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Contributor
esmaeilk
Posts: 23
Registered: ‎11-15-2013

Element count escalates quickly!

163 Views, 11 Replies
12-15-2013 12:58 AM

Why does Sim CFD 2014 on my system counts 90 million elements for a simple model with 30 flat surfaces for a mesh size of 0.2? On other systems mesh sizes of 0.01 sum to about 1 million elements for much more complicated shapes. Is there something wrong?

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wildej
Posts: 961
Registered: ‎08-25-2011

Re: Element count escalates quickly!

12-16-2013 01:42 AM in reply to: esmaeilk

Hi esmaeilk,

 

What happens when you actually mesh it? The mesh count preview can be innaccurate sometimes.

Once you have it meshed, the total mesh count will be shown in the Output Bar.

 

Kind regards,

Jon



Jon Wilde
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OmkarJ
Posts: 440
Registered: ‎10-02-2012

Re: Element count escalates quickly!

12-16-2013 04:06 AM in reply to: esmaeilk
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esmaeilk
Posts: 23
Registered: ‎11-15-2013

Re: Element count escalates quickly!

12-16-2013 06:21 AM in reply to: wildej

I ran the simulation and it turned out to be about 3.7 million elements, however, I noticed that the system used 20GB of ram to generate the mesh volume. Isn't it supposed to be 2GB per 1 million elements?

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OmkarJ
Posts: 440
Registered: ‎10-02-2012

Re: Element count escalates quickly!

12-16-2013 06:30 AM in reply to: esmaeilk

~2GB/million generally applies for Solver, when the NS equations are being solved and iterations are run. Here, we are merely generating a mesh, and Mesher generally requires ~1GB/million.

 

At any rate, usage of 20GB for 3.7 million sounds extreme. Are you sure you didn't incorrectly measure the memory usage (extra 0 etc)? Also you should spot the memory usage when the message "optimizing volume mesh" is shown. If you wat until mesh is completed, the Solver kicks in, and the memory usage is escalated accordingly.

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Contributor
esmaeilk
Posts: 23
Registered: ‎11-15-2013

Re: Element count escalates quickly!

12-16-2013 06:40 AM in reply to: OmkarJ
I'm pretty sure it was 20GB while creating the volume mesh and it took a few hours, I was staring at the screen all night! Is it possible that it has something to do with Multi-Threating?

My system has 12 cpu cores and 48GB of ram, I cant understand why the system cant run simulations ;(
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OmkarJ
Posts: 440
Registered: ‎10-02-2012

Re: Element count escalates quickly!

12-16-2013 06:49 AM in reply to: esmaeilk

Multi-threading (flag)  will help you in reducing the time required for the meshing rather than increasing it. Can you post an image of your domain? Also, it may be worthwhile to use coarse mesh initially and refine it gradually. You will have better grasp on memory usage and size of mesh. 

 

Also be advised that SimCFD uses only 2^n cores. Don't know if this will help, but try defining your Solver using 8 cores and se if this changes anything.

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Contributor
esmaeilk
Posts: 23
Registered: ‎11-15-2013

Re: Element count escalates quickly!

12-16-2013 06:51 AM in reply to: OmkarJ

With a uniform mesh size of 2 for a small box you can see that all of the memory is exhausted and the system is now on page file/virtual memory.

screenshot.png

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OmkarJ
Posts: 440
Registered: ‎10-02-2012

Re: Element count escalates quickly!

12-16-2013 07:05 AM in reply to: esmaeilk

Well, you want to see the memory usage of only SimCFDMesher.exe, and not by the whole system!  See attached pic. Make sure you click on "Shw processes from all users."

 

 

mesh_memory.jpg

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Contributor
esmaeilk
Posts: 23
Registered: ‎11-15-2013

Re: Element count escalates quickly!

12-16-2013 07:10 AM in reply to: OmkarJ

my bad, here it isscreenshot.png

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