Constraint Settings
Most constraint nodes include a Constraint Settings section, which is only available when Advanced Physics Options is selected in the Show More Options dialog box. This section provides settings controlling how reaction terms are applied, when applicable, and whether to use pointwise standard constraints or weak constraints. Choose to Apply reaction terms on:
•
All physics (symmetric) to apply reaction terms symmetrically on all dependent variables taking part in the constraint.
•
Current physics (internally symmetric) to apply reaction terms symmetrically only on the dependent variables in the physics where the constraint is added. This leaves other physics unaffected by the constraint.
•
Individual dependent variables to apply reaction terms only on selected variables. For most physics, this makes the constraint unidirectional and often nonsymmetric.
Select the Use weak constraints check box to replace the pointwise standard constraints with weak constraints (see Weak Constraints below). Note that this option introduces additional equations and dependent variables. If you use pointwise constraints (the default; the Use weak constraints check box is cleared), then select a Constraint method for the pointwise constraints: Elemental or Nodal:
•
Choose Elemental (the default) to make the software assemble the constraint on each node in each element; that is, there are usually several constraints at the same global coordinates because elements in the computational mesh overlap at nodes.
•
Choose Nodal to make the software assemble a single constraint for each global node point. The nodal constraint method provides an averaging of the constraints from adjacent elements, which can be beneficial when the constraint has discontinuities between mesh elements (for example, due to discontinuities of the boundary normal). Another case where nodal constraints can be useful is in boundary conditions involving a coupling operator (such as continuity or periodic conditions). With elemental constraints, locking effects can sometimes occur because the coupling operator might map to slightly different points in the source boundary when it is applied to the same node point in different mesh elements.
Not all constraints provide all the above options. Some reaction term methods can be missing and weak constraints are not allowed. Some constraint nodes can also implement additional options.