NodalNormals System

The NodalNormals system is used to define the outward-facing normal of a boundary at a node. The system is mostly used through the AddNodalNormalsAction.

The nodal normals are stored in auxiliary Lagrange variables named nodal_normal_x/y/z. They may be of first or second order to accommodate both mesh orders.

The nodal normals on boundaries are computed in two steps: - first a NodalNormalsPreprocessor populates the nodal_normal_x/y/z variables with the local quadrature weight times the gradient of the shape function - then a NodalNormalsEvaluator normalizes each component so that the nodal normal has a norm of 1

On corners, the first step is replaced by obtaining the normal from the Assembly.