Debugging failed mesh

protontim

I had a relatively simple part that refuses to mesh. Sometimes with a very small change in geometry it will mesh. I have attached the part showing a geometry that will not mesh. I seem to be flying blind when it comes to where and how the mesh fails. Is there a good way to troubleshoot the mesh failure? Is there a better meshing tool on the market? I seem to spend most of my time fighting meshgen... Mecway works great. Meshgen not so much.

Thanks

protontim

In looking at things closer, it appears that the STEP file has some faces that should be edges instead of faces. Not sure why my CAD program is generating those faces. I think they are most likely the problem. Is there a way to edit the faces so that the meshing program is happy?

protontim

Here is the model cleaned up a bit. Still doesn't mesh. Looking for a way to isolate cause of failure

Victor

Suggestions:

1) Look for weird parts on the geometry preview. Your 2nd file here seems to have two surfaces overlapping which you can sometimes see from the random dots shown in the attachment. These usually indicate one surface showing through another because they're at almost the same location.

2) Do a surface mesh then look for gaps/overlapping surfaces/etc. Two tools to help with this are View->Open cracks and Labs->Find non-manifold shells. The latter selects shell element edges that have the wrong number of adjacent elements (ie. anything other than 1).

3) Set a suitable maximum element size. Sometimes the default of no maximum causes failure. That doesn't seem to help in this case though.

4) If surface meshing fails, as it does here, export the same geometry from your CAD program as an STL file, then open it in Mecway and do the same checks described in step 2. I tried this using FreeCAD to convert STEP to STL. The 2nd file shows some non-manifold edges while the 1st file shows this edge/face problem you identified with some triangles flattened into lines. It might be these two different problems with each file.

5) Download the Netgen application from Sourceforge. Others have had some success with the geometry healing tool in that, or just having it work when the one in Mecway doesn't.

Sergio

Normally what makes you fails the meshing algorithm is a very small surface or other small error on the model. In order to isolate what I do is in the CAD program is divide the volume in two sub-volumes, with any tool that your cad could have. Then import this two volumes in the mesher program (Mecway or Netgen), normally one part would be able to mesh and the other don't. What this means? Well, that the geometrical small glitch is in the not meshed volume. Then I came back to the cad and check the geometry to find this error. If the half geometry still is too complex to find directly the error, them I repeat the process, division by half, import and mesh to find where the error is.

For having meshables parts is fundamental to have a well modeled part, avoid direct editions or automatic sew operations, this last will force and deform in weird shapes the edges of the surfaces to create a solid part, and there is were the mesher will fail or create very tinny elements. If you are the designer of the part is easy to keep the model clear and remove the small radius and features, the problem become when you receive a complex finished part without history tree, removing small radius can be challenging or impossible at all.

Victor

That's an excellent and very general technique Sergio. Also useful for models that won't solve.

protontim

Vic and Sergio, your input is very helpful. I have Netgen 5 installed on my machine and I will see if some of the healing works. If not I think I can cut the model into two pieces that do not include the very tiny edge surface. I can then mesh them and bond them back together. The surface is so small I think the model should still be accurate enough with that portion missing. Thanks again for your help.

protontim

I cut the part in two with the cut line just 0.000001 inches from the problem area. There was no gap between the parts. Interestingly both parts meshed and then I bonded them back together. I can only guess at why this might have worked (problem area was at part edge not in center?) but the good news is that it work. Thanks again for the tips on how to better trouble shoot.