder were less than 1/100 of span over whole test span. moreover, both cases (iec load test & nema load test) did not reach the yield stress of material. doi: https://doi.org/10.36956/sms.v2i1.311 56 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 figure 20. max. deflection at the middle of span figure 21. max. bending stress at the middle of span 3.4 comparative analysis as given in table 8, a comparison is made with the hand calculation results and results obtained from fea. overall, the results present a good correlation. the maximum error is about 10% in the deflection of 3.6m span (iec) and it might occur because not only the effects induced the holes in the web were not considered in simplified hand calculation but also allowing the beam to rotate around the longitudinal axis. 3.5 constructability verification the straight length of cable ladder shall be at least equal to the longest span (3.6m) obtained from fea because more than two splicing units between supports are not allowed [14]. in other words, the straight length of cable ladder is not able to be shorter than support span, 3.6m in order to minimize its weight the weight of 3.6m cable ladder is it concludes the longest span from fea is acceptable in view of material handling because its weight meets the criteria(≤46.26kg) in section 2.6. 3.6 case study table 9. input data for case study [19] data description data detail remark project a liquified natural gas terminal facility supplied cable ladder straight section 7620m support material cost $100 the lowest cost splicing unit material cost (per 1 pair) $10/pair [1] labor rate $60 ($/hour) support installation time 6 hour/ea cable ladder splicing time 0.25 hour/pair note: [1] this cost is obtained via personal communication. to estimate the benefits from the longer support span, a liquified natural gas (lng) terminal facility project was table 8. hand calculation versus fea span (m) max deflection at mid-span (mm) max bending stress at mid-span (n/mm2) hand cal.(a) fea(b) (a)/(b) hand cal.(c) fea(d) (c)/(d) 3(nema) 5.8 6.3 0.93 92.8 93.5 0.99 3.3(nema) 8.5 9.1 0.94 112.3 111.4 1.01 3.6(nema) 12.0 12.6 0.95 133.6 129.4 1.03 3.9(nema) 16.5 17.2 0.96 156.8 153.4 1.02 3.6 (iec) 3.2 2.9 1.10 55.1 51 1.08 doi: https://doi.org/10.36956/sms.v2i1.311 57 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 selected for the case study. this lng facility had been built by using b-line’s products and all required information for the case study is available in the paper generated by b-line. this study explains what kinds of benefits compared to the design based on 3m span can be obtained by utilizing 3.6m support span which is quite feasible in view of constructability. the case study was carried out as following steps. step 1: to define the input data for case study. the information from b-line’s lng facility project was used for the case study. table 9 shows the input data to evaluate the economic impacts of longer span. step 2: to estimate the reduced quantity of support. according to b-line’s bill of material for target project, total 7620m cable ladder straight section had been supplied. by using total length of cable ladder straight section, minimum required support quantity for each span can be calculated as minimum support qty(ea)= where as a result, total 423ea structural steel support for cable ladder straight section can be roughly reduced by changing the support span from 3m to 3.6m. step 3: to calculate the positive cost impacts for support material. the cost for 423ea steel structural support is: step 4 to evaluate the cost savings for splicing unit. the splicing units of cable ladder are demonstrated in figure 22. the splicing units are used for connecting the two pieces of cable ladder straight section. in general, one pair splicing unit is required for each support span length because cable ladder straight section length is equal to support span length to minimize its weight. thus, reduced splicing unit quantity is same as the saved support quantity. figure 22. splicing unit for cable ladder [13] splicing unit material coat savings ( ) =reduced splicing unit qty(pair) ×unit price of splicing unit ( /pair) 4,230 ( )=423 (ea)×10( /ea) step 5 to obtain the labor cost savings for cable ladder support installation. labor cost savings for cable ladder support installation are: =labor rate( /hour)×manhour for installation(hour/ea) ×saved support qty(ea) 152,280 ( )=60 ( /hour)×0.25(hour/pair)×423(pair) step 6 to get the labor cost decrease for cable ladder splicing. the labor cost impacts for cable ladder splicing can be calculated as below: =labor rate( /hour)×manhour for splicing(hour/pair) ×reduced splicing unit qty(pair) 6,345 ( )=60 ( /hour)×0.25(hour/pair)×423(pair) step 7 to summarize the benefits of new span. total economic benefits by employing optimal span, 3.6m are summarized in table 10. compared to 3m support span design, about 205,155$ can be lower by utilizing the 3.6m support span. table 10. summary of cost savings description cost savings ($) cable ladder support material 42,300 splicing unit material 4,230 labor cost for support installation 15,2280 labor cost for cable ladder splicing 6,345 total cost savings 205,155 4. discussions in cable ladder system design, although the cable doi: https://doi.org/10.36956/sms.v2i1.311 58 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 weight is a chief factor to determine the support span, the method to calculate maximum cable load had not been well defined in earlier research studies. by using the formula derived in this research, the maximum cable weight to be installed on the ladder can be estimated. the cable ladder which is a kind of slender steel beam might fail due to lateral torsional buckling before yielding the plastic hinge. through fea, the greatest span has been estimated as 3.6m when the c channel side rail in figure 2 is applied. compared to the span length of offshore practice, it makes 20% improvement without increasing the cross-section of cable ladder and contributes to reduce the overall ladder system cost such as material cost, labor cost and others. in view of constructability, the weight of 3.6m straight ladder is suitable for manual handling and installation and it is able to give more attractive results when it is applied to the larger project that the proportion in the straight run of cable ladder is greater. although there were some approaches to extend the span by increasing the thickness of side rail, it might be a big challenge in view of constructability. for instance, it not only causes the difficulty of material handling because of getting much heavier but also increases the risk of injury during the installation of heavier ladder. finally, although the optimal span in this study does not give the large cost saving in view of total project cost, it can be one of contributions to save offshore oil and gas project cost. 5. conclusions the findings from this study can be summarized as: according to data from previous projects, the dominated maximum cable ladder support span is 3m. both nema ve-1 and iec 61537 are the mainly used standards to determine the largest support span in offshore oil and gas industry. however, there is no well-defined guidance to estimate the greatest cable weight which can be filled on the cable ladder. on top of that, the formulas in the structural steel design standard such as can/csa s16-14, eurocode 3 are difficult to be used to get the critical bending moment of cable ladder due to its geometry partially restrained by rung. (1)according to nec, control cables can be filled much more in cross section of cable ladder compared to power cables because they do not cause the heat generation problem. therefore, the largest cable weight which can be calculated by assuming 50% of fill area of cable ladder is fully filled with the control cables. (2)based on the side rail geometry frequently used in offshore industry, fea has been conducted to find the longest span which meet both nema ve-1 and iec 61537. as a result, optimal span is 3.6m which is 0.6m longer compared to the offshore typical practice. moreover, the weight of cable ladder for new span is still suitable for material handling without additional manpower. (3)when a longer span was applied to a liquefied natural gas terminal facility as case study, about 17% cost saving could be obtained for cable ladder support system. although the proportion of cable ladder support system in the cost of the project is small, it can be one of the contributions to save offshore oil and gas project cost. references [1] sieminski, a. international energy outlook. energy information administration (eia), 2014, 18. [2] ioss. ioss introduction [online], 2015. available: https://ioss.info/page/index.php [accessed]. [3] ekstrom, c. m., wesley, d. lateral-torsional buckling of steel channel beams. division of structural engineering chalmers university of technology gothenburg, 2017. [4] kalupa, c.j. guide for design of electrical cable tray systems[j]. ieee transactions on industry applications, 1977, 6: 533-538. [5] desmond, t.p., dermitzakis, s.n. effective-length factors for buckling of cable-tray supports[j]. nuclear engineering and design, 1987, 103(3): 313-332. [6] reigles, d.g., brachmann, i., johnson, w.h., gürbüz, o. test-based approach to cable tray support system analysis and design: behavior and test methods[j]. nuclear engineering and design, 2016, 302: 27-36. [7] masoni, p., pasquale, g.a., mazzieri, c., morgana, a. seismic tests of cable tray systems, 1989. [8] huang, b., lu, w., mosalam, k.m. shaking table tests of the cable tray system in nuclear power plants[j]. journal of performance of constructed facilities, 2017, 31(4): 04017018. [9] khalid, m., baofeng, h. performance-based earthquake engineering methodology for seismic evaluation of cable tray systems for nuclear power plants, 2019. [10] de normalisation, c. e. env 1993-1-1 eurocode 3, design of steel structures, part 1.1-general rules and rules for buildings. european committee for standardization, brussels, belgium, 1993. [11] en, b. 10088-1: 2005, stainless steels-part1: list of stainless steels. cen, 2005. [12] en, b. 10088-2: 2014. stainless steels: technical delivery conditions for sheet/plate and strip of corrodoi: https://doi.org/10.36956/sms.v2i1.311 59 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 sion resisting steels for general purposes, 2014. [13] oglaend. oglaend system product [online]. 2020b. available: https://www.oglaend-system.com/selector/ [accessed]. [14] nema. nema ve 1-2017 metal cable tray systems. national electrical manufacturers association, 2017. [15] commission, i. i. e. iec 61537: cable management– cable tray systems and cable ladder systems. geneva (switzerland): international electrotechnical commission, 2016. [16] association, n. f. p. nfpa 70: national electrical code, national fire protection assoc, 2011. [17] university of alberta. buckling [online], 2020. available: https://sites.ualberta.ca/~wmoussa/ansystutorial/it/ buckling/buckling.html [accessed]. [18] waters, t. r., putz-anderson, v., garg, a. applications manual for the revised niosh lifting equation, 1994. [19] b-line. cost saving calculator [online], 2020a. available: https://www.eaton.com/content/dam/eaton/products/support-systems/cable-management/structural-steel-savings/structural-steel-savings-engineering-guide-brochure.pdf [accessed]. doi: https://doi.org/10.36956/sms.v2i1.311 1 sustainable marine structures | volume 04 | issue 01 | january 2022 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2022 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). *corresponding author: chunling zhang, college of marine science, shanghai ocean university, shanghai, 201306, china; email: clzhang@shou.edu.cn shenglong yang, key laboratory of east china sea & oceanic fishery resources exploitation and utilization, ministry of agriculture, shanghai, 200090, china; email: ysl6782195@126.com doi: http://dx.doi.org/10.36956/sms.v4i1.474 article thermocline model for estimating argo sea surface temperature chunling zhang1* mengli zhang1 zhenfeng wang2 song hu1 danyang wang1 shenglong yang3* 1. college of marine science, shanghai ocean university, shanghai, 201306, china 2. project management office of china national scientific seafloor observatory, tongji university, shanghai, 200092, china 3. key laboratory of east china sea & oceanic fishery resources exploitation and utilization, ministry of agriculture, shanghai, 200090, china article info abstract article history received: 28 december 2021 accepted: 4 january 2022 published online: 14 january 2022 argo has become an important constituent of the global ocean observation system. however, due to the lack of sea surface measurements from most argo profiles, the application of argo data is still limited. in this study, a thermocline model was constructed based on three key thermocline parameters, i.e, thermocline upper depth, the thermocline bottom depth, and thermocline temperature gradient. following the model, we estimated the sea surface temperature of argo profiles by providing the relationship between sea surface and subsurface temperature. we tested the effectiveness of our proposed model using statistical analysis and by comparing the sea surface temperature with the results obtained from traditional methods and in situ observations in the pacific ocean. the root mean square errors of results obtained from thermocline model were found to be significantly reduced compared to the extrapolation results and satellite retrieved temperature results. the correlation coefficient between the estimation result and in situ observation was 0.967. argo surface temperature, estimated by the thermocline model, has been theoretically proved to be reliable. thus, our model generates theoretically feasible data present the mesoscale phenomenon in more detail. overall, this study compensates for the lack surface observation of argo, and provides a new tool to establish complete argo data sets. keywords: argo sea surface temperature thermocline model the pacific ocean 2 sustainable marine structures | volume 04 | issue 01 | january 2022 1. introduction global argo array, consisting of more than 3000 profiling floats, has become an important constituent of the global ocean observation system. they are configured and pumped to ensure the highest quality data acquisition from global ocean. to avoid the degradation of salinity accuracy owing to sea surface contaminants, the pump is turned off at ~5 dbar beneath the sea surface as the argo float ascends. therefore, the conventional argo floats obtain temperature and salinity measurements from depths of ~52000 m. although sea surface temperature (sst) is the key indicator of climate change, it is integral for both ocean circulation and climate change studies [1]. the combination of argo and satellite sst has been used in several studies [2-4], even though neither the spatial nor the temporal resolution of the two data sets are similar. a sst salinity (sts) sensor, developed by sea-bird electronics inc., was used on the argo float and in the aquarius sea surface salinity mission, to measure sst and salinity. this sensor can be used in conjunction with the main sbe-41 cp ctd installed in an argo float [5]. the sts sensor samples at 1 hz concurrently with the sbe-41 cp ctd near the float park depth (960980 dbar) and subsequently in the upper ocean (320 dbar) just before the sbe-41 cp is turned off. with the increasing demands of such new argo floats, a large number of nearsurface temperature and salinity data are expected to be generated for ocean and atmospheric research. however, the stability of the new argo floats with sts sensor still needs to be significantly improved. the sts sensor were first put into use in october, 2008; however, by the end of 2020, the number of sts sensors launched by international argo plan member countries was still <1000. at present, near-surface temperature and salinity data are significantly lesser compared to that required for climate prediction and data assimilation. therefore, it is necessary to use statistical methods to estimate sst with the help of argo subsurface data. it is necessary to assimilate argo alone or in combination with other observations to generate gridded dataset with the aid of data assimilation techniques, which can be directly used for studies [6]. due to the lack of surface measurements, some argo gridded dataset considers 5 m (the nearest surface observation depth of traditional argo float) as the first surface layer without using additional data [7,8]. most of argo datasets consider satellite sst or the added surface measurement data obtained from observation stations as the surface data [9-12]. roemmich and gilson obtained argo observations at ~0‒2000 m by linear interpolation and generated climate data for 58 vertical depths [13]. some other scholars used satellite sst directly, for determining surface temperature of argo dataset or adopted akima’s extrapolation method to obtain sst [14,15]. the increasing volume of in situ observations are far behind that of argo. moreover, in situ data cannot match the increasing volume and temporal length of argo observations in the near future. in the past few decades, the satellite derived sst has become a primary data source owing to its global spatial coverage and high temporal resolution, however, it is not based on in situ measurements. the retrieved satellite data is significantly different from sst measured in situ at depths of ~0.22 m [16]. the simple combination of satellite sst and argo subsurface data produces large errors [17]. several studies employ widely used extrapolation techniques, which are simple method and provide a rough estimation of temperature and salinity. to avoid these short-comings, we propose a parametric model based on thermocline parameters. the sst in the pacific ocean was estimated using the subsurface argo data to verify the accuracy of this model. the argo observations and the principle of the used method are described in section 2. in section 3, we verify our results, and apply them to discuss the thermocline and vertical temperature structure in section 4. finally, in section 5, we present our conclusions. 2. materials and methods 2.1 data processing three types of marine data are open-accessed for worldwide research, including argo subsurface profiles, global temperature and salinity profile project (gtspp) data, and argo near-surface temperature (argo nst). the traditional argo profiles used to calculate the model parameters were provided by china argo real-time data center (ftp://ftp.argo.org.cn/pub/argo/global/). due to the dependence of our proposed methods on thermocline parameters, test data that reflect notable thermocline characters are required. considering the number of argo observations, data from august, 2020 was chosen as the test data. the test data consisted of a total of 12,726 profiles measured during august, 2020 in the pacific ocean (figure 1a). the data passed a series of quality control tests, such as the test of observation parameters and layers, land, ocean and region detection, density inversion test, the test of range of temperature and salinity, and time judgment [18]. meanwhile, the estimated sst from argo subsurface data depended on the initial depth as different reference layers provided different results. these results were weighted by comparing with gtspp sea surface observations obtained from buoy stations at ftp://ftp.argo.org.cn/pub/argo/global/ 3 sustainable marine structures | volume 04 | issue 01 | january 2022 depths of ~0.22 m. the gtspp profiles are obtained from national oceanic and atmospheric administration (noaa) (http://data.nodc.noaa.gov/gtspp/best.nc/). after removing duplicate data, a total of 6230 profiles during august, 2020, which were mostly located in the equatorial pacific region was obtained (figure 1b). argo nst observation was used to verify the results estimated from our proposed model. argo nst data of the same period are available on the national oceanography centre’s (noc) ftp website (ftp://ftp.pol.ac.uk/pub/bodc/ argo/nst/). these floats with non-pumped near-surface temperatures are deployed and processed by the british oceanographic data centre, the indian national centre for ocean information services, the japan meteorological agency, the scripps institution of oceanography, and the university of washington, respectively. collectively, a total number of 540 profiles were used in this study, and most of them were primarily located in the western part of the pacific ocean (figure 1b). 2.2 thermocline model the model proposed in this study estimates the sst base at the mixed layer depth (mld) or the thermocline upper depth, the thermocline bottom depth (tbd), and thermocline temperature gradient (ttg). these key parameters were calculated by the maximum angle method [19-21]. the proposed model was improved and a new application in estimating argo surface temperature. we constructed the model depicted in equation (1) by considering the minimal possible degrees of freedom. figure 2 illustrates the principle behind the proposed model. the estimated sst of argo from subsurface temperature was different for different reference layers. in this study, 10 m, 20 m, 30 m, 50 m, 75 m, 100 m, 125 m, 150 m, and 200 m were chosen as reference layers to estimate sst in the pacific ocean. subsequently, nine different temperatures measured at each grid were averaged according to (equation 2): 0 , (0 mld) ttg( mld), (mld tbd) = ≤ ≤ = − − ≤ ≤ z z z p sst t z p sst t z z (1) 9 , , 1 2 2 , ,9 , 1 , exp( ( ) / )= = = = − − ∑ ∑ i j i j j i i j i j i i j j b sst sst b r r l b (2) where sst is sea surface temperature. tz is the subsurface temperature at the depth of z estimated by argo temperature profile data. the parameters p0 and pz represent sea surface and subsurface pressure, respectively. to ensure the continuity of tz and tz’ (the differential of tz ) at tbd, the temperature function at depth below the tbd was adopted as g a u s s f u n c t i o n 0 0( + tbd)( ) exp[ ], ( tbd)− +− = − ≥ w w z d td d w z z z t t t t z h , similar to that used in previous work [19]. hw is the depth scale and ttd is the temperature at tbd obtained by dichotomy. td is the temperature in the deepest l a y e r. b a s e o n c o n t i n u i t y t ( t b d + 0 ) = t ( t b d 0 ) and (tbd 0) (tbd 0) ttg+ −= =dt dt dz dz , differentiation of the gauss function with respect to z is 1/( 1)0 [ ]( ) wth th d hg z w t t −= − . the w parameter should be less than 1, otherwise, z0 becomes significantly large, and temperature starts decreasing with depth. table 1 shows the root mean square errors (rmses) of the estimated results with different w and h. when w is constant, the rmse values decrease initially, and subsequently increases. the rmse values are least value when h=2000 m. moreover, h is constant figure 1. locations of argo subsurface profiles (a), and (b) gtsspp or argo near surface observations. 4 sustainable marine structures | volume 04 | issue 01 | january 2022 and the rmses of the estimated temperatures are the least when w=0.5. hence, w and h were set as 0.5 and 2000 m, respectively, to ensure the least rmse at a temperature of 0.637 °c. ssti is the estimated sst at the i th section of the argo profile. ssti,j is the estimated temperature at ith profile according to jth (j=1,2,…9) datum layer. rij is the rmse for ssti, j and gtspp data. the different results at different starting depth have minimum temperature rmse compared with gtspp when the correlation scale l has a value of 2 degrees (figure 3). 2.3 algorithm of thermocline parameters to estimate the sst by equations (1) and (2) described in section 2.2, the key parameters—mld, tbd, ttg should be determined. the maximum angle method [20,21], a simple and objective method, was adopted to calculate these parameters with the argo dataset of august, 2020. it not only uses the main feature (vertically uniform) of the mixed layer (i.e., temperature (or density) deviation and vertical gradient criteria) but also uses the main characteristics of the thermocline (sharp gradient) beneath the mixed layer. however, this method can be improved, when the variable is strictly monotonous, the depth of density mixed layer is regarded as isothermal layer depth. to ensure a monotonous profile, the maximum angle method of the potential density profile was used to determine thermocline parameters via argo observations. figure 4 illustrates the methodology used by a potential density profile. the vertical density difference represents the total variability of potential density. theoretically, the variability of the vertical density difference is approximately zero in the constant-density layer, and it becomes larger in the pycnocline beneath the mixed layer. it is reasonable to identify the main parts of the pycnocline between the two depths. the main depths were set corresponding to 10% and 70% difference in vertical density. the mld and tbd were determined between the main depths by point to point linear polynomial fitting. figure 4 provides a schematic representation of the vector fitting used in our proposed method. at depth zk (marked by a circle in figure 4), both vectors (downward positive) were constructed by linear polynomial fitting of the profile data from zk-1 to zk. the subscript k increases downward with k = 1 at the surface or at the nearest location to the surface. in the constant-density (isothermal) layer, the angle θ reaches its maximum value (see figure 4b), and is smaller if zk is inside (figure 4a) or outside (figure 4c) the table 1. estimated rmses of sst (°c) with different w and h values w = 0.1 w = 0.25 w = 0.5 w = 0.6 w = 0.8 h=1000 m 1.123 0.971 0.805 0.812 0.877 h=1500 m 0.908 0. 884 0.795 0.819 0.830 h=2000 m 0.782 0.761 0.637 0.800 0.802 h=3000 m 0.851 0.780 0.711 0.873 0.935 h=5500 m 0.893 0.852 0.790 0. 963 1.020 figure 2. principle of thermocline parametric model. sst denotes sea surface temperature. the parameters h1, h2 and h represent mixed layer depth, thermocline bottom depth, and depth scale, respectively. figure 3. different rmses of sst (°c) for different correlation scale l. 5 sustainable marine structures | volume 04 | issue 01 | january 2022 mixed layer. thus, the maximum angle principle can be used to determine the mixed layer depth (θmax, mldzk). in practice, the angle θ is difficult to calculate, therefore, tan θ was used instead. figure 4. illustration of the max angle method. the dots represent density of each depth. the vector angles (indicated by θ) have small value inside or outside the mixed layer depth ((a) and (c)), and it has the largest value at the depth of thermocline upper depth. in order to ensure the stability of the simulation results from the sbpom model, the time of the outer mode (positive compression mold) was set to 20 s and the time of the inner mode (oblique compression mold) was set to 600 s. the bathymetric topography was based on the general bathymetry chart of the oceans (gebco), which has a minimum water depth of 10 m. the maximum water depth was set to 5000 m, and water depths exceeding 5000 m were replaced by 5000 m to match the maximum water depth in the soda data. the spatial resolution of the simulated sea surface temperature from the sbpom model is a 0.25° grid at a 1-hour interval. 3. validation of the results 3.1 correlation analysis the estimation of sst from subsurface temperature using the thermal parametric model (figure 2) is based on the hypothesis proposed by chu and fan [20]. the linear correlation coefficient between sst anomaly and mld anomaly is significantly larger than that between sst anomaly and other parameters, i.e., | r1|>| r2|, | r1|>| r3|in formula mld’=r1sst’, tbd’=r2sst’, ttg’=r3sst’ where, r1, r2, r3 are the regression coefficients of mld’, tbd’, ttg’, respectively. the parameter anomalies (sst’, mld’, tbd’, ttg’) were obtained from the thermal parameters (sst, mld, tbd, ttg) by subtracting their mean values within a 1o×1o grid cell at each observation locations. figure 5 shows the scatter plot between sst’ and (mld’, tbd’, ttg’) in the pacific ocean. the data points concentrate around the fitting line in figure 5a. although the data points in figure 5b and 5c plot relatively far away from the fitting line, three absolute values of r obtained by linear regression indicate that 'mld has the largest correlation coefficient with 'sst among all subsurface parameters. the correlation coefficients between sst’ and mld’, tbd’, and ttg’ were 0.249, −0.046, and 8.334e-04, respectively. the significance of the correlation was evaluated by statistical analyses 2 2 1 r n t r − = − , where the t distribution had a degree of freedom of n-2. here, r is the correlation coefficient and n is the number of analyzed samples (19,200). the critical value of t at significance level of 0.005 was 2.576 (t0.005 (19200-2)=2.576). three absolute values of t between sst’ and mld’, tbd’, and ttg’ were 1.832, ‒0.326, and 0.059, respectively. these values were less than the critical value of 2.576. in other words, we can suggest that the analyzed data are within the uncertainty of the statistical test. from the above analysis, we conclude that the correlation coefficient between the two short timescale parameters sst’ and mld’ is significantly larger than that between 'sst and the long timescale parameters (tbd’, ttg’). this in turn theoretically confirmed the reliability of estimating sst based on thermal parametric model in the pacific ocean. figure 5. correlation analysis between sea surface temperature anomaly and thermocline parameter anomaly. (a) the correlation coefficients between sea surface temperature anomaly and mixed layer depth anomaly, (b) thermocline bottom depth anomaly, and (c) thermocline gradient are represented by r1, r2, and r3, respectively. the parameter t indicates t-critical at significance level of 0.005. 6 sustainable marine structures | volume 04 | issue 01 | january 2022 3.2 comparison with observations the commonly used methods to obtain argo surface temperature include extrapolation method proposed by akima [22] and satellite derived sst. according to the thermocline model (described in 2.2), the estimation of sst was based on reference layers (10 m, 20 m, 30 m, 50 m, 75 m, 100 m, 125 m, 150 m, 200 m) and different results were weighted by gauss function. next, we compared the temperature results from the different datum layers, the thermocline model (recorded as sst), akima extrapolation (named as extra), and satellite amsr-e sst (indicated by satellite) by considering the data obtained from gtspp and argo nst observations as true values. table 2 lists the rmses of temperature estimated from the nine different datums, weight-averaged sst based on equation (2), the surface temperature obtained by extrapolation (extra) and satellite amsr-e sst (satellite) compared with gtspp and argo nst. it is evinced that the temperature rmses increase with the datum depth in the results obtained from thermocline model. the weighed-averaged sst has smaller rmse of 1.04 °c and 0.99 °c compared to that of gtspp and argo nst, respectively. however, the rmses of estimated temperatures corresponding to the nine datum layers were all less than 1.6 °c for the two base datasets. the rmses between the extra surface temperature and the two practical datasets have a value of >1.8 °c, which are larger than all estimations. the rmses between the satellite amsr-e sst and the two practical datasets are ~2 °c and 1.5 °c relative to gtspp and argo nst, respectively. although both gtspp and argo nst are sparse and asymmetrical in space, table 2 illustrates that the sst estimated by thermocline parametric model is more close to in situ observation compared to satellite and extra. meanwhile it indicates that weighted mean method (formula (2)) can improve the accuracy of estimation. moreover, the in situ argo nst and gtspp data were not used during the estimation process, as discussed below. thus, the test was strictly independent. t h e c o r r e l a t i o n a n a l y s i s r e s u l t s a n d a b s o l u t e temperature errors of sst derived from thermocline model sst (figure 6a), extrapolated results (indicated by extra in figure 5b), and satellite derived (figure 6 c) are displayed in figure 6. figures 6(a1), (b1), and (c1) provide the correlation coefficient r, rmse, regression line, and its confidence interval with confidence level of 90%. it is evident that sst in the pacific ocean is in better agreement with argo nst compared to extra or satellite. the sst data points concentrate around the fitting line 0.99 1.05y x= + , and have the smallest residual standard deviation (s = 1.72) compared to other methods. the correlation coefficient between sst and argo nst was 0.967, which is smaller than the other results. the distribution of extra and satellite data points are more dispersed, with linear fitting coefficients of 0.87 and 0.89, respectively. both extra and satellite derived results have high correlation with the argo nst with correlation coefficients of 0.911 and 0.937, respectively. however, their rmses were significantly larger than that of sst. the maximum absolute temperature errors of thermocline model shown in figure 5 a2 are <1 °c. in fact, most of the errors in the estimated temperature were <0.5 °c. there are a few profiles near 40 °n with temperature errors of ~ 1 °c. most of the errors in temperature estimated by extrapolation and satellite based were >1.5 °c, with the maximum error exceeding 2.5 °c in the northwest pacific. argo nst data shown in figure 6 are sparse in the equatorial region. the gtspp observations were primarily obtained from the anchor buoys in tropical pacific. figure 7 shows the absolute temperature errors between the different results and gtspp in the equatorial pacific. the temperature errors of sst obtained from the thermocline model (figure 7a) were minor at all observation locations. most of the sst errors were <0.5 °c with a few temperature errors being in the range of 0.51.0 °c. in contrast, the errors in temperature of extra and satellite displayed a skewed distribution, especially in the extrapolation results (figure 7b). most of these errors in extra temperature exceed 1.5 °c and half of the total errors were approximately at 2.5 °c. in the satellite results (figure 7 b), the errors in temperature were concentrated at 0.5‒2.0 °c, which are smaller than that obtained in the extra results but larger than in the thermocline model sst errors. thus, both theoretical statistics and observation comparisons show that the thermocline model can provide more accurate results. 4. discussion 4.1 thermocline parameters analysis three thermocline parameters involved in this study table 2. rmses of the estimated temperature (°c) for different sst and in situ observation results 10m 20m 30m 50m 75m 100m 125m 150m 200m sst extra satellite gtspp 1.13 1.15 1.18 1.10 1.20 1.52 1.59 1.44 1.51 1.04 1.94 1.96 argo nst 1.04 1.21 1.21 1.16 1.26 1.28 1.35 1.48 1.54 0.99 1.84 1.50 7 sustainable marine structures | volume 04 | issue 01 | january 2022 vary with respect to different timescales. the mld has a short correlation timescale. on the other hand, the tbd and ttg have longer correlation timescales. the strongest thermocline in the northern hemisphere and the weakest in the southern hemisphere appears during august [23]. this is reflected from the distribution of thermocline parameters of august, 2020 obtained from argo profiles and gridded by the optimal interpolation [24,25] (figure 8). there are more than 60% mlds lesser than 100 m as obtained by argo profiles. most of them are in the northern pacific (figure 8 (a1)). the mld in the southern pacific are concentrated at 100300 m. most of the deeper mld are located to the south of 40 °s, where there is no noticeable thermocline in august and the vertical temperature variation is not evident. it indicates that the thermocline disappears rapidly in this region. figure 8 (a2) displays the variation of the mean mld with latitude. the mld gradually deepens from 60 °n to 40 °n, and figure 6. scatter diagrams of correlation analysis (a1, b1, c1) and absolute temperature errors (a1, a2, a3) between different results and the argo nst observation. the results of sst obtained using thermocline model, extra obtained by extrapolation, and satellite surface temperature are represented by (a), (b), and (c), respectively. the red lines represent the 95% confidence interval of the regression line (black line) with the residual standard deviation (indicated by s). the correlation coefficient is represented by r. 8 sustainable marine structures | volume 04 | issue 01 | january 2022 become shallow in the subarctic. the mean mld is lower than 50 m in the northern pacific, and has a value of more than 100 m in the 40 °s‒60 °s. these results agree with previous studies [23,26,27]. thermocline bottom depth is deeper than 100 m, and has higher values in the southern pacific shown in figure 8 (c). its zonal mean value represents increasing trend from north to south similar to the mld. during august, the thermocline is evident in the northern pacific. the corresponding tbd is also shallow with a mean value of <200 m. the southern pacific is characterized by a deeper tbd with a zonal mean value of 300-500 m, and it is even deeper than 800 m at approximately 45 °s. on the other hand, the tbd is ~300 m in the equatorial pacific. temperature gradient represents the strength of the thermocline. figure 8 (b) illustrates the distribution of ttg and its zonal average. ttg varies from 0 to 0.15 °c/m. ttg is higher than 0.09 °c/m in the tropical pacific region of 10 °s‒10 °n (figure 8 (b1)). compared to southern pacific, the ttg is stronger in most of the northern pacific region, especially in the regions between 45 °n and 25 °n, where the ttg is generally higher than 0.06 °c/m. the mean ttgs of the northern pacific are higher than 0.06 °c/m with a value of 0.15 °c/m at approximately 10 °n, as shown in its zonal mean distribution (figure 8 (b2)). on the other hand, the southern pacific has a mean ttg of <0.05 °c/m, and the thermocline is notably weakened in the southern hemisphere. ttg is almost close to zero at south of 40 °s, where there is no apparent thermocline. figure 7. scatter of absolute temperature errors between thermocline model (a), extrapolation (b), and satellite surface temperature (c) and gtspp data. 9 sustainable marine structures | volume 04 | issue 01 | january 2022 4.2 distribution of sea surface temperature the thermocline parameter model in section 2.2 provides the monthly distribution of sst. as shown in figure 9, the surface temperature distribution in the pacific ocean shows a trend of increasing temperature in the equatorial region (> 25 °c) and decreasing temperature in the high latitude region. the temperature generally drops below 10 °c in the sub antarctic and sub polar regions. this reflects the change of solar radiation with latitude. the isotherms are sparse in the range of 20 °s20 °n. with temperature transition from the tropics to the polar regions, the isotherms become gradually denser. the isotherms reflect the characters of the polar front at approximately 40 °latitudes. the eastern isotherm between 40 °s and 40 °n bends to low latitudes under the influence of cold current. on the other hand, the western isotherm bends to high latitudes under the influence of warm current. to the south of 40 °s, the isotherm is almost parallel to the latitude. there exists evident warm pool in the equatorial region of the western pacific. the center of the warm pool (29 °c isotherm) lies between 5 °s‒25 °n during august. these characteristics are consistent with the results obtained from historical observation data and have the potential to extract mesoscale information completely. figure 8. spatial distribution (a1, b1, c1) and latitude mean (a2, b2, c2) of mixed layer depth (a), thermocline temperature gradient (b), and thermocline bottom depth (c). 10 sustainable marine structures | volume 04 | issue 01 | january 2022 figure 9. distribution of the sea surface temperature during august, 2020 in the pacific ocean. 5. conclusions as one of the important constituents of the global ocean observation system, argo floats collect temperature and salinity data of upper global ocean rapidly, accurately, and extensively. argo profiles are increasing at the rate of one hundred thousand sections each year. meanwhile, sst is an important parameter for both ocean circulation and climate change studies, and several studies rely on complete three-dimension temperature information. therefore, estimating the argo sst using available statistic methods has major practical and scientific significance. based on a thermocline parametric model, the maximum angle method has been used in this study to calculate the model parameters (mld, ttg and tbd), and subsequently, sst was estimated using argo subsurface temperature. the estimated results were compared with near surface temperature observations, and were theoretically tested using correlation analysis. the results illustrate that the estimated sstw is reliable and credible. in this paper, the maximum angle method was adopted to determine the model parameters (mld, ttg and tbd). this method is novel, and has stronger theoretical foundation compared to previous methods (e.g. gradient criterion and curvature method). the mixed layer depth obtained by this method is realistic. while using the maximum angle method, the analysis variable should be strictly monotonous. therefore, the density mixed layer was considered as temperature mixed layer depth in this study. since the barrier layer was ignored, it is expected to generate certain errors in our model. it is possible to reduce such errors by adopting the temperature profile and combining data from other models in the regions with existing barrier layers. in addition, the thermocline model employed in this study provides the function between sst and subsurface temperature based on the determined parameters mld, ttg, tbd etc. for this reason, the accuracy of sst estimated using this method is expected to be relatively lower when the thermoclines are not distinct. further research is required to overcome these shortcomings. since the pacific ocean was considered as an experimental region to verify the effectiveness of this thermocline model, our study provides a new idea for the construction of argo sst model in global ocean. author contributions conceptualization, c.z. and c.w.; methodology, c.z., z.w., and c.w.; validation, m.z., d.w., and s.h.; formal analysis, c.z. and c.w.; investigation, c.z.; resources, c.z; writing original draft preparation, c.z. and c.w.; writing—review and editing, z.w. and s.h.; visualization, m.z. and d.w.; funding acquisition, c.z. all authors have read and agreed to the published version of the manuscript. funding this research was funded by the national nature foundation nos. 4210060098, the argo buoy project under grant d-8006-21-0082, the foundation of key laboratory of ocean fishery development under grant a12006-21-200201, and the foundation of fishery resources comprehensive scientific surveys in the northwest pacific d-8021-21-0109-01. data availability statement three categories of data used to support the results of this study are included in the article. argo float data were collected and made freely available by the china argo real-time data center (ftp://ftp.argo.org.cn/pub/argo/ global/). argo nst observation data of the same period are available on the national oceanography centre’s (noc) ftp website (ftp://ftp.pol.ac.uk/pub/bodc/argo/ nst/). the gtspp profiles are obtained from national oceanic and atmospheric administration (noaa) (http:// data.nodc.noaa.gov/gtspp/best.nc/). acknowledgments we are grateful to the anonymous reviewers for critically going through the manuscript and for providing necessary comments. we also thank prof. chu p of department of oceanography, naval postgraduate school for several beneficial discussions. xu jianping ftp://ftp.argo.org.cn/pub/argo/global/ ftp://ftp.argo.org.cn/pub/argo/global/ 11 sustainable marine structures | volume 04 | issue 01 | january 2022 of the second institute of oceanography is thanked for his comments and english revision. we wish to thank the colleagues at the china argo real-time data center for numerous presentations and informal discussions that led to the successful 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[25] zhang, c.l., xu, j.p., bao, x., et al., 2013. an effective method for improving the accuracy of argo objective analysis. acta oceanologica sinica. 32, 6677. [26] zhang, c.l., wang, z.f., liu, y., 2021. an argo-based experiment providing near-real-time subsurface oceanic environmental information for fishery data. fisheries oceanography. 30, 85-98. [27] lu, j., qiao, f.l., wei, z.x., teng, y., xia, c.sh., 2008. study on distribution of mixed layer depth in the world ocean in summer. advances in marine science. 26, 145-155. 19 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v1i2.141 sustainable marine structures http://ojs.nassg.org/index.php/sms article zoning marine disposal for dredged material management: a case study in vietnam do gia khanh1,3 do thi thu huong2 vu duy vinh2 tran dinh lan2,3* 1. hai phong department of science and technology 2. institute of marine environment and resources/vast 3. graduate university of science and technology article info abstract article history received: 9 october 2020 accepted: 21 october 2020 published online: 31 october 2020 the fast growth of hai phong ports in the two last decades requires not only their upgrading facilities but also expanding port area and dredging their shipping channels (existing and new ones) that generate a huge amount of unused dredged materials. while all existing dumping sites in sea waters and on land get over capacity, looking for new dumping sites in sea waters is an urgent need. this study is to zone coastal waters of hai phong for suitable dumping sites meeting sustainable coastal management. multi-criteria overlay analysis on gis platform was employed with the criteria of natural conditions, environment and socio-economics for zoning coastal waters of hai phong. these criteria were detailed into eight subcriteria and then developed to eight gis weighted thematic sub-layers of bottom depth, litho-hydrodynamics, ecosystems, distribution of benthos, distance to residential areas and tourist sites, distance to aquaculture area, distance to ecosystems and distance to conservation areas. analysis results show the highly suitable zone for dredged material dumping in south, south west hai phong at depth below 15m to the deeper areas. disposals of dredged materials in the zone would minimize impacts on the environment, ecology and socio-economics in surrounding waters and coastal areas. keywords: mcoa marine dumping shipping channel sustainable criteria environmental impacts hai phong ports 1. introduction shipping channel material dredging that is vital to many harbors worldwide to maintain their operation normally generates some amount of dredged materials. these materials disposed on mainland, islands or in open waters can make not only benefits (reuse, recycle, etc.) to socio-economic development [13] but also negative impacts on the environment [5,13,16]. for many years, environmental impacts of dredged material disposal sites, particularly in marine waters have been studied and assessed for all environmental components as sediment, water and biological issues [1,4,9]. to mitigate environmental impacts of dumping in sea waters, london convention 1972 (annex iii) issued eight general criteria on characteristics of dumping sites, dumped materials and potentially impacted ecosystems to determine dumping area and sites. following these general criteria, some nations have developed their adapted criteria. for example, the united states in 1992 issued ocean dumping *corresponding author: tran dinh lan, institute of marine environment and resources/vast; graduate university of science and technology; email: lantd@imer.vast.vn 20 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 act with detail regulations on management, dumping materials and conditions, and criteria for disposal sites [2]. australia [14] and ireland issued sea dumping acts with their specific criteria for dumping sites . vietnam recently mentioned a marine dumping regulation in the law on resources and environment of seas and islands. hai phong sea ports designed by the government of vietnam as the main gate and taking an important role for socio-economic development in north vietnam are located close to the high ecological conservation areas of cat ba biosphere reserve listed by mab (man and the biosphere)/unesco (2004) and ha long bay natural heritage recognized by unesco (1994), and next to the famous touristic area of do son that remarkably contributes to economic growth of hai phong. the channels of hai phong sea ports are also considered as the main route for the development of the maritime industry in north vietnam. however, these channels are in sedimentation and dredged every year. according to the northern maritime safety corporation of vietnam, the needs of sandy and muddy dredging annually to maintain the channels are up to 2.5-3 million tons with minimum cost estimated around 40-50 billion vnd (vietnamese currency). recently, hai phong sea ports have been expanded seaward with the construction of a new harbor namely lach huyen international gateway port that will be able to receive ships of 100,000 dwt (dead weight tonnage). it is obvious that the development of hai phong ports needs to dredge a huge amount of sediments for construction stage and shipping channel maintenance annually. however, a serious raising problem is where to dispose the dredged materials, while all selected sites inland and in coastal areas are in over capacity. to tackle the problem, some sites in offshore waters were proposed but minimal environmental impacts when disposal of dredged materials, especially on the areas of high ecological values as cat ba biosphere reserve and ha long bay heritage. this study is based on multiple criteria overlay analysis using geographic information system (gis) to zone areas suitable for disposing dredged materials to meet the goal of sustainable management of sea port area. 2. materials and methods 2.1 study area the study area is in hai phong coastal zone bordering with the districts of hai an, do son and kien thuy in the north, cat hai district (with cat ba biosphere reserve and close to ha long bay natural heritage) in the east, the gulf of tonkin in the south and the west. there are six large rivers discharging in the study area (figure 1), being strongly influenced by the rainy season and dominated by tide with the highest amplitude over 4m. seabed is fairly flat with a depth up to 30m. the area is affected by waves with their height of 0.5 to 0.9m average, reaching a maximum of 5.6m and the direction changes seasonally. surface sediments on sea bottom are mainly small grey-brown and greenish-grey silt [15]. figure 1. study area and survey stations source: project dt.mt.2015.721 surrounding the study area, the ports and maritime activities of hai phong have been developed in bach dang and cam estuaries and recently expanded seaward to construct new international port of lach huyen associated with the economic zone of dinh vu cat hai. the total goods throughput of hai phong ports was increased by 25 times for 32 years, 50.1 million tons in 2012 compared to 2 million tons in 1980. from 2000 to 2013, the number of ships entering the port increased by 1.5 times. the growth rate of goods through the ports reached 15-20% per year. as such, the amount of dredged materials in hai phong seaport area also ranged from 650 m3 to 2000 m3 (20112016) (table 1). hai phong shipping channel system includes 8 sections of total 91.4km long with four main channels of 43km (lach huyen, ha nam, bach dang, song cam). all the channels have been in heavy sedimentation. in addition to economic concerning activities, do son marine tourist area visited by millions tourists annually is located in the northwest. marine fishing that greatly contributes to the hai phong gross domestic production takes place in three major fishing grounds as cat ba, coastal thai binh estuary to quang ninh and offshore long chau ba lat [7]. aquaculture with large potential areas stretches from cat hai, tien lang, kien thuy, do son, duong kinh doi: https://doi.org/10.36956/sms.v1i2.141 21 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 and hai an. over the past ten years, the area of brackish aquaculture ponds annually has expanded slightly, while the area of marine culture, including intertidal culture (clams, etc.) and cage culture tends to highly increase, especially in cat hai district. in east and southeast study area is the cat ba island conservation with cat ba national park and cat ba biosphere reserve including four marine ecosystems of mangroves, tidal flats, corals, and soft bottom. in which, coral ecosystem with a total of 177 species is limitedly distributed in southeast cat ba islands and long chau islands, relatively far from the area with marine activity. mangrove ecosystems with a total of 31 species, spread out nearly 18 thousand hectares, mainly in the coastal communes of phu long, cat hai, bang la and the river mouths of bach dang, cam, lach tray, van uc, thai binh. it is quite diverse in species of the ecosystem [15]. tidal flat ecosystem is spatially distributed along the coast of the islands and tidal zones from cat ba to thai binh estuary. it is diverse in species but distributed uneven and highly dependent on bottom materials (sand, gravel, reef and mud, sandy mud) [15]. of the ecosystem, benthic communities with 340 species belonging to 186 genera, 84 families have been recorded. the ecosystem of soft bottom (including water mass) is largest but less biologically diverse than others. about 400 species and subspecies of phytoplankton, 131 species of zooplankton, 196 species of marine fish have been found. the biodiversity index (h’) of the soft bottom ecosystem ranged from 0 (zero) to 2.72, averaging 1.72, indicating a low bio-diversity in the area. 2.2 materials data on natural condition, marine environment and ecosystems were mainly resulted from the hai phong city-level project “study on scientific basics for planning dredged material disposal sites in the hai phong coastal area” coded dt-mt.2015.721 in the period 20152017 and the vast project coded khcbbi.01/18-20 implemented in 2018-2020. gis layers on natural condition were referred to the simulation outcomes using litho-hydrodynamic numerical modeling recently [17]. socioeconomic data and documents were collected from statistic books of hai phong city, socio-economic annual reports of the city (including land use maps) and the project reports of lach huyen international gateway port. besides, data and information were also contributed by interviews of relevant agencies as hai phong maritime administration, hai phong department of natural resources and environment, local authorities of coastal and island districts. 2.3 methods z o n i n g d r e d g e d m a t e r i a l d i s p o s a l t o m i n i m i z e environmental impacts for port and maritime sustainable management will follow the approach of sustainable development. in overall, multi-criteria overlay analysis (mcoa) on gis platform (arcgis 10.1) is the main method to employ to zone disposing dredged materials from ports and shipping channels in hai phong. to do this mcoa, a database of a 1/50,000 base map and gis layers of natural condition, environment and ecosystem, and socioeconomics was established based on data collected from the projects and other books, reports. after making the layers in gis platform, they were assigned with weights aggregated from delphi analysis and then overlaid to get results of zoning maps (figure 2). table 1. the mass of sediment dredging for maintenance and construction of seaport channels in hai phong during 2011-2016 the mass 2011 2012 2013 2014 2015 2016 dredging for maintenance and construction of jetties (m3) 840.000 645.000 875.500 797.320 798.800 300.700 dredging for maintenance of hai phong channels (m3) 985.884 1.262.000 679.984 1.022.299 1.112.419 119.699 dredging for maintenance of pha rung channel (m3) 164.634 99.727 51.849 57.297 60.104 221.561 total (m3) 1.990.518 2.006.727 1.607.333 1.876.916 1.971.323 641.960 source: project đt.mt.2015.721 doi: https://doi.org/10.36956/sms.v1i2.141 22 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 figure 2. multi-criteria gis overlay analysis for zoning marine area of dredged material disposal note: data on environmental and ecological characteristics was collected in sampling and observing stations at three layers (surface, middle and bottom) of water columns covering the whole study area (figure 1) for two seasons (dry and rainy) in 2015-2017 and 2018-2019 supplementation. sampling and analyzing environmental and ecological parameters followed the methods issued in the national regulations of the ministry of natural resources and environment of vietnam (monre) [10],[11]. data on the characteristics of marine and coastal ecosystems were gathered via surveys employing published professional methods [8]. relevant data on socioeconomics were selected from related year books and reports and put in sheets of microsoft office excel 2007. after that, collected data were managed in the gis database. development of criteria: following three poles (social, economic and environmental) of sustainable development a p p r o a c h , t h r e e r e l e v a n t c r i t e r i a ( e n v i r o n m e n t a l , social and economic) were established. based on its characteristics, each was detailed into sub-criteria with specific values. the values were determined by reference to some similar studies and the analysis of relevant current status characteristics of the study area done by the projects dt-mt.2015.721 and khcbbi.01/18-20. making gis layers and weight assignment: based on 1/50,000 base map of the study area, collected data divided into three groups of environment (including natural condition and ecological features) and socioeconomics were input in gis software to produce thematic normalized layers. data on the environment were used in gis platform to develop spatial thematic layers, including: litho-hydrodynamic layers (currents and accretion-erosion) that were referred to previous study[17] , bathymetry layer, layers of protected areas and coastal ecosystems, and benthic distribution layers. data on socio-economics were employed for developing spatial thematic layers on shipping channels, residential areas and tourist sites. each gis thematic layer was attributed with sub-criterion values. to assign weights to the layers and their criteria and attributes (weight assignment as follows: 1low, 2 medium, 3high), the delphi method [6] was applied with 35 expert respondents. the weight was determined through a comparative evaluation of attribute pairs of the relevant factors regarding the likelihood suitability of pixels. the evaluation process of weight determination was performed according to saaty matrix [12]. the importance of input layers and their attributes was determined by applying a 9-point saaty pair matrix. spatial analysis for zoning of disposal areas: multicriteria analytical gis overlay was the integration of the normalized layers on the suitability levels for dredging materials and weighted overlaying. the overlaying model (figure 2) resulted in a new layer showing the suitability for disposing with suitable values in the range 0-1. the zone with values close to 1 (one) would meet all conditions of natural characteristics, socio-economics and environment and ecology, being the most suitable for minimal impact dumping dredged materials, and vice versa, the zones with values closer to 0 (zero) would not match. 3. results and discussions 3.1 potential environment impacts of disposing dredged materials in hai phong port waters on environmental quality of hai phong port area, all monitoring parameters of front waters required by the government of vietnam have met national technical regulations although in some ports, water has been locally polluted by oil (according to the project dtmt.2015.721). dredged material dumping in the coastal waters of hai phong ports would have potentially environmental and ecological impacts. one of the obvious and foreseeable direct impacts is the impact on the benthic fauna at the dumping sites, changing or destroying the benthic fauna and flora at the sites, although in this area the benthic doi: https://doi.org/10.36956/sms.v1i2.141 23 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 fauna and flora are quite poor. the impacts on water and sediment environment quality and socio-economics are also difficult to avoid. these key impacts are summarized as follows. impacts of increasing water turbidity at disposal sites and surrounding areas: when dumping dredged materials (composed of over 80% muddy clay according to the project dt-mt.2015.721) marine water at the sites and surrounding areas will be increasingly turbid. the increasing of water turbidity potentially impacts on benthos at the sites and adjacent ecosystems, tourist beaches, aquaculture and nursery grounds, fisheries. besides, the dumping for years can have cumulative environment impacts of sedimentary pollutants that meet at present national technical regulations. impacts of dumping dredged materials on socioeconomics are much related to increasing cost of material transport from dredging sites to disposal sites. to minimize the impacts on valuable ecosystems in the conservation areas of cat ba biosphere reserve and ha long bay natural heritage, the dumping zones and sites must be far enough from the dredging sites. this makes transport cost increased (cost of vnd 8,424 for 1 cubic meter of dredged materials per 1 km maritime transport according to hai phong people committee decision). besides, increasing shipping density in shipping channels in the port areas will make the increase of maritime incidents. 3.2 development of criteria three criteria were identified according to the principles of sustainable use of natural resources and environmental protection, including economic, environmental and social criteria. the combination of economics and society generated a socio-economic criteria. these criteria were developed and then consulted with experts, scientists, managers, within the framework of the project dt.mt.2015.721 and khcbbi.01/18-20 (table 2). 3.2.1 environmental criteria to develop the criteria, the following basic issues were taken into account: natural condition (two first criteria), environmental issues and ecological features: criterion of seafloor topography (bathymetry): the dumping area should be located in a region stable, minor affected by currents and waves, and no sedimentation. this was to prevent dumping materials from diffusing back the water environment. criterion of litho-hydrodynamics: this included the parameters of currents, waves, sediment transportation and changes in bottom topography. changes in bottom topography is normally resulted from litho-hydrodynamic conditions of the area [17]. these results showed that the suitable dumping site was placed with the smallest topographic changes under all meteorological conditions, including monsoons and typhoons. the hydrodynamic criteria were quantified digitally as an input to the gis multi-criteria overlay analysis. criterion of dispersing suspended sediment: for suspended matter from the dumping sites not affecting the sensitive areas of ecology and socio-economics of hai phong as cat ba islands, long chau islands, do son beaches, the dumping sites should be located in the zones as far as possible from those islands and beaches. however, this criterion was difficult to be quantitative. as such, a numerical model simulation on the influence of suspended matter to the surrounding sea was referred [17]. criteria of distances to marine ecosystems and marine conservation areas (corals, sea grass, mangroves and other tidal wetlands): the simulation results of suspended matter dispersion [17] and some works [3] indicated that the ecosystems, marine conservation areas could be impacted by dredged materials at the dumping sites within 5km distance. therefore, dumping in the zones in a distance of 5-10km (and farther) from the ecosystems and the conservation areas was relatively safe. criterion of benthic distribution: a biodiversity index (h’) was used to set up a criterion for benthic distribution. based on the classification of bio-diversity index for environmental quality, the areas with h’<1 (less biodiversity) indicating bad environment were suitable for dredged material dumping (not much impacting on benthos and the environment). the areas with h’ ranged from 1-3 were relatively suitable for the dumping. whereas, the areas with h’ greater than 3 were not suitable for dumping. criteria for distribution of fishing grounds and nursery grounds: fishing and nursery grounds are negatively impacted by pollutant dispersion in sea water. in the area, pollutants from dredged materials could seriously impact on the grounds within a distance of less than or equal to 5km from the dumping zones [17]. therefore, a distance of 5-10 km and the farther could be relevant to dumping areas. doi: https://doi.org/10.36956/sms.v1i2.141 24 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 table 2. combination of criteria system used for determining the suitable dumping sites criteria sub-criteria attributes data sources natural condition and environment bottom depth <6m topographic map, nautical chart (base maps) 6-20m 20-30m >30m litho-hydro dynamics erosion numerical model [11]sedimentation marine ecosystems (corals, sea grasses, mangroves, beaches, tidal flats, underwater soft bottom) <5,000m project research results 5,000-10,000m >10,000m distribution of benthos h’<1 project research results 1<h’<3 h’>3 socioeconomics distance to residential areas, touristic sites (beaches) <5,000m administrative maps (base maps) 5,000-10,000m >10,000m distance to shipping channels <5,000m nautical charts (base maps) 5,000-10,000m >10,000m distance to aquaculture area <5,000m land use maps5,000-10,000m >10,000m distance to conservation areas, underwater planned structures and facilities <5,000m land use maps 5,000-10,000m >10,000m source: project đt.mt.2015.721 3.2.2 social-economic criteria to minimize the impacts of dredged material disposal on the city socio-economic development, the dumping area should be: (1) far away from residential areas and coastal tourist areas; (2) not on areas to be planned for underwater structures such as optical fiber systems, electrical cables, power lines, gas pipes, sewage pipes; (3) certain safe distance from the shipping channels to prevent dredged materials from their re-settlement on the channels. criterion of coastal residential areas: residential areas would be directly affected by dumping and the most concern when conducting any socio-economic development activity. the environmental impacts of dredged material dumping must be minimum in these areas. this means dumping areas should be as far as possible. a distance of at least 10km [3] was taken for the criterion. tourist beach criterion: beaches in tourism use include do son, cat co 1, 2, 3, cat dua, van boi and tung thu (cat ba islands). the environmental impacts of the dredging materials from dumping areas on beaches must be minimal. this means dumping areas should be as far as possible. a distance of at least 10km [3] was taken for the criterion. criterion of aquaculture area: dredged material dumping might negatively impact on aquaculture area adjacent to disposal sites, decreasing aquaculture productivity and yield. a distance of 5km and farther from the disposal sites [17] should be kept. criteria of socio-economic development planning (underwater planned structures and facilities): the dumping area cannot be in an area that already exists or is planned for underground infrastructure such as fiber optic cable, electric cable, gas pipeline, wastewater pipe ... in terms of economics, the distance from dumping area to dredging site is a major concern. disposal sites closed to dredging areas are more convenient and economical for dredged material transportation. furthermore, the transport of dredged materials to dumping sites will generate more emissions, noises and busier shipping. therefore, it is not only of saving the cost of transporting but also of environmental protection and maritime safety. according to the project dt.mt.2015.721 and other works [3], the suitable distance of 10km from the dumping site should be taken into account. 3.3 zoning dredged material disposal to minimize environmental impacts 3.3.1 weight assignment weight assignment was made for criteria, sub-criteria and their attributes. the 9-point pair matrix resulted in the values of the criteria, sub-criteria and attributes (tables 3,4,5). table 3. importance of criteria in dumping site selection no. criteria weight 1 natural condition 0.36 2 environment 0.33 3 socio-economics 0.31 table 3 presents three key criteria that were weighted in the total weight being 1 (one). among the three criteria, the criteria of natural condition was most important, followed by the environmental criteria and the socioeconomic criteria. weighting detail criteria (sub-criteria) was done in the same way as for the three key criteria. of the natural condition, the sub-criterion of lithohydrodynamic was more important than the remain one. similarly, the sub-criterion of ecosystems and the doi: https://doi.org/10.36956/sms.v1i2.141 25 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 distance to conservation area were more weighted than others (table 4). the weights of attributes (table 5) show the more importance of farther distances from impacted objects (shipping channels, aquaculture areas, conservation areas, residential areas, etc.). for benthos, the bottom area with h’ less than 1 was the most suitable for dumping. table 4. the weights of the sub-criteria criteria sub-criteria weight natural condition bottom depth (m) 0.4 litho-hydrodynamics 0,6 environment ecosystems 0.65 distribution of benthos 0.35 socio-economics distance to conservation areas (m) 0.39 distance to residential areas, touristic spots (m) 0.30 distance to shipping channels (m) 0.15 distance to aquaculture area (m) 0.16 table 5. the weights of the attributes of each subcriterion sub-criteria attributes weight bottom depth <6m 0.0445 6 < 20m 0.1034 20 < 30m 0.2646 ≥30m 0.5874 litho-hydrodynamics accretion 0.9000 erosion 0.1000 distance to residential areas, tourist sites <5,000m 0.0581 5,000-10,000m 0.2067 >10,000m 0.7352 distance to shipping channels <5,000m 0.0581 5,000-10,000m 0.2067 >10,000m 0.7352 distance to aquaculture area <5,000m 0.0581 5,000-10,000m 0.2067 >10,000m 0.7352 distance to conservation areas <5,000m 0.0581 5,000-10,000m 0.2067 >10,000m 0.7352 ecosystems (beaches, mangroves, corals and tidal wetlands) <5,000m 0.0581 5,000-10,000m 0.2067 >10,000m 0.7352 distribution of benthos h’ <1 0.7352 1<h’<3 0.2067 h>3 0.0581 3.3.2 zoning dredged material disposal zoning of suitable dumping area was performed through a weighted overlay of thematic layers of the criteria in arc gis 10.1.the gis thematic layer of environmental criteria included four sub-layers of bottom depth, lithohydrodynamics, ecosystems and benthic distribution. the gis thematic layer of socio-economics was composed of four sub-layers of distance to residential areas, tourist sites, distance to shipping channels, distance to aquaculture area and distance to conservation areas. gis thematic sub-layers of criteria with their weighted attributes were built in gis database and then overlaid following multi-criteria gis overlay analysis model (figure 2). a new layer outcome showed one zone (green) at the range of above 0.5 to 0.65, being highly suitable for the dumping and the another zone (red and yellow) of under 0.5, being low suitable or not matching criteria for the dumping. also, from the outcome of the mcoa (figure 3), it shows that deep-sea areas (below 15m deep to the deeper), offshore to the south, southwest have a higher suitability (values above 0.5) than other zones. figure 3. zones of suitability for dredged material dumping 3.4 discussions considering that being dredged from the shipping channels in hai phong, the environmental quality of dredged materials meeting the permissible limits issued by the ministry of natural resources and environment of vietnam, the effects of turbidity and sedimentation by the dredged material dumping in coastal waters of hai phong ports are accepted when the dumping takes place in the highly suitable zone. the dispersion and sedimentation doi: https://doi.org/10.36956/sms.v1i2.141 26 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 of dredged materials dumped into coastal waters can generally degrade marine and coastal ecosystems, pollute the waters used for economic activities such as tourism, aquaculture and fishing ... therefore, the environmental impacts from disposal sites in the zone, when put into operation, will be focused on turbidity. some recent studies in the study area found the existence of the maximum turbidity zone of the cam river bach dang estuary (emt) with the maximum turbidity concentrated in the area of the saline intrusion and decreasing when salinity increases (1-15%o) [18], and could be spatially distributed up to 15km seaward from the coast during the low tide in the rainy season [18]. thus, the area suitable for dumping is outside of the maximum turbidity zone and in the area with the sedimentation rate reaching about 10-20mm/ year [17]. it can be seen that the dredged material dumping at sites in this zone is quite suitable for the development trend of the bottom topography as well as ecological and environmental. the results of the 3-dimensional numerical model (3d) of the project dt.mt.2015.721 [3] also showed that, in the rainy and dry seasons, the turbid area from the depth below 15m to 25m for dumping would be expected to have a minor impact on the coastal area of cat ba islands in sea bad conditions that occur during the s, sw directional waves. the predicted cases with other wind and wave directions hardly affect the coastal areas of cat ba-long chau islands, cat hai coastal areas and do son beaches. thus, the turbid waters caused by the dredged material disposals in the area are suitable because dredged material dispersion is only in a narrow range due to the diversion of the tidal currents. this turbid area in some cases has a minor impact on the coastal waters of cat ba with the concentration of suspended sediment increasing below 10mg/l in the bottom layer, not significantly in the upper layers. the proposed appropriate zone for dredged material dumping will meet the increasingly urgent need of hai phong city. however, this area is located quite far from the dredging areas. this can increase the cost of transporting dredged materials from the dredging area to dumping sites. transportation cost incurred for 1m3 of dredged materials per 1km is estimated at vnd 8,424 this price applies to the transportation distance from km 6 onwards. although this increases the cost of channel dredging, it may still be much lower than the environmental costs and losses incurring if dumping closer to shore. therefore, it is not possible to place disposal sites closer as it may cause unpredictable impacts, especially impacts on the cat ba biosphere reserve and the coral areas surrounding long chau island. 4. conclusions eight sub-criteria of sustainable development criteria of socio-economics and the environment developed and weighted included bottom depth, litho-hydrodynamics, ecosystems, distribution of benthos, distance to residential areas and tourist sites, distance to aquaculture area, distance to ecosystems and distance to conservation areas. these sub-criteria were developed in gis platform and then analyzed using multi-criteria gis overlay model. the analysis results show that the zone below 15m deep, to the south and southwest is highly suitable than others for dredged material disposing. in the zone, the factors of topographical depth, low biodiversity, medium to relatively high sedimentation rate, minor negative impacts on important ecosystems meet criteria for sustainable management of coastal area of hai phong. the dumping of the dredged materials offshore in this zone may incur costs for the maintenance and dredging of shipping channels in hai phong. this issue requires further research in costs benefits with the integration of environmental ecological factors to ensure rational use of resources and environmental protection in coastal areas. acknowledgement the authors gratefully acknowledge the support of the project coded dt-mt.2015.721, the vast project "study on scientific basics to develop indices for sustainable use assessment of tourist beaches in north coastal vietnam", coded khcbbi-01/18-20 and the vast scientific research support coded nvcc 23.03/20-20. references [1] chih-feng chen, chiu-wen chen, chih-ming kao, cheng-di dong. impact of disposal of dredged material on sediment quality in the kaohsiung ocean dredged material disposal site, taiwan. chemosphere, 2018, 191: 555-565. [2] claudia copeland. ocean dumping act: a summary of the law. congressional research service 7-5700, rs20028, 2016. www.crs.gov . [3] duy vinh v., ouillon s. van uu d. estuarine turbidity maxima and variations of aggregate parameters in the cam-nam trieu estuary, north vietnam, in early wet season. water, 2018, 10(68). [4] environment and climate change canada. canadian environmental sustainability indicators: monitoring disposal at sea. consulted on month day, year, 2017. available at: www.canada.ca/en/environment-climate-change/services/environmental-indicators/monitoring-disposdoi: https://doi.org/10.36956/sms.v1i2.141 27 sustainable marine structures | volume 01 | issue 02 | july 2019 distributed under creative commons license 4.0 al-at-sea.html [5] gi hoon hong, suk hyun kim, burton c suedel joan u clarke and jongbum kim, 2009. a decision-analysis approach for contaminated dredged material management in south korea. integrated environmental assessment and management, 2009, 6(1): 72-82. [6] harold a. limestone, murray turnoff (edt.). the delphi method techniques and applications. portland state university and new jersey institute of technology, 2002: 618. [7] imtiaz ahmed chandio, abd nasir b. matori, khamaruzaman b. wanyusof, mir aftab hussain talpur, abdul-lateef balogun, damo umar lawal. gis-based analytic hierarchy process as a multi-criteria decision analysis instrument: a review. arab j geosci,2013, 6: 3059-3066. [8] kalo pakoa, kim friedman, bradley moore, emmanuel tardy and ian bertram. assessing tropical marine invertebrates: a manual for pacific island resource managers. secretariat of the pacific community headquarters noumea, new caledonia, 2014: 118. [9] mccook, l.j., schaffelke, b., apte, s.c., brinkman, r., brodie, j., erftemeijer, p., eyre, b., hoogerwerf, f., irvine, i., jones, r., king, b., marsh, h., masini, r., morton, r., pitcher, r., rasheed, m., sheaves, m., symonds, a., warne, m.st.j. synthesis of current knowledge of the biophysical impacts of dredging and disposal on the great barrier reef: report of an independent panel of experts. great barrier reef marine park authority, townsville, 2015. [10] ministry of natural resources and environment (vietnam). national technical regulations for marine water quality (qcvn 10-mt:2015/btnmt), 2015. [11] ministry of natural resources and environment (vietnam). national technical regulations for sediment quality (qcvn 43-mt:2017/btnmt), 2017. [12] saaty, t.l. decision making with the analytic hierarchy process. int j serv sci., 2008, 1(1): 83-98. [13] sabine elisabeth apitz. waste or resource? classifying and scoring dredged material management strategies in terms of the waste hierarchy. j. soils sediments, 2010, 10: 1657-1668. [14] samantha paredes, sean pascoe, louisa coglan, sarah jennings, satoshi yamazakic and james innesa. at-sea dumping of dredge spoil: an overview of the australian policy and legislative framework. australasian journal of environmental management, 2017, 24(2): 184-199. [15] tran duc thanh (ed.), bui quang san, nguyen van can, tran dinh lan, nguyen van quan, luu van dieu, nguyen thi thu, tran anh tu, nguyen thi kim anh, 2015. nature and environment on the coast of hai phong. publishing house of natural sciences and technology, hanoi, 2015: 310. (in vietnamese). [16] u.s army corps of engineers, 2017. preliminary assessment dredged material management plan for san juan harbor puerto rico. san juan harbor puerto rico navigation project, 2017: 21. [17] vu duy vinh, tran dinh lan. impact of the wave climate conditions on sediment transport and morphological change in the hai phong coastal area. j. marine science and technology, 2018, 18(1): 10-28. doi: 10.15625/1859-3097/14/2/4475 [18] vu duy vinh, tran duc thanh. application of the numerical model to study on maximum turbidity zones in bach dang estuary. journal of marine science and technology, 2012, 3: 1-12. doi: https://doi.org/10.36956/sms.v1i2.141 35 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v2i1.306 sustainable marine structures http://ojs.nassg.org/index.php/sms article bibliometric study applied to the overtopping wave energy converter device maycon da silveira paiva leonardo da silva silveira liércio andré isoldi bianca neves machado* federal university of rio grande and federal university of rio grande do sul, brazil. article info abstract article history received: 30 december 2020 accepted: 24 january 2021 published online: 31 january 2021 the present study aims to analyze the state of the art of scientific studies about the overtopping device used to convert sea wave energy into electrical energy, by means the bibliometric methodology. the development of this study took place through the selection of articles from conference proceedings, as well as national and international journals. the bibliometric methodology consists of a statistical tool that allows quantifying the measurement of production indexes. using selected keywords, it was conducted a survey of studies in the online databases of science direct, scielo and google scholar. the works found then went through a filtering process, in order to limit the bibliometric study only to studies about overtopping devices as sea wave energy converter (wec). finally, the investigation of these selected articles was carried out under the optics of production and authorship study, content study and study of bibliographic references. where it was identified growth in publications related to the topic, methodologies used and, among other indicators, the authors most cited in the analyzed articles. the predominant keywords used were “wave energy converter” and “overtopping”. it was noted that brazilian universities are leaders in the productivity, presenting more than 36% of the scientific production regarding overtopping wecs. keywords: bibliometry overtopping device wave energy converter state of the art 1. introduction due to the global energy demand and the growing concern to reduce greenhouse gas emissions, the interest in research for renewable sources of energy has intensified. however, renewable does not mean clean, brazil for example has an energy matrix based on renewable sources, around 83% of the produced electricity according to empresa de pesquisa energética (epe)a, still most of this energy originates from hydroelectric plants, which are also responsible for the emission of methane and dioxide of carbon. as stated by [1], the emission of greenhouse gases caused by hydroelectric plants are comparable with the emission carried out by thermoelectric plants. the authors still estimate that in certain cases the emission from hydroelectric plants is higher than some thermoelectric ahttps://www.epe.gov.br/pt/abcdenergia/matriz-energetica-e-eletrica *corresponding author: bianca neves machado, federal university of rio grande do sul brazil; email: bianca.machado@ufrgs.br 36 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 plants. according to [2], the ocean represents one of the largest renewable resources present on the planet, containing energy available in different forms, which can be used to generate electricity. in conjunction with that, [3] states that the ocean contains the potential to supply a significant part of the electric energy global need through the utilization of the energy provided by the sea waves. as [4] points out, oceanic waves represent mechanical energy in transition resulting from the sum of the kinetic and surface wave potentials. it is possible to transform such energy into electrical energy through the use of wave energy converters (wecs). these devices allow an alternative way to obtain energy from clean and renewable sources. thus, the use of renewable energy sources provides environmental gains, opening up space for technological development and the production of new knowledge on the energy field [5]. conforming [6], wave energy conversion has become a growing field in the renewable energy sector, since in recent decades both scientific and industrial communities have shown interest in wave energy. in order to improve research related to the extraction of sea wave energy, the present research seeks to survey the state of the art of the one specific wec type, the overtopping device. therefore, the present study is carried out through the methodological perspective of bibliometry, applied to studies of production and authorship, content and bibliographic references of articles selected from national and international conference proceedings and journals available in online databases. therefore, this study can assist researchers in making decisions to implement new research, in addition to identifying studies already carried out that may come to serve as a theoretical reference in future researches. 1.1 wave energy converter classifications after decades of research and development regarding the wave energy extraction technologies, there are different proposed wec devices. according to [7], the usual method of classifying the wecs is based upon their main operating principle, but it is also possible to add another qualifier to specify the device accordingly to their location. although there are several conversion techniques patented, the different concepts for wecs can be divided into some distinct types, established on its operating principle [8]. figure 1 illustrates the categorization approach used by international energy agency (iea)ocean energy systemsb. bhttps://www.ocean-energy-systems.org/index.php figure 1. categorization of wave energy technologies (adapted from [3]) concerning the location, according to [9] the wecs can be classified in agreement with their installation depth: onshore, when accessible by land; nearshore, installed near the coast; offshore, devices installed away from the coast. figure 2 illustrates the classification conforming to the location. it is also worth noting that each of these locations have advantages and disadvantages over the others: (1) in accordance with [10], onshore devices have immediate advantages as easier installation and maintenance, absence of large submarine cables extension and absence of complex fastening systems. (2) on the other hand, the nearshore devices are used to extract the potency directly from the wave breaking zone [11]. (3) offshore devices are located in high depth areas and thus benefit from the most energetic waves and present a lower visual impact [12]. figure 2. classification regarding the wec location (from [13]) doi: https://doi.org/10.36956/sms.v2i1.306 37 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 the target of the present study is the overtopping wec, regardless of device location. the operating principle of the overtopping wec is based on the accumulation of water in an elevated reservoir in relation to the average level of the free surface of the sea. the accumulated water, when returned to the sea, activates low-fall hydraulic turbines coupled to electrical generators of common manufacture. the accumulation of water in the elevated reservoir occurs through the incident waves that climb and exceed the top of the ramp [14-15]. figure 3 shows the operating principle of the overtopping device. figure 3. schematic representation of the overtopping operating principle (adapted from [16]) 2. methodology in the present paper, the bibliometric methodology is used to investigate the state of the art concerning the overtopping wec device, as suggested by [17], under three optics: (1) production and authorship study (aiming to demonstrate the total number of publications per year, defining the authors and educational institutions of each article, in order to identify the most prolific ones); (2) content study (where the selected articles analysis occurs in regard to the research theme, the keywords and methodologies most used in their construction); (3) study of bibliographic references (identifying of the most widely disseminated papers in the studied area). the bibliometry, according to [18], is a statistical tool that maps and generates different treatment indicators for information and knowledge management. also, [19] increase that the bibliometric study evaluates the texts of scientific production already carried out in specific areas of knowledge. the bibliometric methodology was used in this study since it is a tool for measuring scientific production. in consonance with [20], the main advantage of a bibliometric study is the standardization of procedures, facilitating the collected data measurement, unlike other research methodologies generally performed in engineering studies, such as the exhaustive search technique, for example. in addition, this methodology reveals information about the scientific productions carried out to date, the important aspects already treated and adding knowledge to new publications that seek to study subjects that have not yet been explored. regarding the infrastructure for the present study development, the resources used to accomplish the overtopping device state of art survey were computer, internet and access to online databases such as science direct, scielo (scientific electronic library online) and google scholar. in order to improve the obtained results accuracy, it was defined that the search for each keyword in the databases should be completed on the same day that it started, avoiding changes in the search results, due to the constant changes on the online databases. 3. results and discussion the presentation of the obtained results is divided into two stages: the first consists of surveying the articles that shall be analyzed, while the second part effectively consists of the bibliometric analysis of the selected articles. concerning the first stage, the keywords in portuguese to be searched in the databases were defined as: “conversor de energia das ondas”, “energia das ondas”, “galgamento”, and “design construtal”, as well as the following corresponding english words: “wave energy converter”, “wave energy”, “overtopping” and “constructal design”. moreover, the initial period of the study was not limited, i.e., all articles found in the databases for these keywords until the month of april 2019 were taken in consideration. so, table 1 shows the total of articles found by keyword investigation. table 1. total articles found by keyword keywords files files without repetitions articles conversor de energia das ondas 80 79 27 energia das ondas 186 164 130 galgamento 135 114 58 design construtal 66 61 22 wave energy converter 392 373 323 wave energy 2175 2124 2122 overtopping 314 278 268 constructal design 251 215 211 total 3599 3408 3161 doi: https://doi.org/10.36956/sms.v2i1.306 38 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 table 2. articles selected for the bibliometric investigation title index overtopping device numerical study: openfoam solution verification and evaluation of curved ramps performances [21] numerical implementation and sensitivity analysis of a wave energy converter in a time-dependent mild-slope equation model [22] development of a composite sea wall wave energy converter system [23] wave farm impact based on realistic wave-wec interaction [24] prototype overtopping breakwater for wave energy conversion at port of naples [25] wave loadings acting on innovative rubble mound breakwater for overtopping wave energy conversion [26] stability analysis of a non-conventional breakwater for wave energy conversion [27] numerical study of the effect of the relative depth on the overtopping wave energy converters according to constructal design [28] the new wave energy converter wavecat: concept and laboratory tests [29] overtopping measurements on the wave dragon nissum bredning prototype [30] numerical approach of the main physical operational principle of several wave energy converters: oscillating water column, overtopping and submerged plate [31] constructal design de um dispositivo de galgamento onshore em escala real para uma profundidade fixa [32] numerical study on overtopping performance of a multi-level breakwater for wave energy conversion [33] energia das ondas do mar: modelagem computacional de um dispositivo de galgamento [34] influence of slot width on the performance of multi-stage overtopping wave energy converters [35] simulation studies of the basic non-linear effects of wave-energy conversion by an overtopping water-column [36] prototype testing of the wave energy converter wave dragon [37] vertical distribution of wave overtopping for design of multi level overtopping based wave energy converters [38] numerical prediction for overtopping performance of owec [39] experimental study on overtopping performance of a circular ramp wave energy converter [40] experimental study on multi-level overtopping wave energy converter under regular wave conditions [41] análise numérica da geometria da rampa de um dispositivo de galgamento onshore em escala real aplicando o design construtal [42] ssg wave energy converter: design, reliability and hydraulic performance of an innovative overtopping device [43] análise numérica de um dispositivo de galgamento onshore comparando a influência de uma onda monocromática e de um espectro de ondas [44] estudo dos procedimentos numéricos para simulação de um dispositivo de galgamento [45] geometric evaluation of the main operational principle of an overtopping wave energy converter by means of constructal design [46] an approximate solution for the wave energy shadow in the lee of an array of overtopping type wave energy converters [47] numerical simulation of wave flow over the overtopping breakwater for energy conversion (obrec) device [48] wave energy device and breakwater integration: a review [49] aproveitamento da energia do mar através do espraiamento em estruturas costeiras [50] the breakwater, from wave breaker to wave catcher [51] measurements of overtopping flow time series on the wave dragon, wave energy converter [52] modelagem computacional do princípio de funcionamento de um conversor de energia das ondas do mar em energia elétrica do tipo seawave slot-cone generator (ssg) [53] the ssg wave energy converter: performance, status and recent developments [54] innovative rubble mound breakwaters for overtopping wave energy conversion [55] doi: https://doi.org/10.36956/sms.v2i1.306 39 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 as shown in table 1, after completion of the data collection process, a total of 3599 articles was obtained, 191 of which were discarded due to being repeated at least once. in a second filtering, works that consisted of dissertations, thesis, patents and reports were discarded, listing only scientific articles, due to the fact that they cover the present study scope, thus leaving 3161 files. in the next selection stage, the remaining articles were gathered in a single file folder, disregarding their keywords. where the presence of repetitions was found again and, after excluding them, the total number of articles was reduced from 3161 to 2846. finally, an analysis began in order to determine which articles presented studies about the overtopping device for energy production, thus accounting for a total of 35 documents selected for the bibliometric analysis. after the selection of articles on the interested topic, it was then decided to investigate these documents under the three optics of study proposed by [17]: production and authorship; content; bibliographic references. the full list of selected articles can be seen on table 2. 3.1 production and authorship study this analysis aims to demonstrate the total number of publications about overtopping wecs per year and also to define the authors of each article. moreover, the study seeks to identify the most prolific authors and educational institutions, ordering them according to the number of publications in the period. in order to demonstrate the temporal progression of scientific production, a histogram that condenses the publication data by year was elaborated. thus, in figure 4, it can be seen that the first article found in the databases on the generator topic was developed by [36]. the article is called “simulation studies of the basic non-linear effects of wave-energy conversion by an overtopping water-column” and aims to analyze the results of simulations of a mathematical model for this energy conversion system. it was also observed, in figure 4, that the year 2017 has the largest number of publications, which corresponds to approximately 14.3% of the total publications on the topic. furthermore, one can observe that the number of publications has grown since 2013, only decreasing in 2018. it should be noted that the mentioned period corresponds to about 70% of publications in the area. figure 4. evolution of published articles found in the databases figure 5 shows a classification of the sample regarding the number of authors per article, being possible to observe that articles produced by three to seven authors predominate (80%). on the other hand, 11.43% are written by two or one authors and 8.57% were elaborated by eight or more authors. figure 5. number of authors per article as for the authorship study of the articles, it was sought to verify the most prolific authors on the subject through an analysis that considers the largest participation in the articles sample, as indicated in table 3. it is worth mentioning that, in this sample, all authors shown in the articles are considered, regardless of their authorship position, totaling 162 authors. table 4 shows the researchers with names mentioned in at least three articles, being these authors present in 48.77% of the articles in the area. it is also noticeable that 9 authors were mentioned twice and another 65 were mentioned only once. finishing the authorship study, it is doi: https://doi.org/10.36956/sms.v2i1.306 40 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 observable in table 4 which institutions contributed most to the scientific production of the researched theme. it is worth noting that the institutions were based on the author’s affiliation as cited in the articles. table 3. the most prolific authors in the sample author articles percentage (%) elizaldo domingues dos santos 9 5.56 liércio andré isoldi 9 5.56 diego vicinanza 7 4.32 mateus das neves gomes 7 4.32 luiz alberto oliveira rocha 6 3.70 jens peter kofoed 5 3.09 marcelo moraes goulart 5 3.09 jaifer corrêa martins 4 2.47 jeferson avila souza 4 2.47 pasquali contestabile 4 2.47 zhen liu 4 2.47 bianca neves machado 3 1.85 enrico di lauro 3 1.85 gregorio iglesias 3 1.85 hongda shi 3 1.85 peter bak frigaard 3 1.85 table 4. institutions of authors of the articles institution articles percentage (%) federal university of rio grande, brazil 48 29.63 aalborg university, denmark 12 7.41 university of campania luigi vanvitelli, italy 12 7.41 federal university of rio grande do sul, brazil 11 6.79 ocean university of china, china 10 6.17 university of plymouth, england 6 3.70 out of 37 institutions that participated in this sample of articles published in conference proceedings or journals (see table 2), the first seven universities correspond to just over 61% of published articles, as can be seen in table 4. in this analysis, federal university of rio grande, aalborg university, university of campania luigi vanvitelli and federal university of rio grande do sul stand out as the institutions with the greatest production of scientific articles regarding the study of overtopping wecs. 3.2 content study as previously announced, the bibliometric study performed in this paper is composed of different optics of analysis, among them, the content study. in this stage, the content of the selected articles was investigated, carrying out an analysis about the research theme, keywords and methodologies most used in their elaboration. although the articles selected for this analysis had been filtered so only researches about overtopping wec remain, they may also present different themes. as may be seen in figure 6, there are studies that deal with the physical principle of operation of overtopping device, while others are more specific, such as studies regarding the sea-wave slot-cone generator (ssg), an overtopping device with multiple stages, or even the constructal design (a method applied for the geometric evaluation of the overtopping wecs). figure 6. articles theme in sequence, table 5 exhibits the five keywords most frequently presented in the analyzed articles, it is possible to recognize that all are presented in english and have been cited at least six times. it should also be highlighted that “wave energy converter”, “overtopping”, “wave dragon”, “numerical model” and “overtopping device” represent 31.74% of the keywords used. doi: https://doi.org/10.36956/sms.v2i1.306 41 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 table 5. keywords most present in the articles keywords articles percentage (%) wave energy converter 13 8.97 overtopping 12 8.28 wave dragon 9 6.21 numerical model 6 4.14 overtopping device 6 4.14 in addition to the keywords presented in table 5, it is worth noting that another 76 words were found, of which: 7 keywords were presented three times (2.07%); 9 keywords present in two articles each (1.38%); 60 keywords cited only once (0.69%). totaling 81 different keywords present on the 35 investigated articles. finally, concluding the content study, figure 7 shows the research methodologies used in the analyzed articles. figure 7. methodologies used in the articles among the 3 research methodologies observed in the investigated articles, the numerical study stands out as the most frequently utilized, being present at 21 articles (60%). this methodology is often used to computationally simulate the working principle of the overtopping wec aiming to evaluate its performance under particular conditions, defined by the researchers, such as distinctive geometries for the device or different wave climates. 3.3 study of bibliographic references the state of the art bibliometric investigation of the overtopping wec device proposed in this study also aims to identify the most widely disseminated papers in the area and their authors. then, there is the study of bibliographic references, which consists of the analysis of the references presented in the investigated articles. therefore, the references present in the 35 articles were analyzed, which totalize 1147 productions by 450 different authors. table 6 illustrates the 20 most cited authors, who were referenced at least nine times each, representing 34.87% of the citations in the investigated articles. note that another 430 authors are not present in the table 6. in order to illustrate the relationship among these authors and the amount of citations made to them a histogram was elaborated, which is shown in figure 8. table 6. most cited authors cited name full name citations percentage (%) kofoed, j. p. jens peter kofoed 71 6.19 vicinanza, d. diego vicinanza 51 4.45 contestabile, p. pasquale contestabile 25 2.18 margheritini, l. lucia margheritini 25 2.18 liu, z. zhen liu 24 2.09 buccino, m. mariano buccino 21 1.83 iglesias, g. gregorio iglesias 21 1.83 falcao, a. f. de o. antónio f. de oliveira falcão 20 1.74 beels, c. charlotte beels 17 1.48 bejan, a. adrian bejan 16 1.39 van der meer, j. w. jentsje w. van der meer 16 1.39 bergillos, r. j. rafael j. bergillos 12 1.05 iuppa, c. claudio iuppa 12 1.05 gomes, m das n mateus das neves gomes 11 0.96 lópez, i. iraide lópez 11 0.96 takahashi, s. shigeo takahashi 10 0.87 tedd, j. james tedd 10 0.87 goda, y. yoshimi goda 9 0.78 santos, e. d. dos elizaldo domingues dos santos 9 0.78 victor, l. lander victor 9 0.78 doi: https://doi.org/10.36956/sms.v2i1.306 42 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 figure 8. relation between the citations and authors not shown in table 6 at the end of the study of bibliographic references, it is possible to highlight the papers with the greatest dissemination within the research area. therefore, table 7 presents the studies with the highest citation index within the analyzed articles. finally, after conducting a search for the most cited studies, it was inferred that only the one entitled “wave overtopping of marine structures utilization of wave energy” is not a scientific article, but a doctoral thesis [56]. 4. conclusions the present study aimed to characterize the scientific production regarding the application of overtopping devices in the conversion of wave energy into electricity. therefore, it was performed an analysis of articles available in the online databases science direct, scielo and google scholar through the bibliometric study of articles published in conference proceedings and journals, under the perspective of production and authorship study, content study and study of bibliographic references. as a result of this research, it was possible to identify the brazilian federal university of rio grande as the main content generator on the subject, followed by the danish aalborg university, the italian university of campania luigi vanvitelli and the brazilian federal university of rio grande do sul. it is notable that these brazilian universities are leaders in productivity regarding the researched topic, containing affiliated authors present in more than 36% of the scientific production related to the subject. furthermore, the most used keywords by the authors of the area were identified, being “wave energy converter” and “overtopping” the predominant ones. while, with regard to scientific research methodologies, it was found that the most used is the numerical methodology. finally, regarding bibliographic references, the danish author jens peter kofoed stands out as the most cited, as well as his work “wave overtopping of marine structures utilization table 7. most cited studies in the analyzed articles authors title [index] citations (percentage) jens peter kofoed wave overtopping of marine structures utilization of wave energy [56] 18 (4.83 %) jens peter kofoed, peter bak frigaard, erik friis-madsen, hans chr. sørensen. prototype testing of the wave energy converter wave dragon [37] 17 (4.56 %) lucia margheritini, diego vicinanza, peter bak frigaard. ssg wave energy converter: design, reliability and hydraulic performance of an innovative overtopping device [43] 15 (4.02 %) antónio f. de oliveira falcão wave energy utilization: a review of the technologies [57] 11 (2.95 %) charlotte beels, peter troch, kenneth de visch, jens peter kofoed, griet de backe. application of time-dependent mild slope equations for the simulation of wake effects in the lee of a farm of wave dragon wave energy [58] 11 (2.95 %) doi: https://doi.org/10.36956/sms.v2i1.306 43 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 of wave energy”. given the greater accuracy of the results obtained through this statistical analysis when compared to the results coming, for example, from the exhaustive search technique, most commonly used to survey state of the art in engineering, it concludes that the bibliometric technique effectively contributed to the survey of the state of the art of the overtopping devices applied to wave energy conversion. in future works the intention is to apply the bibliometric methodology to other types of wec, for instance the oscillating water column (owc) device. acknowledgments paiva, m. s. acknowledge the conselho nacional de desenvolvimento científico e tecnológico – cnpq (edital pibic-furg) for the cientific iniciation scholarship. isoldi, l. a. and machado, b. n. thank the fundação de amparo à pesquisa do rio grande do sul (fapergs) by the financial support (edital 02/2017 pqg, process 17/2551-0001-111-2). isoldi, l. a. 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[58] beels, c., troch, p., de visch, k., kofoed, j. p., de backer, g. application of time-dependent mild slope equations for the simulation of wake effects in the lee of a farm of wave dragon wave energy, renewable energy, 2010, 35. doi: https://doi.org/10.36956/sms.v2i1.306 37 sustainable marine structures | volume 05 | issue 01 | march 2023 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2023 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). doi: http://dx.doi.org/10.36956/sms.v5i1.856 *corresponding author: haichao li, college of shipbuilding engineering, harbin engineering university, harbin, heilongjiang, 150001, china; email: lihaichao@hrbeu.edu.cn article vibration isolation characteristics of impedance-balanced ship equipment foundation under unbalanced excitation yuxuan qin yinbing wang fuzhen pang zhiqi fu haichao li* college of shipbuilding engineering, harbin engineering university, harbin, heilongjiang, 150001, china article info abstract article history received: 29 april 2023 revised: 10 june 2023 accepted: june 25 2023 published online: june 30 2023 a new type of impedance-balanced ship equipment foundation structure based on the principle of impedance balancing using a “discontinuous panel-vibration isolation liquid layer-foundation structure” is proposed to solve the problem of poor low-frequency vibration isolation of the foundation under unbalanced excitation of shipboard equipment. based on the finite element method, the influence of characteristic parameters of the foundation panel structure on its vibration reduction characteristics under unbalanced excitation is explored. the results show that the vibration isolation level of the impedance-balanced foundation is 10 db higher than the traditional foundation in the low-frequency band of 10500 hz when subjected to combined excitation of concentrated force and moment. increasing the thickness of the impedance-balanced foundation panel can enhance the isolation effect. increasing the number of sub-panels can effectively reduce the vibration response of the foundation panel and enhance the isolation performance of the foundation. the connection stiffness between sub-panels has a small effect on the isolation performance of the foundation. keywords: ship equipment foundation impedance-balanced design vibration isolation and reduction methods 1. introduction as the main structure connecting the equipment to the ship structure, the equipment foundation acts as a main medium for the transmission of vibration energy from the equipment to the outside of the ship. the impedance characteristic of the foundation is a critical parameter that characterizes the ability of the foundation structure to resist mechanical vibration. it is also the main index to reflect the vibration isolation performance of the equipment foundation [1,2]. thus, the analysis of foundation impedance is important for the vibration reduction and isolation design of the foundation structure [3,4]. to enhance the vibration isolation performance of equipment foundations, peng [5] proposed an impedance matching design method for ship foundations. this approach modifies the structural characteristic parameters and shapes of the foundation to achieve mutual matching between its impedance and that of the internal excitation http://dx.doi.org/10.36956/sms.v5i1.856 38 sustainable marine structures | volume 05 | issue 01 | march 2023 source, thereby achieving low radiation noise levels for ships. li [6] compared the vibration acceleration and underwater radiation noise of the foundation structure before and after the installation of damping materials, which provided support for the low-noise optimization design of the surface ship structure. wang et al. [7] found through research that the application of damping materials can reduce the value of equipment foundation vibration amplitude in the intermediate frequency range above 60 hz. yang et al. [8,9] proposed a unified impedance model for ship vibration reduction that comprehensively optimized the structural dynamic layout of stiffness, damping mass and damping material to enhance the vibration reduction capability of the foundation structure. ling and wu [10] used the finite element method to study the suppression effect of multi-stage isolation mass on structural sound propagation. liu et al. [11] further revealed the suppression mechanism of vibration damping mass on structural sound transmission through case analysis and experimental verification. yuan et al. [12] discussed the two indirect force estimation approaches, and experiments showed that indirect approaches could be good choices for determining the output forces of machinery in ships. chen et al. [13] established an isolation vibration system with distributed dynamic absorbers and found that it could increase the frequency range of the absorbers. ye et al. [14] combined a mathematical model of particle damping, developed a design method of particle damping optimization, solved the problem of high-frequency vibration in the power device, proposed to combine it with active control technology, and verified that it can achieve low-medium-high broadband vibration control of ship equipment. based on scaled model experiments, wu et al. [15] proposed a hysteresis nonlinear foundation structure with mrd and verified its effectiveness in low-frequency line spectrum vibration. gong et al. [16] discussed the effect of damping mass on the propagation of vibration waves in pipelines based on the impedance mismatch principle and numerical analysis methods, and the results showed that damping mass has a beneficial damping effect in the medium to high frequency range. to achieve the purpose of impedance mismatch, qi et al. [17] used a modern type of vertically symmetric foundation with low stiffness isolators and high input impedance to control the coupled vibration and noise radiation of the propeller shaft system. wang [18] proposed the combination of active or semi-active control with dynamic absorbers to reduce the vibration transmitted to the deck and hull from power equipment and piping systems. chen et al. [19] derived the expression of pressure-resistant strength of airbag isolators from the thin shell non-distance theory and verified the reliability of airbag isolators. du and li [20] investigated the nonlinear vibration mechanism of the ship rotating machinery with an airbag isolator under heaving motion. bu et al. [21] proposed a multiobjective collaborative attitude control method for double-layer airbag isolator devices under flexible support conditions. to effectively reduce the vertical and horizontal stiffness of the airbag isolator, yin et al. [22] adopted a composite airbag structure with serial hardelastic layers. li et al. [23] designed a highly adjustable magnetorheological elastomer-based isolator for real-time adaptive control, which can change the lateral stiffness of the isolator under moderate magnetic field levels. for complex mechanical systems, wu et al. [24] analyzed the quantitative relationship between the impedance of the two transmission channel systems and the isolation effect of the mechanical system and the transmission loss of the pipeline system based on the hammer test method. the experimental results show that the impedance can be increased and the isolation effect can be improved by strengthening the foundation reinforcement or changing the elastic element properties/layout of the pipeline system. ye [25] proposed a method to improve the impedance of the foundation by optimizing the structural variables of the foundation without altering the structural shape of the foundation and verifying its effectiveness. dario et al. [26] developed an isolation system to optimize the tuned mass damper inertial device, which allows the inertial instrument and damper to be installed in series, resulting in a lower mass and more effective alternative than conventional tuned mass dampers. maciejewski et al. [27] conducted numerical simulation and optimization design of a vibration isolation system. they established a mathematical model for vibration reduction and obtained an optimal method for high-efficiency vibration isolation by simulating the dynamic behavior of the system under diverse working conditions. in light of the research summarized in this review, it is apparent that improving the mechanical impedance matching or impedance mismatch by increasing the damping mass, changing the shape or material properties of the foundation structure, etc. [28], has improved the vibration reduction and isolation performance of the system. it may be necessary to increase foundation mass or decrease foundation stiffness in order to further extend the isolation frequency range of the foundation using the method to lower frequencies, but doing so could result in issues like excess foundation mass or inadequate stiffness, which are detrimental to the lightweight design of ship structures and structural safety. therefore, this paper proposes a foundation impedance-balanced method, 39 sustainable marine structures | volume 05 | issue 01 | march 2023 which uses a vibration isolation liquid layer instead of the traditional foundation support structure in the design of the foundation structure to transform the excitation force point and line transmission into surface transmission. to improve the vibration isolation performance of the foundation, the impedance of the foundation is balanced and distributed by interrupting the continuous propagation of vibration waves through the discontinuous panel structure. the vibrational isolation effect of the proposed method is calculated using the finite element method, and the effect of the device foundation panel structural parameters on the vibrational properties is investigated. 2. principles and characterization methods of impedance balancing 2.1 impedance-balanced principle assuming that the total force f and total impedance z transmitted to the foundation structure by the same equipment are constant, the equipment is connected to the foundation structure through machine feet. the equipment excitation is transmitted only through the foot of the machine to the foundation structure. if the number of machine feet is n, the force transmitted to the foundation through the k-th machine foot is f k, and the input impedance at the k-th machine foot is zk, so we have: 1 1 1 , 1 n n n k k k k k k f f x f x = = = = = =∑ ∑ ∑ (1) 1 1 1 , 1 n n n k k k k k k z z y z y = = = = = =∑ ∑ ∑ (2) where kk f x f = , kk z y z = , the total power flowing into the foundation is p. 2 1 1 n n k k k k k f p p z= = = =∑ ∑ (3) from equations (1)-(3), it can be concluded that: 2 2 1 n k k k x f p y z=   =     ∑ (4) when k kx y= , the system can obtain the minimum input power, that is, when the force/impedance distribution of the foundation is balanced, the energy transmitted from the equipment to the foundation is the lowest. figure 1 compares the vibration response of the foundation structure under different loading modes. it can be seen that when the excitation force is the same, the vibrational response of the base structure is weaker when the force is uniformly distributed over the surface compared to the case of concentrated point force loading. therefore, if the unbalanced excitation force of the equipment can be transformed into a distributed force, the transmission of vibration energy can be effectively reduced and the vibration isolation level of the foundation can be improved. 100 200 300 400 500 20 40 60 80 100 120 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) concentrated load uniform load figure 1. comparison of average vibration acceleration levels of structures under different loading forms. 2.2 impedance-balanced characterization method this paper proposes the concept of impedancebalanced design for the foundation, which reflects the level of impedance balancing of the foundation under the current structure form through the difference of input impedance curves at several points in a certain frequency range. the specific definition is as follows. assuming that n loading points are uniformly selected on the surface of the foundation structure, each loading point has an input impedance 0 ( ) iz f at frequency f, and the standard deviation si of the n loading points on the foundation at frequency i is expressed as: 2 0 0 1 ( ) n i i i i z z s n = − = ∑ (5) 0 iz represents the average input impedance of each loading point at frequency i. in order to eliminate the effect of high or low levels of data values on the dispersion of the sample values, the dispersion coefficient is calculated, which is defined as follows: 0 i i i s v z = (6) the ratio of the standard deviation to the mean of 40 sustainable marine structures | volume 05 | issue 01 | march 2023 the data. therefore, within the [a, b] frequency band, impedance standard deviation curve r(si) and discrete coefficient curve d(vi), average the curve values at each frequency point, get foundation impedance discretization coefficient zdc, defined as: 1 m i i v zdc m == ∑ (7) where m is the number of analysis frequencies in the [a, b] frequency band. similarly, take the reciprocal of the foundation impedance discretization coefficient to obtain the foundation impedance-balanced coefficient zsc, which represents the degree of equipment foundation impedance balancing, defined as: 1 1 m i i m zsc zdc v = = = ∑ (8) 3. impedance-balanced ship equipment foundation model and vibration reduction effect 3.1 impedance-balanced ship equipment foundation model this article proposes a new type of ship equipment foundation structure with impedance-balanced, as shown in figure 2. replace the complete continuous panel with a discontinuous foundation panel, and replace the traditional support structure with a vibration isolation liquid layer, so that the surface waves transmitted to the structure surface undergo waveform conversion at the fluid solid interface, diminishing in the form of liquid surface waves, so as to balance the distribution of input impedance at various locations of the foundation panel. keeping the impedance dispersion coefficient curve of the foundation at a low level effectively reduces the vibrational response under the excitation force of the device. equipment discontinuous panelfluid-filled sac ship structure bottom plate figure 2. schematic diagram of impedance-balanced foundation structure. 3.2 fem model of impedance-balanced ship equipment foundation for complex structures such as the ship foundation, the finite element method is commonly used for numerical analysis. in order to improve the efficiency of simulation calculations, the paper proposes to use the structureacoustic coupling finite element method for analysis. the liquid is assumed to be ideal fluid and the influence of the fluid-filled sac on the isolation characteristics of the foundation is ignored. the sonic wave is a small amplitude sonic wave and there is no energy loss during the propagation process. the structure-acoustic coupling dynamic equation is expressed as follows: impedance-balanced, as shown in figure 2. replace the complete continuous panel with a discontinuous foundation panel, and replace the traditional support structure with a vibration isolation liquid layer, so that the surface waves transmitted to the structure surface undergo waveform conversion at the fluid solid interface, diminishing in the form of liquid surface waves, so as to balance the distribution of input impedance at various locations of the foundation panel. keeping the impedance dispersion coefficient curve of the foundation at a low level effectively reduces the vibrational response under the excitation force of the device. figure 2. schematic diagram of impedance-balanced foundation structure. 3.2 fem model of impedance-balanced ship equipment foundation for complex structures such as the ship foundation, the finite element method is commonly used for numerical analysis. in order to improve the efficiency of simulation calculations, the paper proposes to use structure-acoustic coupling finite element method for analysis. the liquid is assumed to be ideal fluid and the influence of the fluid-filled sac on the isolation characteristics of the foundation is ignored. the sonic wave is a small amplitude sonic wave and there is no energy loss during the propagation process. the structure-acoustic coupling dynamic equation is expressed as follows: a a a 0 0 0 0ta a m c fx x xk q q m c fpkp p                                          (9) am , ac and ak represent the mass matrix, damping matrix, and stiffness matrix of the fluid, respectively. p is the acoustic pressure vector, and ak is the load vector of the acoustic field excitation. q is the structure-acoustic coupling matrix, and  is the density of the fluid. equation (9) can be rewritten as follows utilising the modal superposition principle and the helmholtz equation:     2 2 2 a t a a a a fxk j c m q pq k j c m f                            (10) (9) am , ac and ak represent the mass matrix, damping matrix, and stiffness matrix of the fluid, respectively. p is the acoustic pressure vector, and ak is the load vector of the acoustic field excitation. q is the structure-acoustic coupling matrix, and ρ is the density of the fluid. equation (9) can be rewritten as follows utilising the modal superposition principle and the helmholtz equation: ( ) ( ) 2 2 2 a t a a a a fxk j c m q pq k j c m f ωω ω ρ ω ω ω ω   + −   =     + −        (10) where ω is the circular frequency, and j = 1, ( )f ω represents the modal load. equation (10) is the solution equation for structural vibration and radiated acoustic field based on structureacoustic coupling theory. by solving the above equation, the structural vibration and radiated noise under a given excitation load can be calculated. e s t a b l i s h f i n i t e e l e m e n t m o d e l s f o r t r a d i t i o n a l foundation and impedance-balanced foundation structures respectively. the computational model is shown in figure 3, where the bottom boundary condition of the foundation is fixed on all four sides. the load is applied to the foundation panel in the form of a unite excitation force. spring elements are used to connect each adjacent foundation panel. after the convergence calculation, the finite element mesh size of the structure was set as 0.005 m while the acoustic mesh size was 0.01 m. the total number of finite element meshes is about 280,000. the main structural parameters and material properties of traditional and impedance-balanced foundation are shown in table 1. the main material parameters are 41 sustainable marine structures | volume 05 | issue 01 | march 2023 shown in table 2. (a) traditional foundation structure model (b) impedance-balanced foundation structure model figure 3. schematic diagram of foundation structure. table 1. main structural parameters of traditional and impedance-balanced foundation. panel size 2.0 m × 1.6 m panel thickness 0.02 m foundation plate thickness 0.03 m web plate thickness 0.01 m total height of foundation 0.2 m liquid layer thickness 0.2 m foundation material q235 steel liquid layer material water table 2. main material parameters. material steel material water density 7850 kg/m3 density 1000 kg/m3 elastic module 2.1 × 1011 pa bulk volume 2.2 × 109 pa poisson ratio 0.3 3.3 impedance-balanced foundation isolation effect as shown in figure 4, to verify the isolation effect of the impedance-balanced foundation, the concentrated force of 1 n and moment load of 1 n·m were applied at the midpoint and both sides of the panels of impedance-balanced foundation and traditional foundation respectively. the calculation and analysis frequency band was 10-500 hz. set evenly distributed assessment points on the surface of the panel and bottom plate on the foundation, and use the average vibration acceleration level of the assessment points as the evaluation standard. the calculation results are shown in figures 5-6. bracket panel bottom plate moment concentrated force observation points moment figure 4. schematic diagrams of measurement point layout and the loading situation. 100 200 300 400 500 -20 -10 0 10 20 30 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) traditional base impedance homogenized base figure 5. comparison of average vibration level difference between two types of foundations subjected to concentrated force. 100 200 300 400 500 -20 -10 0 10 20 30 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) traditional base impedance homogenized base figure 6. comparison of average vibration level difference between two types of foundations subjected to the combined action of concentrated force and moment. figures 5-6 show that the impedance-balanced foun42 sustainable marine structures | volume 05 | issue 01 | march 2023 dation performs better than the traditional foundation in the frequency range of 0-500 hz when the foundation structure is subjected to a concentrated force, with an average isolation level of 10 db higher than that of the traditional foundation. however, the isolation level of the impedance-balanced foundation in the frequency range of 0-100 hz is lower than that of the conventional foundation when the focused force and moment load are coupled to the foundation. the impedance-balanced foundation’s isolation level, which is more than 12 db higher than that of the conventional foundation in the frequency range of 100-500 hz, can reach up to 30 db at the 125 hz frequency point. therefore, it can be seen that the impedance-balanced foundation has better isolation performance in a wide frequency range. 4. analysis of the impedance-balanced foundation isolation characteristics 4.1 the influence of the structural form of the foundation panel the influence of panel thickness on the isolation characteristics of the impedance-balanced foundation based on the above structural model, analyze and calculate the impact of changes in the thickness of the foundation panel on the vibration isolation characteristics of the foundation structure. to improve computational efficiency, the above model is further simplified into a shell structure model. the thickness of the foundation panel is 10 mm, 15 mm, and 20 mm, respectively. the calculation results of the average vibration acceleration level of the lower surface of the foundation are shown in figure 7, and the difference in the foundation vibration level is shown in figure 8. 100 200 300 400 500 60 80 100 120 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) t=10mm t=15mm t=20mm figure 7. average vibration acceleration level curve of assessment points with different thicknesses of foundation panels. from figures 7-8, it can be seen that as the thickness of the foundation panel increases, the average level of the assessment points of the hull structure under the foundation decreases overall. when the thickness is greater than 15 mm, further increasing the thickness does not reduce the system’s vibration level. as the frequency gradually increases, the peak acceleration response shifts to the high frequency. this is because the increase in thickness increases the stiffness of the foundation system. by comparing the results in figure 8, it is found that, although the increase in thickness makes the foundation exhibits a stronger vibration isolation effect at most frequency points, not all frequency point positions within the analysis frequency band have increased vibration level difference, and even negative vibration level difference have been calculated at some frequency points. therefore, i n t h e d e s i g n p r o c e s s o f t h e i m p e d a n c e b a l a n c e d foundation, it is necessary to combine the excitation load characteristics of the equipment with adjusting the panel thickness. 100 200 300 400 500 -10 0 10 20 30 40 50 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) t=10mm t=15mm t=20mm figure 8. average vibration level difference curve of assessment points with different thicknesses of foundation panels. the influence of panel layout on the vibration isolation characteristics of the impedance-balanced foundation with a reasonable discussion of the foundation panel, the elastic waves in the response plane of the panel can be effectively isolated and controlled, thus effectively increasing the vibration reduction and isolation level of the foundation. to investigate the influence of panel layout on the vibration characteristics of impedancebalanced foundation, taking the four layout schemes shown in table 3 and figure 9 as examples, the vibration response of the foundation under different panel layout modes was calculated, and the calculation frequency band and loading method were the same as the previous text. 43 sustainable marine structures | volume 05 | issue 01 | march 2023 the comparison of the vibration response and vibration level difference of different schemes of the foundation is shown in figures 10-11. it can be seen that in the 10-500 hz frequency band, after disassembling the foundation panel, the vibration isolation characteristics of the foundation will change. in the 10-500 hz analysis frequency band, scheme 4 causes the lowest level of structural vibration response. in each scheme, as the number of sub-panels increases, the number of peaks in the response curve will decrease, and the curve has a tendency to shift towards high frequencies. from the vibration level difference curves of each scheme, it can be observed that scheme 1 has a higher vibration isolation effect at 10-100 hz, the average isolation level is about 10 db. table 3. size parameters of fluid-filled sac under different layout schemes of the foundation. disassembly scheme number of panels/ piece single foundation panel size/m scheme 1 2 0.90 × 1.60 scheme 2 3 0.60 × 1.60 scheme 3 4 0.90 × 0.70 scheme 4 6 0.60 × 0.70 0.9 m 1.6 mp1 p2 0.6 m 1.6 m p1 p2 p3 (a) scheme 1 (b) scheme 2 0.9 m 0.7 mp1 p2 p3 p4 0.6 m 0.7 m p1 p2 p3 p4 p5 p6 (c) scheme 3 (d) scheme 4 figure 9. schematic diagrams of different layout schemes for the foundation panel. 100 200 300 400 500 60 80 100 120 140 160 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) whole plate scheme1(1×2) scheme2(1×3) scheme3(2×2) scheme4(2×3) figure 10. average vibration acceleration level curve of the bottom plate with different layout schemes of the foundation panel. 44 sustainable marine structures | volume 05 | issue 01 | march 2023 100 200 300 400 500 -20 -10 0 10 20 30 40 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) whole plate scheme1(1×2) scheme2(1×3) scheme3(2×2) scheme4(2×3) figure 11. vibration level difference curve of assessment points with different layout schemes of foundation panels. 4.2 influence of foundation panel connection stiffness to investigate the influence of the stiffness of the foundation panel connection on the vibration reduction and isolation characteristics of the foundation, based on the foundation model of scheme iii mentioned above, the average vibration acceleration level of the foundation plate was calculated when the hinge stiffness between the foundation panels was 500 n·m2, 1000 n·m2 and 1500 n·m2, respectively. the calculation results are shown in figures 12-13. 100 200 300 400 500 40 60 80 100 120 140 160 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) k=500 k=1000 k=1500 figure 12. average vibration acceleration level curve of the foundation plate with different connection stiffness of the foundation panel. from figures12-13, it can be seen that in the frequency band of 10-500 hz, when the stiffness of the hinge connections among the panels increases, the acceleration response curves of each structure remain basically consistent, and the frequencies corresponding to the positions with larger responses in the curves remain basically unchanged. the maximum isolation level in the frequency range of 10-500 hz is 25 db. this is because the increase in the stiffness of the connections between the foundations has a limited effect on the overall natural character of the foundations. the lower the stiffness, the more pronounced the oscillation of the vibration level difference curve in the frequency band. however, as the stiffness increases, the change in the vibration level difference curve is relatively stable. 100 200 300 400 500 -10 0 10 20 30 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) k=500 k=1000 k=1500 figure 13. average vibration acceleration level difference curve of foundation panel with different connection stiffness. 4.3 the vibration isolation property of the impedancebalanced foundation subjected to white noise excitation using white noise excitation in the calculation of isolation performance is of significant importance. white noise excitation is a signal with constant average power spectral density across all frequencies. by containing components of various frequencies, the use of white noise excitation allows for a more comprehensive evaluation of the performance of the isolation system, providing a valuable reference for isolation design and optimization. therefore, this paper conducts the calculation of impedance-balanced foundation isolation performance under white noise excitation based on the aforementioned model. the calculation results are shown in figure 14. from figure 14, it can be observed that the impedancebalanced foundation isolation performance, under white noise excitation, exhibits a similar curve trend to that under unit force excitation. both show effective isolation in the frequency range of 10-150 hz, with maximum isolation of 18 db at 100 hz. however, the isolation effectiveness is weaker in the frequency range greater 45 sustainable marine structures | volume 05 | issue 01 | march 2023 than 300 hz. therefore, it can be concluded that the impedance-balanced foundation possesses favorable lowfrequency isolation performance. 100 200 300 400 500 -10 0 10 20 30 a c c e l e r a t i o n l e v e l ( d b ( r e f = 1 0 6 m / s 2 ) ) frequency (hz) figure 14. average vibration acceleration level curve of the foundation plate with different connection stiffness of the foundation panel. 5. conclusions this paper proposes a vibration reduction method based on the principle of impedance balancing and designs an impedance-balanced foundation with a “discontinuous p a n e l v i b r a t i o n i s o l a t i o n l i q u i d l a y e rf o u n d a t i o n structure”. based on the structure-acoustic coupling finite element method, the vibration reduction characteristics of the impedance-balanced foundation under unbalanced excitation of the equipment are studied, and the influence of the structural parameters of the foundation panel on its vibration reduction characteristics is explored. the main conclusions are as follows: (1) the vibration level difference of the impedancebalanced foundation is higher than that of the traditional foundation with 10 db in the low-frequency band of 10500 hz subjected to the combined action of unbalanced excitation force and moment. (2) the thickness and quantity of the panel have an influence on the isolation performance of the impedancebalanced foundation. furthermore, the impedancebalanced foundation exhibits superior vibration isolation performance within the low-frequency range of 10150 hz. when the number of sub-panels is 4 and the arrangement is 2 * 2, the isolation performance of the foundation is better among the four layout schemes considered in this paper. the effect of panel connection stiffness on the isolation performance of the foundation is not obvious. funding this study was funded by the national natural science foundation of china (grant numbers. u2006229 and 52101351) data availability statement the data used to support the findings of this study are included within the article. conflict of interest the authors declare that there is no conflict of interest. references [1] yao, y.r., zhu, sh.j., 2003. li yong pin lv xiang ying han shu qiu she bei dui ji zuo de ji li (chinese) [on determination of the exciting force of the equipment from the frequency-response function]. chuan hai gong cheng. 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marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 doi: http://dx.doi.org/10.36956/sms.v3i1.378 sustainable marine structures http://ojs.nassg.org/index.php/sms/index article application of fourth industrial revolution technologies to marine aquaculture for future food: imperatives, challenges and prospects sitti raehanah m. shaleh1　rossita shapawi1　abentin estim1　ching fui fui1　ag. asri ag. ibrahim2　audrey daning tuzan1　lim leong seng1　chen cheng ann1　alter jimat2　 burhan japar3　saleem mustafa1* 1. borneo marine research institute, universiti malaysia sabah, kota kinabalu, sabah, 88400, malaysia 2. faculty of computing and informatics, universiti malaysia sabah, kota kinabalu, sabah, 88400, malaysia 3. korporasi kemajuan perikanan dan nelayan (ko-nelayan), wisma pertanian sabah, kota kinabalu, sabah, 88994, malaysia article info abstract article history received: 25 may 2021 accepted: 28 may 2021 published online: 10 june 2021 this study was undertaken to examine the options and feasibility of deploying new technologies for transforming the aquaculture sector with the objective of increasing the production efficiency. selection of technologies to obtain the expected outcome should, obviously, be consistent with the criteria of sustainable development. there is a range of technologies being suggested for driving change in aquaculture to enhance its contribution to food security. it is necessary to highlight the complexity of issues for systems approach that can shape the course of development of aquaculture so that it can live-up to the expected fish demand by 2030 in addition to the current quantity of 82.1 million tons. some of the fourth industrial revolution (ir4.0) technologies suggested to achieve this target envisage the use of real-time monitoring, integration of a constant stream of data from connected production systems and intelligent automation in controls. this requires application of mobile devices, internet of things (iot), smart sensors, artificial intelligence (ai), big data analytics, robotics as well as augmented virtual and mixed reality. ai is receiving more attention due to many reasons. its use in aquaculture can happen in many ways, for example, in detecting and mitigating stress on the captive fish which is considered critical for the success of aquaculture. while the technology intensification in aquaculture holds a great potential but there are constraints in deploying ir4.0 tools in aquaculture. possible solutions and practical options, especially with respect to future food choices are highlighted in this paper. keywords: food security aquaculture 4.0 digitalization imitation seafood sustainable solutions 　 *corresponding author: saleem mustafa, borneo marine research institute, universiti malaysia sabah, kota kinabalu, sabah, 88400, malaysia; email: saleem@ums.edu.my 1. introduction aquaculture has grown dramatically in the past five decades, with total fish production from this sector amounting to 82.1 million tons [1]. it is widely recognized as a potential sustainable solution for food security and an answer to the need for cost-effective animal protein with low-carbon and ecological footprint. fish 23 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 doi: http://dx.doi.org/10.36956/sms.v3i1.378 demand is projected to increase in the range of 112.1114.1 million tons by 2030, requiring an additional 3032 million tons of fish [2-4]. this is a great challenge that requires a real transformation. landings from capture fisheries are unlikely to increase due to depletion of resources and impairment of ocean ecosystem [5]. aquaculture production should increase to ensure adequate supplies. aquaculture has recently surpassed the capture fisheries in production and is expected to share 62% of the food fish by 2030 [6]. the incremental research and developments have been going on and have contributed significantly to positioning of aquaculture to where it stands today. however, it is inconceivable to meet this high level of demand without transformation. because the seafood demand has outweighed production, there is a need for a fast-track approach to producing fish using disruptive innovations and technologies that hold promise for revolutionizing the aquaculture industry. fourth industrial revolution (or ir4.0) offers a range of technologies, and some can be adapted for aquaculture systems. it is appropriate to apply the term ‘aquaculture 4.0’ to aquatic farming driven by these disruptive technologies. some interesting work has appeared in this area [7-11]. when the sustainability is taking a center stage in food production, it is necessary to generate a strategic framework comprising the purpose or goals and drivers aligned with the united nations’ sustainable development goals (sdgs) to resonate with the global narrative. aquaculture 4.0 envisages more automation in selected functions, bridging the physical and digital operations through cyber-physical systems using computers for monitoring and algorithmically controlling different mechanisms and processes, and regulating the production by closed-loop data. potential areas of application of aquaculture 4.0 technologies are highlighted in this paper together with the reasons for transformation, challenges and prospects with special focus on future food choices. 2. technology intensification certain new terms such as ‘precision aquaculture’, ‘smart aquaculture’ and ‘digital farming’ are associated with technology intensification in aquaculture. these terms are often used interchangeably but there are subtle differences. precision aquaculture refers to use of digital techniques in monitoring and optimization of the culture system. this implies regulating the supply of inputs in amounts exactly needed to prevent waste, reduce cost and minimize environmental impacts. smart farming envisages application of information and data technologies in effective ways for better results. digital aquaculture combines elements of precision aquaculture and smart aquaculture to advance the technology intensification for big data analysis, use of web-based platforms and machine learning among other innovative tools. disruptive innovations and technologies of aquaculture 4.0 are believed to hold key to transforming aquaculture towards seafood security targets. a comprehensive review of the application of various technological tools, including sensors, robots, 3d prints, drones and artificial intelligence (ai) in aquaculture development has been published recently [12]. aquaculture industries, and r & d organizations are giving increasing attention to embracing modern technologies wherever feasible and affordable. it is being considered as a way of making a major turnaround in aquaculture. many disrupting solutions are aimed at achieving better output with reduced resource inputs, improved nutritional quality of the harvest, and compliance with the sustainability criteria. this will offer a fast-track approach to meeting the fish production targets through four possible ways: • greater intelligent automation of the various operations. • bridging the physical and digital world through cyber-physical systems using computers. • monitoring and algorithmically controlling different mechanisms. • regulating production steps by closed loop data. inputs for deployment of modern technologies are in the form of data collections through iot concept such as wireless network sensors and the analysis of big data with the techniques of ai. for a start, some selective technologies can be tested for their potential outcomes in terms of sustainable production. aquaculture 4.0 is closely associated with the aforementioned technology-intensive aquatic farming. fore [13] has outlined main steps in modern aquaculture systems (figure 1) that are aimed at: 1) improving the accuracy, precision and repeatability in the farming processes, 2) facilitating a greater degree of automation or inbuilt controls in regular monitoring of the farming system, 3) providing a dependable decision support system characterized by a computerized program for collecting and analyzing the data, and synthesizing information that can be used to solve the problem by computer algorithms or human intervention or both, and 4) reducing dependencies on manual labor, and subjective assessments. 24 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 observing sensors online monitoring interpretation predictive models system simulation decision making decision support system artificial intelligence action automation integrated operations figure 1. key steps in the production process. the overall objective through all these interventions is to improve productivity, resource efficiency, environmental sustainability and economic benefits. the fish stocked in cultural facilities should be able to perform and express its biological activities. these bio-responses need to be observed (step-1) and interpreted for assessment of fish condition (step-2) which will form the basis for making decisions on whether or not any interventions are needed (step-3), and enforcing actions based on the decision for expected outcomes (step-4). these steps in the production process can be assisted by appropriate technologies. a model of digital aquaculture system comprising the various tools of technology is presented in figure 2. figure 2. model of a smart aquaculture system. reproduced with permission from tetsuo and kobayashi [14]. system integration that involves connecting the various aquaculture sub-systems to function as a whole or complete unit of operation as can be seen from figure 2 is the key to success of an intelligent aquaculture [15]. among the aquaculture 4.0 technologies, ai is receiving an increasing interest. in a complex system of aquatic food production, ai deployment can happen in many ways. it requires aligning the biological data with computers and understanding how the system works for solving specific problems. basically, these procedures involve artificial neural network (ann). ann is a computational model inspired by neural network of the human nervous system. it mimics the pathways of brain function where the sense organs perceive stimuli that are transmitted through sensory nerves to the brain that decides how to respond to the stimuli and sends the information through motor nerves to the effector organs to act accordingly. this provides the foundation of ai where flow of information happens through algorithmic pathways. ann comprises nodes which in biology are termed as neurons (or nerve cells) [16]. there are multiple nodes arranged in three layers: input layer, hidden layer and output layer (figure 3). figure 3. three layers of nodes in ann. • input layer: comprises the input nodes that bring information from external environment into the network and pass it on to the hidden layer. information processing and computation are not carried out here. • hidden layer: comprises nodes that have no direct connection with the outside environment (and hence the name ‘hidden’ nodes). their role is to perform computations and to transfer the information to the output nodes. • output layer: consists of nodes that are responsible for transferring the information to the effector organs which act according to the instructions to produce the end-result or outcome. nodes from these adjacent layers have connections between them. when an input (stimulus) enters the node, it gets multiplied by a weight value [17]. weight represents the strength of the signal (or impulse) and determines how much influence the input will have on the output. weights are the real values associated with the stimulus. because all inputs (stimuli) are not equal, therefore, weight values are different. doi: http://dx.doi.org/10.36956/sms.v3i1.378 25 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 weights are applied within the nodes of the hidden layer. there is a system in the hidden layer called as an ‘activation function’ that takes the input delivered by input nodes and multiplies it by weight. hidden layer also carries out distillation or filtration of inputs (information/ stimuli). it identifies and selects only the important information from the inputs, leaving out the information that is redundant or of no major consequence. if the input (impulse) is relevant and important (higher weight) it is processed for a response. if weights are close to zero, they have lesser importance and stimuli with such weights are filtered out while those of higher weights are retained and processed for response by the fish. there is one more entity called ‘bias’ (b). bias is added to the weighted sum and fed through activation function as a constant value (=1) which is the bias unit. by adding the value ‘1’ the bias creates a non-zero y-intercept in the linear regression. this enables the ann to fit the data when all inputs are equal to zero, or in other words, to generate an output when input is zero. it allows shifting linearity to either right or left to help the model to fit the given data. diagrammatically, this pathway can be shown in figure 4. figure 4. response transmission pathway in ann. mathematical transformation of this pathway can be expressed by the equation: input (x) x weight (w) +bias (b)  output (y). each input (x) is assigned a ‘weight’ (w) value based on its relative importance to all the other inputs. transformation of input into valuable output forms the basis of mathematical constructs where the hidden layer is located between the input and output of the algorithm, and in which weights are applied to the inputs and directed through an activation function as the output. bias is a mathematical entity that is applied to introduce non-linearity in the ann model. therefore, bias is a constant which helps the model in a way that it can fit best in a regression and is an additional parameter in the neural network which is used to adjust the output along with the weighted sum of the inputs. in other words, bias is an assumption made by a mathematical/ computer model to make the target function easier to process. bias unit is not connected to or influenced by the input layer activity. it is a fixed value that is added but this role does not amount to any ‘real activity’ (unlike the weight). thus, the steepness of the sigmoid curve depends on the weight of the inputs, not the bias. this is evident from the simple formula: output = sum (inputs x weights) + bias from a biological perspective it is better to explain that the activation function is not any structural or anatomical entity but a functional process in the form of mathematical equations that determine the output of a neural network [18]. all input values are close to zero before weight is applied but once multiplied by weights and summed up they get accumulated, requiring rationalization to keep them in an acceptable range for appropriate output. activation function also helps in normalizing the output of each neuron. this envisages reorganization of weighted data and data cleaning by eliminating duplicate and redundant data. after normalization in the activation function, it is possible to generate output that is needed by a fish to respond to conditions it is exposed to. as mentioned earlier, the node (neuron) receives a series of inputs (stimuli) and these are acted upon by weight and bias for transformation of input data in the hidden layer, and then the information moves into the next (output) layer of the ann that tunes it to produce the desired outcome in a specified range for the effectors to react. complexity of neuronal network requires such a normalization for a rationalized output. since there are many factors in the cultural environment in which the fish is exposed, the simpler form of the equation: input (x) x weight (w) + bias (b) output should transform into the following formula: output, y = f (x1 x w1 + x2 x w2 + x3 x w3) + b. neurons of the hidden layer apply the ‘activation function’ (f) to the weighted sum of the inputs because of which the fish responds differently according to the nature of stimuli and the needs of the situation. activation function provides the type of non-linearity between the inputs and outputs that is biologically logical under a real-world situation. it deserves emphasis that the linear models cannot characterize the nature of relationship between input and output. without this (activation function), the ann can only generate linear models that do not represent the practical possibilities because most real-world data is non-linear. response of any aquaculture animal in a cultural system or even in the wild is inherently nonlinear in nature. to elaborate it further, it characterizes a situation doi: http://dx.doi.org/10.36956/sms.v3i1.378 26 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 where there is no straight-line or direct relationship between an independent variable and a dependent variable. ann models the input-output that defines the complexity of the perception and processing of the response mechanism in the fish. in ann, the weight and bias can be considered as learnable parameters. in biological systems, this amounts to rationalization but in ann these parameters (weight and bias) are randomized and adjusted toward the desired values for the correct output. this is where machine learning is involved. because the hidden layer has many neurons and without activation function there will be a combined linear output in response to different inputs. if that is the case, fish response to multiple stimuli will be the same with full energy mobilized into it! addition of bias reduces the variance and hence introduces flexibility by addition of a constant value to the sum of input + weight. this is done by shifting the result of activation function towards the positive or negative side. weight reflects the strength of the connection. it determines the amount of influence a change in the input will exert on the output. a low weight value will have no change on the input, and alternatively a higher weight value will markedly change the output. if weight value is low, it means that the sensation (stimulus) is within the threshold limits of the fish, and it is not necessary for the fish to react. 3. constraints and options the main factors constraining technology intensification are: 1) reluctance to change, especially in the case of small enterprises, 2) investment risk that weighs heavily in decision-making in large-scale enterprises, 3) shortage of skilled human resources, and 4) lack of gainful employment opportunities for graduates who have the knowledge for high-tech operations. the prospects for aquaculture sector to transform would be brighter with the realization of the inability of the current systems to meet the fish production targets and when significant benefits from technology-intensive systems become apparent. another reason which will influence market perception will be when the consumers demand to know the methods of growing food and tracer technology gains a foothold. there are three directions for the future growth of aquaculture industry: optimization of existing cultural systems, genetic modification and new species as future food. 3.1 optimization of existing culture systems aquaculture industry has a track record of improving the rearing systems. knowledge and technological interventions have always supported the production and diversification of aquaculture. as a result, aquaculture has grown at the rate of 7.5 9 % annually to emerge as the fastest developing food sector [19,20]. yet, barring a few selected species of fish, the success in commercial-scale seed production of even the high-value fish remains elusive. most of the seed supplies still come from wild populations. captive breeding of bivalve molluscs and sea cucumbers is not always successful. commercial-scale production of lobster seed in hatcheries remains a challenge. established aquaculture systems such as those for high-value finfish (groupers, seabass), shrimp and crab have been increasing production to meet the demand in the face of stabilization or decline of capture fisheries using the existing infrastructure. these systems require input of new knowledge for meeting the requirements of sustainable development. 3.2 genetic modification certain genetic modifications have demonstrated a quantum increase in fish growth. growth rate of some transgenic fish can be increased by 400-600% while simultaneously reducing the feed input [21]. genetically engineered tilapia has been reported to put on weight 300 % faster [22]. genetically modified atlantic salmon attains market size in half the time (16-18 months) compared to the conventional one that takes 32-36 months [23]. potential candidate species are certainly those that fetch a high price in the market. in malaysia and many other countries, the giant grouper (epinephelus lanceolatus) is highly valued but so far there are no attempts for gene transfer in this species. nevertheless, such high-value species remain possible candidates. even with the stateof-the-art farming methods, good care in the hatchery and rich diet, the giant grouper could not gain 1 kg/year. obviously, there are limits to growth. growth can be modulated but it remains within the range set by the genetic and physiological factors. giant grouper grows to 2.5 meters and attains 400 kg of body weight in about 3540 years or even more, gaining about 600 g/year or 1 kg/18 months [24]. farmed groupers are reared for about for one year and are generally harvested for marketing when 400 600 g. producing genetically modified organisms (gmos) is a controversial topic. although market forces see benefits, but conservation biologists are concerned about the ecosystem implications of gmos in case of their entry into the wild. consumer perception about gmos is divided between acceptance and rejection. resolution of this issue will take time. future food security challenges and climate change doi: http://dx.doi.org/10.36956/sms.v3i1.378 27 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 adaptations will probably shape the cost/benefit analysis of genetically modified fish. for now, the aquaculture can remain focused on the non-controversial methods of production. 3.3 new species as future food while optimization of culture systems of currently used species will continue its transformation trajectory, new species can be tested for potential development as future seafood. being new candidates, it will be easier to apply modern technologies for starting from scratch for sustainable production since it will be free from the legacies of the existing infrastructure and practices. as a dynamic sector, aquaculture has been diversifying and adapting over time for better production and sustainability. however, now the food security challenges are different and require more efforts for screening new candidate species and selecting those that possess biological attributes needed for sustainable aquaculture. the criteria for selecting new species should be based on multiple qualities. currently, out of 33,600 species of finfish recorded so far, only 608 species have been tried for aquaculture [3]. the number of invertebrate species is much higher. of these, there are only 10 top farmed species, and this number includes shellfish as well as seaweeds in addition to finfish. 3.3.1 criteria for selection  adaptability to captivity at high-stocking density.  high rate of survival and fast growth.  acceptance of artificial diets and nutritional efficiency.  ability of physiological systems to accept interventions aimed at developing farmed fish as functional food.  resilience to the effects of climate change and other external drivers.  amenability to farming in compliance with sustainability requirements.  consumer preference and marketability. 3.3.2 advantages of selecting new species (1) aquaculture industry can make a fresh start, without the need for replacing the existing expensive culture infrastructure. (2) culture systems for the new species can be designed in response to prevailing challenges. (3) leveraging of past experience. (4) new systems could offer scope for: a) disruptive innovations. b) green technology based on circular / decarbonized production models. c) potential for developing into functional seafood system through bioencapsulated ration or other means. 4. tilapia (oreochromis niloticus) as a model tilapia (oreochromis niloticus) is the subject of an ongoing study. it is a commercially important fish globally. tilapia ranks among the top 10 farmed species in the world that are expected to drive future growth of aquaculture and is expected to yield 7.3 million tons a year by 2030 [6]. being one the most thoroughly investigated finfish in the world, the data generated on its performance in culture systems offers a great deal of insights needed for ai application. some basic attributes of tilapia specifically suitable for ai application in areas such as stress detection include:  a strong receptor-effector system.  well-defined behavioral changes in response to environmental factors (stressors).  sensory systems having a remarkable ability of perceiving external stimuli and provoking reaction in a way that helps the fish adjust to the prevailing conditions. stress-detecting algorithms can help in timely mitigating stress and even prevention, and in optimizing culture conditions. reducing stress on captive fish is vitally important for sustainable production [25]. the stress response of the fish has been documented by several authors in the past [26-34]. a simplified response of tilapia to stress factors is shown in table 1. a real-life response system is complex, depending on many factors. the response is modulated by magnitude of stress factors and their possible interdependence, and duration of exposure. this should be considered in algorithm development. still, such data provide a scientific basis for developing algorithms to detect and mitigate the stress factors for optimizing the culture conditions. table 1. response of tilapia to stress factors. variable fish response temperature, oc decrease in opercular movement with temperature decline. do, mg/l reduced random movement, decline in swimming activity. increased surfacing, crowding, sluggish response to stimuli. salinity, ppt increased opercular rate, increased vertical movement, disorientation, exhaustion, more time at bottom. unionized ammonia (mg/l) initial shock, increased agitation followed by decline, increased vertical movement, disorientation. the fish is exposed to different stimuli at the same time doi: http://dx.doi.org/10.36956/sms.v3i1.378 28 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 in the culture system or wild environment and reacts as appropriate. the stress factors that serve as stimuli may be:  decline in dissolved oxygen  increase in nitrite and ammonia  rise in water temperature  visual factors  auditory factors  others their perception and transmission are depicted in figure 5. figure 5. architecture of multi-layer perception network for prediction of selected water quality parameters. these stimuli are different in scale and in producing physiological effects in the fish. their lethal effects are unequal. the stimulus-response, therefore, cannot be a linear process. thus, in a real-world situation the fish cannot live with the same (or linear) response to factors that are profoundly different. specific nature of visible response provides the basis of algorithm development. learning from the fish’s stimuli filtering system for response prioritization and modulating an effective outcome are necessary for mathematical constructs of ai. just as there are different impulses or stimuli or stress factors, there should be multiple algorithms to perform the calculations on the input data to be able to compute the output (=biological response of fish). a biological ann model that maps the inputs and outputs is complex and has a high level of dimensionality to factors such as dissolved oxygen deficiency, spike in ammonia concentration or change in salinity, thus requiring big data and analytics. an ongoing study on stress-detecting algorithm for tilapia aquaculture optimization through artificial intelligence intervention consists of following components: (1) data collection: ph, temperature, salinity, and do) 10 minutes for 1 month. (2) summation of the data. (3) ann design specifications. (4) network designing. (5) testing the ann design by comparing the actual data with the predicated data output. for practical purposes and prompt mitigation action, a real-time monitoring of cultural conditions through sensors and the fish’s visible (behavioural) response through visual analytics will be required. use of sensors will be for water quality measurement, but information of monitoring and assessment of fish behaviour and condition will also be very helpful in managing the cultural system. production efficiency will be high if the fish is in a physiologically robust condition that supports faster growth and health. the process would involve consolidation of sensor-generated data and computer (digital) vision through interactive interfaces that provide a scientific basis for timely action and data interpretation for decision support system (dss). dss is a computerized system for collecting and analyzing data, synthesizing the required information to support an efficient decision-making for solving problems in aquaculture systems. it will comprise integrated components in the form of: physical objects (“things”) such as sensors, software and other multiple technologies, real-time analytics and machine learning, stocked fish, and transfer of data over a network without human-to-human or even human to computer interaction. this defines the iot in a digital aquaculture system with specific features for: automation of control systems, real-time monitoring of water quality and stocked fish, reduced dependencies on technical personnel, doing away with subjective assessments and improved production efficiency. 5. future food choices as pointed out earlier, digitalization of existing aquaculture systems can be gradually increased, but it will be more practically convenient and cost-effective to develop aquaculture 4.0 systems for certain future foods, especially microalgae, seaweed and mushrooms. there is nothing very technical about this popular term ‘future food’. some authors define it as food that we will be eating in 20 years' time, but it is better to refrain from fixing any year or decade as it seems arbitrary. food security is a challenge for the world and is likely to get bigger in near future. what we will be eating in the future is a matter that is receiving a great deal of attention (table 2). when it comes to seafood, we expect to consume: (1) more of the same food that we are consuming now. (2) same seafood produced in different ways. (3) same seafood raised by different culture systems (for example. organic farming). (4) new species as functional food. (5) 3d-printed seafood. doi: http://dx.doi.org/10.36956/sms.v3i1.378 29 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 table 2. trends in future seafood. known types of foods currently harvested advantages from future farmingspecies in the current production systems species in the future production systems fish, shrimp, crab from capture fisheries or aquaculture. organic fish, shrimp, and crab produced through certified organic aquaculture methods. better for health. lobster from the wild population. hatchery-produced and farmed lobster. increase in supply. decrease in overfishing pressure. fish farmed as primary food. fish as functional food through bioencapsulated/ fortified diet. specific health benefits. microalgae harvested from the sea. commercial-scale production under controlled conditions. exploring the potential of new species could open many horizons for their use as functional or regular food for humans. mushroom (fungi). known or new species raised through agri-aquaculture systems “mush-aquaculture”. mushrooms are a source of nutraceuticals and therapeutic substances, and bioactive compounds of functional significance. application of ai and other tools of current technologies to future aquatic food is practically more plausible due to a number of reasons: 1) opportunity to select species that can be grown on a fast track, 2) determining amenability of new species to technology-intensive farming systems, 3) shaping the production systems consistent with the sustainability requirements, and 4) using species according to their: a) ability to accept nutrient fortification and bioencapsulation, b) qualities that make them acceptable as functional food when modulated, c) biological capacities for accepting integration into a system of macro-cascading for eco-friendly spinoff benefits or socio-economic dividends, and d) suitability for organic aquaculture. these topics have been elaborated in this paper. 6. emerging area: imitation seafood there is a growing interest in imitation seafood. several plant-based recipes for imitation fish are being developed, for example, raw tuna and salmon. the 3d printed imitation seafoods are opening a vast horizon of new opportunities. this is an area with enormous potential for:  ‘secret’ recipes  innovation  entrepreneurship  graduate employment  start-ups. making plant-based fish alternative will require interdisciplinary collaboration involving aquaculture, food science and technology, culinary art, psychology and economics. interdisciplinary research is making it possible to produce vegetable-based products that taste like a fish. with more efforts it might be possible to process tomato or other vegetables into a product that resembles the taste of grouper, hump-head wrasse or other species! this topic can inspire researchers of all ages and backgrounds to push the boundaries of innovation and entrepreneurship. however, momentum for such future foods should develop for the sake of human health, environment, creating new areas for entrepreneurship and life-long learning. it requires changing the mindset. in the words of a protagonist of regenerative agriculture, charles massy “today’s problems cannot be solved with today’s mind”, and thus, we need to change our mindscapes before we can change our food security landscapes. promising sources of ingredients for imitation seafood are seaweeds and mushroom among others. malaysia has a vast coastal marine area for seaweed farming. the growing conditions are favorable. mushrooms are easy to farm under certain agri-aquaculture systems due to their survival and growing conditions in a tropical climate. they do not carry out photosynthesis and, thus, there is no need for vast sun-exposed areas. fibrous nature of mushrooms offers the advantage to turn them into products that in some way resemble that from animal sources. furthermore, mushrooms do not have a strong taste or flavour, and this helps in culinary processing for imitation. use of mushrooms in such future foods will intensify interest in exploring the most suitable edible species out of the thousands that are known to occur. there are good and bad practices that can be associated with the imitation seafood (table 3). table 3. good and bad practices requiring attention. good practices 1. environment-friendly. 2. spare animals from the stress of captivity, cruelty and sacrifice. 3. free of seafood poisoning risk. 4. free of zoonotic infection concerns. 5. easy to manipulate nutritional and organoleptic quality by culinary processing. 6. easy to develop into functional food. 7. produced according to demand and save the product from loss in case of supply chain disruption. bad practices 1. counterfeit food products containing false claims of functional properties or even containing harmful substances. doi: http://dx.doi.org/10.36956/sms.v3i1.378 30 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 7. solutions quality control offers the best solution to curb malpractices in the imitation seafood business. once the consumer interest picks up, the market is likely to expand and the public will be better informed. the nature of ingredients, quality assurance, price, awareness campaigns and consumer appeal will determine their success in the market. certification procedures, traceability and blockchain will be needed to ensure that only quality product enters the market and consumers get what is claimed by the producers of the food item on the label. blockchain has the capability to trace the entire lifecycle of food products from origin to consumers. it can help combat fraud in the food market, boost transparency in operations involved in processing. it will be possible to track and trace any seafood in the market and might emerge as the solution to the critically important food safety. 8. conclusions aquaculture has grown rapidly over the recent decades. with the stagnation in capture fisheries landings, aquaculture should further enhance its contribution to seafood supply and food security. it has reached a stage that the trend of incremental change can shift towards transformation using ir4.0 technologies. there is an urgent need to examine if the current research and development efforts are following a system / systems / systemic or systematic approach. investment in future food necessitates a serious introspection for an outcome-based and solution-oriented research that is linked to market demand and societal welfare, and is also rooted in environmental sustainability. acknowledgement this study was supported by aquaculture flagship program of universiti malaysia sabah. references [1] sofia. the state of world fisheries and aquaculture. food and agriculture organization, rome, italy, 2020. [2] kobayashi, m., msangi, s., batka, m. et al. fish to 2030: the role and opportunity for aquaculture. aquaculture economics and management, 2015, 19 (3), 282-300. [3] cai, j. and leung, p.s. (2017). short-term projection of global fish demand and supply gaps. fisheries and aquaculture technical paper no. 607, food and agriculture organization, rome, italy, 2017. [4] fao. the state of world fisheries and aquaculture. food and agriculture organization, rome, italy, 2018. [5] mustafa, s. and saad, s. coral triangle: marine biodiversity and fisheries sustainability. in: leal filho w., azul a.m., brandli l., lange salvia a., wall t. (eds) life below water. encyclopedia of the un sustainable development goals. springer, cham, switzerland, 2021. [6] wb. fish farms to produce nearly two-thirds of global food fish supply by 2030. the world bank, washington, dc, 2014. [7] mustafa, f.h., bagul, a.h.b.p., senoo, s. and shapawi, r. a review of smart fish farming system. journal of aquaculture engineering and fisheries research, 2016, 2 (4), 193 200. [8] vik, j.o. digi sal: towards the digital salmonfrom a reactive to a proactive research strategy in aquaculture. norway university of life sciences, oslo, norway, 2016. [9] lu, h. d., yu, x., & liu, g. q. abnormal behavior detection method of fish school under low dissolved oxygen stress based on image processing and compressed sensing. journal of zhejiang university (agriculture and life ences), 2018, 44(4), 499506. [10] chen, y. q., li, s. f., liu, h. m., tao, p. application of intelligent technology in animal husbandry and aquaculture industry. 14th international conference on computer science & education (iccse). ieee, toronto, on, canada, 2019. [11] helland, s. how digitalization is refining aquaculture research. the fish site. the fish site, hatch accelerator holding limited, cork, ireland, 2020. [12] mustafa,s., estim, a., shapawi, r., et al. technological applications and adaptations in aquaculture for progress towards sustainable development and seafood security. iop publishing, bristol, uk, 2021. [13] fore, m. precision fish farming: a new framework to improve aquaculture, part 1. global aquaculture alliance. new hampshire avenue, portsmouth, usa, 2019. [14] tetsuo, i. and kobayashi, t. smart aquaculture system: a remote feeding system with smartphones. proceedings of the 2019 ieee 23 international symposium on consumer technologies, pages 93-96. doi: v10.1109/isce.2019.8901026. [15] li, d. and li, c. intelligent aquaculture. world aquaculture society, los angeles, usa, 2021. [16] ogajanovski, g. everything you need to know about neural netyworks and back propagationmachine learning easy and fun. towards data science, media, canada, 2019. [17] alammar, j. a visual and interactive guide to the basics of neural networks. creative commons attribudoi: http://dx.doi.org/10.36956/sms.v3i1.378 31 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 tions, 2018. [18] nizrak, a. comparison of activation function for deep neural networks. yildiz technical university, istanbul, turkey. [19] sofia. the state of world fisheries and aquaculture food and agriculture organization, rome, italy, 2018. [20] iffo. aquaculture. iffo marine ingredients organization, london, uk, 2021. [21] towers, l. importance of transgenic fish to global aquaculturea review. the fish site, hatch accelerator holding limited, cork, ireland, 2016. [22] muir, w.m. the threats and benefits of gm fish. embo report, 2004, 5 (7), 654 659. [23] williams, d. genetically modified salmon to hit us markets. cgtn america, washington, dc, 2019. [24] tucker, j.w. species profile: grouper aquaculture. southern regional aquaculture center (srac), publication no. 721. fort pierce, florida, usa, division of marine science harbor branch oceanographic institution, 1999. [25] aerts, j. stress in aquaculture: a rough guide. the fish site, hatch accelerator holdings, cork, ireland, 2019. [26] fernandes, m.n., rantin, f.t. relationships between oxygen availability and metabolic cost of breathing in nile tilapia (oreochromis niloticus): aquacultural consequences. aquaculture, 1994, 27:339-346. [27] moreira, p.s.a. and volpato, g.l. conditioning of stress in nile tilapia. journal of fish biology 2004, 64, 961-969. [28] jian-yu, x., xiang-wen, m., ying, l. et al. behavioral response of tilapia (oreochromis niloticus) to acute ammonia stress no0nitored by computer vision. journal of zhejiang university. science, 2005, 812 816. [29] xu, j., liu, y., cui, s. et al. behavioral responses of tilapia (oreochromis niloticus) to acute fluctuations in dissolved oxygen levels as monitored by computer vision. aquaculture engineering 2006, 35, 207 217. [30] barreto, r.e., volpato, g.l., faturi, c.b., et al. aggressive behaviour traits predict physiological stress responses in nile tilapia (oreochromis niloticus). marine and freshwater behavior and physiology, 2009, 42,109-118. [31] barreto, r.e., miyai, c.a., sanches, f.h.c. et al. blood cues induce antipredator behavior in nile tilapia conspecifics. plosone, 2013, 8: e54642. [32] hassan, m., zakariah, m.i., wahab, w. et al. histopathological and behavioral changes in oreochromis sp. after exposure to different salinities. journal of fisheries cand livestock production, 2013, 1, 103. doi: 10.4172/2332-2608.1000103. [33] king, m. and sardella, b. the effects of acclimation temperature, salinity, and behavior on the thermal tolerance of mozambique tilapia (oreochromis mossambicus). journal of experimental zoology part a ecological and integrative physiology, 2017, 327(7) https://doi.org/10.1002/jez.2113. [34] panase, p., saenphet, s. and saenphet, k. biochemical and physiological responses of nile tilapia, oreochromis niloticus lin subjected to cold shock of water temperature. aquaculture reports, 2018, 11, 17-23. doi: http://dx.doi.org/10.36956/sms.v3i1.378 1 sustainable marine structures | volume 05 | issue 02 | september 2023 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2023 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). doi: http://dx.doi.org/10.36956/sms.v5i3.875 article enhancing friction stir welding in fishing boat construction through deep learning-based optimization erfan maleki1 okan unal2,3 seyed mahmoud seyedi sahebari4 kazem reza kashyzadeh5* nima amiri6 1. mechanical engineering department, politecnico di milano, milan, 20156, italy 2. mechanical engineering department, karabuk university, karabuk, 78050, turkey 3. modern surface engineering laboratory, karabuk university, karabuk, 78050, turkey 4. department of mechanical and manufacturing engineering, ontario tech university, l1g 0c5on, oshawa, canada 5. department of transport, academy of engineering, rudn university, 6 miklukho-maklaya street, moscow, 117198, russian federation 6. paul m. rady department of mechanical engineering, university of colorado, boulder, co, 80309, united states article info abstract article history received: 17 june 2023 revised: 10 august 2023 accepted: 18 august 2023 published online: 19 august 2023 in the present study, the authors have attempted to present a novel approach for the prediction, analysis, and optimization of the friction stir welding (fsw) process based on the deep neural network (dnn) model. to obtain the dnn structure with high accuracy, the most focus has been on the number of hidden layers and the activation functions. the dnn was developed by a small database containing results of tensile and hardness tests of welded 7075-t6 aluminum alloy. this material and the production method were selected based on the application in the construction of fishing boat flooring, because on the one hand, it faces the corrosion caused by proximity to sea water and on the other hand, due to direct contact with human food, i.e., fish etc., antibacterial issues should be considered. all the major parameters of the fsw process, including axial force, rotational speed, and traverse speed as well as tool diameter and tool hardness, were considered to investigate their correspondence effects on the tensile strength and hardness of welded zone. the most important achievement of this research showed that by using sae for pre-training of neural networks, higher accuracy can be obtained in predicting responses. finally, the optimal values for various welding parameters were reported as rotational speed: 1600 rpm, traverse speed: 65 mm/min, axial force: 8 kn, shoulder and pin diameters: 15.5 and 5.75 mm, and tool hardness: 50 hrc. keywords: simulation and modelling welding friction stir welding deep neural network optimization *corresponding author: kazem reza kashyzadeh, department of transport, academy of engineering, rudn university, 6 miklukho-maklaya street, moscow, 117198, russian federation; email: reza-kashi-zade-ka@rudn.ru https://creativecommons.org/licenses/by-nc/4.0/ https://creativecommons.org/licenses/by-nc/4.0/ http://dx.doi.org/10.36956/sms.v5i3.875 https://orcid.org/0000-0003-0552-9950 2 sustainable marine structures | volume 05 | issue 02 | september 2023 1. introduction one of the oldest methods of non-separable connections, which is widely used in various industries, is welding. in fact, large structures cannot be produced in one piece, such as the body of ships, airplanes, trains, subways, and ground vehicles [1,2]. therefore, it is necessary to connect different parts to each other and create an assembly. hence, depending on the application of the connection, different types of welding are used in various industries, each of which has advantages and disadvantages compared to the others [3]. for example, the biggest challenge for all types of welding methods is the creation of tensile residual stress in the welding area [4] or microstructure change in the heat-affected zone (haz), both of which lead to a decrease in joint strength [5,6]. in other words, these two areas are prone to damage and cracks. however, some additional disadvantages arise when an intermediate material is used for welding. therefore, in large industries, it is usually tried to use welding methods that do not require an electrode or additional material, such as resistance spot welding (rsw) in the automotive industry [7]. moreover, the fsw process which was first presented by the welding institute (twi) in 1991 [8], has emerged as an effective alternative to traditional metal inert gas (mig) welding for use in marine applications, particularly as the industry moves towards increased use of aluminum alloys. based on the twi report in 2007, 171 large organizations and companies received licenses to manufacture shipbuilding from aluminum extrusion by fsw process, especially, al7075 is used to manufacture aluminum panels for deep freezing of fishing boats. in this regard, one of the biggest challenges and concerns in the manufacturing is to optimize the strength of welded joints via the welding process. the powerful combination of reduced weight from aluminum and increased strength of fsw welds can yield spectacular benefits for marine designs. generally, fsw is well suited for marine applications because of the nature of the welds [9]. during the last decades, the selection of the favorable parameters of this process to obtain the optimal properties of the welded parts is remained challenging and widely considered by many researchers. in this regard, the goal is to increase the quality and improve the strength of the connection, and for this purpose, various techniques have been used. the number of publications in this field is very large and a comprehensive study is required for a detailed review, which is beyond the scope of the present research. however, some of the efforts made to optimize aluminum parts welded in this way are collected in table 1. as presented in table 1, scientists paid the most attention to data mining methods such as taguchi method (tm), linear regression method (lrm), analysis of variance (anova), and response surface method (rsm) to optimize different parameters of fsw process. in addition, the main goal was to improve the tensile strength and hardness of the connection. in recent years, attention has been paid to machine learning methods such as artificial intelligence (ai) for modeling and optimizing friction stir welding of aluminum alloys. nevertheless, the present article includes the most comprehensive laboratory results and six input parameters. also, the deep machine learning method was used to provide a new approach in optimizing the friction stir welding process of aluminum parts. recently, the advantages and accuracy of using deep neural network (dnn) technique compared to artificial neural network (ann) have been evident and proven in various fields of engineering [28,29]. padhy et al. have published a comprehensive review on the fsw technology and the effects of process parameters on the material characterization and metallurgical properties like microstructure [30]. in addition, gangwar and ramulu have focused on the titanium alloys joints by fsw [31]. also, to improve the quality of this type of welded joint, the effects of two parameters of the tool and the thickness of the raw material sheets have been evaluated. after that, microstructure, material properties (i.e., hardness), mechanical properties (i.e., tensile, fatigue, and fracture toughness), residual stress field, and temperature distribution have been studied. mohanty et al. have utilized rsm to examine the effects of tool shoulder and probe profile geometries simultaneously on the fsw of aluminum sheets [32]. in this research, three parameters of tool type, tool probe diameter, and shoulder flat surface, each of them at three different levels, were considered as input to the rsm analysis. also, connection strength, weld cross section area, and grain size in both welded area and haz were considered as output. the results showed that straight cylindrical fsw tool with the minimum level of probe diameter provided better strength of welded joint. ahmed et al. have optimized fsw process parameters to achieve the maximum tensile strength and hardness of welded 5451al sheets by performing taguchi sensitivity analysis [33]. they stated that the pin profile of the tool is the most effective factor in both outputs with more than 60% effectiveness. moreover, research on the connection of thick aluminum plates through fsw has also been carried out [34]. before this, in most articles, the connection of thin sheets up to 5 or 6 mm has been considered. in this regard, kumar et al. have proposed a trapezoidal pin of tool to reach a free-defect connection of 12 mm thick aluminum sheets. 3 sustainable marine structures | volume 05 | issue 02 | september 2023 in general, many parameters are important in industrial constructions, which are ultimately directly or indirectly related to the economic field and cost. for example, in the construction of a fishing boat, it is possible to refer to the initial costs including the preparation of the raw material i.e., aluminum alloy, the construction design including the dimensions and thicknesses of the sheets for the construction of the ship, and finally the construction method and the type of connection of the sheets to each other. on the other hand, considering the working conditions in the vicinity of sea water and the corrosion as a result, and on the other hand, in direct connection with fish and antibacterial issues, it is necessary to choose the type of alloy and heat treatment correctly. finally, in order to reduce production time and ultimately reduce the cost of free-defect production, in order to minimize repairs, it is necessary to optimize the production process. apart from these cases, just the free-defect construction is not enough, and it must have enough strength so that it does not have problems after some time of use [35]. for this purpose, in addition to examining the tensile strength, it is better to study the hardness and microstructure in the welded area. therefore, the results of such research can satisfy part of the demands stated above. table 1. a summary of the research conducted to optimize the friction stir welding of aluminum parts. reference year material method parameters objective [10] 2015 aa6082-t6 taguchi joint geometries: butt, lap, and t-shaped ultimate tensile strength [11] 2010 aa1050 grey relation analysis and taguchi rotating speed, welding speed, and shoulder diameter tensile strength and elongation [12] 2015 aa8011 taguchi-based grey relational analysis tool shoulder diameter, rotational speed, welding speed, and axial load tensile strength and microhardness [13] 2016 cast aa7075/sicp composite response surface methodology, regression model, and fuzzy grey relational analysis approach spindle speed, travelling speed, downward force, and percentage of sic added to aa7075 ultimate tensile strength and percentage elongation [14] 2019 aa6082/sic/10p composite taguchi approach and analysis of variance (anova) tool rotation speed, welding speed, and tool tilt angle ultimate tensile strength [15] 2018 dissimilar alloys (aa6082/aa5083) taguchi method, grey relational method, weight method, and analysis of variance (anova) tool rotation speed, welding speed, tool pin profile, and shoulder diameter ultimate tensile strength and elongation [16] 2008 rde-40 aluminium alloy taguchi technique and analysis of variance (anova) rotational speed, traverse speed, and axial force tensile strength [17] 2010 aa7075-t6 response surface methodology and analysis of variance (anova) tool rotational speed, welding speed, axial force, tool shoulder diameter, pin diameter, and tool hardness tensile strength [18] 2017 al5052-h32 alloy response surface methodology tool profile, rotational speed, welding speed, and tool tilt angle tensile strength and elongation [19] 2012 dissimilar alloy: aa6061-t6 and aa7075-t6 response surface methodology rotational speed, welding speed, and axial force ultimate tensile strength, yield strength, and displacement [20] 2009 cast aluminum alloy a319 taguchi method and analysis of variance (anova) tool rotation speed, welding speed, and axial force tensile strength [21] 2021 dissimilar aluminum alloys 6061 and 5083 response surface methodology tool pin profile, tool rotation speed, feed rate, and tool tilt angle ultimate tensile strength, yield strength, and microhardness [22] 2021 dissimilar aa7075-t651 and aa6061 taguchi technique and analysis of variance (anova) tool offset, pin profile of tool, and tilt angle of tool tensile strength [23] 2022 armor-grade aluminum alloys aa5083 response surface methodology, regression, and analysis of variance (anova) shoulder diameter, shoulder flatness, pin profile, and welding speed ultimate and yield tensile strength and elongation 4 sustainable marine structures | volume 05 | issue 02 | september 2023 in the fsw, a tool moves along the joint line of two plates (similar or dissimilar) that simultaneously rotates and therefore it creates frictional heat that mechanically intermixes the metals and forges the hot and softened metal by the applied axial force. figure 1 depicts the schematic of the fsw process and its effective parameters such as axial force, rotational and traverse speeds as well as tool geometry and hardness. as mentioned, in the fsw both mechanical and thermal processes are involved which show their effects in the welding zone and its surrounding regions and divide it into four major parts of weld nugget (wn), thermo-mechanically affected zone (tmaz), heat affected zone (haz), and base material (bm) that can be described as fully recrystallized region, area that plastically deformed without recrystallization, thermal affected, and region of original properties, respectively [36]. because of the variety of physical phenomena in the fsw process, its analysis and optimization have become very complicated. therefore, scholars have tried to solve the problems in this field by considering different alternative approaches of experiments like modeling and optimization methods [37]. in this regard, chu et al. have performed mechanical and microstructural optimization in the fsw joint of al-li alloy [38]. they used rsm and box-behnken experimental design to maximize static strength (i.e., tensile and shear stresses). moreover, electron backscattering diffraction (ebsd) and differential scanning calorimetry (dsc) observations have been utilized to optimize hardness and reach the ultrafine grains. sreenivasan et al. have optimized fsw process parameters for joining composite materials (i.e., aa7075sic) [39]. they considered different parameters, including friction pressure, spindle speed, burn-off length, and upset pressure, in three levels, as the input variables in the optimization algorithms. also, they tried to optimize hardness and ultimate tensile strength (uts). to achieve this goal, they employed two methods of linear regression and genetic algorithm. in a similar study, fsw process parameters have been optimized to obtain the maximum joint strength and the highest elongation [40]. also, heidarzadeh et al. have employed anova and rsm analysis to present mathematical relationships between the strength, elongation, and hardness of the connection in terms of fsw process parameters, including rotation speed, traverse speed, and axial force. they stated that the hardness reduces by raising the rotation speed and axial force and decreasing the traverse speed at the same time. moreover, rotation speed and axial force are the most important factors that affect the strength and elongation values, respectively. after that, heidarzadeh continued his research in this field with a focus on material properties and imaging observations, including ebsd and tem [41]. he et al. have published a review report on the numerical simulation of fsw process [42]. they discussed different techniques for process simulation and presented the results obtained from them. however, methods based on artificial intelligence such as neural networks are remarkably applied in different aspects of science and engineering [43-46] as well as their application for modeling of fsw process [47-49]. in general, a neural network has three major layers of input, hidden, and output [50,51]. a literature review conducted in this research shows that shallow neural network (snn), as the primary generation of artificial neural networks, has been mostly used in the simulation of fsw. in fact, snns have 1 or 2 hidden layers which are generally trained by back-propagation (bp) algorithm [46]. these networks besides their beneficial applications have some limitations. the most important limitation of snns is that a large number of data sets are required for their development. recently, by considering the improvements achieved in the training of neural networks by deep learning presented by hinton et al. [52]; it is feasible to develop deep neural network with higher efficiency by employing small data set [53]. as an innovation, the current paper aims to show the capability of the dnn for prediction, analysis, and optimization of the fsw process for the first time by using reference year material method parameters objective [24] 2021 dissimilar aluminum alloys of aa 7075-o and aa 5052-o grade taguchi approach and analysis of variance (anova) tool pin profile, tool rotational speed, feed rate, and tool offset tensile strength and microhardness [25] 2018 dissimilar aa5083-o and aa6063-t6 aluminum alloys artificial intelligence and genetic algorithm tool rotational speed, welding speed, shoulder diameter, and pin diameter tensile strength, microhardness, and grain size [26] 2021 dissimilar aa3103 and aa7075 aluminum alloys taguchi method tool rotation speed, feed rate, and tool pin profile hardness, tensile strength, and impact strength [27] 2018 armor-marine grade aa7039 desirability approach: rsm & anova rotational speed, feed rate, and tilt angle ultimate tensile strength and tensile elongation table 1 continued 5 sustainable marine structures | volume 05 | issue 02 | september 2023 small data set. in the following, the authors have attempted to assess strength and hardness in the welded zone in terms of different process parameters as well as pin and shoulder features (i.e., hardness and diameter). 2. experimental data the data used in this research were extracted from the paper published by rajakumar et al. [54]. in order to conduct experiments, they prepared rolled sheets of 7075-t6 aluminum alloy with a thickness of 5 mm and dimensions of 150 × 300 mm. the ultimate and yield tensile strengths of the sheets are 485 and 410 mpa, respectively. table 2 also presents the chemical composition of this material. next, friction stir welding operation perpendicular to the rolling was performed as a single pulse and with non-consumable tools. the details of this process are shown in figure 2. in the next step, tensile test samples were fabricated according to the astm standard. they prepared two types of smooth and notched samples. all tests were performed at room temperature and at a speed of 0.5 mm/min. however, in the present study, only the laboratory results for smooth samples were used. moreover, vickers microhardness in the welded zone was measured by applying a force of 50 gr. figure 1. schematic illustration of the fsw process and parameters affecting welded joint quality. table 2. chemical composition of prepared sheets. element mg mn zn fe cu si al value (%) 2.10 0.12 5.10 0.35 1.2 0.58 90.55 figure 2. dimensional details of sheets, sheets rolling and welding process directions. 6 sustainable marine structures | volume 05 | issue 02 | september 2023 3. dnn developing a dnn with four hidden layers was developed to model the fsw process by using experimental data described in the previous section. this experimental dataset was selected because it includes high amounts of effective parameters of fsw process. nevertheless, the data used for this simulation is given in the appendix (table a1). also, the first author has used these data previously for providing a model based on the common snn with bp method [48]. hence, the innovation of the present work with the previous one is to present a novel modified neural network based on deep learning. parameters of axial force, rotational and traverse speeds as well as shoulder and pin diameters, and tool hardness were considered to investigate their related influences on the strength and hardness of welded zone. to this end, 25 and 5 data were used for the training and testing steps, respectively. in addition, in order to develop dnn, as the dataset is small, a stacked auto-encoder (sae) was used for pre-training of dnn. sae is a specific hidden layer snn that has the same input and output layers and also has the same number of neurons in each layer of it with respect to the main dnn architecture. used dnn along with linking to sae is presented in figure 3. also, the accuracy of predicted results was determined via correlation coefficient (r2). the obtained accuracies for the developed dnn with and without sae for both training and testing steps based on equation (1) are reported in table 3. common snn with bp method [48]. hence, the innovation of the present work with the previous one is to present a novel modified neural network based on deep learning. parameters of axial force, rotational and traverse speeds as well as shoulder and pin diameters, and tool hardness were considered to investigate their related influences on the strength and hardness of welded zone. to this end, 25 and 5 data were used for the training and testing steps, respectively. in addition, in order to develop dnn, as the dataset is small, a stacked auto-encoder (sae) was used for pre-training of dnn. sae is a specific hidden layer snn that has the same input and output layers and also has the same number of neurons in each layer of it with respect to the main dnn architecture. used dnn along with linking to sae is presented in figure 3. also, the accuracy of predicted results was determined via correlation coefficient (2). the obtained accuracies for the developed dnn with and without sae for both training and testing steps based on equation (1) are reported in table 3. figure 3. used dnn along with linking to sae.  = =1  (,−)(,−) =1  (,−)2(,−)2 (1) table 3. obtained values of accuracies for developed dnn. developed dnn accuracy without sae-train 0.982 without sae-test 0.974 with sae-train 0.996 (1) figure 3. used dnn along with linking to sae. table 3. obtained values of accuracies for developed dnn. developed dnn accuracy without sae-train 0.982 without sae-test 0.974 with sae-train 0.996 with sae-test 0.993 7 sustainable marine structures | volume 05 | issue 02 | september 2023 4. results and discussions based on the results of the determination of accuracies that show the dnn was developed well, parametric analysis was performed. in figure 4 and figure 5, the effects of welding process parameters and tool features on the welded zone strength and hardness are continuously revealed respectively in a general condition and interval of each parameter for the applied analyses are shown at the bottom of each contour. the region that has ≤ 95% of the considered experimental value was specified in each 2d contour by a black line. it can be seen that, in the same graph whole prediction, analysis, and optimization can be carried out with accuracy close to 100% (r2 ≈ 1). from figure 4, as the rotation speed increases, the strength of the welded zone always increases, which is consistent with the results of ahmed et al. in the study of 2022 [33]. also, with the increase of the axial force, the strength improves, but its changes are not significant compared to the rotational speed parameter and it depends on the values of other parameters. ref no. 33 also deals with the optimization of process parameters. the authors showed that the tensile strength of fsw joint considering the feed rate of 18 mm/min is much higher than the tensile strength of fsw joint with feed rates of 16 and 20 mm/min. in other words, the tensile strength of the connection increases with the increase of the feed rate in the range of 16 to 18 mm/min, and it decreases with the increase of the feed rate in the range of 18 to 20 mm/min. therefore, this interpretation is exactly in accordance with the results presented in figure 4. moreover, the contour presented in figure 4b indicates that if the rotational speed is less than 1000 rpm, changes in axial force do not affect the strength. however, all the results presented in this section are considering the welding conditions in this study and different results may be obtained in other conditions. therefore, more studies are needed to generalize the results to other conditions, which is on the agenda of this research group for its future studies. furthermore, by focusing on the hardness in the welded zone as a response, it is seen that the hardness increases with increasing rotational speed. but in interaction with other parameters, i.e., axial force and transverse speed, there is an intermediate area where the highest hardness is obtained within this specific area and the lowest hardness is obtained outside this area. for example, it is clear from figure 4f that setting the rotational speed in the range of 1500 to 1700 rpm and also the axial force between 7 and 9 kn can result in the highest hardness in the welded zone. as shown in figure 5, no specific trends can be found between the system responses (i.e., strength and hardness in the welded zone) and tool characteristics, including pin and shoulder diameters and their hardness. in other words, the interaction between various parameters of this section must be checked with more precision and laboratory data and it is very difficult and perhaps unlikely to be able to independently declare the effect of one of these parameters on the output, because depending on the conditions of other parameters, there is a possibility of changing the state of the response. it is clearly evident in the contours with yellow color theme (i.e., figure 5d, e, and f) that there are different circular and elliptical layers, therefore, there is a specific area in each contour that should be tried to select the characteristics of the tool in such a way that the responses be placed within these areas. in summary, according to all the achievements presented above, in order to obtain the optimal parameters, all the contours should be placed on each other at the same time and the common space between the areas marked by black lines should be selected. in this way, optimal values of rotational speed, traverse speed, axial force, shoulder diameter, pin diameter, and tool hardness are specified as 1600 rpm, 65 mm/min, 8 kn, 15.5 mm, 5.75 mm, and 50 hrc, respectively. 8 sustainable marine structures | volume 05 | issue 02 | september 2023 figure 4. parametric analysis of the effects of axial force, rotational and traverse speeds on strength (a-c) and hardness (d-f) of welded zone. 9 sustainable marine structures | volume 05 | issue 02 | september 2023 figure 5. parametric analysis of the effects of shoulder diameter, pin diameter, and tool hardness on strength (a-c) and hardness (d-f) of welded zone. 10 sustainable marine structures | volume 05 | issue 02 | september 2023 5. conclusions the application of dnn to model the fsw process was investigated in this study. the obtained results revealed that by using sae for pre-training of neural networks higher accuracy can be obtained. in addition, it can be concluded that by applying dnn on small dataset with discrete values, continuous values for whole considered intervals can be predicted for parametric analysis of fsw. moreover, these 2d contours with the accuracy of close to 100% can be easily used for further analysis and optimization. however, one of the challenges in this research was that the small dataset was used to estimate the tensile strength, but more studies are needed to optimize the hardness, and no specific trend was found for hardness changes in the welded area according to the investigated parameters. therefore, in future research, the authors seek to perform more tests using design of experiment (doe) techniques such as taguchi method and considering more input parameters. in addition, the authors agree with the opinion of many reports that the main causes of failures of mechanical parts are the fatigue phenomenon [55]. therefore, in the future research series, this research team seeks to model, analyse, and optimize the friction stir welding process of aluminium sheets with the aim of improving the fatigue life of the joint. for this, they will use various techniques including data mining, artificial intelligence, deep learning, etc. to make a comprehensive study. also, the accuracy of the methods will be compared with each other and the advantages and disadvantages of each of them will be discussed. author contributions conceptualization, e.m., o.u., and k.r.k.; methodology, e.m., o.u., s.m.s.s., and k.r.k.; software, e.m., o.u., and s.m.s.s.; validation, e.m., and o.u.; formal analysis, e.m., o.u., and k.r.k.; investigation, e.m., o.u., s.m.s.s., k.r.k., and n.a.; resources, e.m., o.u., and k.r.k.; data curation, e.m., and o.u.; writing—original draft preparation, e.m., o.u., s.m.s.s., and k.r.k.; writing—review and editing, k.r.k.; visualization, e.m., o.u., and k.r.k.; supervision, e.m., o.u., and k.r.k.; project administration, e.m., and k.r.k.; funding acquisition, e.m., o.u., and k.r.k., all authors have read and agreed to the published version of the manuscript. funding this research received no external funding. acknowledgement this paper has been supported by the rudn university strategic academic leadership program. data availability the data that support the findings of this study are available from the corresponding author upon reasonable request. conflict of interest the authors declare no conflict of interest. references [1] gite, r.a., loharkar, p.k., shimpi, r., 2019. friction stir welding parameters and application: a review. materials today: proceedings. 19, 361-365. doi: https://doi.org/10.1016/j.matpr.2019.07.613 [2] reza kashyzadeh, k., ghorbani, s., 2023. high-cycle fatigue behavior and 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on fatigue damage. applied mechanics and materials. 87, 230-237. doi: https://doi.org/10.4028/www.scientific.net/ amm.87.230 appendix a the data used in this research, including various weldtable a1. the data used in the current study, including welding conditions and testing results [48]. case no. fsw process parameters tool features responses in welded zone rotational speed transverse speed axial force shoulder diameter pin diameter tool hardness strength hardness (rpm) (mm/min) (kn) (mm) (mm) (hrc) (mpa) (vhn) 1 1400 60 8 15 5 45 314 203 2 1800 60 8 15 5 45 310 185 3 1400 40 8 15 5 45 279 194 4 1400 60 8 15 5 45 310 198 5 1400 80 8 15 5 45 308 197 6 1400 60 7 15 5 45 282 180 7 1400 60 8 15 5 45 314 199 https://doi.org/10.1016/j.ijfatigue.2022.106841 https://doi.org/10.1016/j.matchar.2019.109877 https://doi.org/10.1016/j.ijfatigue.2018.06.004 https://doi.org/10.3390/buildings12040438 https://doi.org/10.1016/j.matdes.2015.12.005 https://doi.org/10.1088/1757-899x/103/1/012034 https://doi.org/10.1016/j.matdes.2012.07.025 https://doi.org/10.1007/s10999-021-09570-w https://doi.org/10.1016/j.engfailanal.2023.107128 https://doi.org/10.1162/neco.2006.18.7.1527 https://doi.org/10.1016/j.matdes.2018.11.060 https://doi.org/10.1016/j.matdes.2010.08.025 https://doi.org/10.4028/www.scientific.net/amm.87.230 https://doi.org/10.4028/www.scientific.net/amm.87.230 14 sustainable marine structures | volume 05 | issue 02 | september 2023 ing conditions and laboratory results of tensile and microhardness tests, are given in table a1 [48]. case no. fsw process parameters tool features responses in welded zone rotational speed transverse speed axial force shoulder diameter pin diameter tool hardness strength hardness (rpm) (mm/min) (kn) (mm) (mm) (hrc) (mpa) (vhn) 8 1400 60 8 12 5 45 280 193 9 1400 60 8 15 5 45 310 198 10 1400 60 8 18 5 45 256 197 11 1400 60 8 15 4 45 292 194 12 1400 60 8 15 5 45 310 198 13 1400 60 8 15 6 45 300 197 14 1400 60 8 15 5 40 261 186 15 1400 60 8 15 5 45 313 198 16 900 60 8 15 5 45 245 175 17 1200 60 8 15 5 45 290 191 18 1400 20 8 15 5 45 255 180 19 1400 100 8 15 5 45 245 179 20 1400 60 6 15 5 45 263 173 21 1400 60 10 15 5 45 285 171 22 1400 60 8 9 5 45 242 178 23 1400 60 8 21 5 45 296 187 24 1400 60 8 15 3 45 264 181 25 1400 60 8 15 7 45 284 178 26 1400 60 8 15 5 33 271 178 27 1400 60 8 15 5 56 282 178 28 1400 60 9 15 5 45 301 190 29 1400 60 8 15 5 50 310 192 30 1600 60 8 15 5 45 314 202 table a1 continued 8 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 doi: http://dx.doi.org/10.36956/sms.v3i1.316 sustainable marine structures http://ojs.nassg.org/index.php/sms/index article non-linearity analysis of ship roll gyro-stabilizer control system sathit p.1*　chatchapol c.2　phansak i.3 1. department of maritime engineering, faculty of international maritime studies, kasetsart university, chonburi, 20230, thailand 2. department of mechanical engineering, faculty of engineering, kasetsart university, bangkok, 10900, thailand 3. department of nautical science and maritime logistics, faculty of international maritime studies, kasetsart university, chonburi, 20230, thailand article info abstract article history received: 19 january 2021 accepted: 24 may 2021 published online: 30 may 2021 a gyro-stabilizer is the interesting system that it can apply to marine vessels for diminishes roll motion. today it has potentially light weight with no hydrodynamics drag and effective at zero forward speed. the twin-gyroscope was chosen. almost, the modelling for designing the system use linear model that it might not comprehensive mission requirement such as high sea condition. the non-linearity analysis was proved by comparison the results between linear and non-linear model of gyro-stabilizer throughout frequency domain also same wave input, constrains and limitations. moreover, they were cross checked by simulating in time domain. the comparison of interested of linear and non-linear close loop model in frequency domain has demonstrated the similar characteristics but gave different values at same frequency obviously. the results were confirmed again by simulation in irregular beam sea on time domain and they demonstrate the difference of behavior of both systems while the gyro-stabilizers are switching on and off. from the resulting analysis, the non-linear gyro-stabilizer model gives more real results that correspond to more accuracy in a designing gyro-stabilizer control system for various amplitudes and frequencies operating condition especially high sea condition. keywords: active gyro-stabilizer twin gyro-stabilizer ship large roll motion system identification inverse problems non-linear damping moment non-linear restoring moment 　 *corresponding author: sathit p., department of maritime engineering, faculty of international maritime studies, kasetsart university, chonburi, 20230, thailand; email: sathit.pon@ku.th 1. introduction of the six modes of motions of marine vessel, roll motion is the important mode to be realized. it is the greatest reason to capsize also affect to operation of crews, passengers comfortable and cargos damage, when a vessel is excited by wave load at high sea. in order to diminish amplitude of roll motion, roll stabilizer system becomes an important role. more than 100 years, many types of roll stabilizer have been engineered by many researchers and designer. the following example, bilge keels, sloshing, sliding weight, gyro, u-tube, sea-ducted, variable angle fins, hydro-foil keel fin and rotating cylinder etc. since 1995, chadwick [1] had gathered types of roll stabilizers and it has been classified by control method to be passive and active control. the passive control is the control system does not require any external power source to operate the control device but the active control system does opposite way [2]. some types of stabilizer are only passive control as bilge keels and sloshing. some types are only active control such as variable angle fins and rotating cylinder. and some types are both as sliding weight, 9 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 doi: http://dx.doi.org/10.36956/sms.v3i1.316 u-tube, sea-ducted and gyro. another way, haghighi and jahed-motlagh [3] have mentioned classification of system control types that can be classified as either external or internal control systems. the external control system is systems generate resisting load (forces and moments) outside a ship hull and the internal control system is systems generate resisting load inside [4]. the principal advantages of internal systems are not hydrodynamic drag and effective zero forward but it has heavyweight, volume penalty and there are limited in stabilisation capability. the external systems have lightweight but it creates hydrodynamic drag and ineffective at zero forward speed [5,6]. the following above mention and nowadays technology, a gyro-stabilizer become to be an interesting system at present. because it has a combination of internal and external control system advantages: potentially light weight with no hydrodynamic drag and is effective at zero forward speed. a gyro-stabilizer system is to use resisting moments, which moments are the cross product between angular momentum vector of flywheel and angular velocity vector around precession axis. the resisting moment is applied to vehicle or other to resist external excitation moments that are keeping minimal oscillatory amplitude of rolling vehicle. however, this paper focus on a gyro-stabilizer is applied to small ships. background stories of gyro-stabilizers, it has been applied to various inventions. the first gyro-stabilizer application was invented by brennan [7]. brennan used twin gyro that it had counter-rotating flywheels to stabilize unstable vehicle (two-wheel monorail car). this invention had similar patents [8,9,10]. more researches, gyro-stabilizers were applied to stabilize to two-wheel vehicles such as a bicycle [11] and motorcycles [12]. in 1996, brown and his team published about the using gyro-stabilizer that provides mechanical stabilization and steering a single-wheel robot [13]. another field, nasa used the advantage of gyro-stabilizer to control attitude of large space structures or satellite [14]. in additional, gyro-stabilizers have been applied to maritime field, e.g., autonomous under water vehicle [15,16], torpedo [17] and free surface vehicle etc. the first record of a gyro-stabilizer in marine vehicles was found accidentally, howell torpedo, it was installed rapid rotation of fly-wheel. there was 16 inches a steel wheel diameter and was spun up to 16,000 rpm. the torpedo was experimented for locking target on u.s. navy boat [17]. for the first time of free surface vehicle, a gyro-stabilizer device was passive system that it was utilized to diminish roll motion [18,19,20]. active gyro-stabilizer systems were developed from passive systems. the first system was proposed by elmer sperry in 1908 [21]. recently, many researchers have proposed related new researches of gyro-stabilizer with novel control methods. townsend et al. [4] published a new active gyrostabiliser system for ride control of marine vehicle. mcgookin et al. [22] published application of mpc and sliding mode control to ifac benchmark models. perez and steinmann [23] demonstrated analysis of ship roll gyrostabilizer control that revisited the modelling of coupled vessel-gyrostabilizer and also describes design trade-offs under performance limitation. haghighi and jahed-motlagh [3] proposed ship roll stabilization via sliding mode control and gyrostabilizer. for designing ship roll gyro-stabilizers, a preliminary design is important thing. in order to design it, designers need to know wave loads, ship motion (ship model) and actuator characteristics (gyro-stabilizer model). almost, modelling of designing uses an equation of motion in linear model that it may not comprehensive mission requirement, such as large roll motion from both high amplitudes and frequencies of waves. normally, these have to be non-linear model under limitations that have more correction and accuracy also failure cases from system instability. the failure cases may not occur in linear modelling but it was found in non-linear. from these reasons, it becomes the motivation of this study. both linear and non-linear model of gyro-stabilizer and ship were concerned. non-linear system modelling of gyro-stabilizer was comprised of ship rolling model and single axis gimbal gyroscope model (non-linear equation of motion). normally, non-linearity of gyro-stabilizer model appears in restoring term and exciting moment term. however non-linearity of ship roll model able to appear all terms of equation of motion (term of inertia, damping, restoring and exciting moment). in order to formulate non-linear ship roll model, the system identification method is used to find non-linear coefficients of added inertia, damping and restoring term of ship. the system identification methods of ship roll motion can be found in many papers such as masri et al. (1993) [24], chassiakos and marsi (1996) [25], liang et al. (1997) [26], liang et al. (2001) [27], jang et al. (2009) [28], jang et al. (2010) [29], jang (2011) [30] and jang et al. (2011) [31] etc. however, in this paper uses method of pongdung et al. [32] which is the novel method and able to find all of non-linear terms of ship model. the objective of this presentation is to analyse non-linearity of ship roll twin gyro-stabilizer control system under limitations of wave load and precession angle via frequency domain analysis and time domain simulation. 2. principals and theories analysis of gyro-stabilizer system has three parts that is realised. it comprised of water wave model, ship 10 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 model and gyro-stabilizer model. in order to reach the present objective, the regular and irregular deep water wave models are selected to set simulation cases. the ship and gyro-stabilizer models is concerned both linear and non-linear model to observe and analyze effects of system non-linearity from simulation results. the general principle of gyroscopic stabilization, its torque is produced by gyro-stabilizer that installed in a ship opposes roll exciting moment from water wave. this exciting moment disturbs the angular momentum of flywheel such that develops precession motion. the cross product of flywheel angular momentum and precession rate induces moment to resist the exciting moment in opposite direction [33]. figure 1 explains working principle of gyro-stabilizer that is installed in a marine vessel. at present, twin-flywheels are selected, and there are spinning and precession angle rotate in opposite direction. its result cancels the side effect of gyroscopic moments in the other directions (normally in pitch and yaw of ship). figure 2 displays the working of twin gyro-stabilizer. figure 1. illustration single gyro-stabilizer installation and its working principle figure 2. demonstration working principle of twin gyro-stabilizer and elimination of its side effect of gyro-stabilisation moment 2.1 full non-linear gyro-stabilizer model the prediction of gyro-stabilizer performances was modelled via the two equations of motions. the first equation is the ship model and the second equation is gyro-stabilizer model. consideration a ship motion, while it is excited by water wave that is demonstrated in figure 3. instantaneous, the ship is rolled by moment of inertia in counter clockwise and is acted by wave, which wave free surface has β (wave slope angle) against horizontal line. the y axis of body fix frame has φ (roll angle) against horizontal line. thus θ is relative angle between roll and wave slope angle. the following newton’s second law, the equation of motion of ship can be written as ( ( )) ( ) ( ) 0i i θ θ b θ θ c θ θ44 44 44 44+ + + =a ¨ ¨   (1) where 44i is moment of inertia of ship that is a constant value. 44 ( )ai θ is non-linear added moment of inertia function. 44 ( )b θ is non-linear damping moment function and 44 ( )c θ is non-linear restoring moment function. in order to find non-linear functions, non-parametric system identification method is used. briefly, pongdung’s method [32] is chosen to determine non-linear functions because it able to find all non-linear functions in equation 1 synchronously. the method needs measured motion data from free roll decay experiment or cfd (computational fluid dynamics) to formulate inverse problem. actually, the responses are outputs and are calculated via equation of motion that the non-linear functions of each term are known variable values. on the other hand, the responses become to input (measured data) in inverse problem and the non-linear functions become to output (unknown variables). each moment terms are solved by inverse problem formalism and stabilized by landweber’s regularization method. its solutions are chosen the optimal solution through l-curve criterion. finally, the zero-crossing detection technique of measured data is compared with that solution for identifying each moment function and reconstruction them. for more detail can see in pongdung et al. [32]. figure 3. rolling of ship on water wave free surface when all non-linear functions is known, substituting doi: http://dx.doi.org/10.36956/sms.v3i1.316 11 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 θ φ β= − into equation 1, it becomes [ ( )]( ) [ ( )]( ) + φ − φ − = i i β β b β β [ ( )]( ) 0 44 44 44 c β β44 + φ− φ− + φ − φ −a ¨ ¨ ¨ ¨    (2) rearranging equation 2, it yields + φ − φ = + φ− + φ − + φ −       i i β b β [ ( )] [ ( )]    44 44 44 b β β c β β c β i i β β 44 44 44 44 44 + φ− φ+ φ − φ ( a       ¨ ¨ ¨ )  [ ( )]    ( a   ¨ ¨ ¨ ) (3) equation 3 is the full nonlinear ship motion: left-hand side is ship moment and right-hand side is exciting moment. the equation 3 has the same coefficient function in the same term of inertia, damping and restoring: the roll angle and wave slope are equal values at steady state on time domain, but at transient are not. thus, define τ i i θ β b θ β c θ βw a= + + +[ ( )] [ ( )] [ ( )]44 44 44 44 ¨ ¨   (4) the wave slope β is determined from equation 5, which it is regular linear wave (deep water wave). η x t η kx ωt( , sin) = −0 ( ) (5) where 0η is wave amplitude, k is wave number, x is distance in x direction, ω is angular frequency and t is time. when differentiate equation 4 with x , it becomes to wave slope equation follow as equation 6. then wave slope velocity and acceleration are equation 7 and 8 respectively. ( ) 0 , cos( ) d x t k t dx η β η ω= = − (6) 0 sin( )k tβ η ω ω= − (7) 2 0 cos( )k tβ η ω ω= − − (8) thus, a model for motion of the ship in roll together with and n -spinning-wheel gyro-stabilizer can be expressed follows as block diagram in figure 4. then it can be formulated in equation of motion follow as equation 9 and 10. i i θ b θ c θ τ τ44 44 44 44+ φ+ φ + φ = −a w g( ) ( ) ( ) ¨ ¨   (9) i α b α c α τ τg g g s p ¨ + + = − sin (10) where α ,α and α in equation 9 are precession angle, precession rate and precession acceleration respectively. the following equation 10 gi , and gc are moment of inertia, damping and restoring coefficient of gyro-stabilizer about precession axis. equation 9 represents the full non-linear ship roll dynamics, while equation 10 represents the non-linear dynamics of gyro-stabilizer about the precession axis. the following equation 9 and equation 10 associate coupled system, the wave-induce roll moment ( wτ ) excite the ship rolling. when roll motion develops, the roll rate induces a moment about the precession axis of spinning wheels ( sτ ). and then the spinning wheels develop precession, its reaction moment resists on the ship with opposes direction of the wave-induce moment ( gτ ). τ k αs g= φ cos (11) τ nk α αg g=  cos (12) w h e r e gk i s s p i n n i n g a n g u l a r m o m e n t u m ( g spin spink iω= ) the roll stabilization moment for passive system can be modified the precession damping and stiffness as well as leave the gyro to free work. for an active system, it is controlled through the precession dynamics via the precession control moment that is pd controller and expressed follow p p dk kτ α α= +  (13) where pk is proportional control gain and dk is derivative control gain. the advantage of this control law is no needing ship roll sensors. figure 4. block diagram of full non-linear twin gyro-stabilizer model doi: http://dx.doi.org/10.36956/sms.v3i1.316 12 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 2.2 linear gyro-stabilizer model in the past, analysis any control systems via equation of motions were treated to be linear differential equation. there are reduced complexity and able to transform to s-domain, and then change s-domain to be frequency domain. at steady state, the analysis control systems through frequency domain are proper. this section uses almost equation from perez and steinmann (2009) [23] from equation 9 and equation 10, the models are linearized: for small angle of roll and precession, the coefficients of left-hand side are constant value. however, let define, φ ≈ φ cosα (14) α α α cos ≈ (15) and sin α α≈ (16) hence, the linear equation expressed as follow: (i i b c τ τ44 44 44 44+ φ+ φ + φ = −a w g) ¨  (17) i α b α c α τ τg g g s p ¨ + + = − (18) τ i i β b β c βw a= + + +( 44 44 44 44) ¨  (19) τ ks g= φ (20) τ nk αg g=  (21) note that, pτ no changes in linear model. and linear gyro-stabilizer system is demonstrated in figure 5. figure 5. block diagram linear twin gyro-stabilizer model from zero condition, thus the open loop transfer function is h sol ( ) = = φ τ s ol w ( ( s ) ) ( )i i s b s c44 44 44 44+ + +a 2 1 (22) the close loop transfer function is (23) where ( )ol sφ and ( )cl sφ are laplace transforms open and close loop roll angle respectively. and the transfer function of precession angle to roll angle is h scl ( ) = = φ τ s cl w ( ( s ) ) (i s b s c i s b s c nk s44 44 442 2 ' ' 2 2+ + + + + i s b s cg g g 2 ' ' )( + + g g g g) h spr ( ) = = = α s α s φ( ( s) ) φ  ( ( s) ) i s b s cg g g 2 ' '+ + k sg (24) where b b kg g d ' = + (25) c c kg g p ' = + (26) the transfer function of precession angle to wave exciting roll moment that is the result from equation 23 and 24 is = h s h s h s ( pw pr cl i s b s c i s b s c nk s44 44 44 ( ) 2 2 ' ' 2 2 = = + + + + + τ s α s w ( ( ) ) )( k s ( g g g g g ) ( ) ) (27) rearranging equation 24, it yields h spr ( ) =        k i g g               s2 + + b c i ig g s g g ' ' (28) and the roots are p1,2 = − ± − b b c i i ig g g g g g ' ' '        2 4 (29) both roots are negative real roots (stability condition) if and only if, 0gb′ > , 0gc′ > also constraint of doi: http://dx.doi.org/10.36956/sms.v3i1.316 13 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0         b c i ig g g g ' '2 > 4 (30) the following equation 13, the proportional term is set during design due to centre of mass location, normally locate below the precession axis, which like a pendulum, the gc′ value is fixed. thus, the control moment becomes τ k αp d=  (31) from equation 30, it able to formulate the condition of two poles to be real root: b c ig g g ' '> 4 (32) it can set as b γ c i rg g g ' '= 4 , 1> (33) then substitute equation 33 in to equation 25, it become k γ c i b rd g g g= −4 , 1 ' > (34) this derivative control gain is used through under constrained performance follow section 2.4 2.3 control performance and limitations in order to observe the objective performance, the output sensitivity function is defined as: s s( )  φ φ ol cl ( ( s s ) ) (35) the bode’s integral constraint is ∫ ∞ 0 log 0s jω dω( ) = (36) and the roll reduction (complementary sensitivity function) is defined as rr ω s jω( ) = − =1 ( ) φ − φol cl( jω jω φcl ) ( jω) ( ) (37) the integral constrain becomes ∫ ∞ 0 log 1 0− =rr jω dω( ) (38) another form of roll reduction function is rr ω( ) = −         1 h jω h jω ol cl ( ( ) ) (39) note that, the roll reduction values possible to be negative or positive values but less than 1 along interested range of frequency. the meaning of negative value is roll amplification. the meaning of positive value is roll reduction. then the roll reduction close to 1, it has better performance. 2.4 constrained performance the additional constrain is cause by the precession angle limiting due to mechanical design. if the precession angle reaches this limit, the device may get damage or deteriorate. additionally, it may causes of roll amplification rather than roll reduction of ship: phase of resisting moment cannot eliminate wave induce roll moment. for a regular wave of frequency 0ω and wave height 0 sh , it induces roll exciting moment amplitude 0 wτ . the following equation 27, it can be obtained the amplitude of precession angle: a 0 = h jω τpw ( 0 ) 0w (40) the given constrain is the maximum precession angle maxα , it can be obtained the optimal of gb′ that it take the precession angle close to its limit: ( ) ( )( )( )* 0 0 0max0arg min ,pw g wh j bγγ ω α ω γ τ> ′= − (41) 3. cases study configurations and numerical experiment setup to carry out the aim of this presentation, the non-linear gyro-stabilizer system is validated with linear gyro-stabilizer system to observe and analyze its performance at the same environment and limitation. the vessel was set to zero speed and moved against beam sea direction. in order to determine the system design point, assume that the system was designed for deep water wave, significant wave height of 0.04 m, all frequency of its. in order to observe and analyze non-linearity of a gyro-stabilizer system, this present, v-hull section was selected because it is a general section profile of highspeed boat and small ship that are suited. the dimensions of selected v-hull are demonstrated in figure 6. both linear and non-linear equation of motion was found via doi: http://dx.doi.org/10.36956/sms.v3i1.316 14 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 measured data that were the result from cfd method, xflow commercial program. the simulations are set to be unsteady flow. there is free roll decay method, which was set initial condition of roll angles are 5, 10, 15, 20, 25 and 30 degrees. according to cfd simulation results, the example of measured data from simulation case, which was set 30 degree of initial condition was demonstrated in figure 7. figure 6. the v-hull geometry and dimension for simulation figure 7. measured data from cfd of initial condition 30 degree the linear ship model was formulated from logarithmic decrement method. the method appropriates to small roll motion less than 8 degree. it requires only roll angle data (measured data from cfd) to detect maxima or minima values, where are used to find estimated exponential function. the function leads to determine the damping ratio and natural frequency. there can be converted to add moment of inertia, damping coefficient. however, restoring coefficient can be found from inclination calculation. according to this method, the details of calculation were omitted in this presentation. for this paper, the simulation of 5 degree of initial condition was used. the estimating of exponential function was shown on figure 8. according to estimated exponential function the linear ship model is 0.3255 0.0494 19.7321 0φ+ φ + φ = ¨  (42) note that, in free roll motion test θ φ= , there are not have relative motion between free surface and roll motion angle and 44 0.26i = . figure 8. determination of exponential function from roll angle data of 5 degree initial condition the non-linear ship model was formulated by reconstruction non-linear damping coefficient and added moment of inertia via systems identification method that used all of measured data (roll angle, angular velocity and angular acceleration) and all initial condition from cfd method. the non-linear restoring coefficient function was known via inclination calculation. the calculation result was fitted by polynomial function follow as equation 43 and its curve was shown at the top of figure 9. c + φ − φ + φ − φ + φ − φ + 344.3239 283.2101 148.2937 49.4689 10.4220 1.4402 0.1454 44 (φ = − φ + φ − φ) 6 4 2 19.7321 108.8680 258.2096 12 10 8 18 16 14 (43) the non-linear damping coefficient function was found by accumulating the damping moment data point from system identification method, and there were taken by curve fitting method which is shown in the middle of figure 9. then the moment function was divided by φ , thus the non-linear damping coefficient is b44 (φ = φ + ) 0.1588 0.13912 (44) from the same procedure of formulating non-linear damping moment, the added moment of inertia fitting curve is shown at the bottom of figure 9 and its average doi: http://dx.doi.org/10.36956/sms.v3i1.316 15 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 value is i44a       φ = ¨ 0.066 (45) the full non-linear ship model was simulated on free decay motion with 30 degree initial condition to verify its accuracy. the simulated result of roll angle via equation 1 was plotted in figure 10 also result from linear model and measured roll angle from cfd. it proves that the non-linear model is better accuracy more than linear model, when both results were compared with measured roll angle from cfd. hence, the non-linear ship model has enough accuracy and can be used in this presentation. figure 9. the estimating functions of restoring moment (top), damping moment (middle) and added moment of inertia (bottom) figure 10. the comparison of simulations between results of non-linear ship model (system identification method) and linear ship model (logarithmic decrement method) with measured data from cfd the non-linear and liner gyro-stabilizer model was used according to equation10 and equation 18 respectively. there have same characteristic coefficients. the gyro-stabilizer was assumed that its speed is constant at 300 rpm ( spinω ), the moment of inertia about spin axis is 0.0125 kg-m2 ( spini ) and the moment of inertia about precession axis is 0.0005 kg-m2 ( gi ). the damping coefficient is zero 0gb = , there is on friction about precession axis. the restoring coefficient is zero; the center of gravity position was located at middle of spin and precession axis (no effect of pendulum). the following equation 13, the proportional gain pk is fixed value of 0.1. the derivative gain was determined via equation 34 and equation 41. both linear and non-linear systems were determined through frequency domain and simulated with regular waves, which the range of frequencies is 0 to 14.84 rad/ s. the simulation cases of linear system were varied wave amplitudes from 0η = 0.02 m up to 01.5η . the linear simulation case of 0η was set to be reference case. the *γ of each wave amplitude of simulation cases follow equation 41 were gathered, and then they were used in simulation cases of full non-linear system. the full non-linear system was simulated in time domain with only amplitude of 0η . moreover, in order to find a design trade-off, the *γ of each wave amplitude of linear system were used. the name of simulation cases are described in table 1. table 1. the description of simulation cases case name description gyro-model ship-model lsol linear open loop system linear lscl linear close loop system linear linear lscl @ 0cη linear close loop system that determined with wave amplitudes of 0cη ( c =1.1, 1.2, 1.3, 1.4 and 1.5) linear linear fnsol full non-linear open loop system non-linear fnscl full non-linear close loop system non-linear non-linear fnscl@ 0cη full non-linear close loop system with the *γ values of each wave amplitude of lsol ( c =1.1, 1.2, 1.3, 1.4 and 1.5 ) non-linear non-linear 4. results and discussions in order to examine the characteristics of performances of non-linear gyro-stabilizer system, the linear system was determined first. the following figure 11 – 14, they show the results of linear gyro-stabilizer characteristics. figure 11 show exciting moment (input), the result from equation 19. the graph was also plotted stokes limit; the exciting moment cannot exceed this line at upper doi: http://dx.doi.org/10.36956/sms.v3i1.316 16 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 side. stokes and exciting moment line of amplitude 0.02 m intersect at 14.84 rad/s, which it was set to be maximum value of frequency range. all lines have tough at ω = 7.786 rad/s that is natural frequency of linear vessel model because it has the same coefficients. and then, when frequencies increase, the exciting moment rapidly increase. it is obviously the increasing of wave amplitudes correspond to increasing exciting moment. figure 12 and 13 are they were *γ values and precession angles of each wave amplitude respectively. they simultaneously determined via equation 27 and 41. figure 12 shows the minimum *γ values of each wave amplitude. all wave amplitudes gave *γ values of 1 until the system gets the exciting frequency that makes the precession angle reach its limit value (60 degree, also observe figure 13). it has been called critical point. from this point *γ value rapidly increasing to keep precession angle does not exceed 60 degree. as the higher wave amplitude, the critical points have appeared at lower frequency. figure 13 shows the precession angles in frequency domain. the trend of precession angle resembles the pose of exciting moment in figure 11. however, the crests of all lines about exciting frequency value of 2 were affected from turning proportional gain pk that was fixed value of 0.1. and the higher wave amplitude gives the higher precession angle. the flat band at high exciting frequency that has constant value of 60 degree is explained as above paragraph. figure 14 shows the roll angle responses. at the lower exciting frequency from critical point, the result trends resemble precession angle but it rapidly increases when the exciting frequency increase from critical point. the increasing rapidly of roll angle from the critical point is caused by the precession angle reach its limit, which it cannot have more precession rate to create resisting moment for cancel exciting moment. moreover, at the higher wave amplitude gives the higher roll angle response. figure 11. exciting moment of the linear gyro-stabilizer model figure 12. estimating of *γ values each wave amplitude from equation 41 figure 13. precession angles of linear gyro-stabilizer model so that determined via equation 27 and 41 with the following *γ values each wave amplitude in figure 12 figure 14. roll angle responses of linear gyro-stabilizer model each wave amplitude via equation 23 the following linear model results consistent and reasonable to each other. they can be used to compare with the non-linear system in the same wave condition. howdoi: http://dx.doi.org/10.36956/sms.v3i1.316 17 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 ever, according to section 3, the non-linear gyro-stabilizer system model was assumed as it was designed to operate in beam sea that it has significant wave height ( 1 3h ) of 0.04 m ( 0η = 0.02 m). but it cannot directly determine *γ through transfer function like linear system model. thus the *γ values each wave amplitude from linear model were applied to non-linear model. the non-linear system needs to simulate in time domain and collected the amplitude simulation results at steady state. hence, figure 15 18 illustrate the comparison between linear and non-linear model. some data of non-linear model disappear because of its solutions became unstable (no steady state) when the precession angle reached the limit angle. figure 15 shows the exciting moments both open and close loop of linear and non-linear system. they have the trend like exciting moments of linear system. linear open loop and close loop exciting moments are same line because they have same coefficients of vessel model. the all non-linear exciting moment lines are above liner exciting moment at high frequencies from around the natural frequency. the difference of exciting moment values causes of the coefficient functions follow as equation 4 that related to θ , θ and θ. figure 16 shows the precession angle result that all non-linear precession angles have the same line until they reach to a limited angle at the exciting frequency value of 11.85 rad/s. and almost values are above linear system. the cause of all non-linear precession angles has the same values. they used same *γ =1 as following figure 12. after they reach the limited angle at higher frequencies, the data lost because the system became unstable so that it now has steady state. however, the non-linear system back to stable at the end of lines because of the increasing of *γ value (see figure 12) able to reduce the precession angles below limited angle. and then, they obviously show the higher *γ each wave amplitude gave lower precession angle at the higher frequencies. the following figure 17, roll angle responses of the open and closed-loop of linear and non-linear systems are shown. the comparison between open-loop of linear and non-linear system obviously difference behavior along frequencies range; the linear open-loop system is fair curve, while the non-linear closed-loop system has the apex at the frequency value of 6 rad/s. this is the important cause to deep studying throughout non-linear gyro-stabilizer system; a difference response behavior will give the difference a system design point. the linear and non-linear closed-loop systems have a same trend. all non-linear roll angle responses have same values until they reach the frequency of 11.85 rad/s and almost roll angle responses values are above the linear line. the closed-loop non-linear system uses more precession angle than linear system but they give more roll angle responses than linear system. after the critical point of linear closed loop system, all lines of roll angle responses increase and approach to open-loop systems because precession angles were forced and reduced to constant in linear model and non-linear model respectively. this reason refers to inefficiency of the systems, when the precession angle reaches the limited angle. figure 18 explains the responses in view of a relative roll angle response and can say that are the inverse behavior of a roll angle response. while the stabilizer attempt to keep roll angle approach to zero, the difference between a wave slope and roll angle increase (see relation in figure 3). figure 15. comparison exciting moments between non-linear and linear gyro-stabilizer models; the linear model of 0η was set to be the reference figure 16. comparison precession angle responses between non-linear and linear gyro-stabilizer models; the linear model of 0η was set to be the reference doi: http://dx.doi.org/10.36956/sms.v3i1.316 18 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 figure 17. comparison roll angle responses between non-linear and linear gyro-stabilizer models; the linear model of 0η was set to be the reference figure 18. comparison relative roll angle responses between non-linear and linear gyro-stabilizer models; the linear model of wave amplitude 0η was set to be the reference figure 19. precession angle responses of linear and non-linear gyro-stabilizer model of wave amplitude 0η and fix γ =10.6 the non-linear behaviors were analysed and explained throughout frequency domain as they were mentioned above. however, in reality, a *γ value cannot adjust base on frequency domain as following figure 12; a frequency cannot know immediately in time domain. thus a *γ will be selected only one value from figure 12 so that appropriate with operation requirements. the *γ value of 10.6 was selected. it locates at the right end of line lscl @ 0η . the value is the highest value, which forces the precession angle to work do not exceed the limited angle throughout the frequency range. then the selected value was used for both linear and non-linear gyro-stabilizer system. the results were plotted follow as figure 19 22 in frequency domain. in order to examine the effect of non-linearity, linear and non-linear gyro-stabilizer system model were simulated in irregular wave model of bretschneider’s [34] method that it has significant wave height of 0.04 m and the results were plot in figure 23. the following figure 19, the precession angles of non-linear system work under the limited angle throughout frequency range. it has same characteristic of linear system but has different values. hence, the roll angle response in figure 20 is consequence of precession angle. the roll angle response of non-linear system has same characteristic of linear system but has different values as well. figure 21 shows the frequency response results. the peak of frequency response of non-linear open-loop system that refers to the natural frequency of vessel is different from linear open-loop system. the curve of linear closed-loop system is fair curve and approach to zero throughout the frequency range. the curve of non-linear closed-loop system has same behaviour of open-loop and its peak is lower. according to figure 22, the reduction rates of linear and non-linear system are shown. the reduction rate refers to the efficiency of the stabilizer system. the non-linear system has the reduction rate values near linear system at the frequencies lower than 6 rad/s. but at the higher frequencies value, the reduction rate values of non-linear system are lower. according to the previous results, the *γ value was selected and fixed. they are made to clearly understand and proved that the non-linearity of non-linear model give a lot of different results at all. thus, the designing base on linear model may give the wrong respond in reality. in order to prove again, the linear and non-linear gyro-stabilizer system models were simulated in same irregular beam sea on time domain. assume that, precession angle is limited by mechanism at 90 degree but the *γ value was selected from the limited angle at 60 degree of regular wave amplitude in order to let it has margin to prevent a doi: http://dx.doi.org/10.36956/sms.v3i1.316 19 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 damage when the gyro-stabilizer system get higher amplitude in irregular wave. figure 20. roll angle responses of open and close loop condition of linear and non-linear gyro-stabilizer model of wave amplitude 0η that the close loop model was set the fix value of γ =10.6 figure 21. comparison of frequency responses of open and close loop condition of linear and non-linear gyro-stabilizer model of wave amplitude 0η that the close loop models were set the fix value of γ =10.6 figure 22. comparison of reduction rate between linear and non-linear gyro-stabilizer model of wave amplitude 0η that the close loop models were set the fix value of γ =10.6 in the following figure 23, the setting of gyro stabilizer simulation cases (linear and non-linear system) were simulated in irregular wave model. the gyro-stabilizers were switched off first, and then begin to switched on at 20 second of simulation time to observe the difference of behaviors when the gyro-stabilizer models were switch off and on. the systems performances were gathered and shown in table 2 in root mean square. at the top of figure 23, the exciting moments of linear and non-linear system were shown. they were induced from the same irregular wave model but it gave exciting moment amplitude and phase shift slightly difference. the rms of exciting moment of linear model has the value less than non-linear model so that accord to figure 15. when the stabilizer switched off, the vessel did not stabilize. the roll angle response of linear model shown at the middle of figure 23 has the rms value more than non-linear model slightly. these results accord to figure 20. when the gyro-stabilizers were switched on, the precession began to move for stabilize the vessel, the roll angle responses were reduced. the precession angle responses were shown at the bottom of figure 23. as the gyro-stabilizer switched on, the precession angle of linear model has rms value more than non-linear accord to figure 19. and the roll angle response of linear model has rms value lower than non-linear model. however, the reduction rate (rr) of linear system has rms value more than non-linear system and so very different. as the mentioned these results, they clearly show that the designing via the linear model cloud makes the gyro-stabilizer system miss the design point of mission requirements. on the other hand, the non-linear system model cloud gives more approach to reality for designing follow mission requirements. table 2. the root mean square values (rms) of gyro-stabilizer system performances in irregular beam sea according to figure 23; the significant wave height and average wave frequency is 0.04 m and 10.68 rad/s respectively. model wτ [nm] α [deg] φ [deg] rr [-] lsol 14.5 21.56 fnlsol 15.38 18.57 lscl 14.5 32.03 4.75 0.78 fnlscl 15.05 31.13 11.46 0.38 doi: http://dx.doi.org/10.36956/sms.v3i1.316 20 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 figure 23. comparision of linear and non-linear gyrostabilizer system model when they are swicthed off and on in irregular wave with γ =10. 5. conclusions a gyro-stabilizer is the interesting system that it can apply to marine vessels for diminishes roll motion. today it has potentially light weight with no hydrodynamics drag and effective at zero forward speed. the twin-gyroscope was chosen for this presentation because of it not has side effect moment. almost, the modelling for designing the system use linear model that it might not comprehensive mission requirement such as high sea condition (high wave amplitude and various frequencies). thus, the non-linear model becomes important role because it able to give the interested results approach to reality more than linear model. the non-linearity analysis was proved by comparison the results between linear and non-linear model of gyro-stabilizer throughout frequency domain also same wave input, constrains and limitations. moreover, they were cross-checked by simulating in time domain. actually, controller gains of the non-linear model cannot directly determine the appropriated turning gain dk via frequency domain analysis. hence the dk of non-linear model was approximated by selecting the *γ value so that resulted to dk from linear model at the highest frequency value of selected wave amplitude. the comparison of interested results as wave exciting moment wτ , precession angle α , roll angle response φ and reduction rate of linear and non-linear close loop model in frequency domain has demonstrated the similar characteristics but gave different values at same frequency obviously. the results were confirmed again by simulation in irregular beam sea on time domain and they demonstrate the difference of behavior of both systems while the gyro-stabilizer was switching on and off. from the resulting analysis, the non-linear gyro-stabilizer model gives the results closer to realistic that correspond to more accuracy in a designing gyro-stabilizer control system for various amplitudes and frequencies operating condition especially high sea condition. references [1] chadwick, j.h. (1955), “on the stabilization of roll”, trans. soc. naval arch. marine eng, 63, 237-280. [2] marzouk, o.a. and nayfeh, a.h. (2009), “control of ship roll using passive and active anti roll tanks”, ocean engineering, 36(9), 661-671. [3] haghighi, h. and jahed-motlagh, m.r. (2012), "ship roll stabilization via ssliding mode control and gyrostabilizer", bul. inst. politeh. iai autom. control comput. sci. sect. j, 1, 51-61. [4] townsend n.c., murphy, a.j. and shenoi, r.a. (2007), “a new active gyrostabiliser system for ride control of marine vehicles”. ocean engineering, 34 (11-12), 1607-1617. [5] lewis, v.e. (1986), “principles of naval architecture”. the society of naval architects and marine engineers. chapter ix. [6] lloyd, a.r.j.m. (1998), “seakeeping ship behaviour in rough weather”. ellis horwood ltd. [7] brennan, l. (1905), "means for imparting stability to unstable bodies", us patent 796893. [8] sperry, e.a. (1908), “steadying device for vehicles”, patent us 907907. [9] schilovski, p.p. (1909), “gyrocar”, patent gb 12021. [10] schilovski, p.p. (1914), “gyrocar”, patent gb 12940. [11] beznos, a.v., formal’sky, a.m., gurfinkel, e.v., jicharev, d.n., lensky, a.v., savitsky, k.v. and tchesalin, l.s. (1998). “control of autonomous motion of twowheel bicycle with gyroscopic stabilization”, proceedings—ieee international conference on robotics and automation 3, 2670-2675. [12] karnopp, d. (2002), “tilt control for gyro-stabilized two-wheeled vehicles”. vehicle system dynamics, 37 (2), 145-156. [13] brown, h.b., jr. and xu, y. (1996), "a single-wheel, gyroscopically stabilized robot", proc. of the 1996 ieee int. conf. on rob. and autom, minneapolis, minnesota. [14] aubrun, j.n. and margulies, g. (1979). “gyrodampers for large scale space structures”, technical report, nasa cr-159 171. [15] woolsey, c.a. and leonard, n.e. (2002), “stabilizing underwater vehicle motion using internal rotors”, automatica, 38 (12), 2053-2062. [16] schultz, c. and woolsey, c.a. (2003), “an experimental platform for validating internal actuator control strategies”, in: ifac workshop on guidance and control of underwater vehicles, april 2003, newport, south wales, uk, 209-214. [17] sperry, e.a. (1910), “the gyroscope for marine purdoi: http://dx.doi.org/10.36956/sms.v3i1.316 21 sustainable marine structures | volume 03 | issue 01 | january 2021 distributed under creative commons license 4.0 poses”, transactions of the society of naval architects and marine engineers xviii, 143-154. [18] schlick, e.o. (1904a), “device for minimising the oscillatory movements of ships”, patent us 769493. [19] schlick, e.o. (1904b). “the gyroscopic effect of flywheels on board ship”, transactions of the institute of naval architects, 23, 117-134. [20] forbes, t.c. (1904), “device for steadying ships” patent us 769693. [21] sperry, e.a. (1908), “steadying device for vehicles”, patent us 907907. [22] mcgookin, m., anderson, d. and mcgookin, e. 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(2011), “a new method for measuring nonharmonic periodic excitation forces in nonlinear damped systems”, mechanical systems and signal processing. 25(6), 2219-2228. [32] pongduang, s., chungchoo, c. and iamraksa, p. (2020), “nonparametric identification of nonlinear added mass moment of inertia and damping moment characteristics of large-amplitude ship roll motion”, journal of marine science and application, 19(2), 17-27. [33] arnold, r.n. and maunder, l. (1961), “gyrodynamics and its engineering applications”, academic press, new york and london. [34] bretschneider, c.l. (1959), “wave variability and wave spectra for win-generated gravity waves”, technical memorandum no. 118, beach erosion board, u.s. army corps of engineers, washington, dc, usa. doi: http://dx.doi.org/10.36956/sms.v3i1.316 1 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v2i2.300 sustainable marine structures http://ojs.nassg.org/index.php/sms article study the role of maritime energy management in achieving the united nations sustainable development goals (un sdgs), in particular, goal 7, in oman maritime community hamid reza soltani motlagh* department of maritime engineering, international maritime college of oman (imco), suhar, oman article info abstract article history received: 21 december 2020 accepted: 15 march 2021 published online: 30 march 2021 sustainability is a concept for achieving integration and balance in development to preserve and use resources properly by providing new solutions to overcome structural, social and economic misconceptions to prevent further degradation and waste of natural resources and create a better future for human societies. sustainable development can be defined as a strategy for the correct use of resources, by modifying and redefining consumption patterns and avoiding one-sided development approaches. therefore, sustainable development is defined as a long-term and unlimited solution for aligning different concepts (social, economic, and environmental), seemingly independent but related and influencing each other. this paper examines the challenges and capacities of the oman maritime community and maritime energy management's role in terms of sustainable development. to analyze this issue, the role of key players in oman's maritime industry, such as the oman fisheries company and the oman shipping company, has been studied with the five main indicators of sustainable development goals, including people, the planet, peace, welfare, and partnership. keywords: sustainable development maritime energy maritime community oman maritime energy management unsdgs development goals 1. introduction in 2015, the un general assembly issued a strategic document called the sustainable development goals-agenda 2030, and the member states committed to doing it. this document contains 17 essential goals for sustainable development in different fields with the same approach and the goal [31]. these 17 goals, along with 169 related targets, encompass three key areas, including environmental, economic, and social, that significantly impact the planet and humanity as vital issues [31]. according to the agenda 2030, all countries are determined and undertake to provide and design a roadmap and plan of action on ending poverty and hunger of the people, protect the planet, prosperity for humanity, peace and mobilize resources for the implementation of the objectives of the global partnership on what is stated in the sustainable development goals. the most important factor for achieving these goals is the determination and responsibility of all people and all stakeholders and industries to achieve them. the maritime industry is one of the main players in achieving these goals. the responsibility of all people, stakeholders, and *corresponding author: hamid reza soltani motlagh, department of maritime engineering, international maritime college of oman (imco), suhar, oman; email: hamid@imco.edu.om 2 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 industries to achieve these goals. the maritime industry is one of the main players in achieving these goals. therefore, as the industry’s principal source, the international maritime organization (imo) has issued and clarified the necessary roadmaps and guidelines in all areas relevant to these goals for sustainable development[8]. among these areas is the topic of energy and its management, as identified in goal number seven and has been addressed. therefore, the international maritime organization, in the field of energy and its management, focuses on facilitating international cooperation and global partnerships for the deployment and access to modern, sustainable, and affordable energy in the maritime industry, which is mentioned as the global maritime energy efficiency partnerships project (glomeep) and being implemented in partnership with the united nations development programme (undp), global environment facility (gef) and imo [8]. the project aims to provide a platform and a framework to build the capacity needed to increase energy efficiency and enhance marine energy management by increasing participation at national, regional, and global levels, focusing on developing countries [8]. another important project, which imo is currently undertaking is the global maritime technology cooperation center (mtcc) network (gmn) that focuses on mitigating the impact of the maritime industry on climate change and providing technical solutions to developing and less developed countries [4]. the maersk shipping company has defined the company’s position and responsibility for each of the sustainable development goals and the type of impact those goals have, on the company’s goals and vision [12]. in 2019, for example, five pacific states entered into a treaty that would emit greenhouse gas emissions from the ship’s fuel consumption. in the first phase, and by 2030, it has reduced by 40 percent, and by 2050, it will reach zero [32]. another example is the blue generation project, which is currently underway in the european economic area and aims to create sustainable employment for young people without a job [1]. this paper examines oman’s maritime industry and its maritime energy management role in achieving sustainable development goals, with a particular view to goal seven on energy and energy management. 2. literature reviewmaritime industries and sdgs in a study on the maritime industry’s role in achieving the goals of sustainable development, five areas have been mentioned as opportunities. all sustainable development goals are within the scope of these opportunities and include the paris agreement, sustainable infrastructure, ocean life protection, sustainable ocean economies in the future, and accountability for practical action in this area[3]. in energy, which is defined under goal 7, the development and implementation of methods to reduce greenhouse gas emissions on ships and other marine industries are emphasized through supportive strategies, development of standards, and financial incentives. also, the extraction of energy from oceanic resources or available in the oceans with the aim of sustainability in the ocean economics is one of the opportunities expressed in this study [3]. a research on the shipping industry’s effectiveness shows that in viewpoint of the type and intensity of the effect, very directly and with high impact, shipping can affect goals 7 and 13 related to clean energy and climate action, respectively. the effects of shipping on other targets are moderately direct or indirect, with moderate to low intensity. on this basis, shipping can help renewable energy by creating the necessary platform and providing support and technical services, for the extraction, harvesting and distribution of this type of energy [3]. moving to alternative fuels with zero emissions, using renewable energy, or improving energy efficiency, and providing a platform for developing innovative methods in all ship operations, are other things that can be considered in terms of achieving sustainable shipping and fulfillment of agenda 2030. looking at the global shipping fleet in regard of number, the effectiveness of implementing strategies related to renewable energy can be very high in achieving the targets set in goal 7 [3]. maritime industry can play a key role in this by synergizing partnerships with the public, private sectors, other industries and its powerful imo (international maritime organization) platform. besides, the maritime industry can take effective steps towards achieving goal 17 by exchanging experiences and technical knowledge in various fields and participating in developing strategies and roadmaps for sustainable development [3]. another study points out the limitations that researchers face in examining the maritime industry’s current position concerning the current situation and the vision of sustainable development goals. lack of access to information from many private shipping companies, providing various interpretations and interpretations of goal 10 as reducing inequality, are among these limitations. as this study emphasizes the fundamental role of the shipping and maritime industry in reducing inequality by increasdoi: https://doi.org/10.36956/sms.v2i2.300 3 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 ing and expanding access to logistics resources, it points to further research on the role of shipping and logistics in goal 10 [33]. according to this study, most of the information used in the analysis of the current situation and the maritime industry’s interaction with the agenda 2030 has been done generally and mainly based on the data of container companies or liner lines. accordingly, although container companies account for a large volume of global shipping, they may not fully reflect other actors’ conditions in the field of maritime transport [33]. by defining the concept of sustainable shipping, the international maritime organization has identified areas in which the maritime industry can assist and support the implementation and achievement of each of the sustainable development goals and, ultimately, the achievement of a sustainable planet. imo plays an irreplaceable role in facilitating global trade by providing a suitable platform for cooperation and participation of all countries in maritime transport, as the least expensive transportation method with the most efficient energy consumption. according to this approach, sustainable and secure maritime transport is one of the main pillars of sustainable development with a poverty reduction approach by providing access to basic goods for nations [8]. one of the major threats to food security and achieving a sustainable food chain is illegal fishing. since fish is one of the main sources of food for most people globally, illegal fishing is an important obstacle to ending hunger, a serious threat to the protection and sustainability of the marine environment, and the livelihood of fishermen who work legally [8]. the formulation and implementation of laws to reduce the emission of harmful gases is another imo move that is taken to achieve a sustainable environment and is very effective and vital for communities’ well-being, especially in coastal areas and cities. one of these decisions is implementing the convention on the reduction of sulfur in the fuel oil consumption of ships, which has been implemented since the beginning of 2020 and has affected the health and lives of coastal residents through environmental protection [8]. since achieving the concept of sustainability in all its dimensions requires comprehensive education by providing equal opportunities for all nations of the world, the imo also develops the necessary standards in the form of an international convention on seafarers’ training, not only added on transport safety marine but also in all stages of training, it has emphasized on environmental protection and safety at sea [8]. from the perspective of gender equality in education, the imo view is formed to provide job opportunities by empowering and facilitating education for women. the imo believes that women’s activities alongside men in various maritime industry sectors contribute to the development, productivity, and economic growth of communities [8]. due to fact that achieving a sustainable society without access to clean water and sanitation, as the most vital element of human needs, is difficult or impossible, the imo has emphasized the management of ship waste and the prevention of waste disposal at sea, intending to preserve water resources and prevent water pollution. the london convention can be considered the most effective imo guideline that has been developed in this regard [8]. one of the most important and effective imo projects being implemented in partnership with the united nations development program and the global environment facility is to focus on the participation of all countries and the use of all regional and trans-regional capacities for marine energy efficiency, and supports carbonation programs and companies active in this field [8]. this capacity building, in addition to improving energy efficiency in the marine industry, is also emphasized in the climate mitigation program and is actively pursued and supported through various projects with the support of developing or less developed countries. . this support is provided through synergy and international partnership to facilitate access to new technologies in clean fuels, optimize energy consumption, attracting investment to develop energy infrastructure and transferring technical knowledge related to renewable energy [8]. providing job opportunities for sustainable economic growth is one of the imo’s focuses on achieving sustainable development goals. the need for seafarers is obvious as a basic element in the maritime industry. attention to working and living conditions, social security, and their problems are at the forefront of what the imo emphasizes[8]. imo support for sustainable economic growth is not limited to the shipping sector. participate in the development of port infrastructure, pay special attention to creative and innovative technologies, extract energy from marine resources, promote the maritime tourism industry, support fisheries and maritime security, among other imo-supported sectors, in order to strengthen and contribute to economic growth all nations nationally, regionally and globally [8]. other global contributions that the imo emphasizes in achieving the goals of sustainable development, and which has adopted an important strategy so far, are the development of protocols and implementing laws in various doi: https://doi.org/10.36956/sms.v2i2.300 4 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 sectors of the maritime industry to reduce greenhouse gas emissions, and support practical and ambitious methods in stopping and combating climate change caused by the maritime industry [8]. protecting the resources of the oceans and seas, through conventions related to the prohibition of waste disposal at sea, noise pollution caused by ships traffic, preventing the transfer of harmful marine organisms by the water of ballast tanks of ships, and improving the safety and quality of shipbuilding and navigation are other important issues that the imo is committed to, as the highest decision-maker in the maritime industry [8]. contributing to the development of maritime education institutions, to strengthen the scientific strength of countries and prepare regulatory regimes on shipping issues by training experts in this field is another support coverage that the imo is committed to and knows it an important part of the sustainable development process with the approach of peaceful development of societies [8]. imo’s extensive cooperation with a wide range of projects, the private sector, and environmental centers, has the potential to enable this international organization to achieve the goals of sustainable development and the development of innovative methods, both in education and in the fields of provides design, construction, the safety of ships and optimization of ships’ energy consumption [8]. a research published by the european commission on sustainable maritime transport with an environmentally friendly approach to port activities emphasized the need to encourage operators who meet approved environmental standards in all their activities to reduce greenhouse gas emissions and energy optimization. according to this plan, which has been implemented in many european ports since 2011, ships that use methods and fuels to reduce emissions can pay lower port costs as a reward [5]. in a study in norway, it has been pointed out the importance of governments’ role through the actions of sustainable development in the maritime industry. according to this research, the government can achieve sustainable development goals by formulating specific programs and strategies and investing in infrastructure based on the development of zero-emission solutions in the maritime industry, with a special look at innovative solutions [10]. intelligent transportation, automated ships, and the use of alternative fuels, such as hydrogen, biogas, battery, and natural gas, are among the possible solutions in this study. also, synergism in the participation of public and private sectors, by providing a suitable platform for research on creative projects, using research and training institutions’ capacity, can accelerate this process [10]. as one of the most important companies in the field of maritime transport, maersk shipping company intends to reduce its carbon dioxide emissions by 60% in 2030 compared to 2008 and onwards, reduce gas emissions to zero by 2050. to achieve this strategy, maersk focuses on working with all stakeholders to develop the policy and framework needed to achieve this goal and sustainable shipping in line with the goals of sustainable development[11]. in line with sustainable development goals in terms of economic growth and environmental protection, maersk company is moving in the direction of active participation through investment and creating opportunities in the ship recycling industry in its organizational strategy. reducing inequality by providing the same job opportunities by creating an inclusive culture, along with gender diversity at different organizational levels, is a key element in the company’s commitment to achieving sustainable shipping[11]. the installation of scrubbers system in the company’s fleet and the use of fuel with low sulfur content have been done according to international laws and to reduce air emissions. in this direction, the company is actively involved in meeting the goals of sustainable development in human health and environmental protection by investing and supporting solutions to reduce air emissions [11]. preserving the oceans’ health and life as a great natural heritage for human beings is another issue of concern to this company. the importance of the seas’ life is so vital that a large part of this important human resource in providing a livelihood for the people of the world is exposed to various threats from various aspects [11]. the most critical threats to marine life, which is growing at an alarming rate, is the influx of large amounts of plastic waste into the seas. strict implementation of regional and international guidelines regarding ballast water and waste management system, support, and close cooperation with companies active in ocean cleaning and ocean science research centers is what maersk company pursues the health of the seas [11]. free transportation for health services, with the support of mercy ships, for sustainable welfare and health, reducing economic gaps, and providing a platform for underdeveloped countries, is an approach taken by the mediterranean shipping company as part of its sustainable development goals. providing voluntary logistics services, financial support, and voluntary services in various fields, in natural disasters in different countries, and across borders are other supports that this company provides along the sustainable development path [14]. gender equality in order to eliminate discrimination and create equal opportunities for women in various secdoi: https://doi.org/10.36956/sms.v2i2.300 5 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 tors related to the company’s activities is also emphasized in the company’s annual report on sustainable maritime transport [14]. important decisions and programs identified in the msc annual report include partnership in the development of the ship recycling industry, improving waste management, minimizing the destructive environmental impacts caused by this industry,improving the quality of workers’ education, and pay attention to health status. the continuous and sustainable staff training program is another key and prominent item in its programs, including onboard staff and onshore personnel [14]. providing the necessary facilities for sustainable water management in various places and providing access to clean water by modern and reliable treatment systems are other projects that msc has implemented in different parts of the world, and intends to develop and implement it elsewhere based on its sustainable development plan. investment in robotics and automation in antwerp’s port to reduce emissions, installation and operation of wind turbines to generate electricity, optimize water consumption. intelligent separation and recycling of waste in this port, are among the methods used to increase sustainability in the port, which is intended by the company [14]. the challenge of climate change resulting from traditional transportation and finding solutions that can respond to climate change is another requirement for sustainable development that msc has invested in. an example of this investment is in the installation of equipment and finite element modeling in container terminal cranes in some ports, which can lead to improved performance in a wider range of air temperature changes and increase the stability of cranes by installing water tanks in the lower part of the crane structure and thus reduce its center of gravity. these cases greatly help the crane structure resistance in bad weather conditions and natural disasters such as earthquakes and improve ports’ sustainability [14]. utilizing of various technical solutions such as making changes and modifications in bow, rudder, and propeller, on-line and continuous monitoring of the ship’s hull in terms of cleanliness, using anti-fouling paints, increasing the carrying capacity, installing the necessary equipment for cold-iron, the use of the air lubrication system is part of the measures that the company has taken to optimize energy consumption and reduce emissions in its active vessels and projects under construction [14]. in 2018, a program was formed to aim the synergy of global leadership to achieve sustainable development goals in collaboration with the international association of ports and harbors and several major ports in different countries, known as the world ports sustainability program (wpsp).in the energy and climate sectors, projects focus on creative projects to reduce ship emissions in ports, improve port operations, generate electricity from renewable sources, carbon capture methods, and the climate change approach [35]. these projects’ priorities are in port call optimization, providing low carbon fuel for ships and supplying electricity to ships from land through renewable energy sources to reduce greenhouse gases [35]. in sustainable development goals related to gender equality, health, social responsibilities, and education, various projects are being implemented in ports or are about to be implemented. allocate a portion of port revenue to develop coastal school infrastructure and improve the quality of health centers in the area, along with women’s participation in the maritime industry to empower them, provide scholarships in areas related to port operations, and marine pilots are among the projects outlined in this report [35]. regarding environmentally friendly and resilient infrastructure, most projects for port sustainability are related to the use of information technology and intelligent systems in improving supply chain and port operations along with meeting the needs of the market and stakeholders through codified planning with a view to development. in this regard, the principle of flexibility in infrastructure development is very important, so that part of this development is related to environmental monitoring using digital methods. the other part is focused on the exchange of information between the port and stakeholders [35]. most of this program’s projects are related to the interaction and development of communication between the port and neighboring cities, which is related to the environmental impacts and social interactions of the ports on the surrounding communities and requires effective communication and participation of both parties in sustainable development. this partnership and interaction are defined in the form of creative initiatives and projects that can meet the needs of the surrounding communities, such as the development of the local economy, the expansion of green areas, and investment in education [35]. also, environmental considerations arising from the existence of ports and port operations such as waste management, noise, and air pollution, conservation of water resources and ecosystems in the region, in addition to managing ports in accordance with the goals of sustainable development, is another aspect that has been considered in effective participation projects of ports and local communities [35]. doi: https://doi.org/10.36956/sms.v2i2.300 6 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 3. oman overviewpeople, environment, and economy oman is located in western asia and has a coast to the north with the gulf of oman and the east by the arabian sea. oman’s coast reaches more than two thousand kilometers [20]. oman’s population in 2019 is estimated to be around five million, and it is projected to reach over five million by 2020 [25]. in the same year, most of the population is between 25 and 34 years old, whereas the number of males is twice that of females, and 60% of oman’s population are of working age [25]. in the environment, oman has committed itself to protect the environment by joining almost all international treaties [2]. oman also has a ministry of environment and climate affairs, which demonstrates the importance of the country’s environment [16]. economically, according to the latest world bank report, oman has the highest economic growth in its region. the report expects growth to continue in the coming years with more investment in the upstream and infrastructure industries [30]. 4. background of oman maritime community oman has a long history of sailing and shipbuilding due to its long coastlines and is one of the leading countries in this industry. oman’s shipping dates back to over 4,500 years ago, which has been in contact with other countries worldwide, especially india and the countries of north and east africa. the omanis have been highly skilled in boat construction and maritime navigation with a well-known port in the world [15]. its background has long been active in two major maritime areas, namely maritime trade and fishing, and is still one of the most critical industries in the country even today. archaeological findings at the ports of oman, which include objects and equipment from china and other countries, indicate antiquity in the country’s maritime sector carried out by oman ships [13]. with its long and significant coastlines, the fisheries sector, as an essential source of food supply, has a long history in the country that caters to local and regional needs [34]. with the expansion of knowledge in the maritime industry, the country is active in other related industries, such as dry-dock, oceangoing ship repair and maintenance and passenger ferries, as well as in the field of maritime trade and fisheries. in 1989, oman set up the oman fisheries company to take a significant step towards global markets. in this regard, oman fisheries company established and launched six processing plants with the most advanced equipment and currently exports products to more than 55 countries[21]. oman shipping company was established in 2003 to meet the rapidly evolving needs of the country’s industries. with a fleet of natural gas vessels, large oil tankers, chemical tankers, bulk carriers, general cargoes, and container carriers, the company plays a vital role in shipping and development. the main approach and purpose of the company are to provide efficient and reliable services to national, regional, and global customers, taking into account the high level of standard and safety, while at the same time taking an exclusive look at environmental protection [26]. one of the active industries in the oman maritime industry is oman drydock, which was established in 2006 to promote modest industrial structure growth. its services include repairing and converting large ships in various models and are also active in providing services to the oil, gas, and infrastructure industries [18] [19]. in passenger transport, the oman national ferries company (nfc) started operating in 2006 to contribute to the promotion and development of maritime transport, especially in the domestic sectors, and to establish an effective connection between the country’s ports [17]. the service provided by the company is not limited to passenger transport, and in addition to scheduled inter-port services, it has been providing dedicated trips since 2008 [17]. 5. local challenges and needs to examine the challenges and needs of marine energy management with what is stated in the sustainable development goals and goal 7, should first review the defined upstream documents and then review the documentation available in the oman country. the growing need and increasing demand for energy, as the driving force behind the development, along with population growth and the expansion of industries, are significant challenges in achieving sustainable development goals. this challenge is crucial in balanced growth, consistent and sustained management of the various sectors involved in energy development. including the sections as follows: 1)awareness of existing and potential resources. 2)investigating and calculating the capacity of existing or available renewable and sustainable energy sources. 3)finding practical and cost-effective solutions to optimally and efficiently use energy resources. 4)a clear plan and roadmap for developing the infrastructure needed in energy management in a coordinated doi: https://doi.org/10.36956/sms.v2i2.300 7 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 and balanced manner. 5)mobilizing existing national and international facilities for investment in energy infrastructure or optimizing the use of existing resources. 6)human resources training, and skilled people, to manage energy or operate new systems. 7)investing in research and development, in close cooperation with science and education communities and the industry with governments’ participation to facilitate and accelerate it. 8)a passion and interest in applying innovative technologies and techniques with a positive attitude. increase partnerships at the national, regional, and international levels, for synergies, overcome the impediments and ultimately use the successful models and designs used in other countries to accelerate sustainable development. the imbalance, and the uneven growth, in each of the above sectors can pose a new challenge to energy management. instituting this global resolve, in the form of a national movement, and utilizing all available capacities to encourage and extend this approach through a targeted program in the organizational structure of education and country management, can be a constructive move towards sustainable development. other challenges include resistance from organizations or people to change behavior and consumption patterns due to lack of need, lack of transparency towards development goals, and lack of awareness of the need for energy management, low cost of energy consumption, lack of social accountability, in the public and community level [29]. the high initial cost of investment in renewable energy production, especially in countries with oil and gas resources, and low energy prices reduce their tendency to use new energy[29]. another challenge is the lack of confidence in innovative and modern designs and methods, which create resistance and doubt in the industry body in applying new solutions. many of these innovative designs and solutions are still in the pilot phase and require further research and development. meanwhile, only a limited number of countries have done so. in oman, the ministry of transport and communications (motc), as a standard and related reference, with the international maritime organization, and the oman maritime industry, has been working on explaining and updating roadmaps and sustainable plans development goals [23]. time is also challenging. over time, the amount of non-renewable and hydrocarbon fuels decreases every day, and their environmental effects deeper and last longer. regional threats, internal conflicts, insecurity, and instability of countries, which transmit a large part of countries’ ability to cope with these threats, as well as increasing the riskiness of investing in the energy sector and thereby reducing or disabling them in attracting foreign or even domestic investment, is another challenge. some countries’ geographical location, sometimes even unintentionally, may affect these threats, even if they do not play a role in the threats. the oman ministry of transport and communications’ annual report, released in 2018, outlines the need for efficient and sustainable transport and the development of access at reasonable and cost-effective rates, as set out in the ministry’s mission [23]. next much more comprehensive document on sustainable development goals is the 2019 supreme council for planning (scop) report, which has done a thorough review of each of oman’s sustainable development goals. the study emphasizes the need for all countries to meet and address challenges at the regional and global levels [28]. among these challenges are fossil fuels and oil, which are essential and influential variables on the economy and global challenges such as the recession in the economy have also been mentioned. population growth and changing population patterns towards a young and jobseeker are other challenges in the country [28]. the critical programs in this field are optimizing and targeting budgets using energy-saving methods and looking at using environmentally friendly and sustainable models [28]. changing the oil-based economic pattern, diversifying the economy, decreasing oil dependence and income to reduce the effects of oil prices are among the needs of target countries [28]. investment issues is other concern, especially the private sector, which was not acceptable due to some legal barriers. it needs laws and procedures that encourage the private sector to invest. the private sector is also one factor contributing to the reduction of unemployment and job opportunities, which is a severe and significant challenge for achieving development goals [31]. provide supportive policies to attract young people by the private sector or supporting young people to start a business is cited as a solution to this challenge. there is a need for stability in the economy and the growth and development of domestic production while creating new job opportunities and improving policies and laws to facilitate employment, including government goals and programs. another point is the training of the skilled workforce needed, given the market need and familiarity with the new technologies, which has led to the establishment of the national youth organization in oman [28]. oman is doi: https://doi.org/10.36956/sms.v2i2.300 8 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 working to overcome the challenges of achieving goal 7 of sustainable development and moving towards renewable energy by developing a clear roadmap called the national energy strategy [28]. these include a plan to reduce fifty percent of the gas used in the oil industry and use solar energy as an alternative and sustainable energy by the beginning of 2026 [28]. other challenging energy topics, the existence, and stability of government subsidies and support, access to gas as an energy source, population growth as a consequence of the growth of energy consumption, and ultimately, the growth and development of industries and increasing energy demand [28]. regarding renewable energy, this technology’s continued use remains a significant challenge, and besides raising professional people who can respond to this new model of energy. instance of these projects are the “mirra” project, which has replaced gas consumption in one of the oman oil fields by using solar power generation and generating more than 1,000 megawatts of electricity [28]. oman, given the international maritime organization’s acceptance of its regulations, as its principal source of industry, is bound to enforce these rules. therefore, it can be said that the implementation and adherence to these laws and guidelines are in line with the goals of sustainable development. including these rules and regulations are guidelines for the ship energy efficiency management plan (seemp) to reduce fuel consumption and reduce pollution [7]. besides, guidelines for the energy efficiency design index (eedi) required for the construction of new vessels are also included in the plans used for marine energy management [7]. in 2019, the oman shipping company ordered the construction of three very large oil tanker vessels at the daewoo shipbuilding company in south korea. important and essential in this order is the eco-friendliness of these ships and the new generation of this class of ships [24]. in the matter of ships and vessels other than those required by the imo guidelines, and shipping companies required to implement it, no report or solution was found, especially on renewable energy use. in 2019, an international conference on marine engineering and technology was organized by the oman military college of technology. it covered various chapters, including optimizing fuel consumption and using renewable energy in the maritime industry [6]. such approaches can, in addition to driving existing national and international capacities toward an acquaintance with modern knowledge or innovative designs and solutions, plays a vital role in the synergies and active partnerships between the various sectors of the industry, especially in relation to scientific and industrial centers, and in line with development goals. concerning the training of expert and knowledgeable staff, familiar with the issues of energy management, the ministry of transport and communications of oman has emphasized that the manner of issuance of documents is based on seafarers’ training, certification and watchkeeping standards and as a result, people should be thoroughly familiar with the rules and guidelines of the international maritime organization, including the objectives of sustainable development, increasing efficiency, and energy management [23]. it seems that professional development is not limited to people working in the fleet. about energy management, there is also a need for people capable of policy and decision making and be familiar with economic, environmental issues and safety, requiring a plan to train these people and to use them to improve energy management and energy consumption [22]. what seems to be critical here is the focus solely on the technical aspect of energy efficiency management. this concentration has focused on the specific design considerations when building a ship and implementing a supervisory and management system on energy use, especially of the fleet[9]. this point of view can be led to other issues being overlooked or even neglected aspects and topics such as the workforce’s role or even gender in energy efficiency management [9]. 6. analysis by using five p’s of sustainable development this section examines the role of key players in oman’s maritime industry including, oman fisheries company and oman shipping company, in five key areas and indicators in sustainable development goals, including people, planet, peace, prosperity, and partnership. achieving sustainable development goals in the maritime industry will certainly not be achieved unless all stakeholders are directly or indirectly involved. where sustainable development goals are accepted, in the form of a blueprint, including a set of goals designed in different parts, synergy and stakeholder engagement can be very useful because of the shared purpose. 6.1 people as an essential part of the food chain, fisheries play a vital role in maintaining healthy nutrition and reducing hunger. oman fisheries, both domestically and regionally and internationally, have been instrumental in reducing doi: https://doi.org/10.36956/sms.v2i2.300 9 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 hunger by having a significant market share of fish and related products. the emphasis on food and health under its goals reflects its commitment to public health. providing healthy, appropriate, and quality food is one indicator of a sustainable society [21]. one of the hallmarks of any underdeveloped country can be the country’s high poverty rate. as a result of inadequate explanations of wealth, class distinctions and gap, and lack of access to adequate food, growing poverty is moving towards deepening. key factors in reducing poverty are provided equal opportunities and creating appropriate employment opportunities, and the abundance and availability of adequate food. oman fisheries have helped significantly reduce poverty rates both domestically and internationally, by providing a suitable environment for the supply and distribution of sufficient food, both for domestic consumption and to meet some international food needs [21]. the oman shipping company has been instrumental in expanding domestic trade and creating new job opportunities by creating a secure business route and expanding trade internationally [26]. the expansion of commerce has enabled the expansion of the logistics and commerce sector, industries, and related small businesses. the development of roads, residences, warehouses, out-of-doors restaurants, repair shops, and even the development of these required training centers are only part of this activated chain. in other words, the activation and expansion of shipping, both directly and indirectly, can lead to sustainable development. 6.2 planet the oman fisheries company considers itself responsible for the conservation and protection of the environment and the prevention of pollution of the seas. this company has also allocated a portion of its profits to the marine environment and upgraded its safety knowledge. the company focuses on preserving the marine environment and clean water, focusing on preserving marine resources and healthy food. in the company’s vision, the emphasis is on the sustainability of the fisheries’ environment [21]. the country approved and implemented a law prohibiting trawl fishing in 2011 to protect the marine environment and its resources [34]. as stated, in 2019, the oman shipping company ordered the construction of three very large tanker vessels to the daewoo shipbuilding company [24]. a few months later, the company commissioned two more eco-friendly tanker ships with the daewoo shipbuilding company [27]. what was highlighted in these orders was the emphasis on environmentally-friendly, eco-friendly, which demonstrates the company’s strong commitment to protecting the environment through modern shipbuilding technologies. the company also emphasizes the strict implementation of international maritime law and regulations in marine environment protection as a committed member of the global maritime community [26]. 6.3 peace one of the most critical indicators in the field of peace is the security in that community. the security of each community reflects people’s attitudes in societies in the field of ethical, social, and economic indicators. poverty, unemployment, and illiteracy are threats to any country’s security that can lead to instability and conflict and are one of the biggest obstacles to sustainable growth. oman’s fisheries company has had a significant impact on the development of peace by affecting various sectors and ways of affecting the country’s security. creating job opportunities and sustained employment has reduced the poverty rate and, as a result, increased community mental health and well-being. also, proper and healthy nutrition has enhanced security [21]. the development of a skilled and efficient workforce, which contributes to the growth of literacy and expertise, has added to the promotion of security and, ultimately, sustainable peace. one of the goals of oman shipping company is to provide safe and reliable service to all customers [26]. due to the volume of cargo movement and other required products of the country, which is mostly done by the company’s fleet, it has had a significant impact on supplying the country’s people with needs in the field of import and export, as well as providing economic security for the people. oman shipping company is one of the most active companies in sustainable peace. 6.4 prosperity the oman fisheries company has been able, by employing a large number of young people, to play an important role in reducing the unemployment rate and thereby increasing people’s well-being [21]. the existence of this industry and the creation of a distribution chain have created many jobs, directly and indirectly, in the field, leading to increased levels of public welfare [21]. on the other hand, with the optimization of this trade and new technologies in the production and supply of fishery products, energy consumption has improved and decreased compared to traditional systems. also, the reduction of energy consumption and the use doi: https://doi.org/10.36956/sms.v2i2.300 10 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 of new technologies have reduced the price of finished goods and, consequently, increased the people’s purchasing power, which is a move forward in the sustainable prosperity of the people [26]. the oman shipping company has a well-planned program to recruit labor from the omani youth. this job is equally available to all, regardless of gender [26]. providing these enduring job opportunities enhances happiness and ultimately sustained prosperity. oman shipping company has provided a scholarship to those interested in studying marine engineering and nautical science. in addition to its support for the maritime industry, the company has also provided an opportunity for undergraduates to pursue an internship on the company’s fleet [26]. this excellent performance has not only increased the sense of hope and satisfaction among young people but has also made a positive step towards achieving sustainable development goals. 6.5 partnership the oman fisheries company has one of the best partnership models in sustainable development with the granting of shares to fishers. this decision led them to increase their level of responsibility as they participate in fisheries. the company is also a reliable trading partner for other countries by exporting fish and other fishery products to more than 55 countries. considering part of its profits in creating new job opportunities for fishermen, coastal women, and new markets, it has also increased the level of participation at the domestic level [26]. the oman shipping company is moving towards sustainable development by providing the appropriate infrastructure and facilities needed by domestic, regional, and international maritime transport industries. this partnership encompasses a wide range of industries. the oman shipping company is equipped with its maritime fleet, in various maritime shipping areas, including tankers, containers, bulk carriers, general cargoes, and chemical tankers; it has been able to play a unique role in the development and stability of this partnership by providing safe and orderly services [26]. key partners in domestic supply include the orpic company (the largest petrochemical company in oman), sohar aluminium, and oman lng company. regional offerings include indian sail company active in steel trading and internationally includes shell oil co., bp oil co., and brazilian vale company active in mining trading [26]. 7. conclusions in studying the marine industry of oman, in line with sustainable development goal # 7, and the five relevant and influential areas of this document, namely the people, the planet, peace, prosperity, and partnership, seem to be a distinct and well-structured program at different levels that demonstrates national determination in the right direction towards development goals. sectors and stakeholders of the country’s maritime industry are moving alongside each other in pursuit of these goals, along with the synergy and overlap, which is a good sign of achieving sustainable development goals. meanwhile, some areas and sectors of the maritime industry that have the potential to achieve sustainable development goals have not been addressed. among these areas can be mentioned, ocean energy, aquaculture, coastal tourism, marine biotechnology, renewable energy use in ports and ships, deep-sea mining. on the other hand, annual and documented reports that specifically address sustainable development goals have not been published by companies involved in the maritime industry. these reports can lead to precise targeting, benchmarking, analysis of current conditions, and explaining new strategies and ways to move smarter on the path to development goals. one of the appropriate approaches in sustainable development could be modeling plans and methods being implemented by other countries. finally, although oman is on the right track towards development goals, it can accelerate and create effective solutions by focusing on new technologies and innovative designs and more productive industry linkages with science centers. references [1] blue generation project, n.d. 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(2018). oman ministry of transport annual report 2018. retrieved from https://motc.gov.om [24] oman observer, oman shipping to invest in 3 new vlccs. oman observer, june 26, 2019. retrieved from https://www.omanobserver.om/oman-shippingto-invest-in-3-new-vlccs/ [25] oman-population, n.d. retrieved from https://www. worldometers.info/world-population/oman-population/ [26] oman shipping company, n.d. retrieved from https://www.omanship.co.om/about/about-osc [27] prabhu c., oman shipping inks deal for two new eco-friendly crude carriers. oman observer, january 18, 2019.retrieved from https://www.omanobserver.om/oman-shipping-inks-deal-for-two-new-ecofriendly-crude-carriers/ [28] supreme council for planning, first voluntary national review of the sultanate of oman 2019. retrieved from https://www.scp.gov.om/pdf/sustainable.pdf doi: https://doi.org/10.36956/sms.v2i2.300 12 sustainable marine structures | volume 02 | issue 02 | july 2020 distributed under creative commons license 4.0 [29] sustainability, shipping’s critical role in meeting many of the un sdgs, 2018. retrieved from https:// safety4sea.com/cm-shippings-critical-role-in-meeting-many-of-the-un-sdgs/ [30] times news service, oman to have best growth rate in gcc in 2020, says world bank. times of oman, may, 18, 2019. retrieved from https://timesofoman. com/article/1314904/oman/oman-to-have-bestgrowth-rate-in-gcc-in-2020-says-world-bank [31] united nations general assembly resolution, transforming our world: the 2030 agenda for sustainable development, a/res/70/1, 2015. retrieved from https://www.un.org/ga/search/view_doc.asp?symbol=a/res/70/1&lang=e [32] wahlen c.b., five pacific countries launch partnership to decarbonize shipping industry. sdg knowledge hub, october, 3, 2019.retrieved from https:// sdg.iisd.org/news/five-pacific-countries-launch-partnership-to-decarbonize-shipping-industry/ [33] wang x., yuen k.f., wong y.d., li k.x. how can the maritime industry meet sustainable development goals? an analysis of sustainability reports from the social entrepreneurship perspective, 2019. retrieved from https://www.researchgate.net/publication/337019080_how_can_the_maritime_industry_meet_sustainable_development_goals_an_ analysis_of_sustainability_reports_from_the_social_ entrepreneurship_perspective [34] world bank, sustainable management of the fisheries sector in oman: a vision for shared prosperity, 2015. retrieved from https://www.worldbank.org/ en/country/gcc/publication/sustainable-managementof-the-fisheries-sector-in-oman-a-vision-for-sharedprosperity [35] world ports sustainability program, world ports sustainability report 2020, 2021. retrieved from https://sustainableworldports.org/wp-content/uploads/world-ports-sustainability-report-2020-fin.pdf doi: https://doi.org/10.36956/sms.v2i2.300 24 sustainable marine structures | volume 05 | issue 01 | march 2023 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2023 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). doi: http://dx.doi.org/10.36956/sms.v5i1.824 *corresponding author: razon chandra saha, head of research and innovation, saif powertec limited, dhaka, 1212, bangladesh; email: razon864@yahoo.com article the role of chittagong port authority to develop other national ports in bangladesh to provide maritime logistics support in south asia razon chandra saha* head of research and innovation, saif powertec limited, dhaka, 1212, bangladesh article info abstract article history received: 5 march 2023 revised: 25 april 2023 accepted: 5 may 2023 published online: 16 may 2023 chittagong port is the principal seaport in bangladesh that has contributed to the national economy with the opportunity to be a world-class regional port in south asia. cooperation among the three national ports chittagong, mongla and payra is essential to do maritime logistics business in the region after serving the nation proudly. here, chittagong port authority (cpa) has the opportunity to help others in the process of port development for increasing efficiency and productivity by providing financial and technical assistance because of its financial and technical capabilities as a pioneer seaport in the port world. this paper examines the role of cpa to bolster and develop the underutilized mongla port and newly established payra port, where qualitative research methodology is applied to explore the ways, by which cpa can assist, link and integrate with others effectively, especially in developing the port infrastructure and inland transport networks. in addition, the research found the prospectus of mongla and payra to supply port services to the neighbors india, nepal, and bhutan as well as serve the south-west part of china with the aim of increasing regional connectivity and promoting international trade in those basically landlocked areas and countries of asia. keywords: bangladesh maritime logistics qualitative china connectivity 1. introduction chittagong port is the principal seaport in bangladesh that has contributed to the national economy with the opportunity to be a world-class regional port in south asia. cooperation among the three national ports chittagong, mongla and payra is essential to do maritime logistics business in the region after serving the nation proudly. here, chittagong port authority (cpa) has the opportunity to help others in the process of port development for increasing efficiency and productivity by providing financial and technical assistance because of its financial and technical capabilities as a pioneer seaport in the port world. maritime logistics and port connectivity are playing important roles in promoting regional economic http://dx.doi.org/10.36956/sms.v5i1.812 mailto:razon864@yahoo.com 25 sustainable marine structures | volume 05 | issue 01 | march 2023 development that is closely associated with the efficiency and quality of shipping and port activities [1]. ominously, bangladeshi seaports are not yet considered efficient by the global standard in terms of technical or non-technically especially operational efficiency, infrastructural bottleneck, backward transport networks, poor information technology usage, financial delay in investment and poor port management [2]. mention that the strong relationship between the port and port city or city is weakening both in economic and geographical terms [3]. moreover, a port is the heart of the transport system to interfaces among various transport modes to enhance connectivity to their hinterlands and forelands [1,4]. in essence, port development is required in bangladesh for facilitating the domestic import-export trade and supporting the south asian region for economic growth and trade development that will be treated as a maritime transport business. this paper started with a special discussion on “country moves with us” where the importance of port facilities for bangladesh is described and then turned to the next section of research methodology where qualitative research methodology is followed to get the empirical reflection of experts on port management. after that related works of kinds of literature on port performance, competitiveness and governance stated with short literature on south asian maritime transport system, including bangladesh’s port facilities, intermodal freight transportation and inland transport networks for understanding gaps in the literature for developing ports of bangladesh for increasing maritime logistics support to south asia. furthermore, this research attributed the statement and feelings of the respondents in the qualitative research findings section. based on the literature review and qualitative research findings, one section was added for analyzing the role of cpa to develop all ports of bangladesh inspired the next section for creating a regional common platform for transport connectivity. finally, the paper concluded with the future directions that will help to extract important points for port development in bangladesh. moreover, port authorities have a stake in innovation for improving operations, gaining competitive advantage, achieving and maintaining a ‘license to operate’, and finally achieving resilience against a changing environment [5]. this paper examines the role of cpa to bolster and develop the underutilized mongla port and newly established payra port where qualitative research methodology is applied to explore the ways by which cpa can assist, link and integrate with others effectively, especially in developing port infrastructure and inland transport networks. in addition, the research found the prospectus of mongla and payra to supply port services to the neighbors india, nepal and bhutan as well as serve the south-west part of china with the aim of increasing regional connectivity and promoting international trade in those basically landlocked areas and countries of asia. 2. country moves with us chittagong port has the slogan of “country moves with us” which featured its importance in the national economy and social responsibility to all citizens of bangladesh. driven in particular, bangladesh is moving forward with the performance of chittagong port inevitably. most of the import-export trade of bangladesh is performed by seaports where chittagong port is managing more than 90% of trade and the country is dependent on the performance of chittagong port. brightly, the chittagong port master plan researched by hpc (hamburg port consultancy) projected the container traffic in 2.7, 4.4, 5.1 and 5.4 million teus (twenty feet equivalents units of containers) for the years 2020, 2025, 2030 and 2040 respectively that will be doubled within the next 20 years [6]. from the research of kharel [7], it is found that nepal and bhutan are striving to get reasonable port access in south asia where they are paying 42% excess cost with the penalty of a time burden for using the ports of india. here, they are using the congested and inefficient ports of india, whereas chittagong and mongla ports of bangladesh are potential alternative ports for them. moreover, freedom of transit is appreciated by all in south asia, especially for landlocked countries nepal and bhutan to access bangladesh markets and seaports predictably. furthermore, the opportunity remains for china, india and myanmar to use the ports of bangladesh to decrease the transport cost and develop their countries’ dark areas that are basically landlocked or undeveloped. in order to handle all modes of transport, both coming from the sea or hinterland, it is crucial to develop a port in which the speed of handling is set at the highest level [8]. he most important value-added and investment level in port-related manufacturing and logistics support by creating space in the supply chain to show better port performance [9]. if there is no cooperation between the actors in the port community, the assessment of rates on performance could not be generated and may not be useful in the process of port development [10]. in this situation, as a leader and pioneer in port management, cpa has to show the path to other national ports to increase productivity, compete with others and enable maritime transport as a part of port governance in the modern world. to unfold, ports have to serve the nation together where port cooperation is appreciated because the fate of the nation is highly dependent on the import-export trade where the country is moving forward with the best perfor26 sustainable marine structures | volume 05 | issue 01 | march 2023 mance of port superciliously. 3. research methodology social research is a collection of methods and methodologies that needs to apply systematically for producing scientifically based knowledge and it’s an exciting process of discovery where persistence, personal integrity, and tolerance for ambiguity are required to complete the research successfully [11]. preliminary, to analyze of the basic two research questions (how cpa can play a vital role to develop underutilized mongla port and newly established payra port? how cpa can assist, link and integrate with others effectively?), followed the qualitative research methodology of neuman [11], and followed the field research for taking the interview with people acting in the research area. finally, qualitative research methodology is applied to get the real thought of the actors who are related to the performance and motion of the bangladesh port sector. the qualitative process always strives the get new things or innovations from the respondents that will contrast with the literature review and secondary source information appropriately. extraordinarily, unctad (united nations conference on trade and development) published its first research paper on “port cooperation” in 1996 where cooperation between ports within the country or region had attributed highly and to date this paper is the great direction for ports in managing their activities by providing or getting helps each other. this paper is the main document in selecting the areas where cpa can work with other national ports for bolsters own capacity and guide others on how to bring the standards like a cpa to attract port users and international traders. in this connection, three major indicators are chosen for this research which are port performance, competitiveness and governance and by increasing the international standard level of those indicators, it is possible to provide maritime logistics support nationally, regionally and internationally. furthermore, cpa has to play a vital role to support mongla and payra with the aim of developing their capacity based on the literature of unctad [12] and extracting the below types of cooperation in developing the overall port sector of bangladesh. 1) institutional. arrange to support other ports by inspiring governments, international development organizations like adb (asian development bank), aiib (asian infrastructure investment bank), world bank and others exclusively for capital investment in the port infrastructure, equipment purchase and facilities development. 2) industrial. organize other ports and group with international associations like iaph or regional port association in getting technical assistance and emergency troubleshooting. 3) commercial. guide how to negotiate with the international investor for long-term investment in the bangladesh port sector and show how they will be benefited from this investment gradually. overall, in addition to secondary literature review including the unctad [12] research paper, qualitative research methodology was applied to know the role of cpa in cooperating with others for serving south asia by providing integrated maritime logistics support efficiently and economically. 4. limitations the related experts who are in driving positions as port users, traders and port authority representatives, all replied that research is essential to develop the port sector of bangladesh. but nobody is interested to provide answers officially. that resulted in a small sample size in qualitative data collection (21 out of 60 which is only 35%). in addition, it was not possible to quantify the amount of investment by cpa to other national ports such as payra and mongla also inland terminals pict (pangaon inland container terminal) and dhaka rail icd. 5. literature review to follow the research methodology, the port cooperation paper of unctad [12] is reviewed to find out the gaps in port development. the basic approach of this research is to develop the port sector of bangladesh by using the performance, productivity and strategic position of chittagong port. the direct literature of chittagong port is rare where related literature is attributed accordingly. mention that port development is not increasing land and other facilities, it is crucial to attracting the port users by showing that port authority increased the land and others by creating synergies in developing connections in the port clusters [13]. the issue of competition and cooperation among the various players is always important in the cost-profit trade-off involving risk evaluations in port management. in some geographical contexts, the researcher found the tendency toward cooperation between ports is both organic and part of a deliberate strategy to promote competition within a shared hinterland [17]. the literature review mainly focused on the three basic indicators which are port performance, competitiveness and governance discussed one after another. 5.1 port performance the requirements for seaport services are growing 27 sustainable marine structures | volume 05 | issue 01 | march 2023 day by day to cope with the increased demand for cargo and information flow [14]. as container traffic keeps growing and physical expansion is constrained by the limited supply of available land around most ports, port facilities will need to become more productive if they are to remain competitive where assessing how ports perform is useful not only for transport planning but also for informing port management, policy, and regulation [15]. in addition, cariou et al. [16] addressed the challenges in cargo handling operations particularly in a container that needs of going beyond ports within their seaport activities. mention that the port reform initiative helped some countries with their significant improvements in port performance whereas others are re-thinking or yet not started the process because of its complexity and adjustment over time [17,18]. port productivity and performance are related to the effectiveness of the supply chain as a whole where ports and users can take advantage of complementary strategies and capabilities to improve the port performance technically [19]. in the empirical analysis, zhao et al. [3] provided their concept on the port characteristics where maritime connections, hinterland connectivity and port efficiency are the major variables in port networks. talley [20] concluded that technically efficient optimum throughput, cost-efficient optimum throughput and effective optimum throughput are the economic objectives of a port that will satisfy all stakeholders of a specific port. in the context of port performance, dappe and suarez-aleman [15] identified three major viewpoints which are operational, economic, and financial. here, the operational perspective refers to the quality of the outputs provided in port services and facilities efficiently and timely. after that, the economic angle takes into account factors such as the mix of inputs used, the technology used to transform inputs into outputs along with the port’s productive scale. twofold objectives of the port are strategic productivity and growth that are related to efficiency and expansion of the port performance respectively [10]. lastly, the financial perspective addresses the mix of financial resources and profitability indicators. however, ports are complex places where performance is influenced by many factors including size, location, ownership, infrastructure, facilities, and others, but people or human resources are the most vital resource to get optimum performance [21]. in addition, smart ports always adopted smart people to show their efficiency in port operations and management. throughput volumes are the main indicator in measuring port performance in the port industry, but it is not the regional economic impact of the port and its attractiveness to the port-related industries in the region [9]. a port may reduce time-related costs by reducing the congestion and turnaround time of the vessel that processes the quality of the port service as a part of port performance, in general [20]. 5.2 port competitiveness port competitiveness has focused on the analysis of specific services rendered by ports or port activities where actors are involved often motivated by opposing interests and non-convergent objectives [22]. historically, port authorities were created at the national or regional level for integrating the port activities and also for port development [17]. the port authority is a part of port community that is composed of a set of actors that are related to logistics lines and also lead and drive the port community [10]. hales et al. [23] showed the significant effects of five variables of volume competitiveness (vc) and investment competitiveness (ic). identification of drivers of port competitiveness and identification of together with the measurement of the drivers in economies of scale in shipping especially being proactive in making hinterland strategies by port authorities, governance changes in framework and management level of port authority, degree of competition for attracting customers and investor, inter-firm networks in building relations between local and international stakeholders and in the aim featuring green and sustainable port planning efficiently [24]. the variables that are stated by hales et al. [23] in figure 1 and parola et al. [24] in figure 2 are common factors that need to consider by all for port competitiveness and taking the initiative to develop and compete in the business rivalry of the port sector in the south asia or bay of bengal. figure 1. port competitiveness [23]. 5.3 port governance the port policy generally and port governance more specifically reflected the changes in government and politics within a nation always [17]. public port authority acts as both landlord and regulatory bodies where port operations are performed by private companies denoted as the best 28 sustainable marine structures | volume 05 | issue 01 | march 2023 model of port governance [18]. port governance always increased the port’s effectiveness and competitiveness in the change of port management. the change in governance structures constitutes an important pillar in view of the achievement of sustainable development of ports including economic, social and environmental challenges. a port that was denoted as major engine for driving economics is a significant lever for governance to manage trade and catch economic benefits nicely [25]. with enormous containerization of maritime cargo, the container port industry is very competitive in serving the hinterland by filling all kinds of demands where south asian countries’ port tariffs are reasonable, but associated cost or indirect costs with the port tariffs are very high where inefficiencies play a more significant role in shippers’ port choices [15]. extension of ports often failed due to the lack of attention to the potential negative environmental impacts [8]. figure 2. drivers of port competitiveness [24]. the intermodal transport development has a great impact on further economic globalization that changed the overall transport system and supply chain where functional integration is impossible without intermodal transport chain [26]. nowadays, ports are facilitating intermodal transportation directly to the shipper/consignee as a part of integrated maritime logistics support and increasing the hinterland. national and regional interests, as well as those of port cities, are often at odds with each other. most importantly, the inland transport network is an obstacle by the government on the false plea of safety, security and religious politics [27,28]. lastly, due to the ongoing commercialization of port authorities and the progressive pressure of stakeholders, port performance indicators are in new shape with the socioeconomic interest in a port [9]. consequently, port authorities are in charge of hardware dimensions of port development for ensuring and enabling efficient management of supply chains through policy actions that should be aimed at improving infrastructure and inland connections by keeping the criteria of environmental, social and economic sustainability to promote the hinterland and ensure [22]. international organizations like the imf (international monetary fund), and world bank believe that south asia presents a bright spot amid the gloomy global outlook [29]. in bangladesh, chittagong and mongla ports are managed by port authorities where major approval authority is the ministry of shipping under the government where cpa exercises a high-level degree of operational and financial autonomy [15]. the south asian port sector attracted significant interest from private investors in the late 2000s. development of port facilities at chittagong port bangladesh’s largest port has been slow. although occupancy at the cpa container berths is high and rising, there is a pressing need for more investment in a capacity where mongla has had excess capacity for many years [15]. intermodal freight transportation is lagging behind in bangladesh and there is no established intermodal network except the chittagong-dhaka container transportation with the general rail network. recently added the rict (riverine inland container terminal) that named “pangaon” in dhaka but it also handling in chittagong port yard. ports are an integral part of the supply chain for managing and coordinating the materials and information flow [14]. despite the predilection for promoting port privatization, full privatization has not been without its problems and critics [17]. due to the complexity of seaports and the large number of firms in a port, port performance indicators are useful to measure whether the development of the port is satisfactory or not and learn how to improve the performance also communicates the performance of the port to a wide range of stakeholders [9]. to enhance the capacity of a port management, it is essential to strengthen the networks of the hinterland exclusively. the development of the global supply chain bounded to change the traditional role of ports (loading and discharging operations) and enhanced the capacity to a new role as efficient distribution of products across the supply chain and integrated logistics service providers as a part of the global distribution channel [19]. port investors always look forward to tying with the port cities to get all kinds of logistics facilities and security for supporting the maritime trade because port-city relationship exhibits substantial significance in the development of port by attracting international investor and their hinterland while 29 sustainable marine structures | volume 05 | issue 01 | march 2023 also sufficient spatial economic disassociation and environmental tension [3]. talley [20] advised considering the operations, economic and port management objectives in port performance. in summary, the above-mentioned literature demonstrated the port performance, competitiveness and governance are appreciated in that port development to build strong relationships among the stakeholders by port authorities. in addition, the intermodal network is very weak in bangladesh and south asia, for this reason, bangladeshi ports are unable to expand their hinterland and go to the neighboring area’s in the lack of regional cooperation and desire for transport integration among the south asian countries apparently. 6. qualitative research survey findings the five main basic research questions are guiding this paper as the theme of the qualitative research survey with the aim of open-ended questions. in order to explore per questionnaire, 21 interviews were conducted from june 2018 to august 2018. after field testing and setting the research questions, an invitation was sent to 60 persons who are experts in the shipping field, port management and port users. here, questions are asked to the respondents with the aim of acquiring knowledge on port development in bangladesh as below: 6.1 role of cpa in developing other national ports possibly, the existing development status of bangladeshi ports where the role of cpa is appreciable because of their participation in establishing the third seaport payra and full finance in constructing the inland riverine container terminal “pangaon”. however, the role of cpa in logistics and supply chain is very crucial in terms of efficiency, competitiveness and value-added productivity. the port has a congestion problem where vessel turnaround time is comparatively high. however, the technique of handling cargo and containers by expert persons of the port authority is appreciated by the port community of the world. there are lots of opportunities for cpas to work in the port and maritime logistics parts especially in the development of rail, road, inland waterways, coastal, airport and time-trend. mongla port is the underutilized port in bangladesh where the government established a new seaport payra to facilitate the demand for deep seaports as well as serve the neighbouring countries of south asia especially nepal, bhutan and seven sisters of india. it is argued that financial, technical assistance must be provided to other seaports for the development and as a part of corporate social responsibilities, in addition, to the exchange of human resources and deploying them in other ports for training and develop the employee of mongla and payra ports. all respondents advised them to cpa for taking leadership in developing the port sector and provide financial assistance to other ports from their profit and contingency fund also arrange finance from a financial institution or government to invest in the port infrastructure, purchasing equipment and other development works by which other ports can show the productivity and attract users. in addition, cpa is technically sound in managing port operations, vessel management and port affairs where they can assist other ports by giving technical assistance for increasing efficiency. one respondent suggested that cpa must create the environment and situation by liaison with the government and private sector for developing other national ports for captivating the continuously growing volume of freight and container and need to think together. 6.2 integration among the seaports of bangladesh this is the time to integrate all seaports of bangladesh and decrease the dependency on chittagong port where cpa has to play a vital role to develop all seaports. respondents were tensed about the labour productivity, performance of equipment and wretched condition of roads and highways, poor railway connection, etc. they thought that cpa has to work on the quick development of all ports to cope with the containerization and mechanization of ports with the port hinterland freight distribution system and support the foreland by establishing a floating terminal in the bay of bengal. in addition, they appealed to the government to consider port planning and development as a priority activity to facilitate all trades in the country. moreover, integration is highly required to fulfill the standard demand of obor (one belt and one road) and competition may be raised among the seaports of bangladesh, india and myanmar enthusiastically, therefore, integration among the ports of bangladesh is appreciated to help each other in the process of development. however, the need to comply with the basic goals of various forums like bbin (bangladesh-bhutan-india-nepal forum for transport connectivity), bcim (bangladesh-china-india-myanmar forum for regional cooperation), bimstec (the bay of bengal initiative for multi-sectorial technical and economic cooperation), saarc (south asian association for regional cooperation) and asean (association of southeast asian nations) etc. lastly, all claimed to set the deep seaport in chittagong and initiative must be taken by the management of cpa. 30 sustainable marine structures | volume 05 | issue 01 | march 2023 overall, all respondents discussed that the integration of all seaports leading by chittagong port will make a chance to provide transit facilities to the neighbours by rail, road and river. in addition, cpa will finance the inland connectivity infrastructure cost where a good port transport network will be developed and respondents were optimistic about the process of port development. mention that this transit issue is forecasted as derived demand of using bangladeshi seaports, especially by india, nepal and bhutan [30,35] as per figure 3. figure 3. inland transport connectivity and the role of chittagong port as a development partner of other national port mongla and payra [30]. 6.3 challenges in developing the port sector of bangladesh by cpa it is not easy to develop the port sector by cpa as bangladesh is facing huge obstacles in developing the port sector. latest experience in setting deep seaport in the sonadia. most of the respondents argued that cpa is facing huge challenges in developing the port sector of bangladesh. recent participation in building the inland container terminal “pangaon” nearby the capital city dhaka is appreciated by all, in addition, to direct involvement in establishing the 3rd seaport “payra” in 2013. however, cpa is facing challenges in developing its own capacity and striving to increase the container jetty, terminal and handling equipment. furthermore, the below challenges are discussed arguably. respondents found too many challenges in developing the port sector of bangladesh and stated as below:  geopolitical and foreign policies are affecting to take strategic decisions in the port development of bangladesh especially negative approaches of neighbouring countries by which deep seaport construction is delayed and not sure of its finance in the bay of bengal.  poor quality of roads and highways along with old models of trucks and trailers that consume passage time also environmental degradation by co2 emissions highly.  shortage of liaison among the port authority, city corporation and city development authority to make common development of chittagong port.  an inefficient transit regime with a lag behind transport infrastructure and not having the future trade forecast for the region and country that is not facilitating or increasing the cargo and container handling capacity of bangladeshi ports individually.  research on port development regarding bangladesh and south asia is fully absent and undermined for a long time and not considered by all where adb is trying to forecast some data and related research is conducted by the world bank on a minimum scale.  to create synergies in the port sector by making common standards for all ports and rendering guaranteed reliability to port users.  there is no benchmarking statistical data for the port authority to take a decision on how much development is required in terms of infrastructure and others and the port has to follow the full government process of procurement that time bounded.  continuous pressure on cpa for managing all cargo and containers where other ports are under-utilized. in this connection, cooperation from the government, port users and others is limited to divert the vessel or container in an alternative way.  the political will of the government in the port development and consideration of development projects and finance over there as the government has to perform in all cases.  for environmental sustainability, priority may be given to the intermodal instead of multimodal that pollutes the environment and need to use various modes of transport at different points or nodes. in addition, internalization is a great challenge to face congestion, local pollution, accidents, ghg & co2 emission, energy efficiency, etc. 31 sustainable marine structures | volume 05 | issue 01 | march 2023  the desire of neighbours and world port investors for capital investment and making a regional port in bangladesh where chittagong is viable in all aspects.  development of a rail transport network with spatial transportation and introduction of a double decker container transport line between the major cities of the country.  full privatization of port sector or develop the port under the banner of ppp (public private partnerships) to reduce the pressure of capital investment by port authority. the most important statement received was “every challenge is achievable subject to the dedication of all port authorities and positive approach of the government by putting the port sector in their political circle”. forecasting the increase in port throughput, due to infrastructural enhancement, is a major challenge for many different reasons. 6.4 sustainability of port sectors in bangladesh the experience of cpa will help to take national approaches to sustainability in the volatile port sector and the role of government is highly appreciated. “port cooperation” is the main theme of port sustainability that may exceed from the national boundary to abroad by making liaison with neighbours ports or international forums of the port authority or associations. the turnaround time of an incoming vessel in chittagong port is very high in south asia but the average performance in managing container vessels is good. but there are some records of collapsing the total supply chain of the port that is harming the brand name of chittagong port as well as the country. due to the breakdown in managing container flow, ocean freight is increased by the international carrier unjustifiably. on the other hand, cpas are used to manage such a crisis from their vast experience in the port sector. critically, the bad performance brought negative opinions in the mind of respondents where they argued for good port management by experienced people in chittagong port and suggested making contingency or backup plans for avoiding such situations that bound to pay extra for the port users unexpectedly. respondents described the worst situation of mangle port and its authority (mpa). they found an idle and unskilled person who is managing the port only by name without adding any value-added service to the port users. several times, the government had taken necessary initiatives to bring efficiency and attract the business community to use the port at a minimal tariff, but due to poor category service, interest in mongla port is uncertain. most of the respondents were advised to take over the mpa by cpa and manage accordingly. to sustain the current trends of port activities, respondents suggested taking a long-term development plan and may lease the mongla port to the international terminal operator who will handle the operations as well as manage the customer by fixing the hinterland. environmental sustainability is a growing concern of the port industry and needs to promote intermodal transportation, which is environmentally friendly and make long-term sustainable development of the port in developing energy and operational efficiency plan at the port yard and inland transportation. all appreciated the steps by cpa for taking carbon tax from vessels under the port-protected areas of cpa. 6.5 inland transport networks development two important issues are key factors in port development, one is inland transport network development and another one is specific ift (intermodal freight transportation) system development for facilitating the inbound and outbound freight by applying just in time approach. greatly, 21 respondents argued for road modes for developing inland transport networks in bangladesh urgently where cpa may play a vital role in assisting the government and other port authorities by providing financial assistance or arranging finance for inland transport network development by using the surface or spatial transportation rather than choosing rail and waterways modes exceptionally as the road is speedy transport mode in bangladesh till date. all respondents favored the urgent development of roads and highways because congestion and passage time are very high which resulted in high freight for sending cargo to the port and vice versa. in addition, the intermodal freight transportation system will not be implemented without the good condition of roads and highways. after that freight rail network development is a priority area where cpa is able to invest in starting the double decker container line from chittagong port to dhaka and inspire rail authority in constructing a dedicated rail track for freight transportation as rail is cheap and safe transportation system and suitable for intermodal transportation. lastly, they argued for inland waterway transportation and are happy to know that the container is transported by waterways from chittagong to nearby dhaka. for better utilization of existing trucks and trailers, it is of utmost requirement to renovate all roads and highways with bridges and culverts. emphasize given on the access roads to ports and major cities and industrial areas. most of the respondents deliberated their opinion on transit facilities to the government and stated that the present condition of road and highways are not suitable to provide 32 sustainable marine structures | volume 05 | issue 01 | march 2023 such facilities to anyone. even so, it is hard to mitigate the domestic’s demand for port transportation facilities to cover all import-export trade timely. one respondent stated that only for bad road communication, mongla port is underutilized. therefore, need to invest in the infrastructural development of roads and highways where cpa may invest to create better facilities to/from the access port easily. cpa has its own icd (inland container depot) in dhaka and the container is in operation from chittagong port to dhaka and respondents are worried about the time that is taken by the rail hugely and not appropriate in container transportation. for any container transportation, it is taking 5 to 6 days whereas road haulage time is a maximum of 2 days. overall, current rail transportation is not feasible for all and needs to improve the freight rail networks. furthermore, we have the best connection to inland waterways. the recent development of rict nearby dhaka and the opening of the door to private investors for constructing private rict may improve inland waterway transportation. some respondents argued for common transport networks in three seaports to exchange the equipment and preserve special funds for emergency response in a breakdown in any ports and quick renovation of inland transport networks. in addition, for smooth operations of break-bulk cargo in the bay of bengal, a quality coaster or inland vessel is required to decrease the turnaround time and it is essential to establish a floating terminal for avoiding multiple handling of cargo & containers in the port jetty. it will attract coastal shipping among asian countries and direct entry to the inland terminal. some of the respondents attended in the open-ended questions where they suggested cpa take full responsibility to build an integrated intermodal freight transportation network of road, rail and inland waterways for domestic container transportation and establish a dry port nearby cross-border to provide maritime logistics support to the neighbours for doing “transport business” and arrange same for other national ports. 7. compare and contrast with the aim of developing seaports, many governments created port authorities especially to progress the port development commercially [13]. based on the literature and qualitative research survey, the below points are considered to bring the standard of maritime logistics of bangladeshi seaports with the aim of serving nationally, regionally and internationally: the shipping industry is showing the potential to improve the energy efficiency that started from ocean passage to shipyard (terminal, jetty and other places) and it’s a part of port performance in the present world [31]. another factor that is influencing the port authorities to inspire the shipping companies to use natural gas (lpg-liquefied petroleum gas, lngliquefied natural gas and others) instead of fossil fuel. to cope with the challenges and opportunities of the 21st century maritime silk road for better connectivity and economic cooperation, it is essential to develop the country itself to stay in the bay of bengal meaningfully and had the opportunity to serve the landlocked region, india’s northeast, china’s southern, nepal and bhutan that would be the value added to the regional development and economic growth [32]. in figure 4, bangladeshi seaports are well connected with the regional hub port colombo, sri lanka, klang and tanjung pelepas of malaysia and singapore. this research found the opportunity to stay within the region which means tagging with chennai and visakhapatnam of india, in addition to colombo, sri lanka. strategically, it will increase the regional bonding in south asia and open the opportunity for indian ports for using bangladeshi seaports as a maritime load center for seven sisters of india, nepal and bhutan. as india is a good development partner of bangladesh and is interested to use chittagong and mongla port for their basically landlocked parts, it will be a great opportunity for bangladeshi ports for developing port facilities through the leadership of chittagong port actively. figure 4. foreland connectivity of bangladeshi seaports developed by the author. map was taken from google [33]. alam [28] stated that bangladeshi ports are able to serve as the gateway to reach the landlock nepal & bhutan, india’s seven sisters for facilitating global trade. moreover, he added that subject to port development, it is possible to connect ports with southern china and it will be the great one in between the overland surface road and maritime silk road. environmental sustainability in any seaports that need innovation where research is required to make it 33 sustainable marine structures | volume 05 | issue 01 | march 2023 successful. safety and security are great concerns for hinterland operations by ports where the port has to clear all the obstacles for attracting the port users or traders within the established hinterland [34]. however, to overcome the challenges and problem areas will need the political will to facilitate the changes because the government is continuing to fight financial fires and ports are perhaps not a key priority in many cases [17]. overall, structural, operational and organizational changes are required for strengthening the capacity of cpa to build the port sector from the viewpoint of port performance, competitiveness and governance. finally, chittagong port has the first mover key advantages in the bay of bengal or south asia to provide maritime logistics support and offer free access to all where port development is essential. developed ports added some new indicators like emissions of greenhouse gases, investment flow and economic impact of a port but remember that depending on the port structure, different performance indicators are relevant for different ports [9]. the concept of integration in the port sector is highly concerned with the intermodal activities that focused on the conditions of efficiency and effectiveness of intermodal container transportation, and organizational integration that is undertaken by foreland & hinterland connections [22]. lastly, activities, resources and inter-organizational relationships between the players in the network are critical and essential to the port’s value created by port development. a successful growth strategy for south asia would need to rely on a balanced, multifaceted approach in a dynamic global environment [29]. this is due to negative outlook for ports and existing operating environment is really competitive, risky and mired in slower growth. this is true that port infrastructure is still relatively backward and not in a standing position with the internationally developed port standard comparatively. greater uncertainty in the operating environment, governing policy, and sufficient infrastructure development to make a model port in south asia, still chittagong port is lagging behind accordingly in this connection, it is a good way to develop other national ports and divert the cargo and container to reduce the pressure towards cpa. overall, port development is essential and it may be done by cpa or the bangladesh government urgently. here, trade forecast, regional development and recent institutional cooperation are the national and international pressure to develop bangladeshi seaports inevitable and urgent. 8. regional common platform for transport connectivity south asia is an important place for moving business trends to asia where the location of bangladeshi seaports is important strategically and a key factor for all to do foreign business as well as export and import trade profitably. port infrastructure development is highly important to regional economic development [13]. for a common platform in providing seaport access to all in a specific region, it is important to cooperate with each other irrespective of profit or port rivalry where it may be treated as social responsibility. goals are too general to provide sufficient directions for the authority and reform as and where required and increase the ability to safeguard the public interests of the country and region proudly. the absence of transit agreements for a long time among south asian countries fractured the regional integration process [28]. in addition, underpinning all trends of greater devolution, privatization and communication and approaches the desire to govern ports in a way that makes them more profitable and efficient, and, increasingly, a way that makes them more sustainable and greener [17]. bhatta [36] examined that regional economic integration depends on the commonality of the political purposes of the member countries where india has to favor and sacrifice to all for emerging as a regional entity in the international political system. however, a recent initiative of india and bangladesh in developing transport connections in the region is moving ahead toward increased regional participation in trade and commerce [28]. in relation to improving the global transport system, the availability of transport operations contributes to the value creation for accomplishing the qualitative attributes of demand such as reliability, punctuality, frequency, availability of infrastructure and security [14]. to assess the disruption risk of asian ports, lam and su [37] identified that climate change, oil spills, security and social and political instability are increasing the concern to all. as trade volumes are growing significantly, port disruptions are comprehensive studies for putting operational performance. a reliable freight transport system is essential for the modern world economy where marginal supply chains are involved with seaport activities greatly [37]. overall, the regional common platform for transport connectivity highly depends on two factors: the openness of india to open the so-called “chicken necks” land connection among india, nepal, bhutan and bangladesh that will allow getting free access by all including china and myanmar: another one is the free access opportunity in bangladeshi seaports subject to the development of inland transport networks by bangladesh. 9. conclusions chittagong port is the principal seaport of bangladesh 34 sustainable marine structures | volume 05 | issue 01 | march 2023 managed by the cpa and is able to serve all modern seaport facilities to the port users for driving above 90% import-export trade of bangladesh [38]. port authority in leading leadership roles sets the larger role for terminal operators who bear the market’s considerable risk and face the demands of an increasingly stringent environment regime [5]. bangladesh acutely needs the deep seaport in the bay of bengal to increase the supply side against the increased demand for port facilities, in addition, to supporting the neighbours or region for doing port transport business as a part of economic sustainability [32,35]. historically, the port is the entry point of international trade for a country that helps to attract the international trader to do business and it’s a key logistics performance indicator. a recent development in port sector is containerization and mechanization, and the port has to set as per new dimensions that are required by international shipping company and terminal operators. in this context, de langen and van der lugt [13] argued from the operational perspective of public sector port authority for promoting general interests the port operations handled by third parties are a part of port development. nowadays, port authority is an increasingly commercial role to bring the developer or work as a port development company due to the containerization and mechanization of port activities also developing inland connections with the urban cities and major industrial areas. remarkably, the continuous changes in the international maritime transportation and further movement of cargo and container towards the hinterland, structured the total transportation solutions to the port users, traders and stakeholders accordingly. due to poor connection between the bangladeshi seaports and hinterland as well as inadequate standard port facilities of mongla port, chittagong port has to manage the excess pressure of freight and face challenges in providing maritime logistics support to mitigate the demand of domestic port facilities where opportunity remains to serve south asia by using the geographical advantages or positional standing in the bay of bengal greatly. this paper aimed to explore how cpa assists other national ports and port infrastructure that will be developed with the port efficiency and productivity and all ports will serve the nation equally against the domestic demand of maritime logistics or port services. in line with such motivation, mongla and payra will develop accordingly to supply port services to the neighbours india, nepal and bhutan as well as serving the south-west part of china with the aim of increasing regional connectivity and promoting international trade in those basically landlocked areas and countries of asia. overall, future directions will help to cpa for playing a vital role in port development and related infrastructure development in bangladesh for doing “transport business” in south asia. 10. future directions on the basis of the literature review, qualitative research survey and innovations for the seaport, research attributed the below future directions for port sectors of bangladesh as well as for cpa that will help them in the process of port development in bangladesh: 1) bangladesh is the only country in the indian subcontinent in which the private sector does not play a meaningful role in the container port sector [15]. therefore, port privatization scope needs to inspire or utilize and make joint ventures with local and international investors in the port sector as a cheap way to develop the port economically. 2) ppps model has advantages in funding where ports are able to build and updates the assets such as handling equipment, container storage facilities, channel dredging and others including infrastructural development [23]. to attract international investors in the port sector, it is good to appoint international terminal operators. nowadays, terminal operators are managing not only the terminal but also managing the customers of the hinterland and increasing the hinterland by offering various port services at an affordable price. 3) port users are always thinking about the port facilities, but it is also a factor in selecting port that has good inland transport connections with the shipper/consignee premises. thus, emphasis should be given to the inland transport network development. 4) most of the containerized cargo is managed at the dry port and must have a rail network to connect between the port and dry port, in addition to a road connection. bangladesh has to build dry ports with smooth inland connections with ports in major cities for domestic cargo and in cross-border areas to serve the neighbours. 5) having the opportunities to provide maritime logistics support, bangladesh has to open the door of ports and promote regional connectivity in the transport sector. 6) government has to follow up the logistics performance indicator (lpi) of the world bank and must take necessary reform initiatives to increase the value of lpi for attracting the world trader to do business with bangladesh and use the bangladeshi seaports in the competitive port tariff. 7) geopolitics is a problem for investment in the port sector where india and china is a key factors to build a deep seaport in the bay of bengal [32]. government has to take a deep seaport initiative in chittagong and share with the development partner countries for investing in the deep seaport projects. 35 sustainable marine structures | volume 05 | issue 01 | march 2023 8) with much talk, the floating crane is an innovation for ports that increased productivity and promote the modal shift for handling a large volume of containers [5]. cpa has to take the initiative to set up a floating container terminal for handling feeder vessels towards mongla, payra and rict pangaon to save time and decrease the number of handling at the port area. 9) maritime governance is playing a key role in developing the prestigious standing in the world [39]. to integrate all seaports of bangladesh, it is essential to create a maritime commission for monitoring the port productivity, governance and facilities. 10) research is a developmental feature to focus on the gaps and necessary guidelines and directions to take initiative for future development. research on port development is essential as this chapter is far lagging behind in bangladesh including south asia. conflict of interest the opinions are solely from the researcher and there is no conflict of interest with the employer saif powertec limited. mention that saif powertec limited is not involved in any part of this research and is not responsible for any comments from anywhere. acknowledgement i am greatly indebted to theo notteboom, geraldine knatz and francesco parola who inspired me to conduct this research on south asian ports and focus on the role of bangladesh in port development. in addition, i am grateful to my ph.d. supervisor professor, dr. md. shamsul hoque, bangladesh university of engineering and technology (buet) who guided me to complete the research successfully. references [1] lee, p.t.w., lun, y.v., lai, k.h., et al., 2016. maritime logistics and port connectivity in the globalised economy. transportation research part e: logistics and transportation review. 100(95), 323-325. 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[cited jan. 2017 18] available from: http://cpa.portal.gov.bd/sites/default/files/files/ cpa.portal.gov.bd/page/4a3e1831_9543_416f_957d_ 079e2a12363a/cpa-overview-2015-2016.pdf [39] roe, m., 2013. maritime governance and policy-making: the need for process rather than form. the asian journal of shipping and logistics. 29(2), 167-186. http://hdl.handle.net/10986/30494 https://doi.org/10.1080/03088839.2014.932557 https://doi.org/10.1108/ijlm-06-2015-0101 https://doi.org/10.1080/01441647.2016.1231232 https://archive.thedailystar.net/suppliments/2010/02/ds19/segment2/initiative.html https://archive.thedailystar.net/suppliments/2010/02/ds19/segment2/initiative.html https://archive.thedailystar.net/suppliments/2010/02/ds19/segment2/initiative.html https://www.thedailystar.net/news-detail-195662 https://doi.org/10.1111/pafo.12059 https://www.google.com/maps/@13.1052733,95.8688982,5z https://doi.org/10.1080/03088839.2015.1016560 http://cpa.portal.gov.bd/sites/default/files/files/cpa.portal.gov.bd/page/4a3e1831_9543_416f_957d_079e2a12363a/cpa-overview-2015-2016.pdf http://cpa.portal.gov.bd/sites/default/files/files/cpa.portal.gov.bd/page/4a3e1831_9543_416f_957d_079e2a12363a/cpa-overview-2015-2016.pdf http://cpa.portal.gov.bd/sites/default/files/files/cpa.portal.gov.bd/page/4a3e1831_9543_416f_957d_079e2a12363a/cpa-overview-2015-2016.pdf 40 sustainable marine structures | volume 04 | issue 02 | july 2022 sustainable marine structures https://ojs.nassg.org/index.php/sms copyright © 2022 by the author(s). published by nan yang academy of sciences pte ltd. this is an open access article under the creative commons attribution-noncommercial 4.0 international (cc by-nc 4.0) license. (https://creativecommons.org/licenses/ by-nc/4.0/). *corresponding author: xiangyuan zheng, institute for ocean engineering, tsinghua university shenzhen international graduate school, guangdong, china; email: zheng.xiangyuan@sz.tsinghua.edu.cn doi: http://dx.doi.org/10.36956/sms.v4i2.617 review current status and future trends for mooring systems of floating offshore wind turbines ruyan yang1 xiangyuan zheng1* jinlu chen1 yufei wu2 1. institute for ocean engineering, tsinghua university shenzhen international graduate school, guangdong, china 2. guangdong provincial key laboratory of durability for marine civil engineering, shenzhen university, shenzhen, 518060, china article info abstract article history received: 1 august 2022 revised: 19 august 2022 accepted: 13 september 2022 published online: 22 september 2022 with the increasing demand of energy and the limitation of bottom-fixed wind turbines in moderate and deep waters, floating offshore wind turbines are doomed to be the right technical choice and they are bound to enter a new era of rapid development. the mooring system is a vital system of a floating wind turbine for station-keeping under harsh environmental conditions. in terms of existing floating wind turbine projects, this paper is devoted to discussing the current status of mooring systems and mooring equipment. this paper also presents the mooring analysis methods and points out the technical difficulties and challenges in mooring design, installation, operation and maintenance stages. finally, the developing trends of the mooring system are summarized, aiming to provide a reference for future mooring research. keywords: mooring system mooring equipment mooring analysis floating offshore wind turbines mooring line anchor 1. introduction stimulated by global low-carbon policies and promoted by the development of new energy, the wind energy, a kind of renewable clean energy, has been exploited worldwide for its advantages of sustainability and huge reserves, as well as for the increasing maturity of technologies in power engineering, mechanical engineering and offshore engineering. compared with the land wind energy, the ocean wind energy is more abundant, more stable, vaster in spaces for exploitation, and of fewer impacts on the environment [1]. the wind power has gained rapid development as of 2021 with a globally accumulated capacity of 837 gw, among which the accumulated offshore capacity (bottom-fixed plus floating) has reached 56 gw. further, the offshore wind energy is doomed to have a bright prospect in human’s history by reaching 380 gw by the end of 2030 and 2,000 gw by 2050 [2]. in the past decades, the majority of offshore wind farms was restricted to the offshore shallow water where mailto:zheng.xiangyuan@sz.tsinghua.edu.cn 41 sustainable marine structures | volume 04 | issue 02 | july 2022 bottom-fixed wind turbines were predominantly deployed. the wind turbine foundations include monopile, jacket, tripod and so on. however, their feasibility is limited by the water depth up to 50 m [3,4]. a higher construction and installation cost will be incurred in moderate and deep waters. by comparison, the floating wind turbine (fwt) is more mobile and flexible to deploy, easier to dismantle, and more suitable for relatively deeper waters. in addition, the deployment site of fwts is far away from the coastline, eliminating the harm of noise and electromagnetic waves to the environment [5]. also, compared to nearshore fixed turbines, a larger capacity of turbine like the 9.5 mw units in kincardine uk can be installed onto floating structures to harness more power so as to achieve a higher levelized cost of energy (lcoe) [6]. all these advantages have pushed fwts to take on an important historical mission in the development of ocean renewable energy. in recent ten years, more and more fwt projects have been constructed in moderate and even deep waters. table 1 summarizes the worldwide fwt projects already commissioned or being constructed, among which the hywind tampen project has reached water depth as deep as 300 m. the accumulated capacity for the commissioned fwts as of 2021 has exceeded 121.4 mw [2]. for a fwt, its mooring system is a crucial system for the station-keeping purpose. the mooring system generally consists of mooring lines, connectors and anchors. in rough seas, the floating foundation of a fwt interacts with the mooring system and the mooring lines restrain the motion of the floater by providing sufficient restoring forces mainly in horizontal directions. particularly in extreme environment conditions, the floater’s motion displacement, mooring line tension, wind turbine pitch angle and acceleration should meet the requirements of specification in codes and standards, such as dnvgl os e301, api rp 2sk, api rp 2sm etc. for the design of a mooring system, not only the hydrodynamic performance but also the cost of fabrication and installation should be taken into account [7]. hence, it is one of the objectives in this paper to review the current status of fwts’ mooring systems. table 1. world floating wind turbine projects and their mooring systems as of july 2022 (commissioned or to be commissioned*) country year project wind turbine capacity (mw) floating foundation type water depth (m) mooring type france 2019 floatgen 2 barge 33 semi-taut france 2022* groix-belle-ile 4×6 semi-submersible 55-70 semi-taut france 2023* efgl 3×10 semi-submersible 70-100 catenary france 2024* eolmed 3×10 barge 55 catenary norway 2009 hywind ⅰ 2.3 spar 220 catenary norway 2021 tetraspar demo 3.6 spar 200 catenary norway 2022* hywind tampen 11×8 spar 260-300 catenary portugal 2020 windfloat atlantic 3×8.4 semi-submersible 100 catenary united kingdom 2017 hywind scotland 5×6 spar 95-109 catenary united kingdom 2021 kincardine 5×9.5+2 semi-submersible 60-80 catenary japan 2013 fukushina ph1 2 semi-submersible 120 catenary japan 2016 fukushina ph2 7 semi-submersible 120 catenary japan 2016 fukushina ph3 5 spar 120 catenary japan 2019 hibiki 3.2 barge 55 catenary china 2021 sanxia yinling 5.5 semi-submersible 29.2 catenary china 2022* haizhuang fuyao 6.2 semi-submersible 65 catenary 42 sustainable marine structures | volume 04 | issue 02 | july 2022 2. types of mooring systems the mooring systems are classified in a variety of types, according to their mooring line configurations and materials, operation requirements and layout characteristics. depending on the mooring line configuration, the mooring systems of fwts mainly include three types, i.e., catenary moorings, taut moorings and tether moorings. 2.1 catenary mooring the catenary mooring refers to a suspended mooring line that is in the shape of a catenary under the effect of self-gravity while the bottom of the mooring line lies on the seabed (see figure 1). as such, the anchor point only bears horizontal force. the catenary mooring usually uses the steel chain as the material of mooring lines. the restoring force comes from the gravity of the mooring line itself. it is generally applied to the water depth below 1000 m, especially less than 500 m [8]. with the increase of water depth, the length and weight of mooring lines will increase significantly, resulting in a high cost and reduced deck payload of the floater. at the same time, the mooring radius will also increase obviously, affecting the laying of submarine pipelines and ship navigation. figure 1. the catenary mooring system [9] so far, the catenary mooring has been most widely used for floating oil and gas platform, as well as fwts (see table 1), because of the following advantages: a. the catenary mooring has a simple structure and stable reliability. b. it is economical in the water depth below 500 m. c. the mooring chain has relatively easier fabrication and simpler installation as compared to taut moorings and tether moorings. the world’s first commercial floating wind farm, hywind scotland, consists of five 6 mw wind turbines that are 25 km away from peterhead scotland. in the water of 95 m ~ 109 m, every fwt adopts a spar foundation with draft of 78 m. since its center of gravity is lower than the center of buoyancy, the structure has superior stability even in harsh seas [10]. the five fwts are anchored to the seabed through three catenary mooring chains. each mooring chain is about 900 m long with a diameter of 0.09 m. the mooring chains are connected to the floater through a delta connection using the bridle so as to obtain the extra yaw stiffness (figure 2). the bridle is usually used in spar foundations rather than semi-submersible foundations, because in semi-submersible foundations there is sufficient distance between a fairlead and the center of rotation, leading to enough yaw stiffness. three suction anchors for each turbine are 5 m in diameter, 16 m tall, with an approximate anchor radius of 850 m [11]. in addition, a special fairlead chain stopper system (see figure 3) was developed by macgregor specially for mooring wind turbines in hywind scotland wind farm. it can rotate both horizontally and vertically in order to prevent the out-of-plane bending fatigue of the mooring chains [12]. figure 2. hywind scotland mooring system [11] figure 3. hywind scotland fairlead chain stopper system [11] sanxia yinling (figure 4), the first fwt at the yangjiang offshore wind farm in guangdong province of china, is a fwt demo project with the typhoon-resistant technology. the site is about 30 km offshore with water depth of 29.2 m. the floater adopts a semi-submersible structure of three columns with a diameter of 11.8 m. it has a total displacement (include ballast) of 13,000 t and a design draft of 13.5 m. the mooring system is designed as 3 groups of catenary mooring lines, each composed of 3 mooring lines. each mooring line is made up of 4 seg43 sustainable marine structures | volume 04 | issue 02 | july 2022 ments, including a chain segment near the fairlead end, a clump segment, a wire rope segment and a chain segment near the anchor end, from top to bottom. the top end of the mooring line is equipped with a chain stopper and the bottom end is anchored on the seabed by a suction anchor. figure 4. china sanxia yinling [13] nowadays, fwts are in the high-speed development path towards large tonnage. also, the new fwt projects will be principally deployed in the water depth of 100 m ~ 300 m. under this circumstance, catenary moorings will still be the mainstream options in the near future. 2.2 taut mooring the taut mooring system has mooring lines that are taut in tension between the fairlead on the floater and the anchor point on the seabed (figure 5) such that there are no bottom lying lines. typically, the angle between the line and the seabed is between 30 degrees and 45 degrees. therefore, the anchor point should bear both horizontal and vertical forces. examples of such anchoring structures include suction anchors and vertical load anchors. the taut mooring system usually uses wire ropes, high-strength nylon ropes, polyester cables or other synthetic materials. the recovery force is primarily provided by the axial tensile deformation of the mooring line [14]. in deep water, the taut mooring can greatly reduce the length and weight of mooring lines, as well as the mooring radius. nonetheless, in shallow water, the stiffness of the mooring line should be very large, excessively increasing the tension of the mooring line. as a consequence, it is more suitable for floaters in deep and ultra-deep waters [8], though over the last two decades a number of applications to wave energy converters in moderate water depths have been realized [15]. figure 5. the taut mooring system [9] in existing fwt projects, only a couple of turbines use semi-taut moorings, such as floatgen and groix-belle-ile (being constructed) in france (see table 1). floatgen has a reinforced concrete foundation designed by ideol. the foundation is designed as a barge to improve its stability [16] while the damping pool in the central opening of foundation is used to suppress foundation’s wave-frequency motions. the dimensions of the square-ring shaped foundation are 36 m in breadth, 9.5 m in height and 7.5 m in draft. floatgen’s semi-taut mooring system consists of six mooring lines, assigned into three groups. from the fairlead to the drag embedment anchor, a single mooring line is composed of a top chain, a nylon cable and a bottom chain. such an innovative use of nylon cables is a worldwide premiere for the permanent mooring of a large floater in offshore engineering. simultaneously, the mooring lines are equipped with buoys to prevent friction with the seabed, as well as to balance the self-weight of the mooring lines. such a novel mooring system satisfies two seemingly paradoxical requirements at the same time. one is the competitive fabrication and installation cost and the other is the ability to keep the floater stable in rough seas [17]. compared to the catenary mooring system, the taut mooring system possesses the following advantages: a. the mooring radius is significantly reduced, leading to a smaller seabed area occupied by mooring equipment and fewer risks of collision with other underwater equipment nearby. b. the restoring stiffness of the mooring line is larger, providing larger restoring forces. therefore, the horizontal offset of the floater can be greatly reduced. c. the material of the mooring line has a lighter weight. thus, not only the self-weight of the mooring system but also the load of mooring system on the foundation is reduced. d. the length of the underwater mooring line is greatly shortened, making the taut mooring very competitive in cost in deep and ultra-deep waters. e. the material like nylon and polyester is outstanding 44 sustainable marine structures | volume 04 | issue 02 | july 2022 in mechanical performance, especially fatigue resistance and corrosion resistance. figure 6. floatgen and its mooring system [18] nonetheless, the mooring lines need to bear huge tension and axial stress under harsh operating states. under the influence of alternating loads for a long life span, the underwater nylon cables are prone to fatigue failure and material aging. furthermore, storage, transportation and installation processes all raise strict requirements on cables. in an improper operation, the scrap damage may occur due to cable breakage or abrasion. the sediment entering the cable will also pose a great threat to the mooring system [19]. all these lead to a high cost of fabrication and installation, which is a recognized disadvantage of the taut mooring. 2.3 tether mooring the tension leg platform (tlp) shown in figure 7 is vertically moored by tendons (also called tethers). the tendon consists of steel tubes with high axial stiffness. the buoyancy of the tlp is greater than its own gravity and the excessive buoyancy is balanced by the pre-tension in tendons. as a result, the stability of the floating foundation principally depends on the mooring system [5]. the anchors like driven piles and gravity anchors are required to withstand large vertical loads. the tether mooring is particularly suitable for the water depth greater than 300 m and its common applications go to oil and gas platforms in gulf of mexico. since the tendons are vertically connected to the seabed, the mooring radius is small. however, the fabrication process of a tendon is extremely complicated and delicate. also, the tendon installation requires special installation vessels that can both keep the foundation stable and connect the tendons. consequently, a high fabrication and installation cost is incurred during tether moorings. in addition, its risks are enormous. if one tendon fails, the stability of the foundation will suddenly decrease, causing a high risk of capsizing [21]. due to the pre-tension of tendons, the natural heave frequency of the tlp is extremely high (2 hz ~ 4 hz). this will cause high frequency response problems, such as springing and ringing [22]. for these reasons, the tether moorings have not been used on a large scale for fwts yet. the tlp concept for a fwt stays at the stage of small-scale tests and numerical calculations. figure 7. sketch of fwt with tether mooring [20] the gicon-sof project (see figure 8), a tension-leg fwt with the tether mooring, was initiated in 2009. the floating foundation consists of four columns, anchored to the seabed by four vertical tendons and additional eight slanting tendons. in 2013, a 1:37 scaled model test of the gicon-sof 2 mw foundation was carried out at the maritime research institute netherlands (marin) [23,24]. in 2016, the combined wind and wave tests were conducted for a 6 mw turbine on the gicon-sof foundation and the experimental results showed very satisfactory performance for its stability. though it was reported that gicon-sof would have prototype sea trials with a 6 mw ~ 8 mw turbine [25], so far no trials have been implemented. 2.4 other classifications of moorings depending on the duration of the offshore operation, mooring systems are classified into two categories, temporary moorings and permanent moorings. the temporary mooring is applied to temporary platforms or vessels that operate for periods ranging from a few days to several months, while the permanent mooring is used for floating 45 sustainable marine structures | volume 04 | issue 02 | july 2022 structures that operate in fixed sea areas for a long time. in terms of the design life, the operation time can be several years or several decades. figure 8. gicon-sof project (left) and its model test (right) [26] the mooring systems can also be categorized into spread moorings and single-point moorings according to the requirement of restricting the heading of the floater. the spread mooring, where mooring lines are distributed around the platform, can restrict the offset and heading of the platform from all directions. the single-point mooring is often used for ship-shaped floating structures under severe sea conditions with frequent changes in wind, wave and current directions. it has one or more mooring lines connected with the rotating center, so that the floater has a weathervane effect and can rotate with the direction of wind, waves and currents. the single-point mooring is commonly used in the floating production storage and offloading (fpso). though the single-point mooring has not been applied to an actual fwt project, it was adopted by the eolink [27] fwt concept (figure 9). unlike most fwts, it can spin around its rotating center to face the wind. the patented single point mooring is able to withstand large tide range in shallow water as well [27], but this concept has not been applied to real fwt project yet. figure 9. eolink with single-point mooring [27] 3. mooring system equipment the mooring system for fwts chiefly contains mooring lines, anchors and connectors. this section discusses the current status of mooring equipment. 3.1 mooring lines 3.1.1 chain the chain is a common mooring line component with a simple connection and good abrasion-resistance property. the mooring chain is made of a plurality of steel links welded and connected with each other. according to the link form, chains are divided into two kinds: studlink chains and stud-less chains (figure 10). the studlink chain has a stud in the middle to prevent it from entangling and it is often used for temporary moorings, requiring multiple retractions. the stud-less chain, without a stud inside, is about 10% lighter than the stud-link chain with the same breaking strength. there are other advantages for the stud-less chain. for example, there is no loosening of the stud, no cracks at the joints of the stud and it is easier to fabricate and inspect. as a result, the stud-less chain is preferred for permanent moorings. figure 10. stud-less chain (left) and stud-link chain (right) [9] chains have a wide variety of diameters and grades. the nominal diameter of ocean engineering chains ranges from 70 mm to 200 mm. the classification standard provides several grades based on tensile strengths, shown in table 2. the grades include r3, r3s, r4, r4s, r5 and r6. r7 is still under development. table 2. the performance of different grades of mooring chains [29] grade yield stress (n/mm2) tensile strength (n/mm2) elongation (%) r3 410 690 17 r3s 490 770 15 r4 580 860 12 r4s 700 960 12 r5 760 1000 12 r6 900 1100 12 in terms of manufacturers, the jiangsu yaxing company in china can produce ultra-high strength r6 chains that have been successfully used in a deep-water drilling plat46 sustainable marine structures | volume 04 | issue 02 | july 2022 form. such chains meet the latest international codes and standards, reaching an internationally advanced level. 3.1.2 wire rope the wire rope is made up of multiple strands of metals that wound into a spiral. the wire rope in mooring system usually includes six strands, eight strands and spiral strands, shown in figure 11. generally, with more strands, the wire rope has a greater breaking strength, but a heavier weight and a higher fabrication cost. six strands and eight strands are preferred in the temporary mooring. they are easier to fabricate because they can bend on a winch. nevertheless, they tend to produce rotational torque when stretched, causing torsion of the wire rope. by contrast, spiral strands are torque neutral, since they have multiple layers wound in opposite directions. moreover, the spiral wire rope has better corrosion resistance due to its compact structure. the uniform surface of the spiral wire rope also makes it easier to be sheathed, such as the polyurethane sheath. based on the above advantages, the spiral wire rope is suitable for permanent moorings [30]. under the same breaking load, the wire rope is lighter and more elastic than the chain, but the structure of the wire rope is more complicated and vulnerable, and its fabrication and installation costs are higher. it is often used in taut moorings or as the middle division of catenary moorings. as for manufactures, the juli company in china supplies various types of wire ropes such as 1870, 1960, 2160 etc. globally, the neptune company in singapore and the bridon company in uk have leading manufacturing capabilities [8]. figure 11. various types of wire ropes [7] 3.1.3 synthetic fiber rope the materials of synthetic fiber ropes involve polyester, high molecular polyethylene (hmpe), aramid, and so on. the structural composition of a synthetic fiber rope is shown in figure 12. due to its elastic property, the synthetic fiber rope is appropriate for taut moorings. nonetheless, the complex mechanical properties of synthetic fiber ropes bring new challenges to mooring analysis, including its variable stiffness, creep and slack-taut issues. figure 12. composition of a synthetic fiber rope [31] in deep water, the synthetic fiber rope is propitious to reduce the weight and length of mooring lines. the main advantages of synthetic fiber rope include high elasticity, high strength (900 mpa or higher) and low weight. to be specific, under the same breaking force the mass per unit length is only 1/10 of that of the chain or 1/3 of that of the wire rope and the weight is even lighter in water. additionally, it possesses prominent fatigue resistance performance and excellent corrosion resistance performance [32]. nevertheless, it is likely to be damaged by sharp objects. sands would also invade the jacket and damage the rope. concerning the manufactures, lankhorst in netherland has more than 200 years of manufacturing experience. its gama98 synthetic fiber rope is made of parallel rope cores within an outer jacket. the tension and length of each parallel rope can be precisely controlled during fabrication [33]. the sixiong rope industry in china completed the production and manufacturing of synthetic fiber ropes that have been successfully used by the cnooc lingshui17-2 project for offshore gas exploitation, achieving a huge breakthrough in the field of mooring rope manufacturing. 3.2 anchors the choice of anchors is mainly determined by the water depth, the condition of soil and the load type that the anchor point needs to bear. also, the cost of transportation and installation is a key factor. typical ocean engineering anchors are shown in the figure 13, categorized by water depths (shallow to ultra-deep) and soil types (hard to soft). 3.2.1 gravity anchor the gravity anchor is the simplest and oldest anchor foundation in existence. it provides anchor force through the friction with the seabed and its own weight. as a result, the gravity anchor is generally large in size and usually made of steel and concrete. normally, it is inexpensive to install, but only suitable for medium to hard soil conditions and difficult to remove during decommissioning. 3.2.2 driven pile the driven pile is a hollow steel pipe that can bear 47 sustainable marine structures | volume 04 | issue 02 | july 2022 both horizontal and vertical loads generated by the friction resistance between the pile and the surrounding soil. in general, the driven pile must be driven deep enough below the seabed to achieve the desired holding capacity. it is usually installed by pilling hammers or vibratory hammers. there are also some limitations of the driven pile. for instance, the disturbance to the seabed cannot be ignored. also, when the water depth exceeds 1000 m, the strict installation requirements for equipment leads to a great difficulty of piling. three driven piles have been used in haizhuang fuyao in china. figure 13. typical mooring anchors [9] 3.2.3 drag embedment anchor the drag embedment anchor is one of the most commonly used anchors presently. it offers the horizontal load in the same direction as the installation direction. it is for this reason that the drag embedment anchor is often used in catenary moorings. in addition, certain drag embedment anchors are capable of offering vertical forces now. generally, the main soil resistance occurs in front of the anchor, and therefore the resistance largely depends on its fluke area [34]. drag embedment anchors have been used in floatgen france, hibiki japan, windfloat atlantic portugal and so on. 3.2.4 suction anchor suction anchors are suitable for a wide range of water depths, mainly used in clay, sand and granular layers. recent applications to fwt projects include hywind scotland uk, sanxia yinling china, hywind tampen norway etc., among which the hywind scotland and the hywind tampen use a shared anchoring system. the suction anchor can withstand large horizontal and vertical loads of mooring lines. it must be specially designed for soil conditions. moreover, it is complex to construct and expensive to install. divers or remote operated vehicles (rov) are required to install and remove the submersible pumps. the suction anchor is generally a steel cylindrical pipe with an open bottom and a closed top. when installed, the suction anchor is lowered to the seabed and the lower edge of the pipe is embedded into the soil by its own weight. then, the water in the suction pile is continuously pumped out to reduce the pressure inside the cylinder. the vertical pressure produced by the internal and external pressure difference acts on the top of the pipe, so that the pipe will be continuously pressed into the soil until the cylinder body is all drained and the bottom is closed [35] (figure 14). in this figure, ‘l’ denotes the depth to which the suction anchor sinks under the force from hydrostatic pressure difference. figure 14. installation process of the suction anchor [36] 3.2.5 torpedo pile the torpedo pile, driven into the seabed by its own kinetic energy, can withstand both horizontal and vertical loads. the torpedo pile has a small size and good pullout resistance. also, it is omnidirectional and self-installed, so that it is adaptive for ultra-deep water. nevertheless, considerations arise to the large usage of steel and its inability to recycle. 3.2.6 vertical load anchor the vertical load anchor is installed in the same way as the drag embedment anchor, but it penetrates deeper into the soil. the vertical load anchor can bear both horizontal and vertical loads. it is primarily utilized in deep-water moorings. 48 sustainable marine structures | volume 04 | issue 02 | july 2022 3.2.7 summary driven piles, drag embedment anchors and suction anchors have been widely applied to fwt projects. gravity anchors are often used for fwts in shallow waters provided the soil penetration is sufficiently deep. torpedo piles and vertical load anchors are not in practical use for fwts while they have been popularly adopted in deep-water oil and gas exploration. nonetheless, as the offshore wind development trends towards deep waters, torpedo piles and vertical load anchors will become the potential choice. 3.3 connectors connectors are used to connect the mooring line components. common connectors in marine engineering include shackles, kenter shackles, pear shackles and swivels. however, due to the limited fatigue life, they can only be used in temporary moorings rather than permanent moorings. since it is hard to inspect and replace connectors in permanent moorings, the connector must be robust and durable. the recommended connectors in permanent moorings include long term mooring (ltm) d-shackles and h-shackles. d-shackle (figure 15 left) consists of a bow component and a pin component. h-shackle (figure 15 right), named for its shape, can be used to connect chains to chains, chains to wire ropes, chains to synthetic fiber ropes etc. other types of connectors may be allowed to use in permanent moorings if the fatigue life and the structural strength are qualified. figure 15. d-shackle (left) and h-shackle (right) [7] 4. mooring analyses this section is committed to discussing the differences and features of mooring analysis methods including static, quasistatic and dynamic analyses, frequency-domain and time-domain analyses, uncoupled and coupled analyses. 4.1 static, quasistatic and dynamic analyses generally, the motion responses of a floater under environmental loads can be divided into three categories of motions: steady state, low frequency and wave frequency. the response of a mooring system in the steady state can be obtained by static analysis. meanwhile, the low-frequency response can be analyzed by a static method as well, for the period of the motion is long [37]. one of the typical methods of static analysis is the catenary equation method in which the environmental loads are regarded as static, in order to determine the equilibrium position of the floater, the geometric shape of the mooring lines and the tension distribution along the mooring lines. however, the static analysis ignores the coupling between the foundation and the mooring system, the fluid force on the mooring lines and the elastic deformation of the mooring lines, etc. as a result, the static method can hardly meet the requirements of accuracy when the floater is expected to experience large motions and it is only applicable to the preliminary design of a mooring system. following the preliminary design, the dynamic response of the whole system should be determined. in this process, the usually adopted methods include the quasistatic analysis and the dynamic analysis. the quasistatic approach ignores the vertical motion of the mooring system and the dynamic effects of the mooring lines, i.e., added mass, damping, drag force and fluid acceleration. in this approach, the motion of the foundation is subdivided into various instantaneous states and the equilibrium position is acquired by using the static analysis for these instantaneous states. the main shortcoming of this method is that it does not consider the influence of the dynamic effects of the mooring lines on floater’s wave-frequency motions. hence, if wave-frequency impact is negligible, the quasistatic method can be used to predict the response of the whole system. furthermore, it has been proved [38] that the quasistatic method can achieve satisfactory prediction by using a safety factor with high efficiency. on the contrary, the dynamic analysis accounts for the time varying properties of the mooring lines. such an approach is able to accurately simulate the nonlinear characteristics, such as the nonlinear hydrodynamic force on mooring lines, the nonlinear deformation of the mooring lines, and the friction between the mooring lines and seabed, etc. the commonly used methods in dynamic analysis include the finite element method and the centralized mass method. kwan [37] figured out that the ratio of tensions calculated by dynamic analysis to those calculated by quasistatic analysis is in the range of 1.2 to 19.5. in general, the dynamic analysis is recommended to predict 49 sustainable marine structures | volume 04 | issue 02 | july 2022 the responses of floater and mooring lines. 4.2 frequency-domain and time-domain analyses frequency-domain analysis is a simple and efficient technique. in frequency-domain analysis, the response of the system is made up of frequency-dependent components and solved by the principle of linear superposition of different frequencies. moreover, the frequency-domain analysis not only determines the motions of the floater and the tension of the mooring lines separately, but also analyzes the mean response, low frequency response and wave frequency response respectively as well. the recommended analysis procedures provided in api rp 2sk [39] are shown as follows: a. determine the mean environmental loads acting on the floater and predict the equilibrium position using static analysis. b. determine the low-frequency motion using hydrodynamic analysis. in this process, the mooring stiffness at the equilibrium position is required. c. determine the wave-frequency motion using raos. d. determine the motions of the floater and the tension of the mooring lines using dynamic or quasistatic analysis. e. compare the maximum offset and maximum mooring line tension against the design criteria. however, when using the frequency-domain analysis, its limitations should be noticed. this approach is linearized, and therefore it approximates the nonlinearities including the nonlinear deformation of the mooring lines, geometric nonlinearity, fluid loads and bottom friction etc. furthermore, the extreme value is obtained from statistical distributions rather than directly from time-domain simulations. on the other hand, though the nonlinear spectral analysis can be adopted for the dynamic analysis, due to its complexity it is seldom used by engineers. the time-domain analysis is more time-consuming but more accurate than the frequency-domain analysis. it is able to simulate all nonlinearities. also, the time-domain analysis accounts for the coupling between the mean response, low-frequency response and wave-frequency response. the steps recommended by api rp 2sk [39] are summarized as follows: a. establish the hydrodynamic model including the floater and the mooring systems simultaneously. determine the wind force and current force coefficients. b. run the time-domain simulation in the mooring analysis software (like orcaflex) and repeat it several times for different seeds. c. obtain the extreme value of the floater offset and the mooring lines tension by a proper statistical analysis method. d. compare the maximum offset and maximum mooring line tension against the design criteria. the time-domain analysis is especially preferred for shallow water moorings, mooring lines with composite materials and/or other nonlinear situations, while the frequency-domain analysis is chosen for its efficiency. 4.3 uncoupled and coupled analyses in uncoupled analysis, the response of the floater and the mooring system are analyzed separately by two independent steps. the first step is to obtain the motion response of the floater based on the three-dimensional potential theory, where the effects of the mooring system are simulated as nonlinear displacement-dependent forces. subsequently, the motion response of the floater is regarded as the excitation at the top end of the mooring lines and the dynamic response of the mooring lines is gained [40]. in this approach, the damping forces from the mooring system are either neglected or simplified as linear forces acting on the floater. in addition, usually the current loads on the mooring system are also not considered. however, the foundation and the mooring system are coupled with each other in reality. besides, the uncoupled method may produce substantial errors especially in deep water environment where the current loads is pronounced and the damping from the mooring system is remarkable [41]. consequently, in this situation, the coupled analysis is required to determine the interaction between the floater and the mooring system. in the coupled analysis, the rigid model of the floater together with the slender model of the mooring system are solved simultaneously through the nonlinear time-domain analysis. the coupled response is obtained at every time step in order to fully capture all coupling effects such as stiffness, damping and inertia forces [42]. this approach is accurate though it is somehow time-consuming. nowadays, the coupled analysis is routinely used in the offshore wind industry. several software has the capacity of doing coupled dynamic analysis for a fwt in the multi-hour storm. 5. key challenges and development trends of mooring systems 5.1 key challenges of mooring systems this section is dedicated to the technical difficulties in engineering practice and challenges in research and development of the mooring system from its whole life cycle: design, installation, operation and maintenance stages. 50 sustainable marine structures | volume 04 | issue 02 | july 2022 5.1.1 challenges in design stage design for shallow-water moorings the design for the deep-water mooring is relatively straightforward, as it is a proven technology in offshore engineering. but for a fwt in shallow-water environment, if catenary moorings are adopted, the length of chains need to be extremely long and the mooring radius usually reaches ten or twenty times of the water depth, in case that the anchor point is pulled up from the seabed when the maximum offset occurs. even if a clump is connected to the chain to lessen the chain length, the mooring radius is still more than ten times of the water depth. therefore, the amount of mooring chains used in shallow water is enormous, resulting in a high cost and ineffective use of ocean farm space. sometimes, the cost of the mooring system may approach or even exceed the cost of the foundation itself. similarly, the taut mooring is also hard to be applied in shallow-water environment. when subjected to large environment loads like wind and waves, a fwt’s motions may be remarkable. the taut mooring line needs to bear the station-keeping loads through its elastic deformation. due to its large stiffness, the mooring line therefore experiences huge dynamic tension. the peak dynamic tension is more than ten times larger than the tension at the static offset. as the displacement of a floating megawatt turbine is becoming larger and larger, such a dynamic response characteristic of taut mooring inhibits its application to shallow-water power exploitation [43-45]. slack-taut issue of mooring lines due to floater’s motions, particularly sway, surge and heave, the slack-to-taut cyclic process frequently occurs in mooring lines, accompanied with snap tension. the snap tension can be several times or even a dozen times larger than the mean tension [46], causing the rupture of mooring lines to take place. this would quickly make mooring lines fail and would seriously affect the station-keeping of the foundation [47,48]. thus, when the aero-hydro-servo-elastic coupling analysis is conducted for predicting the dynamic response of a fwt, the snap tension in mooring lines needs to be taken into account. nonetheless, how the slack-taut cycles develop in mooring lines is unclear, not alone the detailed influence factors and the controlling mechanism of snap tension in mooring lines. nonlinear problems of mooring line materials the elastic modulus of the wire rope is usually considered as a constant for its linear elasticity. differentially, the polyester fiber rope has viscoelastic property, that is, the fiber rope has both elastic property of solid deformation and viscous property of liquid flow. its stiffness changes with motion period, smoothness and load duration [49]. as a result, it is difficult to directly simulate the dynamic characteristics of the polyester fiber rope. for a composite material mooring system, the recovery stiffness of the whole mooring system is nonlinear because the material properties of distinct mooring materials are completely different. this makes numerical modelling more complicated and numerical simulation more time-consuming. further, for a hybrid mooring, since segmented calculations are often adopted, the issue of discontinuous stiffness emerges. 5.1.2 challenges in installation stage twist in mooring lines the long-term integrity of the mooring system is so critical that the twist introduced in mooring lines should be zero or minimized during the pre-lay of mooring lines and the final hook-up to the floating foundation. if twist exists in the wire rope, it will be easy to induce bird-caging and premature failure. and if twist exists in the chain, it will significantly reduce its strength and fatigue performance. therefore, it is essential to take additional protective measures to avoid introducing twist during the installation process, despite increasing installation time and cost. at present, the effective methods to forestall twist include the use of low-torque pull-in lines, the use of a second line to balance the torque and the use of in-line swivels. it is also worth mentioning that nowadays the accurate level of twist acceptance in the mooring system remains unclear. under different levels of twist, neither could the long-term performance of chains or wire ropes be predicted precisely. currently, only rough guidelines are available to use, but there is no baseline. hence, it is an urgency to develop systematic data for the torque-twist behavior of chains and wire ropes, in order to predict the reduced strength and fatigue life. damage to mooring lines during installation, damage to wire ropes may occur. special care should be taken during the operation of extracting wire ropes from the installation reel. during this process, the wire rope would easily get crushed or tangled. a proper operation to prevent knotting is to pull the wire rope straight down from a reel or mount it on a revolving stage. if damage occurs, the remedial measure should be taken, for example, to provide additional corrosion pro51 sustainable marine structures | volume 04 | issue 02 | july 2022 tection in the damaged sheath area. but if damage occurs in deep-water operations, the cost of damage assessments and remedial measures would be much higher [50]. 5.1.3 challenges in operation and maintenance stage development of mooring line tension monitoring system for station-keeping and sea-keeping of a fwt, it would be helpful if the time-varying mooring line tension can be timely and accurately recorded. from the monitoring system, precious on-site measurement data, cognition of marine environment and adaptability of floating foundation can be all acquired to improve the technology of integrity management. the traditional technique for mooring line tension monitoring system is to infer the mooring line tension by measuring the mooring line angle. such a technique is of great uncertainty in the calculation process [51]. moreover, most of existing mooring line tension monitoring systems stop functioning after two years of operation due to the harsh environment [52]. for an advanced monitoring system, the automatic design of linkage for adjusting operation needs to be involved. presently, it is still a great challenge to develop a tension monitoring system with accurate measurement, long service life and advanced automation [53]. increasing complexity of mooring operations as the amount of subsea infrastructure quickly grows, many new operations are carried out next to existent infrastructure. consequently, the operators have to work close to the existing subsea facilities and pipelines. for catenary moorings and taut moorings, it is relatively easier to carry out the operation and maintenance operations for a fwt, because the foundation can be easily disconnected with the mooring system and towed back to the port for maintenance. but for tether moorings, special attention needs to be paid to when removing the tendons from the foundation. any improper operation may give rise to the capsizing of the floater especially for a fwt whose center of gravity is taller than that of an oil platform. 5.2 developing trends of mooring systems hybrid mooring system concept the traditional mooring system has its own applicable scope and limitations. aforementioned, the catenary mooring has a too large mooring radius and too long mooring chains, while the taut mooring has excessive dynamic tension. accordingly, the hybrid mooring system concept was brought up to solve these problems. one kind of hybrid mooring concepts is the usage of clumps and buoys. clumps increase the restoring force of mooring lines, and therefore restrict the floater’s offset under extreme conditions. the application of buoys helps to increase the vertical distance between mooring lines and other subsea equipment. also, buoys can offset the weight of mooring chains partly supported by the floater. a new hybrid mooring system was proposed for a semi-submersible foundation by yuan et al. [54] buoys and clumps were respectively connected to the top and bottom of a traditional taut mooring line. it was reported that the tension of the mooring lines was greatly reduced. xu et al. [55] analyzed and compared three different hybrid mooring systems and carried out a series of wave model tests to investigate their mooring performance. through this research, a new hybrid mooring system was recommended to significantly reduce the dynamic tension. the other kind of hybrid mooring concept consists of several segments, each of a different mooring material [56]. the mooring line comprises a bottom chain, a high modulus polyethylene rope, a polyester rope and a top chain from the bottom to top. such a hybrid mooring system is able to offer an appropriate stiffness and to resist the abrasion between the mooring line and the seabed simultaneously. shallow-water mooring presently, almost all fwt projects commissioned are located in moderate and shallow waters, since the cost and technical challenges incurred from environmental conditions (i.e. wind and waves) rapidly grow with increasing offshore distance and water depth. the more mature bottom-fixed wind turbines can be a good usher for fwts. but as mentioned in section 5.1.1, traditional mooring systems are not suitable for shallow water. so far there is no mooring system with good mooring performance and competitive cost for the deployment of fwts in shallow water. the recent sanxia yinling fwt project has encountered the mooring embarrassment in 29.2 m water depth [13]. more and more studies have been carried out to deal with shallow-water mooring. benassai et al. [57] analyzed the motion performance of the tri-floater wind turbine at a water depth of 50 m ~ 200 m, considering both catenary moorings and taut moorings. a series of parametric studies were carried out to identify the better mooring configuration. campanile et al. [58] studied the effects of mooring line number, foundation admissible offset and space between adjacent turbines in water depths of 50 m ~ 80 m and 200 m ~ 300 m. besides, the cost of installation file:///e:/%e6%94%b6%e7%a8%bf%e5%8c%ba/%e8%8b%b1%e6%96%87/javascript:; file:///e:/%e6%94%b6%e7%a8%bf%e5%8c%ba/%e8%8b%b1%e6%96%87/javascript:; 52 sustainable marine structures | volume 04 | issue 02 | july 2022 and maintenance was preliminarily analyzed. xu et al. [43] put forward seven mooring concepts for a fwt in the water depth of 50 m and compared the concepts in terms of reliability and cost. in their study, six mooring design concepts were recommended for future research. new mooring material the high performance of the synthetic fiber rope is beneficial to its application in the mooring system. different synthetic materials lead to the diversity of synthetic fiber ropes. in addition to a large number of applications of polyethylene terephthalate (pet), nylon, high modulus polyethylene, new synthetic fiber materials with higher performance are being developed, such as polyethylene naphthalate (pen) and liquid crystal aromatic polyester (lcap) etc. by comparison, pen has a better mechanical performance and it is about twice as stiff as the conventional grade of pet. furthermore, its performance of ultraviolet resistance and availability to maintain strength in a wet environment are better. however, the manufacturing capacity of pen is limited and the cost is rather high. lcap is one of polyester materials. it is much stronger and stiffer than traditional synthetic fiber materials. it can avoid axial compression fatigue, creep and abrasion problems. at present, the supply of lcap is very limited. consequently, the cost is more expensive than any other synthetic material [59,60]. 6. conclusions this paper summarizes the current status of the mooring system and the mooring equipment of fwts, and points out the features of mooring analysis methods and the technical challenges. the developing trends of the mooring system are also given. the conclusions are drawn as follows: 1) common mooring systems applied to fwts include catenary moorings, taut moorings and tether moorings. the design and analysis show that the catenary mooring is suitable for medium water depth, while the taut mooring and the tether mooring could be applicable to deep waters. a mooring system particularly suitable for shallow water has not been developed yet, whereas the fwt era is embracing seas of moderate depth, as reflected in table 1. at present, most of the existing fwt projects adopt catenary moorings and a few projects adopt semi-taut moorings. tether moorings are still in the stage of model tests. some hybrid concepts can reduce the motion of a fwt under extreme environmental conditions and offer competitive cost as well, but they still need further research. 2) the mooring system still has some technical difficulties and challenges in its whole life cycle of design, installation, operation and maintenance stages: in the design stage, outstanding issues include the design for shallow-water moorings, the influence mechanism of slack-taut process on the tension response of the mooring system, and the nonlinearity of mooring line materials. in the installation stage, special attention should be paid to avoid the twist in mooring lines and the damage to mooring lines. in the operation and maintenance stage, it is urgent to develop an advanced mooring line tension monitoring technology. 3) the moving trends in mooring research include transformation from traditional mooring schemes to hybrid moorings, from deep water to moderate and shallow waters, and from traditional mooring materials to high-performance composite mooring materials. acknowledgement the financial supports received from china national science foundation program (52071186), shenzhen science and technology program (grant no. kqtd20200820113004005), the key promotion program of high quality marine economy development by guangdong province of china (gdnrc [2022] 33) and the major program of stable sponsorship for higher institutions (shenzhen science & technology commission, wdzc20200819174646001) are greatly acknowledged. conflict of interest there is no conflict of interest. references [1] manwell, j.f., mccowan, j.g., rogers, a.l., 2006. wind energy explained: theory, design and application. wind engineering. 30(2), 169-170. 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[60] davies, p., weller, s.d., johanning, l., et al., 2014. a review of synthetic fiber moorings for marine energy applications. 5th international conference on ocean energy (icoe 2014), 4th-6th november 2014, halifax. 1 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 doi: https://doi.org/10.36956/sms.v2i1.238 sustainable marine structures http://ojs.nassg.org/index.php/sms article oceans and covid-19: perspectives, reflections, recovery and regulatory frameworks saleem mustafa1* john hill2 rossita shapawi1 sitti raehanah m. shaleh1 abentin estim1 zarinah waheed1 madihah jafar sidik1 chen cheng ann1 lim leong seng1 1. borneo marine research institute, universiti malaysia sabah, 88400 kota kinabalu, sabah, malaysia 2. la trobe university, melbourne, victoria, 3086, australia article info abstract article history received: 20 november 2020 accepted: 2 december 2020 published online: 30 december 2020 covid-19 pandemic has created an unprecedented public health crisis, taken about 1.4 million lives so far, infected almost 70 million people around the world, battered the global economy and paralyzed the normal activity. this situation is evolving so rapidly that the data on numbers of infections and deaths are changing daily and the economic impacts are difficult to evaluate at this stage and probably will not be exactly known in the near future. it is important to determine the genesis of the outbreak to understand the root causes of covid-19 and to prevent such pandemics from occurring in the future. it is believed that the virus originated in a seafood market in wuhan (china) that was also trading in wildlife for human consumption. such practices are associated with the habitat degradation and biodiversity loss, leading to an imbalance of the natural ecosystems. the zoonotic spillover of this infectious outbreak is a reflection of the impairment of natural systems. scientific and anecdotal evidences demonstrate the significance of marine critical habitats in combating and containing human diseases. there are many other ways in which the oceans can help in human health. in addition to providing an analysis of the covid-19 outbreak, this paper also suggests knowledge-based and informed measures that need to be applied to prevent a repeat of such catastrophic events while highlighting the role of oceans in this context. plans and strategies for recovering the global economy and ensuring its resilience will require incorporating nature-based solutions and ecosystem restoration. the sustainability of the ocean is a key consideration in the development of a framework for post-covid-19 recovery and this aspect is the major focus of this paper. keywords: ocean solutions pandemic natural capital coastal architecture 1. introduction the novel coronavirus outbreak that originated in wuhan, china, in december 2019 has become a global pandemic (covid-19). it has created an unprecedented public health crisis, taken 1.4 million lives so far, infected 70 million people around the world, battered the economy, plunged the world into recession and paralyzed normal living activities. less highlighted is the challenge that this *corresponding author: saleem mustafa, borneo marine research institute, universiti malaysia sabah, 88400 kota kinabalu, sabah, malaysia; email: saleem@ums.edu.my 2 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 pandemic has posed to the oceans and the global goals of development (sustainable development goals, sdgs). even before the broader transformations required to achieving the objectives and targets of sdgs (2016-2030) were recognized, covid-19 took the world by storm, shutting down economies, confining people to homes and disrupting daily life. there are short-term, medium-term and long-term consequences of this pandemic. governments released bailout payments and stimulus packages and mobilized resources for public health security. the enforced lockdowns and the consequential restrictions are gradually being relaxed but “post-lockdown” is not synonymous with “post-covid-19” as long as the coronavirus is prevailing. this virus transmits easily from person to person, infects healthcare staff despite their special protective gear and remains active on hard surfaces and in aerosols, which are signs of its adaptability and potential of becoming endemic in human populations. until large populations survive the infection and have antibodies, and effective vaccines immunize the population against the infection, the covid-19 threat will persist. thus, a return to normal lifestyles in all their facets that prevailed before the viral outbreak is not an imminent prospect. without the prescribed precautions, further outbreaks are inevitable. social distancing and other protective measures have reduced infections to lower levels and flattened the curve in several countries but the virus is around and billions of people remain vulnerable. the fact that malaysia and some other countries have not seen high rates of infection at the levels of the usa, france, italy, uk, latin america and asia means that most people still remain vulnerable without having antibodies to fight the disease. we do not know how effective the vaccine will be and how long the immunity will last. this pandemic will make it more difficult to achieve the targets of sdgs, but an in-depth analysis of the goal requirements motivates prioritization of investments in selective actions within each goal. while sdg3 (good health and wellbeing) specifically deals with this matter, others concerned with poverty reduction, fighting hunger and malnutrition and sanitation have a bearing on human health. in this context, the role of oceans should be recognized and appreciated and efforts directed towards boosting the resilience of marine ecosystem for the benefit of human health and general wellbeing. covid-19 crisis is a timely reminder to reflect on the ocean as a fundamental life-support system that can benefit humanity when faced with major challenges. oceans cover 70% of the earth’s surface and contain 97.5% of the total amount of water on the planet. goods and services supporting the formal and informal sectors of marine economy (“blue economy”) are collectively valued at $2.5 trillion a year, constituting the 7th largest economy in the world (in terms of gross domestic product) that is supported by ocean assets worth $24 trillion [1]. the first-sale value of fish amounts to us$401 billion [2]. if the assessment of the world economic forum is given credence, more than 3 billion people depend on the oceans for their livelihoods. fish provides 3.3 billion people with 20% of the animal protein [2]. the per capita fish consumption averages 20.5 kg. fishing activity, which is one sub-sector of the ocean economy, declined by about 6.5% as a result of restrictions enforced by governments to break the cycle of infection [3]. post-covid-19 course of action will have to tackle these complex issues that are inter-related and call for a holistic response to place the world on a recovery roadmap. this paper considers the genesis of the pandemic and places the role of oceans in an appropriate perspective, and also suggests knowledge-based measures for sustainable solutions. the impact of covid-19 extends far beyond the number of people infected and killed by the virus. it has produced ramifications across the world and these are redefining the economic, political and social landscapes [4]. tackling these consequences calls for a rational policy sequencing [5] based on comprehensive analysis of sectoral variations in the covid-19related areas, so as to facilitate the sector-specific responses [6] through policy reviews and structural transformations. in this context, it is appropriate to link these issues with the role of oceans in mitigation strategies. this global common is neither immune to the covid-19 crisis nor short of solutions to mitigate its impacts and, therefore, deserves due recognition in efforts towards harmonizing human systems and natural ecosystems. this unprecedented situation calls for in-depth analysis of interrelated issues and implications of mitigation measures. 2. genesis of novel coronavirus outbreak linked to the seafood market covid-19 is a subject of intense discussion in the media of mass communication and social media. while this exposure has played a significant role in public awareness, some misconceptions still remain in the public mind. not all viral coronavirus postings can be accepted as facts. there is a dire need to filter these messages and select those facts that are backed by science. it is true that the doi: https://doi.org/10.36956/sms.v2i1.238 3 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 pathogen was first detected in late 2019. this triggered a series of responses, the timelines of which have been reported by the relevant institutions [7]. although the exact origin of the coronavirus is still being debated, the overwhelming evidence is that the first human infection occurred in the huanan seafood market in wuhan [8]. it should be emphasised that the infection did not occur as a consequence of seafood consumption but from wild animals. this seafood market covers a vast area where livestock are kept alongside dead animals and live wild animals are openly traded for human consumption. the available evidence suggests that this novel coronavirus originated from bats and passed through an intermediate animal, probably a snake, a pangolin or a dog (still unconfirmed), before infecting a human host. based on genomic analysis, two scenarios have been proposed [9]. firstly, the virus evolved into its current pathogenic state in an intermediate animal and thus already had features that made it pathogenic to humans and spread rapidly in the population. secondly, the non-pathogenic form of the virus directly entered the human beings and acquired the pathogenic state. in the absence of any substantial structural changes in the virus reported since its outbreak, it is evident that it is already well adapted to the human body system. it should be understood that these viruses are nucleoprotein bodies (in some cases with an additional lipid envelop) in search of cellular machinery of host cells to reproduce. they are capable of reprogramming and using host cell resources to make copies of themselves. if the virus has indeed originated from bats, it is possible that the consumption of this flying mammal or an intermediate host led to its exploring a new (human) host through a process called as the “zoonotic spill-over”. if the primary and intermediate hosts are under stress due to excessive exploitation and habitat degradation then their internal environment may not be ideally conducive to the viral pathogen which would opportunistically explore other hosts, including humans. hence, when species are removed from their natural populations in large numbers, the ecosystem is disturbed, the relationship between the pathogens and their natural hosts is disrupted, and the pathogens tend to seek new hosts among other animals, and this spillover ends in humans. likewise, if wildlife taken out from their natural habitats is held in close contact with other species, then the species not naturally known to harbour the coronaviruses could become potential hosts. obviously, the wild animals maintained in captivity in small enclosures are under stress and become vulnerable to the viruses. the virus can also be transmitted to farmed animals if they are in close proximity to infected wildlife in markets and thus become an easy route to human consumers even though they do not consume such wildlife. this pandemic has also exposed the inhumane treatment of animals as well as continued exploitation of wildlife despite international agreements for the conservation of all levels of biodiversity. probably, the seriousness of the message contained in these and other highly scholarly scientific findings could not reach the stage of translation of the recommendations under the convention of biological diversity (cbd) and sdgs. ironically, the covid-19 pandemic is a significant alarm signal for non-compliance of the international biodiversity policy. the convention on the “biological diversity strategic plan 20112020”, which laid down the “20 aichi biodiversity targets”, is nearing its term. there have been obvious weaknesses and grey areas in governance, as a result of which, habitat destruction and depletion of certain species targeted for human consumption have remained the major drivers of the global biodiversity crisis and degradation of natural ecosystem functions. one such function is the control of infectious diseases. scientists have developed conceptual constructs of ecosystem thresholds and have examined trends that demonstrate the link between biodiversity loss and the emergence and transmission of infectious diseases [10,11]. covid-19 prevalence is a reflection of disruption of the complex interactions in the web of life comprising pathogens, vectors and hosts. it should be emphasized that biodiversity of habitats, species and their genes provides stability to the ecosystem, which is essential for both ecological and human health. the depletion or deletion of one species changes the way other species mutually interact. a broader issue surrounding the covid-19 crisis is that “justice for the environment” means improving and maintaining a healthy environment for the benefit of society and all other life forms. when boundaries of resilience of the earth’s natural systems are breached and ecosystems are pushed to tipping points, nature cannot continue to sustainably provide the essential services on which humanity depends for its welfare [12]. the fact that 50% the world’s gross domestic product is dependent on natural resources deserves emphasis [13]. humans have not accorded justice to the environment and the consequences are now becoming evident. progress in a post-covid-19 recovery will involve transitioning from linear economies to circular economies, starting with development of sustainable seadoi: https://doi.org/10.36956/sms.v2i1.238 4 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 food systems but not limited to this sector. 3. covid-19 and the oceans a survey of covid-19-related publications reveals that inadequate attention has been given to the ocean perspectives despite their relevance. apart from the role of oceans in seafood supply and mitigating the impact of climate change and diseases linked to this phenomenon, the oceans have a direct role in combating human pathogens. a ground-breaking work [14] provided evidences that show that seagrass meadows (figure 1) remove pathogens of humans, fishes and invertebrates from seawater. role of these flowering marine plants is supplemented by the coastal vegetation represented by mangroves (figure 2). many researchers have highlighted how the destruction of biodiversity and natural capital has perpetuated many new pathogens. in adopting a broader perspective, it has been comprehensively elaborated that the changes in ecosystems influence the behavior of human pathogens and the degree of disease prevalence in the society [15]. covid-19 crisis should promote research into the fundamental causes that give rise to deadly viruses and focus on conservation strategies of “natural capital” and the “global commons” which have been plundered and degraded for generations. undoubtedly, the biggest global common is the ocean. the pandemic is a reminder that eliminating something (coronavirus) that looks lifeless, unable to grow and reproduce on its own, can be so daunting. the simple chemical complexes of the virus that use host cells to assume the proportions of a global pandemic and emerge to become a formidable threat to humanity should strengthen our resolve for preventive actions. figure 1. seagrasses combat human pathogens figure 2. mangroves build resilience in seagrass meadows oceans provide us high-quality seafood rich in protein and other nutrients that nourish our body, improve health and strengthen the capacity to fight diseases while reducing inflammation. according to the latest estimates as much as 84.5 million tons of fish was harvested from the ocean in 2018 [16]. the fish supplies have a major share in the first sale value amounting to us$ 401 billion [2]. the seafood is also free of the infections such as middle-east respiratory syndrome (mers), swine flu (h1n1), severe acute respiratory syndrome (sars) and bird flu (h5n1) or the human version of the “mad cow” known by the name creutzfeldt-jakob disease (vcjd). there is no evidence linking covid-19 to seafood, and this virus does not infect marine animals [17]. further, many marine organisms are sources of bioactive compounds that are suitable for development of functional foods that improve health beyond the basic nutrition and reduce the risk of disease. there is a large number of marine bio active ingredients that meet the criteria of functional foods, including polyunsaturated fatty acids (eicosapentaenoic and docosahexaenoic), minerals, trace elements and vitamins, and anticancer substances. selenium present in measurable amounts in shrimps, lobsters, crabs and oysters is a proven antioxidant and has immunity-boosting properties that support the immune function and provide resistance against viral infections [1820]. also, there are potent compounds possessing antibiotic properties that can act against a range of bacteria [21]. further, there are several polysaccharides derived from marine microalgae and seaweeds that have been shown to possess antimicrobial, antiproliferative, anti-inflammatory and immunomodulatory properties [22]. the screening of natural products derived from marine life has yielded a large number of compounds that are potential antiviral drugs [23,24], and many have demonstrated effectiveness against bacteria [25,26], fungal infections [27] and parasites [28]. in fact, there doi: https://doi.org/10.36956/sms.v2i1.238 5 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 are many pharmacological products already available in the market including the alternative antiviral medicines [23]. post-covid-19 research should motivate more interest in marine bioprospecting, marine cultures, antimicrobial trials and marine drug development. the scope of exploring oceans for possible drug discoveries is significant because of the complex environmental conditions that marine organisms have to deal with to survive and thrive. they develop strategies and mechanisms that involve producing chemical metabolites for interand intraspecific signalling, deterrence against predators, inhibiting the adverse activities of surrounding life forms and producing safeguards from pathogenic microbial forms [29]. chemical compounds produced metabolically (secondary metabolites) are known to possess bioactivity and medicinal properties [30]. viruses pose a special challenge due to a limited number of targets in their structure, rapid rate of evolution of their genes and emergence of drug-resistance pathways and mutations that result in new strains [31]. furthermore, viruses are difficult to culture and most laboratories are not equipped to undertake this sophisticated and risky trial that can be undertaken in living cells. for a virus such as covid-19, the risk is manifold because the full extent of the dangers and the exact nature of immune system needed to defend it are unknown. in discussing the scope of marine bioprospecting for products of pharmacological significance, the need for international cooperation in this area of research through a policy review for accessibility to marine biodiversity hotspots and benefit-sharing has been recently highlighted [32]. the rapidity with which the coronavirus has spread and its pathogenicity are responsible for the present increasing infection rates and death tolls. vaccines take time to develop and be tested and to become commercially available. hence, populations at large remain vulnerable and depend on preventive measures such as isolation and social distancing to remain healthy. the risk of infection will continue until the majority of people (70-90%) become immune either after safe recovery with antibodies or immunity through vaccination. this breaks the chain of transmission, and slows down the pandemic because there are not enough infected carriers to transmit the pathogen to others. the search for complex bioactive compounds in marine organisms must, therefore, continue. because of their complexity, there is a possibility of discovering some novel compounds that can combat the unknown pathogens and to a certain extent protect populations until such time that effective and clinically validated solutions evolve. meanwhile, scientists and media of mass communication can also dispel the traditional belief in the healing and curative properties of products of wildlife origin such as shark fins, dugong body parts and sea turtle eggs, for which there are no scientific evidences to support specific medicinal benefits from their consumption. in the case of covid-19, the wise course of action, therefore, is for individuals to stay healthy by protecting the immune system, observing social distancing, using face masks and practicing prescribed hygienic procedures such as hand sanitizing. generally, good nutrition and a healthy immune system offer protection from many health problems but are no guarantee against covid-19. prevention guidelines should continue until effective vaccines are available to the population. countries that have not seen a high rate of infection means that most of the population remains vulnerable without antibodies protection. there is a need to continue practicing the measures for protection from covid-19. there are many uncertified products available in the market portrayed as a means of preventing and curing covid-19. these are not effective against covid-19 and their use may even be harmful to the body immune system [33-35]. by contrast, marine bioactive compounds developed by intensive research, analysis and trials could to be somewhat effective if guidelines for their use are followed. their potency and effectiveness can be put on trial as a fast track approach to combating infections as new vaccines emerge. the potential of corals in treating human diseases is currently under investigation. the target of these studies is the chemical defence system of these reef-building animals which are sessile and which chemically shield them from many predators in the sea (figure 3). figure 3. many marine species in coral reefs are sources of bioactive compounds that can combat pathogens oceans also have a highly significant role in mitigating climate change that is known to increase infectious disdoi: https://doi.org/10.36956/sms.v2i1.238 6 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 ease occurrence and transmission [36]. interesting observations have been canvassed in the media on how the lockdown of cities and drastic curtailment of commercial activities have provided “healing” to the ocean. there is accumulating evidence which shows that halting of industrial fishing operations by deep sea fishing fleets due to lockdown and market closures and quarantine procedures that required social distancing, have eased pressure on fisheries stocks. interruption of commercial shipping operations and other industrial activities have also provided some reprieve to the marine ecosystem. considering that 80% of worldwide trade (in total volume) is handled by the maritime industry [37], the effects of human activity reduction are likely to be significant [38]. however, sightings of rare or semi-rare forms of marine life are anecdotal at this stage but are sufficiently significant to reflect the extent of ecological footprint of anthropogenic activities that encroached on the marine wildlife habitats. it is premature to present scientific data underlying ecosystem conditions as related to covid-19 lockdowns, but early signs suggest marked improvements can be expected. however, there are also negative impacts on the oceans due to covid-19, such as the widespread disposal of used personal protective equipment (ppe), particularly masks, gloves, visors and gowns, which has become an additional threat to the oceans that are already reeling under the enormous weight of global plastic waste [39]. marine enforcements, especially in marine protected areas (mpas), are also constrained during lockdowns and this could have allowed “illegal, unreported and unregulated (iuu)” activities to occur. the extent of these is difficult to ascertain due to the suspension of monitoring. closure of mpas has led to a drastic decline or complete disruption of nature tourism, leading to decline in income which is an important source of revenue for conservation agencies and livelihoods of local communities. suspension of on-going research needed for the restoration of marine biodiversity means delay in data collection required for informed management decisions. there is a delay or postponement of key un meetings such as the “biodiversity conference 15th ‘conference of the parties’ (cop15) and the ‘convention on biological diversity’ (cbd)”, scheduled for 2020 as a landmark year for conservation. this means less time is available for reviewing the achievements of the “strategic plan for biodiversity” (2011-2020) and for chartering the future courses of action on issues as critical as resource mobilization and capacity-building among others. commercial maritime activities will be restored as this pandemic is brought under control. these can be shaped according to the criteria outlined in a recent publication for developing the “blue economy” [40]. weather the precovid-19 “business-as-usual” scenario will prevail or new policies will be formulated for making a radical departure for real transformation towards sustainability, remains speculative. the urban paradigm that has long prevailed until the covid-19 outbreak has led to concentration of industrial activities and human settlements along the coast lines. currently, 40% of the world’s population of 7.8 billion lives within 100 km of coasts. many environmental impact studies, especially through modeling, have justified coastal zone urbanization by presenting “ecofriendly” mitigation measures and attractive infrastructure designs. ironically, these metropolises have suffered the most from the coronavirus infection [41] and also are facing the onslaught of climate change impacts. urban planners should, therefore, consider the risks involved in developing high-density clusters along coastlines. the practical viability of virtual online activities including business meetings and trade and product promotions can be effectively conducted remotely, without clustering people into limited spaces dictated by the dysfunctional systems of planning. this reduces traffic jams, accident risks and greenhouse emissions, and spares open spaces from turning into pandemic hotspots. given the experience with conservation interventions, it might help to some extent to continue the momentum for pushing the ocean ecosystem agenda for policy support. the central argument is that the sdgs cannot be achieved without a healthy ocean [42] and the world is risking human health and wellbeing by placing ocean health at risk. this explains the significance of sdg14: life below water (conserve and sustainably use the oceans, seas and marine resources for sustainable development). to help protect the ocean, 193 member states of the united nations agreed to conserve 10% of their coastal and marine environment by 2020 (this year) following the requirements of cbd through mpas as an effective spatial, ecosystem-based management tool [43]. the world is trailing far behind despite this being the aichi target 11 of cbd as well as target 5 of sdg14. this is a significant target to achieve since current research shows that at least 30% of the oceans must be protected to meet the goals of global conservation [44] and the multiple resources they provide to society. the post-2020 global biodiversity agenda before “cbd cop15” will have to be based on the achievements and extent of delivery of the cbd “strategic plan for biodiversity 2011 2020” and adopting the post-2020 global biodiversity framework. the latter should be structured to ensure protection of 30% of the world’s oceans by 2030 doi: https://doi.org/10.36956/sms.v2i1.238 7 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 via effectively regulated networks of mpas in which destructive or resource-depleting extractive activities are not allowed. efforts should be made to link the post-2020 global biodiversity framework with the sdgs and identifying indicators for assessment. this will contribute to our efforts towards science-informed policy responses consistent with the united nations proclamation of decade of ocean science for sustainable development (2021 2030). also, specific policies should evolve under the purview of “blue economy” and “blue growth” to fast-track solutions to pending and emerging problems. this is a matter of utmost urgency as lockdowns worldwide ease and economies recover. fortunately, there is an unprecedented clamour among scientists, environmentalists and rational thinkers to leverage their knowledge for supporting “bluegreen growth” as a “new normal” in a post-covid-19 world. the global environment is at a crossroads and farsighted decisions are urgently needed to build resilience in natural systems, to protect oceans, to make a rapid transition into sustainable pathways for a long-term human welfare and to combat infections and enhance human quality of life. the recovery roadmaps suggested earlier [40,45,46], can be considered in terms of building a strong and sustainable ocean economy post covid-19. future developments have to be balanced, covering land-based “green economy” as well as ocean-based “blue economy”. lopsided considerations that in the past ignored the potential of oceans have to be corrected by a comprehensive cost-benefit analysis. an example is that of food supply. land-based food crops use scarce land and the dwindling resources of freshwater, and need fertilizers and pesticides to maximise output, whereas seaweed farming (figure 4) for food does not need any of these commodities. covid-19 recovery plans should envisage sector-wise transformations in ocean-based activities. the unsustainable fisheries practices should progress towards “ecosystem approach to fisheries management” (eafm). aquaculture systems put pressure on marine resources by commercial-scale production of fish meal and fish oil and because their effluents create environmental and human health issues. these should follow aquaponics, “integrated multi-trophic aquaculture” (imta) and other ecological farming methods. likewise, rebuilding of fishery stocks can be achieved by responsible stock enhancement and sea ranching. conservation of marine biodiversity by expanding and enforcing mpas can increase fishery harvests. these and other areas requiring “blue growth” and “blue economy” are summarized in figure 5. for these sectors, the appropriate application of digital technologies associated with “industrial revolution 4.0” (ir 4.0) will be helpful in boosting knowledge-based “blue growth” and expanding the “blue economy”. these technologies supplement the successful application of existing practices or replacement of those constraining “blue growth”. an example is “big data” technology that can assist conservation of natural capital, especially oceans, where there is an enormity of data to process for timely decision-making and for preventing and containing pandemics. figure 4. seaweed farming is among the low-carbon sectors of blue economy. farmers in balambangan region of borneo traditionally harvest seaweeds from marine farms figure 5. areas requiring attention for developing a sustainable blue economy 4. new normal and the new world order the “seismic” impact of covid-19 in terms of the human infection and death tolls has caused economic doi: https://doi.org/10.36956/sms.v2i1.238 8 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 disruptions and social upheavals which have projected a “new world order”. overall a 3% contraction of the world economy in 2020 was projected by the international monetary fund (imf). the need for a collective response to this pandemic is paramount. international cooperation is needed to contain it and a global endeavour is necessary to pre-empt its recurrence in the future. viruses do not respect borders and in such mitigation efforts, a global consensus must be achieved according to ethical guidelines without the constraints of sovereign rights. the “new world order” should have agreements to examine national policies with international ramifications and should have objective tools to seek accountability beyond the purview of vetoes in matters concerning global human health. also, there should be structured systems of responsibilities and accountabilities to be applied worldwide. further, the world requires a global consensus on an action blueprint and a systems approach. while institutions and instruments have been developed by the united nations, the covid-19 outbreak exposes their weaknesses in terms of practicality in enforcement. this should trigger “disruptive” approaches that can reject the ineffective prevailing systems. a post-covid-19 world order should be based on the concept of a “collective future” for humanity and guided by the principles of oneness. a roadmap in the form of un sdgs is already available for implementation. under this framework, a robust global disease surveillance program, with a mandate to operate worldwide, can assist in achieving global health security. epidemics arising in any part of the world can pose threats globally. responses to health emergencies cannot succeed if a new world order ignores this issue of fundamental importance. unfettered access should be provided to un institutions to monitor specific areas of concern for compliance as a matter of routine. this will also benefit the global population by eliminating potential origins of infectious diseases, give early warning of outbreaks and mobilize resources wherever and whenever these are needed. through international cooperation, national institutions can obtain essential resources for epidemic control and for preventing its spread beyond epicentres, through a transparent framework of monitoring and action. sdg17 (partnership for the goals) envisages steps for strengthening implementation and revitalization of the global partnership for sustainable development. world needs to develop new mechanisms for achieving these objectives in the hindsight of covid-19. covid-19 pandemic has shaken the world socially and economically unlike any other disaster in recent decades. concerned that covid-19 is a threat multiplier, three emergencies health, social and physical development that might add to the pre-existing inequalities and vulnerabilities have been identified [47]. the extent to which different countries address these will depend on their socio-economic status, political efficiency and governance frameworks. in general terms, the following issues need to be addressed in the aftermath of covid-19 (table 1). table 1. suggestions for a post-covid-19 action plan s.no. suggested actions 1. review targets of sdgs with greater emphasis on epidemiological issues, while devising effective implementation and monitoring methods. 2. prioritise research on knowledge gaps in identifying the critical control points for zoonotic spill-over from wildlife to control its wider transmission. 3. develop national policies for strengthening emerging areas such as marine bioprospecting for pharmaceuticals and protection of ecosystem services; research should move beyond screening to drug development. 4. develop sustainable seafood production systems as a substitute for terrestrial wildlife exploitation to minimize the risk of infectious outbreaks from the potential zoonotic spill-overs. 5. invest more resources in self-reliance and supply chains especially pertaining to seafood to buffer stocks from unanticipated problems inherent in global and local supply chains. 6. digitalise the economic sectors such as seafood supplies. 7. invest in “blue-green” architecture for coastal and marine infrastructure via design innovations. 8. harness the potential of “big data” technology to identify vulnerabilities in society for devising strategies for addressing the weaknesses and sustainable management of the natural capital of oceans. 5. systems thinking for sustainability the role of higher education institutions in the postcovid-19 response and recovery is critically important since the roadmaps for recovery will be knowledge-based and driven by “systems thinking” which is basically a holistic analysis and understanding of the entire complex system that has multiple linkages and interactions. this approach encourages exploration of the inter-relationships, perspectives and boundaries of a problem systematically that cannot be solved by examining one element or an aspect of a complex issue. a systems thinking approach is relevant to topics of sustainability that require seeing the “big picture” in order to identify multiple leverage points that can be addressed to achieve a positive transformation which can be considered adaptive management [48]. an interdisciplinary approach is necessary for a holistic analysis, especially when issues require defining the complexity of connections of the oceans with pandemics. currently, more advanced interdisciplinary research in this area is doi: https://doi.org/10.36956/sms.v2i1.238 9 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 essential at institutions of higher education. many universities have acquired or enhanced basic digital capabilities as a result of covid-19 restrictions and lockdowns in order to continue to undertake their primary roles by using online platforms for lectures, meetings and conferences. these systems will be reviewed when the feedback from the audience will be available to indicate the depth of their engagement through online delivery and how this compares with the conventional face-toface delivery. it is possible that the teaching and learning portfolio will be a mix of “conventional” and “on-line” strategies as the universities are called upon to provide appropriate education and training to address the changing employment market trends. a radical shift towards digitalization and online education will create a new education paradigm in conjunction with openness, transparency and plagiarism control. in addition, the effectiveness of such systems can effect a transformative change in the promotion of sustainability. a detailed account has been presented [49] on the role of institutions of higher education in a rapidly changing educational landscape. digitalization demands expensive infrastructure. at a time when global economies are entering recessions and bordering on depression and unemployment is ballooning, there are serious national budgetary challenges that need prudent fiscal management and new strategic directions backed by a “systems thinking” model. for food producing sectors such as fisheries and aquaculture, there can be no abrupt departure from the time-tested methods of production but some associated activities can undergo digital transformation. these sectors have suffered from lack of adequate attention towards start-ups and disruptive innovations. in a “new normal” environment, r & d investment should ensure that funded projects yield productive sustainable outcomes and meet the requirements of sdgs. nature-inspired designs of development can bring significant changes to education with sustainability perspectives. it stimulates a dynamic new way of imparting education in sustainable development, stem, creative problem-solving and systems thinking [50]. such a holistic study paradigm is inclusive and engaging which can inculcate a quest for self-learning and creative and “out-of-thebox” thinking even beyond the confines of the classroom. there is scope for reforming existing sectors as well as opening new ocean-based industries to absorb both graduates and low-pay workers to empower economic and social recovery, while sustaining natural capital. the higher education sector will have to invest in developing critical masses of experts in “blue-green” growth to focus on sustainable ocean-based economy in response to the postcovid-19 recovery. these institutions have to demonstrate how blue growth and development can proceed while ensuring that the natural marine assets continue to provide resources and services for societal wellbeing. this involves structural innovation to underpin sustained growth and generate new employment and economic opportunities. the obsolete old model of growth that eroded the natural capital and resilience of the global commons, leading to water scarcity, biodiversity loss, resource bottlenecks, environmental degradation and climate change has to be rejected [51]. the new model will unambiguously prove economic dividends from investments in low-carbon, resource efficient, clean production and consumption, resilience and circularity and other attributes of sustainability in the development projects and sustainability programs. thus, the strategic teaching and learning plans of universities will have to change to include inbuilt systems of rationalization and accountability at all levels. this is necessary if the higher education system is to remain viable and be able to maximize its contribution to post-covid-19 recovery. in addition, universities should continue to invest in on-line professional activities such as webinars particularly when these are focused on conservation and sustainability issues. this saves time and budget, and reduces impact on the environment. it can continue while some of the budgetary allocation that is normally utilized for such purposes can be diverted to ocean conservation projects. it is essential that the higher education institutions are involved in national development plans since they can pursue problem-solving research transcending the disciplinary boundaries and participate in community enhancement projects. for maritime countries, community-based projects related to ocean conservation and protection will bolster interest in resilient and sustainable blue economy. the term “disruptive” should not remain confined to research in the areas of ocean sciences and technology, and seafood security but must also find purposeful applications in the entrepreneurial programs of the universities to facilitate the post-covid-19 recovery. it will need a radical shift from the culture of inflating the conglomeration aimed at achieving scores for which there are no immediate social innovation outcomes to the focused human resources that can help the society and economy in the increasingly uncertain future, especially for the graduates. the ocean is classic global commons that represents an interconnected system of this planet’s marine water which comprises most of the hydrosphere. it offers multiple solutions. humanity knows many of them, gives little attention to others and is ignorant of the potential of several doi: https://doi.org/10.36956/sms.v2i1.238 10 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 ocean services due to knowledge limitations. events such as the covid-19 shed light on the knowledge gaps that need to be filled. a topic of vital importance is green architecture for innovative designs for environment-friendly coastal and marine infrastructure. it is not only for new development projects but also for design modifications in the existing coastal infrastructure that faces the vagaries of nature and exposes people living and working in high densities to a greater vulnerability to viral diseases. high density urban areas have been particularly badly affected by covid-19 due to concentration of people living and working there (with no physical or social distancing considerations!), their connectivity to transport to destinations outside their boundaries and healthcare facilities [52]. these areas do not measure up to “smart city” ranking and have become an outdated model of development. especially in coastal areas, the “smart city” concept should include “green metrics” and be classed as “green smart cities” in post-covid-19 recovery. introducing nature-based strategies into coastal infrastructure such as greenways, green alleys, esplanades, precincts and resort islands that can incorporate marine habitat restoration, will bolster resilience and enhance the concept of sustainable living. traditional coastal communities living harmoniously with marine ecosystems have been practicing sustainable living for generations (figures 6-8). the seas and oceans have sustainably provided these communities with the food and raw materials they need. highend infrastructure, such as tourist resorts, will require a robust and comprehensive “green architecture” plan to be created and implemented. figure 6. mangrove-integrated fish farming practised by traditional coastal community in tuaran, sabah, malaysia figure 7. fish catch is higher where mangroves are in a healthy condition figure 8. environment friendly traditional seaweed farming using discarded plastic bottles as floats by the indigenous coastal communities in banggi island ports and harbours should introduce the concept of “living shorelines” in the form of coastal vegetation and wetland areas so as to control erosion and stabilize seafronts, while providing habitats for marine species and wildlife and recreational spaces for human use [53]. oxygen-rich clear air, shade, carbon sequestration, pollution mitigation, and a healthy environment, are inherent components of such infrastructures. human resources development in these fields will enhance employment opportunities, provide income stability, strengthen community welfare and change public perception in favour of sustainable living. further, “green architecture” and “sustainable development” concepts should be introduced into school and higher education curricula, in conjunction with related practical sessions in appropriate environments. perhaps, nature-inspired outdoor teaching of certain course contents will help shape the architecture of educational programs that will go beyond the green architecture of the doi: https://doi.org/10.36956/sms.v2i1.238 11 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 coastal infrastructure to encompass the essence of sustainable development. 6. conclusions covid-19 has plunged the world into an unchartered territory with a great deal of uncertainty as to the structure and stability of the “new world” which will emerge. it has overwhelmed the healthcare system of even the richest and the most industrialized countries by the sheer number of people seeking medical assistance. global economies are in a free fall and supply chains are in disarray. the world is in urgent need of visionary strategies and a strong resolve for transformative actions to protect public health and economies, and to sustainably manage the “global commons”. it is of major concern that such catastrophic event might be repeated without bringing dramatic changes to existing systems based on a holistic understanding of the present situation, coupled with a globalized system of pathogen surveillance. although current sdgs have been tested by the severity of the pandemic, their objectives and targets still offer solutions to the prevailing crisis, in terms of the need to reassess our development priorities, focusing on human health, food security, livelihood and emphasizing the importance of natural capital. the shockwaves and fallout of covid-19 should motivate mitigation opportunities which could improve public health, lead to greater self-reliance, give certainty to supply chains and enhance levels of environmental conservation coupled with supporting a blue economy. institutions of higher education can seize this opportunity to prioritizing research, focussing on these key issues and pursuing natural sustainability innovations. the natural capital provides resilience and a means for buffering pandemic shocks, and it must be preserved by establishing ecological boundaries and identifying tipping points that contribute to preventing major reoccurrences. the shrinking of “safe spaces” threatens biodiversity which is the fabric of stability. while concerns for the preservation of biodiversity are widespread, transition into action is limited since multiple strategies are involved. these include: a) more investment in linking biodiversity to issues that concern the general public in daily life such as food security, health and wellbeing and the economy, and b) globalizing nature conservation monitoring and disease surveillance systems. covid-19 has clearly emphasised the need to reassess national priorities in areas of critical importance such as “blue growth” and “blue economy”. post-covid-19 recovery should be knowledge-based and driven by a “systems thinking” process. institutions of higher education need to respond to covid-19 by undertaking significant restructuring of curricular and research so as to be resilient, relevant and be able to contribute to rebuilding the post-covid-19 world. post-covid-19 recovery is an opportunity for all responsible institutions to facilitate transformative actions towards re-establishing the relationship of humanity with the natural world and particularly with the marine environment. further, with respect to an ocean-focused policy, there should an element of ocean accounting in national statistics of individual countries comprising the value of marine goods and services, the impact of “blue growth” on the economy, the socio-economic condition of local 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[9] sri. covid-19 coronavirus epidemic has a natural origin. scripps research institute, california, usa, 2020. [10] keesing, f., belden, l.k., daszak, p., dobson, a. impacts of biodiversity on the emergence and transmission of infectious diseases. nature, 2010, 468: 647-652. [11] ostfeld, r. s. biodiversity loss and the ecology of infectious disease. the lancet planetary health, 2017, doi: https://doi.org/10.36956/sms.v2i1.238 12 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 1(1). d o i : h t t p s : / / d o i . o r g / 1 0 . 1 0 1 6 / s 2 5 4 2 5 1 9 6 (17)30010-4 [12] munson, s.m., reed, s.c., penuelas, j., mcdowell, n.g. et al. ecosystem thresholds, tipping points, and critical transitions”, new phytologist, 2018, 218(4), doi: doi.org/10.1111/nph.15145 [13] wef. half of world’s gdp moderately or highly dependent on nature. world economic forum, geneva, switzerland, 2020. [14] lamb, j.b., van de water, j.a.j.m., bourne, d.g., altier, c. et al. seagrass ecosystems reduce exposure to bacterial pathogens of humans, fishes, and invertebrates. science, 2017, 355(6326): 731-733. [15] washington, h. human dependence on nature: how to solve the environmental crisis. taylor & francis, london & new york, 2013. [16] fao. state of the world fisheries and aquaculture. food and agriculture organization, rome, italy, 2020. [17] bondad-reantaso, m.g., mackinnon, b., hao, b., huang, j. et al. viewpoint: sars-cov-2 (the cause of covid-19 in humans) is not known to infect aquatic food animals nor contaminate their products. asian fisheries science, 2020, 33: 74-78. [18] broome c.s., mcardle f., kyle j.a.m., andrews f., et al. an increase in selenium intake improves immune function and poliovirus handling in adults with marginal selenium status. american journal of clinical nutrition, 2004, 80: 154-162. [19] gill, h., walker, g. selenium, immune function and resistance to viral infections. nutrition and dietetics, 2008, 65: s41-s47. [20] ivory, k., prieto, e., spinks, c., armah, c.n. et al. selenium supplementation has beneficial and detrimental effects on immunity to influenza vaccine in older adults. clinical nutrition, 2017, 36(2): 407415. [21] tortorella, e., tedesco, p., esposito, f. p., january, g.g. et al. antibiotics from deep-sea microorganisms: current discoveries and perspectives. marine drugs, 2018, 16(10). doi: 10.3390/md16100355 [22] raposo, m.f., d. j., de morais, a.m.b., de morais, r.m.s.c. marine polysaccharides from algae with potential biomedical applications. marine drugs, 2015, 13(5): 2967-3028. [23] jarred, y.b., lu, y. marine compounds and heir antiviral activities. antiviral research, 2010, 86, 231240. [24] raveh, a., delekta p.c., dobry, c.j., peng, w., et al. discovery of potent broad spectrum antivirals derived from marine actinobacteria. 2013, plos one, 8(12): e82318. doi: https://doi.org/10.1371/journal.pone.0082318 [25] pidot, s., ishida, k., cyrulies, m., hertweck, c. discovery of clostrubin, an exceptional polyphenolic polyketide antibiotic from a strictly anaerobic bacterium. angewandte chemie international edition, 2014, 53: 7856-7859. [26] böhringer, n., fisch, k.m., schillo, d., bara, r. et al. antimicrobial potential of bacteria associated with marine sea slugs from north sulawesi, indonesia. frontiers in microbiology, 2017, 8: 1092. doi: 10.3389/fmicb.2017.01092 [27] karpiński, t.m. marine macrolides with antibacterial and/or antifungal activity. marine drugs, 2019, 17(241). [28] imperatore, c. , gimmelli, r. , persico, m. , casertano, m. et al. investigating the antiparasitic potential of the marine sesquiterpene avarone, its reduced form avarol, and the novel semisynthetic thiazinoquinone analogue thiazoavarone. marine drugs, 2020, 18(112). doi: 10.3390/md18020112 [29] lindequist, u. marine-derived pharmaceuticals: challenges and opportunities. biomolecules and therapeutics, 2016, 24(6): 561 571. [30] newman, d.j., cragg, g.m. drugs and drug candidates from marine sources: an assessment of the current “state of play. planta medica, 2016, 82: 775-789. [31] martins, n., imler, j.-l., meignin, c. discovery of novel targets for antivirals: learning from flies”, current opinion on virology, 2016, 20: 64-70. [32] mustafa, s., estim, a., saleh, s.r.m. a call for open access for marine bioprospecting. environmental policy & law, 2019, 49(4-5): 232-236. [33] ema. beware of falsified medicines from unregistered websites. european medicines agency, amsterdam, the netherlands, 2020. [34] fda. beware of fraudulent coronavirus tests, vaccines and treatments. food and drug administration, maryland, usa, 2020. [35] who. coronavirus disease (covid-19) advice for the public. world health organization, geneva, switzerland, 2020b. [36] who. climate change and human health risks and responses”, world health organization, geneva, switzerland, 2020c. [37] unctad. review of maritime transport. united nations conference on trade and development. geneva, switzerland, 2018. [38] bickley, s.j., macintyre, a., torgler, b. sink or swim: the covid-19 impact on environmental doi: https://doi.org/10.36956/sms.v2i1.238 13 sustainable marine structures | volume 02 | issue 01 | january 2020 distributed under creative commons license 4.0 health, fish levels and illicit maritime activity. behavioural and social science, nature research, springer nature, cham, switzerland, 2020. [39] picheta, r. coronavirus is causing a flurry of plastic waste campaigners fear it may be permanent. cable news network, 2020. [40] mustafa, s., estim, a. blue economy and blue growth in the context of development policies and priorities in malaysia. penerbit ums, kota kinabalu, malaysia, 2019. [41] osava, m. prioritizing life or the economy will determine the post-pandemic focus in urban areas. ips, rome, italy, 2020. [42] claudet, j., loiseau, c., sostres, m., zupan, m. underprotected marine protected areas in a global biodiversity hotspot. one earth, 2020, 2(4): 380 384. [43] lubchenco, j., grorud-colvert, k. making waves: the science and politics of ocean protection. science, 2015, 350: 382-383. [44] o’leary, b.c., winther-janson, m., bainbridge, j.m., aitken, j. et al. effective coverage targets for ocean protection. conservation letters, 2016, 9: 398-404. [45] mustafa, s., shapawi, r. ed. aquaculture ecosystems: adaptability & sustainability. wiley-blackwell, west sussex, uk, 2015. [46] teleki, k., mccauley, d., thienemann, g.f. eight ways to rebuild a stronger ocean economy after covid-19. world resources institute, washington, d.c, 2020. [47] mohammed, a. covid-19 pandemic exposes global frailties and inequalities. un news, united nations, new york, 2020. [48] allen, w. learning for sustainability. will allen & associates, richmond, va, usa, 2020. [49] mustafa, s., estim, a., shapawi, r. higher education and sustainable development of marine resources. in: encyclopaedia of the un sustainable development goals: life below water (walter leal filho, pinar gökçin özuyar, anabela marisa azul, luciana londero brandli and tony wall, eds.), springer nature, cham, switzerland, 2020. [50] bi transforming education: a conversation on fostering students’ reconnection with nature. biomimicry institute, missoula, mt, usa, 2020. [51] oecd. towards green growth. organization for economic cooperation and development, paris, france, 2011. [52] datta, a. will covid-19 change how our cities are designed in the future. geospatial worldgeospatial media and communication, noida, india, 2020. [53] beyer, l., anderson, j. collaboration on need-based solutions is key to resilient city infrastructure. world resources institute, washington, dc, 2020. doi: https://doi.org/10.36956/sms.v2i1.238 50 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 doi: http://dx.doi.org/10.36956/sms.v3i2.433 sustainable marine structures http://ojs.nassg.org/index.php/sms/index article status stock and sustainable management measures for moroccan sardines abdelaziz mounir1,2* mohammed znari1,2 hayat elmghazl1,2 hassan alahyane3 noreddine chouikh4 nawal hichami5 1. laboratory of water, biodiversity & climate change, department of biology, faculty of sciences, semlalia, cadi ayyad university, marrakech, 40000, morocco 2. the natural history museum of marrakech, research centre on biodiversity, cadi ayyad university, bd allal el fassi, marrakech, morocco 3. laboratory of molecular and ecophysiology modelling, faculty of sciences semlalia, university cadi ayyad, marrakech, 40000, morocco 4. laboratory of aliments, environnement and health, faculty of sciences and techniques, university cadi ayyad, marrakech, morocco 5. laboratory of biotechnology & sustainable development of natural ressources, polydisciplinary faculty of beni mellal, sultan moulay slimane university, mghila, beni mellal, 23000, morocco article info abstract article history received: 20 august 2021 accepted: 22 september 2021 published online: 15 october 2021 this article summarizes the state of stocks of sardine, sardina pilchardus in moroccan waters at the end of 2016 and 2018. these stocks varies according to the region,they are now in a sustainable exploitation situation: atlantic sardine, but also stocks that have reached or are still in over-exploitation levels: mediterranean sardine. the fi shing pressure exerted on the sardine stock exceeds the optimal level by 40%. due to the degradation of the fragile marine environment of the mediterranean region, generated by pollution of various origins, the overexploitation of juveniles in the coastal strip, non-responsible practices and the use of non-fi shing gear selective, it is imperative to take the necessary measures to protect the marine environment and ensure rational and sustainable exploitation of the resource. (high commission plan 2006 report). keywords: sardina pilchardus exploitation stock variation environment moroccan waters 　 *corresponding author: abdelaziz mounir, laboratory of water, biodiversity & climate change, department of biology, faculty of sciences, semlalia, cadi ayyad university, marrakech, 40000, morocco; the natural history museum of marrakech, research centre on biodiversity, cadi ayyad university, bd allal el fassi, marrakech, morocco; email: mnraziz1980@gmail.com 1. introduction the northwest african upwelling system of morocco, is the most productive in the world, in terms of primary productivity. this productivity results in large fish biomass mainly dominated by small pelagic fi sh, which are the main exploited living resources of the region. in a context of shared management by several countries of the region’s fi shery resources, understanding the factors that control the spatial distribution of small pelagic popula51 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 tions and the evolution of their abundance is crucial for fisheries and the region’s socio-economic development. morocco has two maritime frontages of approximately 3,500 km of coastline, supported by an exclusive economic zone1 (eez) of 200 nautical miles in the atlantic. these advantages, combined with the existence of a upwelling2 zone, considered among the most important in the world, make the moroccan coast one of the most fish-rich zones, with an annual production potential that exceeds 1.5 million tons of fish. a relatively large specific diversity characterizes this reservoir of fishery wealth. the fishing sector represents between 2% and 3% of gross domestic product (gdp) and generates around 170,000 direct jobs and 500,000 other indirect ones while providing sources of income for around 3 million people [1]. in 2015, national fishery production exceeded 1.35 million tons (worth 10.8 billion dirhams), mainly small pelagic (84% in volume and 25% in value). thanks to this production, morocco ranks 17th among producer countries (capture fishing) and first on the african continent [2]. this production is mainly generated by a fishing fleet of coastal and artisanal vessels (56% in volume; 54% in value) and deep-sea vessels (34% in volume; 44% in value). however, despite the importance of national fishery production, moroccans’ consumption of fishery products remains limited to levels below the world average (13.3 kg/inhabitant against 19.3 kg/inhabitant on the scale in 2012). morocco has set itself the strategic objective, within the “halieutis” plan framework, of bringing this average to 16 kg/inhabitant/year around 2020. starting from producers’ objective aiming to maximize their income and facing demand for fishery products that continues to grow, especially in a context of increasingly imposed globalization, the fishery sector has become particularly dependent on the rest of the world and other sectors of the economy. this strong dependence on the rest of the world places the fishing sector in a situation of vulnerability in the face of various hazards in the international economic environment. the availability of fishery resources is one of the factors driving the dynamics of the fishery production system. this resource is dynamic in nature and constantly interacts with the bio-physicochemical system, characterizing its natural environment and the socio-economic and regulatory subsystems in which fishing activities are carried out. if the socio-economic conditions are favorable, the abundance of the exploited resource can potentially lead to fishing efforts. on the other hand, the increase in the latter beyond biologically sustainable limits can ultimately lead to a decrease in the availability of resources, thus affecting the balance between supply, demand and price of fish. the sustainability of fishery resources will only be ensured through management systems that can adapt fishing pressure to the optimal level of stocks. the main control variable for this is fishing effort. the context and fishery issues have changed a lot, going from questions of prospecting and development of new fisheries to issues of biodiversity conservation, conservation in the face of over-exploitation, development, understanding of the effects of climate change or security marine 2. fluctuations in small pelagic the environnemet factors influence the distribution and fisheries abundance. this is the case for small pelagic fish, which are essential elements of marine ecosystems due to their intermediate food web position and large biomass. in upwelling ecosystems, the total biomass of fish is generally dominated by small pelagic, often a species of anchovy and/or a species of sardine or sardinella. we speak of ecosystems structured in “wasp-waist” [3,4], because of the small number of small pelagic species that constitute this intermediate trophic level. in this case, control of the trophic chain would be carried out by the intermediate link, the small pelagic. thus, this intermediate-level will play a central role in the structure and the dynamics of the ecosystem, both by “top-down” type control (control of upper predators on the lower trophic links) on the plankton which it feeds and by bottom-up control on the many marine predators that consume them” [5]. fluctuations in the abundance of pelagic fish stocks reflect significant changes in structure and functioning in upwelling ecosystems. significant mortalities have been observed at higher trophic levels (birds, marine mammals, large predatory fish) in response to the decrease in the abundance of their prey. pelagic resources consist mainly of sardines, mackerel, anchovies, horse mackerel and tuna. these highly displaced and unstable resources experience more or less significant fluctuations in their abundance and distribution. the southern area of the kingdom has known, in recent years, variations in their abundance and their composition by species. studying the effects of environmental change on fish populations, especially sardines, is complicated because environmental factors can affect various processes at different levels of biological organization” [6-9]. fish has complex life cycles, including several different life stages (egg, larva, juvenile and adult), each of which can be affected in different ways by environmental changes. in fish populations, changes induced by changes in the environment doi: http://dx.doi.org/10.36956/sms.v3i2.433 52 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 can result from four mechanisms, often linked together: (i) a physiological response to changes in environmental parameters, such as temperature, (ii) a response behavioral, for example, by avoiding unfavorable conditions and displacement to new more favorable habitats, (iii) population dynamics, resulting from changes in the balance between mortality, growth and reproduction rates, (iv) productivity changes and/or trophic interactions in the ecosystem. in addition, (v) commercial exploitation greatly affects the abundance and distribution of fish and can interact with the effects of environmental change. 3. sardines are an important but unstable resource world production of small pelagic represents around 39 million tons, or more than a third of the catches total, making small pelagic the most fished species group in the world (fao). over the past 60 years, catches have largely evolved according to variations in the resource. small pelagic constitute the largest group of species targeted by the “milling fishery,” whose catches are intended to manufacture fish meal and fish oils, mainly consumed by the aquaculture sector. with the development of intensive aquaculture to meet ever-increasing needs, small pelagic are diverted from their primary vocation to feed the poorest populations directly. in many countries of the world, and particularly in developing countries, small pelagic are an important source of protein and nutrients at affordable prices. these small pelagic fish thus occupy an important weight in the food and the world economy. instability is one of the major characteristics of small pelagic resources. significant changes (by a factor of 1000) in abundance over a few decades are characteristic in small pelagic. long-term alternations of dominant species are observed in most upwelling ecosystems, such as the alternation between sardines and anchovies in the humboldt, benguela and kuroshio currents off japan” [10]. the scientific community widely accepts that this high variability is caused by the synergy of different factors, including main overfishing and environmental conditions. the biological characteristics of small pelagic (short lifespan, high fertility, high natural mortality rate, dependence of plankton for their food) make them very sensitive to environmental forcing” [11,12]. in addition, because they are very mobile and good swimmers, pelagic fish can react quickly to changes in their environment. small pelagic have a so-called “r” reproduction strategy (favoring a high growth rate) and can potentially double their populations within a few months, the age of first reproduction generally being between 6 and 18 months” [13]. finally, their gregarious behavior facilitates their detection, and their catches contribute to their variability in abundance. also, several stocks of small pelagic have suffered historical collapses, such as anchovies in peru in 1972, sardines in south africa between 1965 1966 “ [14] and in namibia between 1970 1971” [15]. the small pelagic resources, consisting of fish species on the surface or between the two water’s layers (sardine, mackerel, horse mackerel, anchovies and sardinella), represent the main fishery potential of the moroccan eez. small pelagic fishing occupies an important place in the fishing sector in morocco due to the size and the dynamism of the fleet which practices it, the quantities sold in the various sectors supplied with the products of this fishing and the number of ‘direct and indirect jobs generated. fishing for small pelagic extends across the entire moroccan, atlantic and mediterranean continental shelf. the national fleet mainly leads it from different ports in the kingdom and a foreign fleet operating under charter or fishing agreements. the fishery for small pelagic has developed along the moroccan mediterranean and atlantic coast with a historic shift in the fishing area to the south at the atlantic coast. indeed, after exploitation of the northern sardine stock (tangier-el jadida) during the 1930s, fishing developed further south and the port of safi became the first sardinian port during the 1970s. then, 80, with the opening of tan-tan, laâyoune and that of tarfaya, the fishery moved further south, making the sidi ifni cap boujdour area (area b) the main area of activity of the moroccan sardine fleet. this development was reflected, notably from the 1990s, by a change in the evolution of landings, with a decrease in sardine catches in the north zone and the safi-sidi ifni zone (zone a) and a continuous increase in sardine catch in zone b. the increase in sardine catches in zone b was accompanied by a change in the destination of production; the by-product industry absorbed the large share of landings, intended before the 1990s mainly for canned. south of cap boujdour (zone c), an area historically exploited by a foreign fleet, the national small pelagic fishery began during the 1980s, with large-scale purse seiners (thona type fishing) and from the 1990s with a coastal sardine fleet. this development of activity in zone c is supported by the opening of the port of dakhla in 2001 and by the arrival of modern vessels which have added to the traditional purse seiners and have supported the development of the freezing sector. in addition, authorizations to charter foreign vessels (freezer pelagic trawlers, purse seiners and pelagic trawlers rsw type) were granted, from 1997 to operators of the dakhla and laayoune ocdoi: http://dx.doi.org/10.36956/sms.v3i2.433 53 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 topus freezing sector, as part of the program assistance in the conversion of excess processing overcapacity in this sector and also in the context of the development of the national small pelagic fishery in this area. artisanal fishing activity has also emerged since 2008; this fishing is practiced by boats that operate from fishing sites in the region on mackerel, generally during the closed periods of octopus fishing. potentials currently offered for small pelagic species are available in the area south of cap bojdour and are variable depending on stocks. certain populations (sardinella, mackerel, horse mackerel) form part of the straddling stocks exploited in the moroccan eez and in the eezs of the other countries of the northwest african region. sardines remain the dominant species in morocco, while the availability of other species varies from one area to another and from year to year. sardine, the dominant pelagic species in upwelling ecosystems the moroccan atlantic ecosystems are characterized by upwelling that promotes nutrient enrichment of the coastal strip, making these ecosystems very productive areas that support the most abundant fisheries in the world. in fact, despite a relatively modest area of less than 3% of the surface of the oceans, these regions concentrate a significant part of the fishing volume, representing 40% of the world catches of marine species” [5,10]. however, these upwelling ecosystems are very dynamic and show high variability at all spatial and temporal scales. small pelagic fish are dominant in biomass in these ecosystems, mainly sardine and anchovy species, whose population dynamics are often linked to the very high physical variability of upwelling. understanding the mechanisms linking environmental fluctuations to the recruitment of these species is one of the major challenges for fisheries in these regions. a striking example is the large-scale fluctuations in sardines and anchovies observed in the main upwelling zones of the world” [16-18]. when one species has high biomass, the other species have relatively low biomass and vice versa. changes in species biomass are generally accompanied by an expansion and/or contraction of their distribution areas” [19,20]. however, there is no general theory yet, shifts in ecosystem shifts [21]. that has occurred in response to climate change have been suggested as the main cause of fluctuations in sardines and anchovies” [22,23]. many studies have suggested that these regime changes are associated with structural changes in the ecosystem (temperature, wind, upwelling but also the size of plankton particles), leading to favorable environmental conditions for a species rather than ‘’ another” [18,19,24]. this is the case for the peruvian anchovy (engraulisringens), characterized in the 1960s by very large landings reaching 13 million tons in 1970, which collapsed during the 1970s and 1980s. since the early 1990s, landings of anchovies from peru have resumed and have hovered around 7 million tonnes, with a drop observed in recent years. in parallel, catches of chilean sardinops (sardinopssagax) have exploded in 15 years (1978-1992), reaching 10 million tons per year. since 1992, landings have almost disappeared” [25]. the causes of large variations in the biomass of small pelagic fish, whether mainly due to natural variability (due to environmental changes and/or interactions between species), exploitation, or both, are still long-discussed [10,20]. 4. canary upwelling the canary islands’ upwelling is located along the northwest coast of africa, from gibraltar (36°n) to southern senegal (10°n) and runs along the coasts of morocco, mauritania, gambia and senegal. it results in a general surface current running along the coast from north to south. in this region, three upwelling zones have been described [26,27]. upwelling has a strong seasonality between 11 ° n and 21 ° n and between 26 ° n and 35 ° n, and remains intense all year round between 20 ° n and 26 ° n. at high latitudes (26 ° n-35 ° n), the intensity of upwelling is low and intensifies in summer and autumn and weakens in winter and spring. at low latitudes (11 ° n-21 ° n), it disappears completely during the summer months. the distribution of water bodies in the region has been summarized by barton et al [28]. from a biogeographic point of view, the area can be divided into two main areas: to the north, the southeastern limit of the north atlantic subtropical gyre (nacw) and to the south, the north of the northeast tropical atlantic gyre (sacw). the area includes part of the eastern edge of the subtropical gyre with the azores current (ac, for azores current) whose southern branch feeds the canary current (cc, for canary current), which flows along the african coasts. arrived at the cap blanc level (21°n), the cc branches off to the east to form the courant nord equatorial (nec, for north equatorial current). south of cap blanc, we find the north equatorial counter current (necc) [29,30]. the two current systems in the region carry the water of very different temperatures. a frontal zone at their meeting point separates them with a strong thermal gradient [31]. this front is located at cap blanc in the hot season and at cap roxo in the cold season. the coastline of the northwest african system is characterized by a succession of capes (cape ghir (31 ° n), doi: http://dx.doi.org/10.36956/sms.v3i2.433 54 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 cape yubi (28 ° n), cape bojador (26 ° n), cap blanc (21 ° n) and cape verde (15 ° n) and bays. the continental shelf is generally wide (50 km) compared to other large upwelling systems, reaching 150 km in the central part, around 25 ° n offshore western sahara [32]. two groups of islands are found off the coast, the canary islands at 27 ° 29 ° n and the cape verde islands at 14 ° 18 ° n. the coasts senegalo-mauritaniennes are appreciably oriented in the meridian direction; the transport of ekman to the broad one is produced there by the trade winds of north, northeast and northwest having a component parallel to the coast. these winds prevail in the region in winter and spring and are responsible for a vertical supply of nutrient-rich waters by virtue of the principle of mass conservation [33]. the movement of the intertropical convergence zone (itcz) causes a clear alternation between a dry season which generally extends from november to may and a wet season from june to october. during the dry season, corresponding to winter in the northern hemisphere, the itcz reaches its southernmost position, while it oscillates north during the wet season boreal summer. this area is characterized by high spatial and seasonal variability in sea surface temperatures (sst) and primary productivity. the southern part of the area is characterized by warmer and richer chlorophyll-a waters than the northern part. seasonal variations are also very marked. the temperature can vary from 16-18 °c in february-march (cold season) to 30 °c in july-october (hot season). strong latitudinal temperature gradients exist in the region with a larger and narrower temperature change between 20 ° -22 ° n. these latitudinal variations in temperature depending on heat exchanges with the atmosphere and the intensity of the upwelling. the nw african ecosystem’s nutrients distribution is typical of a coastal upwelling zone where cold waters rich in nutritive salts are advected in the euphotic layer where primary production develops. the fertilization mechanisms of the marine environment change according to the season and the region depending on the situation of the climatic action centers and the morphology of the underwater coast [34]. the two main bodies of water (nacw and sacw) have different nutrient contents. a significant southern-north gradient is observed with waters clearly richer in nutrients in the south [35]. in the north west african upwelling system, it is recognized that there are two types or phases of organic production: a so-called “balanced” phase where the phytoplankton and zooplankton peaks are simultaneous, and another socalled “unbalanced” phase where these two peaks are offset in time (the zoo succeeds to the phyto) [34] and this has significant impacts on the productivity of the region. south of cap blanc, seasonal maximums of phytoplankton and zooplankton are in phase [36,37]. further north and especially in morocco, there is a significant gap between the development of phytoplankton which takes place in summer during the upwelling and that of zooplankton which is maximum in autumn or winter [38]. the nw african upwelling system is the most productive in terms of primary production of the four ebus (> 5 gc m2 d-1 and> 10 mg m-3 of chl-a) [29,39]. this high productivity supports a wide variety of pelagic fish species. 5. operating modes fishing fleet the exploitation of small pelagic resources in the moroccan eez is carried out by three main types of means of production, which operate under different regimes legal access to the resource (fishing license and fishing agreement). these fleets differ according to their size and their fishing strategies. the coastal fleet operates along the atlantic and mediterranean coast and is made up of: • moroccan coastal purse seiners with a gross tonnage ranging from 50 tons (tx) to 130 tons and a variant power between 300 hp and 550 hp. the gear used is the purse seine, the characteristics of which vary according to the size of the fishing units, the fishing area and the size of the catch. the length varies between 350 and 460 fathoms and the fall between 40 and 60 fathoms. the bulk storage system in the holds, traditionally used in the atlantic, has been gradually replaced by the use of plastic boxes for handling small pelagicin order to control the quantities caught and promote their quality. this system is almost generalized in the main ports (a limited percentage of bulk is still admitted, ie 30% at the level of the southern ports). • spanish coastal purse seiners classified in the “artisanal pelagic fishing” section at the level of the 2014-2018 protocol of the morocco-european union fishing agreement. these vessels are authorized to fish beyond 2 nautical miles calculated from the baseline. their fishing area is limited to the south by the parallel 34 ° 18’n. fishing units with the possibility of fishing are of a tonnage less than 100 tx and use the purse seine as fishing gear. this fleet, which used to target anchovy (engraulisencrasicolus) in the past, has now directed its effort towards fishing for sardines (sardina pilchardus). an extension of the fishing zone to the south, up to parallel 33 ° 25’00’’n is planned for 5 purse seiners. this measure is subject to regular evaluation in order to examine the possible interactions between the european union fleet and the moroccan fleets. 3.1.2 the offshore doi: http://dx.doi.org/10.36956/sms.v3i2.433 55 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 fleet this fleet operates south of cap boujdor and is made up of: • pelagic trawlers type rsw, flying the moroccan flag, equipped with a conservation system on board type rsw (refregerated sea water). the average gross tonnage (grt) is 762 tons and the average engine power is 2524 hp. these trawlers are authorized to fish between cap boujdor and cap blanc (26 ° 07’n20 ° 46’n), beyond 8 nautical miles calculated from the baseline. the fishing gear used is the pelagic or semi-pelagic trawl, the size of the smallest mesh of which must be equal to or greater than 40 mm of stretched mesh. these trawlers operate under an individual quota system per boat. • russian freezer pelagic trawlers with an on-board freezing system and devices for processing and processing fish into flour. they operate under the morocco russia fishing agreement. russian trawlers have an average capacity of 6,334 tons and an average engine power of 6,515 hp. resources and fisheries for small pelagictock and moroccan fisheries report 2016 30 • european pelagic trawlers: classified under the heading “industrial pelagic fishing” at the level of the 2014-2018 protocol of the morocco-eu fisheries agreement. the gear used is the pelagic trawl, the mesh of the pocket of which is fixed at 40 mm targeting small pelagic, sardines and sardinella, as well as horse mackerel and mackerel. the units authorized to fish are of three categories: vessels of a tonnage greater than or equal to 3000 gross tonnage (gt), vessels of a tonnage less than or equal to 3000 gt greater than or equal to 150 gt and vessels of ‘’ a gauge of less than 150 gt. the accessible fishing area is located south of parallel 29 ° n these freezer trawlers should operate beyond 15 nautical miles calculated from the baseline. concerning fresh fishing trawlers, they can exercise their activity up to 8 nautical miles from the baseline. these pelagic trawlers have an average capacity of 6,560 gt and an average driving power of 5,220 kw. the artisanal fleet this fleet operates between saidia and boujdor. it is made up of small boats whose gross tonnage generally exceeds 2 tx for the majority while it can reach 8 tx in certain regions. this artisanal fleet is targeting small pelagic has constantly been developing in recent years. in fact, by the end of 2014, approximately 2,000 boats employing more than 10,340 fishermen had practiced the fishing activity for small pelagiceasonally or permanently. the majority were identified in the central area between safi and boujdor. in the mediterranean zone, two regions are distinct according to the type of fishing unit used and the fishing methods for small pelagic: ● eastern mediterranean: the small seine is used by boats operating at night and essentially targeting the sardines and horse mackerel. the fishing operation is done by means of two units: (1) the active boat (mampara) having the design of a large boat (5 to 7m) decked with inboard engines from 60 to 120 cv, (2) the boat au feu (lamparo) is used to attract pelagic fish by the light of lamps. fish gather near the boat before surrounding them with the purse seine. there are two types of lamparo, electric and gas. ● western mediterranean: the small seine is used by fishing units locally called “chebbaks”. the fishing unit is composed of three boats: (1) the boat whose length can reach up to 9 m and a maximum tonnage of 5 grt, (2) the fireboat (lamparo) and (3) a small rowboat to hold the front of the seine. • atlantic: in the atlantic zone, the small seine is used by boats, particularly at the level of the ports because of the existence of a port infrastructure favoring safe exits and returns, but also with the availability and the ease of fuel and ice supply. fishing is practiced by a single boat in the entire region north of safi and by two to three boats in the resources and fisheries of small pelagictate of stocks and moroccan fisheries 2016, 31 regions south of safi. the period of use of the small seine varies from one port to another. it is dependent on the climatic conditions and the availability of the caught product. the small seine called “swilka” has a length that varies from 60 to 350 fathoms and a width of 8 to 50 fathoms. the stretched mesh of the net is 9 mm. fishing activities generally take place near the coast at depths between 10 and 50 fathoms. 6. conclusions the sardine stocks located along the moroccan atlantic coast live and breed in seasonal or permanent upwelling areas. upwelling is by its very nature a dispersive, fluctuating process that varies widely from year to year, from area to season and from season to season. for sardines, it seems difficult to satisfy the retention constraint, which is an important process conditioning the existence and longterm maintenance of a population in a given environment [40]. sardines are, however, capable of developing huge biomass. this is the result of an adaptation of the reproductive strategies to the environmental characteristics of the upwellings in order to offer optimal conditions for the development of the larvae. in the central zone (28-32 ° n) of the atlantic coast of morocco, the main spawning season is offset from the upwelling season. in short, a responsible attitude towards this resource requires the conservation not only of specific diversity but doi: http://dx.doi.org/10.36956/sms.v3i2.433 56 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 also that of the entire genetic heritage. therefore, responsible management must have as a preliminary stage the definition of management units that necessarily involve identifying population units constituting a stand, particularly when it comes to small pelagic known for their instability as well in time than in space. therefore, the need to improve scientific knowledge on the biology of the species (area and spawning period, diet, stock unit, etc.), on migration, and the conditions of its exploitation s’ is gradually imposed. the importance of respecting the biological rest period of the agarophyte g. sesquipedale which provides economic benefits for rural communities along the coasts where the algae form important deposits; adopting responsible behavior in harvesting and encouraging the uprooting of gelidium thalli whose size is greater than 10 cm. indeed, a thallus that does double weighs twice as much and contains more agar; respect for the ecosystem including not only marine plants but also other forms of marine life; raising the awareness of divers as to the danger which threatens the resource if the rocky substrate is destroyed or degraded, it represents the support and the point of fixation of the algae. references [1] fao (2015). résume sur l'état des stocks de petits pélagiques dans la zone nord de l'atlantique centre-est copace : principaux résultats du groupe de travail de la fao sur l'évaluation des petits pélagiques au large de l'afrique du nord-ouest. comité des pêches pour l'atlantique centre-est sous-comité scientifique septième session tenerife, espagne, 14 16 octobre 2015. cecaf/sscvii/2015/2. [2] fao (2015). report of the workshop on the age estimation of sardine and sardinella in northwest africa casablanca, morocco, 20-25 july 2015. fao fisheries report no. 1122. available at ftp://ftp.fao.org/fi/ document/cecaf/cecaf_ssc7/ref4b.pdf. [3] bakun, a., 2006. wasp-waist populations and marine ecosystem dynamics: navigating the “predator pit” topographies. progress in oceanography, 68: 271288. [4] rice, j., 1995. food web theory, marine food webs, and what climate change may do to northern marine fish populations. in: r.j. beamish (ed.), climate change and northern fish populations, canadian special publication, fisheries and aquatic sciences, 121, 561-568. [5] cury p, et al., 2000. small pelagics in upwelling systems: patterns of interaction and structural changes in “wasp-waist” ecosystems. ices j mar sci 57(3), 603-618. 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[15] crawford, r. j. m., shannon, l. v., d. e., pollock., 1987. the benguela ecosystem. 4. the major fish and invertebrate resources. in oceanography and marine biology. an annual review. 25. barnes, m. (ed.). aberdeen; university press: 353-505. [16] chavez, f.p., ryan, j., lluch-cota, s.e., niquen, c.m., 2003. from anchovies to sardines and back: multidecadal change in the pacific ocean. science 299(5604), 217-221. [17] takasuka, a., oozeki, y., kubota, h., lluch-cota, doi: http://dx.doi.org/10.36956/sms.v3i2.433 57 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 s.e., 2008. contrasting spawning temperature optima: why are anchovy and sardine regime shifts synchronous across the north pacific? prog oceanogr 77(2-3), 225-232. [18] lindegren m, checkley, d.m., 2013. temperature dependence of pacific sardine (sardinops sagax) recruitment in the california current revisited and revised. can j fish aquat sci 70(2), 245-252. [19] rykaczewski, r.r, checkley, d.m, j.r., 2008. influence of ocean winds on the pelagic ecosystem in upwelling regions. proc natl acad sci usa 105(6), 1965-1970. [20] alheit, j., roy, c., kifani, s., 2009. decadal-scale variability in populations. climate change and small pelagic fish, 285-299. [21] lluch-belda, d., et al., 1989. worldwide fluctuations of sardine and anchovy stocks— the regime problem. s afr j mar sci 8(1), 195-205. [22] maccall, a.d., 2009. climate change and small pelagic fish, eds checkley dm, alheit j, oozeki y (cambridge univ press, cambridge, uk), pp 285299. [23] hichami, n. and mounir a., 2019. “ecological aspects of anchovy : engraulis encrasicolus (engraulidae. teleostei) in the moroccan atlantic cost,” international journal of innovation and scientific research, vol. 41, no. 2, pp. 80-91. [24] canales, t.m., law, r., wiff, r., blanchard, j. l. 2015. changes in the size-structure of a multispecies pelagic fishery off northern chile. fisheries research, 161, 261-268. [25] swartzman, g., bertrand, a., gutiérrez, m., bertrand, s., and vasquez, l., 2008. the relationship of anchovy and sardine to water masses in the peruvian humboldt current system from 1983 to 2005. progress in oceanography, 79, 228-237. [26] cropper e.t., hanna e. and bigg g.r.; 2014: spatial and temporal seasonal trends in coastal upwelling off northwest africa, 1981-2012. deep sea res., 86, 94111. [27] benazzouz a., mordane s., orbi a., chagdali m., hilmi k., atillah a., pelegri j. l., demarcq hervé. (2014). an improved coastal upwelling index from sea surface temperature using satellite-based approach: the case of the canary current upwelling system. continental shelf research, 81, p. 38-54. issn 0278-4343. [28] barton, e., aristegui, j., tett, p., cantón, m., garc?abraun, j., hernández-león, s., nykjaer, l., et al. 1998. the transition zone of the canary current upwelling region. progress in oceanography, 41, 455504. [29] arístegui, j., barton, e. d., álvarez-salgado, x. a., santos, a. m. p., figueiras, f. g., kifani, s., hernández-león, s., et al., 2009. sub-regional ecosystem variability in the canary current upwelling. progress in oceanography 83, 33-48. [30] mittelstaedt, e., 1991. the ocean boundary along the northwest african coast: circulation and oceanographic properties at the sea surface. progress in oceanography 26, 307355. doi: 10.1016/0079-6611(91)90011-a. [31] chavance, p., ba, i., krivospichenko, s., 1991. les ressources pélagiques de la zee mauritanienne. bull. cent. nat. rech. océanogr. et des pêches, nouadhibou., 23, 2872. [32] arístegui, j., alvarez-salgado, x. a., barton, e. d., figueiras, f. g., hernandez-león, s., roy, c., and santos, a., 2006. oceanography and fisheries of the canary 177 current/iberian region of the eastern north atlantic (18a, e). the global coastal ocean: interdisciplinary regional studies and syntheses, 14: 879. [33] pickett, m.h., paduan, j.d., 2003. ekman transport and pumping in the california current based on the u.s. navy’s high-resolution atmospheric model coamps. journal of geophysical research 108 (c10), 3327. doi: 10.1029/2003jc00190. [34] binet, d., 1991. dynamique du plancton dans les eaux côtières ouest-africaines : écosystèmes équilibrés et déséquilibrés. in : pêcheries ouest-africaines, variabilité, instabilité et changement (cury p. & c. roy, eds). paris : orstom., pages 117-136. [35] mbaye, b.c., brochier, t., echevin, v., lazar, a., lévy, m., mason, e., gaye, a. t. machu, e. 2015 .do sardinella aurita spawning seasons match local retention patterns in the senegalese-mauritanian upwelling region? fisheries oceanography 24, 69-89. doi: 10.1111/fog.12094. [36] medina-gaertner, m., 1985. etude du oplanton côtière de la baie de dakar et de son utilisation par les poissons comme source de nourriture. phd thesis, université de bretagne occidentale. [37] furnestin, m., 1957. chaetognathes et zooplancton du secteur atlantique marocain. rev. trav.inst. pêches marit., 2j, 2j(1-2) :356p. [38] touré, d., 1983. contribution à l'étude de l'upwelldoi: http://dx.doi.org/10.36956/sms.v3i2.433 58 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 ing de la baie de gorée (dakarsénégal) et de ses conséquences sur le développement de la biomasse phytoplanclonique. doc. sci. centre rech. océanogr. dakar-thiaroye, 93, 186p. [39] lathuilière, c., echevin, v. and lévy, m., 2008. seasonal and intraseasonal surface chlorophyll-a variability along the northwest african coast. journal of geophysical research 113. [40] sinclair, m. 1988. marine populations: an essay on population regulation and speciation. university of washington press, seattle. 252 pp. doi: http://dx.doi.org/10.36956/sms.v3i2.433 15 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 http://dx.doi.org/10.36956/sms.v3i2.432 sustainable marine structures http://ojs.nassg.org/index.php/sms/index review knowledge and opportunities from the plastisphere: a prelude for the search of plastic degrading bacteria on coastal environments luis felipe avilés-ramírez1 joanna m. ortiz-alcantara2 ma. leticia arena-ortiz2* 1. faculty of sciences, national autonomous university of mexico (unam), yucatán, mexico 2. laboratory of ecogenomic studies, faculty of sciences, national autonomous university of mexico (unam), yucatán, mexico article info abstract article history received: 2 august 2021 accepted: 30 august 2021 published online: 15 september 2021 plastic pollution has become an urgent issue, since its invasion to every ecosystem has led to multiple impacts on the environment and human populations. certain microbial strains and genera had shown the ability to biodegrade plastic sources under laboratory conditions. in this minireview, we collect and analyze scientific papers and reports of this microbial activity as we contextualize this information on the global plastic pollution problem, to provide an updated state of the art of plastic biodegradation with microbial agents. along with a broad understanding of the general process of plastic biodegradation hosted by microorganisms. the contributions of this minireview come from the identification of research gaps, as well as proposals for new approaches. one of the main proposals focuses on coastal environments and in particular coastal wetlands as a great microbiome source with potential for plastic biodegradation, whether reported or undiscovered. our final proposal consists of the application of this knowledge into technologic tools and strategies that have a remarkable impact on the battle against the plastic pollution problem. keywords: plastic biodegradation bacteria plastisphere bioremediation coastal environments 　 *corresponding author: ma. leticia arena-ortiz, laboratory of ecogenomic studies, faculty of sciences, national autonomous university of mexico (unam), yucatán, mexico; email: leticia.arena@ciencias.unam.mx 1. introduction the plastic pollution problem plastics are synthetic or semi-synthetic polymers mainly produced from petrochemicals, characterized by their high resistance/density relationship, their great thermal and electric isolation properties, as well as resistance to acids, alkalis and solvents [1]. these materials have applications in multiple industries and business sectors like trading, packing, building materials, medical and pharmaceutical uses, automotive industry, home appliances, agriculture and many mass production products for the everyday human consumption [2,3]. these polymers pollute and invade a lot of environments due to the single-use and improper waste management. the main plastic types considered environmental pollutants are high-density polyethylene (hdpe), low-density polyethylene (ldpe), polyvinyl chloride (pvc), polystyrene (ps), polypropylene (pp), polyester (pes), polyamide (pa) and polyethylene terephthalate (pet) [4]. plastic pollution has become one of the biggest environmental threats by invading every ecosystem. it has been reported the presence of plastic debris (microplastics) 16 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 from deep-sea sediments [5], to the highest areas of the mount everest [6]. the presence of microplastics in the human placenta has been documented as well [7]. around 13 million tons of plastic have been thrown to oceans annually, besides the global annual production of 300 million tons of plastic debris [8]. in méxico, nearly 83,343 tons of trash are collected daily [9] and in the municipal solid waste composition, plastic spans 10.9% [10]. main consequences of this pollutant relay on contamination of water sources like rivers, lakes or oceans leading to the formation of continental sized trash patches in the middle of the pacific ocean [11]. also, additives and other compounds present in plastics impact on coastal, marine and inland soils, damaging their physicochemical properties and fertility [12]. biotic impacts come from mutilation, intoxication and asphyxia of marine, coastal and terrestrial organisms [13]. human population affectations include the intake of microplastic polluted food [14] to neurotoxic damage from pah´s, phthalates and pcb´s [15]. furthermore, plastic residues represent public health and economic hazards to human communities. 2. coastal wetland ecosystem goods and services worldwide ecosystems shelter goods and services that provide human populations resources for their basic needs; these so-called ecosystem services and natural capital [16] are in decay because of environmental issues such as plastic contamination. this situation is a threat to global human economics and welfare, ever since biodiversity is linked in so many complex ways to ecosystem functionalities and their output ecosystem services [17]. particularly, coastal wetlands provide human population wide and diverse goods and services due to the enormous biodiversity within these ecosystems. some of these goods and services are categorized as ecosystem services framework [18]. supporting ecosystem services include the primary production of microbiotic (bacteria, fungi, protozoea) and macrobiotic (migratory birds and commercial interest fish and crustaceans) life forms, soil formation and enrichment. provisioning goods and services are represented by sources like fresh water, seafood, honey and woods. regulating functions such as climate regulation by carbon dioxide sequestration and flood and storms mitigation. the cultural category is covered as aesthetics, recreational, educative and spiritual values for native human population as well as foreign people through ecotourism [19]. 3. microbial biodegradation of plastics environmental plastic pollution solutions have become an urgent subject and an interesting approach could be just below ourselves. diverse microbes have shown the ability to degrade plastics; particularly bacterial strains isolated from different environments that have been studied and reported in diverse scientific publications. some of these papers are reviewed in the present study. bacteria have been widely researched in plastic biodegradation matter, since they are easy for cultivation and isolation, and the facility for bioprospecting metabolic pathways, ecological functions and subproduct related information through metagenomic analysis and sequencing of the 16s ribosomal gene [20,21]. in this review, scientific evidence of plastic biodegradation hosted by bacteria dates from at least 1991 [22,23]. in general, research has focused on confirming and assessing plastic degradation by bacteria either through in vitro or in situ assays. depolymerization activity is usually measured with diverse methodology such as visual assessment through detecting roughening, cracking and biofilm formation [24], clear-zone tests [25], weight loss estimates in microbial exposure [26], respiratory activity evaluation such as co2 production or o2 consumption [27]. as well as detection of the activity of specific enzymes or byproducts of depolymerization activity [28,29]. 4. bacterial biodegradation state of the art in the present review, we summarize some bacterial strains and species that have the ability to biodegrade plastic, with complementary information about the habitat of the bacteria, type of plastic degraded, byproducts, enzyme and the bibliographic reference to the paper. this information is categorized and divided based on the type of environment where the bacteria were isolated. table 1 shows previous scientific research results from bacteria isolated from anthropic environments, such as municipal waste disposal sites, sewage water, industrial activated sludges or purchased pre-cultured strains from laboratories and microbial strains collections. aquatic environment native bacteria are represented in table 2. aquatic environments that hold bacterial sources are wide and diverse and some of the most studied environments are sea water and soil, abyssal water and soil, freshwater like rivers and lakes. some of the least studied are coastal soil and water, highlighting coastal wetland ecosystems. http://dx.doi.org/10.36956/sms.v3i2.432 17 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 table 1. municipal waste disposal sites/other human environments id habitat plastic type degraded degradation byproducts enzyme reference pseudomonas, penicillium, rhodotorula, hyalodendron landfill low density polyethylene (ldpe), polyurethane (pu), polyvinyl chloride (pvc) polyethylene glycol — alcano monoxigenase, same as found on hydrocarbon biodegradation (seneviratne, 2006) [26] ideonella sakaiensis sediment from petrecycling site. polyethylene terephthalate (pet) terephthalic acid (tpa) & ethylene glycol (eg) mono(2-hydroxyethyl) (mhet) terephthalic acid [30] pseudomonas final waste deposition site low density polyethylene (ldpe) — — [31] pseudomonas myk1 and bacillus myk2 digester sewage sludge polylactic acid (pla) co2 and ch4 — [27] comamonas acidovorans city soil samples polyester-type polyurethanes adipic acid and diethylene glycol — [32] pseudomonas aeruginosa previously isolated microorganisms (microteca/microlibrary) pet, pu, pp, abs, hdpe, pvc, abs, ps — — [24] acidovorax delafieldii city soil samples poly(tetramethylene succinate)-co(tetramethylene adipate) (pbsa) — lipase [33] bacillus subtilis, bacillus cereus, bacillus lentus, pseudomonas aeruginosa, staphylococcus aureus, klebsiella pneumoniae, streptococcus pyogenes, escherichia coli, proteus vulgaris, micrococcus. fadama soil polythene plastic bags and environmental plastic materials — polyurethanases (koutny et al., 2006). [34] brevibacillus borstelensis soil from polyethylene waste deposition site branched low-density polyethylene — — [35] rhodococcus ruber sediments with polyethylene debris from agriculture use polyethylene — esterases [36] streptomyces viridosporus, streptomyces badius and streptomyces setonii enzymes from cultured s. viridosporus, s badius and s setonii starch-polyethylene degradable plastic films primary and secondary alcohols — [23] pseudomonas putida (aj) and ochrobactrum (td) dangerous waste disposal site vinyl chloride — — [37] pseudomonas fluorescens naval research laboratory, wahington d.c. polyester polyurethane — enzyme with protease activity [38] thermomonospora fusca compost from green waste aliphatic-aromatic copolyesters (synthesized from 1,4-butanediol, adipic acid, and terephthalic acid (bta)) — — [39] schlegelella thermodepolymerans and pseudomonas indica (k2) activated sludge poly(3hydroxybutyrate-co-3mercaptopropionate). [poly(3hb-co 3mp)] 3hb oligomer linked as thioester poly(3hydroxybutyrate)(3hb) depolymerase [40] http://dx.doi.org/10.36956/sms.v3i2.432 18 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 id habitat plastic type degraded degradation byproducts enzyme reference clostridium botulinum and clostridium acetobutylicum sewage slugde and methane sludge poly(b-hydroxybutyrate) (phb), poly(bhydroxybutyrateco-11.6%-bhydroxyvalerate) (phbv) and the synthetic polyester poly(ocaprolactone) (pcl) — pcl depolymerizing [25] bacillus amylolyticus, bacillus firmus, bacillus subtilis, pseudomonas putida, pseudomonas fluorescens municipal solid waste from compost plant polyethylene bags — — [41] bacillus cereus, b. megaterium, b. subtilis, brevibacillus borstelensis culture fields polyethylene hydrocarbons (saturated and unsaturated) and alcohols of higher molecular weight — [42] rhodococcus rhodoshrous purchased isolates from american type culture collection high density polyethylene (hdpe), low density polyethylene (ldpe) and linear low-density polyethylene (lldpe) films with balanced content of antioxidants and pro-oxidants (manganese+iron or manganese+iron+cobalt) — — [43] actinomadura sp. s14, actinomadura sp. tf1, streptomyces sp. apl3 y laceyella sp. tp4 compost soil polyester biodegradable plastics; polylactic acid (pla), polycaprolactone (pcl), poly-(butylene succinate) (pbs) & polybutylene succinateco-adipate (pbsa) — s14, tf1 & tp4 produced pla and pbsa depolymerase (50°c), apl3 (40°c). actinomadura sp. s14 (pcl depolymerase) actinomadura sp.tf1 (pla depolymerase), streptomyces sp. apl3 (pbs depolymerase), laceyella sp.tp4 (pbsa depolymerase) [44] paenibacillus amylolyticus tb-13 (bacillus amylolyticus) sediment samples from multiple sites poly(lactic acid), poly(butylene succinate), poly(butylene succinateco-adipate), poly(caprolactone) and poly(ethylene succinate) — proteases and esterases [45] streptomyces sp. af-111 sewage sludge from treatment plant rawalpindi pakistan poly(3-hydroxybutyrateco-3-hydroxyvalerate) (phbv) — phbv depolymerase [28] bacillus sp. af8, pseudomonas sp af9, micrococcus sp. 10, arthrobacter sp. af11, and corynebacterium sp. af12 soil from plastic deposition sites poly [4,4’-methylenebis (phenyl isocyanate)-alt 1,4-butanediol/poly (butylene adipate)] (polyurethane, pu) p-nitrophenol (spectroscopy), co2 (sturm test) esterase polyurethanases (plate assay with coomassie blue r 250). [29] pn24 bacillus cereus, pn12 bacillus pumilus, lnr3 arthrobacter. waste deposition sites and artificially developed soil beds containing maleic anhydride glucose, and small pieces of polyethylene. high and low-density polyethylenes (hdpe/ ldpe) — — [46] http://dx.doi.org/10.36956/sms.v3i2.432 19 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 table 2. marine, freshwater and coastal environments id habitat plastic type degraded degradation by-products enzyme reference pseudomonas, staphyloccoccus, moraxella, micrococcus, streptococcus mangrove soil polyethylene bags and plastic cups — — [47] pseudomonas (pseudomonas stutzeri) river water high molecular weight polyethylene glycols (peg´s) glyoxylic acid peg dehydrogenase (single polypeptide) [22] rhodobacteraceae, rhodospirillaceae, oceanospirillaceae, glaciecola seawater poly(3-hydroxybutyrateco-3hydroxyhexanoate) (phbh) — — [48] shenawella (ct01), moritella (ct12, jt01, jt04), psychrobacter (jt05) and pseudomonas (jt08) marine dephts soil poly ε-caprolactone (pcl), aliphatic polyesters — — [49] terrabacter tumescens, terracoccus luteus, brevibacillus reuszeri, agrobacterium tumefaciens, burkholderia vietnamiensis, duganella zoogloeoides, pseudomonas lemoignei, ralstonia eutropha, ralstonia pickettii, matsuebacter chitosanotabidus, roseateles depolymerans, rhodoferax fermentans, variovorax paradoxus, serratia marcescens, acinetobacter calcoaceticus, acinetobacter junii, pseudomonas pavonaceae, pseudomonas rhodesiae, pseudomonas amygdali, pseudomonas veronii soil samples (ando-soil, woody area at shimatsakuba, brown lowlands soils, sandy riverside soil and riverside mud) poly(βhydroxyalkanoate), poly(ε caprolactone), poly(hexamethylene carbonate), or poly(tetramethylene succinate) — — [50] bacillus mojavensis th309 bio-deteriorated plastic waste from tidal zone on carsamba coast of samsun poly(e-caprolactone) (pcl) — esterase (bmest) [51] alcalinovorax, hyphomonas and cycloclasticus. seawater and soil samples poly(ethylene terephthalate) (pet) & biodegradable plastic bags (bd) insoluble by-products of the hydrolytic degradation of pet. esterase [52] pseudomonas pachastrellae jcm12285 marine plastic debris in coastal seawater poly(ε-caprolactone) (pcl) — pcl hydrolase [53] gammaproteobacteria, alphaproteobacteria, and flavobacteria (class level) microplastics exposed to seawater from coastal zones polypropylene (pp) and polyvinyl chloride (pvc) microplastics — — [54] arcobacter and colwellia three types of coastal marine sediment from spurn point, humber estuary, u.k. low density polyethylene (ldpe) microplastics — — [55] bacillus cereus and bacillus gottheilii sediments from matang mangrove in perak polyethylene (pe), polyethylene terephthalate (pet), polypropylene (pp), and polystyrene (ps) — — [56] lysinibacillus fusiformis strain vasb14/wl and bacillus cereus strain vasb1/ts rhizosphere samples from mangrove (aviccenia marina) soil polythene — — [57] http://dx.doi.org/10.36956/sms.v3i2.432 20 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 table 3. macrofauna gut microbiome (holobionts) id habitat plastic type degraded degradation by-products enzyme reference escherichia, shigella, asaia and acinetobacter,rhodocytophaga, bergeyella, diaphorobacter, hydrogenophaga, zhizhongheella. gut microbiome from galleria mellonella low-density polyethylene (ldpe) glycol — [59] enterobacteriaceae, spiroplasmataceae, and enterococcaceae gut microbes from t. obscurus and t. molitor (purchased from insect breeding plants) polystyrene (ps) — — [60] dyella, lysobacter, and leptothrix microbes from larvae t. molitor gut. larvae purchased from market polystyrene (ps) and low-density polyethylene (ldpe) foams — — [61] family enterobacteriaceae, sphingobacteriaceae, and aeromonadaceae microbiome gut from soil snail a. fulica purchased from jiaxing hong fu breeding farm (zhejiang, china), expanded polystyrene (ps) foam — — [62] serratia sp. strain wsw microflora from p. davidis larvae gut polystyrene (ps) styrofoam — — [63] actinobacteria (microbacterium awajiense, rhodococcus jostii, mycobacterium vanbaalenii and streptomyces fulvissimus) and firmicutes (bacillus simplex and bacillus sp.) earthworm´s gut ldpe volatile compounds (octadecane, eicosane, docosane and tricosane) and nanoplastics [64] bacillus and serratia microbial gut from g. mellonella l. larvae purchased from huiyude co. polyethylene (pe) and polystyrene (ps) long chain fatty acids as the metabolic intermediates of plastics in the residual polymers — [65] microbial research has focused on new sources. one of the most popular in recent years is the gut microbiome from organisms such as coleoptera, lepidoptera, lumbricidae and certain mollusks. some organisms contain bacterial strains capable of degrading complex chemical structured materials such as wax or wood timbers. assays on these organisms and their gut microbiota have shown a certain capacity of degrading plastic samples as well (table 3). these host organisms could also be referred to as holobionts [58]. 5. general process of biodegradation by microorganisms for a better comprehension of the topic, a deeper understanding of the biodegradation process is required. thus this metabolic mechanism is the core of the activity and eventual application of plastic degradation through bacterial strains. the biodegradation process may differ depending on the genera and species, but the main process is illustrated in figure 1 and described as follows: the general microbial biodegradation process can be described in three stages: biodeterioration, biofragmentation and assimilation [66]. at the time environmental abiotic degradation occurs vias mechanical, chemical, photocatalytic thermal and ozone-induced degradation [67]. biodeterioration it all begins when the plastic material is exposed to the environment (where abiotic degradation factors join the process), then, bacteria start to settle down into the plastic surface to form a biofilm or the so called “plastisphere” [68]. microbial activity of consortia (i.e. protein and enzymatic activity) causes deterioration of physical, mechanical and chemical properties of the polymer, leading to cracking of surfaces, formation of oligomers, monomers, as well as http://dx.doi.org/10.36956/sms.v3i2.432 21 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 carbon and nitrogen sources [66]. biofragmentation in order to reach polymer assimilation, microorganisms have to break polymer bonds for cellular absorption of oligomers and monomers, since polymer chemical structure is too big and complex to be directly absorbed by microorganisms [69]. this goal is reached through the secretion of polymer-specific enzymes and free radical generation [66]. action of extracellular enzymes on a polymer is generally defined as the concept of depolymerization [70]. bio fragmentation could lead to microplastic formation if the plastic media is not assimilated yet by microorganisms [64]. assimilation this stage is defined for the real absorption of the plastic atoms into the microbial cell; providing essential needs such as energy, electrons and elementary sources like carbon, nitrogen and phosphorus. microorganisms are able to sustain and reproduce at the time they produce energy via aerobic respiration, anaerobic respiration or fermentation [66]. as a result of polymer cleavage, monomer/oligomer absorption and metabolic processation; microbes can release mineral molecules, contributing to natural biogeo chemical processes, as well as organic molecules, which some could be ecotoxic threats under certain conditions and degrees [66]. mineralization differs by the presence of carbon dioxide and water under aerobic conditions, and methane and carbon dioxide for anaerobic [67]. some byproducts laid by microbial metabolic activity through the biodegradation process could have potential use for other technological or industrial uses and applications [71]. the chemical reactions resulting from plastic biodegradation through aerobic and anaerobic respiration are illustrated by equation 1 and equation 2. c plastic + o2  co2 + h2o + c residual + biomass equation 1. aerobic microbial biodegradation of plastic [72]. c plastic  ch4 + co2 + h2o + c residual + biomass equation 2. anaerobic microbial biodegradation of plastic [72]. aerobic microbial biodegradation of plastics (equation 1) is performed by the use of oxygen as electron acceptor, breaking down organic chemicals into smaller organic compounds or monomers. carbon dioxide and water are excreted as byproducts of the cleavage. meanwhile, in anaerobic microbial biodegradation (equation 2), microbes set nitrate, sulphate, iron, manganese and carbon dioxide as electron acceptors due to lack of oxygen for the cleavage and formation of smaller compounds [72]. all these stages of the general biodegradation process of plastic through microbial activity are illustrated in figure 1. figure 1. general biodegradation process by microorganisms. the three stages of biodeterioration are illustrated as detailed previously in this review. note that the chem, mech, photo, °c and o3 symbols represent chemical degradation, mechanical degradation, photodegradation, temperature and ozone, as they are abiotic drivers for plastic degradation on the environment. 6. conclusions some remarkable features about the state of the art is that bacterial strains come mostly from the bias to the human environment, rather than natural ecosystems. waste and trash disposal sites, recycling sites, city soil samples and laboratory or purchased strains are the most common origins for plastic degrading bacteria. otherwise, if natural environments are also well covered, most research papers focus on marine environments, mainly in seawater exposure experiments, leaving a great research gap and an opportunity for studies on coastal and wetland environments, considering that these ecosystems have great biodiversity. microbial biodegradation of plastic is known to be an environmentally friendly, cheap and acceptable way for plastic waste treatment [29], so waste management actions should pay some attention to these potential opportunities. this knowledge could be applied into technological developments for bioremediation or biomitigation of plastic polluted ecosystems. as well as integrate to municipal waste management plans, which even today are not well designed nor applied to most urban and rural locations. incursions into new strategies and solutions to plastic pollution will cause positive impacts on the world's ecosystems and human population, with the participation of every government level, as well as corporations and non-governmental organizations. some other positive impacts of development and action on this subject rely on the achievement of united nation´s 2030 sustainable development goals. in such objectives as good health and well-being, clean water and sanitation, climate action, life below water, life on land and partnerships for the goals. industrial companies could benefit from economic incenhttp://dx.doi.org/10.36956/sms.v3i2.432 22 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 tives, positive publicity and product mark-up as a result of extending their value chain responsibility by contributing into plastic-pollution mitigation initiatives. acknowledgements the research group acknowledges the papiit project it202418 for financial support, to the umdi-sisal and to the faculty of sciences of the national autonomous university of mexico for the facilities granted to carry out this work. conflict of interest the authors have no conflict of interest to declare. references [1] cristán-frías, a., ize-lema, i. and 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(2017) biodegradation of synthetic and natural plastic by microorganisms. appl environ microbiol 5: 8-19. doi: 10.12691/jaem-5-1-2. http://dx.doi.org/10.36956/sms.v3i2.432 39 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 http://dx.doi.org/10.36956/sms.v3i2.434 sustainable marine structures http://ojs.nassg.org/index.php/sms/index article abundance and distribution, growth pattern, sex ratio and gonadosomatic index (gsi) of liza falcipinnis (valenciennes, 1836) from ojo axis of badagry creeks, lagos, nigeria adeboyejo, o.a.* clarke, e.o. hammed, a.m. whenu, o.o. abayomi, j.p. olarewaju, o.m. department of fisheries, faculty of science, lagos state university, ojo, lagos, nigeria article info abstract article history received: 23 august 2021 accepted: 15 september 2021 published online: 25 september 2021 a study on seasonal abundance, morphometric and meristic data, growth pattern, condition factor, sex ratio and gonadosomatic index of liza falcipinnis (valenciennes, 1836) from the ojo axis of badagry creek, nigeria was conducted from may 2019 to march 2020. a total of 1012 species were randomly selected, having 499 females and 513 males. the length frequency analysis and length-weight relationships (lwr) were determined. sex ratio was determined by chi-square analysis. the results showed that morphometric data are: 0.5 2.5 mm for ed, 2.1 12 mm for hl, 1.7 8.1 mm for hd, 2.5 11.7 for bd, 2.6 233.3 mm for tl and 9.23 1006 g for bw for the combined sexes. the slope (b) shows an allometric growth pattern. the intercept ‘a’ and slope ‘b’ of the lwr (logw = a + blogl) were log w= 15.39+ 0.34 logl (r= 0.54) for combined sexes, log w= 12.49+ 0.02 log l (r= 0.38) for males and log w= 18.23+ 0.01 log l (r=0.16) for females. the length frequency distribution indicated that species were dominated by two year classes (ages 1 and 2). condition factors were generally low. the values ranged between 0.68 0.85 for combined sexes. the gonadosomatic index for female was highest in august, 2019 (17.77%) with mean±sd of 2.88±0.75; which indicated the peak of spawning period in the study area. sex ratio difference was significant (p<0.05). sexual differences were significant; the females are phenotypically larger than the male. keywords: growth pattern length-weight-relationships (lwr) gonadosomatic index (gsi) condition factor creeks fish biology 　 *corresponding author: adeboyejo, o.a., department of fisheries, faculty of science, lagos state university, ojo, lagos, nigeria; email: adeboyejoakintade@yahoo.co.uk 1. introduction liza falcipinnis, is a bony fish of the family mugilidae, class actinopterygii (ray-finned fishes) and the order perciformes. the family consists of 17 genera and 80 species. although, chelon, liza, mugil and valamugil. liza dumerilli (grooved mullet), l. grandisquamis (largescale mullet), l. argentea (flat-tail mullet) and l. triscuspider (stripped mullet) are said to be the most common members of the genus liza. [24] reported on the aspects of l. falcipinnis from the lagos lagoon, nigeria. mugilidae are cultured in many countries due to their high-quality flesh. according to [31], they are of great economic importance in tropical inland waters of west africa and they play significant roles in the ecology of african freshwater. they are easily recognizable with their thick yet streamlined bodies, hard angled mouth, large, cycloid or faintly ctenoid scales, sub abdominal pelvic fin and two widely separated dorsal fin, the first containing only four spines [33]. they have no lateral line, pectoral fin is high on body 40 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 and mouth is small terminal or inferior with pre-maxillae protractile, their teeth are small, feeble and could be hidden [31]. body is elongated, cylindrical with broad flattened head with blunt snout (figure 1). they are silvery in colour, often with 3 to 9 longitudinal streaks on the back, fins are hyaline and husky. the streamlined body of the mullet allows them to avoid numerous predators that attack their schools on the shallow inshore water. they spawn in the sea and then enter lagoon, estuaries and freshwater for feeding [19]. length-weight relationship (lwr) shows that the average weight of fish at a given length by making use of a mathematical equation to show relationships between the two. fish can attain either isometric or allometric growth [32]. isometric growth indicates that both length and weight are increasing at the same rate. allometric growth can be either positive or negative. positive allometric implies increase in weight with increase in length. negative allometric implies the fish becomes lighter as its length increases. however, lwr is assumed to be uniform for an entire fish stock in stock assessment studies [14]. knowledge of the relationship between the length and weight of a given species is useful to transform the length structures obtained into the weights of fish captured and to monitor health status of a population. [4], opined that fluctuation in fish growth is a common phenomenon in tropical and subtropical waters because of environmental variations, spawning and dynamics of food composition. condition factor (cf) is an estimation of general well-being of fish as stated by [27] and is based on the hypothesis or assumption that heavier fish (at a given length) are in better condition than the lighter ones. the condition factor of 1.0 or greater indicates the good condition of fish while less than 1.0 shows bad condition [2]. it is a useful index for estimating growth rate and age and for assessing environmental quality and can be influenced by season, sex, type of food organism consumed by fish, age, and environmental conditions. the gonadosomatic index (gsi), is described as gonad mass as a percentage of total body weight and is widely used as a simple measure of the extent of reproductive investment, gonadal development and maturity of fish in relation to spawning [12,9]. gonadosomatic index of fish increases with maturity and abruptly declines after spawning. gsi is particularly helpful in identifying season of spawning as the female gonads increase in size prior to spawning [18]. study on reproductive biology of fish is essential for conservation and selecting fish candidates of aquaculture from the wild. reproduction is an important physiological system that is crucial in the life cycle of fish. fecundity is the number of ripened or vitellogenin eggs or oocytes in the female prior to the next spawning period and varies intraand interspecifically. it is also stated that the number of eggs produced by fish in a spawning season is species-specific and varies with genetic characteristics, size, age, environmental factors and physiological conditions of the fish. for instance, large female fish in better condition tend to exhibit higher fecundity than those in poor condition. this information is useful in estimating spawning stock biomass and management [18]. in the study area, liza falcipinnis is known to be abundant and this has been related to their feeding habits. the monthly incidence of occurrence of l. falcipinnis in canoe landings of artisanal fishermen in the ojo axis of badagry creek showed that it occurred in the lagoon on a yearround basis. however, there is not enough information on the species in the study area. this research is therefore geared towards reporting significant data on the species’ condition factor, fish growth pattern, and reproductive biology (gonadosomatic index gsi) with the hope that this scientific information can be useful in the ecological, biological management and also biodiversity of the species. this information is needful for sustainable management of liza falcipinnis in ojo axis of badagry creek, where it is caught in large numbers with unregulated fishing gears and methods. the major problem of this research is that adult sizes of the fish were rarely caught in ojo lagoon. the specific objectives are to determine the species’ growth pattern using lengthweight relationship (lwr) of the vonbertalanffy growth equation; length frequency of the year classes in the population using petersen method; condition factor (k-factor) i.e. condition of well-being of the species; the gonadosomatic index of the species (gsi) and sex ratio using the chi-square (x2). 2. study area ojo axis of badagry creek is along the badagry water system in the northern area, this is shown in figure 1 (marked x) in the map of the lagos lagoon complex, which comprises of the epe lagoon in the south; lagos lagoon in the middle, ologe lagoon and the badagry creek in the north. the ojo axis of the creek extends from ojo army barracks down to ijanikin local government area headquarters, lagos state. the samples were collected specifically within coordinates: 6o28n 3o11e and 6.467on 3.183oe. [24] stated that badagry creek is a long stretch of water body that runs parallel to the atlantic ocean in the south; it extends from lake nokue near port-novo to apapa area of lagos, and from there opens into the ocean through the lagos harbour. fish species are highly diversed in the ojo creek; examples are ethmalosa, gobioides, cynoglossus, pomadasys, pseudotolithus, tilapia, liza, clarias, selene, macrobrachium and callinectes. http://dx.doi.org/10.36956/sms.v3i2.434 41 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 figure 1. map of the lagos lagoon complex, showing the ojo axis (marked x) of badagry creek, lagos, nigeria 3. material and methods 3.1 fish sample collection and laboratory analysis edible fishes were procured from the fishermen on the creek (ojo) on a monthly basis from may, 2019 to march, 2020. the sampling gears used for fishing by the fishermen include baited long lines, cast nets and set gill net. a total of at least 1012 samples of liza falcipinnis were collected for the analysis. the samples were transported in an ice chest to the fisheries laboratory at the department of fisheries, lagos state university, ojo, lagos state for proper identification and examination. fish identification was made to the lowest taxonomic level. relative abundance of species was calculated by dividing number making up a species by the total number of fish sampled multiplied by 100%. the total and standard length of fish sampled were measured using measuring board graduated in cm. range of the length frequency was determined and recorded. weight was measured using a weighing balance. the average weight of these samples was used to estimate the number of individuals from the total catch for the week. the biometric data such as total length were taken to the nearest grams. identification was done as following [3]. figure 2. sample of liza falcipinnis (mullet) from ojo axis of badagry creek, lagos, nigeria 3.2 length weight relationship and length frequency analysis the length weight relationships were obtained from the linear regression analysis intercept:a = [ the slope (‘b’) as: a n d t h e c o r r e l a t i o n c o e f f i c i e n t (‘r ’) a s : = where: x= lengths of fish, y= weights of fish, and n= number of specimens. the length-weight relationships for males and female specimens were obtained and a scattered diagram was drawn to determine the statistical relationships. the relationship was expressed as: w= a + bl. the same data was converted to logarithms and straight-line graph was drawn and the relative slope (b) was obtained from the relationship:log10w= a + b log10 l. 3.3 length-frequency method (petersen method) the method currently in use for the analysis of length-frequency data; all finds their origin from the work of petersen (petersen methods). with this method, the assumptions were made as to the time interval separating the various peaks of one length frequency sample. these peaks were assumed to represent distinct age groups in a year class. 3.4 condition factor (k) fulton’s condition factor (k) obtained for both sexes was expressed as: k = 100w/l3 where w= weight of fish (g), l= length of fish (mm). therefore, the condition factor (k) was used to compare the condition, fatness or wellbeing of both sexes of the fish [22]. 3.5 sex ratio the differentia in sex distribution of the pollution of synodontis clarias was determined from the separation of sexes into males and females. the chi-square technique was used where the observed (x2tab) was measured against the chi-square calculated (x2cal) as expressed below: x2 = (o e)2 /e http://dx.doi.org/10.36956/sms.v3i2.434 42 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 3.6 gonadosomatic index (gsi) the gonadosomatic index (gsi) was determined or calculated based on the formula suggested by [22] which is expressed as: 4. results 4.1 seasonal abundance seasonal variations in number and weight are shown in figure 4 for both sexes. highest catches in the total number of fish occurred in june 2019; while the highest catches in weight occurred in february 2020 in the study area. however, figure 5 showed the seasonal abundance in the population of female liza falcipinnis from ojo axis of badagry creek. it reveals that the highest female catches in number were in october, december 2019, and february 2020. this thus coincides with peak of rainy season, while the highest peak of catches in weight was reported in february 2020. the male sex showed a different seasonal distribution. the male had the peak population in number in june 2019 and march 2020 with a corresponding highest catch in weight in the same month as shown in figure 3. the population distribution in terms of catches was lowest from august to february 2020 for the males in term of weight and total number of fish. 4.2 morphometric analysis and length weight relationships the result of the monthly morphometric analysis, length weight relationship and condition factor of liza falcipinnis from ojo axis of badagry creek from may, 2019 to march, 2020 are presented in table 1. the mean length for combined sexes was between 15.9 cm (may, 2019) and 30.5 cm (jan 2020). the mean weight was between 35.19 g (may, 2019) to 247.4 g (feb, 2020). however, the intercept of the length weight relationships was positive through-out the year, values were between 8.9 cm to 17.6 cm. the slope of the graph was equally all positive which suggests positive allormetrism, the lowest b value was 0.02 and the highest value was 0.1, this is shown in figure 3, 4 and 5. the correlation coefficients (r) were generally high from 0.46 to 0.8. the mean length for female was between 15.89 cm (may 2019) to 31.74 cm (jan 2020). the mean weight was between 34.29 g (may, 2019) and 296.09 g (feb, 2020). the length weight relationship for female was positive through-out the year. values were between 7.64 cm and 18.20 cm. the slope of the graph was also positive which showed an allometric growth pattern. the lowest b value was 0.02 and the highest was 0.11 (table 1). the correlation coefficient (r) was generally high from 0.55 to 0.96. the mean length for male was between 15.92 cm (may) and 28.42 (november). the mean weight was between 35.7 g (may, 2019) and 161.44 g (jan 2020) (table 1). table 1. changes in seasonal abundance of liza falcipinnis in ojo axis of badagry creek, lagos month combine sexes females males no of fish % no of fish total wt (g) % total wt no. of fish % no of fish total wt (g) % total wt no of fish % no of fish total wt (g) % total wt may 74 7.31 2604.2 2.2 27 5.4 925.9 1.3 47 9.2 1678.1 3.6 june 146 14.4 10163.9 8.6 33 6.6 3156.7 4.8 113 22.0 7007.8 15.2 july 119 11.8 9698.1 8.2 35 7.0 4448.5 6.2 84 16.2 5249.6 11.4 august 96 9.5 11041.1 9.3 45 9.0 6182.8 8.8 51 9.9 4858.3 10.5 september 91 9.0 9361.4 8.0 51 10.2 5347.6 7.4 40 7.9 4091.9 8.8 october 94 9.3 12227.8 10.3 60 12.2 7900.6 10.9 34 6.6 4327.1 9.4 november 54 5.3 8122.7 6.8 38 7.6 5598.0 7.7 16 3.1 2524.7 5.5 december 88 8.7 12119.5 10.2 62 12.4 8579.0 11.9 26 5.1 3540.5 7.7 january 73 7.2 11192.3 9.5 51 10.2 7802.1 10.8 22 4.1 3390.2 7.4 february 86 8.5 21275.8 18.0 61 12.2 18061.5 25.0 25 4.9 3214.3 6.9 march 91 9.0 10361.88 8.8 36 7.2 4133.7 5.7 55 10.9 6226.1 13.5 note: wt = fish weight in grams. http://dx.doi.org/10.36956/sms.v3i2.434 43 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 figure 4. standard length-weight relationship in combined sexes of liza falzipinnis from ojo axis of badagry creek, lagos nigeria figure 5. length-weight relationship of female liza falzipinnis from ojo axis of badagry creek figure 3. changes in seasonal abundance of (1) combine sex, (2) females and (3) males of liza falcipinnis from ojo axis of badagry creek, lagos-nigeria. table 2. morphometric measurements in liza falcipinnis from ojo axis of badagry creek, nigeria morphometric measurements (mm)l combined sex(n = 1012) males(n = 513) females(n = 499) range mean±sd range mean±sd range mean±sd min max min max min max eye diameter (ed) 0.5 2.5 1.23±0.1 0.7 2.6 1.13±0.22 0.5 2.5 1.34±0.68 head length (hl) 2.1 12 4.63±0.5 2.1 10.4 4.25±0.94 2.5 12 5.03±1.23 head depth (hd) 1.7 8.1 3.56±0.4 1.7 7.7 3.27±0.75 2.0 8.1 3.85±0.86 body depth (bd) 2.5 11.7 4.68±0.5 2.5 9.7 4.35±0.87 2.6 11.7 5.02±1.1 total length (tl) 2.6 233.3 24.95±2.8 12.5 44.4 21.78±4.88 2.6 233.3 26.19±10.6 body weight (g) 9.23 1006 121.7±55.1 9.23 700 107.1±40.6 15.6 1006 134.6±62.9 http://dx.doi.org/10.36956/sms.v3i2.434 44 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 figure 6. length-weight relationship of male liza falzipinnis from ojo axis of badagry creek 4.3 length frequency analysis fish total length measurements were categorized into 21 modal classes for combined sexes which showed a bi modal distribution of liza falcipinnis from ojo axis of badagry creek. the cohort were from 1.9 cm to 39.9 cm (tl). the modal length was from 17.19 cm to 19 cm and 22.8 cm to 24.7 cm for combined sexes with frequency of 17.8% of the population and 17.5%. the distribution of species in the population skewed more to the right, this means that they were larger fish species in the sampled population. there was large number of fish between 17.1 cm and 19 cm and between 22.8 cm to 24.7 cm (tl). two age groups (age 1 and 2) were obtained from the sampled population which was ascertained from the modal distribution of length frequency histogram in figure 7[a] for combined sex of liza falcipinnis from ojo axis of badagry creek lagos nigeria. total length measurement for female liza falcipinnis were categorized into 18 modal classes as shown in figure 7[b]. the cohort were from 2.2 cm to 39.6 cm (tl). modal length was from 24.2 cm to 26.4 cm with frequency of 14.3% of the population. there were large numbers of fish between 24.2 cm and 26.4 cm. two age groups (age 1 and 2) were also obtained from the sampled population through the length frequency histogram (figure 7). the total length measurement for male liza falcipinnis from ojo axis of badagry creek were categorized into 21 modal classes (figure 7c). the cohort were from 0.1 cm to 46.2 cm. modal lengths were from 19.8 cm to 22 cm with frequency of 9.1% of the population. there was a large number of fish between 17.6 cm and 22 cm. two age group from the sampled population were observed in length frequency histogram. 4.4 condition factor the condition factor of the combined sex is shown and elucidated in table 2 and it showed that the fish were not in good condition with the lowest condition factor of 0.68 (dec., 2019) while the highest condition was 0.85 (june, 2020). these values showed that the female liza falcipinnis from ojo axis of badagry creek were in better condition. the females gained more weight than the males. the females had the best condition in february (0.83) and the poorest condition in october (0.69), the males had a better relative increase of condition which was observed in june 2019 and low condition in november 2019 (0.68). 4.5 sex ratio samples of liza falcipinnis from ojo axis of badagry creek showed differences in the distribution in term of sexual dimorphism (distribution of male and female species). this is shown in table 4. sexual differences were observed throughout the year. the males were numerically more dominant than the female (p<0.05) in may table 3. summary of monthly morphometric analysis, length-weight relationship and condition factors of liza falcipinnis from ojo axis of badagry creek, lagos. (2019 2020) months combine sexes females males mean length mean weight a b r2 k mean length mean weight a b r2 k mean length mean weight a b r2 k may 15.91 35.19 8.92 0.1 0.86 0.83 15.89 34.29 8.68 0.11 0.96 0.81 15.92 35.7 9.05 0.1 0.82 0.83 june 19.83 69.62 10.52 0.07 0.77 0.85 22.72 95.64 11.25 0.06 0.55 0,79 18.98 62.02 10.38 0.07 0.79 0.86 july 20.73 82.19 11.71 0.05 0.85 0.81 24.67 127.10 13.73 0.04 0.91 0.79 19.08 63.25 11.1 0.06 0.81 0.83 august 24.60 115.01 8.97 0.1 0.85 0.76 26.56 137.4 11.52 0.09 0.83 0.73 22.87 95.26 5.72 0.14 0.82 0.8 september 23.37 102.87 8.13 0.1 0.71 0.81 23.64 104.86 7.64 0.11 0.73 0.79 22.97 99.8 9.13 0.1 0.68 0.82 october 26.21 130.08 10.48 0.1 0.77 0.70 26.28 131.68 10.96 0.09 0.72 0.69 26.08 127.27 9.82 0.1 0.85 0.71 november 27.64 150.42 17.59 0.05 0.60 0.72 27.32 147.32 17.05 0.05 0.83 0.73 28.42 157.79 19.87 0.03 0.16 0.69 december 27.19 137.72 16.52 0.06 0.89 0.68 27.21 138.37 16.58 0.06 0.87 0.68 27.15 136.17 16.44 0.06 0.93 0.68 january 30.54 155.45 17.60 0.04 0.66 0.70 31.74 152.98 17.94 0.04 0.68 0.69 27.63 161.44 16.59 0.05 0.64 0.74 february 28.04 247.39 16.98 0.02 0.78 0.82 29.95 296.09 18.20 0.02 0.79 0.83 23.39 128.57 13.61 0.04 0.85 0.81 march 24.48 112.63 11.34 0.07 0.46 0.77 24.34 114.88 10.97 0.07 0.65 0.79 24.56 111.18 11.46 0.08 0.42 0.75 note: lwr = length-weight relationship, a = intercept, b = slope of graph, r = correlation coefficient, k-factor = condition factor, mean length in cm and mean weight in grams http://dx.doi.org/10.36956/sms.v3i2.434 45 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 (2.0: 1.0), june (3.4: 1.0), july (2.4: 1.0), august (1.1: 1.0), 2019 and march (1.5: 1.0), 2020. the monthly sex ratio analysis (male: female) is in favour of the females; in september (1:1.3), october (1:1.8), november (1:2.4), december (1:2.4), january (1:2.3) and february (1:2.4). however, the chi-square analysis (table 4) revealed a rejection of the null hypothesis [there were no differences in sex distribution] (p<0.05), because the chi calculated (xcal) values were significantly higher than chi tabulated (x tab) for most part of the period of study; except for the months of august (0.38), and september (1.33), as against the chi tab of 3.841. figure 7. length frequency distribution (histogram) of combined sexes [a], male [b] and females [c]; liza falcipinnis from ojo axis of badagry creek, lagos, nigeria. 4.6 gonadosomatic index (gsi) and spawning period the monthly gonadosomatic index (gsi) values for female liza falcipinnis from ojo axis of badagry creek is shown in table 5. gsi values varied from 0.73 6.16 (2.3±2.79) in may, 0.17 10.12 (1.75±5.35) in june, 0.1 3.84 (1.27±1.91) in july, 0.24 17.77 (2.88±9.45) in august, 0.19 1.81 (0.92±0.81) in september, 0.4 4.78 (1.56±2.27) in october, 0.6 5.39 (2.05±2.46) in november, 0.78 8.24 (3.27±3.8) in december, 2019; 0.13 8.6 (2.18±4.42) in january, 0.14 9.97 (2.15+5.19) in february, and 0.47 10.03 (3.28±4.91) in march, 2020 respectively. gsi value for the female were found to vary with time (monthly) and the highest index observed was in august, 2019 (17.77) with mean of 2.88±0.75 and the lowest in july, 2019 (0.1) with mean of 1.27±0.01. table 4. sex distribution, ratio and chi-square analysis of liza falcipinnis in the monthly samples from ojo axis of badagry creek, lagos months no. of fish combined sexes e no. of males (o) no. of females (o) sex ratio m:f e male e female x2 cal x2 tab at [p<0.05 may 74 37 47 27 2.0:1.0 2.70 2.70 5.41 3.841 june 146 73 113 33 3.4:1.0 21.92 21.92 43.84 3.841 july 119 59.5 84 35 2.4:1.0 10.09 10.09 20.18 3.841 august 96 48 51 45 1.1:1.0 0.19 0.19 0.38 3.841 september 91 45.5 40 51 1.0:1.3 0.66 0.66 1.33 3.841 october 94 47 34 60 1.0:1.8 3.60 3.60 7.19 3.841 november 54 27 16 38 1.0:2.4 4.48 4.48 8.96 3.841 december 88 44 26 62 1.0:2.4 7.36 7.36 14.73 3.841 january 73 36.5 22 51 1.0:2.3 5.76 5.76 11.52 3.841 february 86 43 25 61 1.0:2.4 7.53 7.53 15.07 3.841 march 91 45.5 55 36 1.5:1.0 1.98 1.98 3.97 3.841 note: e = expected, o = observed, x2 = chi-square, x2tab = tabulated chi square < 0.05 confidence limit and x 2 cal = chi-square calculated http://dx.doi.org/10.36956/sms.v3i2.434 46 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 table 5. monthly gsi for female liza falcipinnis in ojo axis badagry creek, lagos months min gsi max gsi mean gsi+sd may 0.73 6.16 2.3±2.79 june 0.17 10.12 1.75±5.35 july 0.1 3.84 1.27±1.91 august 0.24 17.77 2.88±9.45 september 0.19 1.81 0.92±0.81 october 0.4 4.78 1.56±2.27 november 0.6 5.39 2.05±2.46 december 0.78 8.24 3.27±3.8 january 0.13 8.6 2.18±4.42 february 0.14 9.97 2.15±5.19 march 0.47 10.03 3.28±4.91 5. discussion relative high abundance of liza falcipinnis in ojo axis of badagry creek was observed in the study, during the study period. although, the total number caught for each month varied (as shown in table 1) and this can be related to seasonal changes, fishing activities, recruitment, availability of food and changes in the behaviour of the fish. this opinion was shared by [28] who worked on the biology of two species of catfishes: synodontis schall and synodontis nigrita from queue river, benin. they reported that high species yield in catches during april and may corresponds to the beginning of rainy season, when food availability is highest due to flood introducing nutrients and mixing of water by rapid currents. such ecological situations are favourable to fishes and may cause them to venture out of their hidden crevices making them vulnerable for fishing. the current study reveals that the highest catches by number was in june and july 2019. this result corresponds with the above result as reviewed. increase in fish abundance due to the combination of physiochemical properties and presence of food items has been reported by [11]. however, catches in weight was contrasted to catches in number, which showed that there is overfishing in the study area. morphometric and meristic characters were studied on liza falcipinnis, 6 morphometrics and 4 meristic characters were examined for each sex. it was compared to find out the phenotypic differences in the population (table 2). the morphometric measurements between male and female liza falcipinnis showed some slight variations, but not sufficient to discriminate between male and female sexes. the male and female individuals showed similarities with each other with respect to all morphological characteristics. the variation between both sexes revealed that the female exhibited higher measurement values than that of the male which was supported by [24] who observed similar results. the present study revealed that though some variations were observed in each morphometric and meristic characters between sexes, but such variations or differences were insignificant (p<0.05). therefore, this indicated a negligible effect of sex on variations in the morphometric and meristic characters. this report agrees with [34]. the above data indicates that the female sex is phenotypically larger than the male. [34] and [8] reported that both meristic and morphometric character of fish maybe influenced by certain environmental factors e.g. turbidity, food availability, temperature, therefore variation showed in the present study on morphological characters among male and female of liza falcipinnis might be as a result of differences in the environmental condition of the habitat, availability of food, sample size, sex condition, sexual maturity; all these may lead to produce the phenotypic differences between the male and female sexes of species as previously corroborated by some workers including [29], [17] and [13]. growth of fish can be described as either allometric or isometric depending on the value of ‘b’ (regression coefficient). the b value of liza falcipinnis from ojo axis badagry creek were 0.04, 0.01 and 0.02 for combined, male, and female sexes respectively. this indicated that the fish exhibited a negative allometric growth pattern which shows that the species under this study became thinner as they grew longer. the results also showed that the species are in poor condition and were not robust enough, relative to its length. similarly, to [15] who reported a weak correlation coefficient (r) for australian mullet with r = 0.87 for males and 0.86 for females. in this current study, the r2 values were 0.54 for combined sexes, 0.16 for females and 0.38 for males, showing a strong relationship between total length and body weight measurements of the fish. though, there was increase in total length with corresponding increase in bodyweight; the general condition of the species in the study area are considered slightly weak. length weight relationship are useful tools for fisheries research because they allow the conversion of growth in length equation to growth in weight for use in stock assessment model, and allows for the estimation of biomass from length observation, also, the estimate of the condition of the fish and are useful tools for regional comparism of life histories of certain species [25]. the condition factor of fish is regarded as the fitness or relative well-being of the fish. it indicates the general metabolism of fish. these values indicated poor well-being of the assessed fish. [7] related low condition to the period when accumulated fat is used for spawning, while high values indicate a period of increase rate of feeding followed by a gradual increase in accumulated fat, which suggest preparation for a new reproductive period. this http://dx.doi.org/10.36956/sms.v3i2.434 47 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 result is similar to the report of [24] on the same species from badagry creek. he reported condition value of 0.0079, 0.0087, 0.0097 for immature, males, and females respectively. he therefore suggested that the reason for low condition of liza falcipinnis from badagry creek is due to ecological and environmental factors and also an indication of how well the species is in this water body. the value for condition factor in this study varied slightly between the male and female fish. the slight variation could be attributed to food availability, gonad development and gender of fish [30,16]. the length frequency distribution of all the species were not having equal interval due to the presence of small sized fish in the assessed population. the length frequency distribution graph (figure 7a, 7b and 7c) indicated that the liza falcipinnis from ojo axis of badagry creek were dominated by two modal lengths or year classes or age groups/cohorts (representing ages 1 and 2). for combined sexes, the sampled population was dominated by fish of length 24.2 26.4 cm, while the male population was dominated by fish of length 19.6 22 cm. this observation implies that the females have bigger dominant sizes within the population. gonadosomatic index is one of the essential parameters in studying the reproductive biology of the fish. it’s used to describe the gonadal stage or development/ spawning stage/level of ripeness of the ovary in the different sexes of fish. in this study, the gonadosomatic index (gsi) for female liza falcipinnis from ojo axis of badagry creek was studied between may 2019 to march, 2020. the gsi was highest in august 2019 with 17.77% (as shown in figure 3) which indicated the peak of spawning in this species in the study area. figure 3 shows that gonadal maturation actually began in june (2019) and was completed in august (2019) which coincides with the peak period of rain season. it decreased thereafter from september (2019) to november (2019) showing a period of sexual rest. [10] reported that gonadal maturity began in september (dry season) and was completed in november (rain season) for the same species from two lagoons in cote d-ivoire and this coincide with flood season of the area and thus creates an ideal condition for the survival of larval and fingerlings due to abundance of food. during flood season nutrients are drained by the rich run-off in organic matter, the decomposition of organic matter enriches the environment in mineral salts which will lead to proliferation of algae according to [20]. the availability of food during this period is utilized by the larvae therefore they do not have to travel long distance in search of food as opined by [26]. sexual dimorphism or unbalanced sex ratio in the mullet has been observed by several authors: [24,1,5] amongst others. the prevalence of one of the sexes is a relatively frequent phenomenon in many teleosts and this could come from differential growth according to sex. in the current study, the males were dominant in may, june, july, august, 2019, and march, 2020. (2:1, 3.4:1, 2.4:1, 1.1:1, and 1.5:1 respectively). the variation was an indication that sex was in favour of the males during this period. sex ratio that favoured the females may account for its reproductive success in ojo axis of badagry creek. the female sex was dominant in september, october, november, december, 2019, january and february, 2020. (1:1.3, 1:1.8, 1:2.4, 1:2.4, 1:2.3, 1:2.4 male: female respectively). [10] also reported the dominance of female liza falcipinnis from ebrie and grand-lahou lagoon. he stated that the reason may be due to higher mortality of the male at larva stage and less accessibility of the male due to ethological differences related to sex. according to [6] and [17] the female mugilidae reaches sexual maturity at larger size than the male. 6. conclusions the implication of the results is that fish abundance (by number) in june and july, 2019 prompted more fishing activities leading to recruitment overfishing and growth overfishing. sexual differences in relation to seasonal abundance were clearly observed and highlighted. the female sex is phenotypically larger than the male. the report thus concludes that both meristic and morphometric characters of fish maybe influenced by certain environmental factors. the growth of the species was negatively allormetric. there was increase in total length with corresponding increase in bodyweight; but the general condition of the species in the study area are considered slightly weak. the results are essential because they allow the conversion of growth in length equation to growth in weight for use in stock assessment model. the values of condition factor indicate poor well-being of the assessed fish. the males were dominant in may, june, july, august, 2019, and march, 2020. the sex variation showed that sex was in favour of the males during some period. sex ratio favoured the females during reproductive periods which coincides with the months of september, october, november, december, 2019, january and february, 2020 in the study area. the gsi was the highest in august 2019 with 17.77%. gonadal maturation actually began in june (2019) and was completed in august (2019) which coincides with the peak period of rain season. http://dx.doi.org/10.36956/sms.v3i2.434 48 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 references [1] abou-seedo, f. & dadzie, s. 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[18] idowu, e.o., (2017): aspects of the biology of hepsetus odoe in ado-ekiti reservoir ekiti, nigeria ph.d thesis, university of ibadan, ibadan. [19] king, r.p. (1995): length-weight relationships of nigerian coastal water fishes. naga iclarm quarterly; 19(4):53-58. [20] komoé, k. (2010): distribution of phytoplankton in the complex lagoon; de grand-lahou (côte d’ivoire). thèse de doctorat. université abidjan cocody. 341 p. [21] kurian, a. (1975): the identification of grey mullet species by disc electrophoresis. aquaculture 5:99106. [22] lagler, k. f., miller, j. e., may, r. r. and passino, d. r. (1977): ichthyology. 2nd edition.wiley and sons inc., new york, 505 p. [23] lawson, e.o., jimoh, a.a. (2010): aspects of the biology of grey mullet, mugil cephalus, in lagos lagoon, nigeria. aacl bioflux; 3 (3): 181-193. [24] lawson, e.o., akintola, s.o., olatunde, o.a. (2010): aspects of the biology of sickle fin mullet, liza falcipinnis (valenciennes, 1836) from badagry creek, lagos, nigeria. nature and sciences; 8(11): 168-182. [25] montoupolos, d.k., stergious, k.i. (2000): weightlength and length-length relationships for 40 fish http://dx.doi.org/10.36956/sms.v3i2.434 49 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 species of the aegean sea (hellas). journal of applied ichthyology: 21:23-45. [26] offem, b.o., adegbejo-samsons, y., and omoniyi, i.j. (2007): biological assessment of oreochromis niloticus (pisces: cichlida, linne, 1958) in a tropical flood plain river. african journal of biotechnology, 6 (16). [27] oribhabor, b.j., ogbeigbu, a.e., udo, m.t. (2011): the length-weight relationship of brackish water/ marine fish species assemblage in niger delta mangrove creek, nigeria. current research journal of biological science. 3(6):616-21. [28] philippe, a. laleye. (2006) length-weight and length-length relationships of fishes from the ouémé river in bénin (west africa). [29] poulet, n. y., reyjol, h., collier and s. lek. (2005): does fish scale morphology allow the identification of population at a local scale? a case study for rostrum dace, leuciscus burdigalensis in river viaur (sw france). aquatic sciences, 67(1): 122-127. [30] quilang, j.p., basiao, z.u., pagulayan, r.c., roderos, r.r. and barios, e.b. (2007): meristic and morphometric variation in the silver perch, leiopotherapon plumbeus (kner, 1864), from three lakes in the philippines. journal of applied. ichthyology, 23(5): 561-567. [31] robert, b.i. & jessa, h.o. (2003): studies on aspects of the biology of tilapia mariae (boulenger,1899) (osteichthyes cichlidae) in ethiope river, niger delta, nigeria. african zoology, 38 (2): 255 264. [32] sakar, u.k., khan, g.e., dabas, a., palhak, a.k., mir, j.i., rebello, j.c., pal, a. and singh, s.p. (2013): length-weight relationship and condition factor of selected freshwater fish species found in river ganga, gomti and rapti. india journal of environmental biology.; 23:123-32. [33] sinovcic, g., franicevic, m., zorica, b. and cileskec, v. (2004): length-weight and length-length relationships for 10 pelagic fish species from the adriatic sea. (crotia). j. appl. ichthyol. 20: 156158. [34] turan, c., s. yalcin, f., turan, e., okur, and i. akyurt ,(2005): morphometric comparisons of african catfish, clarias gariepinus, populations in turkey. folia zoologica, 54(1-2): 165-172. http://dx.doi.org/10.36956/sms.v3i2.434 1 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 copyright journal of architectural environment & structural engineering research is licensed under a creative commons-non-commercial 4.0 international copyright (cc bync4.0). readers shall have the right to copy and distribute articles in this journal in any form in any medium, and may also modify, convert or create on the basis of articles. in sharing and using articles in this journal, the user must indicate the author and source, and mark the changes made in articles. copyright © bilingual publishing co. all rights reserved. http://dx.doi.org/10.36956/sms.v3i2.431 sustainable marine structures http://ojs.nassg.org/index.php/sms/index article on the impact of brazil's largest recent oil spill on regional oceans liana de figueiredo mendes1 patrícia pinheiro beck eichler2,3* tatiana leite4 ana beatriz alves bennemann1 clara de souza melo1 andressa lima ferreira2,3 khalil bow ltaif garcia2 luzia liniane do nascimento silva2 christofer paul barker3 helenice vital2 moab praxedes gomes2 priscila f. m. lopes1 1. department of ecology, federal university of rio grande do norte (ufrn), university campus, lagoa nova, 59072970 natal, rn, brazil 2. graduate program in geodynamics and geophysics (ppgg), laboratory of marine geology and geophysics and environmental monitoring, federal university of rio grande do norte (ufrn), university campos, lagoa nova, 59072970 natal, rn, brazil 3. www.ecologicproject.com (california, usa) 4. department of ecology and zoology, federal university of santa catarina, trindade, 88040-900, florianópolis, sc, brazil article info abstract article history received: 5 august 2021 accepted: 28 august 2021 published online: 10 september 2021 in 2019, an oil spill in brazil, of unknown origin, severely impacted coastal environs with the worst environmental disaster ever recorded in any tropical coastal region globally severely damaging south pirangi reef area in the state of rio grande do norte (rn). here we discuss acute and chronic impacts including chemical contamination and economic consequences all over the world and show some evidence of the oil spill in this biodiverse area. moreover, the lapse between the moment of the disaster, and the action to manage it, was hampered by a political agenda coinciding with local and global tragedies that redirected public attention. meanwhile almost 2 years have passed still without the offending party identification or culpability; and poor communities may continue to absorb its deleterious impacts for decades without consideration or compensation. this disaster occurred during the brazilian government’s current issues involving extensive environmental mismanagement, resulting in a slow response from an inept system. it is with urgent necessity to spotlight this tragedy in this unique and sensitive reef habitat experiencing the ongoing damaging effects that include socio-economic losses not yet addressed. keywords: environmental impacts socioeconomic losses government brazilian coast oil spill disaster 　 *corresponding author: patrícia pinheiro beck eichler, graduate program in geodynamics and geophysics (ppgg), laboratory of marine geology and geophysics and environmental monitoring, federal university of rio grande do norte (ufrn), university campos, lagoa nova, 59072-970 natal, rn, brazil; email: patriciaeichler@gmail.com 1. introduction in late july 2019, brazil passively witnessed its first major oil spill disaster, quickly reaching about 3000 km of the country’s northeast coast [1-5], which holds one of the main marine diversity areas in the south atlantic [6]. although the peak of the spill seems to have been in september [7], the oil arrived on beaches and in estuaries until 2 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 at least the end of 2019 (figure 1). due to currents, local hydrodynamics and geography, the oil quickly spread into a north and a south branch [8], traveling via the subsurface (between 50 cm and 1 m deep). it reached at least nine northeastern states [9] affecting about 55 marine protected areas [3]. to a lesser extent, the oil also arrived at two additional states in the southeast of brazil. such an impact, duration and extension explain why this spill is considered the worst environmental oil disaster ever recorded in tropical coastal regions [3]. figure 1. a) locations affected by the oil spill along the brazilian coast (updated in 03/19/2020). b) sergipe state. c) maraú, bahia state. source: http://www.ibama.gov.br/manchasdeoleo-localidadesatingidas. examples from brazilian northeastern sites affected by the oil spill: source: http://www.ibama.gov.br/manchasdeoleo-galeria. the crude oil spilled was formed by a complex chemical mixture of thousands of hydrocarbon-type compounds and small amounts of chelated heavy metals [10]. the origin of the spill itself remains a mystery even two years later! a significant amount of oil has been removed from the beaches, totaling about 5000 tons, in an effort coordinated by state institutions, the navy and ibama (brazilian institute of the environment), but especially pioneered by the civil society volunteers [11]. apart from the less visible environmental consequences, such as the accumulation of hydrocarbons in the food chain as of january 15, 2020, at least 159 oiled animals had been reported, of which 112 were found dead [12]. in according to [13] the spill probably occurred by buoyancy problems on the tanker losing its cargo. they hypothesis that the leak was caused by tanker buoyancy problems (hull rupture or engine failure) results in leak or dumping of a part of its cargo in the subsurface waters. the estimated volume (5000-12,500 m3) was similar to what was expected in a continuous leak from an internal compartment tanker with the size between panamax and suezmax. in addition to immediate and visible consequences, such as habitat pollution and the death of oiled animals, oil spill disasters have multiple short and long-term consequences on entire social and ecological systems that rely on the now contaminated environment. as such, oil spills should be approached in a broad, integrated and multidisciplinary way. integrated scientific approaches should include disciplines and topics such as oceanography (chemistry, physics, and biology), ecology, spatial modeling, geology, toxicology, epidemiology, microbiology, fisheries, sociology, psychology and economics. if properly implemented, such an approach could provide more effective mitigation pathways and help develop strategies to avoid future disasters, and aid in decision and policymaking [14]. given the tools and technology available to prevent, deal with and mitigate spills, it is surprising that such a disaster did not merit a transparent cooperative approach in brazil. the government first ignored the warnings, and then dismissed the criticism regarding its inaction and dismantling of environmental policies, including specific measures to deal with oil spills, and then finally it ideologized the debate. in the end, it acted only when confronted by the federal prosecution service [11], and after the media started registering the risks that marine-dependent people and volunteers were exposing themselves to while cleaning the beaches. still, the federal measures were limited to cleaning the beaches and releasing insufficient funding for research, which was supplemented by more supportive technical and financial help from the affected states. brazil has opted for the easy way out hoping the problem either will disappear on its own or be forgotten as the more visible impacts fade away. this strategy may be facilitated, as the burden of contamination will be heavier on more vulnerable and powerless segments of the population, such as fishers and gleaners. these kinds of articles on the oil spill along the brazilian coast in 2019 have shown that the response from brazil’s government to this disaster was slow, late, and with flawed remediation plans. even though some of these important articles report the largest accident, they lack policies and research regarding severity of oil spills, environmental toxicity of the oil, and acute and chronic toxicity to communities (figure 2). besides that, the adverse impacts of the oil spill disaster upon brazil’s environment, economy and society were previously described mostly in portuguese [4,7,15-17] which unfortunately lacks international outreach and visibility. fewer articles, with more impact [2,4,13,18-22] have brought to attention information on the oil spill along brazil’s northeast and southeast seaboard, trying to find answers and fill data gaps on the geochemistry and identification of the source of the oily material. discussion about environmental monitoring and response measures that must be implemented to minimize the ecological, economic, and social http://dx.doi.org/10.36956/sms.v3i2.431 3 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 effects of the spill; which is particularly relevant in areas with high tropical biodiversity while experiencing high social inequality, which is presently the case of this northeastern accident in according to [3]. even more recently, [23] argue that there is still a clear need for coordinated state interventions to mitigation the impacts, considering it’s environmental, social, economic, human health and political dimensions even now, two years later. they have conducted focus meeting discussions with fishing communities in alagoas (one of the most severely impacted states) to assess the local perceptions on the oil spill impacts and they estimate the impact of the oil spill on income generation and food security of coastal communities. the authors also analyzed the government action to handle such impacts and propose a set of recommendations to help alleviate the dramatic effects of this environmental disaster and to prepare for future ones. figure 2. map showing area of affected area and the acute damages on the plankton, nekton, benthos, water and sediment. almost 2 years later now, here we show that basic questions remain unanswered, including the scope of the ecological and social impacts of this spill. it is necessary to understand the dimension of these impacts, how long they are expected to last, anticipate collateral damages, and then propose mitigation options and mechanisms to reduce the magnitude of any future spill. as the oil becomes less and less visible to the naked eye, and the world is ravaged by new disasters (e.g. covid-19 pandemic), and it is easy to let the largest oil spill in the south atlantic fall into oblivion, leaving it to nature and for local human communities to bear its consequences for the decades to come. our paper deals with a specific site, the “pirangi reef area”, which was subjected to the oil spill in october 2019, and was previously studied in 2013 and 2014 with no spotting of oil patches in the sediment or in the water [24]. after the oil spill, we sampled new sites to compare and discuss questions on the human-induced changes on the reef system; therefore, water and surface sediments were recovered from areas of small reef patches near tourism boating sites. 2. background on oil impacts over marine ecosystems the release of hydrocarbons from oil spills into marine environments has immediate and acute effects on living organisms. in addition, chronic contamination has an effect over time as hydrogen sulphide, methane and ammonia are released in the environment acidifying the water-sediment interface. dealing effectively with these impacts includes understanding how pollutants and contaminants in general are released and how they behave in the environment [25]. for example, hydrocarbon petroleum products are quite reactive in aerobic environments via microbial and photochemical reactions [26-29], and the production of hydrogen sulphide (h2s) is a result of the microbial breakdown of organic materials of crude oil in the absence of oxygen. hydrogen sulphide is a gas without color, and is flammable, poisonous and corrosive, noticeable by its rotten egg smell and with toxicity similar to carbon monoxide prevents cellular respiration. monitoring and early detection of h2s could mean the difference between life and death. the contamination impact in the medium and long term is a silent one caused by oil being partially degraded and absorbed by the environment. concentrations of pahs sufficient to affect individual health following oil spills are common and can remain for long periods in some habitats [30,31]. the polycyclic aromatic hydrocarbons (pahs) present in oil are immunotoxic to several wild aquatic species. the effects of immune toxicity include damage to the resistance of organisms, making them more subject to new diseases and increased parasitism, delaying population recovery [32], and teleost fish embryo is particularly sensitive to pahs causing problems related to cardiac development [30]. a significant amount of oil (between 10 to 30%) has been found on the surface of marine substrates, increasing acute epifauna and infauna mortality by contamination and asphyxiation. the organisms that do not die may chronically incorporate the toxic substance in their tissues, http://dx.doi.org/10.36956/sms.v3i2.431 4 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 which then accumulates along the food chain [25]. another serious consequence of crude oil in the sediment is the acidification and subsequent dissolution of calcium carbonate shells, ranging from microorganisms (foraminifera) to macro organisms (mollusks) as already evidenced by [24]. studies on the catastrophic deepwater horizon (dwh) event in the gulf of mexico (gom), in april 2010, which showed that the composition/accumulation of oil on the seabed was strongly influenced by sediment, texture, composition and sedimentary processes and accumulation rates [14]. it is known that certain types of oil will affect sedimentation in different ways. heavier and thicker types of oil, which is the type identified in the brazilian spill, are expected to settle on the substrate. oil sedimentation may increase if the oil mixes with sand and sinks [25], which is again the case of brazil’s coast where the oil has extensively affected its sand beaches. a variety of immediately known effects can be identified from organisms directly exposed to oil, such as oilsoaked birds and turtles. ingestion, direct contact and oiling are part of the immediate threats compromising and affecting animal digestion, and causing eye and nostril irritation, in addition to inhalation of toxic vapors, asphyxiation and suffocation. particles dispersed in water accumulates in the most sensitive epithelial tissue, such as gills and mucous membranes, obstructing and causing tissue degeneration. filter feeder animals, such as bivalves, can ingest enough oil to the point of incapacitating their feeding. other larger benthic animals such as octopuses, lobsters and morays that live in burrows and use them as shelter are most directly affected by the direct oil contact. organisms with oiled gills are unable to obtain enough body oxygenation and soluble hydrocarbons enters the bloodstream through the respiratory tract. another effect of oil dispersion into the open sea refers to the influence on plankton surface layers. plankton is the first element in the food chain, supporting a considerable diversity of marine mammals, fish and invertebrates (table 1) [12,25,33-36]. hydrocarbon bioaccumulation is one of the major concerns when an oil spill occurs, but many of the components of oil and petroleum products are biodegradable at some level of the food chain [25] and evidences of the bioaccumulation phenomenon is scarce but can occur [37]. however, it is known that fish are especially sensitive to petrogenic compounds in their early stages of life (cardiotoxicity, phototoxicity), in addition to the carcinogenicity of pahs and their impacts on the metabolic, immune and reproductive systems [38]. considering the worldwide scenario of pollutants that are being discarded in the seas, contamination and chemical analysis is mandatory to continue investigations to guarantee the health of ecosystems. the dimension of the environmental coastal impacts caused by oil spills also depends on the type of coast. the sensitivity of different substrates to oil varies considerably, from rocky shores to gravel beaches, sand, fine sand, mangroves, and coral reefs [25,37]. the oil that hit the brazilian northeast coast, especially visible on sandy beaches, had an immediate and acute impact on the marine life of the intertidal zone. however, the extent of the coast affected included a great diversity of ecosystems beyond sand beaches, including estuaries, mangroves, reefs, coastal lagoons, riverbanks, etc. the prompt response of volunteers, and later of the government, removed much of the large and more visible patches of oil from the beaches. however, the days and months that followed the peak of the spill were marked by reports of people returning home with their feet stained with oil after walking on apparently clean beaches. smaller particles of oil on the sand can reach an extremely diverse benthic community, including mega, macro and half fauna formed by crustacean, polychaeta, nematodes and mollusks [39,40]. these animals are the also low on the benthic trophic chain and make the link with other environments through feeding various animals in the water column; and the level of contamination in the trophic web needs further investigation. in addition to the widely affected sandy beaches, the oil reached a range of habitats, from rocky outcrops to some highly vulnerable ones, such as mangroves, estuaries and reefs. these are not homogeneous habitats; they are subject to peculiar local coastal hydrodynamic regimes and present distinctions regarding shape, size and nature of their substrate. rocky outcrops, for instance, can be severely affected, especially through the accumulation of thick layers of oil on their emerged portions where puddles rich in flora and fauna are formed [25]. although yet to be fully quantified and assessed, preliminary evidence suggests that the abundant brazilian northeastern rocky outcrops have undergone a similar oil accumulation process. mangroves, in turn, are sheltered ecosystems with low hydrodynamics, a scenario that favors the accumulation of fine sediments retaining contaminants for long periods. they are particularly sensitive to this type of pollution, first because the breathing of their aerial roots can be seriously impaired by a thin oil layer. secondly, mangroves host numerous permanent and seasonal species. many of these species, including some of commercial interest to fisheries, use the mangroves as nursery sites, spending sensitive periods of their life cycle there [25,41]. in addition, due to the important connectivity of species in the marine http://dx.doi.org/10.36956/sms.v3i2.431 5 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 table 1. possible effects of contamination on marine biota on the coast affected by the south atlantic oil spill, considering duration of the effect (permanence) due to the gradual transformation and degradation of the oil and occurrence chance. effect reason reason based on local reality permanence (short, medium or long term) occurrence chance reference supporting the listed effect damage or animal death by oiling oiling, covering and oil adhesion are very common in birds, turtles and marine mammals. these animals depend on regular contact with the water surface for feeding or surface breathing. approximately 130 oiled animals were registered in the first 4 months of the oil's arrival, about 90 sea turtles and 40 birds. there is no previous record of oiled mammals. short *** (cedre 2007; ibama, 2019b; shigenaka & milton 2003; fry & lowenstine 1985) damage or animal death by direct contact with oil particles oil particles can accumulate on epithelial tissue on gills, mucous membranes, clogging and damage them. filter animals such as mollusks can suffer a toxic effect making them incapable of feeding. organisms with oiled gills cannot accomplish oxygen exchange; soluble hydrocarbons can enter the bloodstream through the respiratory tract. the toxicity can be acute, for example with rapid death of organisms by ingestion. other effects occur when the organism’s survival capacity decreases due to decreased growth and reproduction rate. the presence of oil was recorded in several filter mollusks such as oysters (crassostrea spp.), in the gills and digestive tract of fishes, legs and mouth area of crabs. short, medium and long term *** (cedre 2007; ibama, 2019b; viñas et al., 2009; law & hellou, 1999; uno et al., 2017; fleeger et al., 2003) chemical contamination causing malfunction in marine organisms and ecosystem polycyclic aromatic hydrocarbons (pahs) are the most toxic components of oil spills, mainly which are soluble and quickly available for marine organisms. this toxicity is the result of formation of metabolites by organisms which are associated with the dna resulting in organism malfunctioning. cardiotoxicity, phototoxicity and carcinogenicity in fish early stages of life not recorded. insufficient research. medium and long term * cedre 2007; jeong et al., 2015; pérezcadahía et al., 2004; collier et al 2013; johnston & roberts, 2009; johnston et al, 2015; cesar et al, 2014; venturini & tommasi, 2004; venturini et al, 2008; camargo et al., 2017. the occurrence chance is based on the expert opinion of the authors associated with what is known in the literature (* little evidence in the literature; ** some evidence; *** strong evidence). by default, regional impacts are also local, while national impacts are local and regional. http://dx.doi.org/10.36956/sms.v3i2.431 6 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 environment, the oil pollution of mangroves can affect ecological productivity in the short, medium and longterm, compromising the biodiversity in general, and in fisheries in particular. reef coral ecosystems are protected by mucus secreted by their polyps and can withstand small isolated oil accidents, especially because a protective layer of water usually remains between the corals and the smooth oil surface. however, depending on the type of incident (intensity and repetition) and the polluting agent, these invertebrates can suffocate [25]. studies that modeled the distribution, destination and effects of oil, associated with toxicity tests of various species, suggested that more thorough conclusions about the damages caused by oil spills to natural resources is only elucidated after several years of monitoring and information [42]. poor cleaning, negligent monitoring and insufficient research, as brazil has demonstrated, will not only delay conclusions, but also provide insufficient and inconclusive data. some effects of contamination on marine biota are shown in table 1. 3. socioeconomic impacts oil spills also have significant consequences on human livelihoods, by affecting social, cultural and economic activities (table 2). coastal tourism is immediately affected by tourists afraid of possible health effects caused by direct contact with oil [43]. coastal tourism is one of the main economic activities in the brazilian tourism sector, given the country’s permanent favorable weather, especially in the northeast. according to anecdotic information from the media, hotels and tourist activities were greatly impacted at the peak of the spill when the oil was clearly visible in the sea and on the beaches [44]. as the oil reached the mangroves, aquaculture, especially exotic white shrimp (litopenaeus vannamei), and salt production were affected as well. the northeast is the main exporter of brazilian shrimp [45] and produces 98% of brazilian salt [46]. although it is yet to be quantified, the economic effects on tourist operators, farmers and salt businesses are expected to be less damaged than on artisanal fishermen and their families which are among the most economically vulnerable coastal groups [47]. while larger businesses can possibly endure some level of economic hardship caused by such a disaster, this is often not the case for the local subsistence communities and commercial fisheries that depend on the sea. in the state of bahia alone, an estimated 43,000 fishermen were affected by the disaster [44]. fisheries were inevitably affected in brazil because the risks of contamination directly interfered with the sale of fish, with up to 50% drop in income being mentioned by artisanal fishers [23]. although part of this loss was due to decreased catches, due to a lower consumer demand, fishermen also lost income due to lower prices enforced by middlemen even in areas not directly affected by the oil spill. women working in fisheries, as gleaners for example, are especially vulnerable because the types of habitats they tend to use (mangroves and sandbanks) and the animals they tend to exploit (e.g., mollusks) are amongst the most sensitive to oil contamination because they are filters [48]. thus, a coastal oil disaster may accentuate gender vulnerability in fishing communities. some eventual government support is likely to benefit only a small portion of fishers as per bureaucratic requirements, such as being registered by the fisheries secretariat, which gives them the right of a fishing license. in some of the northeastern states, about 10% of the artisanal fishers have a fishing license. even if less bureaucratic means is adopted, such as having the villages and their local fishing associations identify the fishers to be compensated temporarily, this is still unlikely to fix their economic losses. this would be so because the fish from brazilian artisanal fisheries are part of complex value chains, often with invisible links and no taxes attached [49,50]. additionally, fishers and their families are subject to different levels of health problems, from those caused by the direct contact with oil to psychological ones related to the socioeconomic uncertainty generated by the spill, such as the perspective of job loss and food insecurity [51]. these effects can last for years and are not usually accounted for by governments in places where oil disasters have happened [52,53]. 4. methodology photographs and videos released at the time of the event of the oil spill disaster confirmed by national media, locations where the oil was deposited on the marine substrate. we collected water and sediment samples in pirangi reef area in rio grande do norte state, once oil was spotted at this site in 2019. this specific site of pirangi was studied in 2013 and 2014 with no spotting of oil patches or other forms in the sediment and in the water in according to [24]. after the oil spill, we sampled new sediment sites in october 2019 to compare with the same methodology described in by the abovementioned authors. we intend in this study to discuss questions on the human-induced changes on the reef system, therefore water and surface sediment were recovered by scuba divers from 55 stations at reefs at pirangi in june 2013 and july 2014 (figure 3). samples were recovered from reef areas, sandy sediments, and macroalgae substratum using a small knife. in pirangi in 2013, stations 16 to 20, 27, and 28 and stations 3 to 15 in 2014 were sampled from areas of small reef patches near http://dx.doi.org/10.36956/sms.v3i2.431 7 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 table 2. possible socioeconomic and health effects on the coastal human communities affected by the south atlantic oil spill. effect reason based on local reality effect scale impact reason scale reference supporting the listed effect reduced fishing catches fish and seafood mortality may affect catches local * fishers and gleaners are majorly from the small local communities affected. industrial fisheries are less common in the region and tend to fish offshore areas, which are less likely to have been affected with the same magnitude (born et al. 2003) reduced fisheries income fish and seafood mortality and lower demand may force prices and revenues down. some middlemen might abuse the vulnerability of coastal fishers local *** the same as above (garza-gil et al. 2006; mccrea-strub et al. 2011) changes in fishing grounds and effort if closer grounds are contaminated, fishers that have the means may switch grounds, with consequences on effort (e.g.: need to use different gear or spending more fuel to reach further grounds) local ** fishers in the region tend to fish closer to their homes, especially if they are small-scale (born et al. 2003) loss of food sovereignty if fish and seafood are contaminated, coastal communities may need to purchase protein they would otherwise get for cheaper (just at the cost of their work and gear). however, there is a chance they would return to fishing even if still contaminated for not being able to afford purchasing protein local * coastal communities are the only ones that rely directly on marine resources (jonasson et al. 2019) increased food insecurity the dependency on external markets, conditioned to money payment, may force people to reduce their protein intake. externally acquired protein may be of lower nutritional quality (e.g., canned meat and highly processed protein). even if locals resume fishing, their food might not have the same quality due to contamination local ** same as above (osuagwu and olaifa 2018) contamination from ingesting seafood heavy metals (cadmium, mercury and lead) from the spill can accumulate in the food chain, potentially causing neurological and reproductive damages, and even cancer. in the absence of affordable alternatives, locals may keep ingesting contaminated seafood regional *** especially important for the locals, but the fish sourced locally can be sold in the state markets (solomon and janssen 2010) contamination from direct contact with oil removal of oil using makeshift gear (or no gear) expose people to defatting (resulting in dermatitis and skin infection), and temporary eye, nose, or throat irritation, nausea, or headaches. those exposed for longer can have dna damage regional ** in addition to local volunteers, people from the region (and elsewhere) travelled to the contaminated sites to help with the clean up (solomon and janssen 2010) increased rates of psychological problems increased rates of unemployment, reduced income and lack of clean (and free food) can increase the rates of depression, anxiety, post-traumatic stress disorder, and psychological stress local ** effect limited to those directly affected (solomon and janssen 2010) http://dx.doi.org/10.36956/sms.v3i2.431 8 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 effect reason based on local reality effect scale impact reason scale reference supporting the listed effect loss of cultural services, such as destruction of historically used grounds for work or leisure coastal communities rely on coastal habitats for their wellbeing and traditions. local * coastal cultural ecosystem services associated to fisheries are locally dependent (outeiro et al. 2019) shrimp farming this activity is developed in the mangrove, supposed to be one of the environments most affected by the spill national the region is the main national producer and international exporter of shrimp in brazil (duke 2016) algae aquaculture practiced in banks very close to the shore, this activity is likely to have been widely affected by the spill agar-producing algae are exported to the remaining states (yang et al. 2020) community-based tourism local * although more of an informal activity, it is relevant for some traditional communities as a source of income (bordelon et al. 2015) coastal tourism vacancy rate may increase soon after a disaster as tourists are afraid of contamination or fear that the site has lost its landscape attractions (e.g., clear water and white sand beaches) regional * decreased taxes will particularly affect the states that have a strong reliance on tourism, but the impacts are expected to last while they are visually perceived (price-howard and holladay 2014) increased in gender inequality mangroves and sand banks, which are among the most affected areas, are especially harvested by female gleaners. men often fish offshore, where some of them can target unaffected stocks local ** women in fishing communities are expected to being affected by the spill (defiesta and badayosjover 2014) the intensity of the effect is based on the authors’ expert opinion associated to what is known in the literature (*little evidence in the literature; **some evidence; ***strong evidence). impacts that are regional are by default also local, while those that are national, are also local and regional. tourism boating sites. each area was sampled twice, but exact station locations differed from 2013 to 2014. figure 3. a) random sampling points of the sediment collection carried out in june 2013, july 2014 (no oil spotting), and october/2019 (with 95% of samples containing oil). b) portion of reef substrate with oil crude collected in pirangi (rn). c) sediment in a sieve showing oil pollution. in october of 2019, after the oil spill, we focused on the pium river area and sampled 15 more sediment, reefs and microalgae, and water samples to observe the presence of oil. processing of marine sediments followed standard procedures from [24,54] where a fixed volume of 50 cm3 of sediment was washed over a 63 µm sieve to retire silt and clay and spot oil in analyzed sediment. 5. results along the entire northeastern coast, considerable particles and portions of oil were buried in the sand and in organisms mainly due to the movements of coastal hydrodynamics. sampling done in october 2019 in the same area previously sampled in 2013 and 2014 shows that more than 95% of the unconsolidated sediment samples, including some corals, had some evidence of oil (figure 3). this is a striking contrast with samples done in the same region with the same methodology in two previous consecutive years (2013 and 2014), which showed no evidence of oil on the seabed and was evidenced by [4]. figure 3 shows maps from 2013 and 2014 published data and no mention of oil in the sediment study; and samples collected in 2019 (figure 4) with oil evidences on 95% of samples. oil mixed with sand has been found from a few centimeters to almost 10 cm deep into the sediment in beaches, and also buried in water depths between 3 and 12 m in some of the local reefs and estuaries. river pium’s estuary and the reefs of pirangi do sul, indicates that the scope of http://dx.doi.org/10.36956/sms.v3i2.431 9 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 the contamination is far beyond what was previously assumed. thus, there is a considerable range of threats and impacts on the marine biota, many of which are yet to be assessed on the brazilian coast, especially given that the area affected is on a continental scale (about 2500 km). to date, the magnitude of the event is given by the oil that has been removed in the form of stains or fragments on the surface of beaches. figure 4. the official map with damaged sites by ibama, which the site of pirangi and pium river are not included. they were however severely affected by the oil accident event in 2019. 6. discussion almost twenty months after the first signs of the spill, governmental investigations are yet to clarify crucial points such as the origin, extent and cause of the spill, and specific characteristics of the oil, which seriously compromised immediate and posterior actions. still no estimate of the amount of oil that remains on marine sediments, estuaries or mangroves, or the amount that has infiltrated into the brazilian sand beaches, and the magnitude of an oil accident cannot be measured by the amount of oil that has been removed and sighted on beaches and coastal areas. as an example, brazilian tropical reef ecosystems are not, in general, built by corals, but by a rich diversity of species that vary according to the region [55]. this peculiar formation of brazilian reefs prevents comparisons with previous oil spills in different reefs of the world when mucus secreted by the polyps of the corals could withstand isolated oil accidents [25]. thus, it is reasonable to assume that the living surface of these ecosystems may be impacted in the medium and long term, and thus chemical contamination on the reefs of the affected area must be investigated in detail considering their ecological and socioeconomic importance. this indicates that the scope of the contamination continues its reach far beyond what was previously assumed since the brazilian coastal area affected is very large on a continental scale. 6.1 political scenario in the event of a major oil disaster, such as this one we are reporting, immediate containment and waste removal should happen, but not as isolated actions: they should be accompanied by the application of robust and effective strategies including waste containment, cleaning and removal protocols. the federal government took more than 40 days to adopt the contingency plan for oil pollution incidents (pnc from portuguese) previously in place since 2013, and they only implemented the contingency plan after being confronted by the federal prosecution service twice [11]. part of this inaction was due to a systematic dismantlement and clearing of the brazilian environmental programs, especially during 2019 [56]. in april 2019, less than four months before the oil spill, the federal government extinguished several councils, committees, commissions and collegiate bodies associated with the federal public administration (decree 9,759 / 2019). this included two committees that were part of the pnc, explaining why it took so long for it to be implemented. a timely implementation of the pnc would have decreased the damage extension, instead, the official government response in the acute period of contamination was groundless propagandized ideological accusations (against venezuela, for example) or, when these smoke screens did not work, the public got the silent treatment. little information was disclosed other than the locations on a map affected by the oil spill along the brazilian coast (updated in 03/19/2020) by federal agency ibama, the brazilian institute of environmental and renewable natural resources. after spotting oil in the water, a specific scientific mission was performed to evaluate the water and sediments situation in pirangi do sul . we have observed extensive areas where oil spillage has acutely damaged the ecosystem as a whole. this coral reef has been evaluated since 2013 [24,54,57,58] with no mention of oil in this specific site, until 2019 when we verified that it was impacted by this oil accident. we have then added a new information on the ibama original map as it follows in figure 3 that includes the present site of pirangi and pium river as severely affected by the oil accident event in 2019 as we have shown in this article. under pressure by public opinion, in december 2019, the government published a timid research call of about $320,000 us (maximum of us $25,000.00 per project), being a negligible amount to properly investigate the exhttp://dx.doi.org/10.36956/sms.v3i2.431 10 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 tension of the damage caused by the oil spill accident. and in the same period, mcti through “ciências do mar”, a program with actions forecasting 2019 to 2030 with the objective of managing knowledge for the conservation and sustainable use of the sea, launched an emergency action with the financing of approximately $1.4 million us for research groups already established (incts and pelds) to develop research for impact by oil spills. some state governments, on the other hand, although insufficient, have been more proactive and provided more amounts of funding. state initiatives have also counted on partnerships and collaborations with public and private research institutions, associations, universities and non-profit organizations. while the origin of the oil remains a mystery, and any scientific effort to clarify that should have been welcome, the scientific community in brazil has been subject to a smear campaign to discredit its findings and opinions. this is especially strong when academics denounce attacks on the environment and/or human rights, which make the topic of an oil spill especially delicate, as it touches on both issues [59]. so far, and despite the length of time passed, none of the hypotheses on the origin of the spill has been confirmed due to lack of scientific consistency. perhaps not surprisingly, many of these hypotheses have been aired first by the government, which has been effective in pointing fingers, but far less efficient in providing reliable and robust information. for example, the oil has been suggested to leak from: 1) oil tankers in waters beyond 200 nautical miles from brazil, 2) cleaning of a vessel, 3) sinking of a foreign vessel with hull drilling and continued oil leakage, and 4) continued leakage from the national oil exploited in the pre-salt layer. however, we still have no concluding remarks. 6.2 future directions oil production, transportation and consumption continue to carry risks in the 21st century, which makes it necessary to think about the adoption of new policies that encourage cleaner and safer production associated with ambitious preventive and mitigation disaster plans. when disasters happen, they should teach us lessons on how to avoid them and how to make sure that the most vulnerable, in nature and in society, will not be the ones paying the highest price. it is a societal duty, including academia and government, to ensure these disasters are properly investigated and the consequences accounted for, even when media interest refocuses public attention. these types of efforts require working in partnership, where the scientific community is not to blame for societal problems, but rather as a door to alternatives for this disaster and prevention of future environmental problems brazil and the rest of the world may face. a new disaster, even of a global magnitude, such as the ongoing pandemic (covid-19), should not be a reason or distraction to forget about previous disasters, especially in places where poorer human communities suffer the highest losses. the unavailability of transparent results hinders actions focused on solving the problem. this impact scenario, as witnessed, still has potential damages not yet measured or mitigated, leading us to a series of important considerations in order to have a less compromising future situation that is aggravated in countries of large territorial extension and high social inequality, such as brazil. it is essential and basic to have operating government protocols in place for immediate actions for oil removal, compensation for socioeconomic losses, assessments of the level of contamination in habitats, organisms and human beings. in addition to urgent measures, habitat recovery and monitoring of the level of contaminants must be used in order to guarantee the health of the environment. integrating the various scientific areas of knowledge is essential for a holistic approach on this broad topic. for example, to understand the sum of stressors in reef environments, such as we are currently facing with warming waters and coral bleaching in tropical reefs off the brazilian coast. however, it is no longer possible to hide the urgent need for a change in actions in the face of the use of natural resources and oil exploration. the behavioral distortions in consonant with unrestrained consumption typical of societies that aim at high productivity, lead us to environmental catastrophes, scarcity, and contamination of our own resources. we have already opened our eyes and see the problems, now we need to make the necessary changes. in the absence of monitoring, this type of impact remains unrelated to past oil spill events, preventing further protective and mitigation measures for future disasters. a strategy for mapping impact on benthic habitats also needs to be addressed and discussed to increase better responses. acknowledgments this work was carried out under the scope of inct ambtropic phase ii (cnpq process 465634/2014-1) linked to the emergency action to combat the 2019 oil spill of the mcti (dti-a 381360/2020-2 fellowship to ppb eichler). we are grateful to the anpprh 22 and the capes (coordenação de aperfeiçoamento de pessoal de nível superior) project "oceanographic process in the http://dx.doi.org/10.36956/sms.v3i2.431 11 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 breaking of the continental shelf of northeastern brazil: scientific foundations for special marine planning" for the finan cial assistance granted, to the crews of the vessels used, and to all colleagues of ggemma/ufrn.we are grateful to capes (coordenação de aperfeiçoamento de pessoal de nível superior) for funding support through projects special visiting professor (pve 151-2012, auxpe 242-2013), and ciências do mar ii (23038.004320/20141) that enabled a pos doc fellowship for p.p.b. eichler at moss landing marine laboratories of san jose state university (mlml/sjsu), and at the ocean sciences department of the university of california at santa cruz (ucsc) (88887.305531/2018-00, 88881.188496/201801 and 9999.000098/2017-05). we are also thankful to cnpq for the research grants for co-author gomes m.p (pq 302483/20195) and for co-author vital h (pq 311413/2016-1, pq 315742/2020-8), and to osc oceanica for supporting liana mendes throughout the research. we are especially thankful to the ggemma lab team (ppgg/ufrn) that made possible to carry out this work and to the 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[56] d. abessa, a. famá, & l. buruaem. the systematic dismantling of brazilian environmental laws risks losses on all fronts. nature ecology & evolution 3 (2019), pp. 510–511. doi: 10.1038/s41559-019-0855-9. [57] eichler, p., vital, h. and sen gupta, b.k., 2014. anthropogenic perturbation of coral reef environments near natal, brazil: clues from symbiont-bearing benthic foraminifera. agufm, 2014, pp.gc21a-0511. [58] eichler, p.p.b., farias, c.l.c.d., santos, d., amorim, a., mendonça, a., vital, h. and gomes, m.p., 2018. foraminifera biodiversity coupled with environmental quality in pium river estuary and pirangi coral reef (rn, brazil). tecnologias para a sustentabilidade | debates interdisciplinares ix. doi: 10.19177/978-85-8019-206-3.23-41. [59] p.p. layrargues. quando os ecologistas incomodam: a desregulação ambiental pública no brasil sob o signo do anti-ecologismo. revista pesquisa em políticas públicas, 12, (2018), pp.1-30. doi: 10.18829/rp3.v0i12.26952. http://dx.doi.org/10.36956/sms.v3i2.431 26 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 http://dx.doi.org/10.36956/sms.v3i2.436 sustainable marine structures http://ojs.nassg.org/index.php/sms/index article present status of aquatic resource and its catch of mogra river in bangladesh chakraborty, b. k.1* verma a. k.2 muniya, s.3 1. department of fisheries, bangladesh and agricultural university, bangladesh 2. govt. p. g. college, saidabad, prayaagraj, india 3. bangladesh agricultural university, bangladesh article info abstract article history received: 15 august 2021 accepted: 8 september 2021 published online: 20 september 2021 bangladesh is very rich in aquatic fauna with a biodiversity. the present study, conducted during 2015 to 2019, recorded a total number of 131 species (104 fish, 09 prawn, 01 snail, 04 crabs, and 13 turtles) belonging to 26 families were identified from the mogra river and its flood plain. about ten types of fishing gears, different crafts, hook and line were found operative in the river. increasing rates of using current jal (16.0-26.40%) and kapuri jal (11.0-16.70%) were identified as detrimental gears destroying different species. the fish productivity was decreased dramatically from 170.63±10.81mt to 134.75±8.02 mt with a decreasing percentage of 6.26 to 21.03% within five years. three important aquatic species turtiles (cyclemys oldhami, melanocheelys trjuuga and morenia petersi) became rare and 17 commercially important aquatic species were at the edge of extinction (critically endangered, cr). from the study, 67 species were recorded in the endangered (en) category, 20 species vulnerable status (vu), 11 species lower risk (lr), 07 species least concern (lc) and 04 data deficient (df). to save the existing aquatic species in the studied riverine ecosystem and ensure better livelihood of the fishes, a team of local management committee, similar to the hilsa fisheries management technology is needed. keywords: aquatic fauna biodiversity rare critically endangered endangered illegal fishing over exploitation 　 *corresponding author: chakraborty, b. k., department of fisheries, bangladesh and agricultural university, bangladesh; email: bborty@gmail.com 1. introduction river ecosystems and biodiversity help in maintaining the ecological balance of the waterbody. there is a necessity of ecological balance for widespread biodiversity and the ecological balance is an indispensable need for human survival [1]. the biodiversity conservation and environmental ethics both are required for sustainable development and survival of aquatic flora and fauna because biodiversity is the foundation of human life [2]. biodiversity has become a major concern to the fisheries biologists against the backdrop of rapid decline in the natural population of fish and aquatic biota across all the continents of the world. biodiversity encompasses genetic species, assemblage, ecosystem and land cape levels of biological organization with structural, compositional and functional components [3,4]. though loss of aquatic species has been occurring rapidly, the aquatic organisms have received comparatively little attention from conservation biologists [5]. a rich diversity of fish species is important to the ecology and sustainable productivity of the flood plains [6]. the resource of aquatic fauna in bangladesh are 27 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 http://dx.doi.org/10.36956/sms.v3i2.436 under severe threat due to over-exploitation and environmental degradation, which includes human interventions through construction of flood control embankments, drainage structures and sluice gates, conversion of inundated land to cropland thereby reducing water area and indiscriminate use of pesticides. pollution from domestic, industrial and agrochemicals wastes has resulted in extinction of a considerable amount of aquatic biota in some stretches of the open water system [7,8]. the upper region of the mogra river is connected with bisnai river and kangshow river. the riverine flows across the atpara and modon upazilla of netrokona district from northern to southern tharail and itna upazilla of kishorgong district, before joining the surma river. the water flow is continuous in the river. during monsoon, the water flow comes down from the upper region of kangshow river and water flow does not confine within the banks. as a result, it causes floods in some area of atpara and modan upazilla every year. figure 1. location of mogra river in the netrokona district, bangladesh. once upon a time, mogra river was an abundance of native wild fishes, shrimp, crabs and reptiles. due to over-exploitation and various ecological changes of the mogra river, important fish species, and reptiles disappeared. now this river is under great stress and its existence is endangered because of the changing aquatic ecosystems. the upper stream of the riverine system is siltated, which reduces the rate of water flow and causes habitat degradation. like other floodplains, the feeding and breeding grounds of fishes in and around the river have been reducing drastically from various human created obstacles. indiscriminate destructive fishing practices, soil erosion, siltation, construction of flood control and drainage structures, and agro-chemicals and pesticide have caused havoc to the aquatic biodiversity in bangladesh. 2. methodology experimental design mogra river was studied during 2015-2019 with particular emphasis on soil and water quality, biological productivity and status exploitation of the fishery resources. the river comprises an average length of 20-22 km long course. for the purpose of the study the river course was divided into upper and lower regions based on soil structure, water quality and fishing activities. the river courses of atpara to nazirgonj constitute the upper region while the nazirgonj to madon constituted the lower region, where in the mogra river joins with the surma river. study of water quality parameters the bamboo made meter scale was used to measure water depth. water temperature (oc) was recorded using a celsius thermometer and transparency (cm) was measured using a secchi disc (20 cm diameter). dissolved oxygen (mg/l) and ph were measured directly using a digital electronic oxygen meter (ysi, model 58, usa) and an electronic ph meter (jenway, model 3020, uk). alkalinity was determined following the titrimetric method. sampling of fish the investigation was conducted from 2015-2019 and was sampled simultaneously for winter (mid november to mid february), pre monsoon (mid february to april), monsoon (may to august) and post monsoon (september to mid november) for assessment of fish abundance and availability. data collection the study was based on both primary and secondary data, comprehensive literature review and extracts of local knowledge and information. an organized sampling program spread over a reasonably long time is needed to get a true picture of the catch and composition. this study, being a rapid survey, gives only a broad picture of the stock of fishes, prawn, crabs and turtiles that could be obtained through market survey (brojer bazar, nazirgong bazar, teligati bazar, madon sadar bazar) and interaction with fishers in the riverside and even in the river and secondary data were collected from the department of fisheries (dof) and the internet. the number of six codes (cr, e, en, vu, lr, lc and dd) of iucn was followed to categorize the coservation of status of fishes recorded from the river and to compare the trend among shannon index value of different years [9]. 28 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 shannon diversity index where: h = the shannon diversity index, pi = fraction of the entire population made up of species i, s = numbers of species encountered, ∑ = sum from species 1 to species s. note: the power to which the base e (e = 2.718281828.) must be raised to obtain a number is called the natural logarithm (ln) of the number. analysis of experimental data the data were analyzed through one way anova using mstat followed by duncan’s multiple range test to find out whether any significant difference existed among the different means [10]. 3. results and discussion morphometry and hydrodynamics of experimental river generally, there are three main sources of water input into the river ecosystem viz. overspill from the higher river channel, surface flow and regeneration. water flows were resolved by both rainfall and flooded water from the meghaloya's hilly range, india. in upper region, this river is connected with khongsa and bisnai river. flooding of the river originated from the kangshow and bisnai river. surface run-off and increased in river height due to inflow of rainwater (flood) from the upper stretch, cause inundation of floodplains. the more water gain or exchange of water took place during southwest monsoon when floodplains were flooded. the early flood phase (april to june) occurred in the early monsoon when the water level in basin was relatively low. the water level in the floodplain rises and falls depending on the water level in adjacent rivers. the deep flood phase (june to september) began when the water level in the river, causing deep flooding in the four unions of atpara and madon upazillas. floodwater in flood plains began started receding in the post-monsoon season (october to december). the water loss by various means caused shrinkage of the effective water area and lowering of depth in the river which is very similar to the study of chakraborty et al. [11]. physical characteristics soil texture of the mogra river bed varied from sandy to loam sand. soil texture of upper river bed was having 90.80±6.02 sandy, 7.30±2.43 loam sand and 1.9±1.72% clay. the dominance of sand (58.30±5.18) was also recorded in the lower region of the river (table 1). table 1. physical features of sediment of the mogra river. location soil texture of the river bed (%) sandy loam sand clay upper region 40.20±4.32 43.60±5.03 17.4±3.22 lower region 38.30±4.18 42.10±4.06 19.60±3.54 the waterw depth of the mogra river exhibited a decreasing with an average value of 3.55±0.64 3.41±0.55, 3.321±0.584 3.207±0.44 and 3.01±0.41 m during the study period (figure 2). the highest depth of the river was recorded in the year 2015 and the lowest depth was found in the year 2019 and the equation of the trend line was y= -0.128x +3.684 (r2 = 0.981). the alarming trend of decrease in water depth (figure 2) was majorly due to rapid siltation [11]. the observed values of the value of the physico-chemical parameters of the river water are given in table 2. the temperature, transparency, ph, dissolve oxygen and alkalinity of water were found to be more or less in the desired range. the variations in mean water temperature of the river were not statistically significant (p>0.05). water temperature of the river showed an increasing trend in monsoon and post monsoon and decreasing trend in winter which was similar observation of mathew [12]. mean secchi disk transparency differed significantly (p<0.05), during the study period. higher values were recorded during post monsoon and summer months due to reduced flow and relatively stable conditions of water as observed by others [13]. the ph of the studied river did not differ significantly (p>0.05). transparency was consistently higher in upper region and in the deeper portion of the river. a significant rise in ph during pre-monsoon and a drop in winter was noted in the river. the mean dissolved oxygen (do) did not differ significantly (p>0.05). the ph and oxygen values of the river agreed more or less similar with the findings of apha [14] and boyd [15]. water alkalinity levels were recorded medium to high as reported by clesceri et al. [16]. it differed significantly (p<0.05) with time. lowest value of alkalinity was recorded in the in the winter during 2015. http://dx.doi.org/10.36956/sms.v3i2.436 29 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 figure 2. water depth of the mogra river between the year 2015 and 2019 capture method the fishers used wooden boats as a major craft. they used seine net (bar jal and komor jal), thela jal, dharma jal, bua jal, lift net, cast net, current jal and various types of fish trap, hook and line according to season and availability of different species of fishes. wide variability in fish traps (vair, dugair, ghuni and pholo etc.) and hook and line (barshi, fulkuichi, jhupi aikra etc.) were used to capture different groups of aquatic lives. figure 3 shows a remarkable yearly increase in fishing effort by using illegal fishing gear like gill net (current jal) and bar jal (kaperi jal) in the total catch. the percentage of catch from current jal were 14.00%, 16.20%, 19.80%, 22.00% and 26.20%; and bar jal (kaperi jal) 12.00%, 13.70%, 14.50%,15.10% and 16.50%; and hook and line 10.00, 10.50, 11.00, 11.60 and 11.70% in the year 2015, 2016, 2017, 2018 and 2019, respectively. significant difference in catch (p<0.05) by current jal and bar jal (kaperi jal) and hook and line were identified. the contribution of catch by komor jal were 13.00%, 12.80%, 12.50%, 12.30% and 11.70% in the years 2015, 2016, 2017, 2018 and 2019, respectively. figure 3. contribution of different fishing gears during the study period (20152019). use of different fishing gears also differed significantly (p<0.05). haroon et al. [17] reported eighteen types of fishing gears from the sylhet sub-basin and thirteen types from mymensingh sub-basin which is very similar to this study. the catch using thela jal, dharma jal, bua jal, lift net, cast net, fish trap and hook and line were found decreasing and differed significantly (p<0.05). a decreasing trend in the catch of the river and its flood plains were recorded and the findings were similar to that of chakraborty et al., and sugunan and bhattacharjya [11,18]. fish catch and composition an organized sampling program was run for a long time to get a real picture of the catch and composition of the river. the present investigation gave a broad picture of the stock of fishes and other aquatic lives obtained through market survey, landing center and interaction with fishers in the river. from the fishing activity in the mogra river, occurrence of 104 species of fish, 09 species of prawn, 01 species of snail and 04 species of crabs, and 13 species of turtles belonging to a total 26 families were recorded. fishing activity run throughout the year. during monsoon and post monsoon, fishers used lift net, current table 2. physico-chemical parameters of experimental mogra river. parameters years 2015 2016 2017 2018 2019 temperature (oc) 25.74±5.01 (14.04-32.20) 26.17±6.12 (13.73-32.40) 26.48±6.08 (14.11-31.85) 26.88±6.26 (14.00-32.01) 26.14±5.88 (14.15-32.08) transparency (cm) 40.04±6.24d (30.10-50.16) 50.38±7.02a (32.22-58.14) 44.55±6.41c (28.15-50.30) 37.19±6.88e (27.55-50.25) 47.23±6.74b (29.55-55.22) ph 7.05± 2.04 (6.90-8.86) 7.66±2.22 (6.80-8.88) 8.05±2.03 (6.85-9.07) 7.77±1.88 (6.90-8.88) 8.08±2.01 (6.75-8.90) dissolved oxygen (mg/l) 6.95±1.84 (4.18-8.04) 8.84±1.88 (4.55-9.05) 7.70±1.99 (5.44-8.66) 7.22±1.72 (5.41-8.05) 7.09±1.96 (5.04-8.48) alkalinity (mg/l) 142.02±10.04a (111.22-151.05) 120.66±7.22e (110.88-135.02) 126.18±7.05d (107.22-138.15) 131.52±8.07c (110.40-140.32) 136.38±7.04b (111.16-144.55) figures with different superscripts in the same row varied significantly (p>0.05). figures in the parenthesis indicate the range. http://dx.doi.org/10.36956/sms.v3i2.436 30 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 jal, cast net, traps, and line and hooks to catch fishes. fishermen also operated kata fishing by seine net (bar jal and komor jal) in winter and spring. the catch is consisted of knife fish, major carp and minor carp, small fish, cat fish and small cat fish, eels, prawn, crabs and reptiles (table 3 and figure 4). the assessment of yearly total catch from the river was around 170.63±10.81 mt, 159.93±9.80 mt 150.98±10.66 mt, 143.16±9.80 ton and 134.75±8.02 mt during 2015, 2016, 2017, 2018 and 2019, respectivly (figure 5). the catch trend line was exponential type and the equation was y= 180.3e-0.05x (r2 = 0.999). figure 4. the production of different groups of aquatic lives in the mogra river in the year 2015 to 2019. figure 5. decreasing trend in the total production of aquatic lives in the mogra river during 2015 to 2019. the fish catch showed a decrease percentage at the rate of 6.26%, 11.52%, 16.10% and 21.03% of catch in the years 2015-2016, 2016-2017, 2017-2018 and 20182019, with respect to the catch of 2015 (figure 6) and which exhibited a linear trend line and the equation was y= 4.889x + 1.5.5 (r2 = 0.999). a decrease trend in production from the river was clearly pronounced within the study period of five years which was similar to the study of chakraborty and mirza [19,20] and moyle and leidy [21]. although the production of all the recorded groups decreased during the study, it was pronounced more for reptiles. figure 6. decreasing percentage of total production of aquatic lives in the mogra river during 2015 to 2019. table 3 and figure 7 exhibited the conservation status of the 131 aquatic wild animals of the mogra river and identified as e04 (3%), cr-17 (12%), en-67 (51%), vu-20 (15%), lr-11 (9%), lc-7 (9%) and dd-06 (4%), respectively. figure 7. conservation status of the recorded aquatic species in the mogra river. status code: eextinct, crcritically endangered, enendangered, vuvulnerable, lrlower risk, lc not threatened dd=data deficient (as per iucn [22]). the total catch in different years differed significantly (p<0.05). commercial important pata kachim, cyclemys oldhami, kali kachhap, melanocheelys trjuuga and bengal eyed turtile, morenia petersi were rarely found in the years 2015 to 2017 in the river. however these species were not recorded during 2019. channa marulius, puntius sarana, barilius tileo, sicamugil casoasia, rohtee cotio, bagarius yarrellii, mystus seenghala, bagarius yarrellii, chaca chaca, rama chandramara, sisor rabdophorus, pseudolaguvia muricata, pseudolaguvia inornata and reptiles (indotestudo elongata, batagur baska, geoclemys hamiltonii and pangshura tecta (17 species) were reported as critically endangered and facing an extremely high risk of extinction in the river system (table 3). according to iucn [23], in bangladesh, about 56 freshwater fish species are critically or somewhat endangered. due to over http://dx.doi.org/10.36956/sms.v3i2.436 31 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 table 3. status and distribution of mogra river of northern bangladesh. sl no group/ family local name scientific name production (mt) statussomeswari river 2015 2016 2017 2018 2019 snake headed 1 notopteridae chitol notopterus chitala 0.70 ±0.09 0.65 ±0.05 0.59 ±0.05 0.54 ±0.03 0.50 ±0.02 en 2 notopteridae foli notopterus notopterus 0.50 ±0.04 0.44 ±0.03 0.37 ±0.02 0.33 ±0.01 0.30 ±0.01 en 3 belonidae kakila xenentodon cancila 1.90 ±0.44 1.70 ±0.40 1.55 ±0.41 1.38 ±1.10 1.26 ±0.07 lr 4 channidae gojar channa marulius 0.60 ±0.20 0.53 ±0.09 0.50 ±0.07 0.48 ±0.05 0.44 ±0.03 cr 5 channidae soal channa striata 1.03 ±0.51 1.00 ±0.10 0.97 ±0.08 0.98 ±0.09 0.92 ±0.06 en 6 channidae gachua channa gachua 1.88 ±0.50 1.70 ±0.50 1.68 ±0.44 1.66 ±0.42 1.62 ±0.41 cr 7 channidae taki channa punctata 2.08 ±0.60 2.00 ±0.55 1.98 ±0.50 1.95 ±0.44 1.90 ±0.42 lr subtotal 8.89 ±0.69 8.02 ±0.68 7.64 ±0.64 7.32 ±0.63 6.94 ±0.62 major carps 1 cyprinidae catla catla catla 1.98 ±0.80 1.84 ±0.65 1.80 ±0.60 1.73 ±0.54 1.65 ±0.50 en 2 cyprinidae rui labeo rohita 3.01 ±0.30 2.88 ±0.30 2.81 ±0.30 2.71 ±0.27 2.60 ±0.21 en 3 cyprinidae mrigal cirrhinus mrigala 3.04 ±0.26 3.0 ±0.24 2.97 ±0.22 2.90 ±0.21 2.78 ±0.20 en 4 cyprinidae kalbaus labeo calbasu 2.3 ±0.19 2.25 ±0.18 2.21 ±0.17 2.16 ±0.10 2.07 ±0.10 en 5 cyprinidae ghonia labeo gonius 2.80 ±0.17 2.50 ±0.16 2.30 ±0.14 2.20 ±0.11 1.97 ±0.10 en 6 cyprinidae reba cirrhinus reba 1.80 ±0.11 1.60 ±0.10 1.40 ±0.09 1.20 ±0.08 1.10 ±0.06 en 7 cyprinidae common carp cyprinus carpio 5.50 ±1.84 5.20 ±1.70 5.00 ±1.22 4.80 ±1.10 4.50 ±1.00 vu 8 cyprinidae grass carp ctenopharyngodon idella 3.60 ±1.24 3.30 ±1.11 3.00 ±1.01 2.95 ±1.00 2.88 ±0.98 vu sub-total 24.03±1.17 22.57±1.12 21.49±1.09 20.65 ±1.08 19.55 ±1.03 minor carp 1 cyprinidae along bengala elanga 1.20 ±0.07 1.10 ±0.06 0.94 ±0.04 0.82 ±0.03 0.69 ±0.01 vu 2 cyprinidae bhangna bata labeo bata 1.10 ±0.06 1.00 ±0.05 0.80 ±0.05 0.65 ±0.04 0.50 ±0.02 en 3 cyprinidae ghora muikha labeo pangusia 1.82 ±0.05 1.80 ±0.05 1.70 ±0.04 1.60 ±0.03 1.50 ±0.03 en 4 cyprinidae jarua/utti chagunius chagunio 0.87 ±0.06 0.70 ±0.05 0.62 ±0.03 0.48 ±0.03 0.38 ±0.01 en 5 cyprinidae puda puntius sarana 0.58 ±0.04 0.45 ±0.03 0.22 ±0.02 0.12 ±0.01 0.01 ±0.01 cr 6 cyprinidae tila koksa barilius tileo 1.01 ±0.08 0.90 ±0.05 0.88 ±0.04 0.84 ±0.03 .81 ±0.01 en 7 cyprinidae bhol raimass bola 0.86 ±0.05 0.72 ±0.04 0.64 ±0.04 0.55 ±003 0.54 ±0.01 en sub-total 7.74 ±0.39 6.67 ±0.43 5.80 ±0.45 5.06 ±0.47 4.43 ±0.46 small fish 1 cyprinidae mola amblypharyngodon mola 1.88 ±0.07 1.77 ±0.06 1.64 ±0.05 1.53 ±0.05 1.45 ±0.03 en http://dx.doi.org/10.36956/sms.v3i2.436 32 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 2 cyprinidae barna baril/ koksa barilius barna 1.20 ±0.05 1.00 ±0.04 1.10 ±0.04 0.96 ±0.02 0.90 ±0.03 en 3 cyprinidae baril barilius bendelisis 0.66 ±0.03 0.59 ±0.01 0.55 ±0.01 0.50 ±001 0.46 ±0.01 en 4 cyprinidae koksa barilius shacra 0.55 ±0.02 0.52 ±0.02 0.49 ±0.02 0.45 ±0.01 0.41 ±0.01 en 5 cyprinidae koksa barilius tileo 0.88 ±0.03 0.87 ±0.03 0.84 ±0.03 0.80 ±0.01 0.78 ±0.0 cr 6 cyprinidae aspidopara/ morar aspidoparia morar 0.66 ±0.04 0.62 ±0.04 0.60 ±0.03 0.58 ±0.02 0.55 ±0.01 en 7 cyprinidae chepchela chela cachius 0.80 ±0.05 0.75 ±0.04 0.66 ±0.03 0.62 ±0.03 0.58 ±0.02 en 8 cyprinidae kashkhaira chela laubuca 0.90 ±0.06 0.88 ±0.04 0.84 ±0.04 0.81 ±0.03 0.78 ±0.03 en 9 mugillidae kachi kholya sicamugil casoasia 0.66 ±0.02 0.60 ±0.01 0.58 ±0.01 0.55 ±001 0.52 ±0.01 cr 10 cyprinidae baspata danio devario 0.55 ±0.03 0.52 ±0.03 0.48 ±0.03 0.45 ±0.02 0.43 ±0.01 en 11 cyprinidae dhela rohtee cotio 0.50 ±0.03 0.40 ±0.02 0.32 ±0.02 0.22 ±0.01 0.12 ±0.0 cr 12 cyprinidae chola punti puntius chola 0.66 ±0.04 0.63 ±0.04 0.62 ±0.03 0.61 ±0.02 0.60 ±0.02 en 13 cyprinidae taka punti puntius conchonius 0.70 ±0.05 0.68 ±0.05 0.64 ±0.04 0.60 ±0.03 0.58 ±0.02 en 14 cyprinidae phutani punti puntius phutunio 0.80 ±0.05 0.78 ±0.05 0.75 ±0.02 0.72 ±0.02 0.68 ±0.01 en 15 cyprinidae jatpunti punti puntius sophore 0.44 ±0.03 0.42 ±0.03 0.40 ±0.02 0.37 ±0.02 0.34 ±0.01 en 16 cyprinidae teri punti puntius terio 0.70 ±0.04 0.67 ±0.04 0.65 ±0.03 0.63 ±0.02 0.60 ±0.02 en 17 cyprinidae tit punti puntius ticto 0.83 ±0.05 0.80 ±0.05 0.77 ±0.04 0.74 ±0.03 0.70 ±0.02 vu 18 cyprinidae fulchela salmostoma phulo 0.78 ±0.04 0.75 ±0.04 0.73 ±0.03 0.70 ±0.02 0.68 ±0.02 en 19 cyprinidae darkina esomus danricus 0.50 ±0.03 0.48 ±0.02 0.45 ±0.02 0.42 ±0.02 0.12 ±0.01 vu 20 cyprinidae kanpona oryzias melastigma 1.00 ±0.03 0.98 ±0.03 0.95 ±0.03 0.92 ±0.02 0.88 ±0.01 vu 21 clupeidae kachki corica soborna 0.40 ±0.03 0.38 ±0.02 0.36 ±0.02 0.28 ±0.02 0.23 ±0.01 dd 22 cobitidae balitora psilorhynchus balitora 0.40 ±0.02 0.40 ±0.02 0.37 ±0.02 0.35 ±0.01 0.33 ±0.01 en 23 cobitidae balitora psilorhynchus rahmani 0.37 ±0.02 0.36 ±0.01 0.22 ±0.01 0.09 ±001 0.08 ±0.01 lc 24 cobitidae river stone carp/ titari psilorhynchus sucatio 0.70 ±0.07 0.66 ±0.06 0.64 ±0.04 0.63 ±0.05 0.60 ±0.03 en 25 cobitidae bilturi /bali chata acanthocobitis botia 0.50 ±0.03 0.47 ±0.03 0.44 ±0.02 0.42 ±0.02 0.38 ±0.01 en 26 cobitidae river loach/ balichata acanthocobitis zonalternans 0.70 ±0.05 0.68 ±0.04 0.64 ±0.03 0.60 ±0.02 0.56 ±0.03 vu 27 cobitidae koirka nemacheilus corica 0.60 ±0.04 0.58 ±0.03 0.56 ±0.02 0.53 ±0.01 0.50 ±0.2 lr 28 cobitidae creek loach schistura beavani 0.40 ±0.03 0.38 ±0.04 0.36 ±0.03 0.35 ±0.02 0.32 ±0.02 vu 29 cobitidae corica loach/ korika schistura corica 0.70 ±0.05 0.66 ±0.05 0.63 ±0.05 0.60 ±0.04 0.57 ±0.04 lr 30 cobitidae savon khorka schistura savona 0.66 ±0.04 0.62 ±0.03 0.60 ±0.03 0.57 ±0.02 0.55 ±0.02 lr 31 cobitidae dari schistura scaturigina 0.40 ±0.03 0.38 ±0.02 0.36 ±0.02 0.35 ±0.02 0.32 ±0.01 en http://dx.doi.org/10.36956/sms.v3i2.436 33 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 32 cobitidae bengal loach / bou mach botia dario 0.60 ±0.05 0.55 ±0.04 0.53 ±0.04 0.51 ±0.02 0.48 ±0.02 vu 33 cobitidae hora loach botia dayi 0.60 ±0.05 0.58 ±0.04 0.56 ±0.03 0.53 ±0.03 0.50 ±0.01 en 34 cobitidae loach/ puiya lepidocephalichthys goalparensis 0.90 ±0.05 0.88 ±0.04 0.85 ±0.02 0.83 ±0.02 0.81 ±0.02 en 35 cobitidae goalpara loach neoeucirrhichthys maydelli 0.55 ±0.04 0.52 ±0.04 0.50 ±0.03 0.48 ±0.02 0.45 ±0.01 en 36 cobitidae gonga loach/ poia/ ghar poia somileptes gongota 0.60 ±0.05 0.58 ±0.05 0.55 ±0.04 0.53 ±0.03 0.50 ±0.02 vu 37 cobitidae rani botia lohachata 0.44 ±0.04 0.41 ±0.04 0.38 ±0.03 0.36 ±0.03 0.33 ±0.01 lr 38 cobitidae rani lepidocephalichthys annandalei 0.55 ±0.03 0.53 ±0.03 0.52 ±0.02 0.50 ±0.02 0.47 ±0.02 en 39 cobitidae balichata nemachilus botia 0.77 ±0.04 0.74 ±0.04 0.73 ±0.02 0.71 ±0.03 0.68 ±0.03 en 40 centropomidae chanda chanda nama 1.50 ±0.08 1.47 ±0.05 1.44 ±0.04 1.36 ±004 1.28 ±0.03 lc 41 centropomidae chanda pseudambasis bacuculis 1.20 ±0.08 1.16 ±0.06 1.15 ±0.05 1.13 ±0.04 1.08 ±0.04 en 42 centropomidae ranga chanda pseudambasis ranga 0.80 ±0.05 0.74 ±0.04 0.70 ±0.03 0.68 ±0.03 0.66 ±0.02 lc 43 gobiidae baila glossogobus giuris 1.20 ±0.07 1.10 ±0.06 1.00 ±0.05 0.98 ±0.04 0.94 ±0.04 dd 44. tetradontidae potka tetradon cutcutia 1.50 ±0.08 1.44 ±0.07 1.44 ±0.06 1.36 ±0.04 1.32 ±0.04 en sub-total 32.72 ±0.32 29.53±0.29 29.63±0.30 28.14 ±0.29 26.63 ±0.28 cat fish 1 bagridae ayre mystus aor 2.20 ±0.12 2.10 ±0.11 2.00 ±0.10 1.98 ±0.10 1.90 ±0.09 en 2 bagridae guizza mystus seenghala 3.00 ±0.20 2.89 ±0.17 2.75 ±0.14 2.66 ±0.11 2.55 ±0.11 cr 3 schilbeidae shilong silonia silondia 1.00 ±0.09 0.97 ±0.08 0.93 ±0.09 0.90 ±0.07 0.88 ±0.08 en 4 siluridae boal wallago attu 5.03 ±1.84 4.90 ±1.71 4.70 ±1.81 4.40 ±1.70 41.00 ±1.40 lr 5 bagridae baghair bagarius yarrellii 2.08 ±0.80 1.66 ±0.70 1.20 ±0.7 1.11 ±0.68 1.00 ±0.65 cr 6 chacidae cheka chaca chaca 1.50 ±0.10 1.30 ±0.09 1.00 ±0.08 0.96 ±0.08 0.90 ±0.05 cr 7 bagridae gangmagur mystus menoda 2.85 ±0.90 2.55 ±0.80 2.33 ±0.78 2.00 ±0.74 1.88 ±0.60 en 8 bagridae rita rita rita 2.55 ±0.81 2.50 ±0.70 2.44 ±0.70 2.20 ±0.60 2.09 ±0.50 en sub total 20.21±1.21 18.87±1.22 17.35±1.24 16.21 ±1.15 15.30 ±1.08 small cat fish 1 bagridae gulsa mystus cavasius 2.20 ±0.12 2.10 ±0.11 2.08 ±0.08 2.03 ±0.07 1.90 ±0.06 en 2 bagridae tengra mystus vitttus 2.70 ±0.11 2.60 ±0.11 2.50 ±0.10 2.45 ±0.10 2.40 ±0.08 en 3 bagridae bujuri mystus tengra 2.70 ±0.11 2.66 ±0.11 2.60 ±0.08 2.55 ±0.07 2.51 ±0.06 vu 4 bagridae gura tengra/ futki bujuri rama chandramara 0.70 ±0.06 0.60 ±0.04 0.50 ±0.03 0.48 ±0.03 0.39 ±.0.02 cr 5 bagridae menoda catfish /arwari hemibagrus menoda 0.80 ±0.07 0.77 ±0.05 0.75 ±0.05 0.73 ±0.04 0.70 ±0.02 en 6 bagridae kerala mystus mystus armatus 0.90 ±0.04 0.85 ±0.04 0.80 ±0.03 0.75 ±0.03 0.70 ±.0.02 en http://dx.doi.org/10.36956/sms.v3i2.436 34 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 7 bagridae day's mystus/ tengra mystus bleekeri 0.75 ±0.07 0.74 ±0.05 0.72 ±0.05 0.70 ±0.04 0.68 ±0.02 en 8 schilbeidae kajuli ailia coila 0.90 ±0.08 0.86 ±0.07 0.84 ±0.06 0.81 ±0.05 0.79 ±0.04 en 9 siluridae kani pabda ompok bimaculatus 1.58 ±0.08 1.50 ±0.07 1.48 ±0.06 1.41 ±0.06 1.37 ±0.05 en 10 siluridae madhu pabda ompok pabda 1.77 ±0.09 1.60 ±0.08 1.55 ±0.07 1.52 ±0.06 1.48 ±0.05 vu 11 siluridae ompok pabda ompok pabo 1.20 ±0.06 1.17 ±0.05 1.14 ±0.06 1.10 ±0.04 1.00 ±0.04 en 12 schilbeidae gharua clupisoma garua 1.07 ±0.08 0.96 ±0.06 0.94 ±0.07 0.88 ±0.07 0.80 ±0.05 en 13 schilbeidae muri bacha clupisoma murias 1.40 ±0.05 1.30 ±0.05 1.26 ±0.05 1.20 0.04 1.14 ±0.03 en 14 schilbeidae batasi pseudeutropius atherinoides 1.00 ±0.05 0.97 ±0.05 0.95 ±0.03 0.92 ±0.02 0.90 ±.0.02 vu 15 schilbeidae bacha eutropiichthys vacha 0.90 ±0.04 0.88 ±0.05 0.85 ±0.04 0.83 ±0.04 0.80 ±0.02 en 16 sisoridae kutakanti hara hara 0.60 ±0.04 0.55 ±0.04 0.49 ±0.04 0.45 ±0.04 0.44 ±0.04 lr 17 sisoridae kutakanti hara jerdoni 1.10 ±0.07 1.04 ±0.06 1.00 ±0.06 0.99 ±0.05 0.96 ±0.04 en 18 sisoridae gang tengra nangra nangra 0.90 ±0.04 0.88 ±0.03 0.85 ±0.04 0.82 0.04 0.79 ±0.03 vu 19 sisoridae chenua sisor rabdophorus 0.35 ±0.02 0.30 ±0.02 0.25 ±0.03 0.16 ±0.02 0.08 ±.0.02 cr 20 sisoridae conta catfish/ kuta kanti conta conta 1.24 ±0.07 1.20 ±0.06 1.15 ±0.05 1.11 ±0.04 1.05 ±0.02 dd 21 sisoridae kutakanti erethistes pusillus 1.00 ±0.02 0.97 ±0.02 0.93 ±0.01 0.12 ±0.01 0.10 ±.0.01 vu 22 sisoridae kani tengra pseudolaguvia muricata 0.55 ±0.04 0.50 ±0.03 0.46 ±0.04 0.43 ±0.03 0.34 ±0.02 cr 23 sisoridae chanua pseudolaguvia inornata 1.44 ±0.09 1.33 ±0.08 1.32 ±0.06 1.32 ±0.05 1.29 ±0.05 cr 24 clariidae cat fish/ magur clarias batrachus 0.50 ±0.03 0.47 ±0.03 0.45 ±0.03 0.43 ±0.02 0.40 ±.0.02 vu 25 heteropneustidae stinging catfish/ shingi heteropneustes fossilis 1.44 ±0.07 1.38 ±0.05 1.32 ±0.05 1.30 ±0.04 1.26 ±0.02 lc 26 chacidae cheka chaca chaca 1.70 ±0.10 1.60 ±0.09 1.15 ±0.08 1.47 ±0.05 1.33 ±.0.05 lr 27 olyridae gagora catfish / gobi arius gagora 1.48 ±0.07 1.40 ±0.06 1.35 ±0.05 1.32 ±0.04 1.27 ±0.02 en sub-total 33.03±0.60 31.45±0.58 30.31±0.57 29.41 ±0.57 28.09 ±0.56 clupidae 1 clupidae chapila gadusia chapra 1.80 ±0.08 1.50 ±0.07 1.12 ±0.06 1.00 ±0.05 1.00 ±0.04 en 2 clupidae hilsa tenualosa ilisha 0.98 ±0.08 0.95 ±0.06 0.90 ±0.04 0.85 ±0.02 0.82 ±0.01 en 3 clupidae gizzard shad/ chapila gonialosa manmina 0.44 ±0.08 0.38 ±0.06 0.34 ±0.04 0.31 ±0.02 0.28 ±0.01 en subtotal 3.22 ±0.68 2.83 ±0.56 2.44 ±0.44 2.16 ±0.36 2.10 ±0.38 eels 1 mastacembeli-dae baim mastacembalus armatus 3.44 ±0.14 3.35 ±0.11 3.33 ±0.09 3.24 ±0.08 3.12 ±0.07 vu 2 synbranchidae kuicha monopterus cuchia 3.09 ±0.10 2.98 ±0.10 2.91 ±0.09 2.80 ±0.08 2.27 ±0.08 en 3 mastacembelidae lesser spiny eel/ tara baim macrognathus aculeatus 2.90 ±0.13 2.83 ±0.12 2.76 ±0.10 2.63 ±0.10 2.54 ±0.09 en http://dx.doi.org/10.36956/sms.v3i2.436 35 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 4 mastacembelidae one-stripe spiny eel macrognathus aral 2.20 ±0.12 2.00 ±0.11 1.95 ±0.09 1.91 ±0.08 1.86 ±0.07 lr 5 mastacembelidae barred spiny eel/ pankal baim macrognathus pancalus 2.55 ±0.13 2.30 ±0.12 2.22 ±0.12 2.12 ±0.11 2.04 ±0.10 en subtotal 14.18 ±0.48 13.44 ±0.54 13.17 ±0.55 12.70 ±0.53 12.26 ±0.51 prawn 1 palaemonidae golda isa machrobrachiu rosenbergii 1.83 ±0.07 1.77 ±0.06 1.68 ±0.05 1.60 ±0.05 1.47 ±0.04 en 2 palaemonidae gura isa machrobrachium biramanicus 2.50 ±0.18 2.42 ±0.16 2.35 ±0.15 2.28 ±0.14 2.20 ±0.15 dd 3 palaemonidae gul isa machrobrachium malcolmsnii 1.61 ±0.09 1.44 ±0.05 1.32 ±0.05 1.25 ±0.04 1.18 ±0.04 vu 4 palaemonidae dimua icha macrobrachium villosimanus 1.90 ±0.20 1.80 ±0.11 1.71 ±0.10 1.64 ±0.09 1.57 ±0.10 lc 5 palaemonidae gura icha or kuncho chingri macrobrachium lamarrei 0.88 ±0.22 0.79 ±0.16 0.80 ±0.15 0.77 ±0.14 0.75 ±0.16 lr 6 palaemonidae kaira icha or beel chingri. macrobrachium dayanum 0.71 ±0.06 0.66 ±0.03 0.60 ±0.03 0.60 ±0.02 0.54 ±0.02 lr 7 palaemonidae chikna chingri. macrobrachium idella 0.92 ±0.02 0.88 ±0.02 0.82 ±0.01 0.77 ±0.01 0.59 ±0.01 dd 8 palaemonidae icha macrobrachium kempi 0.87 ±0.08 0.82 ±0.07 0.78 ±0.04 0.75 ±0.04 0.72 ±0.02 vu 9 palaemonidae chingri macrobrachium superbum 0.90 ±0.06 0.84 ±0.04 0.86 ±0.03 0.80 ±0.02 0.73 ±0.02 lc sub-total: 11.12 ±0.63 11.42 ±0.62 10.92 ±0.60 10.46 ±0.57 7.75 ±0.56 crabs/snail 1 potamidae kakra sartoriana spinigera 2.77 ±0.80 2.73 ±0.61 2.54 ±0.53 2.46 ±0.48 240 ±0.40 dd 2 grapsidae common kakra lobothelphusa woodmasoni 2.60 ±0.06 2.40 ±0.08 2.33 ±0.05 2.10 ±0.08 1.88 ±0.04 lr 3 grapsidae kakra acanthopotamon martensi 2.48 ±0.08 2.33 ±0.07 2.12 ±0.06 2.00 ±0.04 1.90 ±0.03 vu 4 parathelphusidae kakra pyxidognathus fluviatilis 1.08 ±0.03 0.92 ±0.03 0.88 ±0.02 0.82 ±0.02 0.78 ±0.01 lc 5 parathelphusidae kakra austrotelphusa transversa 1.88 ±0.04 1.72 ±0.05 1.44 ±0.04 1.34 ±0.03 1.22 ±0.01 en 6 unionidae bivalve lamellidens marginalis 1.12 ±0.04 1.00 ±0.03 0.90 ±0.02 0.85 ±0.02 0.79 ±0.01 vu sub-total: 11.93 ±0.75 11.10 ±0.76 10.21 ±0.72 9.57 ±0.70 8.97 ±0.67 reptiles 1 testudinidae elongated tortoise/ kachhap indotestudo elongata 0.29 ±0.03 0.22 ±0.02 0.19 ±0.02 0.13 ±0.01 0.09 ±0.01 cr 2 testudinidae asian giant tortoise/ chila kachhap manouria emys 0.35 ±0.04 0.32 ±0.03 0.21 ±0.02 0.18 ±0.02 0.11 ±0.01 en 3 geoemydidae river terrapin /bodo kaitta batagur baska 0.16 ±0.02 0.13 ±0.01 0.09 ±0.01 0.05 ±0.01 0.01 ±0.00 cr 4 geoemydidae painted roofed turtile/dhoor kachim batagur dongoka 0.18 ±0.02 0.14 ±0.02 0.11 ±0.01 0.08 ±0.01 0.03 ±0.07 en 5 geoemydidae oldham,s leaf turtile/ pata kachim cyclemys oldhami 0.26 ±0.02 0.20 ±0.02 0.14 ±0.01 010 ±0.01 0.00 ±0.00 e 6 geoemydidae spottedturtile/ kala kachim geoclemys hamiltonii 0.19 ±0.03 0.14 ±0.02 0.12 ±0.01 0.10 ±0.01 0.07 ±0.01 cr 7 geoemydidae brahminy river turtile/kali kaitta hardella thurjii 0.30 ±0.11 0.24 ±0.05 0.18 ±0.06 0.13 ±0.02 0.07 ±0.01 en 8 geoemydidae shila kachhap melanocheelys tricarinata 0.30 ±0.02 0.26 ±0.01 0.19 ±0.01 0.15 ±0.01 0.08 ±0.00 en http://dx.doi.org/10.36956/sms.v3i2.436 36 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 exploitation and various ecological changes in natural aquatic ecosystem of river and its floodplains, commercially important aquatic lives are in the verge of extinction which is in agreement with the findings of sarker [24]. the total catch data of the river exhibited a constant sharp decrease during 2015 and 2019. some of the important native species were noted to be losing their presence. the capture of fishes, crab and reptiles in the river was recorded highest in 2015-16, but decreased considerably in 2017-2018 and the similar situation continued in 2018-2019. small catfishes and small fishes are dominant groups caught from the river. the observation was similar to the findings of chakraborty and mirza [20], chakraborty [25] and chakraborty et al. [26,11]. as a result, commercially important three aquatic lives of river were recorded to be disappearing during this short 5 years experimental period. a decreasing trend in catch of the river was clearly recorded within five years which was similar to the report of chakraborty and mirza [19] and moyle and leidy [21]. a total of thirteen species of fresh water turtles were found in the mogra river and its floodplain. khan [27] reported that pangshura tecta are mainly distributed between the stretches of the ganges river and the brahmaputra river. bengal eyed turtle, morenia petersi was found in the rivers and its flood plains wetland. das [28] mentioned its occurrence in assam of india. morenia petersi was regularly caught by fishermen and expert tribal hunters. unfortunately, three important species of turtles became rare in their existence as per the catch data, within five years study period. the population of bivalve, lamellidens marginalis as found in the river and its flood plains has also been decreasing which is considered with the observation of ali [29] and chakraborty [25]. during the study period, fresh water pearl bearing mussels (bivalve, lamellidens marginalis) were identified in the river. shells of bivalve were utilized by rural people for production of lime which was utilized in aquaculture and agriculture land, and consumed with betel leaves and nuts. the wildlife comprises amphibians (bufo melanostictus, rana tigerina, rana limnocharis, rana cyanophyctis and salamandra salamandra etc.) aves (whistling duck, great crested grebe, great cormorant, red crested pochard, water cock, swamphen, great black headed gull, gray-headed fish eagle, curlew, spotted redshank etc.) and mammals (musk shrew, fishing cat, small indian jackal, flying fox etc.) were previously reported by chakraborty et al. [26]. the study clearly indicates that the aquatic lives of the river were subjected to over exploitation resulting in gradual decline in their catch. the stock of aquatic animals is reducing due to pollution and destructive fishing practices [30,31,11]. indiscriminate killing of fish occurred due to the use of pesticides in improper doses[6], use of forbidden chemicals, and aerial spray of chemicals as used in paddy field which was very much similar to the observation of chakraborty [31] and mazid [32]. intervention to control floods, adoption of new agricultural technologies and construction of road networks altered the ecology of rivers and its flood plains significantly which supported the views of khan [33] and ali [29]. decreased stock of the wild brood fishes in their breeding ground also resulted in a reduction of biodiversity as noted by nishat [34], zaman [35] and chakraborty [36]. 4. conclusions to save the stock of aquatic species in the river, a team of local management committee like hilsa fisheries management technology is needed to develop a working frame-work. the deeper area of the river must be declared as a sanctuary to protect the aquatic lives, stricken enforcement of fish act-1950 in the river, ensured stopping unplanned construction of flood control embankments, drainage system and sluice gates, conversion of inundated land to cropland (reducing water area); and controlling use of pesticides and agrochemicals in the floodplains of the river can save the ecosystems. the sustained produc9 geoemydidae snail eating turtile/ kali kachhap melanocheelys trjuuga 0.40 ±0.02 0.35 ±0.02 0.30 ±0.01 0.10 ±0.00 0.00 ±0.00 e 10 geoemydidae bengal eyed turtile morenia petersi 0.08 ±0.01 0.06 ±0.01 0.05 ±0.01 0.04 ±0.00 0.0 ±0.00 e 11 geoemydidae indian turtile/ kori kaitta pangshura tecta 0.13 ±0.02 0.10 ±0.01 0.10 ±0.01 0.09 ±0.01 0.07 ±0.01 cr 12 geoemydidae tent turtile/ majhari kaitta pangshura tentoria 0.07 ±0.01 0.06 ±0.01 0.06 ±0.00 0.05 ±0.01 0.04 ±0.00 en 13 trionychidae ganges turtile/ khalua kachim aspideretes gangeticus 0.35 ±0.03 0.32 ±0.02 0.30 ±0.03 0.28 ±0.02 0.16 ±0.01 vu sub-total 3.06 ±0.11 2.54 ±0.10 2.04 ±0.08 1.48 ±0.06 0.73 ±0.05 total 170.63 ±8.81 159.93 ±7.40 150.98 ±6.66 143.16 ±5.87 134.75 ±5.02 http://dx.doi.org/10.36956/sms.v3i2.436 37 sustainable marine structures | volume 03 | issue 02 | july 2021 distributed under creative commons license 4.0 tion level from the river will also ensure livelihood of the fishers. acknowledgement the authors are greatfully acknowledged to department of fisheries, bangladesh for kind suport and cooperation. references [1] verma a. k. 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