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Old   May 18, 2009, 10:35
Default Gambit: Volume Meshing
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Hi Everyone,

I was trying to mesh the flow volume around a small marine vehicle which I'm working on. I followed the steps in the "GAMBIT: Sailboat Tutorial". But when I try to go ahead with tetrahedral volume meshing, it gives me the following error:

"Initialization failed, perturb boundary nodes and try again.
ERROR: TG_Mesh_Domain failed with error code 1
ERROR: Tetrahedral meshing has failed for volume volume.1
This is usually cause by problems in the face meshes
Check the skewness of the face meshes and check that the face mesh sizes are not too large in the areas of small gaps."

Can anyone please tell me that how do I go about correcting this?

Thank you.
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Old   May 18, 2009, 11:55
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Hi!

the answer is given in the error message:

"Check the skewness of the face meshes and check that the face mesh sizes are not too large in the areas of small gaps."

You can check the skewness using the examine mesh button (right lower corner, looks like a mesh and a magnification glass). Select 3D elements and select all possible elements.

Then go to "range" and gambit will show you all mesh elements, coloured by there skewness. Blue is low skewness (= high quality) and red is high skewness (low quality).

Now, limit the range of the displayed elements to the one with the worst quality (above 0.7 or 0.8)
In the region(s) with the worst elements, you have to refine your mesh...

Best wishes
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Old   May 20, 2009, 03:23
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Dear Ralf,

Thank a lot. I tried refining the mesh but must be going in the wrong direction as far as that is concerned, because the one inverted cell refuses to go away.

Please have a look at this picture. It shows where the skewed cells are. Here, surface 1 meets surface 2 almost perpendicularly. Surface 1 is a sweep surface and surface 2 is a cylindrical surface. What should I do to refine the mesh at this junction?

http://picasaweb.google.com/lh/photo...eat=directlink

Thanks a lot for the reply.
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Old   May 20, 2009, 05:09
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the problem seems to be on the radius which lies on the surface 2 (tangent)
It produces very small angle (skewness 's source)
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Old   May 20, 2009, 05:21
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Hi!

it is always hard to join two meshes together.
the sweep mesh option is inflexible, so the mesh on your source face will be the same as the mesh on the end face.

So the attached face must fit to the mesh that is generated with the sweep mesh option....

High quality meshing of(more or less) complex geometries is a major task in CFD. It is not so easy to answer all question to this topic in this form...

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