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-   -   Running in parallel mysteries (http://www.cfd-online.com/Forums/openfoam-solving/114616-running-parallel-mysteries.html)

andreas March 14, 2013 04:40

Running in parallel mysteries
 
Dear foamers,

I want to run a fine mesh (1200*400) on OF and for that I need to run in parallel. I run a first time with some 18cpu and the simulation went to 0.1sec after 3 days. I took the same folder and ran it from the 0.1sec with 36cpu since 4 days, it barely reached the 1.1sec

I then ran some test cases with 1, 2, 4, 8cpu, during 5minutes for a 150*50 mesh. Here are the results:

1cpu: Time = 0.0569324
2cpu: Time = 0.0680509
4cpu: Time = 0.0638118
8cpu: Time = 0.00469057
16cpu: Time = 0.00384501

Quite strange isn't?

To run in parallel, I simply change the "numberOfSubdomains" in the decomposeParDict file and change the n(x y z) in the simpleCoeffs knowing that x*y*z must be equal to the numberOfSubdomains.

That's it, do I have to change any other parameter?

Thank you for your help, I'm quite new in cfd
Andreas

olivierG March 14, 2013 07:30

hello,

A common mistake is to forget the "-parallel" option with the solver, which can explain why it's slower with more core ....

regards,
olivier


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