This paper treats a depot-warehouse system in which demand occurs at the warehouse or retail level. This work differs from a number of other studies in that we allow item demands to be correlated both across warehouses and also correlated in time. Our motivation for this generalization arises from our experience with an actual system of this type used by a major national producer and distributor of consumer products. We observed both high correlations between successive monthly demands (around 0.7) and correlations between demands for an item at different locations (also about 0.7) in a given time period. We derive an explicit expression for the optimal safety stock as a function of the level of correlation through time. The analysis requires two assumptions: 1) the allocation assumption and 2) the equal coefficient of variation assumption. (Similar assumptions have been used by other researchers.) Finally, numerical evaluations are included to illustrate the impact of the various magnitudes of correlation.inventory, multi-echelon, issuing policies, stochastic model

Multi-echelon inventory systems are often controlled as a network of single-echelon inventory systems for simplicity of managerial authority, organizational control, and performance monitoring. This paper explores the amount of suboptimization in such a situation, using an actual demand data set provided by other researchers. We consider low-demand, high-cost items controlled on an (S - 1, S) basis, with all warehouse stockouts met on an emergency-ordering basis. We demonstrate that the suboptimality penalty for this data set is 3% to 5% when single-echelon systems are appropriately parameterized.inventory/production, multi-echelon systems

No abstract

We consider an inventory control problem where it is possible to collect some imperfect information on future demand. We refer to such information as imperfect Advance Demand Information (ADI), which may occur in different forms of applications. A simple example is a company that uses sales representatives to market its products, in which case the collection of sales representatives' information as to the number of customers interested in a product can generate an indication about the future sales of that product, hence it constitutes imperfect ADI. Other applications include internet retailing, Vendor Managed Inventory (VMI) applications and Collaborative Planning, Forecasting, and Replenishment (CPFR) environments. We develop a model that incorporates imperfect ADI with ordering decisions. Under our system settings, we show that the optimal policy is of order-up-to type, where the order level is a function of imperfect ADI. We also provide some characterizations of the optimal solution. We develop an expression for the expected cost benefits of imperfect ADI for the myopic problem. Our analytical and empirical findings reveal the conditions under which imperfect ADI is more valuable.

We characterize optimal policies of a dynamic lot-sizing/vehicle-dispatching problem under dynamic deterministic demands and stochastic lead times. An essential feature of the problem is the structure of the ordering cost, where a fixed cost is incurred every time a batch is initiated (or a vehicle is hired) regardless of the portion of the batch (or vehicle) utilized. Moreover, for every unit of demand not satisfied on time, holding and backorder costs are incurred. Under mild assumptions we show that the demand of a period is satisfied from at most three distinct production (dispatching) epochs. We devise a dynamic programming algorithm to compute the production/dispatching quantities and times.

In this article, we investigate the profitability of remanufacturing option when the manufactured and remanufactured products are segmented to different markets and the production capacity is finite. A single period profit model under substitution is constructed to investigate the system conditions under which remanufacturing is profitable. We present analytical findings and computational results to show profitability of remanufacturing option under substitution policy subject to a capacity constraint of the joint manufacturing/remanufacturing facility.

In our environment, a manufacturer procures material from a supplier and the supplier brings it in bulk to a warehouse. This material is then consigned to the plant area, where it is utilized as an input of the production process. This consignment process is outsourced by the manufacturer and a transportation company is selected via a bidding mechanism. Primarily, we consider the problem of designing parameters of a given contract for the transportation activity. We define three subproblems within the contract design problem that interact with each other to a certain extent. These subproblems are the vehicle dispatching problem, inventory control problem, and contract value problem. We define these problems, exploit their interactions, and propose solution methods. Moreover, we present an approach to design such transportation contracts, which is based on solving these subproblems in an order for an adequate number of contract parameter combinations and selecting the one that minimizes expected total costs for the manufacturer.

a b s t r a c tMotivated by recent empirical evidence, we study the economic impact of inventory record inaccuracies that arise due to execution errors. We model a set of probable events regarding the erroneous registering of sales at each demand arrival. We define correction opportunities that can be used to (at least partially) correct inventory records. We analyze a simple inventory control model with execution errors and correction opportunities, and demonstrate that decisions that consider the existence of recording errors and the mechanisms with which they are corrected can be quite complicated and exhibit complex tradeoffs. To evaluate the economic impact of inventory record inaccuracies, we use a simulation model of a (Q,r) inventory control system and evaluate suboptimalities in cost and customer service that arise as a result of untimely triggering of orders due to inventory record inaccuracies. We show that the economic impact of inventory record inaccuracies can be significant, particularly in systems with small order sizes and low reorder levels.