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 t Ro(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.Little’s Law
Little’s 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 T
Turnover = Throughput / Inventory
= 1/ T
For 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)Little’s 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. Capacity
Process Capacity is the maximum sustainable Flow Rate (Throughput) of a process
The Capacity for a process, the less situations where we have sufficient supply to match demand
Process 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=Min{Available Input rate, Demand Rate, Process Capacity}
Activity 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 Capacity

14. Managing the Flow Rate
Increase Throughput
Manage supply and demand
Increase Process Capacity
Reduce starvation (synchronize flows better)
Reduce blockage (appropriately select buffer sizes)
Increase Effective Capacity
Reduce resource unavailability (maintenance policies, better HR management, less frequent setup/changeover, reduced setup/changeover times
Increase Theoretical Capacity

【第十三章Operational Planning and Control////Forecast】
1.pull/push/make-to-order/make-to-stock
Pull:（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 event
Forecast:About what will happen in future
Plan: About what should happen in future
Forecasts as input

3. Characteristics of Forecasts
Forecasts 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 important
Aggregate 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, experience
e.g., forecasting sales on Internet

Qualitative Methods

Delphi Methods
l. Choose the experts to participate representing a variety of knowledgeable people in different areas
2. Through a questionnaire (or E-mail), obtain forecasts (and any premises or qualifications for the forecasts) from all participants
3. 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 questions
5. Repeat Step 4 as necessary and distribute the final results to all participants
Time Series Methods
A 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 techniques
e.g., forecasting sales of color televisions

Quantitative Forecasting Methods

5. Components of an Observation

Level (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 t
At-1 = Actual sales in period t-1
n = Number of periods in the moving average

7. 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 periods

wt = weight given to time period “t” occurrence (weights must add to one)

Advantages of Moving Average Method
Easily understood 易懂
Easily computed 易算
Provides stable forecasts 预测稳定
Disadvantages of Moving Average Method
Requires 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 < 1 and generally is small for stability of forecasts ( around .1 to .2)

The advantages of exponential smoothing:
(1)Models are surprisingly accurate.
(2)Model formulation is fairly easy.
(3)Readily understood by users.
(4)Little computation is required.
(5)Limited use of historical data.

9. Forecasting Errors in Time Series Analysis&&Measurement of Error
9.1 MAD (mean absolute deviation)(平均绝对离差)—Average forecasting error based on the absolute difference between actual and forecast demands.

The ideal MAD is zero which would mean there is no forecasting error。The larger the MAD, the less the accurate the resulting model
9.2Tracking Signal Formula信号追踪
TS is a measure that indicates whether the forecast average is keeping pace with any genuine upward or downward changes in demand.

9.3 Simple Linear Regression Model

【第八章08. Aggregate Sales and Operations Planning】

1.Production Planning(产品计划) Given specific process planning, process technologies, and production conditions, production planning predetermine varieties, quantities, and schedules of products to be produced according to market demand of products;
产品计划则根据产品市场需求，给出具体的流程计划、技术和生产条件， 决定产品的种类、数量和生产计划。

2. Time Dimensions:
Long-range planning
Greater than one year planning horizon Usually performed in annual increments
Medium-range planning
Six to eighteen months Usually with weekly, monthly or quarterly increments
Short-range planning
One day to less than six months Usually with weekly or daily increments

3。Overview of Operational Planning Activities

Process Planning（主生产计划）determines the specific technologies and procedures required to produce a product a service.决定具体技术和工序
Strategic capacity planning （战略能力计划）determines long-term capabilities (e. g. size and scope) 长期能力
Aggregate planning concerns with setting up production rate by product family or other categories for intermediate term (6-18 months).
Master production scheduling generates the amounts and dates of specific items required by orders. 订单具体项目的数量和数据
Material requirement planning（物料需求计划） takes the end product requirements from MPS and breaks them down into their components and subassemblies to create a material plan (production orders and purchase order).
Operations scheduling（操作安排） allocates jobs to specific machines, production lines or work centers.

4. Aggregate planning-Introduction
Aggregate planning (AP), also called macro planning, addresses problem of deciding how many employees the firm should retain and, for a manufacturing firm, the quantity and the mix of products to be produced.（制造企业的工人雇佣、产品数量等）
The aggregate planning methodology here assume that demand is deterministic, or known in advance.
Main purpose: Specify the optimal combination of
production rate (units completed per unit of time)
workforce level (number of workers)
inventory on hand (inventory carried from previous period)

5. hierarchical production planning
Aggregate planning is closely related to hierarchical production planning (HPP). HPP considers workforce sizes and production rates at variety of levels of the firm

6. Aggregate Production Planning
6.1Relevant Costs
（1）Basic production costs (fixed and variable) 基本生产成本
（2）Costs associated with changes in the production rate (e.g., labor costs) 变动生产成本
（3）Inventory holding costs 存货成本
（4）Backlog (stockout) costs 缺货成本

7.Production Planning Strategies
（1）Chase Strategy（追赶：工人人数变动，工时不变）
Matching the production rate to exactly meet the order rate by hiring and laying off workers as the order rate varies.
（2）Stable Workforce—Variable Work Hours（稳定：工人人数不变，工时变动）
Varying output by varying the number of hours worked through flexible schedules or overtime.
（3）Level Strategy （存货变动）
Maintain a stable workforce working at constant output rate; absorb demand variations with inventory, backlogs, or lost sales.

8. Pure Chase and Pure Level Strategies

9. Aggregate Planning Techniques
（1）Trial and Error
Costing out the production alternatives and choosing the one with the lowest cost.
（2）Linear Programming
（3）Linear Decision Rule
（4）Various Heuristic Methods

***10. Linear Programming (LP)
Linear Programming (LP) is used to determine values of n nonnegative variables to maximize or minimize a linear function of these variables that is m linear constraints of these variables.
Cost Parameters
CH=Cost of hiring one worker;
CF= Cost of firing one worker;
CH= Cost of holding one unit of stock for one period;
CR= Cost of producing one unit product on regular time;
CO= Incremental cost of one unit on overtime;
CU= Idle cost per unit of production;
CS= Cost of subcontract one unit of production;
nt=Number production days in period t;
K=Number of aggregate units produced by one worker in one day;
I0=Initial inventory on hand at the start of the planning horizon;
W0=Initial workforce at the start of the planning horizon;
Dt=Forecast of demand in period t;
Problem Variables:
Wt=Workforce level in period t;
Pt=Production level in period t;
It=Inventory level in period t;
Ht=Number of workers hired in period t;
Ft=Number of workers fired in period t;
Ot=Overtime production in units;
Ut=Worker idle time in units (undertime);
St=Number of units subcontracted from outside;

Subject to ：
（1）the above 3T constraints,
（2）nonnegative constraint: Wt, Pt, It, Ht, Ft, Ot, Ut and St >0, and I0, IT, and W0.

11. Yield (Revenue) Management
The 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 time

2. 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 uncertainty
5）.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 costs>
Setup (or production change) costs 安装/生产机会成本
Costs for arranging specific equipment setups, etc
Ordering costs 订购成本
Costs of someone placing an order, etc
Shortage costs 存储成本
Costs of canceling an order, etc

5. 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 Demand
The 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) system

8. Inventory Systems
Single-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 stock
One time decision under uncertainty
Trade-off:
Ordering too much (waste, salvage value < cost) versus
Ordering too little (excess demand is lost)
Examples:
Restaurant;
Fashion;
High Tech;
Inventory decisions…

报童问题：

Criticial ratio P<Cu/(Co+Cu)
Expected profit if order k

Multi-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)