Error 15 - CTETRA element ### is distorted (zero or negative Jacobian) and node collapse
Hi everyone (especially @Adriano Koga @Q.Nguyen-Dai @tinh )
I've got a fairly large 3D mesh of approximately 6-8 million tetra elements (depending on how I mesh) stemming from a geometrically complex, closed 2D mesh of the model done in another software. When I run the mesh with Optistruct with linear tetra elements, there is absolutely no issue whatsoever in terms of mesh quality. However, as soon as it is converted to or meshed directly with second order tetras, I cannot get rid of the above error 15 - element ### is distorted (zero or negative Jacobian). I tried several ways to remedy this, even by just deleting the elements in question to see if I can progress to a working run (which was not successful yet) as another error - node collapse - pops up. Interestingly, the failing elements during a checking run are not detected when performing a 3D element check, even when checking for Jacobian < 0. How come? For now, I manually pick the failing elements from the error list in the .out file. How can they be detected inside of Hypermesh? I'm trying different options inside the Solid Mesh Optimization utility right now, which I didn't know before, to see what will happen. So to summarize:
1. Why do element quality issues arise when changing from first order tetra do second order tetra with their midnode being half way between corner nodes?
2. How to determine collapsed nodes and/or negative Jacobian values in Hypermesh when the 3D element check will not return any errors?
3. What's the best practice to fix these elements, when their total number is too large to attack manually? Apart from remeshing the whole body, as it does not seem to remedy the problem.
4. If everything else fails, is there a possibility to enforce a run even with failing elements?