Kees Jan Roodbergen

Storage yard operations in container terminals: Literature overview, trends, and research directions

Inbound and outbound containers are temporarily stored in the storage yard at container terminals. A combination of container demand increase and storage yard capacity scarcity create complex operational challenges for storage yard managers. This paper presents an in-depth overview of storage yard operations, including the material handling equipment used, and highlights current industry trends and developments. A classification scheme for storage yard operations is proposed and used to classify scientific journal papers published between 2004 and 2012. The paper also discusses and challenges the current operational paradigms on storage yard operations. Lastly, the paper identifies new avenues for academic research based on current trends and developments in the container terminal industry.

Transport operations in container terminals: Literature overview, trends, research directions and classification scheme

Internal transport operations connect the seaside, yard side, and landside processes at container terminals. This paper presents an in-depth overview of transport operations and the material handling equipment used, highlights current industry trends and developments, and proposes a new classification scheme for transport operations and scientific journal papers published up to 2012. The paper also discusses and challenges current operational paradigms of transport operations. Lastly, the paper identifies new avenues for academic research based on current trends and developments in the container terminal industry.

Improving Order-Picking Response Time at Ankor's Warehouse

Ankor is a wholesaler of tools and garden equipment, carrying such well-known brands as Skandia. Its warehouse is under continuous pressure to improve its efficiency while it is confronted with several specific requirements in its order picking, like the requirement to retrieve heavy products first to prevent damage to other, breakable products. Our research goal was to determine a good combination of policies for storage assignment (assigning products to storage locations) and routing (determining the sequence in which to retrieve products from storage to meet customer demand) for Ankors situation. We adapted existing solution techniques for this problem, overcoming the special characteristics of Ankors operations. With these adapted techniques, we cut the average route length in the order-picking operation by 31 percent. As a result of our study, Ankor implemented a new storage and routing strategy. The study also showed further improvement potentials in the picking process, which Ankor adopted as well. All improvements led to a reduction in the number of order pickers of more than 25 percent.

Simultaneous determination of warehouse layout and control policies

In a supply chain’s order fulfilment process, it is often the warehouse that plays a central role in making the right product available to the right customer at the right time. This paper aims to improve warehouse performance by deriving an effective design method for the simultaneous determination of warehouse layout and the warehouse’s control policies. The authors consider layout variables for the warehouse such as the number of primary aisles utilised, the number of cross-aisles and the aisle length under several different design philosophies. Concurrently, control policies such as storage policies and routing are considered. Simulation is utilised to determine the performance of the various resulting scenarios. A screening and selection procedure is employed to reduce the required number of replications while achieving a predetermined precision in identifying the best configuration. The approach is applied for an industrial partner in this research and the results of experimentation are compared to a baseline scenario which describes a proposed new facility in the Netherlands. The results reveal a large potential for performance improvement.

The pickup and delivery traveling salesman problem with handling costs

This paper introduces the pickup and delivery traveling salesman problem with handling costs (PDTSPH). In the PDTSPH, a single vehicle has to transport loads from origins to destinations. Loading and unloading of the vehicle is operated in a last-in-first-out (LIFO) fashion. However, if a load must be unloaded that was not loaded last, additional handling operations are allowed to unload and reload other loads that block access. Since the additional handling operations take time and effort, penalty costs are associated with them. The aim of the PDTSPH is to find a feasible route such that the total costs, consisting of travel costs and penalty costs, are minimized. We show that the PDTSPH is a generalization of the pickup and delivery traveling salesman problem (PDTSP) and the pickup and delivery traveling salesman problem with LIFO loading (PDTSPL). We propose a large neighborhood search (LNS) heuristic to solve the problem. We compare our LNS heuristic against best known solutions on 163 benchmark instances for the PDTSP and 42 benchmark instances for the PDTSPL. We provide new best known solutions on 52 instances for the PDTSP and on 15 instances for the PDTSPL, besides finding the optimal or best known solution on 102 instances for the PDTSP and on 23 instances for the PDTSPL. The LNS finds optimal or near-optimal solutions on instances for the PDTSPH. Results show that PDTSPH solutions provide large reductions in handling compared to PDTSP solutions, while increasing the travel distance by only a small percentage.

Improved Collaborative Transport Planning at Dutch Logistics Service Provider Fritom

We study the collaborative transport planning for two autonomous business units of Fritom, a Dutch logistics service provider. This difficult planning problem does not fit any existing type of vehicle routing problem proposed in the academic literature; therefore, we define a new problem class, the generalized pickup and delivery problem. We also propose and evaluate methods to structure and improve Fritom’s existing collaborative transport planning process. Using an extensive real-world data set from Fritom, our experiments show that our proposed methods significantly outperform Fritom’s collaborative planning approach in total travel distance. We formulate managerial recommendations for Fritom and describe the implementation process for these recommendations. Finally, we present several recommendations for future research.

Transshipment and rebalancing policies for library books

Library customers can soon order books online and specify a location to collect them from. Libraries exchange books between locations to meet these requests. Two types of exchanges take place: transshipments from library to library to fulfill the requests and rebalancing to redistribute books between libraries. This research determines optimal decisions for transshipments and rebalancing, so that logistic costs in the library system are minimized. In current practice, libraries typically send the book back to the original library after return. We consider a more general policy, in which we rebalance books in anticipation of demand. Moreover, we determine the optimal location from which to transship a book when it is unavailable at the location of demand. By means of stochastic dynamic programming, we derive the optimal policy for small instances. For larger instances we present two heuristics: the cluster and the expected shortage reduction (ESR) heuristic. The ESR heuristic proves to be near-optimal and significantly outperforms current practice.

Managing warehouse efficiency and worker discomfort through enhanced storage assignment decisions

Humans are at the heart of crucial processes in warehouses. Besides the common economic goal of minimising cycle times, we therefore add in this paper the human well-being goal of minimising workers’ discomfort in the context of order picking. We propose a methodology for identifying the most suitable storage location solutions with respect to both goals. The first step in our methodology is to build data-driven empirical models for estimating cycle times and workers’ discomfort. The second step of the methodology entails the use of these empirically grounded models to formulate a bi-objective assignment problem for assigning products to storage locations. The developed methodology is subsequently tested on two actual warehouses. The results of these practical tests show that clear trade-offs exist and that optimising only for discomfort can be costly in terms of cycle time. Based on the results, we provide practical guidelines for taking storage assignment decisions that simultaneously address discomfort and travel distance considerations.

Storage assignment for order picking in multiple-block warehouses

Order picking is a warehousing activity that is concerned with the retrieval of products from storage locations to meet customer demands. In this paper, we provide insights into the interactions between layout, routing and storage assignment, with an emphasis on the effectiveness of various storage assignment methods. To this end, we performed an extensive simulation study. It appears that a selection of appropriate storage assignment policies is possible based only on pick list sizes, so without considering the actual layout of the area.

Order picker routing with product returns and interaction delays

E-commerce companies often use manual order-picking systems in their warehouses since these systems can provide the required flexibility and scalability. Manual systems have been widely studied, but the operating policies may require significant changes for e-commerce settings. First, to maintain consumers’ loyalty, it is important to maintain delivery reliability even on the busiest days. When the number of order pickers in an area increases, however, more delays due to interactions may occur. For example, travel speed may need to be lowered when order pickers pass each other in narrow aisles. Second, many products sold through e-commerce are returned by consumers. Before these returned products can be sold again, they must be reintegrated in the stock. This paper presents hybrid genetic algorithms to determine routes for simultaneous pickup of products in response to consumers’ orders and delivery of returned products to storage locations. Furthermore, interactions between the order pickers are considered in the routing decisions. The developed algorithms use specific warehouse problem characteristics. We identify the mix of pickups and deliveries to realise the highest savings in practice. It is shown that order-picker interactions can be a significant cause for delay and should be accounted for in the routing.