Investigation Of Viscous Damping Terms For A Timoshenko Beam

Data cabling has become a significant portion of a spacecraft\u27s dry mass and can no longer be neglected in structural dynamics models. At higher-frequency modes, the cable dynamics can interact with the bus structure to which they are attached, affecting the over- all dynamics of the spacecraft. Experimental testing has shown an increased damping ratio for cabled versus non-cabled structures, indicating the need for a spacecraft dynamics model that accurately includes the effects of data cable damping. Previous work has modeled cables as shear beams with structural and proportional damping terms. Structural damping models have a tendency to overestimate system damping in higher-frequency modes, while proportional damping results in unrealistic frequency-dependent damping. A time-domain viscous damping model reecting the frequency-independent nature of spacecraft cables is desired. The addition of viscous damping in the form of a “geometric-based” term produced nearly frequency-independent damping in Euler-Bernoulli beams and a similar result in shear beams. This work investigated the effects of a geometric-based damping term in the Timoshenko beam equations. Ten damping terms were included in a Timoshenko beam finite element model and categorized as motion-, rotation-, and strain-based damping. This research shows two trends of modal damping dominated by bending or shear, with no single damping term producing frequency-independent modal damping. The damping results provide further insight into the creation of a frequency-independent damping model