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Old   March 8, 2003, 15:22
Default 3D-mesh Gambit.....
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Hi All,

I am trying to generate a complex 3D mesh in Gambit 2.0, in which there is a tank having bottom face as irregular (like undulating ground and not a plane surface) surface and other faces are planer faces.

I coud mesh it and export the mesh successfully, but, in FLUENT 6.0 I am getting the messages " Grid Check Failed" and "NonPositive Volumes Existed" and as I tried to iterate it showed DIVERGENCE.

Actually in Gambit I created only two volumes which I think are Positive only. So where from the non-postive volums came???

I also do not know what is non-postive volume??

Plz. help me find what must be wrong??

Waiting for reply.....


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Old   March 10, 2003, 02:01
Default Re: 3D-mesh Gambit.....
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Did you check your grid after meshing in GAMBIT? It's probably due to the skewness of the mesh.
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Old   March 10, 2003, 05:14
Default Re: 3D-mesh Gambit.....
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which kind of cell,hex cell or tera cell in your mesh?
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Old   March 10, 2003, 07:46
Default Re: 3D-mesh Gambit.....
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I agree with Michelle. Go check the grid using Gambit. (It's in the same position as the icon for information-volume-mesh, except you have to click the right mouse button) Run a check on all your volume meshes. Gambit should report to you which volume meshes have the problem (e.g negative vol etc)
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Old   March 14, 2003, 07:03
Default Re: 3D-mesh Gambit.....
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Dear Mr. SHR

By this time, I think you have resolved your problem.

I would like to share with exprience with non-positive volume message exist. I did exprience a similar case with you.

Here are what I did to fix the problem.

1. The non-positive message will appear in the Fluent

not in Gambit when you deal with virtual volumes. 2. I did some experiments in gambit and read the

mesh to Fluent 3. I deleted suspected volumes, especially virtual

volumes and read the mesh into the Fluent 4. At the end I found what the problem. The problem

was the existence of two volumes, which should be

only one volume. This volume was the virtual

volume. I deleted this volume and recreated

a single volume. 5. I my self do not understand, what is the

physical meaning of non-positive volume.

You must take a good care if you work with virtual volumes. Here is the tip, if you find something that make you frustrated, do the remedy by omitting the suspected volumes, and read the new mesh to the FLUENT, at the end, you will find the cause of the problem and you can fix the problem too.

Regard Yazid Bindar

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Old   March 17, 2003, 08:06
Default Re: 3D-mesh Gambit.....
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HI all,

Thanx Michelle, ccc, Chris, & Yazid!! for your replies.

I did check the grid(mesh) in Gambit, as U have suggested, but I did not get any clue/warning in Gambit regarding Negative Volume.

Still I am trying to fix the problem.

Regarding Mesh Check in Gambit, I do not know whether I could check it properly, as I doubt now, as to what is the RIGHT PROCESS OF CHECKING THE MESH in GAMBIT.

Please let me know the same in detail so that I can fix this problem.

Dear Yazid, my geometry does not include any Virtual Volume.

Waiting for HELP..

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