Identification of modal parameters of a mdof system by modified L–P wavelet packets

In this paper a methodology for identification of modal parameters of a structural system using wavelet analysis is proposed. The proposed technique differs from the other works on using wavelet for this problem in the choice of the basis function. A modified form of Littlewood–Paley (L–P) basis function is used for the identification of the parameters. This basis has the advantage being more closely representing a vibrating signal. Further it is localized in frequency and hence can be used to detect the frequency and the associated parameters better. With a modification, it is well suited for sub-band coding to detect the parameters with desired accuracy. The current work identifies modal parameters such as natural frequencies and mode shapes of a linear multi-degree of freedom (mdof) system using the wavelet transform. It utilizes wavelet transform to identify natural frequencies and the corresponding mode shapes from the transient response of the system under ambient vibration condition. The estimated natural frequencies and the mode shapes are found to be close to the theoretical values for two simulated 3 and 5 dof systems. This demonstrates the effectiveness of the proposed methodology for system identification.