Change BCs and restart simulation

be89 · February 28, 2017, 11:49

Hello,

I'm trying to simulate a case where the outlet is closed until a certain time, then opens out.

So I ran the first part of the simulation treating the outlet patch as a wall, but now I don't know the way to change BCs (manually or not, I don't care) and restart from there.

Any suggestions?

Thank you

floquation · February 28, 2017, 13:02

Just thinking along with you:

Manually:
You'd have to set "startFrom latestTime;" in controlDict. Then, after stopping the case, you can change the BC in the latest time directory manually to whatever you want it to become. Then restart the case.
Evidently, this process may be automated using (shell) scripts.

Being a 'lil more clever:
Typically things like this may be achieved with groovyBC.
A wall is just a fixedValue (0 0 0) for U and zeroGradient for pressure.
An outlet depends on what you want the outlet to behave like... It could be zeroGradient for velocity and fixed value for pressure, for instance.
Afaik, groovyBC cannot switch between different BC (fixedValue -> zeroGradient), so I reckon it cannot be used for your purpose.
Which takes me back to the manual method (automated with a script). I don't really see an alternative at this point in time.

Note of caution:
If you start of without an outlet, make sure that you do not have an inlet either. Otherwise your case is ill-posed.

February 28, 2017, 11:49	Change BCs and restart simulation	#1
be89 New Member Enrico Bezzi Join Date: Aug 2011 Posts: 9 Rep Power: 15	Hello, I'm trying to simulate a case where the outlet is closed until a certain time, then opens out. So I ran the first part of the simulation treating the outlet patch as a wall, but now I don't know the way to change BCs (manually or not, I don't care) and restart from there. Any suggestions? Thank you

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February 28, 2017, 13:02		#2
floquation Senior Member Kevin van As Join Date: Sep 2014 Location: TU Delft, The Netherlands Posts: 252 Rep Power: 21	Just thinking along with you: Manually: You'd have to set "startFrom latestTime;" in controlDict. Then, after stopping the case, you can change the BC in the latest time directory manually to whatever you want it to become. Then restart the case. Evidently, this process may be automated using (shell) scripts. Being a 'lil more clever: Typically things like this may be achieved with groovyBC. A wall is just a fixedValue (0 0 0) for U and zeroGradient for pressure. An outlet depends on what you want the outlet to behave like... It could be zeroGradient for velocity and fixed value for pressure, for instance. Afaik, groovyBC cannot switch between different BC (fixedValue -> zeroGradient), so I reckon it cannot be used for your purpose. Which takes me back to the manual method (automated with a script). I don't really see an alternative at this point in time. Note of caution: If you start of without an outlet, make sure that you do not have an inlet either. Otherwise your case is ill-posed.