Slip Velocity
The Slip Velocity node facilitates a simplified form of slip friction modeling, which can be used in the case that the direction and speed of the sliding is known. In this case, there is no need to solve for the friction forces and slip orientation.
The selection in the Slip Velocity node is the same as that of its parent Contact node. There can only be one Slip Velocity node under a specific Contact node.
The Slip Velocity and Friction nodes are mutually exclusive.
The Slip Velocity node is only available with some COMSOL products (see https://www.comsol.com/products/specifications/).
Coordinate System Selection
The slip velocity is defined as acting in the tangent plane of the destination boundary, and is given along the directions of a boundary system.
Only boundary systems can be selected. Make sure that the tangents of the selected boundary system are well defined on all destination boundaries.
Friction Parameters
Select a Friction modelCoulomb, Exponential dynamic Coulomb, or User defined. Since the velocity is prescribed, a velocity dependent friction model can be used also in a stationary analysis.
For Coulomb friction, enter the Friction coefficient μ.
For Exponential dynamic Coulomb friction, enter a Static friction coefficient μstat, a Dynamic friction coefficient μdyn and a Friction decay coefficient αdcf.
The effective friction coefficient is
where vslip is the slip velocity.
For both Coulomb type models, you can modify the rules for sliding by providing minimum and maximum shear tractions.
Enter a Cohesion sliding resistance Tcohe to provide an offset to the tangential traction.
Independently, you can enter a Maximum tangential traction Tt,max. This is the maximum tangential traction, independent of the contact pressure. The default expression is Inf, indicating that no limit on the tangential traction is active.
The magnitude of the tangential friction traction, Tt,crit, can be written as
Here, Tn is the contact pressure.
When Friction model is set to User defined, enter an expression to define Tt,crit. This expression can depend on any quantity. However, the implementation of the friction model is only correct if Tt,crit does not depend implicitly on the current friction force.
Prescribed Velocity
Enter the relative velocity between the destination and source boundaries, vslip. The velocity is expressed in the coordinate system provided in the Coordinate System Selection section, interpreted on the destination boundary.
Advanced
To display this section, click the Show More Options button () and select Advanced Physics Options in the Show More Options dialog box.
For numerical reasons, the gap value will not be exactly zero even when the boundaries are in contact. A certain small positive value of the gap must thus be used to determine that the boundaries touch each other, so that friction forces can be introduced. Select a Friction detectionAutomatic or Manual. For Manual, enter an absolute value for the Friction detection tolerance Δfriction, which is the gap when the friction becomes active.
Select Compute frictional dissipation to compute and store to the energy dissipated by friction. This adds one extra set of state variables to be stored. The integration is explicit, and adds only marginally to the computational cost.
You can also request that the total accumulated slip distance it stored by selecting the Store accumulated slip check box.
Including Friction, and The Slip Velocity Node in the Structural Mechanics Modeling chapter.
Tangential Contact with Friction in the Structural Mechanics Theory chapter.
Location in User Interface
Context Menus
Ribbon
Physics tab with Contact selected in the Model Builder tree: