طرح بهینه سازی محصولات و مدل شبیه سازی در یک مرکز توزیع در چند سطح

We consider the product allocation problem in logistics engineering, which allows incorporating various aspects in horizontal and vertical direction. These aspects include carrying time, the turnover rates of products, relevance of product demand, elevator waiting time, vertical transportation time, etc. we develop a 0-1 programming model with two objectives-minimization of total transportation time and maximization of relevance of product demand. In order to obtain average waiting time of every level, we establish an elevator simulation model considering the limitation of elevator capacity. The proposed optimization model can be solved using Genetic algorithm heuristically. A numerical example shows its effectiveness.

Distribution center operation and management is one of the essential parts of manufacturing and service operations. The product layout is a key to distribution center operations. The product layout problem is concerned with the question of positioning products to storage locations. At present literatures on single-level product layout are highly extensive. Though multi-level distribution center is more and more popular in the manufacturing and service sections, research on product layout in a multi-level distribution center has received less attention. The earliest work on the multiple-level layout problem was done by Johnson (1982). He investigated the problem of relative location of facilities in a multiple-floor building. Lai,Xue, and Zhang(2002) investigated a multi-level warehouse layout problem considering multiple storage areas in different levels of a warehouse . Lai,Xue, and Zhang(2006) considered a multi-level warehouse layout problem again and proposed a class of new heuristics by combining a genetic algorithm and path linking strategy to solve the problem. Literatures above share the same assumption - The elevator capacity is enough. That is, the vertical transportation operation is always available. However in real life it is common for product to waiting for the elevator because of the limitation of elevator capacity

Different from existing research, this paper considers the limitation of elevator capacity, i.e., it is common for product to wait for elevator. Since waiting time is random variable which it is hard to obtain theoretically, we establish elevator simulation model to get the average waiting time of every floor. Putting order picking time and average waiting time together, we can get hieratical transportation time .With two objectives-minimization of total