Acoustic waves emitted during a leak are studied both theoretically and experimentally. Two geometries of the leak are considered: a circular hole and a rectangular slit. An expression for the dependence of the frequency of the emitted signal on the pressure difference of the fluid across the leak and the dimensions of the hole or slit is derived. The expression is found to agree with the experimental results obtained for the case of a circular hole over a wide range of pressure differences and hole diameters. It is concluded that a leak may be treated as a resonator that emits acoustic waves at a sharp resonant frequency, besides its well-known characteristics of producing low-frequency noise due to the increase of turbulence in the fluid around the area of the leak.
A simple analytical technique based on the methods of transverse resonance and group velocity is developed in order to predict the propagation of shear (SH) waves emitted from a crack in elastic plates. Since a total solution of the Rayleigh Lamb waves propagation inside the plate is very complicated, the simple SH mode was used to demonstrate the argument of this paper. The effects of varying distances between the crack and the sensor are also discussed.
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