Comparative Study on Storage Location Assignment Problem (SLAP) in Double-Deep 3PL Warehouse

Abstract

Storage Location Assignment Problem (SLAP) is a study on how products should be stored in a warehouse space. Although studies have shown that arranging products based on their duration of stay can decrease the stacker crane travel time, this policy requires exact knowledge of the product's duration of stay. To the best of the author's knowledge, most studies on duration-of-stay storage policy (DOS) are on single-deep automated storage/retrieval systems (AS/RS), and hence their viability in double-deep AS/RS has not yet been extensively studied. To close this literature gap, this paper aims to study the performance of DOS on double-deep AS/RS in third-party logistics (3PL) warehouses. The study starts by building a simulation model of a double-deep automated warehouse. Based on the warehouse model, simulations using three different policies: random storage policy (RAN), closest-open-location storage policy (COL) and DOS are performed. To evaluate the effectiveness of the storage policies, the average dual-command-cycle (DCC) travel time for each operation is compared under varying warehouse conditions. The results indicate that the duration-of-stay (DOS) storage policy consistently outperforms both random (RAN) and closest-open-location (COL) policies in reducing travel time and mitigating blockage. This demonstrates the importance of incorporating expected retrieval behaviour into storage location assignment decisions.