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-   -   parallel computing doesn't speed up (https://www.cfd-online.com/Forums/openfoam-solving/114680-parallel-computing-doesnt-speed-up.html)

najunaju March 15, 2013 09:10

parallel computing doesn't speed up
 
dear fomers,

greetings!

I am running kepsilon model using pisofoam on bluff body with 2D simulation in a Intel core 2 quad processor with 8gb ram. I have four local processors and the simulation is too heavy that to complete 1 iteration it takes 25 seconds. now,

1. if I decompose into 2 or 4 processors (like, 2 1 1 or 2 2 1) the speed is same. doesn't change at all.

2. another surprising thing is, if I decompose into 6 or 8 processors and run through mpi commad, it runs but the speed is same though I have 4 processors. how come it runs in 6 or 8 processors?

I have to have around 1223987 interations which would take 10 to 15 days if I can't use parallel computing effectively.

please help me, please. I will be waiting.

Hiroshiman March 15, 2013 11:35

Hi !
A few questions :
What is the size of your domain ?
What was the exact command you used to run your case ? I used to forget the -parallel parameter at first.

najunaju March 16, 2013 01:43

thank u hiroshiman for ur inquiry.

my domain is 41Dx25D and width is extruded by openfoam, in the width direction there are single cell. I have total 6,00,000 cells to maintain y plus around 1 to 3. D is the height of domain.

I used simple dicomposition with the following command,

mpirun -np 4 pisoFoam -parallel

please help me, if u can. I am running out of time.

Hiroshiman March 18, 2013 10:55

Hi,
with 6E6 cells, the problem should be large enough to be run over a few cpus.

Could you post the output of the solver on the few few first iterations to have a better idea of what's happening ?

najunaju March 21, 2013 04:39

Dear Hiroshiman,

Thank you for your query. I have reduced mesh number and running now, I think this allowable for me.

Thank you again.


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