Excitation and propagation of axisymmetric longitudinal guided waves in pipes immersed in infinite liquid media

The transient elastodynamic responses of the vacuum and liquid-filled pipes surrounded by infinite liquid to axisymmetric external forces are simulated by the acoustic-structural coupled finite element method.The time-frequency distributions of the transients waveforms are obtained by the short-time Fourier transform(STFT).The influence of the distribution of the external forces on the excitation of the guided waves is analyzed based on the above results and dispersion and attenuation curves.The study shows that the L(0,2) mode in the vacuum pipe surrounded by the liquid is suitable to be employed for the pipe inspection because it is the fastest mode in a weakly dispersive and attenuative region of frequency.And it can be excited high efficiently in the above region of frequency if the axisymmetric external force is applied on the inner or outer surface of the pipe axially.Analogously,the L(0,3) and L(0,4) modes in the liquid-filled pipe surrounded by the liquid are suitable for the pipe inspection.