Experimental and Analytical Investigations of Acoustic Wave Propagation using a Reservoir and an Acoustic Lens

In order to clarify acoustic emission testing (AE) wave propagation in an actual storage tank, this paper investigates acoustic emission wave propagation in a reservoir. In this study, a preliminary experiment with and without the test piece was first conducted. The results of the preliminary experiment without the test piece indicated small beam divergence, whereas in the preliminary experiment with the test piece, the wave propagation indicated large beam divergence in the wave due to mode conversion of the Lamb wave generated by the test piece in the experiment. Moreover, in order to simulate actual AE measurements on the bottom floors of an oil storage tank, an acoustic lens and a transmitter with a resonant frequency of 300 kHz and a 0.9 mm thick test piece were used. As a result, although the divergence angle of the acoustic emission wave became small, a large-amplitude wave propagated diagonally, and its velocity was obtained. The measured results were theoretically confirmed by 2D wave propagation simulations based on the finite difference method. Furthermore, a model tank was constructed, and the source location of the acoustic emission wave was estimated using a neural network in order to verify the wave propagation. Compared to the theoretical longitudinal velocity, the error became small when using the experimentally obtained large-amplitude propagation velocity.