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-   -   Simplefoam and Delta t (http://www.cfd-online.com/Forums/openfoam-solving/60350-simplefoam-delta-t.html)

ariorus January 10, 2006 06:55

Hi everybody, I'd like to k
 
Hi everybody,

I'd like to know if it is possible to set the size of the timestep while using the stationary solver simplefoam.
I mean the numerical time step. I guess that the timestep can be different according to the cell size in stationary problems.

In some of my testcases I noticed that in small cells I have convergence problems and I'd like to control the timestep in these cells.

Have I to use icofoam even if I'm interested only in the stationary results?

Thank you for any suggestion.

mattijs January 12, 2006 14:57

simpleFoam uses underrelaxatio
 
simpleFoam uses underrelaxation which is equivalent to local time stepping.

There is no control apart from changing the underrelaxation factor. Try using different discretisation. Or maybe your problem is transient.

ariorus January 13, 2006 04:51

Just after posting my message
 
Just after posting my message I had a look at the code and I realized there was actually no local timestepping, but relaxation. I should have known that.
Sorry for my silly question.

Thank you very much for your answer anyway.

By the way I have another stupid question.

Is that possible that recompiling some solver (simpleFoam in this case) without any changing I get different (best in convergence) results? Or must I have missed something?

Thank you again.

mattijs January 13, 2006 05:02

There might be very small diff
 
There might be very small differences if you compile with/without optimization or on a different machine. We compile with -O3 -ffast-math on a p4.


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