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Old   July 7, 2011, 04:22
Default PC specification for OpenFOAM
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Hi. I am planning to buy a new PC to run complex CFD simulations using OpenFOAM. What shall I be looking for when buying such machines? I would be grateful for any recommendations!!

Thank you in advance.
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Old   July 7, 2011, 04:46
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Quote:
Originally Posted by A.D.E View Post
Hi. I am planning to buy a new PC to run complex CFD simulations using OpenFOAM. What shall I be looking for when buying such machines? I would be grateful for any recommendations!!.
What is "complex", please? How large do you expect the models to become? This is important to ensure sufficient memory. Additionally, go for as many CPUs and cores as possible.

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Old   July 7, 2011, 07:17
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Hi Bastian.

Thank you for the quick reply. I will be looking into external subsonic/transonic compressible flows. My grid might reach 5 million cells. What would you think might be the cheapest option?

Once again thank you for your time and response,

Regards A.D.E
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Old   July 7, 2011, 09:23
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Hello,
As always, it depend of how money you will spend on ...

Anyway, with a small amount of money, the best is to buy 2 to 5 cheap PC with core i5/i7 @ 3.3Ghz with 4 Go ram and Ethernet (~500 each) connection throug a GigaByte switch.
Speedup are far better with multi node than multi core.
NB: i've got a far better speed up with 2 core i5 node, with a 2x2core : 4 process, than on a signle i5 with 4 process. With 4+4, speedup are not so good.
NB2: with ethernet, do not use more than ~ 5 node, unless you add QDR infiniband card.

Olivier
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Old   July 8, 2011, 06:32
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Hi Olivier,

Thank you for your reply. My budget will be between 2500-3000 pounds Uk I hope. So you think that it might be better to buy more than one machine and connect them together? I can not buy one PC and add cores on it?? My knowledge on setting up PCs is limited therefore I would like something good and simple.. Do you have anything like that in mind?

Once again thank you for your consideration and time,

Sincerely,

A.D.E
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Old   July 8, 2011, 07:42
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Hello,

I think the main limitation come from Cache memory.

1) If you go with one multicore station, like dual xeon (i.e "professional workstation"), you may get 2*6 core with one machine @ ~ 3000, so 2x6 = 12 core, with 2*12 = 24 Mo Cache, and ~ 2.6 Ghz/core.

2) If go with 4 pc, core i7, you get 4x4 =16 core and 4x 8Mo = 32 Mo Cache, 3.4Ghz/core, at less than 3000, and with real speed up.

NB: at work, with the same test case, a single core i5 run on 4 core @ 3.3 Ghz are 2.5x faster than a dual xeon, which run on 8 core @ 2.2 Ghz, and with 2 station with core i5, it's 4x faster, so yes, frequency matter too.)

NB2: don't forget to set on one machine a large amount of memory (8/12 Go at least) + graphic card when you will mesh/decompose/ and use paraview ...

NB3: for all other station, 2-4 Go is ok if used only as a compute node (1Mio cell ~ 1 - 1.5 Go ram), and no need of hard drive/screen/...

olivier
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