On the Calculation and Measurement of Modal Damping

The prediction of the sound characteristic of a drive train in early development stages is desirable. However, at the state of the art, the structural dynamics cannot be calculated with satisfactory accuracy. Challenging is especially the calculation of the damping forces, which arise from various and partly nonlinear effects. In practice this leads to the necessity of prototypes to measure the damping, which this contribution aims to overcome. In this paper, the damping is calculated from geometry and material data by considering the contributing effects individually. The resulting modal damping values enable the mode superposition method and are therefore suitable for e.g. elastic multibody simulations. The dominant damping mechanisms in case of solid bodies are material damping and sound radiation. However, the method is in principle capable of incorporating e.g. damping due to joints as well. The method is applied to two solid aluminum and one orthotropic sheet metal test object. The modal damping values for validation are extracted from measured frequency response functions applying the circle fit and the least squares rational fit method. The error introduced by assuming proportional damping, which underlies the damping extraction as well as the simulation, is estimated with an exemplary frequency response function.