Operations Management Unit 11: Managing Inventories (2) 授課教師： 國立臺灣大學工商管理學系 黃崇興 教授 本課程指定教材為 Operations Management: Processes and Supply Chains, 10th ed.,

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Operations Management Unit 11: Managing Inventories (2) 授課教師： 國立臺灣大學工商管理學系 黃崇興 教授 本課程指定教材為 Operations Management: Processes and Supply Chains, 10th ed., Lee J. Krajewski, Larry P. Ritzman, and Manoj K Malhotra, Pearson Education, ©2013 本講義僅引用部分內容，請讀者自行準備。 1 【本著作除另有註明外，採取創用 CC 「姓名標示 －非商業性－相同方式分享」台灣 3.0 版授權釋出】創用 CC 「姓名標示 －非商業性－相同方式分享」台灣 3.0 版

Selecting the Reorder Point When Demand Is Variable and Lead time is Constant 2 where d = average demand per week (or day or months) L = constant lead time in weeks (or days or months) Reorder point=Average demand during lead time + Safety stock =dL + safety stock

Continuous Review Systems When Demand Is Variable and Lead time is Constant 3 p.341 Figure 9.10

Reorder Point 4 Steps to arrive at a Reorder Point 1. service-level policy 2. demand during lead time 3. safety stock and reorder point levels

Demand During Lead Time (cont.) 5 σ dLT = σ d 2 L = σ d L Safety stock and reorder point Safety stock = z σ dLT where z =number of standard deviations needed to achieve the cycle-service level σ dLT =stand deviation of demand during lead time Reorder point = R = dL + safety stock Standard deviation of demand during lead time

Demand During Lead Time 6 p.342 Figure 9.11, 343 Figure 9.12 Average demand during lead time = dL

EXAMPLE 9.5 Reorder Point for Variable Demand 7 p.343

Reorder Point When Both Demand and Lead Time Are Variable 8 Safety stock = zσ dLT where d =Average weekly (or daily or monthly) demand L =Average lead time σ d =Standard deviation of weekly (or daily or monthly) demand σ LT =Standard deviation of the lead time σ dLT = Lσ d 2 + d 2 σ LT 2 R =(Average weekly demand  Average lead time) + Safety stock =dL + Safety stock The equations are more complicated

EXAMPLE 9.6 Reorder Point for Variable Demand and Variable Lead Time 9 p.344

Continuous Review Systems 10 Two-Bin system Calculating total systems costs Total cost =Annual cycle inventory holding cost + Annual ordering cost + Annual safety stock holding cost C = (H) + (S) + (H) (Safety stock) Q2Q2 DQDQ

Periodic Review System (P) 11 P System Four of the original EOQ assumptions maintained p.345, Figure 9.13

EXAMPLE 9.7 How Much to Order in a P System 12 p.346

Periodic Review System when demand is variable and lead time is constant 13 p.347 T = d(P + L) + safety stock for protection interval Safety stock = zσ P + L, where σ P + L =

EXAMPLE 9.8 Calculating P and T 14 p.347, 348

Periodic Review System when both demand and lead time are variable 15 p.348

Hybrid Systems 17 Optional replenishment systems Base-stock system p. 349

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