2.6. Specifying Criteria-Checking Frequency

Specify the frequency at which criteria for each component are checked during solution (NLADAPTIVE,,ON).

VAL1 controls the checking frequency:

  • If VAL1 > 0, the program checks the nonlinear mesh adaptivity criteria every VAL1 substeps.

  • If VAL1 < 0, the program checks VAL1 number of times distributed evenly throughout the load step or defined time interval.

Default: VAL1 = -1.

For mesh-quality-based and contact-based criteria, it is generally a good practice to check the criteria at every two substeps. For a contact-based cohesive zone model in a nonlinear adaptivity framework, however, checking the criteria at every two substeps can lead to a large increase in the number of elements in a small number of substeps; a larger checking interval may therefore be necessary.

For other criteria, a negative value is suggested to avoid over-refinement, as each splitting enlarges the model four or eight times for 2D and 3D, respectively. Too many splittings, therefore, can greatly enlarge a model.

To modify the time range at which criteria-checking occurs, use the VAL2 and VAL3 arguments.

Criteria-checking does not guarantee that splitting and remeshing occurs in a given substep. A new mesh is generated only if any element meets the criteria assigned to it. When splitting and remeshing occurs, the new mesh is used in the subsequent substep.

Splitting or Remeshing Points

Because nonlinear adaptivity does not control the substep length (solution points), it cannot accurately control the number of splitting or remeshing points.

For frequency checking (NLADAPTIVE,,ON,,,-n,StartTime,EndTime), splitting or remeshing may not occur between StartTime and EndTime if no solution point falls between them. Fewer splits or remeshings may occur, even fewer than n, if the number of solution points is less than n.

Conversely, the program may split or remesh n + 1 times if the solution has one point close to StartTime and another close to EndTime. (More than n + 1 splits should not occur.) Splitting n + 1 times is more likely to occur when n is a small value.

When a new mesh is created due to nonlinear adaptivity, the following message (or similar) is issued in the output file:

**** REGENERATE MESH AT SUBSTEP     7 OF LOAD STEP      1 BECAUSE OF NONLINEAR ADAPTIVE CRITERIA
**** NEW MESH HAS BEEN CREATED SUCCESSFULLY. CONTINUE TO SOLVE.

Loads and boundary conditions are mapped from the old mesh to the new mesh automatically.