Viscous vs. structural damping in modal analysis

It is shown that among the various damping mechanisms that are generally encountered in a mechanical structure, only the “viscous component ” actually accounts for energy loss. The remaining portion of the damping force is due to non-linearities, which do not dissipate energy. Consequently, a linear model of a vibratory mechanical system involves only viscous damping, although the damping factor may depend upon the waveform or amplitude of the excitation signal