Acoustical Physics最新文献

The article studies the possibility of using planar nonequidistant antenna arrays in problems of constructing acoustic images. Such antenna arrays can be used, e.g., for diagnostics of various mechanisms in order to determine areas of increased noise emission. Numerical modeling was performed in the paper to determine the advantages of using nonequidistant arrays. Comparisons of modern classical superresolution methods with one of the new methods developed at the Institute of Applied Physics, Russian Academy of Sciences, are given. The results were confirmed in an experiment. The results of the study allow the conclusion that planar sparse nonequidistant antenna arrays make it possible to reduce the number of microphones used or to expand the frequency range in problems of source selection and their spatial resolution.

The characteristics of low-frequency noise fields in shallow-water acoustic waveguides with a heterogeneous bottom structure in the presence of waterlike areas are analyzed through numerical experiments. Two seabed models are considered: an idealized one with a linear change in the sound speed in the bottom along one of the Cartesian coordinates and a realistic one where the sound speed in the bottom depends on all three coordinates. The second model is close to the real situation in one shallow-water area of the Kara Sea. Noise fields from distributed near-surface sources (surface waves) and a point source (ship noise) are studied. Calculations are performed using the wide-angle parabolic equation method. Averaged horizontal and vertical directivity patterns of the surface wave noise field are obtained, as well as average intensity values depending on the sound frequency and position of the receiving vertical array. Spatial dependence of the local source noise level is constructed for bottom areas with different properties. The possibility of detecting areas with a waterlike bottom by recording the noise of a moving vessel with a stationary vertical acoustic array is demonstrated. In the case of distributed sources, it is shown that the averaged noise characteristics weakly depend on the sound speed in the bottom.

The current state of the problem of applying holographic interferometry in underwater acoustics is presented. The discussion of holographic signal processing is focused on solving the problem of monitoring the underwater environment, ensuring the detection, resolution, and localization of underwater noise sources under conditions of low signal-to-noise ratio and spatiotemporal perturbations in the oceanic environment. Localization of the sound source is understood as determining the bearing, radial velocity, range, and depth. Single vector–scalar receivers and linear antenna arrays are considered as the receiving modules. The results of theoretical studies, numerical modeling, and field experiments are provided, allowing for assessment of the efficiency of holographic processing under realistic conditions.

The article proposes a method for constructing an active cancellation system based on an algorithm with a block adaptation procedure in the frequency domain. The proposed method has a high convergence rate and can be implemented on a general-purpose computer. The results of simulation modeling and experimental study of the efficiency of the proposed active cancellation system on the created setup are presented. It is shown that using this method for constructing an active noise control system, a suppression level up to 20 dB can be achieved on the experimental setup and up to 28 dB in the simulation model. Special attention is paid to the architecture of the experimental setup and software used.

A method for estimating the coefficient of sound reflection from the bottom of a waveguide based on field measurements using a vertical array at various distances from the source is discussed. To analyze the spatial-angular structure of the recorded field, the method of coherent states, borrowed from quantum theory, is used. The acoustic analogue of the coherent state expansion allows one to construct a filter to isolate the field component representing the contribution of a given narrow beam of rays. The ratio of the amplitudes of such a field component before and after reflection from the lakebed gives an estimate of the reflection coefficient of the central ray. The efficiency of the approach was tested using numerical simulation data. The results of its application for processing data from a lake experiment are presented.

The possibility of using Rayleigh wave dispersion to localize a source of seismoacoustic radiation is investigated. Compensation for dispersion distortion is at the heart of the well-known methods of wavefront reversal or time reversal methods. A specific feature of the article is the use of the dispersion dependence, which is measured during seismoacoustic signal recording, with subsequent processing of the data obtained. An example of such processing is presented for data recorded in a field experiment. The results indicate the prospects of developing the data interpretation method for seismoacoustic remote diagnostics of natural environments, e.g., for the search and localization of different types of inclusions.

The universal theory of “parametric” sound emitters is presented, taking into account the attenuation and diffraction of interacting waves in the quasi-optical approximation. Expressions are given that describe the structure of the low-frequency field excited by high-frequency waves with arbitrary amplitude and phase distributions on the surface of pump transducers. Universal formulas for calculating directivity patterns are given. The dynamics of pattern formation is described. The results of calculating the regime of highly distorted pump waves containing shock fronts are presented.

The article considers the use of technical tools and methods of low-frequency hydroacoustics for monitoring the variability of average temperatures of underwater sound channels in the Sea of Japan. The authors review the characteristics of the line of powerful interpiston hydroacoustic emitters developed by the Institute of Applied Physics of the Russian Academy of Sciences, which are promising for organizing long acoustic tracks. The results of measuring the electroacoustic characteristics of low-frequency hydroacoustic emitters under natural conditions at depths of up to 150 m are presented, and the use of these emitters for studying the temperature regimes of associated underwater sound channels of the shelf and deep sea on multiscale long tracks in the Sea of Japan is also considered. Based on processing of experimental data on an acoustic path with a length of about 1000 km, obtained in 2022, examples are presented of reconstructing the average water temperature values from data on the sound speed along the acoustic path; the sensitivity of the method is assessed, and the signal-to-noise ratio values achieved in the experiment are analyzed.