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Volume 71, Nº 2 (2025)
КЛАССИЧЕСКИЕ ПРОБЛЕМЫ ЛИНЕЙНОЙ АКУСТИКИ И ТЕОРИИ ВОЛН
Experimental method for determination of energy losses in oscillatory systems based on ARMA-modeling
Resumo
Damping (dissipation, energy losses) is the most important parameter of all mechanical oscillatory systems along with elasticity and inertia. Its special role is due to the fact that it directly determines the maximum amplitudes of free and forced vibrations of systems and, accordingly, their dynamic strength and reliability, noise and ecology. Due to the poor study of the physical processes of damping, it is measured experimentally. This article presents one of the new effective methods for experimental determination of losses, characterized by simplicity, high accuracy and a wide range of applicability. The main attention is paid to the substantiation of the method, its properties and its veryfication in numerical and laboratory experiments. The method is recommended for measuring the losses of composite highly damped oscillatory systems, where known methods do not work or are too complex.
Akustičeskij žurnal. 2025;71(2):155-175
155-175
Vibrational black hole for torsional waves propagating through a rod of variable cross-section
Resumo
The propagation of torsional waves through rods of variable cross-section is considered. With a linear increase in the flattening of the rod, the propagation velocity of the torsional wave decreases linearly and turns to zero at the end of the rod. Yet, the propagation time to the sharpened end is equal to infinity. Such a decelerating structure is called a vibrational black hole in modern terminology. Exact solutions of the equation of torsional vibrations of a sharpened rod with a moment of inertia and a moment of torsion in the form of power functions are given. Corresponding expressions for the input impedance at the initial cross-section are obtained.
Akustičeskij žurnal. 2025;71(2):176-183
176-183
Stopping zones for waves in double-periodic elastic waveguide of bodies connected by thin rods
Resumo
We examine a periodic isotropic and homogeneous elastic waveguide which is composed of identical massive bodies connected by thun horizontal rods and vertical rods joined to a rigid half-space. By means of dimension reduction procedure for the rods and analysis of interacion of rigid motions and singular fields in the body we construct asymptotics of eigenvalues of the model problem in the periodicity cell which depends on the Floquet parameters. As a result, we derive asymptotic formulas for length and position of spectral bands (wave passing zones) and detect spectral bands (wave stopping zones).
Akustičeskij žurnal. 2025;71(2):184-194
184-194
Investigation of the reflection and transmission of sound through an elastic layer with inclusions using the finite element method
Resumo
This paper describes an approach based on the finite element method for numerical modeling of the absorption properties of acoustic materials. The emphasis is on rubber-like materials with inclusions of cavities that provide resonant dissipation mechanisms. An approbation of the developed methodology and a study of the accuracy of the method by comparison with previously published results are presented. An analysis of changes in the acoustic properties of a heterogeneous material under external load conditions in a linear formulation is carried out.
Akustičeskij žurnal. 2025;71(2):195-205
195-205
АКУСТИКА ОКЕАНА. ГИДРОАКУСТИКА
Lines of equal phases and phase invariant in the sound field of the deep sea
Resumo
The spatial-frequency characteristics of the amplitudes and phases of sound pressure in the deep sea have been studied. Analytical relationships have been obtained that allow one to calculate and compare the amplitude-phase structures of water, leaky and trapped modes, as well as the sound pressure field formed by the sum of the modes. The calculations have been performed using the modified WKB (Wentzel–Kramers–Brillouin) approximation. It has been shown that in the deep sea, as in the shallow sea, there are stable lines of equal phases along which, under certain conditions, coherent summation of complex Fourier components is possible. To describe the lines of equal phases, a differential equation has been obtained that uses the phase invariant, already studied in the shallow sea, as a basic parameter. This has made it possible to study the properties of the phase invariant corresponding to water, leaky and trapped modes in all zones of the sound field for the deep sea as well. It is established that at different distances in the field constructed from the sum of all modes, invariant properties are manifested, first of all, those modes that dominate at these distances. It is shown that the leaky modes formed in the near illumination zone and in the shadow zone, formed by steep rays reflected from the bottom, have invariant properties only at large distances from the source. Water and trapped modes have invariant properties in full and at all distances. Recommendations are given on the use of equal phase lines and the phase invariant in processing experimental data and modeling.
Akustičeskij žurnal. 2025;71(2):218-231
218-231
Theoretical analysis of the influence of weakly divergent beams on the formation of the spatio-temporal structure of pulse signals in the Sea of Japan
Resumo
Using numerical modeling based on the mode theory and the geometric-acoustic approximation, it was determined that along with the classical quadruples of pulses present in the space-time field structure, the emergence of additional signals with relatively short delays is caused by the formation of weakly divergent multimode beams in the underwater sound channel of the Sea of Japan, which correspond to smooth extrema in the dependences of the spatial interference period of neighboring modes and their group velocity on the mode number. For one of the two sound speed profiles typical for the Sea of Japan, it was shown that at relatively high frequencies it is possible to receive two groups of additional signals, which correspond to weakly divergent beams formed by modes of relatively low and high orders.
Akustičeskij žurnal. 2025;71(2):232-240
232-240
Acoustic impulse response fluctuations and coherent underwater acoustic communication in shallow waters under autumn conditions
Resumo
The paper presents the results of a full-scale experiment aimed at assessing the temporal variability of the impulse response of a hydroacoustic channel and the efficiency of coherent underwater acoustic communications using bottom transmitters and receivers at frequencies of ~10 kHz on the Black Sea shelf in autumn. Three prominent maxima of variable amplitude were observed in the impulse response structure throughout the experiment (~36 h). The range of variability of the root-mean-square decoding error was ~11 dB, the bit error ratio varied from 0 to 0.10. We found a a strong relationship of the values of decoding errors with the amplitude of the maximum arrival in the structure of the reference impulse response corresponding to a group of rays with one reflection off the surface, as well as with the variation coefficient of high-frequency fluctuations of the amplitude of this arrival in the instantaneous estimate of the impulse response. Using numerical modeling, the hypothesis was confirmed that in autumn conditions, characterized by the absence of a pronounced seasonal thermocline, the main hydrophysical cause of the variability of the amplitude of the main arrival, and, as a consequence, the effectiveness of underwater acoustic communications, consisted in an insignificant (fractions of a degree) change of temperature in the upper layer of sea water.
Akustičeskij žurnal. 2025;71(2):241-259
241-259
АКУСТИЧЕСКАЯ ЭКОЛОГИЯ. ШУМЫ И ВИБРАЦИИ
Sound insulation of fuselage aircraft structures with different composition of resonant elements
Resumo
The problem of reducing noise in the cabin of a propeller aircraft is an urgent task of internal acoustics, since traditional sound-insulating structures do not have sufficient efficiency in the region of low frequencies. One of the promising ways to solve it is the use of resonant systems, with the help of which it is possible to significantly increase the sound insulation of the fuselage structure of the aircraft in this frequency range. In this work, the effect of resonant systems on the sound-insulating ability of flat and cylindrical panels without and with cross stiffening simulating the body bulkhead frame was experimentally determined, as well as the effectiveness of lining the passenger compartment with resonant systems of various compositions was determined. Tests were carried out in sound chambers and on a full-scale stand, which is a real passenger plane. When facing the tested structures, elasto-acoustic compensators of various types with resonant elements made using foil, micalent paper and thermo-polyurethane were used. It is shown that the efficiency of resonant systems can reach 10–20 decibels or more.
Akustičeskij žurnal. 2025;71(2):299-304
299-304
НЕЛИНЕЙНАЯ АКУСТИКА
Numerical simulation of volumetric ultrasound heating of biological tissue with surface cooling
Resumo
One of the undesirable effects of using ultrasound for extracorporeal therapy is skin overheating, caused by both ultrasound absorption and contact with the heated surface of the acoustic transducer. To suppress this effect, a forcibly cooled contact medium can be placed between the skin and the irradiating surface. A novel ultrasonic applicator implementing this approach has recently been proposed and developed at SFU. It uses a rectangular piezoelectric transducer bonded to an aluminum plate for volumetric heating of subcutaneous biotissue. The plate is cooled by circulating cold water through laterally drilled channels. This paper presents a numerical algorithm for calculating the three-dimensional temperature field in the tissue during the operation of this applicator. The simulation was based on the inhomogeneous heat equation. Experimental acoustic holography data obtained for the developed transducer were used to calculate the heat sources in the tissue. An example of heating bovine liver tissue ex vivo is considered, with irradiation times ranging from several seconds to several minutes. The simulation results were compared with experimental data on tissue thermal ablation at an acoustic power of 12 W and an ultrasound frequency of 6.96 MHz. It is shown that the combination of thermal tissue exposure and contact boundary cooling allows for volumetric tissue heating with a temperature maximum at a depth of 8 to 15 mm, while maintaining a negligible temperature change at depths up to 2–3 mm.
Akustičeskij žurnal. 2025;71(2):206-217
206-217
АТМОСФЕРНАЯ И АЭРОАКУСТИКА
Correlation function of equilibrium thermal pressure fluctuations in viscous heat-conducting gas
Resumo
The problem of finding the space-time correlation function of pressure thermal fluctuations of gas near thermodynamic equilibrium is considered. Correlation function of pressure field equilibrium thermal fluctuations is obtained for viscous heat-conducting perfect gasfilling an unbounded Euclidean space. The influence of the boundary on the correlation characteristics of thermal fluctuations of pressure is investigated using the example of a viscous isentropic perfect gas filling a small-section pipe with boundary conditions of a solid wall at the ends and periodic conditions for the case of a pipe closed in a circle.
Akustičeskij žurnal. 2025;71(2):260-272
260-272
ОБРАБОТКА АКУСТИЧЕСКИХ СИГНАЛОВ. КОМПЬЮТЕРНОЕ МОДЕЛИРОВАНИЕ
Compensation of influence of shifting the antenna array transducers on tomography data
Resumo
Method for correction of fields detected by an antenna array with a non-ideal placement of transmitting and receiving transducers has been developed and numerically tested. The shifts of the transducers from their ideal positions are determined in advance. The correction technique involves finding the angular harmonics based on the fields measured with the shifted transducers. Then these found angular harmonics allow us to recalculate the fields at ideal positions of the transducers, as well as directly calculate the scattering amplitude. Such corrected data is the input for the stage of reconstruction of acoustic tomograms, i.e. the internal structure of the object. Numerical modeling has illustrated that the tomograms can be destroyed in the absence of the correction of data measured in real conditions.
Akustičeskij žurnal. 2025;71(2):305-322
305-322
ACOUSTICS OF STRUCTURALLY INHOMOGENEOUS SOLID MEDIA. GEOLOGICAL ACOUSTICS
On the possibility of detecting geological bodies without velocity contrast in the field of surface waves
Resumo
Using a mathematical model within the framework of the linear theory of elasticity, interesting from both theoretical and practical points of view, the problem of surface wave irradiation of an elastic half-space containing a single buried body whose physical properties are different from those of the host medium material, but whose elastic moduli and density change in a consistent manner so that the velocity of both P- and S-waves do not differ from those in the host medium, is considered. It is shown that such buried heterogeneities, despite the lack of velocity contrast, can be detected and mapped both in plan and depth in a broadband field of Rayleigh surface waves by variations in the spectral amplitude of the signal recorded at several points on the surface.
Akustičeskij žurnal. 2025;71(2):273-283
273-283
Statistical characteristics of the internal structure of the seismic background over a hydrocarbon deposit
Resumo
The fine structure of seismic background in the territory of an oil field was studied using polyspectral analysis and surrogate models. Statistical test for Gaussianity and linearity showed that natural seismic background in the frequency range of 1–50 Hz is a nonlinear process. Bicoherence graphs revealed statistically significant peaks of phase-related triplets with a characteristic geometry of peak clustering in the main triangular region. To analyze the quasi-noise component of the seismic background, surrogate time series with a randomized phase spectrum were generated, the bispectra of which are free of triplet peaks. Bispectral analysis of surrogate series showed the presence of a non-Gaussian quasi-noise component in the seismic background in the frequency range of 1–6 Hz. Previously, the results of the analysis of the used set of records by two completely different methods, each of which extracts information from different components of the seismic background — quasi-noise and regular, were published. These studies showed that each of the two components contains information sufficient to estimate the total thickness of the productive intervals under the recording point. Based on the results of the bispectral analysis and the features of the algorithms of the two methods, a conclusion was made that the quadratically phase-related triplets and the non-Gaussian quasi-noise component in the field territory are manifestations of endogenous seismic emission and are generated by the same nonlinear process developing in the vicinity of an oil-saturated reservoir. The mechanism of seismic emission should be sought in the class of phenomena with quadratic nonlinearity. The statistical characteristics of the internal structure of the seismic background near oil wells have similar features that differ greatly from the statistical characteristics of the seismic record near a “dry” well located outside the reservoir and not producing oil. Previously unknown prognostic features of the oil/water saturation type of rocks have been identified.
Akustičeskij žurnal. 2025;71(2):284-298
284-298
ИНФОРМАЦИЯ
Игорь Борисович Есипов (К 80-летию со дня рождения)
Akustičeskij žurnal. 2025;71(2):323-324
323-324