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-   -   (ICEM)Negative volumes instead of thiner layer (http://www.cfd-online.com/Forums/ansys-meshing/67264-icem-negative-volumes-instead-thiner-layer.html)

cbr August 10, 2009 06:11

(ICEM)Negative volumes instead of thiner layer
 
Hi,
I'm preparing 2-D mesh for a wing in ICEM
I need to 7-times decrease thickness of first near-wall layer, because max(y+) is 7 in my result file. But I'm getting negative volume when I set new thickness.
Please help me to fix it, thanks in advance!

PSYMN August 10, 2009 14:46

Kate Moss Thin
 
There is a known defect (see the release guide) about the quality metrics sometimes calling thin hexas inverted…

If your solver is structured, do the checks in the blocking tab, and if the very thin elements look (visually) ok, proceed to your solver and check it there.

If your solver is unstructured, do the checks on the unstructured mesh (Edit Mesh tab)...

On the other hand, you could actually be having a problem with the mesh…

If so, then I am guessing that you probably have a slight misalignment of parts (curves not aligned with surfaces to the same tolerance as your first cell height) and the mesh is trying to follow too closely. In certain situations, refining the mesh below the scale of the geometry quality can invert the boundary layer in the last element when projection changes from one entity to the other. If that is what you find (visually), setting projection limit can really help.

cbr August 19, 2009 03:35

Thanks Simon,

I have invented also another method- scale initial geometry 10 times (for example), create mesh for scaled geometry, open the mesh in pre and scale mesh 0.1 to initial size. Correct volume of thin elements keeps at that transformation in CFX-pre

cbr August 20, 2009 08:45

Everithing great is simple:)

another one solution of this problem is restart ICEM :)

PSYMN August 20, 2009 17:35

Reboot the shuttle...
 
Do you recall that time a few years back when the Space Shuttles computers were acting up and there was a tense 15 minutes while the astronauts had to sit in the dark as the orbiters computers were rebooted? There was some worry about if they would reboot properly, but they did, and then everything was fine.

I often think that as I reboot anything… If it was a good enough solution for NASA…

cbr August 21, 2009 04:26

I'm almost astronaut then, hehe :)


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