供应链系统库存管理风险分担与集中式库存控制RiskPooling&Centralizedinventorycontrol主讲王长琼武汉理工大学物流工程学院
供应链系统库存管理 1 风险分担与集中式库存控制 Risk Pooling & Centralized inventory control 主讲 王长琼 武汉理工大学 物流工程学院
集中式库存与风险分担学习内容和自标（1）与不确定性需求有关的几条原则（2）风险分担的案例（3）集中系统与分散系统的库存比较（4）集中系统与分散系统的权衡
2 集中式库存与风险分担 学习内容和目标 （1）与不确定性需求有关的几条原则 （2）风险分担的案例 （3）集中系统与分散系统的库存比较 （4）集中系统与分散系统的权衡
（1）与不确定性需求有关的几条原则Aggregated(汇聚的)forecastis moreaccurateDemandvariabilityisreduced if one aggregatesdemand across locations.- High demand from one customer may be offset bylow demand from another.Reduction invariabilityallowsa decreaseinsafetystock and thereforereduces average inventory/Standarddeviation,oSS=ZαXOL/Coefficientofvariation,cv=o/u3
（1）与不确定性需求有关的几条原则 • Aggregated(汇聚的) forecast is more accurate • Demand variability is reduced if one aggregates demand across locations. - High demand from one customer may be offset by low demand from another. • Reduction in variability allows a decrease in safety stock and therefore reduces average inventory. 3 Z L ss Standard deviation, Coefficient of variation, cv = /
(2) ACME: Risk Pooling CaseElectronic equipment manufacturer anddistributor2warehouses fordistributioninMassachusettsand New Jersey (partitioning the northeastmarket into two regions) Each retailer (Customer) is assigned to a singlemarket (warehouse)Warehouses receive materials from ChicagoCurrentrule:97%servicelevel(3%probabilityofstock-out)
(2) ACME: Risk Pooling Case • Electronic equipment manufacturer and distributor • 2 warehouses for distribution in Massachusetts and New Jersey (partitioning the northeast market into two regions) • Each retailer (Customer) is assigned to a single market (warehouse) • Warehouses receive materials from Chicago • Current rule: 97 % service level (3 % probability of stock-out) 4
Current distributionsystems:WarehouseOneMarket OneMassachusettsSupplier.ChicagoWarehouseTwoMarket TwoNew JerseyProblems:-over7years ago-1,500products-10000customersinNortheastConsidering an alternative logistics strategy
Market Two Current distribution systems: Supplier Warehouse One Warehouse Two Market One •Chicago Massachusetts New Jersey Problems: - over 7 years ago -1,500 products -10,000 customers in Northeast. Considering an alternative logistics strategy
New ldeaReplacethe2warehouseswithasinglewarehouseThe same service level 97 %Delivery lead times may increaseWhy?Butmaydecreasetotalinventoryconsiderably.i.e.CentralizeddistributionsystemMarketOneWarehouseSupplierMarket TwoSomesuitableplacebetweenParamusandNewton6
New Idea • Replace the 2 warehouses with a single warehouse • The same service level 97 % • Delivery lead times may increase • But may decrease total inventory considerably. Why？ 6 Some suitable place, between Paramus and Newton i.e. Centralized distribution system
(3)Compare thetotalinventoriesof twosystemsHistoricalDataPRODUCTA12374568Week3730334538551858Massachusetts4635414026481855NewJersey78798078788136113TotalPRODUCTB23167845Week33003001Massachusetts24303100New Jersey02630323Total
Historical Data PRODUCT A Week 1 2 3 4 5 6 7 8 Massachusetts 33 45 37 38 55 30 18 58 New Jersey 46 35 41 40 26 48 18 55 Total 79 80 78 78 81 78 36 113 PRODUCT B Week 1 2 3 4 5 6 7 8 Massachusetts 0 3 3 0 0 1 3 0 New Jersey 2 4 3 0 3 1 0 0 Total 2 6 3 0 3 2 3 0 （3） Compare the total inventories of two systems
Compare thetotalinventories of two systemsSummaryof Historical DatagofStatisticsProductAverageCoefficientDemandDemandof VariationAMassachusetts39.313.20.34BMassachusetts1.361.211.125ANewJersey38.612.00.31BNewJersey1.251.581.26ATotal(aggreg.)77.920.710.27BTotal(aggreg.)1.90.812.375LT=1 week
Summary of Historical Data Statistics Product Average Demand of Demand Coefficient of Variation Massachusetts A 39.3 13.2 0.34 Massachusetts B 1.125 1.36 1.21 New Jersey A 38.6 12.0 0.31 New Jersey B 1.25 1.58 1.26 Total (aggreg.) A 77.9 20.71 0.27 Total (aggreg.) B 2.375 1.9 0.81 Compare the total inventories of two systems LT=1 week
InventoryLevels (bycontinuouspolicy)%MaxAvgQROPProdAVGSafetyreducInv.uctDuringStockLTtionA9139.365132197Massach.25.082914B4251.1252.58Massach.19388A6222.8131NewJ38.61529B3524NewJ1.25A118186304132Centr.77.939.3536%B6332.3753.61Centr.392045%Innewsystem,c.v.issmaller,sovariabilityisreducedAVGSS
Inventory Levels (by continuous policy) Prod uct AVG During LT Safety Stock ROP Q Massach. A 39.3 25.08 65 132 Massach. B 1.125 2.58 4 25 New J A 38.6 22.8 62 131 New J B 1.25 3 5 24 Centr. A 77.9 39.35 118 186 Centr. B 2.375 3.61 6 33 Max Avg Inv. % reduc tion 197 91 29 14 193 88 29 15 304 132 36% 39 20 45% In new system, c.v. is smaller, so variability is reduced, ss AVG
SavingsinInventoryAverage inventoryforProductA:- At NJ warehouse is about 88 units-AtMAwarehouseisabout91units- In the centralized warehouse is about 132 units- Average inventory reduced by about 36 percentAverageinventoryforProductB:-At NJ warehouse is about 15 units-AtMAwarehouseisabout14units-ln the centralized warehouse is about 20 units-Average inventory reduced by about 45percent% of reduction of inventory A= (91+88-132)/132= 36%%ofreductionofinventoryB=(14+15-20)/20=45%10
Savings in Inventory • Average inventory for Product A: – At NJ warehouse is about 88 units – At MA warehouse is about 91 units – In the centralized warehouse is about 132 units – Average inventory reduced by about 36 percent • Average inventory for Product B: – At NJ warehouse is about 15 units – At MA warehouse is about 14 units – In the centralized warehouse is about 20 units – Average inventory reduced by about 45 percent 10 % of reduction of inventory A = (91+88-132)/132 = 36% % of reduction of inventory B = (14+15-20)/20=45%