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SHR March 21, 2003 00:17

3-D Mesh Check in Gambit.....
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 got 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??

I did check the grid(mesh) in Gambit, 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.

My geometry does not include any Virtual Volume.

Waiting for HELP..

Thanx in advance...


Alex Munoz March 21, 2003 04:10

Re: 3-D Mesh Check in Gambit.....

The following information was copied from fluent web side in order to give you and accurate answer.

The most common error identified by the grid check is negative volumes in the grid. If the minimum volume is negative, you will need to repair the grid to remove this nonphysical discretization of the solution domain. You may be able to use the Iso-Value... marking ability in the Adapt pull-down menu to locate the problem by marking and displaying cells with volumes less than zero (see Section 25.6). For additional information on checking the grid, see Section 5.5.

A negative value for the minimum volume indicates that one or more cells have improper connectivity. Cells with a negative volume can often be identified using the Iso-Value Adaption capability to mark them for adaption and view them in the graphics window. For more information on creating and viewing isovalue adaption registers, see Section 25.6. You must eliminate these negative volumes before continuing the flow solution process.

I faced this problem one time. I meshed again the domain with a diferent decomposition scheme of the domain.

I sugguest that you try to adapt the actual mesh in fluent, if this does not work check all the edges of your domain in gambit, and decompose the domain in a diferent fashion that the actual one.

Best regards

Alex Munoz

SHR March 22, 2003 02:08

Re: 3-D Mesh Check in Gambit.....
Thanx a lot Alex!

In your reply you mentioned Section 5.5 & 25.6, where are these available? In our Fluent6.0 installation, the documentation is not working so not able to get help while working. If it is available on internet please give me the link.



Alex Munoz March 22, 2003 17:05

Re: 3-D Mesh Check in Gambit.....

You can get this information in fluent webside by clicking in technical support, and then login.

Best regards

Alex Munoz

Alamgir March 25, 2003 04:10

Re: 3-D Mesh Check in Gambit.....

If there any volume overlaps/dual with other it could be happened. So create the geometry again and see how many volume r there? there r joint or discreate? so move each of the volumes and see any unwanted volume that may be the cause of -volume. It was happened for my case once a time. bye/Alamgir

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