looking for a cluster to run a case

miles_davis · October 11, 2011, 11:56

HI

I have a multiphase case on Openfoam 2.0.1.
Actually I am running it on a 12 cores PC under ubunutu-linux.
The total human time for the simulation on such a machine should be 15 days (360h).
I need to speed up the resolution.
Case feature
initial file size : 200Mo
Results : 200Mo*30 saves => approx. 6Go

Does anyone know where and how I can find some solution to run it on a supercluster?

Regards,

Sydney TEKAM

abdul099 · October 11, 2011, 18:38

How many cells does your case contain?

miles_davis · October 12, 2011, 05:39

not that much: one million.
the problem is my simulation are unsteady.

puma · October 12, 2011, 07:14

Hi,

cloudnumbers.com offers computing resources also for Openfoam. But I didn't try it myself.

Cheers

abdul099 · October 20, 2011, 23:57

That's what I thought, the cell count is too low.
Just imagine, you've got a transportation task to solve. You've got 12 vans to do this, every van has to drive the route only once to finish the job. Now you find out, it takes to long. Do you think you will get a significant speedup when using 100 vans? No one of this vans can drive faster due to the speed limit, so it only might take longer due to a self-caused traffic jam...

Translated to your problem: With that low cell count you will not get a significant speedup when using a cluster. You've got only 80 000 cells per core, which is about the lower limit to use per core. When further reducing the cells per core, the solution will even take LONGER, as communication effort increases.
Maybe you could go down to 60 000 cells per core as it is a multiphase flow, but you will never obtain a speedup of factor 2 or 3 just by using more cores.

Unsteady simulations always need some time. As long as it is no trivial testcase, it takes enough time for the user to get impatient. This doesn't make happy, but is close to a law of nature.

miles_davis · October 24, 2011, 15:06

Thanks a lot for this clear explanation.
You saved me a lot of effort!

Regards,

Miles

federvo.mala · March 3, 2012, 19:08

Is there one for Ansys Fluent too?

thanks

October 11, 2011, 11:56	looking for a cluster to run a case	#1
miles_davis Member Miles Join Date: Sep 2011 Posts: 48 Rep Power: 15	HI I have a multiphase case on Openfoam 2.0.1. Actually I am running it on a 12 cores PC under ubunutu-linux. The total human time for the simulation on such a machine should be 15 days (360h). I need to speed up the resolution. Case feature initial file size : 200Mo Results : 200Mo*30 saves => approx. 6Go Does anyone know where and how I can find some solution to run it on a supercluster? Regards, Sydney TEKAM

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October 11, 2011, 18:38		#2
abdul099 Senior Member Join Date: Oct 2009 Location: Germany Posts: 636 Rep Power: 22	How many cells does your case contain?

October 12, 2011, 05:39		#3
miles_davis Member Miles Join Date: Sep 2011 Posts: 48 Rep Power: 15	not that much: one million. the problem is my simulation are unsteady.

October 12, 2011, 07:14		#4
puma New Member Philipp Join Date: Apr 2009 Location: Berlin, Germany Posts: 1 Rep Power: 0	Hi, cloudnumbers.com offers computing resources also for Openfoam. But I didn't try it myself. Cheers

October 20, 2011, 23:57		#5
abdul099 Senior Member Join Date: Oct 2009 Location: Germany Posts: 636 Rep Power: 22	That's what I thought, the cell count is too low. Just imagine, you've got a transportation task to solve. You've got 12 vans to do this, every van has to drive the route only once to finish the job. Now you find out, it takes to long. Do you think you will get a significant speedup when using 100 vans? No one of this vans can drive faster due to the speed limit, so it only might take longer due to a self-caused traffic jam... Translated to your problem: With that low cell count you will not get a significant speedup when using a cluster. You've got only 80 000 cells per core, which is about the lower limit to use per core. When further reducing the cells per core, the solution will even take LONGER, as communication effort increases. Maybe you could go down to 60 000 cells per core as it is a multiphase flow, but you will never obtain a speedup of factor 2 or 3 just by using more cores. Unsteady simulations always need some time. As long as it is no trivial testcase, it takes enough time for the user to get impatient. This doesn't make happy, but is close to a law of nature.

October 24, 2011, 15:06		#6
miles_davis Member Miles Join Date: Sep 2011 Posts: 48 Rep Power: 15	Thanks a lot for this clear explanation. You saved me a lot of effort! Regards, Miles

March 3, 2012, 19:08		#7
federvo.mala Member Join Date: Sep 2011 Location: United Kigdom Posts: 51 Rep Power: 15	Is there one for Ansys Fluent too? thanks