CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   OpenFOAM (http://www.cfd-online.com/Forums/openfoam/)
-   -   Decomposition Methods (http://www.cfd-online.com/Forums/openfoam/71561-decomposition-methods.html)

misakagan January 7, 2010 12:03

Decomposition Methods
 
What decomposition method (Metis, Scotch, simple, hierarchical) you guys favor for large scaled simulations?

olesen January 8, 2010 02:22

Quote:

Originally Posted by misakagan (Post 241803)
What decomposition method (Metis, Scotch, simple, hierarchical) you guys favor for large scaled simulations?

Metis or scotch is what we use, since we generally don't have a better idea ourselves of how to decompose the domain any better (nor the time to figure it out anew for each geometry / cpu count combination).

Simply try out metis/scotch and see if you are happy with the results. You can view the separate processor* domains in paraview (eg, via paraFoam) to see if it matches up with your expectations.

BTW: I believe that future versions of OpenFOAM might be switching to scotch instead of metis due to licensing aspects. I found that the scotch decomposition was fairly similar to metis anyhow.

bastil January 8, 2010 04:35

Quote:

Originally Posted by olesen (Post 241851)
BTW: I believe that future versions of OpenFOAM might be switching to scotch instead of metis due to licensing aspects. I found that the scotch decomposition was fairly similar to metis anyhow.

Regarding licensing I think you may use Metis from 1.5 for testing purposes only. Otherwise, you need to have a license for that. Afaik this is the main reason why it changed to scotch in 1.6.
What I miss is a parallel partitioning method freeing us from the need to have machines with very large memory.

Regards

misakagan January 8, 2010 04:38

Hi.

I'm using also scotch or metis since they do not require any manual input. I checked the subdomains in paraview and they seem to be convenient. But the problem is that I get a terrible speed-up (scaling) if I increase the processor number. In other words, nearly all computational effort is invested on solving the pressure-poisson equation in PISO loop, which does not scale well with increased processor number.

Are you satisfied with parallelisation of OpenFOAM? I'm asking because considering this computational performance I can not simulate anything big. Maybe I'm doing something wrong.

olesen January 8, 2010 04:58

Quote:

Originally Posted by bastil (Post 241867)
Regarding licensing I think you may use Metis from 1.5 for testing purposes only. Otherwise, you need to have a license for that.

Here https://projects.coin-or.org/BuildTo...Metis?rev=1294 it states
Quote:

For commercial-use, the essential restriction is for the vendors not to be reselling Metis.
The restriction appears to apply to the vendor, not the end-user - http://glaros.dtc.umn.edu/gkhome/met...faq#distribute


All times are GMT -4. The time now is 22:29.