Random decrement based FRF estimation

Abstract

The problem of estimating frequency response functions and extracting modal parameter is the topic of this paper. A new method based on the Random Decrement technique combined with Fourier transformation and the traditional pure Fourier transformation based approach is compared with regard to speed and quality. The basis of the new method is the Fourier transformation of the Random Decrement functions which can be used to estimate the frequency response functions. The investigations are based on load and response measurements of a laboratory model of a 3 span bridge. By applying both methods to these measurements the estimation time of the frequency response functions can be compared. The modal parameters estimated by the methods are compared. It is expected that the Random Decrement technique is faster than the traditional method based on pure Fourier Transformations. This is due to the fact that the Random Decrement technique is based on a simple controlled averaging of time segments of the load and response processes. Furthermore, the Random Decrement technique is expected to produce reliable results. The Random Decrement technique will reduce leakage, since the Fourier transformation will be applied to the Random Decrement function, which has a natural decay.