| Multi-unit systems,which can be decoupled or divided into several interrelated units or small-scale systems,are controlled by the same goals or constraints to achieve specific functions by sharing resources.Inertial confinement fusion laser devices,large-scale wind farms and large-scale petroleum facilities are typical complex multi-unit systems.This kind of multi-unit system is characterized by many types and quantities of units,high reliability requirements and high life cycle cost.Therefore,the comprehensive research on the reliability,economy and maintenance management of multi-unit system has attracted more and more attention in academic and engineering fields.This study uses typical multi-unit system as research object,in view of the system task oriented,degradation,failure mode,hierarchy and complexity of economic dependence and so on.Based on the cost management,inventory management and maintenance management theory,we use LCC modeling,METRIC model,LORA,genetic algorithm and iterative algorithm as research methods.A comprehensive study on cost optimization and maintenance strategy of multi-unit system under reliability constraints has carried out.In the core chapters,this paper selects the data of the shenguang prototype device built in2007,the shenguang host device officially,and the new laser device in the design stage as examples to verify the feasibility of the algorithm and model.The main research contents and innovative achievements are as follows:(1)System LCC modeling and spare parts stocking optimization with availability constraints.The system design optimization based on task availability is closely related to its economy.Under the condition that the life of key unit obeys威布尔distribution,the design cost function,manufacturing cost function and maintenance support cost function of multi-unit system are given respectively.Based on the principle of equal cumulative failure probability,a life-cycle cost optimization model with availability constraint is presented.Finally,a multi-unit switch system is taken as an example to verify the feasibility and effectiveness of the model and method.It is found that the number of units and maintenance cycle are the key factors affecting system LCC.Operation management should reduce system LCC by reducing failure maintenance time.(2)Optimization of maintenance strategy for degraded multi-unit systems under reliability constraints.In the case of unit degradation,the problem of reliability design and comprehensive optimization of preventive maintenance strategy become more complex.Considering that the failure of multi-unit system is subject to威布尔distribution,a life-cycle cost optimization model of multi-unit system with reliability constraint is established.Exponential growth of combinatorial size caused by large number of units will lead to difficulty in nonlinear selection.Genetic algorithm programming is used to quickly solve the global optimal solution,including unit reliability in the design stage and system preventive maintenance cycle in the use stage.Finally,the correctness and effectiveness of the model and algorithm are verified through the analysis of typical examples,and the relationship among decision variables such as maintenance improvement factor,unit reliability and preventive maintenance cycle is explored.The research results are helpful to simplify the reliability engineering design process and have certain theoretical and application value.(3)Optimization of multi-level spare parts stocking and maintenance level for multiunit system with availability constraint.METRIC and LORA methods are typically used for maintenance level and spare parts stocking optimization problems.Because LORA does not consider the availability of spare parts,solving LORA and spare parts inventory problems sequentially may result in a suboptimal solution.Based on these considerations,a joint optimization method is proposed to minimize maintenance support costs under system availability constraints.The influence of different faults on the maintenance level and spare parts stocking was expressed by introducing the maintenance capability factor and multiple maintenance strategies into the joint optimization model.Therefore,a bridge relationship between LORA and the METRIC model is established,and an improved iterative algorithm is used to solve the joint optimization model.A typical fleet system was taken as an example to verify the correctness and effectiveness of the model and algorithm.Compared with the separately optimized spare parts stocking and maintenance level,this joint optimization strategy could effectively reduce maintenance support cost.(4)Two-echelon maintenance support cost modeling and strategy optimization for multi-unit system under multiple failure modes.Considering multiple failure modes,the research on spare parts stocking allocation strategy of multi-unit system maintenance support is more suitable for engineering practice.Firstly,from the perspective of influencing the execution result of multi-unit task system,a two-echelon maintenance support guarantee cost model with availability constraint is constructed through a failure classification method.However,multiple failure modes will lead to exponential growth of spare parts stocking configuration combinations,resulting in nonlinear optimization difficulties,which can be solved by developing a fast iteration-greedy heuristic algorithm.Finally,the correctness and effectiveness of the model and algorithm are verified by practical engineering case analysis.The influence of spare parts stocking level,maintenance time and failure mode on maintenance support strategy of different levels of maintenance sites was explored respectively,and suggestions for significant improvement of maintenance support capacity has given.The research results are helpful to improve the operating efficiency of multi-unit system and have certain theoretical and application value.From the perspective of economic dependence and aiming at the complexity of multi-unit system,the research results of multi-unit system cost optimization and maintenance strategy under reliability constraints obtained above will help simplify the optimization process of reliability engineering design of system engineers.It will be beneficial and necessary to improve the overall economy of system development and operation.It is also helpful to enrich the scope and means of systems engineering technology and provide reference for the economic research of other complex systems. |
