Transshipment through crossdocks with inventory and time windows

A major challenge in making supply meet demand is to coordinate transshipments across the supply chain to reduce costs and increase service levels in the face of demand fluctuations, short lead times, warehouse limitations, and transportation and inventory costs. In particular, transshipment through crossdocks, where just‐in‐time objectives prevail, requires precise scheduling between suppliers, crossdocks, and customers. In this work, we study the transshipment problem with supplier and customer time windows where flow is constrained by transportation schedules and warehouse capacities. Transportation is provided by fixed or flexible schedules and lot‐sizing is dealt with through multiple shipments. We develop polynomial‐time algorithms or, otherwise, provide the complexity of the problems studied. © 2005 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

A chessboard model of the U‐boat war in the Atlantic with applications to signals intelligence

This paper uses a simple Monte Carlo model to analyze the influence of signals intelligence on the Second World War's Battle of the Atlantic. The principle measure of effectiveness is the number of U‐boat days of attack to which convoys were subjected. A secondary measure is the number of convoyed ships sunk. The model is validated against historical data and then used to explore the effectiveness of the two sides' signals intelligence. Allied use of signals intelligence is shown to have been capable of completely offsetting German use of signals intelligence, and then some. © 2003 Wiley Periodicals, Inc. Naval Research Logistics, 2005     

To wait or not to wait: Optimal ordering under lead time uncertainty and forecast updating

There has been a dramatic increase over the past decade in the number of firms that source finished product from overseas. Although this has reduced procurement costs, it has increased supply risk; procurement lead times are longer and are often unreliable. In deciding when and how much to order, firms must consider the lead time risk and the demand risk, i.e., the accuracy of their demand forecast. To improve the accuracy of its demand forecast, a firm may update its forecast as the selling season approaches. In this article we consider both forecast updating and lead time uncertainty. We characterize the firm's optimal procurement policy, and we prove that, with multiplicative forecast revisions, the firm's optimal procurement time is independent of the demand forecast evolution but that the optimal procurement quantity is not. This leads to a number of important managerial insights into the firm's planning process. We show that the firm becomes less sensitive to lead time variability as the forecast updating process becomes more efficient. Interestingly, a forecast‐updating firm might procure earlier than a firm with no forecast updating. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009     

Disruption‐management strategies for short life‐cycle products

Supplier diversification, contingent sourcing, and demand switching (whereby a firm shifts customers to a different product if their preferred product is unavailable), are key building blocks of a disruption‐management strategy for firms that sell multiple products over a single season. In this article, we evaluate 12 possible disruption‐management strategies (combinations of the basic building‐block tactics) in the context of a two‐product newsvendor. We investigate the influence of nine attributes of the firm, its supplier(s), and its products on the firs preference for the various strategies. These attributes include supplier reliability, supplier failure correlation, payment responsibility in the event of a supply failure, product contribution margin, product substitutability, demand uncertainties and correlation, and the decision makes risk aversion. Our results show that contingent sourcing is preferred to supplier diversification as the supply risk (failure probability) increases, but diversification is preferred to contingent sourcing as the demand risk (demand uncertainty) increases. We find that demand switching is not effective at managing supply risk if the products are sourced from the same set of suppliers. Demand switching is effective at managing demand risk and so can be preferred to the other tactics if supply risk is low. Risk aversion makes contingent sourcing preferable over a wider set of supply and demand‐risk combinations. We also find a two‐tactic strategy provides almost the same benefit as a three‐tactic strategy for most reasonable supply and demand‐risk combinations. © 2009 Wiley Periodicals, Inc. Naval Research Logistics, 2009