Memory needed for solving a 3 million model

eleazar · February 25, 2011, 05:52

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

siw · February 25, 2011, 06:41

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.

ghorrocks · February 25, 2011, 06:42

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?

joey2007 · February 25, 2011, 14:32

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.

eleazar · February 25, 2011, 19:47

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

ghorrocks · February 26, 2011, 16:35

Visualising symmetry in CFD-post is easy with instance transforms. I think this would be covered in the rotating machinery examples.

February 25, 2011, 05:52	Memory needed for solving a 3 million model	#1
eleazar Member Elena Cortin Join Date: Mar 2009 Location: Paris Posts: 65 Rep Power: 17	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

February 25, 2011, 06:41		#2
siw Senior Member Stuart Join Date: Jul 2009 Location: Portsmouth, England Posts: 742 Rep Power: 26	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.

February 25, 2011, 14:32		#4
joey2007 Senior Member Join Date: Mar 2009 Location: Europe Posts: 169 Rep Power: 17	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. __________________ - - - - - ------------------------------------------------------------------------ Please do not forget: I am not paid for answering your questions. Thousands of issues can cause a division by zero. Please do not capture a thread, with the argument: "I have the same issue ...."

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February 25, 2011, 06:42		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	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?

February 25, 2011, 19:47		#5
eleazar Member Elena Cortin Join Date: Mar 2009 Location: Paris Posts: 65 Rep Power: 17	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

February 26, 2011, 16:35		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,871 Rep Power: 144	Visualising symmetry in CFD-post is easy with instance transforms. I think this would be covered in the rotating machinery examples.