运营管理期末复习(下).doc

11.Inventory存货Inventory: The number of flow units within a process at a specific point in time. 在一个特定的时间点上某个生产流程中产品的数量。Physical inventories include raw materials (RM), work in process (WIP), and finished goods (FG).包括原材料、在制品、成品。Let Ri(t) = Inflow Rate at time tRo(t) = Outflow Rate at time t Ri(t) - Ro(t) = Inventory Accumulation Rate I(t) = I(t-1) + Ri(t) - Ro(t) (Inventory Balance equation)I(t) also fluctuates over time Meaningful Measurement: Average Inventory (I) 12.Littles LawLittles Law states a mathematical relationship between throughput rate,throughput time and the number of work-in-process inventory.Inventory = Throughput x Flow Time I = R x TTurnover = Throughput / Inventory= 1/ TFor given level of throughput in any process, the only way to reduce flow time is to reduce inventory, and vice versa.给定水平下的产出，缩短生产时间的唯一途径就是减少存货，反之亦然。13The following Benefits of shorter flow time?(1)Flow time affects delivery response time, Make-to-order Production system: faster response 缩短交付响应时间。(2)Littles Law: lower inventory 更低的存货(3)New Product Development: early market introduction. 更早的市场导入(4)Products with short seasons (e.g. fashion goods): delay production 短季商品的提早入市13. CapacityProcess Capacity is the maximum sustainable Flow Rate (Throughput) of a processThe Capacity for a process, the less situations where we have sufficient supply to match demandProcess Capacity Depending on the flow unit, the network structure of activities and buffers, the resources allocated to perform them, operating policies流程能力取决于流动单元, 缓冲与活动的网络结构,资源分配,运营策略等Flow Rate=MinAvailable Input rate, Demand Rate, Process CapacityActivity Capacity：It depend on the resource allocation, resource character(resource flexibility, Load Batch), time available, etc（1）Activity Time: the time required by a typical flow unit to complete the activity once（2）Visits: rework requires activities to be repeated several times（3）Work Content: the activity time multiplied by the average number of visits to that activity.Theoretical Capacity（1）Theoretical capacity of a resource unit: Maximum sustainable flow rate if it were fully utilized during its scheduled availability. （2）Theoretical capacity of a Task/activity: The sum of the theoretical capacities of all resource units allocated to this activity（3）Theoretical capacity of a process: Theoretical capacity of its slowest (bottleneck) activity in the process, i.e. Capacity Utilization=Throughput / Theoretical Capacity14. Managing the Flow RateIncrease Throughput Manage supply and demand Increase Process Capacity Reduce starvation (synchronize flows better)Reduce blockage (appropriately select buffer sizes)Increase Effective CapacityReduce resource unavailability (maintenance policies, better HR management, less frequent setup/changeover, reduced setup/changeover timesIncrease Theoretical Capacity【第十三章Operational Planning and Control/Forecast】1.pull/push/make-to-order/make-to-stockPull:（拉） Work triggered by downstream (possibly internal) demand 下游需求（可能是内部的）触发的生产Push: （推）Work triggered by a forecast of demand 有预测需求出发的生产。Make-To-Order: Work performed towards an existing (external) customer order订单生产 Make-To-Stock: Work performed for a yet unknown customer 库存生产 2 What Is Forecasting?Process of predicting a future eventForecast:About what will happen in future Plan: About what should happen in futureForecasts as input3. Characteristics of ForecastsForecasts are always wrong.（预测总是有误的） Should include expected value and measure of error.Long-term forecasts are less accurate than short-term forecast(短期预测比长期预测准确)forecast horizon is importantAggregate forecasts are more accurate than disaggregate forecasts （综合预测比具体预测准确）4. Forecasting Approaches预测方法（1）Qualitative Methods （定性）Used when situation is vague & little data exist（情况模糊、数据少） New products New technology Involves intuition, experiencee.g., forecasting sales on InternetQualitative MethodsDelphi Methodsl. Choose the experts to participate representing a variety of knowledgeable people in different areas2. Through a questionnaire (or E-mail), obtain forecasts (and any premises or qualifications for the forecasts) from all participants3. Summarize the results and redistribute them to the participants along with appropriate new questions 4. Summarize again, refining forecasts and conditions, and again develop new questions5. Repeat Step 4 as necessary and distribute the final results to all participants Time Series MethodsA time series is just collection of past values of the variable being predicted. Time series forecasting models try to predict the future based on past data（2）Quantitative Methods （定量）Used when situation is stable & historical data exist Existing products Current technology Involves mathematical techniquese.g., forecasting sales of color televisionsQuantitative Forecasting Methods5. Components of an ObservationLevel (current deseasonalized demand)：当前非季节性需求6. Simple Moving Average 简单移动平均The simple moving average model assumes an average is a good estimator of future behavior. Ft=Forecasted sales for the period tAt-1=Actual sales in period t-1n=Number of periods in the moving average7. Weighted Moving Average 加权移动平均While the moving average formula implies an equal weight being placed on each value that is being averaged, the weighted moving average permits an unequal weighting on prior time periodswt = weight given to time period “t” occurrence (weights must add to one)Advantages of Moving Average MethodEasily understood 易懂Easily computed 易算Provides stable forecasts 预测稳定Disadvantages of Moving Average MethodRequires saving all past N data points 需要详尽的历史数据Lags behind a trend 预测落后于趋势Ignores complex relationships in data 忽视了数据之间的复杂关系8.Exponential Smoothing Method 指数平滑A type of weighted moving average that applies declining weights to past data. 1. New Forecast = a (most recent observation) + (1 - a) (last forecast) or 2. New Forecast = last forecast + a (last forecast error)where 0 a 0, and I0, IT, and W0.11. Yield (Revenue) ManagementThe concept used in service operations with high-fixed costs and low-variable costs that attempts to match supply and demand (a chase strategy) to maximize capacity utilization.【第十五章Inventory Management】1.what is inventory?The average total number of flow units within a process at a specific point in time2. Why hold Inventory? (De Groote, 1994)1）. 管道/在途的库存, Which is held to maintain process throughput 维持生产流程2）. 季节性的库存，Which is held because of production and capacity smoothing when demand/supply is variable 因季节性生产能力不足而满足需求和供给变化的库存3）.批量库存，规模经济Which is held because it is economical to process more flow units than immediate demand 比起临时需求，批量需求更经济。4）.安全库存，应对不确定性需求、缺货Which is held in addition to expected demand to hedge against supply/demand uncertainty5）.缓冲库存，解耦运作Which is held between process steps to Allow their independent operating 使得缓冲区独立开来，它的暂时停顿不会对对生产流程产生影响。6）.投机库存，用于市场价格投机Which is held because of probable changes in the market prices of inputs or outputs. 3 Why Holding inventory is Cost Money?（1）Financial Cost: 财务成本Physical Holding Cost（管理成本）: storage, Obsolescence, Insurance, security, shrinkage, etc. Cost of (Stuck) Capital（资金成本）: W.Capital investment （2）Increasing Flow Time （增加生产时间）（3）Delaying Detection and Correction of Quality problems(Ch 8) （延迟检查和更正产品质量）（4）Diminishing Incentives to Improve the Process 削减对流程改善的激励作用4.Inventory costsSetup (or production change) costs 安装/生产机会成本Costs for arranging specific equipment setups, etcOrdering costs 订购成本Costs of someone placing an order, etcShortage costs 存储成本Costs of canceling an order, etc5. Independent versus Dependent Demand独立、非独立需求Independent Demand（市场需求）The demand that pertains to the requirements for end products (external market demand).Dependent DemandThe requirements for components that are directly dependent on the demand for the end products in which they are used.（终端产品分解需求）6.库存状态变量Inventory State Variables现有库存On-hand Stock (t)= OH (t)缺货订单Backorders(t)=B(t)净库存Net Stock (t) = IN (t) = OH (t) -B (t)在途库存On-order (t)=OO(t)补货点Inventory Position (t)= IP (t) = IN (t)+OO (t)7 Inventory CONTROL Policy库存控制策略连续盘存Continuous review: inventory is continuously monitored and an order of size Q is placed when the inventory level reaches the reorder point r, or (r, Q) system 定期盘存Periodic review: inventory is checked at regular (periodic) intervals and an order is placed to raise the inventory to a specified threshold (the “order-up-to” level), (T, S) system8. Inventory SystemsSingle-Period Inventory Model 单期库存模型One time purchasing decision (Example: vendor selling t-shirts at a football game)Seeks to balance the costs of inventory overstock and under stockOne time decision under uncertaintyTrade-off:Ordering too much (waste, salvage value cost) versusOrdering too little (excess demand is lost)Examples:Restaurant;Fashion;High Tech;Inventory decisions报童问题：Criticial ratio PCu/(Co+Cu)Expected profit if order kMulti-Period Inventory Models 多期库存模型（1）Fixed-Order Quantity Models数量固定 A system where the order quantity remains constant but the time between orders varies.Event triggered (Example: running out of stock)