Conference publications


XXIV conference

Suppression of nonlinear attenuation of intense acoustic waves due to frequency-selective absorption in a structurally heterogeneous medium

Gusev V.A.

Department of acoustics, Faculty of Physics, Lomonosov Moscow State University, Leninskie gory, Moscow 119991, Russia

1 pp. (accepted)


During the propagation of intense acoustic waves and beams one of the major mechanisms of dissipation is the nonlinear damping associated with the energy transfer in all possible harmonics and their rapid attenuation in comparison with the wave of the fundamental frequency. In optics such a cascade is not formed due to the strong dispersion and the energy exchange occurs only between the several waves that are in synchronism. In acoustics, such a strong dispersion is possible only in limited structures, such as waveguides or media with special dynamics. Another approach to reducing nonlinear damping mechanism – the introduction of additional attenuation for higher harmonics, e.g., second. In this case, the energy transferred to the second harmonic is disappeared and isn't transmitted to spectrum above. In addition, if the second harmonic decreases due to strong attenuation it impacts on the first harmonic, which also contributes to the conservation of wave energy. Medium, providing a strong attenuation on the second harmonic and weak attenuation at the fundamental frequency wave should have frequency-selective properties. An example of such medium is a liquid with gas bubbles. The wave propagation in this medium is qualitatively different for frequencies much lower and much higher than the resonance frequency of the bubble. At low frequencies the wave propagates with an effective speed of sound, and heterogeneity in the concentration of bubbles can lead to the formation of the sound channel and the waveguide wave propagation [1]. Near the resonant frequency of the bubbles dispersion and strong attenuation is observed. It is known that the main part of absorption of liquid with bubbles is due to resonant bubbles. The calculation of the amplitudes of first and second harmonics of an intense acoustic beam is made, taking into account their diffraction divergence under the condition that the second harmonic falls in the region close to resonance and is strongly absorbed. It is shown that indeed the damping of waves of the fundamental frequency decreases with increasing attenuation of the second harmonic. It turned out that the diffraction, leading to additional attenuation, under certain conditions allows to reach large values of the amplitude of the fundamental frequency compared to the plain wave approximation, when diffraction effects are not taken into account.

This work was supported by RFBR grant No. 16-02-00764


1. Gusev V. A., Rudenko O. V. Nonlinear sound in a gas-saturated sediment layer // Acoust. Phys. 2015. T. 61. No. 2. P. 169-182.

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