By adding a Damping subnode to a Contact Model node, you can include viscous damping forces in the contact pressure definition for transient study steps. Including damping can, for example, be useful to stabilize the contact pressure and state for impact problems.

Select the Damping type — Additive or Viscous only.

When Additive is selected, a damping contribution is added to the elastic contact pressure defined by the parent Contact Model node.

Select Viscous only option to use a purely viscous contact pressure model. For both damping types, damping is non-zero only for negative gap velocities (that is, when the overclosure is increasing).

The viscous penalty factor pnv is always defined proportional to the penalty stiffness factor pn. Set Specify to Characteristic time to enter value for τ such that pnv = τ pn. Alternatively, specify a Damping ratio ξ. In this case, the viscous penalty factor is defined by

where ρ is the density of the adjacent domain material, and h is a characteristic size of the mesh element.

Select Offset damping force to shift the activation of damping. When Offset damping force is cleared, the damping force is added when the gap is zero. When selected, enter a value for the Damping tolerance Δdmp. A positive value means that the viscous force starts to act while there is still some gap.

Physics tab with Contact Model selected in the Model Builder tree: