Simulation And Optimization For Inventory Control Of Complex Logistics System

With the rapid development of economic globalization, supply chain andlogistics system is more and more showing characteristics of random, complex,dynamic, multilevel and network. Various enterprises in order to promote theircompetitiveness need to reduce operating costs by improving operationalefficiency and reduce customer response time, so they pay more and moreattention to inventory coordinated optimization problem. The problem hasbecome one of the hot issues of concern for the related scientific researchworkers. Therefore, this paper uses simulation method to study optimizationproblem for the stochastic demand and stochastic lead-time of two-echeloninventory system. The specific contents are as follows:This paper addresses the optimization of the two-echelon inventory systemwhich consists of a supplier and multiple vendors. In the two-echelon inventorysystem the customer demand of each vendor and booking lead-time of thesupplier and all vendors are all random variables, and the supplier and all thevendors make use of the hybrid policy (T, s, S) to manage their inventories. Themathematical model of the two-echelon inventory system, which is to minimizethe expected inventory cost of the whole system by determining the safeinventory s and maximum inventory S of the supplier and each vendor, isproposed. Then the simulation flow is designed and the simulation model of thesystem based on Arena is founded. Finally, according to the system parametersand using Monte Carlo method randomly selected multiple sets of data fromtwo-echelon inventory system which consists of a supplier and three vendors,comparative the simulation results obtain the approximate optimal solution ofthe system.According to the Monte Carlo method low searching efficiency, this paperusing simulation software of Arena embedded VBA design an optimizer whichbase on genetic algorithm.Through the optimizer and emulator to interact witheach other, the parameter of two level inventory is assigned to the simulator,comparison and analysis of simulation results of simulation model to optimizethe two level inventory system. Firstly, According to the characteristics of thetwo-level inventory systems design the optimization algorithm based on geneticalgorithm. Secondly, make emulator simulation results as the algorithm anddesign the algorithm of chromosome coding, crossover operator, mutationoperator and the selection operator. Lastly, using Visual Basic realize the algorithm. Through the Arena built-in VBA events, combined with Arenainternal control and external control method to control simulation model. Theinternal control method can control the simulation operation parameters andvariables. The external control method can control repeated simulation process.The combination of these two methods can not only enhance the simulationefficiency of the two-echelon inventory system but also achieve to control therepeated simulation. The experimental results show that, by using optimizerbased on genetic algorithm to control simulation optimization process, theapproximate optimal result of which is better than Monte Carlo method to obtainthe approximate optimal result and optimizer based on genetic algorithm has ahigh efficiency.