Effect of local resonances on acoustic wave propagation in buried water pipes

The characteristics of the propagating axisymmetric wave are of considerable interest for the purpose of leak detection in buried pipes. In this paper, the effect of local resonances on acoustic wave propagation in buried fluid-filled pipes is investigated based on an analytical model of dispersion characteristics of the predominant mode at low frequencies. A theoretical model of the local resonator is introduced, and subsequently incorporated into the model of wave propagation to predict the frequency response function induced by strong scattering adjacent to the resonance frequencies, when two resonators are located on either side of a water leak. It demonstrates that the presence of the resonators results in the "phase shift" and "modulus reversal" in the frequency response function. To support the theoretical findings, analysis is carried out on the leak noise measured by hydrophones from actual water pipes. Comparison of the frequency response functions show that the model with the effect of local resonances included is a good representation of the experimental set-up. This provides the theoretical basis for better understanding the leak signals measured in practical situations and hence offer a potential improvement over the acoustic techniques based on cross-correlation for water leak detection.