Research On Inventory Control Models And Methods Of The Logistics System

The fundamental objective of studying the logistics system is to reduce the total cost of logistics. But the inventory cost of items is of much more proportion in the total cost of logistics. Therefore, studying the theory and methods of inventory control is very significant for reducing the total cost of logistics. Also, it is a hot spot of logistics theory research.During recent several decades, although the extensive research of the traditional inventory control theory has made much more progress, there is still a cousiderably big gap between the acquired theoretical results and the requirement of practical application due to the complexity and variety of environment. This dissertation starts with the concrete problems that decision makers may encounter while they use the existing inventory theory to make practical inventory decision, and makes further extensive study on the traditional inventory control theory from different aspects. The details are given as belows.1. Extensions for EOQ formula. Firstly, this dissertation extends the classical EOQ formula to the situtation with finite service rate. Secondly, the control problem of lead-time is incorporated into inventory model. Under the assumption that the lead-time梒ost function is exponential one, an integrated decision model is offered to the inventory system with finite service rate to choose rational lead-time and order policy. Tirdly, the paper analyzes the effect of the supplier providing the temporary price discount for a deteriorating item on the original order policy of the inventory system. It provides an optimal decision method for the inventory system to place a temporary order during the temporary price discount period.2. The extensive research for inventory control models with time-varying demand. Through employing discounted cash flow approach, the dissertation studies the effect of the time value of money on the order policy of the inventory system, and presents an inventory control model considering the time value of money for the general time-varying demand. This makes the traditional inventory control model be able to be used under the economic environment of inflation. The paper is the first to integrate the problem of paying the purchasing cost in delay to the inventory system with time-varying demand. It proposes inventory control models for finding the optimal order policy under three rules of the delayed payment. Then, inventory control models with time-varying demand is further extended by relaxing the assumption of equal replenishment cycle and considering the order cost as the sum of one part of fixed cost and the other part of flexible cost proportioned to the order quantity. After that, inventory control problems are studied for the inventory system with multiple warehouses of finite capacity. A multi-warehouse inventory control model is presented for a particular case that the demand of the product in its growth phase is approached by a special exponential increasing function. Finally, by using a special polynomial of degree m to approach the demand of the product in its life time, a dynamic programming model is provided for finding the optimal order policy in the whole life time of the product. Thismodel overcomes the flaws that the existing inventory models are only fit for the growth phase or the declining phase of the product.3. In this dissertation, the traditional production-inventory control models are further extended in several aspects as below. (1)The preventive maintain interruption schedule and the order problem of materials are simultaneously incorporated into the traditional production-inventory control model. An integrated decision model is built for determining the optimal production lot size, its corresponding preventive maintain interruption policy lot size and order policy of materials. (2)The optimal production lot size model for the volume flexible manufacturing system with shortages permitted is presented by considering the production rate as decision variable and the production...