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-   -   help!!!gambit again (http://www.cfd-online.com/Forums/fluent/28140-help-gambit-again.html)

shery January 12, 2001 13:23

help!!!gambit again
 
Hi, I'm trying to mesh a geometry in GAMBIT.The geometry is not very complex but there are some small gaps in there that seems to cause problem in meshing.I'm using Tgrid and every time I try to mesh I get this error massage:" Tetahedral meshing has failed for volume ....this is usually caused by problems in the face meshes.chck the skewness of your face meshes and make sure the face mesh sizes are not too large in areas of small gaps". I had this problem before and by editing some of the defaults I was able to mesh the geometry.But it doesn't seem to work for this one. I appreciate your help. shery

Raza Mirza January 13, 2001 17:53

Re: help!!!gambit again
 
Hi Shery,

The error message from TGrid seems to be fairly descriptive. TGrid, or for that matter any other tet mesher, does not like skewed faces. So if there are fine gaps that need to be meshed, try to make sure that the face triangles in that region are as close to perfect (isosceles, sp???) as possible (that is close to skewness of zero). and then tranistion GRADUALLY from there to regions where you do not need to resolve gaps.

what software are you using for surface triangulation? is the quality of triangulation easily controllable?


shery January 14, 2001 12:44

Re: help!!!gambit again
 
Hi Raza, Thanks for your respond.I'm not sure how I can make the skewness zero in the gaps. I'm using gambit and I think I can't change the quality of trangulation easily.but can you tell me if I could change the quality,what should be changed? thanks again shery

Sandeep January 15, 2001 09:59

Re: help!!!gambit again
 
I had the same problem when meshing in Gambit. Unfortunately you dont have too much control over the tet mesh in gambit. In my case I decomposed the volume into smaller volumes and then meshed each of them with the tet mesh and it worked. You might want to give that a shot.

shery January 15, 2001 12:34

Re: help!!!gambit again
 
Thanks sandeep,I decomposed the volume didn't help that much.If you have any other suggestions please let me know.

Raza Mirza January 16, 2001 00:12

Re: help!!!gambit again
 
Hi Shery,

Although I do not have any experience with Gambit, I have experience with preBFC, fluent's old-old pre-processor. In that you could control the node distribution on the edges. This control would give you some control over surface triangulation. Now I use a third party software that gives me the same flexibility much more easily.

Short answer to your question: If you can control the node distribution on the edges, try putting nodes on the edges that describe the thin gaps such that the space between any two adjacent nodes is half the gap size (or smaller). I do work with geometries that have small gaps that I need to resolve and usually I control the node distribution to control the surface triangulation. In the software I use I can also control some other attributes of the surface mesh.

I hope it helps. As I said, I do not have any experience with Gambit. But I have found Fluent's user support to be very helpful. May be they can tell you if you can or can not control the node distribution.


shery January 16, 2001 12:53

Re: help!!!gambit again
 
thanks Raza for your help.it was very useful.I can control the node distribution on edges in Gambit. I did and it worked for me. thanks again

Raza Mirza January 16, 2001 18:52

Re: help!!!gambit again
 
i'm glad it worked out.


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