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-   -   [ICEM] Merge mesh - non manifold vertices (http://www.cfd-online.com/Forums/ansys-meshing/79435-merge-mesh-non-manifold-vertices.html)

BrolY August 24, 2010 04:12

Merge mesh - non manifold vertices
 
Hi,

In order to mesh a part, I made a tetra mesh for the solid part and an unstructured (Hexa with blocking) mesh for the fluid part.
I want to merge the two meshes by using the command "Merge Nodes - Merge Tolerance". It worked fine.
Then I deleted the fluid interface between the two meshes. I ran the "Check Mesh" option and some errors poped up : it created non-manifold vertices all around curves of the fluid interface.

1) Do you know how to deal with it? I tried to reduce the tolerance, but I don't know how it would influence the results.
2) Are the non-manifold vertices an error or just a problem which could be ignored?
3) Is it the good way to proceed in order to merge two meshes?

Thanks,

PSYMN August 25, 2010 15:16

A manifold node means that a node is surrounded by a ring of surface nodes.

Non-Manifold means that a node is surrounded by 2 or more rings of nodes.

I don't know what your particular problem is, but when the diagnostic found the non-manifold verts (it doesn't create them ;)) it should have created a subset for you, add a layer or two to improve understanding and look at it.

It could be that you have a thin section between surfaces and it has pinched in. The node has a ring of nodes on Surface A and a ring of nodes on surface B. If this is not what you intended, then it alerts you to the problem so you can fix it.

However, this won't hurt the solver and may be fine, if it is what you intended.

Best regards,

Simon

qiulan October 27, 2010 01:00

Dear Simon,
I have encoutered the same problem. could you tell me how to fix the non-manifold vertices? Thank you very much!

Qiulan

PSYMN October 27, 2010 13:59

Fix non manifold
 
The best way to fix them depends on the situation. (an image would help).

Often the best way is with better mesh parameters such as a smaller size or turning on the the thin cuts option so they don't form.

If you just have a few, you can manually repair them with the mesh editing tools. There is a split node command that will fix them, but I usually find it more straight forward to delete the volume mesh, delete and repair the surface mesh, and then regenerate the volume mesh...

Best regards,

Simon

qiulan October 30, 2010 22:07

3 Attachment(s)
Dear Simon,
Thank you very much! I am so appriciate to you for your help.
Here I put the pictures in the attachments. My mission is to simulate the situation of the flow field aroud a moving car with a wind of 35 m/s velocity through a windwall. You can see that in the picture3.png. There are two boxes in the picture.Because the wall has lots of small holes, each only 75 mm,I want to use hybrid grid in a case far-field using hexa grid while the field around the car and wall using tetra grid.In the smaller box, I use tetra grid and hexa gird in the space between the small box and big box.Here the wind blow from the left side, that is from the direction -z.And the car is moving forward,that is toward the direction x. The trouble I have encountered is that when I try to merge the nodes on the interface between the two zones, an error has occoured,saying 'I am trying to include edge XXX,but vertex isn't even in the region1' 'unable to include quade xxx'.I don't know how to deal with it. Sometimes,even if the merge is successful, when I check the grid, errors occour,saying 'problem were found for nonmanifold vertices '.Then I choose to fix the nonmanifold vertices, it says xxx nodes could not be fixed. Picture 2 and picture 1 show the problem.The white part is the nonmanifold vertices.I desperately wonder if there is a bug in the software. Because I did succeed in the first time, but failed from then on. I don't know why. By the way, my operation system is WIN7 64bit. Is it possible that the software has some bugs? If not, how can I solve the problem?
Thank you very much!!
Qiulan


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