ch11 库存(2).ppt

Role of Inventory in the Supply Chain 11.2 怎样确定不确定性和产品的供给水平 需求不确定性的度量 对于时期 i，期望mean Ri，标准差standard deviation ?i ，则k个时期的需求的期望= ，标准差= 协方差covariance ，cov(i,j)= ??i ?j 相关系数?， ?=1表明两个时期的需求完全正相关，?=-1表明两个时期的需求完全负相关，?=0表明两个时期的需求独立。 对于 k个时期 (独立同分布 R, ?R)，期望=kR，标准差= ?R Sqrt(k)，变异系数Coefficient of variation, cv =?/ ? 产品供给水平的测定 产品满足率Product fill rate, fr 在市场的总需求中，以库存产品来满足的那部分需求所占的比率 订单满足率Order fill rate 对于某一具体的订单，可由库存满足订单需求的比率 在单一产品情况下，产品满足率和订单满足率之间的差别并不明显 周期服务水平Cycle service level, CSL (fr) 在所有的补给周期中，能满足所有顾客需求的补给周期所占的比重。 补给周期：在连续的两个补充订货交付点的时间间隔。 即在一个补给周期中不出现缺货的概率 (I) Continuous Review Policy:  Determining Safety Inventory and Cycle Service Level L: Lead time for replenishment R: Average demand per unit time ?R: Standard deviation of demand per period RL: Mean demand during lead time ?L: Standard deviation of demand during lead time CSL: Cycle service level =Prob(demand during lead time ? ROP) ss: Safety inventory ROP: Reorder point Example 11.1-2 - Determine safety inventory and cycle service level of a given policy Given the replenishment policy of BM R = 2,500 /week; ?R = 500 /week； Average lead time: L = 2 weeks; Given continuous review policy: (Q, ROP) = (10000, 6000) ss = ROP-RL=6000-2500*2 =1000 Average Inventory = cycle inventory + ss =Q/2+ss=6000 Average Flow Time = Avg inventory / throughput = 6000/2500 = 2.4 weeks The demand during lead time RL =RL=5000 The standard deviation of the demand in lead time ?L = 707 CSL = Prob(demand during lead time of L weeks=ROP) =F(ROP, RL, ?L) = NORMDIST(ROP, RL, ?L, 1) =0.92 (I) Continuous Review Policy: Evaluating Fill Rate fr: Proportion of customer demand satisfied from stock ESC： the expected shortage 、 per cycle (average demand in excess of reorder point in each replenishment cycle Example 11.3: - Determine Fill Rate of a given policy Following Example 11.1-2, given R = 2,500 /week; ?R = 500; Average lead time: L = 2 weeks; (Q, ROP) = (10000, 6000) and RL=5,000,