The Boundary Stress node adds a boundary condition that represents a general class of conditions also known as traction boundary conditions.

The Boundary condition options for the boundary stress are General stress, Normal stress, and Normal stress, normal flow.

When General stress is selected, the components for the Stress F should be specified. The total stress on the boundary is set equal to the given stress F:

If ∂un/∂n is small, Equation 13-28 states that p ≈ −n·F.

Normal Stress is described for the Open Boundary node.

For Normal stress, normal flow, the magnitude of the Normal stress f0 should be specified. The tangential velocity is set to zero on the boundary:

If ∂un/∂n is small, Equation 13-29 states that p ≈ f0.

When Include gravity is selected and Use reduced pressure not selected in the interface Physical model section, the Compensate for hydrostatic pressure approximation (named Compensate for hydrostatic pressure for incompressible flows) check box is available and selected by default. When it is selected, the hydrostatic pressure is automatically added to the pressure entered in f0 or phydron is added to F depending of the selected option.

This section is displayed by clicking the Show button () and selecting Advanced Physics Options.

If Normal Stress, Normal Flow is selected as the Boundary condition, then to Apply reaction terms on all dependent variables, the All physics (symmetric) option should be selected. Alternatively, the Individual dependent variables could be selected to restrict the reaction terms as needed.