(ICEM)Negative volumes instead of thiner layer

cbr · August 10, 2009, 06:11

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

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

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

@Arash · October 18, 2023, 16:37

Quote:

Originally Posted by cbr

Everithing great is simple

another one solution of this problem is restart ICEM

Hi Dear cbr,

I have exactly the same problem as you. By adjusting the thickness of the first layer near the wall to reach Y+ = 1, negative volume is created for me.

How can I fix this problem?

Thanks in advance.

August 10, 2009, 06:11	(ICEM)Negative volumes instead of thiner layer	#1
cbr New Member Join Date: Aug 2009 Posts: 10 Rep Power: 16	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!

August 10, 2009, 14:46	Kate Moss Thin	#2
PSYMN Senior Member Simon Pereira Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 2,663 Blog Entries: 1 Rep Power: 47	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.

August 20, 2009, 17:35	Reboot the shuttle...	#5
PSYMN Senior Member Simon Pereira Join Date: Mar 2009 Location: Ann Arbor, MI Posts: 2,663 Blog Entries: 1 Rep Power: 47	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…

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August 19, 2009, 03:35		#3
cbr New Member Join Date: Aug 2009 Posts: 10 Rep Power: 16	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

August 20, 2009, 08:45		#4
cbr New Member Join Date: Aug 2009 Posts: 10 Rep Power: 16	Everithing great is simple another one solution of this problem is restart ICEM

August 21, 2009, 04:26		#6
cbr New Member Join Date: Aug 2009 Posts: 10 Rep Power: 16	I'm almost astronaut then, hehe