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-   -   [GAMBIT] negative volume by cooper? (http://www.cfd-online.com/Forums/ansys-meshing/88951-negative-volume-cooper.html)

W.T.S May 31, 2011 05:06

negative volume by cooper?
 
1 Attachment(s)
Hi, dear -MAX-, hi everybody! I don't know why when i use the cooper tool in gambit's volume meshing, it produced many negtive volume even if it 's a rather simple entity. I'm here for help...Attachment 7856

-mAx- May 31, 2011 07:21

*top picture is clear >> not right mesh schema is used

*bottom picture >> check the mesh on axial direction.
You should habe a nice hexa mesh, else Cooper might have problems
The problem doesn't come from the face pointing in our direction

W.T.S May 31, 2011 07:40

Quote:

Originally Posted by -mAx- (Post 309925)
*top picture is clear >> not right mesh schema is used

*bottom picture >> check the mesh on axial direction.
You should habe a nice hexa mesh, else Cooper might have problems
The problem doesn't come from the face pointing in our direction

Sorry ,i'm still not clear, the top one and the bottom one are the two faces of the same entity. when i use cooper and then select these two faces as the source faces, there produced negtive volume. i checked the grids and although the source faces are regular paved grids, as shown in the bottom picture, the grids inside is rather weird. as to the right scheme, it seems only a hex cooper and a hex/wedge cooper are available. i can't figure out where the problem lies.Could you be so kind to tell me?

-mAx- May 31, 2011 07:46

delete your mesh.
Mesh one cap of the volume with pave.
Go to volume mesh and select your volume
Gambit should select automatically cooper scheme.
Mesh the volume (it should also detect the right sources).
You can also enforce the source selection by clicking on top and bottom surfaces

W.T.S May 31, 2011 08:17

Quote:

Originally Posted by -mAx- (Post 309931)
delete your mesh.
Mesh one cap of the volume with pave.
Go to volume mesh and select your volume
Gambit should select automatically cooper scheme.
Mesh the volume (it should also detect the right sources).
You can also enforce the source selection by clicking on top and bottom surfaces

I've tried lots of times just as what you showed me. but i don't konw why it could't be properly meshed. i didn't remesh any source faces as the cooper sheme requires.
I've been successfully meshed the entity(splited to many smaller entities) before with map tool, but you konw ,using map means the cells on the boundary is the biggest and the cells inside is smallest, it's not good to get a delicate boundary layer solution; so i have to use cooper.

-mAx- June 1, 2011 01:31

1 Attachment(s)
ok I assume this is a topology problem.
I could reproduce your weird situation.
If you delete the 2 inner cylinders, the problem has almost disappeared, but the 2 tangential volumes still don't accept cooper mesh.
I don't know why.
I did an 0.1mm extrusion for preventing high skewed elements in sharp corners, and then I applied a full hex mesh on those 2 volumes.
You can in crease quality in this area with a larger extrusion.
Anyway I would try to reconstruct your geometry for having something "clean"
Attachment 7874

W.T.S June 1, 2011 02:06

Quote:

Originally Posted by -mAx- (Post 310053)
ok I assume this is a topology problem.
I could reproduce your weird situation.
If you delete the 2 inner cylinders, the problem has almost disappeared, but the 2 tangential volumes still don't accept cooper mesh.
I don't know why.
I did an 0.1mm extrusion for preventing high skewed elements in sharp corners, and then I applied a full hex mesh on those 2 volumes.
You can in crease quality in this area with a larger extrusion.
Anyway I would try to reconstruct your geometry for having something "clean"
Attachment 7874

Thank you!you're so kind to help me so much!
i've followed what you told me in the last post to make a 0.1mm extrusion and managed to gain a good quality mesh for the 2 tangential volumes . As to the problem of cooper, if it really doesn't accept cooper mesh, i have to use tgrid scheme.


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