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-   -   Decomposition Methods: which ones are best for large scale simulations? (https://www.cfd-online.com/Forums/openfoam-solving/71561-decomposition-methods-ones-best-large-scale-simulations.html)

misakagan January 7, 2010 13:03

Decomposition Methods: which ones are best for large scale simulations?
 
What decomposition method (Metis, Scotch, simple, hierarchical) you guys favor for large scaled simulations?

olesen January 8, 2010 03:22

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 05:35

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 05:38

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 05:58

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

KateEisenhower October 29, 2015 07:13

HI Mark,

can you please tell me how to load the separate processor domains into ParaView?

Best regards,

Kate
Quote:

Originally Posted by olesen (Post 241851)
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.


rnburne October 29, 2015 10:00

Nothing special is needed Kate. From within each processor file make the
VTK conversion, then open Paraview and load as you normally would.
Does this help?

KateEisenhower October 29, 2015 11:41

Sorry, somehow I overlooked the constant directory in the processor files.

Have a nice day,

Kate


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