pedram Pourkarim guilani; Mani Sharifi; parham azimi; maghsoud Amiri
Abstract
Due to the high sensitivity in applying of electronic and mechanical equipment, creating any conditions to increase the reliability of a system is always one of the important issues for system designers. Hence, making academic models much closer to the real word applications is very attractive. In the ...
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Due to the high sensitivity in applying of electronic and mechanical equipment, creating any conditions to increase the reliability of a system is always one of the important issues for system designers. Hence, making academic models much closer to the real word applications is very attractive. In the most studies in the reliability area, it is assumed that the failure rates of the system components are constant and have exponential distributions. This distribution and its attractive memory less property provide simple mathematical relationships in order to obtain the system reliability. But in real word problems, considering time-dependent failure rates is more realistic to model processes. It means that, the system components do not fail with a constant rate during the time horizon; but this failure rate changes over the time. One of the most useful statistical distributions in order to model the time-dependent failure rates is the Weibull distribution. This distribution is not a memory less one, so it was impossible to apply simple and explicit mathematical relationships as the same as exponential distributions for the reliability of a system. Therefore, researchers in this field have used simulation technique in these circumstances which is not an exact method to get near-optimum solutions. In this paper, for the first time, it is tried to obtain a mathematical equation to calculate the reliability function of a system with time-dependent components based on Weibull distribution. Also, in order to validate the proposed method, the results compared with exact solution that exists in literature.
SEYYED ALI Mirnezhad; Parham Azimi; Ahmad Yousefi Hanoomarvar
Abstract
In the present study, the redundancy allocation problem (RAP) of series-parallel system has been investigated to maximize the system's availability. To achieve the research objective, budget, weight and volume constraints, and the maximum and minimum number of elements assigned to each subsystem have ...
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In the present study, the redundancy allocation problem (RAP) of series-parallel system has been investigated to maximize the system's availability. To achieve the research objective, budget, weight and volume constraints, and the maximum and minimum number of elements assigned to each subsystem have been considered. The main innovation of this research is to consider the failure and repair rates of components with non-exponential distribution function in the process of optimization. Taking into account failure and repair rate via non-exponential distribution function makes it impossible to calculate accessibility using mathematical relations. Therefore, the present study has used simulation method to calculate system availability. Since the simulation has no optimization capability On the other hand, in the redundancy allocation problem, it is necessary to evaluate the system availability recurrently in order to find the optimal solution. Further, due to the high degree of difficulty of developed mathematical function, the genetic metaheuristic algorithm was used to solve it. Finally, the efficiency of the genetic algorithm was measured against particle swarm algorithm and simulated annealing algorithm. To compare fairly, the parameters affecting the algorithms are adjusted using the Taguchi method and the algorithms are in their best practice. The computational results prove the high ability of the genetic algorithm in optimizing the concerned problem.
Arman Sajedinejad; Meysam Lotfi
Abstract
In this paper, a non-periodic preventive maintenance scheduling optimization model for multi-component systems is provided based on the maximum availability of system components. In addition to providing the required level of system reliability and satisfy other system constraints (maintenance activities ...
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In this paper, a non-periodic preventive maintenance scheduling optimization model for multi-component systems is provided based on the maximum availability of system components. In addition to providing the required level of system reliability and satisfy other system constraints (maintenance activities and available resources), total costs (direct and indirect) associated with minimal maintenance and, if necessary, one of the maintenance activities include in inspected and serviced simple, preventive repair and preventive replacement for each component, is proposed. Each of these activities uses various sources and regarding the position of the repairing component, effects differently on the reliability of the system. The costs considered include in direct costs (simple service, repair and replacement) as well as indirect costs (out of order and random failures). Since the proposed model has a complex structure, in order to solve the problem, the Genetic Algorithm (G.A) has been used and the results is presented. In the end, performance and use of this model, for a 10-part series - parallel is presented in the form of a case study.
Seyed Alireza Mir Mohammad Sadeghi*,; Mahdi Moghan; Mahdi Keshavarz; Mehrnoosh Keshavarz; Fatemeh Khaje Nori
Abstract
Subway network extension, growing expansion an inherent management complexities, made it necessary to use scientific approach, modern technology and global experiences about maintenance. Many equipments and trains of subway network, consist of repairable items which consume considerable human and financial ...
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Subway network extension, growing expansion an inherent management complexities, made it necessary to use scientific approach, modern technology and global experiences about maintenance. Many equipments and trains of subway network, consist of repairable items which consume considerable human and financial resources of the organization. This paper aims to measure the efficiency and rank ventilation system of Tehran's DC trains and it's subsystems using three-stage relational data envelopment analysis model. About the importance of Tehran’s subway ventilation system, we can say that for 8 months of the year, ventilation system after driving engines which support the movement of trains, gets most important attention of operation management. In this paper with defining ventilation system as decision-making units, we use it to evaluate the system performance and ultimately for maintenance strategy, including an estimate of the maintenance workshop capacity, spare parts and requiring labor. Due to various errors such as human errors, machinery errors, limitations of field data analysis and etc, in this paper fuzzy logic is used to overcome the uncertainly in data. Also, reliability, availability and maintainability analysis, which are most important indicators in the maintenance field, have been used to determine the ventilation system inputs and outputs
Reza Alikhani; Mahmoud Saremi
Abstract
The scheduling of preventive maintenance and replacement is one of the crucial issues in the literature of system reliability and maintenance engineering. The importance of this issue is more evident in series system in which by stopping a component the whole system will stop. However, the quest of the ...
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The scheduling of preventive maintenance and replacement is one of the crucial issues in the literature of system reliability and maintenance engineering. The importance of this issue is more evident in series system in which by stopping a component the whole system will stop. However, the quest of the efficient periodicity maintenance for all of component of a system which has antagonistic objectives is not a trivial task. The aim of this paper is to presenting scheduling model of preventive maintenance and replacement for series system by variable and not predetertmined periods and also by applying inflation in the model. The model is designed based on fuzzy multi-objective and integer non-linear programming. Also the proposed model is solved for a case study with numerical example and furthermore, analysis of various senarios, the effects of inflation on the model will be considered. The results show that applying inflation in the model changes not only scheduling for replacement and maintenance, but also affects the effective age of components
