On Sound Scattering and Acoustic Properties of the Upper Layer of the Sea with Bubble Clouds

Abstract

The presence of bubbles near the sea surface under certain conditions leads to abnormal sound scattering and a significant change in the acoustic properties of the upper layer of the sea. The article presents some results of sound scattering studies under various sea conditions, up to stormy conditions, when extensive bubble clouds arise. By the method of unsteady acoustic spectroscopy, data on the size distribution of bubbles at various depths have been obtained, which can be described by a power function with exponential decay at small bubble sizes of the order of 10 microns. Estimates of the gas content in bubble clouds and their influence on the acoustic characteristics of the upper layer of the sea have been carried out. It is shown that at sufficiently high concentrations, sharp increases in absorption and dispersion of the sound velocity are observed. Modeling of sound propagation in the presence of a quasi-homogeneous bubble layer shows that it leads both to a change in the laws of the average decay of the sound field along the sound propagation path and to a change in the shallow spatial structure of the field.

Cavitation Strength, Acoustic Nonlinearity, and Gas Bubble Distribution in Water

“…Previously conducted studies of the distribution of bubbles in typical real liquids (including seawater) allowed this article to use the model function of bubble size distribution (28) to calculate the effective compressibility β e (11) and, on this basis, to obtain estimates for the absorption coefficient α and the speed of sound c e , Equations ( 21) and ( 22), which were valid for sufficiently high concentrations of bubbles. The article did not have the opportunity to discuss the limits of applicability of the approximations made, but the authors, when conducting the analysis, understood the need to take into account the effects of multiple scattering and the overlap of sound scattering cross-sections at high concentrations of bubbles; therefore, all the calculations were carried out in areas where these effects should not be significant.…”

“…It is also important that the exponent n ∼ 3.3 and the critical dimensions R m and R P are natural parameters that follow from the Garrett-Lee-Farmer theory (GLF) [27]. The measurements of g(R) on a large factual material under similar conditions of moderate sea conditions give values n in the interval n ≈ 3.3 ÷ 3.8 [9][10][11][12][13]18,[26][27][28][29], which is close enough to the estimate n ∼ 3.3 obtained for the inertial interval between the sizes R m and R P , which follow from the theory of GLF [27].…”

Super‐Aerophilic Biomimetic Cactus for Underwater Dispersed Microbubble Capture, Self‐Transport, Coalescence, and Energy Harvesting

“…[50,51] The diameter of bubbles generated by breaking waves is even smaller, typically less than 600 µm, [35] and the average volume concentration is around 10 −5 or less. [34,36] The sizes of these seawater bubbles are much smaller than required by existing bubble energy harvesters, and the bubbles themselves are dispersed across a vast underwater environment in extremely low concentrations. Therefore, the capture as well as converging of microbubbles dispersed in water is a necessary prerequisite for bubble energy harvesting, which is of great significance for ocean in situ energy exploitation and underwater scientific exploration.…”

“…At the surface of the ocean, wave breaking enables large amounts of air to pass into the water. [34][35][36] In the photic zone of the upper and middle layers of the ocean, submersed plants such as algae produce 50% of the oxygen on earth through photosynthesis. [37] At the bottom of the ocean, up to 48 Tg of methane is released annually into seawater from subsea sediments.…”