Identification of the Unconstrained Modes of 3D Axisymmetric Structures from Measurements under Constraining Support Conditions

Abstract

An inverse method for extracting the unconstrained modal parameters of 3D axisymmetric structures from measurements performed under constrained configurations is proposed. The work was originally motivated by the need of knowing the tuning of large historical carillon bells which now lie on reinforcement fixtures, implying a quite different response of the bells from their original suspended state. In this paper, we extend to three-dimensional bodies the identification technique recently developed by the authors for a case of study consisting on a simple discrete mass-spring circular ring. Considering a modal model of a free cylinder as a first approximation of a bell, we present the identification strategy and then illustrate the efficiency of the technique by providing identification results for the original system modal frequencies from the constrained system. By operating directly on the constrained transfer functions measured at the constraint locations, the technique is not prone to modal identification nor to truncation errors, and therefore appears particularly convenient for modal testing on real structures.