For most constraints in the structural mechanics interfaces, you have the possibility to select that certain objects of lower dimensions should be excluded from the main selection. To do this, you must first select Advanced Physics Options. In the settings for a constraint, like for example Prescribed Displacement, new sections named Excluded Surfaces, Excluded Edges, and Excluded Points will then appear. In these sections, you can select geometrical objects which should be excluded from the main selection when the constraint is applied.

In the structural mechanics interfaces, there are many types of complex constraints, and sometimes you may get conflicts or duplicates which makes the model either overconstrained, or problematic for the automatic constraint elimination algorithm. If you are aware of such situations, it is good practice to remove one of the potentially conflicting constraints. One example of such a situation is when you have a Solid-Shell Connection meeting a symmetry plane, as shown in Figure 2-8.

Here you would add a Symmetry condition on a boundary in the Solid Mechanics interface, as well as a Symmetry condition on an edge in the Shell interface. But at the same time, the displacements on whole boundary where the solid meets the shell are controlled by shell degrees of freedom as an effect of the Solid-Shell Connection. As a result, on the edge marked with Conflict in the sketch, the displacements will be controlled both by the symmetry condition is Solid Mechanics, and implicitly through the coupling, by the symmetry condition in the Shell interface. Particularly if the geometry is curved, there is a risk that these constraints are not identical from a numerical point of view. In this case, excluding the conflicting edge from the selected boundary in the Solid Mechanics interface will make the behavior unique and fully predictable.