Fundamental study on estimation of imaginary part ratio of FRFs and damage identification from two simultaneous measurements

Abstract

This paper first presents an estimation method of the imaginary part ratio of the frequency response functions (FRFs) from simultaneous measurements at two different locations on a linear structure. The method is based on the reciprocity theorem and the principle of causality, and assums 1) the structural damping matrix is proportional to the identity matrix and 2) force acts on only one point of the structure at a time, which moves throughout the structure with a constant Fourier amplitude. Then, this paper presents a damage identification method for structures using change in the imaginary part ratios of the FRFs. Structural damage is assumed to be accompanied by changes in element stiffness and structural damping. The validity of the estimation method and the damage identification method is verified through a numerical simulation.