COMSOL 6.4 - Implicit Dynamic Contact Analysis

The contact formulations in COMSOL Multiphysics can be used in transient as well as quasistatic analyses. In truly dynamic problems, where inertial effects are significant, a contact formulation must conserve fundamental quantities, such as linear and angular momentum and energy, across the contact pair. An important class of dynamic problems, where these quantities must be conserved, is impact analysis.

To model dynamic contact events, two specialized contact methods are provided, the and the methods. Both are based on a viscous formulation that constrains the gap rate to be zero, ensuring that the normal contact is dissipative and does not introduce any spurious energy contribution to the system. Since the methods are dissipative, they are mainly intended for short duration events, such as soft impact between two bodies. For prolonged interaction between two bodies, energy dissipation can become significant, and overclosures can become large, since the gap rate is only approximately zero. Both the dissipation and the accuracy are controlled by a penalty factor that for these two methods conceptually represents a dashpot, rather than a spring. It therefore has a characteristic time user input that sets its magnitude. As a rule-of-thumb, it should be of the order of the contact event duration, but the best choice must be decided on a case-by-case basis.

The method also provides the possibility to combine the stiffness and viscous based penalization of the normal contact. For impact analysis, it is often best to use only the viscous formulation by setting the stiffness to .

When modeling dynamic contact, the primary focus is usually on the kinematics between the contacting bodies. If you use the default adaptive time-stepping algorithm, the solver will also attempt to resolve wave propagation in the domains adjacent to the contact pairs. This often leads to unnecessarily small time steps, significantly increasing computation time.

To avoid this, you can switch to a manual time-stepping algorithm in the settings. Choose time steps that are small enough to accurately capture the contact event, since too large steps can introduce spurious energy contributions and cause the simulation to become unstable or diverge.

Implicit time-dependent solvers in COMSOL Multiphysics introduce numerical damping to stabilize time stepping. While this stabilization is often necessary, excessive numerical damping can remove important information from the simulation. For this reason, the BDF solver is not recommended for dynamic contact problems. Instead, when inertial terms are included, the preferred choice is the generalized-α solver.

Regardless of the solver method or settings used, it is good practice to perform an a posteriori check of momentum and energy conservation to ensure that the solution is acceptable.