Elmer Discussion Forum

Hello

I am trying to model a drift of electrons in a gas chamber using StatElecSolve. The geometry is a box with a cilindrical hole. The top and bottom of the box have different voltages. I have a correct mesh, but the sif file have something wrong. The error is:

ERROR:: ElementMetric: Degenerate 3D element: 4650

ElementMetric: DetG:-0.124E-31 Coord: 0.164E-01-0.125E-01 0.102E-01


Could anybody please give me some guidance?!
Thanks so much for any advice.

Gabicerq

Hi,

could you post your sif file and mesh so that someone can have a look on it?

Matthias

Hi

Your mesh may be corrupt. Typically this could mean that some element has degenerate nodes (nodes at same location).

-Peter

Hi Matthias and Peter,

I'm working with gmsh. My .geo file is a bit long. If my mesh file is corrupt, how can i know the degenerated elements?

The files are attached.

Thanks for help!

Gabi

Hi,

don't ask me why, but processing your mesh with the autoclean option of elmergrid seems to solve the problem. At least your case runs for me, whereas I got a solver crash before.

HTH,

Matthias

Hi,

now I have the error message:
I have checked the coordinates of the tetrahedron and they seem OK to me.
Questions:
1. What can I do to find out what is wrong here?
2. How can I avoid it?
3. How can I check the mesh before starting the solver?
4. If the solver processes all timesteps nevertheless, can I trust the results?

Answers & suggestions welcome!

Thank you,

Matthias

P.S.: I have been lucky: I have produced a slightly changed mesh (a little bit more coarse) AND processed it with ElmerGrid -autoclean on the command line. The problem seems to be gone (now I have convergence problems, but that is another story...). But for the mesh I had before, Elmergrid -autoclean did not help. So the problem having been solved by chance, the above questions remain...

Hi,

I reactivate this thread because I have the "Degenerate 3D Elements" error message again.
The questions in the last post remain, and some answers would still be appreciated.
Especially it would be useful to know if there are some tolerances or accuracy limits in Elmer which should not be violated in order to avoid this kind of error.

Thank you,

Matthias


Note: The solver went on with its calculation and eventually converged, but the result looks a bit strange. This answers question 4 above...

Hi Matthias

Do you have a small case on this.

Generally it would suggest that there is an element where two nodes are at the same coordinates, or too close to form any proper element. This could be a property of the initial mesh, or if there are deformations it could results later. I would think that it is not a problem of transferring the mesh, as it most of the time happens ok...

-Peter

Hi Peter,

my mesh file is ~5.5 MB, so too large to post it here. Attempts to make it smaller by changing the geometry make the error go away. I will make a new mesh for my initial geometry tomorrow. If the error persists and I still don't manage to reproduce it with a smaller mesh file, I might zip the big mesh file (result ~ 2 MB) and send it to you by e-mail.

Matthias

Hi Peter,

I have redefined my mesh, and the problem went away. I have kept the old mesh for the records - do you want me to send it to you for debugging purposes?
The strange result I got when the solver converged in spite of the degenerate elements was most probably due to a erroneous hest source setting from my side, so not necessarily due to the degenerate elements.

Matthias