For problems that use the mesh superposition technique (MST) described in Flows with Internal Moving Parts, it is important to have a good mesh near the border of the moving parts. A nonzero gradient of the “inside" field (described in Adaptive Meshing Parameters for Moving Parts) indicates this area. If the gradient inside a given element is above the specified threshold, it needs to be refined. If the gradient is close to zero, the element can be "unrefined" (coarsened), if necessary.

The problems involving large variations of fields is based on fields and domains that you prescribe. The domains and the fields available depend on type of simulation involved. Elements where the variation of the selected fields is too high, are refined.

For problems involving transport of species, the criterion is similar to that described above for the MST, and is based on the gradient of the concentration field.

For blow molding of thick parisons, elements may become distorted or stretched over time. Poor-quality elements are detected and replaced by elements of better quality.

For blow molding and thermoforming simulations in general, it can be important to modify the size of elements in the flow domain based on the shape of the mold in front of them; larger elements can be tolerated in areas that are in contact with the flat areas of the mold, while smaller elements are needed in areas where the mold is curved. Alternatively, it may be necessary to refine the regions of the fluid mesh that are close to any part of the mold; such is the case when modeling the boundary layer of a heat transfer problem, for example.

Note that it is important to anticipate the contact, in order to have smaller elements before contact (after contact, the elements no longer move so it is not necessary to refine them).