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CEL expression as time duration for transient run

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Old   February 5, 2008, 13:31
Default CEL expression as time duration for transient run
  #1
KB
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Hi,

in my model I'd like to investigate the pressure drop of some component as a function of the mass flow rate (stationary flow). Therefore I set up a quasi-stationary model, where I increased the flow rate slowly (starting from zero).

For this I have to fix the time duration for the transient run. But I'd like to stop the run as soon as the pressure drop reaches a certain level.

Does anybody of you have an idea how to formulate such a stopping criterion?

Thanks in advance KB
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Old   February 5, 2008, 17:37
Default Re: CEL expression as time duration for transient
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Glenn Horrocks
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Hi,

Generally this is better done as a series of steady state simulations rather than a transient simulation.

You cannot stop the solver using CCL. You can using a fortran subroutine but I wouldn't bother, just manually stop it when it reaches your criterion. Is there a reason why you need to program it in?

Glenn Horrocks
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Old   February 5, 2008, 18:31
Default Re: CEL expression as time duration for transient
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Rogerio Fernandes Brito
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I agree with Mr. Glenn Horrocks.
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Old   February 6, 2008, 05:30
Default Re: CEL expression as time duration for transient
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KB
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Thanks so far.

The reason for programming is that I have to do this kind of calculation for a valve with different strokes. For each stroke I need only to increase the flow rate until a certain force acting on the valve's tappet is reached. For small strokes (almost closed valve) I do not need big flow rates as this would lead to huge pressure drops that will not occur in practice and are also difficult from a convergence point of view.

The reason for transient run rather than series of steady state runs is that I get a fine resolution of the pressure-vs.-flowrate curve. I also supposed that this procedure it also advantageous for convergence and that the total simulation time for one transient run is less than for, say, 10 to 20 stationary runs. Don't you think, this is true?

Best wishes KB

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Old   February 6, 2008, 17:24
Default Re: CEL expression as time duration for transient
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Glenn Horrocks
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Hi,

Steady state runs have simpler mathematics as no transient terms are present. This means a steady state run should be quicker than a transient run.

Glenn Horrocks
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Old   February 13, 2008, 21:10
Default Re: CEL expression as time duration for transient
  #6
tera
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I have met the same problems. since the valve is moved by the flow force enen the flow rate is setted,so how to make a steady simulation?
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