modelCapacityRestrictedStock

Information

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This is a restricted reservoir of the system dynamics methodology, which accumulates material  (i.e., countable entities, some form of matter) transported by flow components connected to the component's StockPorts. Like a MaterialStock the CapacityRestrictedStock can never become negative—we are not collecting "antimatter"—and will prevent connected flow components from draining its value below zero. Unlike other stocks, minCapacity and maxCapacity are seen as capacity restrictions that for "physical" reasons cannot be violated—the restrictions can be given as either constant parameters (minValue, maxValue) or as variable inputs (u_min, u_max). Accordingly, the component will signal flow restrictions via its port that must be observed by connected flow components.

Implementation

The value of the stock will be set to zero if the calculated value x is less than a very small positive amount and if reinitializeStock = true is chosen in the Advanced tab:

  if reinitializeStock then
    when x < 0 then
      reinit(x, 0);
    end when;
  end if;

CapacityRestrictedStock components will prevent connected flows from draining the stock via their →StockPort connectors' Boolean flags, should the calculated state variable x be less than a very small positive amount:

  inflow.stopInflow = not x < maxCapacity - BusinessSimulation.Constants.small;
  outflow.stopInflow = inflow.stopInflow;

  inflow.stopOutflow = not x > minCapacity + BusinessSimulation.Constants.small;
  outflow.stopOutflow = inflow.stopOutflow;

Notes

• The inflow and outflow →StockPorts are only indicative; in general the reservoir may be filled or drained by flows connected to either port.


• The capacity restrictions are also used to define an admissable range than can be monitored by an assert using useAssert = true in the Advanced tab. The switch causeError controls whether an error or a warning is to be raised.

• The parameter init allows to select →InitializationOptions:
  
  
  • FixedValue (default) will use the parameter initialValue to determine the initial value.
  
  
  • SteadyState will introduce the equation der(x) = 0 in order to find an initial value that establishes equilibrium.
    (Note: Such a solution may not exist and to avoid trivial solution in many cases initialValue -- in this case used as a start value for numerical iteration -- should be set to a value different from zero.)
  
  
  • Free there will be no initial equation and thus the solver is free in solving the initial value problem.

• There is an optional →StockInfoOutput connector.

See also

MaterialStock, InformationLevel

Parameters

Connectors

Components