《供应链系统设计与管理》课程教学课件（讲稿）Lecture 4（Chapter 2）Multiple Order Opportunities

Lecture 32.2.5.Multiple Order Opportunities王长琼武汉理工大学2017.4

Lecture 3 2.2.5. Multiple Order Opportunities 1 王长琼 武汉理工大学 2017,4

ObjectivesUnderstandinginventoryina supplychainWhyinventoryisimportant?How to manage it?SingleStageInventoryControl- Economic Lot Size Model-DemandUncertaintyVMultiple OrderOpportunitiesRiskPooling

Objectives • Understanding inventory in a supply chain Why inventory is important? How to manage it? • Single Stage Inventory Control - Economic Lot Size Model - Demand Uncertainty Multiple Order Opportunities Risk Pooling 2

2.2.5. Multiple Order OpportunitiesOrderproductsonetimeduringayeare.g.Moon-cake,...Orderproductsrepeatedlydistributors order TV set, appliance,...-Whenandhowmuchtoorder?F车板焊换/装配件ABS车换装配供发动机煤配非总成装配线R电动车审年磁茶配换电视机鲁压器装配然安全营装安速指装配线车门快配%转向的力恶装配然高合慕装配线Baisenn安全家装WhatinventoryPOLICIES?3

2.2.5. Multiple Order Opportunities  Order products one time during a year e.g. Moon-cake, .  Order products repeatedly distributors order TV set, appliance, . -When and how much to order?  What inventory POLICIES? 3

Continuousreviewpolicy-inventoryisreviewedcontinuously- an order is placed when the inventory reaches ROp(reorderpoint,aparticularinventorylevel)Periodicreviewpolicy-inventoryisreviewedatregularintervals- appropriate quantityisordered after each reviewR+QInventorypositionLeadInventory leveltimeR0time时间R?Q?

• Continuous review policy – inventory is reviewed continuously – an order is placed when the inventory reaches ROP (reorder point, a particular inventory level). • Periodic review policy – inventory is reviewed at regular intervals – appropriate quantity is ordered after each review. R? Q? 4

2.2.6. Continuous Review PolicyAssumptions:Dailydemand israndomandfollows a normal distribution.Every time the distributor places an order, the distributorpays a fixed cost, K, plus an amount proportional to thequantityordered.Inventoryholding costis chargedperitemper unit timeInventory levelis continuously reviewed,and ifan order isplaced,the order arrivesafter theappropriate lead timeIf a customer orderarrives when the distributoris stockedout, the orderis lost.The distributor specifies a required service level

2.2.6. Continuous Review Policy Assumptions: • Daily demand is random and follows a normal distribution. • Every time the distributor places an order, the distributor pays a fixed cost, K, plus an amount proportional to the quantity ordered. • Inventory holding cost is charged per item per unit time. • 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 the distributor is stocked out, the order is lost. • The distributor specifies a required service level. 5

STD=5STD=10AVG=303040501020FAvG = Average daily demand faced by the distributorSTD = Standard deviation of daily demand faced by thedistributorL=Replenishmentleadtimefromthesuppliertothedistributor in days h = Cost of holding one unit of the product for one dayat the distributorα=serviceleveli.e. the probability of stocking out is 1 - α6

• 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 • α = service level, i.e. the probability of stocking out is 1 - α 6 STD STD AVG=

Continuous Review Policy(Q,R)policy-wheneverinventorylevelfallstoareorderlevelR,placeanorderforQunitsWhat isthevalueof R?andvalueof Q?R+QInventorypositionLeadInventoryleveltimeRSafety stock0time

Continuous Review Policy • (Q,R) policy – whenever inventory level falls to a reorder level R, place an order for Q units • What is the value of R? and value of Q? 7 time R+Q R 0 Lead time Inventory position Inventory level Safety stock

ReorderLevel, RL× AVG+z×STD×LAverage demand during lead time:Lx AvGSafetystock,ssSS= z× STD×L??Why does a distributor holdsafety stock atthe warehouse?8

 Reorder Level, R • Average demand during lead time: L x AVG • Safety stock, ss ss= z  STD L L AVG  z STD L 8 ??Why does a distributor hold safety stock at the warehouse?

Service Level & Safety Factor, zService91%92%94%90%93%95%96%97%98%99%99.9%Level1.291.341.411.481.561.651.751.882.052.333.08Zz is chosen from statistical tables to ensurethat the probability of stockouts during lead time isexactly (1 - α)

Service Level & Safety Factor, z Service Level 90% 91% 92% 93% 94% 95% 96% 97% 98% 99% 99.9% z 1.29 1.34 1.41 1.48 1.56 1.65 1.75 1.88 2.05 2.33 3.08 z is chosen from statistical tables to ensure that the probability of stockouts during lead time is exactly (1 – α)

Continuous Review Policy (Q, R)OrderQuantity,Q:2KDEOQmodel:hD=Averagedemand2K ×AVG(novariabilityindemand)Oh10

Continuous Review Policy (Q, R) • Order Quantity, Q: EOQ model: D=Average demand (no variability in demand) h K AVG Q   2 10 h KD Q * 2 