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-   -   CFX 5.4.1 mesh quality? (http://www.cfd-online.com/Forums/cfx/18676-cfx-5-4-1-mesh-quality.html)

joseph October 11, 2001 14:09

CFX 5.4.1 mesh quality?
 
hi,

can anyone tell me the limitation in mesh quality and the range in which a grid should be with respect to CFX 5.4.1.

how can i control the quality of mesh ?

thanks for you time.

joseph

P.Fonteijn October 11, 2001 16:55

Re: CFX 5.4.1 mesh quality?
 
Roughly your angle should not be less than 5 degrees. To see if you have these you have to verify surface meshes in Build. If angles are less than 8 degrees you will get a warning. When you take a closer look to the surface, you might see the bad grid quality. Redefine the surface and verify again. I don't know what will happen if you ignore the messages about a bad angle. I take 5 degree as critical.

Regards, P. Fonteijn

cfd guy October 15, 2001 10:15

Re: CFX 5.4.1 mesh quality?
 
Hi,
I work with a geometry which I cannot escape from this warnings. Every time I generate the mesh, BUILD tells me two warnings about bad angles, but I cannot modify my surfaces, at least I still didn't think how to do it.
Regards,
cfd guy

P.Fonteijn October 15, 2001 15:55

Re: CFX 5.4.1 mesh quality?
 
Why can't you modify your surfaces? What you always can do is delete your solid, delete the surface that is causing the problems, recreate it in a different manner than you did before, recreate your solid and check using surface meshes the quality of your surface mesh. Or do you have a particular trimmed surface that looks so complicated that you are frightened to delete it? Tell me more and I'll see if I can give some useful hints and tips.

P Fonteijn.

cfd guy October 16, 2001 08:55

Re: CFX 5.4.1 mesh quality?
 
Thanks Fonteijn,
You said exactly what is my problem. I have a particular surface, which causes this bad angles. May I mail you an simple example and see what you can do?
Regards,
cfd guy

Bart Prast October 16, 2001 12:12

Re: CFX 5.4.1 mesh quality?
 
Imported the geometry from an IGES file? Then we have the same problem. The description of surfaces in IGES leaves much to be desired. Better use an interface with a CAD program directly (Pro/Engineer CATIA, etc).

Robin Steed October 16, 2001 13:25

Re: CFX 5.4.1 mesh quality?
 
You don't have to delete the surface. You can re-parameterize the surface using the Create>Surface>Composite feature. If you use this and only select the surface giving you grief, it wil project a new paramterization over the surface. You can then use this new surface to reassemble your B-Rep solid. The only exception is if you have surface normals 180 degrees opposed.

Give it a try.

Regards, Robin

PS: The mesher in CFX-Build 5.5 has improved tolerance for these imperfections. There are also additional tools available in 5.5 for fixing problem geometry.

Robin

P.Fonteijn October 16, 2001 19:13

Re: CFX 5.4.1 mesh quality?
 
Yep. If the suggestions made by Steed or Prast didn't help you, you can send an e-mail to the (updated)address above.

P.Fonteijn

joseph October 18, 2001 14:40

CFX 5.4.1 mesh quality? for robin
 
hi robin,

what do you mean by "The only exception is if you have surface normals 180 degrees opposed"

could you please elaborate on this.

thanks joseph.

Robin Steed October 18, 2001 16:02

Re: CFX 5.4.1 mesh quality? for robin
 
cfd guy,

If you look at a hemisphere, the surface normals at the edge point 180 degrees away from each other. The tool reparameterizes by rotating your model and projecting a regular grid onto it from the screen direction, so if two edges are 180 degrees apart, it cannot avoid them being 90 degrees from the screen normal and the projection fails. The fix in that case is to further break up the surface.

Robin


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