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Is it possible to declare (or re-declare) components depending on the value of a time-dependent variable (as opposed to a parameter)? Conditional declaration has been discussed here numerous times (e.g., #1, #2 and #3), however in those examples, the condition depends on a parameter.

My situation is this: I have two models, NaturalConvectionHeatTransfer and ForcedConvectionHeatTransfer that extend from the same interface PartialHeatTransfer. In a third model, I would like to do something like this:

model MyProblem
  // stripped other declarations
  input v "Velocity of fluid flow";
  replaceable PartialHeatTransfer heatTransfer;
equation 
  if v == 0 then
    // redeclare heatTransfer to be of type NaturalConvectionHeatTransfer
  else
    // redeclare heatTransfer to be of type ForcedConvectionHeatTransfer
  end if;
end MyProblem;

A conditional declaration like Component blah if v==0; certainly does not work if v is not a parameter. Is there any way to achieve my goal? My guess is "no", meaning I will have to re-think the whole concept. However, perhaps someone sees an obvious solution I am missing. Any suggestion how to work around this would be appreciated.

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Dominic Jefferies
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1 Answers1

3

It is not possible. You can, however, model around it by adding both heatTransfer components and switch between them using some dummy components and equations.

http://dx.doi.org/10.3384/ecp14096183 has some implementation hints on how to do it in Modelica slightly inefficiently (and how tools could optimize some of those things away).

sjoelund.se
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  • Thanks a lot once more! The paper gave some interesting insight. For now, I have done just what you suggested - declare both components and switch between them. – Dominic Jefferies Jun 25 '14 at 09:39