Determination of Lamb wave dispersion curves by means of Fourier transform

Abstract

This work reports on methods for determination of Lamb wave dispersion curves by means of Fourier transform (FT). Propagating Lamb waves are sinusoidal in both the frequency domain and the spatial domain. Therefore, the temporal FT may be carried out to go from the time to the frequency domain, and then the spatial FT may be carried out to go to the frequency–wave-number domain, where the amplitudes and the wave-numbers of individual modes may be measured. The result of this transform will be a 2D array of amplitudes at discrete frequencies and wave-numbers. Other method of determination of dispersion curves is based on the solution of FEM task in frequency domain. The frequency spectrum of a time-dependent excitation is defined using FT. Since a small number of frequencies are sufficient to achieve a correct representation of a wide variety of temporal excitations, this approach considerably speeds up the computation by avoiding the temporal FT and by decreasing the number of calculation steps.