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-   -   parallel results different depending on decomposition strategy (http://www.cfd-online.com/Forums/openfoam/69757-parallel-results-different-depending-decomposition-strategy.html)

franzisko November 3, 2009 11:52

parallel results different depending on decomposition strategy
 
hello,
I performed a simulation using simpleFoam and for different parallelization strategies: number of processors, simple/hierarchical/... I get slightly different results. Is there anyone which knows it is ok, or if there is any problem. The difference seems to be small (more or less 1% on drag coefficient for the stationary solution). Where is the part depending on the decomposition method?

thanks a lot,
Francesco

madad2005 November 4, 2009 04:07

Hi Francesco,

I've been having some wider-spread issues with using foam in parallel. I'm assuming the differences you are seeing are due to decomposition of the domain each time with different regions having different ghost cells. 1% does appear to be a lot though. Interestingly, I'm finding that when attempting to run foam in parallel, it appears it is trying to run N number of serial jobs and is killing the memory on my machine. Have you seen similar behaviour?

Regards,

Adriano

madad2005 November 4, 2009 06:35

Well, I finally resolved my problem. I was missing the -parallel command out when executing the parallel job.

franzisko November 4, 2009 07:37

hi adriano,

thanks for your suggestion concerning ghost nodes. I think 1% is a bit too much, too. however, the fields are very similar each other, hence I hope there is no serious problem

intersting behaviour missing -parallel...

bye, francesco


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