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Section 3.14: Constraints Section Up Section 3.14: Constraints Section Subsection 3.14.2: Normal Fluid Velocity Constraint

### 3.14.1 Symmetry Plane

A symmetry plane enforces zero solid displacement normal to a user-selected plane. This constraint is prescribed on a deformable surface of the model and is enforced for every node on that surface. It is the user's responsibility to select only planar surfaces.
<constraint type="symmetry plane" surface="SymmetryPlane01">
<laugon>1</laugon>
<penalty>1e6</penalty>
<tol>1e-6</tol>
<minaug>0</minaug>
<maxaug>50</maxaug>
</constraint>

The surface (SymmetryPlane01 in this example), is defined in the Mesh section. Let denote the nodal displacement vector and let denote the unit normal to the plane; the symmetry plane constraint enforces using a penalty method, optionally with augmented Lagrangian. The reaction force needed to enforce this constraint is evaluated as , where is the user-specified penalty parameter (with units of force per length). To use the augmented Lagrangian method, set laugon to 1, and the Lagrange multiplier will be augmented as . Augmentations terminate when the relative change in is less than the user-specified tolerance tol, or when the number of augmentations exceeds maxaug.
Section 3.14: Constraints Section Up Section 3.14: Constraints Section Subsection 3.14.2: Normal Fluid Velocity Constraint