1、供应链管理（英文课件）Chapter4-Inventory Management2Agenda Multiple Order Opportunities -Continuous Review Policy -Periodic Review Policy3Multi-period Problem4Continuous Review Policy inventory is reviewed continuouslyan order is placed when the inventory reaches a particular level or reorder pointinventory ca
2、n be continuously reviewed(computerized inventory systems are used)5Periodic Review Policyinventory is reviewed at regular intervals appropriate quantity is ordered after each reviewit is impossible or inconvenient to frequently review inventory and place orders if necessary6Inventory Level&Inventor
3、y Position7Continuous Review Policy Daily demand is random and follows a normal distribution.Every time the distributor places an order from the manufacturer,the distributor pays a fixed cost,K,plus an amount proportional to the quantity ordered.Inventory holding cost is charged per item per unit ti
4、me.Inventory level is continuously reviewed,and if an order is placed,the order arrives after the appropriate lead time.If a customer order arrives when there is no inventory on hand to fill the order(i.e.,when the distributor is stocked out),the order is lost.The distributor specifies a required se
5、rvice level.8 AVG=Average daily demand faced by the distributor STD=Standard deviation of daily demand faced by the distributor 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.This implies
6、that the probability of stocking out is 1-Continuous Review Policy9(Q,R)policy whenever inventory level falls to a reorder level R,place an order for Q units What is the value of R?Continuous Review Policy10Continuous Review Policy Average demand during lead time:L x AVG Safety stock:Reorder Level,R
7、:Order Quantity,Q:LSTDzLSTDzAVGLhAVGKQ211Service Level&Safety Factor,zService Level90%91%92%93%94%95%96%97%98%99%99.9%z1.291.341.411.481.561.651.751.882.052.333.08z is chosen from statistical tables to ensure that the probability of stockouts during lead time is exactly 1-12Inventory Level Over Time
8、LSTDzInventory level before receiving an order=Inventory level after receiving an order=Average Inventory=LSTDzQLSTDzQ2 Inventory level as a function of time in a(Q,R)policy13Continuous Review Policy:Example A distributor of TV sets that orders from a manufacturer and sells to retailers Fixed orderi
9、ng cost=$4,500 Cost of a TV set to the distributor=$250 Annual inventory holding cost=18%of product cost Replenishment lead time=2 weeks Expected service level=97%14MonthSeptOct Nov.Dec.Jan.Feb.Mar.Apr.May June July AugSales 200 152 100 221 287 176 151 198 246 309 98 156Continuous Review Policy:Exam
10、pleAverage monthly demand=191.17 Standard deviation of monthly demand=66.53Average weekly demand=Average Monthly Demand/4.3Standard deviation of weekly demand=Monthly standard deviation/4.3 15ParameterAverage weekly demandStandard deviation of weekly demandAverage demand during lead timeSafety stock
11、Reorder pointValue44.5832.0889.1686.2017687.05225018.0Weekly holding cost=Optimal order quantity=67987.58.44500,42QAverage inventory level=679/2+86.20=426Continuous Review Policy:Example16 Average lead time,AVGL Standard deviation,STDL.Reorder Level,R:222STDLAVGSTDAVGLzAVGLAVGRVariable Lead Times222
12、STDLAVGSTDAVGLzAmount of safety stock=hAVGKQ2Order Quantity=17 Inventory level is reviewed periodically at regular intervals An appropriate quantity is ordered after each review Two Cases:Short Intervals(e.g.Daily)Define two inventory levels s and S During each inventory review,if the inventory posi
13、tion falls below s,order enough to raise the inventory position to S.(s,S)policy Longer Intervals(e.g.Weekly or Monthly)May make sense to always order after an inventory level review.Determine a target inventory level,the base-stock level During each review period,the inventory position is reviewed
14、Order enough to raise the inventory position to the base-stock level.Base-stock level policyPeriodic Review Policy18(s,S)policy Calculate the Q and R values as if this were a continuous review model Set s equal to R Set S equal to R+Q.19Base-Stock Level Policy Determine a target inventory level,the
15、base-stock level Each review period,the inventory position is reviewed and order enough to raise the inventory position to the base-stock level Assume:r=length of the review periodL=lead time AVG=average daily demand STD=standard deviation of this daily demand.20 Average demand during an interval of
16、 r+L days=Safety Stock=LrSTDzAVGLr)(Base-Stock Level Policy 21Base-Stock Level Policy Inventory level as a function of time in a periodic review policy22 Assume:distributor places an order for TVs every 3 weeks Lead time is 2 weeks Base-stock level needs to cover 5 weeks Average demand=44.58 x 5=222.9 Safety stock=Base-stock level=223+136=359 Average inventory level=Distributor keeps 5(=203.17/44.58)weeks of supply.Base-Stock Level Policy:Example 58.329.117.203508.329.1258.44323Basic Inventory Models
