上海海事 供应链 ppt第三章【高等教学】

1、Chapter 3 Inventory Management and Risk Pooling,1,高级教育,3.1 Introduction 3.2 A Single Warehouse Inventory Example 3.3 Risk Pooling 3.4 Centralized versus Decentralized Systems 3.5 Managing Inventory in the Supply Chain 3.6 Practical Issues,2,高级教育,3.1 Introduction,Inventory appears in the supply chain

2、 in several forms: Raw material inventory Work-in-process (WIP) inventory Finished product inventory,3,高级教育,Each of these needs its own inventory control mechanism. The difficulty in determining these mechanisms is that efficient production, distribution, and inventory control strategies and improve

3、 service levels must take into account the interactions of the various levels in the supply chain,4,高级教育,Why hold inventory at all? Some of the reasons include: To protect the firm from unexpected changes in customer demand. Customer demand has always been hard to predict, and uncertainty in custome

4、r demand has increased in the last few years owing to,5,高级教育,The short life cycle of an increasing number of products. The presence of many competing products in the marketplace,6,高级教育,The presence in many situations of a significant uncertainty in the quantity and quality of the supply, supplier co

5、sts, and delivery times,7,高级教育,Economies of scale offered by transportation companies which encourage firms to transport large quantities of items, and therefore hold large inventories,8,高级教育,Managing inventory effectively is often difficult. Examples illustrate(P42,9,高级教育,These examples raise two i

6、mportant issues in inventory management: Demand forecasting Order quantity calculation,10,高级教育,3.2 A Single Warehouse Inventory Example,What are the key factors affecting inventory policy? Customer demand Replenishment lead time The number of different products stored at the warehouse The length of

7、the planning horizon Costs, including order cost and inventory holding cost Service level requirement,11,高级教育,3.2.1 The Economic Lot Size Model,The classic Economic Lot Size Model, introduced by Ford W. Harris in 1915, is a simple model that illustrates the trade-offs between ordering and storage co

8、sts,12,高级教育,The model assumes the following: Demand is constant at a rate of D items per day Order quantities are fixed at Q items per order A fixed setup cost ,k ,is incurred every time the warehouse places an order,13,高级教育,An inventory carrying cost ,h, also referred to as a holding cost, is accru

9、ed for every unit held in inventory per day The lead time, the time that elapses between the placement of an order an its receipt, is zero Initial inventory is zero The planning horizon is long (infinite,14,高级教育,This quantity is referred to as the economic order quantity (EOQ,15,高级教育,This simple mod

10、el provides two important insights: An optimal policy balances between inventor holding cost per unit time and setup cost per unit time Total inventory cost is insensitive to order quantities,16,高级教育,3.2.2 The Effect of Demand Uncertainty,The previous model illustrates the trade-offs between setup c

11、osts and inventory holding costs. It ignores, however, issues such as demand uncertainty and forecasting,17,高级教育,Case:swimsuit production,Probabilistic forecast Suppose the manufacturer produces 10,000 units while demand ends at 12,000 swimsuits Profit=125(10,000)-80(10,000)-100,000=350,000 If the c

12、ompany produces 10,000swimsuits and demand is only 8,000 units Profit=125(10,000)+20(2,000)-80(10,000)-100,000=140,000,18,高级教育,Case:swimsuit production,19,高级教育,Case:swimsuit production,20,高级教育,21,高级教育,To summarize: The optimal order quantity is not necessarily equal to forecast, or, average, demand

13、As the order quantity increases, average profit typically increases until the production quantity reaches a certain value, after which the average profit atarts decreasing,22,高级教育,As we increase the production quantity, the risk-that is, the probability of large losses-always increases. At the same

14、time, the probability of large gains also increases. This is the risk/reward trade-off,23,高级教育,The effect of Initial Inventory,The effect of initial inventory (learn it by yourself,24,高级教育,3.2.3 Multiple Order Opportunities,Consider, for instance, a distributor of TV sets. The distributor faces rand

15、om demand for the product and receives the supply from the manufacturer. Since demand is random and the manufacturer has a fixed delivery lead time, the distributor needs to hold inventory, even if no fixed setup cost is charged for ordering the products,25,高级教育,At least 3 reasons explain why the di

16、stributor holds inventory: To satisfy demand occurring during lead time To protect against uncertainty in demand To balance annual inventory holding costs and annual fixed order costs,26,高级教育,3.2.4 No Fixed Order Costs,To answer these questions, we make the following additional assumptions: Daily de

17、mand is random and follows a normal distribution. There is no fixed order cost. Inventory holding cost is charged per item per unit time,27,高级教育,If a customer order arrives when there is no inventory on hand to fill the order, the order is lost. The distributor specifies a required service level. Th

18、e service level is the probability of not stocking out during lead time,28,高级教育,To characterize the inventory policy that the distributor should use, we need the following information: AVG = Average daily demand faced by the distributor STD = Standard deviation of daily demand faced by the distribut

19、or,29,高级教育,L= Replenishment lead time from the supplier to the distributor in days h= Cost of holding one unit of the product for one day at the distributor = Service level,30,高级教育,The average demand during lead time= Safety stock= The order-up-to-level= z=(chosen form statistical tables:table 3.2,3

20、1,高级教育,Example 3.2.1(p53) Average weekly demand= Standard deviation of weekly demand,32,高级教育,3.2.4 No Fixed Order Costs,33,高级教育,Reorder point= EOQ= ss= The order-up-to-level= Example3.2.2(p55,34,高级教育,3.3 Risk Pooling,ACME is considering the following alternative strategy. Replace the two warehouses

21、with a single warehouse located between Paramus and Newton that will serve all customer orders. It allows ACME to achieve either the same service level of 97 percent with much lower inventory or a higher service with the same amount of total inventory,35,高级教育,Intuitively this is explained as follows

22、,With random demand, it is very likely that a higher-than-average demand at one retailer will be offset by a lower-than-average demand at another. As the number of retailers served by a warehouse goes up, this likelihood also goes up,36,高级教育,How much can ACME reduce inventory if the company decides

23、to switch to the centralized system but maintain the same 97 percent service level,37,高级教育,平均库存,产品A在NJ,产品A在M,平均库存=91,产品A在C,平均库存=132， 平均库存降低=（88+91-132）/（88+91）*100,38,高级教育,We summarize the three critical points we have made about risk pooling. Centralizing inventory reduces both safety stock and ave

24、rage inventory in the system. The higher the coefficient of variation, the greater the benefit obtained from centralized systems The benefits from risk pooling depend on the behavior of demand from one market relative to demand from another,39,高级教育,3.4 Centralized versus Decentralized Systems,What a

25、re the trade-offs that we need to consider in comparing centralized distribution systems with decentralized distribution systems? Safety stock Service level Overhead costs Customer lead time Transportation costs,40,高级教育,3.5 Managing Inventory in the Supply Chain,An inventory policy based on the so-ca