When nonlinear mesh adaptivity is applied to problems which do not converge because of mesh distortion, the mesh-quality-based criterion is necessary. The defined components for the criterion should include all elements that undergo large deformations. The component boundaries should be as smooth as possible, like the interfaces of various materials, element types and parts. The defined skewness should be >= 0.8, and the Jacobian ratio should be <=0.2 for higher-order elements. The defined maximum corner angle should range from 150 to 170 (although other values are allowed). The checking frequency should generally be set to every two substeps. If the applied loads or materials are very nonlinear, increase the checking frequency to every substep.

When using nonlinear mesh adaptivity to improve solution accuracy, the energy-based criteria is often the best selection for general simulations. If you are unsure which parts of the model are critical regions for mesh refinement, simply define an energy-based criterion for all solid elements in the model. A default value of 1.0 for the energy criterion should improve most problems.

If you know which regions are critical and require refinement, define the solid elements in those regions as components and create energy-based criteria for them, or use position-based criteria.

When nonlinear mesh adaptivity is applied to problems which would otherwise be unsolvable, but where the deformed mesh is not so distorted (for example, local deformations in buckling/bifurcation or rubber seal problems), combinations of criteria are often required. Use the contact-based criterion only when solid elements touch target elements and more elements/nodes are necessary to simulate details of contact boundaries and filling. Use the position-based criterion for refining elements moving into particular regions (for example, small cavities). Without a fine enough mesh and a sufficient number of degrees of freedom, the simulation may not accurately predict the behavior of material moving into such regions. To refine elements at specific intervals, use the energy-based criterion, specifying a very low value or 0 as the minimum energy for splitting or refinement.

In any case, do not attempt refinement by splitting on a very distorted mesh, as the resulting mesh quality may be worse than that of the original mesh. Morphing and/or topology correction can adjust for mesh distortion to only a very limited extent.

When using nonlinear mesh adaptivity to reduce the number of degrees of freedom of unnecessary fine meshed regions or regions with no critical features, the coarsening condition of the energy-based criteria can be applied for problems where the regions with no critical features develop or are unknown. Position-based criteria with coarsening enabled can be applied when elements are moving in regions where the fine resolution is no longer needed.