Microsoft Word - ETASR_V12_N3_pp8548-8554 Engineering, Technology & Applied Science Research Vol. 12, No. 3, 2022, 8548-8554 8548 www.etasr.com Bella & Zohra: Application of Fminsearch Optimization to Minimize Total Maintenance Cost with the … Application of Fminsearch Optimization to Minimize Total Maintenance Cost with the Aim of Reducing Environmental Degradation Yasmina Bella LAS Laboratory Electrical Engineering Department Ferhat Abbas Sétif University 1 Setif, Algeria b_yasmina2014@ univ-setif.dz Kebbab Fatima Zohra DACHR Electrical Engineering Department Ferhat Abbas Sétif University 1 Setif, Algeria fatimazohra.kebbab@univ-setif.dz Received: 7 March 2022 | Revised: 24 March 2022 | Accepted: 28 March 2022 Abstract-This study examined a production system under deterioration and its impact on the degradation of the environment. The environment degrades as the production system reaches a certain level of deterioration. To reduce environmental degradation, the system's deterioration is monitored through scheduled inspections, after which preventive or corrective actions are taken. To achieve the optimum inspection dates that minimize the average total cost per time unit, the Fminsearch algorithm was applied to calculate the optimal inspection dates for two cases of sequential inspection: periodic and aperiodic. To validate the performance of the proposed Fminsearch algorithm, simulation results were compared with the Nelder-Mead method. The comparison results showed the superiority of the Fminsearch algorithm in optimizing inspection maintenance dates to reduce the environmental degradation ratio. Keywords-environment degradation; fminsearch algorithm optimization; maintenance; Nelder-Mead; production system I. INTRODUCTION Environmental protection is described by international standards to which manufacturers must comply. The degradation of industrial systems can impact the environment in many ways. For example, the process of meeting energy demands raises concerns about energy sustainability and environmental protection, in conjunction with the market and regulatory requirements [1, 2]. Many environmental taxes have been imposed in recent decades all over the world. In the United States, the use of pollution prevention activities has increased significantly in the last two decades. The Pollution Prevention (P2) program is considered one of the main ways to reduce pollution [3, 4]. To ensure the efficient operation of an industrial system and meet the requirements of the environmental protection standards, inspection and maintenance activities are carried out. Inspection aids in controlling the degradation process of a production system and collecting crucial data on its reliability to determine the maintenance measures to be taken. Since the difficulties faced in maintenance inspections are attracting a lot of attention in the industry, many inspection strategies have been developed. In [5], the optimal inspection dates and treats for the sequential inspection strategy were calculated, while a similar model was used in [6]. In [7], the same model was proposed with the estimate of the delay of the inspections, integrating the penalty cost in the mathematical model. The optimal inspection period and the maintenance threshold of system degradation were calculated in [8, 9]. A mathematical model was developed in [10] for the overall cost, including the production cost along with the maintenance action cost. This study analyzed an inspection strategy that covers the environmental impact of the degradation of a production system. This strategy decreases degradation through maintenance actions to reduce environmental impact [11-13]. The system under consideration is submissive to continuous growing degradation. In this system, failure is detected only when it occurs, while the level of degradation of the system is only known after periodic or aperiodic sequential inspections. After checking the level of degradation when it exceeds a threshold, preventive actions are planned after a fixed timeframe, while corrective actions are carried out immediately after a system failure [14]. The main task was to minimize environmental degradation by decreasing the overall maintenance cost. The total cost is made up of the cost of corrective and preventive operations and inspection actions and the cost of penalties due to the environmental impact of system degradation. The main contribution of this study is the resolving of the optimization problem based on the Fminsearch algorithm. This algorithm is a direct search method to reduce non-linear functions [15-17]. II. DESCRIPTION OF THE PROBLEM A. Notations The following notations are used: • ���: The average cost of corrective maintenance. • ���: The average cost per time unit of severe environmental degradation. Corresponding author: Yasmina Bella Engineering, Technology & Applied Science Research Vol. 12, No. 3, 2022, 8548-8554 8549 www.etasr.com Bella & Zohra: Application of Fminsearch Optimization to Minimize Total Maintenance Cost with the … • ����: The average cost of an inspection. • � �: The average cost of preventive maintenance. • � : The timeframe to perform preventive maintenance. • Tth: A random elapsed time from when the system degradation began until it reaches the threshold. • �: Variable of � on the time axis. • ��: The probability density function of �. • � : A random elapsed time from instant � until failure (lifetime of the system after exceeding the threshold). • �: Variable of �, from the instant �. • ��, ��: probability density and distribution function of � respectively. • ����: A random number of examinations during a cycle. • �∗���,��,…���: The vector of examination dates. • Trd: A random time of excessive environmental degradation. • Tcy: A random cycle time measured between two consecutive maintenance actions: preventive or corrective. • ��� : Probability that the cycle will end with corrective maintenance action. • � � : Probability that the cycle will end with preventive maintenance action. • Ctot: The total cost incurred by maintenance and examination operations and by environmental degradation during a cycle. B. Assumptions This study was based on the following assumptions: • After each inspection, two types of action are likely: to leave it as it is or perform preventive maintenance. • Corrective maintenance is performed immediately after a system failure. • The inspection actions are assumed to be perfect, i.e. the inspection reveals the actual level of the system’s degradation without error. • Corrective and preventive maintenance actions are meant to be perfect. • The durations of inspection and maintenance actions are negligible. • System degradation leads to environmental degradation. • The system only fails if its degradation level exceeds the alarm threshold. Such a failure is supposed to be detected automatically (self-declared failure case). • The system works as it should after corrective or preventive maintenance actions. • The costs ���, � � , ���� and ���, with the timeframe � as well as the densities �� and �� are kept in the system’s database. • Preventive maintenance action is scheduled after a timeframe � , if the inspection reveals that the level of degradation has exceeded the alarm threshold, as seen in Figure 1. Any inspections in this interval are canceled. As an example: in the interval [��, �� + � ], the inspections are canceled. Fig. 1. Evolution of system degradation and distribution of examinations over time. III. THE MATHEMATICAL MODEL OF MAINTENANCE COST This section presents the mathematical model of the average total cost per time unit Q of maintenance. Q is defined as the ratio between the average global cost �� ! � and the average cycle time � �"� [18]: # $ �� ! � / � �"� (1) This cost includes the cost of preventive and corrective actions, the inspection cost, and the penalty cost. In the case of corrective action, the average cost is ���� & ����, while the expression �� � & � �� indicates the average cost in the case of preventive maintenance. ������ is defined as the average number of inspections during the time cycle, and their average cost is given by ���� & ������. � �� � is the average time of the critical environmental degradation and the expression ��� & � �� � corresponds to the penalty cost due to severe environmental degradation. The following formula illustrates the average cost: �� ! � $ ���� & ��� � ' �� � & � �� ' ����� & ������� ' ���� & � ���� (2) This formula uses the proposals developed in [4, 18]. The probability ��� that a time cycle will end with corrective actions is given by: ��� $ ∑ ) ����� ' � * �� �����+�,-,-./��0� (3) The probability that corresponds to the case where the time cycle ends with preventive action is given by: � � $ 1 * ��� (4) The average number ������ of examinations during a time cycle is given by: ������ $ ∑ 2 ���0� ) ����3� * �� �����+� ,-4/5 × ) ���� * �� �����+��,- 5 (5) Engineering, Technology & Applied Science Research Vol. 12, No. 3, 2022, 8548-8554 8550 www.etasr.com Bella & Zohra: Application of Fminsearch Optimization to Minimize Total Maintenance Cost with the … The average time � 6�� of excessive environmental degradation through a time cycle is given by: � 6�� $ ∑ ) �) 71 * �����8+�������+�,-39:;< 5,-,-./��0� (6) The expression of the numerator of the function presented by (1) is concluded from (2) - (6) as: �� ! � $ �= ��� * � �> ∑ ) ��=�� ' � * �>�����+�,-,-./��0� ' � � '���� ∑ 2 ���0� ) ����3� * �������+� ,-4/5 ) ���� * �� �����+��,- 5 ' ��� ∑ ) �) 71 * �����8+�� �����+� ,-39:;< 5,-,-./��0� (7) The denominator of (1) is given by: � �"� $ ∑ ) � ?-?-./��0� t ' ) 71 * �����8 +� � ?-39:;∑ ) HI=,- 39:; < >JI� �� K-K-./ L-M/ 3E;G 3N-LO ∑ � �L-M/ ) H�,-4/< �JI� �� K-4/P ) H�,- < � JI� �� �K- P 3NQI ∑ ) �) 7�N is unattained, n increases. If it was attained, iterations stop. Finally, the solution vector of examination dates �� that match up to the minimum value #���� is selected. Fig. 2. Pseudo code of the Fminsearch algorithm. Two techniques were proposed to calculate the optimal inspection dates of the production system: periodic and aperiodic sequential inspection. The results of the Fminsearch algorithm were compared to the Nelder-Mead optimization method [18, 20]. B. Numerical Applications The above procedure was used to estimate the optimal examination dates. The input data were provided: probability densities�� and��, the costs ���, � � ,���, ���� and time flow � . Time was expressed in time units, while cost was expressed in monetary units. λ is the ratio between the mean time � 6�� of severe environmental degradation and the average time � �" � of the time cycle: [ $ \�9]I�\�9F^� (10) Therefore: [ $ ∑ ) Y) 7�3.0.CO;2-0. [7] A. Chelbi and D. 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