Slip (Perfect)

Use the node to prescribe zero normal velocity, and therefore also zero tangential stress, condition on the boundary. Add this node from the submenu. This represents the ideal or perfect slip case, as opposed to non-ideal condition that can be modeled with the Slip Wall feature. The condition reads

This results in a so-called no-penetration condition where no viscous boundary layer is created. Use the condition in places where the viscous losses in the boundary layer are unimportant. Here it is not necessary to mesh the boundary layer, resulting in fewer mesh elements.

When running a model with a perfectly matched layer (PML), it is recommended to not combine a condition with a rational scaling in the PML, as this will lead to a singularity and an error.

Per default, the condition uses a Nitsche formulation (also often referred to as discontinuous Galerkin or penalty formulation) to prevent locking problems on curved surfaces.

Constraint Settings

To display this section, click the button (

) and select in the dialog box.

Select as the if you want to switch from the default Nitsche formulation () to a Lagrange multiplier formulation for the perfect slip condition (this formulation is not suited for an iterative solver). The Lagrange multiplier formulation also prevents locking problems.

Excluded Edges/Points

To display this section, click the button (

) and select in the dialog box. See Suppressing Constraints on Lower Dimensions for details.