Stock and Flow Diagram
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Transcript Stock and Flow Diagram
Stock and Flow Diagram
Roesfiansjah Rasjidin
PS Teknik Industri
FT - UEU
Diagramming Notation
Stock-and-flow diagram is built using a
particular diagramming notation:
Stocks
Flows
Valves and
Clouds.
Stocks
Stocks or levels are represented by rectangles
or boxes
Stock or level variables describe
accumulations in the system.
Flows
Flows or rates are represented by pipes
There are two types of flows which are
inflows and outflows
Inflows are represented by a pipe (arrow)
pointing into (adding to) the stock
Outflows are represented by pipes pointing
out of (substracting from) the stock.
Valves and Clouds
Flow controls are represented by valves
Clouds represent the sources and sinks for the flows
A source represents the stock from which a flow
originating outside the boundary of the model arises
Sinks represent the stocks into which flows leaving
the model boundary drain
Sources and sinks are assumed to have infinite
capacity and can never constrain the flows they
support
The general structure of
stock-and-flow diagram
Valve (Flow
Regulator)
Source
Sink
Stock
Inflow
Outflow
Mathematical representation of
stocks and flows
Stocks accumulate or integrate their flows
t
Stock (t ) [ Inflow ( s ) Outflow ( s )]ds Stock (t 0 )
t0
where inflow(s) represents the value of the inflow at any time s
between the initial time t0 and the current time t
It represents the concept that the stock accumulates its
inflows less its outflows, beginning with an initial value of
Stocks (t0) (Sterman, 2000)
Discussion