DEVELOPMENT AND EXPERIMENTAL VERIFICATION OF DAMPING ENHANCEMENT METHODOLOGIES FOR SPACE STRUCTURES by

A frequency domain system modelling technique is developed for mechanical systems. The technique is derived from Tellegen's Theorem for electrical networks and is applied to discrete mechanical systems. The elements are modelled in terms of their mechanical impedances. A global system model is assembled from the constitutive impedances. The global system model is used to determine the model exact pole locations and system energy dissipation and storage properties. An approximate method for finding modal frequencies and loss factors using the system impedance matrix and assumed modeshapes is developed. This method reduces to Rayleigh's Quotient in the case of an undamped system. Impedance models for several damping enhancement mechanisms are presented. Among these are models for viscoelastic materials, the classical proof mass damper, and a new damping enhancement concept called the shunted piezoelectric. The shunted piezoelectric damping mechanism is based on a piezoelectric material which has its electroded surfaces shunted by an arbitrary electrical circuit. Methods are developed for analyzing this special damper and optimizing its damping properties in the case of shunting by a resister or by a resonant circuit. Parallels are drawn between the resistive shunted piezoelectric and viscoelastic materials and between the resonant shunted piezoelectric and the classical proof mass damper. Experiments were conducted on a 5 meter, 10 bay box truss with a quasi freefree 3 dimensional suspension. A tunable, linear electromechanical driver was implemented for use as a proof mass damper. Electrical feedback of the proof mass position and velocity enabled accurate tuning of the dampers resonant frequency and internal damping. Piezoelectric truss members were designed and constructed for implementation of the shunted piezoelectric damping concepts. These members could replace the standard aluminum