Kun-Shan Wu

Integrated vendor–buyer cooperative inventory models with controllable lead time and ordering cost reduction

This study deals with the lead time and ordering cost reduction problem in the single-vendor single-buyer integrated inventory model. We consider that buyer lead time can be shortened at an extra crashing cost which depends on the lead time length to be reduced and the ordering lot size. Additionally, buyer ordering cost can be reduced through further investment. Two models are presented in this study. The first model assumes that the ordering cost reduction has no relation to lead time crashing. The second model assumes that the lead time and ordering cost reduction are interacted. An iterative procedure is developed to find the optimal solution and numerical examples are presented to illustrate the results of the proposed models.

A minimax distribution free procedure for mixed inventory model with variable lead time

In this article, both lead time and the order quantity are considered as the decision variables of a mixed inventory model. In our studies, we relax the assumption about the form of the cumulative distribution function of the lead-time demand and apply the minimax distribution free procedure to solve the problem. We develop an algorithmic procedure to find the optimal order quantity and optimal lead time. Furthermore, the effects of parameters are also studied.

Coordinating replenishment and pricing policies for non-instantaneous deteriorating items with price-sensitive demand

This article will formulate and solve an inventory system with non-instantaneous deteriorating items and price-sensitive demand. The purpose of this study is to determine the optimal selling price and the length of replenishment cycle such that the total profit per unit time has a maximum value for the retailer. We first establish a proper model for a mathematical formulation. Then we develop several theoretical results and provide the decision-maker with an algorithm to find the optimal solution. Finally, two numerical examples are provided to illustrate the solution procedure, and a sensitivity analysis of the optimal solution with respect to major parameters is carried out.

RETAILER'S ORDERING POLICY FOR NON-INSTANTANEOUS DETERIORATING ITEMS WITH QUANTITY DISCOUNT, STOCK-DEPENDENT DEMAND AND STOCHASTIC BACKORDER RATE

ABSTRACT This article deals with an inventory problem for non-instantaneous deteriorating items with stock-dependent demand when supplier offers an all-unit quantity discount. In the model, shortages are allowed and the backorder rate is a random variable. The purpose of this study is to determine an optimal ordering policy for minimizing the expected total relevant inventory cost for the retailer. We have developed some useful theorems to characterize the optimal solution and provide an easy and useful algorithm to find the optimal order quantity and replenishment time. Furthermore, several numerical examples are given to illustrate the solution procedure for the mathematical model developed. Finally, we also implement sensitivity analysis of the optimal solution with respect to major parameters.

The Single-Vendor Single-Buyer Integrated Inventory Problem With Quality Improvement And Lead Time Reduction — Minimax Distribution-Free Approach

In past two decades, the Japanese successful experience in using Just-In-Time (JIT) production has received a great deal of attention. The underlying goal of JIT is to eliminate waste. This can be achieved through various efforts, such as shortening lead time and improving quality. In this paper, we investigate the impact of investing in quality improvement and lead time reduction on the integrated vendor-buyer inventory model with partial backorders. We assume that the lead time demand probability distribution is unknown, while the mean and standard deviation are known and finite. The minimax distribution-free procedure is applied to solve this problem. Also, numerical examples are given to illustrate the results.

Integrated vendor-buyer inventory system with sublot sampling inspection policy and controllable lead time

This article investigates the impact of inspection policy and lead time reduction on an integrated vendor--buyer inventory system. We assume that an arriving order contains some defective items. The buyer adopts a sublot sampled inspection policy to inspect selected items. The number of defective items in the sublot sampling is a random variable. The buyers lead time is assumed reducible by adding crash cost. Two integrated inventory models with backorders and lost sales are derived. We first assume that the lead time demand follows a normal distribution, and then relax the assumption about the lead time demand distribution function and apply the minimax distribution-free procedure to solve the problem. Consequently, the order quantity, reorder point, lead time and the number of shipments per lot from the vendor to the buyer are decision variables. Iterative procedures are developed to obtain the optimal strategy.

AN EOQ MODEL WITH LIMITED STORAGE CAPACITY UNDER TRADE CREDITS

In the classical economic order quantity (EOQ) inventory model, it was assumed that the retailer must pay for the received items immediately. However, in practice, the supplier not only allows retailer to settle the account after a certain fixed period but also may offer a cash discount to encourage the retailer to pay for his purchases as soon as possible. On the other hand, it is common practice in most inventory systems to hold excess stocks in a rented warehouse whenever the storage capacity of the owned warehouse is insufficient. Therefore, the purpose of this paper is to establish an EOQ model with limited storage capacity, in which the supplier provides cash discount and permissible delay in payments for the retailer. In the model, we develop some useful theorems to characterize the optimal solution and provide a simple method to find the optimal replenishment cycle time and payment time. Finally, several numerical examples are given to illustrate the theoretical results and some managerial insights are also obtained.

An optimal replenishment policy for deteriorating items with stock-dependent demand and relaxed terminal conditions under limited storage space

This paper deals with the problem of determining the optimal replenishment policy for deteriorating items with stock-dependent demand in which the terminal condition of zero-ending inventory is relaxed. In the model, shortages are allowed and partial backlogging/lost sales. That is, the zero/non-zero ending inventory models are considered simultaneously. The items in stock are displayed to the customers in shelves with limited storage capacity. In theoretical analysis, the necessary and sufficient conditions of the existence and uniqueness of the optimal solutions under various cases are shown. We then also provide a simple algorithm to find the optimal solutions for various situations. Further, a couple of numerical examples are presented to demonstrate the developed model and solution procedure, and several management insights are obtained from the numerical examples. Finally, sensitivity analysis of the optimal solution with respect to major parameters is also carried out.

Optimal order policy in response to announced price increase for deteriorating items with limited special order quantity

When a supplier announces an impending price increase due to take effect at a certain time in the future, it is important for each retailer to decide whether to purchase additional stock to take advantage of the present lower price. This study explores the possible effects of price increases on a retailers replenishment policy when the special order quantity is limited and the rate of deterioration of the goods is assumed to be constant. The two situations discussed in this study are as follows: (1) when the special order time coincides with the retailers replenishment time and (2) when the special order time occurs during the retailers sales period. By analysing the total cost savings between special and regular orders during the depletion time of the special order quantity, the optimal order policy for each situation can be determined. We provide several numerical examples to illustrate the theories in practice. Additionally, we conduct a sensitivity analysis on the optimal solution with respect to the main parameters.