7.4. Step 1: Determine the Substep to Initiate Rezoning

If the solution terminated because of a mesh distortion, it is a candidate for rezoning.

It is important to select a suitable substep at which to start rezoning. You must select a converged substep where the restart files are available.

The last converged substep is often a natural choice for initiating rezoning because there is typically less of a remaining load to apply. However, the last converged substep may have more severely distorted elements which can cause larger errors when mapping solution variables (MAPSOLVE), in turn requiring more mapping substeps to balance residual forces or convergence failures. Rezoning from a substep with an extremely distorted mesh may also reduce the accuracy of the final solution, and can even cause the automatic transfer of boundary conditions after remeshing (REMESH,FINISH) to fail.

Typically, the best choice is the first, second, or third converged substep preceding the last converged substep. To determine the best possible substep to initiate rezoning, you may need to enter the POST1 general postprocessor (/POST1) to examine the deformed element shapes, and stress and strain distributions.

If no results data exists for a substep in the results file, you can use program restart features to generate results data for the substep, and then enter POST1 to examine the deformed shape; afterwards, you can reenter the solution processor and initiate rezoning as usual.

Hints for selecting the best substep to initiate rezoning:

The substep should have an obvious mesh distortion but should contain no element having an internal angle too closely approaching, equal to, or exceeding 180 degrees.
The substep should have minimal penetration in contact. Try to avoid substeps where contact status has changed suddenly from previous substeps.
If an error occurs when the program transfers boundary conditions and loads after remeshing (REMESH,FINISH) and the old mesh is severely distorted, try the substep preceding the one most recently chosen.
The best substep is often not the last converged substep, but rather one of the several preceding the last one.
If the last few converged substeps are separated by very small time increments and you have already tried one or more of those substeps unsuccessfully, select a converged substep that is separated from the others by a larger time increment.
If you are still having difficulty obtaining a mesh of reasonable quality because the old mesh is too distorted, try the substep preceding the one most recently chosen.
If the mapping operation (MAPSOLVE) fails to converge even if you allow up to 500 substeps, try the substep preceding the one most recently chosen.

When you have determined the substep at which to initiate rezoning, proceed to Step 2. Initiate Rezoning.