系統(tǒng)動力學(xué)模型講ppt課件-展示頁
2025-05-12 01:32本頁面
【正文】 定系統(tǒng)的邊界 確定系統(tǒng)因素之間因果關(guān)系 建立系統(tǒng)動力學(xué)模型 計算機仿真實驗 結(jié)果分析和模型修正 Vensim軟件介紹 1. 界面及工具 2. 建立因果反饋圖（ causal loop diagrams ）和流圖（ Stock and Flow Diagrams ） 3. 模擬過程 4. 函數(shù)： LOOKUP、 TIME、 STEP What is Vensim? Vensim is a visual modeling tool that allows you to conceptualize, document, simulate, analyze, and optimize models of dynamic systems. Vensim provides a simple and flexible way of building simulation models from causal loop or stock and flow diagrams. By connecting words with arrows, relationships among system variables are entered and recorded as causal connections. This information is used by the Equation Editor to help you form a plete simulation model. You can analyze your model throughout the building process, looking at the causes and uses of a variable, and also at the loops involving the variable. When you have built a model that can be simulated, Vensim lets you thoroughly explore the behavior of the model. Vensim User’s Guide Version 5 1. 界面及工具 標題 Title Bar 菜單 Menu Toolbar 繪圖工具 Sketch Tools ? 狀態(tài)條 Status Bar Structural Analysis Tools Causes Tree — creates a treetype graphical representation showing the causes of the Workbench Uses Tree — create a treetype graphical representation showing the uses of the Workbench Loops — displays a list of all feedback loops passing through the Workbench Document — reviews equations, definitions, units of measure, and selected values for the Workbench Variable. Dataset Analysis Tools Causes Strip Graph — displays simple graphs in a strip, allowing you to trace causality by showing the direct causes (as shown) of the Workbench Graph — displays behavior in a larger graph than the Strip Graph, and contains different options for output than the Strip Graph. Table — generates a table of values for the Workbench Variable. Runs Compare — pares all Lookups and Constants in the first loaded dataset to those in the second loaded dataset. ?分析工具 Analysis Tool Output 控制板 The Control Panel The Control Panel allows you to change internal settings that govern the operation of Vensim, such as which Workbench Variable is selected or what Datasets are loaded. i n t e r e s ts a v i n g si n c o m ew o r ke f f o r t++++? 2. 建立因果反饋圖 ( Causal loop diagram)和建立流圖 (Stock and flow diagram) ?1）建立因果反饋圖（ causal loop diagrams）：以 SavingsInterest為例 演示 3種分析工具： Cause Tree ； Uses Tree；Loops，分析因果反饋圖的邏輯結(jié)構(gòu) s a vi ng si nc om ew or k e ffo rti nt e re s t(s a vi ng s )s a vi ng si nt e re s t (s a vi ng s )w or k e ffo rt i nc om e兩個圖經(jīng)由變量 savings的因果關(guān)系而連接，剛好分別前后對調(diào)；當反饋環(huán)向后回到該變量，則用括號括起來。 4. 反饋結(jié)構(gòu)一定形成閉合回路。 2. 明確變量增減的涵義。 1. 在因果反饋圖中采用名詞，不用動詞。 ? 一階負反饋回路具有 自我平衡 的作用，經(jīng)過若干時間（周、天）后，庫存量會越來越接近于期望庫存量，定貨速率也相應(yīng)地越來越小，庫存差額相應(yīng)地減小。 ? 系統(tǒng)的目標是要求的庫存量，記為 DI。 ? 訂貨速率為 OR,OR可以為正，也可為負。 ? 現(xiàn)假設(shè)初始庫存量為 1000噸，期望庫存量為 6000噸，由當前庫存量調(diào)整到期望庫存量所需要的時間 AT為 5周，試構(gòu)造因果反饋結(jié)構(gòu)并進行計算機仿真模擬。 ? 手工仿真計算的前幾步： 仿真步長 （ 年 ） 總?cè)丝?（ P） 年增長人口數(shù) （ R1） 0 100 2 1 102 2 3 … … … ?(1) birth=birth rate* population ? Units: Year ?(2) birth rate= ? Units: **undefined** ?(3) FINAL TIME = 100 ? Units: Year ? The final time for the simulation. ?(4) INITIAL TIME = 0 ? Units: Year ? The initial time for the simulation. ?(5) population= INTEG (birth,100) ? Units: **undefined** ?(6) SAVEPER = TIME STEP ? Units: Year [0,?] ? The frequency with which output is stored. ?(7) TIME STEP = 1 ? Units: Year [0,?] ? The time step for the simulation. ?注釋： ?INTEGRAL： 積分 即 population是 birth的積分，初始值為 100。 i n t e r e s ts a v i n g si n c o
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