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