DETERMINATION OF FREQUENCY-RESPONSE FUNCTIONS FROM RESPONSE MEASUREMENTS .1. EXTRACTION OF POLES AND ZEROS FROM RESPONSE CEPSTRA

In the current investigation a procedure is proposed to extract poles and zeros of transfer functions from response vibrations. In this proc edure use is made of the deconvolution properties of cepstral analysis , that is, in the cepstrum domain, source and path effects are not onl y additive but also separated into different quefrency regions. The so urce effect is excluded and the complex or differential cepstra of the path are curve-fitted to extract poles and zeros. The Levenberg-Marqu ardt and Ibrahim time domain methods are adapted for the curve-fitting purpose. In the Levenberg-Marquardt method path dominated complex or differential cepstra (after the source effect is removed) are curve-fi tted to their corresponding analytical expressions, while in the Ibrah im time domain method differential cepstra are treated as free respons e data. The advantages and disadvantages of the two methods are compar ed. The validation of this procedure is demonstrated by using the resp onse of a free-free beam to impact and double impact excitations. (C) 1996 Academic Press Limited.