Modeling And Simulation-based Optimization On Control Strategies Of Multi-echelon Inventory In Hybrid Supply Chain

Multi-echelon inventory control is the main form of the management of supply chain inventory,it has been paid extensive attention by scholars both domestic and abroad because of its importance in supply chain management.Process industry,represented by metallurgy and petrochemical industry,has the characteristics such as high investment,high costs,and high resource utilization,so it plays a key role for industrialization.The supply chain of the process industry contains a lot of intermittent production process,it is regarded as the discrete system because of the long production time,which is triggered by the order,while the orders are available at any time in the sales,the processing time is relatively short,and it is considered as a time continuous system.The supply chain,combined by these two parts,presents the characteristics of the hybrid system,which is a kind of typical model of the supply chain.So far,the supply chain of discrete manufacturing industry has been widely studied by scholars in various countries,the development of theory is more mature,and many kinds of inventory control strategies have been obtained.While the research on the hybrid supply chain of the process industry and the results of the multi-echelon inventory control strategy are relatively less,which is far behind the development state of the process industry,and does not match its economic status.Compared with the discrete manufacturing industry,the production of the process industry has the characteristics of mass intermittent production,and its supply mode has more complex influence on the downstream enterprises.Therefore,it puts forward higher requirements for the inventory control of the downstream enterprises.At the same time,a large number of uncertain factors affect the hybrid supply chain of the process industry,as well as the supply chain of the discrete manufacturing industry.The analytical method cannot effectively solve the complex change problem in multi-echelon inventory system of the supply chain.The simulation method is the ideal tool.However,simulation is not an optimization method,it cannot give the optimal solution or satisfactory solution of the problem.It is necessary to combine simulation and optimization technology to form a Simulation-based Optimization(SBO)method to realize the system optimization.In this paper,the simulation model of multi-echelon inventory control system of hybrid supply chain is established based on the supply chain of multi-product mix production in process industry.A variety of mixed inventory control strategies are designed based on the method of control engineering.Based on this simulation model,a simulation-based optimization method is applied to the basic multi-echelon inventory control system.The decision-making problem of hybrid supply chain is optimized,together with multi-echelon inventory control system,which is affected by various uncertainties.The major work of this dissertation focuses on the following five parts.(1)The concept of hybrid system is introduced into the management of supply chain inventory.It is proposed to combine the intermittent batch production link with the continuous sales link in the process industry enterprise.The simulation model of inventory control of hybrid supply chain is established,which is closer to the operation state of enterprises,and can reflect the relationship between supply chain enterprises more appropriately.(2)Multi-product mixed production is realized in the multi-echelon simulation control model of supply chain inventory.The effect of order quantity on production scheduling and delivery time is analyzed when all product orders arrive at the same time.The effect of intermittent production on the inventory control in downstream enterprises is analyzed at the same time.(3)The Push/Pull/CONWIP strategy of multi-echelon production and storage system of discrete manufacturing industry is extended to the hybrid supply chain of process industry.Based on the idea of system design in control engineering,a feedback control strategy FBC for inventory control is designed,and the control theory is applied to supply chain inventory management.The proportional integral control algorithm is used to modify the inventory control strategy,reflecting the characteristics of multidisciplinary and multi technology integration.(4)Considering the characteristics of uneven distribution of resources,unbalanced regional development and regional differences in transportation and demand,the effects of uncertainty of demand,uncertainty of transportation time,uncertainty of productivity and unbalance of demand on inventory control are analyzed.The order variance ratio,the integral of square of error and the mean of maximum error are used as the performance indices to quantify the demand amplification in the supply chain,namely the bullwhip effect.The uncertainty of the hybrid supply chain is quantified by information entropy,and the service level and the stability of the overall operation are evaluated comprehensively.(5)For the uncertainty and dynamics of supply chain and logistics system,simulation method can effectively make up for the deficiency of analytical methods,so it plays an important role in the research on supply chain.The simulation based optimization method is combined with the genetic algorithm,and they are used to optimize the control parameters of each strategy.Simulation-based GA method is proved feasible and effective for optimization of inventory control strategy,and it can provide the decision basis for the enterprises in supply chain.At the same time,the simulation time is effectively saved and the efficiency of the supply chain optimization is improved by setting the case base and choosing the numerical calculation method.