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Memory needed for solving a 3 million model

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Old   February 25, 2011, 05:52
Default Memory needed for solving a 3 million model
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Elena Cortin
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Hi i am dealing with a 3 , 5 million model in CFX, i am having a 6 core 8 giga ram machine and i get the memory error,

is there any option to increase the allowed memory or the cfx need more?

thanks
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Old   February 25, 2011, 06:41
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I think the amount of memory needed depends not only on the mesh element quantity but also on the amount of equations (more terms in the equations) being solved for e.g. more equations/terms are being solved for a multiphase flow with an RSM turb model than a singlephase flow with a one-equation turb model.

I just solved a y+=1, 3.5 million node (8.5 million element) hybrid mesh for an external aerodynamics airflow with the SST turb model and this used about 7-8 GB RAM with CFX v12.1. CFX v13 accesses less memory than v12.1 due to some pointers in the main memory allocation routine having been changed from 8 byte 4 byte integers, which is why I'm staying with v12.1.

However, I think there's some memory scale factors in the CFX-Solver Manager that you might want to read up on.
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Old   February 25, 2011, 06:42
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You will be pushing it to fit that model in a 8gb machine. It might fit, but only just.

Are you running in a 64 bit OS with 64 bit CFX?
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Old   February 25, 2011, 14:32
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CFX does a memory estimation and then allocates the memory which is required. This estimation is conservative and in most cases the run fits in the allocated memory. If not you get error message.

You have to differ between a lack of allocated memory and a lack of physical memory. The error message says what happened. Read it carefully.

If the allocated memory is not enough use the memory switches. If physical memory is not enough, you have to reduce your requirements. If it is just because of a few bytes, reduce paralellization as it produces overhead. You may also try the memory switch with factor smaller than one e.g. 0.98. If you are lucky it works, as the estimation is conservative.
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Old   February 25, 2011, 19:47
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Elena Cortin
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Thank you all finally i did that....

there was a workstation problem...

something else

how can i visuilize the symmetry in cfx pos????? i mean i did a simulation with symetric plane but i need to visualize the mesh + the mirror

how can i do that????

thanks again
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Old   February 26, 2011, 16:35
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Visualising symmetry in CFD-post is easy with instance transforms. I think this would be covered in the rotating machinery examples.
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