Slip
Use the Slip node to prescribe zero normal velocity, and therefore also zero tangential stress, condition on the boundary. Add this node from the Mechanical submenu. 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 Slip condition with a rational scaling in the PML, as this will lead to a singularity and an error.
Per default, the Slip condition uses a so-called discontinuous Galerkin or penalty formulation to prevent locking problems on curved surfaces.
Constraint Settings
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.
Select Use weak constraints if you want to switch from the default discontinuous Galerkin (penalty like) formulation to a Lagrange multiplier formulation for the 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 Show More Options button () and select Advanced Physics Options in the Show More Options dialog box. See Suppressing Constraints on Lower Dimensions for details.