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-   -   True Impact of Using "Relax Mass" Expert parameter for transient runs (http://www.cfd-online.com/Forums/cfx/105456-true-impact-using-relax-mass-expert-parameter-transient-runs.html)

jonny_b July 31, 2012 10:57

True Impact of Using "Relax Mass" Expert parameter for transient runs
 
I'm attempting to start a transient solution using a res file for initial conditions and I get an overflow error around the 3 coeffiecient loop of the first timestep. I thought perhaps applying a relaxation to my solution may help the startup of the run.

Upon reading the CFX help I noticed that under the help section for "relax mass" it statest that default is 0.75 but then in the description it states

Quote:

Changing the value of this parameter can aid convergence for problems that show residual oscillations in separation and reattachment regions. As it relaxes, the mass flow calculation procedure, it should not be used for transient problems (or should be set to 1).
I am curious as to what exactly is impacted when using this relaxation setting for a transient case. My initial thought is that it will only slow down the rate at which transient information changes in time.

Anybody have better insight into this? Further does anyone have any advice as to what relaxation settings might help the startup of my run?

Thanks.

ghorrocks July 31, 2012 19:04

You would have to discuss it with CFX support to get details of exactly what is happening. Full details of expert parameters are not published.

jonny_b August 1, 2012 08:20

I appreciate the reply ghorrocks. I guess I'm not looking for anything in detail, but rather a summary statment as to what the effects on my results would be if I were to use this relaxation in transient runs.

But you are correct that probably my best avenue will be to contact ANSYS support.


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