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# Surface mesh at a point generating degenerate elements

Genius

This geometry (attached) is somehow leading to mesh corruption at the corner highlighted with a pink element (which looks like a tri but is a quad). I cannot solve this. I have tried partitioning, splitting the edge, remeshing etc. without any luck. Exactly the same geometry in another area of the model behaves ok.

I'm still on FEMAP 11.2.0 but we will be updating next week hopefully.

Thanks,

Kava

4 REPLIES

# Re: Surface mesh at a point generating degenerate elements

Genius

I've solved this by deleting the faces and copying adjacent faces into position (then adding them to the body), but perhaps it is still valuable as a geometry test case for the mesher.

# Re: Surface mesh at a point generating degenerate elements

Siemens Phenom

Your problem was that you had a very short curve in the corner of that surface

Curve 60019  Length=0.0000554349

When meshing, FEMAP tries to honor the geometry that you give it. Your quad was not degenerate... it just had one very short edge along that curve.  There are a number of ways to solve this problem. You could simply combine curves along that edge or just suppress that curve using Mesh->Mesh Control->Feature Suppression. Probably the easiest and best way though is to simply use Mesh->Geometry Preparation. It will find this type of problem and more and attempt to fix them automatically. In this case, after doing that you get a totally mapped mesh on this surface.

# Re: Surface mesh at a point generating degenerate elements

Phenom

As a general guide, I suggest using the Meshing Toolbox -> Toggle Entity Locator icon to search for Short Edges (based on Curve Length say, 1/20th  of nominal mesh size).  This is best done before meshing, to avoid the problems, but is also possible to do the same check (among other quality checks) with elements.

It can also be worthwhile to check for small surfaces as well, to see if there are slivers or blips that should be Combined Surfaced with something else.

These sorts of geometry problems are fairly common, particularly if doing midsurfacing of imported thin solids from CAD.  For good or bad (good in my view, because it is always possible to find and address causes), Femap is very, very precise and will only "ignore" stuff if explicitly told to do so.  You may note that if you use Mesh -> Mesh Control -> Size on Surface or Size on Solid, there is an option to Suppress Short Edges.  It would probably be useful if this option also found its way to the Mesh Surface section of the Meshing Toolbox.  Note that this does not cure all geometry detail problems, but would have fixed yours.

# Re: Surface mesh at a point generating degenerate elements

Genius

This is interesting. I had used Solid/Solid Clean initially on the geometry (with default settings). I guess the small edge was not caught at that point. Should it have been?