System DynamicsSystem Dynamics(( 動態系統動態系統 ))

By C. L. HsiehBy C. L. Hsieh

Department of Industrial Department of Industrial Management Management

Aletheia UniversityAletheia University

Introduction (Introduction ( 簡介簡介 ))

A fool with a tool is still a foolA fool with a tool is still a fool Knowing how the elements of a Knowing how the elements of a

system interact & how overall system interact & how overall performance can be improved are performance can be improved are essential to the effective use of essential to the effective use of simulationsimulation

(( 了解系統中了解系統中元件之互動關係元件之互動關係與與執行改善之執行改善之方法方法對於模擬方法能有效運用昰必要的對於模擬方法能有效運用昰必要的 ))

System Definition(System Definition( 系統之定義系統之定義 ))

What is a system? (What is a system? ( 何謂系統何謂系統 ?)?) System is a collection of elements that System is a collection of elements that

functions together to achieve a desired goalfunctions together to achieve a desired goal (( 系統乃是系統乃是一群元件一群元件組合在一起工作，為了要達到一組合在一起工作，為了要達到一

個共同之目標個共同之目標 )) A system consists of multiple elementsA system consists of multiple elements (( 系統包含多重的元素系統包含多重的元素 )) Elements are interrelated & work in Elements are interrelated & work in

cooperationcooperation (( 元素互為相關、且互相合作工作元素互為相關、且互相合作工作 )) A system exists for achieving specific A system exists for achieving specific

objectivesobjectives (( 系統存在昰為了要達到特定目標系統存在昰為了要達到特定目標 ))

System Definition (System Definition ( 系統之定義系統之定義 ))

Processing Systems: (Processing Systems: ( 作業系統作業系統 )) artificial (man-made)artificial (man-made), , dynamic (interact dynamic (interact

with time)with time) && stochastic (random behavior)stochastic (random behavior) ( 人工地、動態地 ( 時間 ) 、隨機地 ( 行為 ))

Service Systems (restaurants, banks)Service Systems (restaurants, banks) (( 服務型系統服務型系統 ,, 如餐廳、銀行如餐廳、銀行 )) Manufacturing Systems (job shops, production Manufacturing Systems (job shops, production

facilities, assembly lines, facilities, assembly lines, warehousing,distribution)warehousing,distribution)

(( 製造型系統製造型系統 ,, 如工作站、設施規劃、生產線組裝、倉 儲、如工作站、設施規劃、生產線組裝、倉 儲、物料分派物料分派 ))

System Elements (System Elements ( 系統之元件系統之元件 ))

Entities(Entities( 實體實體 )), , Activities(Activities( 活動活動 )), , Resources(Resources( 資源資源 )) & & Controls(Controls( 控制控制 ))

System Elements(1) System Elements(1) (( 系統元件系統元件1)1)

EntitiesEntities: Items processed through the system: Items processed through the system (e.g Products, Customers, Documents(e.g Products, Customers, Documents.) .) (( 實體乃昰系統中被處理之項目，如產品、顧客、文件實體乃昰系統中被處理之項目，如產品、顧客、文件 ))

Types of Entities:Types of Entities: (( 實體之種類實體之種類 )) Human or animate (customers, patients, etc.) Human or animate (customers, patients, etc.) (( 有有

生命的生命的 )) Inanimate (parts, documents, bins, etc.) Inanimate (parts, documents, bins, etc.) (( 無生命的無生命的 )) Intangible (calls, emails, etc.) Intangible (calls, emails, etc.) (( 無形的無形的 ))

System Elements(2) System Elements(2) (( 系統元件系統元件2)2)

Activities:Activities: tasks performed in the tasks performed in the system involved in the processing system involved in the processing of of entities entities (e.g Cutting parts, Servicing customers, Repairing machines.).)

(( 活動乃昰系統中處理實體時要做的事情，活動乃昰系統中處理實體時要做的事情，如零件切割、顧客服務、機器修理如零件切割、顧客服務、機器修理 ))

Activities consumes Activities consumes timetime and and involve the use of involve the use of resourcesresources

(( 從事活動須消耗時間與使用資源從事活動須消耗時間與使用資源 ))

System Elements(3) System Elements(3) (( 系統元件系統元件3)3)

Resources:Resources: means by which activities are means by which activities are preformed. They provide preformed. They provide facilitiesfacilities, , equipmentsequipments and and personnelpersonnel for activities for activities

(( 資源昰活動執行之方式、如設備與人力等資源昰活動執行之方式、如設備與人力等 )) Characteristics: Characteristics: capacity, speed, cycle timecapacity, speed, cycle time, , reliabilityreliability (( 特徵：容量、速度、處理時間、可靠度特徵：容量、速度、處理時間、可靠度 )) TypesTypes of Resources: of Resources: (( 資源之種類資源之種類 ))

Human or animate (operators,doctors, etc.) Human or animate (operators,doctors, etc.) (( 有生命的有生命的 )) Inanimate (equipment, tooling, floor space, etc.) Inanimate (equipment, tooling, floor space, etc.) (( 無生命無生命

的的 )) Intangible (information, electronic power, etc.) Intangible (information, electronic power, etc.) (( 無形的無形的 ))

System Elements(4) System Elements(4) (( 系統元件系統元件4)4)

Controls:Controls: dictate dictate howhow, , whenwhen & & where where activities are preformed. activities are preformed.

(( 控制說明活動執行之方法、時間與地點控制說明活動執行之方法、時間與地點 )) Highest Level: Highest Level: schedule, plans & policies schedule, plans & policies (( 高階控制：排程、計劃、決策高階控制：排程、計劃、決策 )) Lowest level:Lowest level: take written procedure, machine take written procedure, machine

control logiccontrol logic (( 低低階控制：計畫執行程序、機器控制邏輯階控制：計畫執行程序、機器控制邏輯 )) Examples: Examples:

Route sequencing Route sequencing (( 排序排序 )) Production Planning Production Planning (( 生產計劃生產計劃 ))

System Complexity (System Complexity ( 系統複雜系統複雜度度 ))

Bounded Rationality- Our limited ability to Bounded Rationality- Our limited ability to grasp real-world complexitygrasp real-world complexity

(( 能力之現實狀況能力之現實狀況──人的能力有限以致無法掌握現人的能力有限以致無法掌握現實問題之複雜度實問題之複雜度 ))

Factors Factors (( 因素，因素， p.28)p.28) Interdependencies : the behavior of one Interdependencies : the behavior of one

element to affect other elements in the element to affect other elements in the systemsystem

(( 相依性 相依性 : : 系統中元素影響其他元素之行為系統中元素影響其他元素之行為 ) ) Variability: producedVariability: produced uncertainty uncertainty (( 變異性 變異性 : : 系統中不確定之因素系統中不確定之因素 ))

Interdependency Interdependency (( 相依性相依性 ) )

Interdependency tight or loose Interdependency tight or loose (( 相依性 相依性 : : 強或強或弱弱 ))

System with tightly coupled interdependency System with tightly coupled interdependency have greater impact on system operation have greater impact on system operation and performance and performance (( 相依性較強之系統對於系統值相依性較強之系統對於系統值作業與執行有較大之衝擊作業與執行有較大之衝擊 ))

Eliminating interdependency is preferred but Eliminating interdependency is preferred but not entirely possible for most systems not entirely possible for most systems (( 我們我們當然希望消除相依性、但大部份系統皆不可能當然希望消除相依性、但大部份系統皆不可能 ) )

例：例： Dedicate resources to single machine (excessive Dedicate resources to single machine (excessive inventories, underutilized resources)inventories, underutilized resources)

Variability Variability (( 變異性變異性 ) ) Variability: System involving Variability: System involving HumanHuman ( ( 人 人 ) )

& & Machinery (Machinery ( 機器機器 ) ) which is which is inevitable inevitable ，， e.g. Supplier delivery, e.g. Supplier delivery, Equipment failure, Unpredictable absenteeEquipment failure, Unpredictable absentee

(( 變異性：乃是系統中人或機器等不可避免之因素，變異性：乃是系統中人或機器等不可避免之因素，如機器故障、人員缺席如機器故障、人員缺席 ))

Type of Variability (see p.30, Table 2.1 ) Type of Variability (see p.30, Table 2.1 ) Activity times Activity times (( 作業時間作業時間 )) Decisions Decisions (( 決策決策 )) Quantities Quantities (( 數量數量 )) Event Intervals Event Intervals (( 事件發生之間隔時間事件發生之間隔時間 )) Attributes Attributes (( 屬性屬性 ))

Performance Metrics (Performance Metrics ( 執行測量值執行測量值 ))

Flow/Cycle/Throughput/lead Time (Flow/Cycle/Throughput/lead Time ( 流量時間流量時間 )) Utilization (Utilization ( 使用率使用率 )) Value-added time (or processing time) (Value-added time (or processing time) ( 加值時間、加值時間、顧客願意支付之時間顧客願意支付之時間 ))

Waiting time (Waiting time ( 等候時間等候時間 )) Flow rate ( production/processing/throughput Flow rate ( production/processing/throughput

rate) (rate) ( 生產率生產率 )) Inventory (queue) levels (Inventory (queue) levels ( 庫存水準庫存水準 )) Yield (Yield ( Reject rate) ( Reject rate) ( 生產率生產率 )) Customer responsiveness (Customer responsiveness ( 庫存滿足訂單之能力庫存滿足訂單之能力 )) Variance (Variance ( 變異數變異數 ))

System Variables (System Variables ( 系統變數系統變數 ) )

Decision Variables (Input Factors): Decision Variables (Input Factors): define how a system worksdefine how a system works(( 決策變數：輸入因子、決定系統運作方式決策變數：輸入因子、決定系統運作方式 )\)\ Controllable /Uncontrollable (Controllable /Uncontrollable ( 分為可控與不可控兩種分為可控與不可控兩種 ))

Controllable VariableControllable Variable

1.1. # of Operators# of Operators

2.2. # of Work Shifts # of Work Shifts

Un-Controllable VariableUn-Controllable Variable

1.1. Service TimeService Time

2.2. Reject Rate at a costReject Rate at a cost

System Variables (System Variables ( 系統變數系統變數 ) )

Response Variables Response Variables (Performance/Output): indicate how a (Performance/Output): indicate how a system performs system performs

(( 反應或輸出變數：呈現系統執行結果反應或輸出變數：呈現系統執行結果 ))

State Variables: indicate system State Variables: indicate system conditions at specific points in timeconditions at specific points in time

(( 狀態變數：系統於某時間點之狀態狀態變數：系統於某時間點之狀態 ))

Examples of Response Var.:• # of Entities Performed• Average Utilization• Performance Metric

Examples of State Var.:• Current # of Entities

waiting to be performed• Status of Teller (busy or

idle)

System Optimization (System Optimization ( 系統最佳化系統最佳化 ))

The Systems ApproachThe Systems Approach ( ( 系統處理程序系統處理程序 ))

Cost Changes of Subsequent Stages of System Development ( 系統發展之成本

因素變化 )

Rule of Tens:

Cost to correct a problem

Summary (Summary ( 結論結論 ))

System Dynamic is essential to System Dynamic is essential to using any tool for planning system using any tool for planning system operationsoperations

(( 動態系統對於使用任何工具於任何系統動態系統對於使用任何工具於任何系統作業是必要的作業是必要的 ))

Systems are made up of Systems are made up of entitiesentities, , resourcesresources, , activitiesactivities, , controlscontrols

(( 系統是由實體、資源、活動與控制所構系統是由實體、資源、活動與控制所構成成 ))

Summary (Summary ( 結論結論 ))

Characteristics of Systems: Characteristics of Systems: interdependencies & variabilityinterdependencies & variability

(( 系統有兩大特徵：相依性與變異性系統有兩大特徵：相依性與變異性 )) Simulation is capable of imitating Simulation is capable of imitating

complex system which tranditional complex system which tranditional analytical techniques cannot do itanalytical techniques cannot do it

(( 模擬可以模仿傳統分析技巧無法解決的模擬可以模仿傳統分析技巧無法解決的複雜系統複雜系統 ))