CloseGap

Determine the rate of flow (action) to close a gap between a quantity and its desired value

Diagram

Information

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The output y is given by the expression:

y = (u_reference - u_current) / u_adjTime

where the time to close the gap (u_adjTime) can alternatively be a constant (adjTime). If the adjustement time is zero, then the output y will be zero as well.

Limitations

The adjustment time must not be negative. Negative values will be caught by an assert statement and will cause the simulation to stop.

Catching a division by zero (e.g., adjustement time is zero) by returning a zero output will not be an adequate structure if some kind of discrete behavior is what is wanted: Adjustement time being zero may then mean that the stock should change immediately which usually only makes sense at defined events. If such discrete behavior is intended this structure should not be used.

Notes

The output may be multiplied with (-1) in order to use the output to control an outflow.
See [6, p. 30] or Jim Hines' Molecules of Structure website (→Close Gap) for more details on the use of this structure within system dynamics.

Parameters (8)

adjTime	Value: 1 Type: Time (s) Description: Time to close the gap
maxRate	Value: inf Type: OutputType Description: Maximum rate feasible
minRate	Value: 0 Type: OutputType Description: Minimum rate feasible
hasConstantAdjTime	Value: true Type: Boolean Description: = true, if the time to close the gap is a constant paramater
invertOutput	Value: false Type: Boolean Description: = true, if the output is to be multiplied with (-1)
clipOutput	Value: false Type: Boolean Description: = true, if the indicated rate is to clipped to not exceed limitations
strict	Value: true Type: Boolean Description: = true, if strict limits with noEvent(..) (constantLimiter.strict) (clip1.strict)
homotopyType	Value: LimiterHomotopy.Linear Type: LimiterHomotopy Description: Simplified model for homotopy-based initialization (clip1.homotopyType)

Connectors (4)

	y	Type: RealOutput Description: Policy output signal
	u_reference	Type: RealInput Description: Desired or reference value for the controlled quantity (i.e., the goal)
	u_current	Type: RealInput Description: Current value of controlled quantity
	u_adjTime	Type: RealInput Description: Time to close the gap

Components (8)

	modelSettings	Type: ModelSettings Description: Setting important global variables within a model
	unchanged1	Type: PassThrough Description: Use the calculated net rate of flow
	invertedAction	Type: Gain Description: This will turn negative rates to positive ones (for use with an outflow)
	unchanged2	Type: PassThrough Description: Use the calculated net rate of flow
	clip1	Type: Clip Description: Clips input signal so that it remains within a given interval
	parAdjTime	Type: ConstantConverterTime Description: Constant time to close the gap (optional)
	gap	Type: Gap Description: Difference between the goal and the current value
	actionToCloseGap	Type: Division_Guarded Description: Rate of (net) flow to close the gap

Used in Components (5)

	SimpleControl BusinessSimulation.CausalLoop Directly influencing a stock to keep it at setpoint value
	ForceToInputValue BusinessSimulation.CausalLoop Flow is obtained as closing the gap to input value
	ForceToStockValue BusinessSimulation.CausalLoop Flow is obtained as closing the gap to input stock value
	HinesCoflow BusinessSimulation.Stocks Accounting for changes in average quality of a stock as new entries with different characteristic flow in
	FirstOrderStockAdjustment BusinessSimulation.MoleculesOfStructure.Policy Maintain a stock at a desired level