Problems with scratch memory while meshing

[maheshh]

Hi all,

I am trying to model the flow around the heatsink. If I keep the mesh coarse then it is not a problem. But I want the element size to be small. The distance between consecutive fins is 1 mm and hence I think my element size (element edge length) should be smalller than the distance between fins. I tried to keep the edge length of 0.5 mm but I get the following error:

"Meshing of volume has been aborted because of lack of memory. Close down other processes and/or choose larger element size. Minimum additional memory required = 1954 MB."

I am working on a machine with following configuration:
2 CPU , 1.66 GHz each
2.0 GB Ram
2.4 GB free space on C drive (where OS is installed) and 60 GB free on other partition (where I have all my Ansys files)

I am looking at the Task Manager and I can see that when I receive this message there is 1.0 GB of Physical Memory stilll available. Then why do I get this error?

On the modeling side, is my thinking wrong? If the distance between fins is 1 mm, then I need an element size subtantially smaller than this distance if I want to model the flow between the fins. Heatsink bounding box is 80x80x50 and I am modeling an enclosure of 84x84x54 around the heatsink (not practical but want to keep it as small as possible). Before I try to mesh the enclosure, I run the VOVLAP command on the 2 volumes (heatsink and enclosure). I can see that element size of 0.5 mm is very small when modeling such a big volume but I am not sure why I get this error message even when I have 1 GB of physical memory free.

Any inputs would be apprciated.

 

[mohr]

Hi Maheshh
Ansys works wiyh your phisical memory AND memory from
swap file.

Try increasing your swap file size. It may help.
Also read memory managment on Ansys help. By the way, are you working with Ansys 7.0 ? because if it is the case,
Ansys does this work automaticaly, marking "use default
memory model" option.

 

[maheshh]

Yes.
I am using Ansys 7.1 and after reading the memory management help found out that it should be taken care of automatically. But apparently it is not.

I increased the element size to 0.9 and then Ansys was able to complete the meshing job. But then when I tried to solve the Flotran problem , it came back with same error.

Mahesh.

 

[mohr]

Hi Maheshh !!

When you have "Meshing of volume has been aborted because of lack of memory. Close down other processes and/or choose larger element size. Minimum additional memory required = 1954 MB." it is warning to you that you are short of additional memory. this additional memory comes from swap file.
Try to increase the size. ( if you can )
How many elements have your model mesh ?

regards

Mohr

 

[maheshh]

The problem was with my model having too many elements. The element size that I was using was very small and hence the total DB size was getting close to 1.5 GB. So I figured I can use better technique to mesh the volume between fins.

Along the length of the fins (80 mm) the changes in parameters like velocity, pressure and film corfficients are not going to vary too much within 2-3 mm. Therefore I kept the element edge length along the length of the fin to be 2 mm (used vsweep to create the mesh). That way I reduced the number of elements tremendously and reduced the size of the DB.

Have started the transient run right now, and will know about the results tomorrow. Hopefully they will turn out ok.

Thanks for all the inputs.

Mahesh.

 

[mohr]

Hi Maheshh !!

How was your work ?? I hope very fine. By the way, did you try to manual mesh configuration with Global size, area size , etc ? It was very helpfull to me with my mechanical
jobs, because you can use relative big elements on model
sector of less importance and you can refine those model
zones of critical importance. Then you will save a lot of memory and time processing.

Cheers

Mohr

 

[maheshh]

The fluid analysis turned out to be fine. The vsweep command worked very well.

But I have another question about meshing. I have 2 volumes glued to each other. Say one small rectangular block glued to a bigger rectangular block. Now I want to know that if I map mesh the smaller block (using vsweep) before the bigger block, can I mesh the bigger block using vsweep also?

The problem I am faced with is that the area of the smaller block which is common to bigger block is already meshed. Now the area around this needs to be mapmeshed and Ansys does not do it. Think about this area is a rectagular area with a smaller rectangular hole in it.

How can I map mesh this bigger block?

Any tips would be helpful.

Regards,

Mahesh.

 

[rikhan]

Mahesh
For your meshing I believe you have to divide the bigger volume in to two. The best way is to divide the bigger volume by workplane equal to the smaller one and then glue them again before using vsweep. I am sure it will work. yeah, dont forget giving similar line divisions.
best of luck
Rehan