Numerical damping is associated with the time-stepping schemes used for integrating second-order systems of equations over time. Mechanical APDL provides the Newmark method and the HHT method for transient dynamic analysis of structural systems. Numerical damping for these schemes is determined by the parameter values specified via the TINTP command.

Numerical damping stabilizes the numerical integration scheme by damping out the unwanted high frequency modes. For the Newmark method, numerical damping also affects the lower modes and reduces the accuracy of integration scheme from second order to first order. For the HHT method, numerical damping affects only the higher modes and always maintains second-order accuracy.

Mechanical APDL uses a default value (TINTP,GAMMA) of 0.005. The value that you select should be based on the problem at hand. A sensible value to try initially is 0.1. Use the lowest possible value that damps out nonphysical response without significantly affecting the final solution. Problems involving rigid body translational motion, other forms of damping, or dissipative mechanisms like plasticity or friction typically require smaller values for numerical damping. Larger numerical damping values are usually necessary for problems involving rigid body rotational motion, elastic collisions (dynamic contact/impact), and large deformations with frequent changes in substep size.

Structural damping refers to physical damping present in the system. You can specify the damping at the material level via viscous material models or dashpots (for example, COMBIN14 elements). At the structural level, you can specify it as modal damping or Rayleigh damping. For more information, see Damping in the Structural Analysis Guide. Structural damping is not applicable to joint elements.