Identification of Rigid Body Parameters Using Experimental Modal Analysis Data

Abstract

A simple direct method is presented here to identify the rigid body parameters of a structure under a free-free condition using the measured vibration data and geometrical co-ordinates of the measurement points relative to an arbitrarily selected general co-ordinate system. These parameters consist of mass, co-ordinates of mass centre, mass-moment of inertia, and the corresponding required principal values and axes. The test structure should be Weakly suspended or soft mounted to ground. The rigid body motion should be carefully selected from the measured transfer functions. Practical considerations like the selection of general co-ordinate system, the measurement and excitation points, the minimum set of measurements etc, to be noted during performing the vibration tests or evaluating the rigid body parameters are illustrated with the help of three practical examples. The accuracy of the identified parameters depends, to a great extent, on these considerations. Comparisons between identified and theoretical results are also given.