Frequency response of structures and the effects of noise on its estimates from the transient response

Abstract

Transient testing techniques have been extensively used in determining the behaviour of a dynamic system and as a means of obtaining its frequency response.This paper deals with the determination of the frequency response of structures by transient testing techniques and is focused on the effects of extraneous noise on the estimate of the frequency response function.The deterministic approach of estimating the frequency response function of a structure by taking the Fourier transform of its transient response is shown to yield very poor results when noise is present either as additional excitation to the structure or at the response.Probabilistic theory is thus necessarily employed in the analysis of the transient response of the structure. The study shows that noise present at the response of a system affects the estimates of its frequency response function derived by considering either the power spectral density function of the response or the autocorrelation function of the response.The theoretical study is completed by the development of a novel analysis technique by which accurate estimates of the frequency response function of the structure may be obtained from transient tests carried out under noisy environmental conditions.