MMG3D Lagrangian motion: cannot maintain body shape

#21

Hello Saleh,
Would you mind to share mesh, displacement and the exact command you are using?
I didn’t get if you are trying to further deform the output of a first run, or you are just running the very same command on the very same initial mesh (I have just checked and it still works on my computer).

Regards,
Luca

#22

Hi Luca,

Yes, I am trying to further deform the output of the first run.

Regards,

#23

Hello Saleh,
I am testing by imposing the same displacement on the output of the first deformation, and I can reproduce your problem. It seems to be an issue with the internal adaptation just after the movement that I haven’t fully identified yet.

Anyway, everything goes smooth if you use -lag 1 (only swap allowed to perform displacement).
While I try to correct the issue, a more robust solution to improve the mesh quality after the displacement could be that of running mmg3d in adaptation mode on the output (in a separate call) with the -optim option on.

Best regards,
Luca

1 Like
#24

The brief version:- Nosurf does not entirely protect surfaces during lag 2 motion, as mesh quality can cause edge splitting/flipping. fixes:

  1. Use latest MMG (pre-5.5 ignores nosurf for some)
  2. Use local Hausdorff parameters to check edge sizes and element quality.
  3. Lag 1 is safer; lag 2 requires caution.
  4. Disable Scotch during compiling.
  5. Programmatically set MMG3D_IPARAM_nosurf = 0 after displacement.

Version + mesh control + parameter enforcement preserves rotor surface.