Emissione acustica nei fenomeni di cavitazione

In this work the sound emission from cavitating bubbles is considered. The motion of a bubble in a liquid is examined and the radiated pressure field analysed in frequency components. Due to the fact that the contributions to the pressure field of the surface distortions are relevant in the proximity of the bubble wall, only volume oscillations are taken into account. The pressure field, as determined by the numerical integration of the Kirkwood-Bethe equation, is compared with the results obtained by taking the dissipative effects into account in a more realistic way. These are connected to the irreversible thermodynamic phenomena that take place in the liquid after the collapse of the bubbles, where formation and propagation of shock waves is observed. The Fourier analysis of the pressure field shows, as principal contribution, two distinct effects, one connected to the monopole oscillation and the other to the shock wave emission. The first accounts for the presence of discrete frequency components in the spectrum, while the second accounts for the white noise. Several considerations of the relative importance of two components in relation to model and prototype test experiments are presented.