Vol 70, No 6 (2024)

In this work, correlation reception of thermal acoustic radiation by a pair of sensors was carried out. The experiment used receivers with different bandwidths, changed the size of the heated sources and the distance from the sources to the receivers, and also shifted the sources in the transverse direction perpendicular to the acoustic axis of the system. For each case, using the relations used in radio astronomy, the correlation functions of thermal acoustic radiation were calculated. It is shown that the cross-correlation functions obtained in experiments and calculated are close, taking into account the measurement error.

The effect of conducting and non-conducting liquids on the characteristics of a piezoelectric resonator with a longitudinal electric field immersed in a liquid was investigated. The resonator, operating on a longitudinal acoustic mode with a resonant frequency of about 4 MHz, was a disk made of X-cut langasite with round electrodes on both sides. The resonator was fixed at the base of a container filled with the liquid under study. Then, the real and imaginary parts of its electrical impedance were measured as a function of frequency using a vector network analyzer. A modernized electromechanical circuit of such a resonator was constructed, taking into account the effect of conductivity and permittivity of the liquid on the change in the effective area of the electrodes. The possibility of determining the elastic modulus, viscosity coefficient of the studied liquid and the values of additional elements of the equivalent circuit by fitting the calculated frequency dependences of the complex electrical impedance of a resonator immersed in liquid to the measured dependences is demonstrated.

The results of a laboratory experiment testing a method for reconstructing a sound field excited by a calibrated source in free space from measurements of a field excited by the same source in a tank with reflecting boundaries are presented. The reconstruction procedure is based on the use of an etalon acoustic monopole and comparison of the fields emitted by it from specially selected points of the tank with the field of the calibrated source. In the experiment, the frequency dependence of the field intensity of the calibrated source averaged over a sphere of large radius was evaluated.

A consistent theory of sound generation in a turbulent boundary layer developing over a flat smooth boundary at low Mach numbers is presented. The main source of sound and the long-wave part of pressure pulsations on the boundary in a streamline are incoming shear (viscous) waves generated by Lighthill quadrupoles in the near-wall region of the turbulent boundary layer. It is shown that with an increase in the Reynolds number (decrease in viscosity), the role of viscosity in sound generation does not decrease, but increases. Quantitative estimates of the spectrum of specific sound power generated in a turbulent boundary layer are given.

Two-dimensional linearized hydrodynamic equations describing the wave propagation in a stratified heavy gas are considered. The hydrodynamic equation system is reformulated as a single Schr?odinger type operator equation. The waves with $\beta \frac{l_z}{l_x}\ll 1$ are considered, where $l_z$ and $l_x$ are the characteristic vertical and horizontal scales, respectively, and the asymptotic behavior of solutions as $\beta \to 0$. It is shown that the set of solutions depending on β form two disjoint classes. For solutions from each of the selected classes, its own, asymptotic as $\beta \to 0$ , approximate equation system is proposed. The selected classes of solutions are acoustic and internal gravity waves. It is shown that the hydrodynamic variables of acoustic and gravity waves are related by certain stationary relationships, different for each class. This allows to pose the problem of separating the contributions of acoustic and gravity waves in the initial condition. The existence of a solution to this wave separation problem is shown. Examples of solving the problem of dividing the general problem into subproblems on the propagation of acoustic and gravity waves are given. Estimates for the division of the energy of the initial disturbance by wave type are obtained.

The propagation of a Rayleigh-type surface acoustic wave (SAW) along the free boundary of a layered half-space with a smooth change in its elastic parameters horizontally is considered analytically and numerically. The change in the amplitude of the SAW for the transition of a wave from a single-layer system to a single-layer, single-layer to two-layer and two-layer to two-layer depending on the elastic parameters, as well as the length of the sounding wave, is calculated. It is shown that the amplitude of SAW decreases with an increase in the velocity of longitudinal waves and the density of the medium as it propagates, and with an increase in the velocity of transverse waves in the medium, the amplitude of SAW can both increase and decrease. The change in the amplitude of surfactants associated with a change in the velocity of longitudinal waves is stronger, therefore this parameter should be taken into account in applied methods. It is shown that the magnitude of the dominant wavelength depends on both the geometric and elastic parameters of the system.

The International Organization for Standardization (ISO) introduced the term “soundscape”, which defined the latter as “an acoustic environment perceived or understood by a person/people in context”. It proposed methods for quantitatively assessing human emotional reactions to a sound environment. In one of the methods, such reactions were represented by coordinates on the “Pleasantness-Eventfulness" plane. The pleasantness coordinate assessed how pleasant the environment was for the subject at the time of the examination, i.e. the properties of the subject, and the eventfulness coordinate assessed how eventful the environment was, i.e. the properties of the environment. The purpose of this work was to verify the standard ISO method. Therefore, an audiovisual examination of the environment was carried out in different locations; pleasantness and eventfulness coordinates were calculated; acoustic characteristics and psychoacoustic characteristics of the environment were recorded and calculated, the latter were then compared with the characteristics of sound landscapes (or pleasantness and eventfulness coordinates). It was shown that a sound environment with physical characteristics higher than established sanitary standards may well be pleasant for a person. The obtained results confirmed the validity, informativeness and integrity of the method for assessing soundscapes, its accessibility for non-professional experts. The characteristics of soundscapes can be used for engineering design of the sound environment of urban areas.

The problem of acoustic wave propagation with thermoviscous boundary conditions is studied. For thermoviscous boundary conditions, a time-dependent formulation is presented based on the concept of a fractional derivative. A weak formulation of the problem is given, which is reduced to a system of Volterra-type integro-differential equations using the finite element method. An implicit finite-difference scheme is constructed for the numerical solution of this system. To verify it, the problem of sound propagation in a thin pipe is modeled, the results of numerical modeling are compared with the analytical solution.

The study of the morphology and auditory mechanisms of the new (evolutionary) external ears of the bottlenose dolphin was continued in the light of the latest morphological and experimental results obtained by the author. For the first time for toothed whales, it has been shown that the bottlenose dolphin (Tursiops truncatus) has three external auditory canals (AC) in the left ear and four in the right ear. However, in contrast to the human AC – located symmetrically on the left and right half of the head, the left and right row of the dolphin AC, having bilateral and rostral-caudal asymmetry, are located at the tip of the rostrum asymmetrically (rostral-ventral). It has been established that the illumination by echo (sound) and shielding by the rostrum and skull of the firsts ACs is fundamentally different from the rest of the ACs, depending on spatial localization of echo (sound). The architecture of the ACs are optimal for the formation of unique signs of echo (sound) localization, and for it in-phase reception by all ACs in the direction of maximum accuracy of hearing localization, without the localization signs, which is fundamentally importance for fine analysis of the echo. In contrast, in human hearing, sound is colored by signs of localization at any position it in space. The mechanisms of localization of echo (sound) and their fundamental difference in dolphins and humans, as well as mechanisms for protecting the dolphin’s hearing from interfering reflections, are considered. It has been established that the auditory mechanisms of the external ears of dolphins and humans are determined by their morphology and functions.