3 Pengantar Vensim

7/31/2019 3 Pengantar Vensim

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Vensim

Download:

http://www.vensim.com/cgibin/download.exe


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Menu dan Toolbar


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MENU File : Open Model, Save, Print, dll. Ed it : copy and paste, search, dll View : manipulating the sketch of the model and for

viewing a model Layou t : manipulate the position and size of elements

in the sketch. M od e l : Simulation Control and the Time Bounds

dialogs, the model checking features, and importing and

exporting datasets. Tools : sets Vensim's global options and allows you tomanipulate Analysis tools

W in d o w s : to switch among different open windows. H e lp : provides access to the on-line help system.


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Toolbar


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Sketch Tools

Lock sketch is locked.

Move/Size move, sizes and selects sketch objects: variables, arrows, etc.

Variable creates variables ( Constants , Auxiliaries and Data).

Box Variable create variables with a box shape (used for Levels or Stocks).

Arrow creates straight or curved arrows.

Rate creates Rate (or flow) construct

Model Variable adds an existing model variable

Shadow Variable adds as a shadow variable

Merge merges two variables into a single variable, etc

Input Output Object adds input Sliders and output graphs and tables to the sketch.

Sketch Comment adds comments and pictures to the sketch.

Unhide Wand unhides (makes visible) variables in a sketch view.

Hide Wand hides variables in a sketch view.

Delete deletes structure, variables in the model, and comments in a sketch.

Equations creates and edits model equations using the Equation Editor.

Reference Modes use to draw and edit reference models.


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Analysis Tool Output


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Control Panel

Variable allows you to choose a variable in your model and select it as the Workbench

Variable.

Time Axis allows you to change or focus the period of time over which Analysis tools

operate.

Scaling enables you to change the scales of output graphs.

Datasets allows you to manipulate the stored datasets (runs).

Graphs brings up the Custom Graph Control.

Placeholders is a control that sets Placeholder Values


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Example of Vensim


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Level

Rate

Auxiliary

Source/Sink

Constant

Flow arc

Cause-and-effect arc


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Level: Stock, accumulation, or state variableA quantity that accumulates over time

Change its value by accumulating or integratingrates

Change continuously over time even when therates are changing discontinuously


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Rate/ Flow: Flow, activity, movement

Change the values of levels

The value of a rate is

Not dependent on previous values of that rate

But dependent on the levels in a system along with

exogenous influences


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Auxiliary: Arise when the formulation of a levels influence on

a rate involves one or more intermediate

calculations Often useful in formulating complex rate equations

Used for ease of communication and clarity

Value changes immediately in response to changesin levels or exogenous influences


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Source and Sink: Source represents systems of levels and rates

outside the boundary of the model

Sink is where flows terminate outside the system


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Example 1(Population and birth)

+

+

Births Population

Births

Population


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Example 2(Children and adults)

Births Children Children maturing Adults

+ + +

+-

+

-

Births

children

Childrenmaturing

Adults


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average lifetime = 8 Units: Year

birth rate = 0.125 Units: fraction/Year

births = Population * birth rate Units: rabbit/Year

deaths = Population / average lifetime

Units: rabbit/Year

Population = INTEG(births - deaths,1000) Units: rabbit


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From Causal Loop DiagramTo Simulat ion Models 1

R

L

Equations

dL/dt = k1*R(t)

R(t) = k2*L(t)

dL/dt = k1*k2*L(t)

Flow Graph

Block Model

L L

k1*k2

Causal Graph

+

+

R L


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From Causal Loop DiagramTo Simulat ion Models 2R1

L

Equations

dL/dt = R1 R2

R2 = k2*L

R1 = k1

dL/dt = k1 - k2*L

Flow Graph

Block Model

R2

L1 L1k2

- k1


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From Causal Loop Diagram

To Simulat ion Models 3

Equations

dL1/dt = R1 R2

dL2/dt = R2 R3

R1 = k1

R2 = K2 * L1

R3 = K3 * L2

dL1/dt = k1 k2*L1

dL2/dt = k2*L1 K3*L2

R1

L1

Flow Graph

R2

L2

R3

L1 L1

k2

-

-

k1

L2 L2

Block Model

k3


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Building construction

Problem statementFixed area of available land for constructionNew buildings are constructed while old buildings are demolishedPrimary state variable will be the total number of buildings over time

Causal Graph

Industrialbuildings

DemolitionConstruction

Fraction of

land occupied

Construction

fraction Averagelifetime

for buildings

Average area

per building

Land available forIndustrial buildings

+

+

+

+

+

+ -

-

-

-


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Simulation models

Industrial

Buildings (B)

Construction (C) Demolition (D)

Construction

fraction

(CF) Fraction ofland occupied

(FLO)Land available forindustrial buildings(LA)

Average areaper building(AA)

Average lifetimefor buildings (AL)

Equations

dBl/dt = Cr Dr

Cr = f1(CF, Bl)

Dr = f2(AL,Bl)

CF = f3(FLO)

FLO = f4(LA,AA,Bl)

Flow Graph

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