General data: Numerical damping

Line target damping

Finite element models may contain spurious high frequency response, a feature inherent in the finite element method. Line target damping is intended only to damp down this high frequency noise, without otherwise affecting the model. The value represents the % critical damping level that will be achieved for oscillations at the shortest natural period of each node. These oscillation periods are typically very short and depend on the segment length and stiffness values of the line section involved.

The % critical damping which results for longer oscillation periods is inversely proportional to the period, and for typical response periods (usually much longer than the shortest nodal natural periods) is usually insignificant. To achieve a significant level of damping at wave period would usually require a very high value of line target damping, and this in turn often requires short time steps and so lengthy simulations. If, therefore, you wish to model the effects of structural damping, we recommend that you use Rayleigh damping.

The target damping is specified independently for tension, bending and torsion. Within broad limits, this damping has little influence on the results of a simulation unless the system is subject to very rapid variations in tension or bending, for example when snatch loads occur. A value between 5% and 50% of target damping is usually appropriate. For details of the way in which these values are applied, see the theory documentation for tension, bending and torsion.