Experimental Evaluation of The Fluid-Structure Interaction under High-frequency Wave Excitation in a Fluid-Filled HDPE Pipe

Transient Based Defect Detection Methods (TBDDM) is a relatively new approach for diagnosing faults, such as leaks and blockages, in urban water supply systems. The effectiveness of these methods relies on the achievable imaging resolution. For increased resolution, the use of high frequency acoustic waves is necessary. At these frequencies, the wavelength is comparable or smaller to the diameter of the pipe and fluid-structure interaction effect becomes prominent. An approximate analytical, impedance based, model that describes wave propagation in fluid filled elastic pipes, is compared against experimental data for a HDPE pipe at a frequency range from 10 to 50 kHz. The analytical group velocity curves match well with the experimental. However, an error is introduced in the calculation of the cut-off frequencies of radial modes. This work presents a novel approach to measure the response of the pipe walls to an acoustic source within the pipe using accelerometers. Experimental dispersion plots are obtained from both the solid and fluid domains and allow the full characterization of the waveguide. In particular, accelerometers capture the shift of the first radial mode from radially propagating to axial as the frequency increases., that corresponds in the group velocity rise for that mode.