Boundary Stress

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

Boundary Condition

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

General Stress

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:

for the compressible and the incompressible formulations.

This boundary condition implicitly sets a constraint on the pressure that for 2D flows is

(13-24)

If ∂un/∂n is small, Equation 13-24 states that p ≈ −n·F.

Normal Stress

Normal Stress is described for the Open Boundary node.

Normal Stress, Normal Flow

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:

for the compressible and the incompressible formulations.

This boundary condition implicitly sets a constraint on the pressure that for 2D flows is

(13-25)

If ∂un/∂n is small, Equation 13-25 states that p ≈ f0.

Constraint Settings

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.