Research On Optimization Models And Policies Of Picking And Storage/Retrieval Efficiency In Warehouse System

Warehouses are an important component of modern supply chains and play a crucial role, which determines the success or failure of businesses. Warehouses can store tentatively the products and work-in-process in order to accommodate the variability of supply chains. These variabilities may be caused by many reasons, for example the consolidation of work-in-process or products from different suppliers; product seasonality; value-added process such as labeling, repacking and product customization. The performance of warehouses plays a tremendous role in determining the efficiency and effectiveness of logistics distribution network in supply chain. Many issues can affect the performance of warehouse system, including order picking, storage/retrieval operation, warehouse design, warehouse layout and warehouse zoning. This dissertation studies the effect of order picking and storage/retrieval operation on the performance of warehouse system.First, the dissertation studies an order batching problem of the picking system. In this problem, the dissertation formulates an order throughput time model, and analyses the effect of order batching on the expected customer order throughput time with variable time window batching. In addition, the dissertation discusses the effect of the number of picking aisles, the expected interarrival time of orders, the length of picking aisles and the percentage of the low storage level on the batch size and the expected throughput time for a customer order.Second, the dissertation considers the optimization problems in the Split-Platform Automated Storage and Retrieval System (SP-AS/RS) with Input and Output (I/O) dwell point policy. The dissertation presents a continuous travel time model of the Dual command Cycle (DC) in the SP-AS/RS under I/O dwell point policy and validates its accuracy by computer simulations. After comparing with the existing model of the Single command Cycle (SC), the dissertation finds that the DC is better than the SC in terms of the expected travel time. Then the dissertation builds two continuous optimal travel time models of the DC in the SP-AS/RS under the I/O dwell point policy. The first model considers the situation, where the storage and retrieval operations locate in a rack, while the second model considers the situation, where the storage and retrieval operations locate in two adjacent racks. Then the dissertation uses convex optimization to analyse the performance of the two proposed models under different situations and validates the accuracy and effectiveness of the two proposed models.Finally, the dissertation studies the optimization problem in the SP-AS/RS with stay dwell point policy. In this problem, the dissertation first builds a travel time model of the DC in the SP-AS/RS under stay dwell point policy. After proposing the travel time model, the dissertation uses computer simulation to validate the accuracy of the proposed model. Then the dissertation compares the proposed model results with those from the existing model of the SC under stay dwell point policy and validates the effectiveness of the proposed model.