A multistage heuristic for storage and retrieval problems in a warehouse with random storage

The warehouse is one of the essential components of logistics and supply chains. The efficiency of the whole chain is affected by the performance of warehouse operations and, more particularly, the storage and retrieval of goods. This paper considers a storage and retrieval problem in a real warehouse with random storage and different types of forklifts, depending on the locations they can access. The problem deals with selecting locations to store/retrieve a predefined set of pallets, assigning an adequately skilled forklift to each operation and determining the order in which each forklift will perform its operations so that the total employed time is minimized. The problem is solved heuristically by decomposing it into three subproblems, each one handling one of the three key decisions of the problem, and taking into account congestion considerations. The paper also studies two modifications of the problem, adding secondary objective functions. Computational results compare the effectiveness of the proposed algorithms for the different problems in a stochastic environment via simulation.