Authors:Yu. I. Bobrovnitskii; T. M. Tomilina Pages: 519 - 526 Abstract: The paper reviews and analyzes the state of the art of the problem on sound absorption in the linear formulation and methods for solving it. It is shown that the majority of publications are reduced, from the viewpoint of absorption efficiency, to the realization of one of two ideal absorbers: a Kirchhoff blackbody and an optimal absorber. These two absorbers have fundamentally different properties: the relative cross section of the blackbody absorber is equal to unity, whereas for the optimal absorber, this is the largest possible value, which can be much larger than unity. The practical problems they solve also differ. Ways of creating modern efficient absorbers are discussed, the most promising of which are absorbers made of acoustic metamaterials, which realize ideal bodies in the optimal way and require developed additive technologies for their manufacture. PubDate: 2018-09-01 DOI: 10.1134/s1063771018040024 Issue No:Vol. 64, No. 5 (2018)

Authors:A. G. Kyurkchan; S. A. Manenkov Pages: 527 - 534 Abstract: Diffraction of the field of a point source by a body of revolution is considered for the case where the body is positioned in a plane layer bounded by a perfectly soft boundary on one side and by a fluid half-space on the other side. Characteristics of the medium inside the layer are assumed to depend in a continuous manner on the vertical coordinate. The proposed method is tested by comparing the results of wave field calculations for the case of a constant sound velocity profile within the plane layer and also by comparing the given method with the surface integral equation method. It is shown that the sound field is considerably affected by inhomogeneity of the medium within the layer. PubDate: 2018-09-01 DOI: 10.1134/s1063771018050056 Issue No:Vol. 64, No. 5 (2018)

Authors:S. A. Nazarov Pages: 535 - 547 Abstract: A gently sloping perturbation of the rigid wall of a planar acoustic waveguide can cause a Wood anomaly, reflected in an enormously rapid change in the diffraction pattern when the cutoff frequencies are approached from below inside a continuous spectrum. Asymptotic analysis has been used to establish the restrictions imposed on the wall perturbation profile that ensure the appearance, enhancement, or disappearance of the anomaly. The asymptotics of the eigenfrequencies is studied and the complex and threshold resonances are discussed. PubDate: 2018-09-01 DOI: 10.1134/s106377101805007x Issue No:Vol. 64, No. 5 (2018)

Authors:V. C. Fedotovskii Pages: 548 - 554 Abstract: —The paper considers the effective inertial and elastic properties of a dispersive composite in the form of an elastic porous medium with empty spherical cavities. It is shown that when the translational vibrations and bulk oscillations of the cavities are in resonance, the dynamic density and compressibility of the porous medium take negative values. Estimates are presented for the internal dynamic parameters, for which the inertial and elastic properties determining the phase velocity and sound attenuation can simultaneously be negative in certain frequency ranges. The porous medium then assumes the properties of a metamaterial with negative sound refraction and other unique acoustic effects. PubDate: 2018-09-01 DOI: 10.1134/s1063771018050020 Issue No:Vol. 64, No. 5 (2018)

Authors:S. N. Gurbatov; O. V. Rudenko; A. V. Tyurina Pages: 555 - 562 Abstract: We study the interaction of noise and regular signals with a front whose steepness increases or decreases owing to nonlinear distortion of the profile of an intense pumping wave. Projective transformation is used, which is a result of one of the Burgers equation symmetries. Signal interaction with the pumping wave at its leading edge results in an increase in signal amplitude, a decrease in its time scale, an increase in the signal evolution rate, and earlier merging of discontinuities. At the trailing edge, an increase in signal amplitude, an increase in the time scale, and deceleration of the evolution rate occur. Formulas are obtained that describe the transformation of the spectrum and the correlation function of noise. Laws of the change in noise energy for both small and large Reynolds numbers are found. We study the interaction of weak noise with a nonstationary shock front in a medium with a finite viscosity. It is shown that, owing to competition between amplification at the shock front and high-frequency attenuation, the dependence on the noise intensity on distance has a nonmonotonic character, and at large distances, the intensity tends to zero, while the correlation time tends to a finite value. PubDate: 2018-09-01 DOI: 10.1134/s106377101804005x Issue No:Vol. 64, No. 5 (2018)

Authors:A. I. Komkin; A. I. Bykov; M. A. Mironov Pages: 563 - 566 Abstract: The effect of sound pressure level on acoustic resistance of an orifice in a baffle is investigated based on the measurements in an impedance tube by the two-microphone method. Dependences of the resistance of an orifice on the diameter of the latter are obtained for the case of nonlinear mode of operation. It is shown that, in this case, the resistance of the orifice depends on its diameter. The dependence of the nonlinear resistance on particle velocity in the orifice is approximated by a linear function. PubDate: 2018-09-01 DOI: 10.1134/s1063771018040085 Issue No:Vol. 64, No. 5 (2018)

Authors:B. R. Akhmetov; A. V. Vakhin Pages: 567 - 571 Abstract: The paper presents experimental research data on the frequency and concentration dependences of additional ultrasound attenuation in mixtures of asphaltene in toluene. The results indicate that additional attenuation is determined by several different processes and has a relaxation nature. By juxtaposing the results to the data from several methods for studying similar model disperse systems, we show that changes in the concentration attenuation coefficient and its frequency dependence can provide additional information on structure transformations and phase transitions. The frequency dependence was measured in a range of 10–23 MHz. The concentration dependence was measured in the same frequency range from 0.1 to 10 wt %. PubDate: 2018-09-01 DOI: 10.1134/s1063771018050019 Issue No:Vol. 64, No. 5 (2018)

Authors:Yu. V. Petukhov; V. G. Burdukovskaya Pages: 572 - 579 Abstract: We consider the patterns manifesting themselves in the formation of the spatial distribution of the intensity of an acoustic field excited by a point source emitting a tone signal in a deep-water oceanic waveguide with an underwater sound channel open to the surface and an acoustically transparent bottom. It is shown that at a certain emission frequency, the diffraction and ray caustics can merge, which leads to an appreciable increase in the acoustic field intensity along characteristic caustic lines on the horizontal distance–depth plane. PubDate: 2018-09-01 DOI: 10.1134/s1063771018040115 Issue No:Vol. 64, No. 5 (2018)

Authors:A. N. Serebryany; E. E. Khimchenko Pages: 580 - 589 Abstract: The paper presents research results on sound velocity variability in the water column based on long-term measurements conducted on stationary platforms on the Crimean and southeastern shelves of the Black Sea in the summer–fall seasons. Measurements consisted of long-term hourly soundings with a miniSVP sound velocity probe, continuous temperature recording with a thermistor chain, and current monitoring with ADCPs. A significant and frequently observed variability in the sound velocity fields was revealed during the passage of inertial internal waves and internal bores, both on the Crimean and Caucasian shelves. PubDate: 2018-09-01 DOI: 10.1134/s1063771018050093 Issue No:Vol. 64, No. 5 (2018)

Authors:V. A. Burov; O. D. Rumyantseva; K. V. Dmitriev Pages: 590 - 595 Abstract: A possibility to create controlled anisotropic illumination in an acoustic tomographic system with correlation processing of experimental data is considered. Fundamental difficulties encountered in setting up anisotrpic illumination in a ring array system are discussed. It is shown that, in systems with focusing elements, illumination is realizable; the output signal-to-interference ratio is estimated. PubDate: 2018-09-01 DOI: 10.1134/s1063771018040036 Issue No:Vol. 64, No. 5 (2018)

Authors:Ming-Song Zou; You-Sheng Wu; Jian-De Liu; Shu-Xiao Liu Pages: 596 - 604 Abstract: A new sono-elastic substructure method is proposed in this paper to improve the computational efficiency of the hull-substructure coupled and fluid-structure interacted vibration and acoustic radiation of a submerged cylindrical-shell-type vehicle. The typical part of the vehicle structure is divided into the main hull and the internal substructures. The fluid-structure interaction problem of the main hull is solved by an analytical method based on the simplified model of a single-hull ring-stiffened cylindrical shell simply supported at both ends. Meanwhile, the substructures are numerically modeled through the Finite Element Method, with the condensed dynamic stiffness matrices of them obtained via the Superelement Method of Modal Synthesis. The main hull and the internal substructures are then integrated according to the boundary compatibility conditions at the connecting parts. Thus, a Mixed Analytical-Numerical Substructure (MANS) method is formulated. The applicability of this method is validated by two numerical examples as well as the test results of a large-scale submerged structural model. It is shown that the MANS method is suitable for the prediction of vibration and acoustic radiation of typical cylindrical-shell-type submerged structures in the medium frequency region. PubDate: 2018-09-01 DOI: 10.1134/s1063771018050111 Issue No:Vol. 64, No. 5 (2018)

Authors:M. A. Ilgamov Pages: 605 - 611 Abstract: —The influence of the mean excess pressure on a cylindrical static bend and vibrations of a plate is studied. Increasing and decreasing this pressure lead to a decrease and increase in deflection, respectively. In the first case, the plate shape stabilizes under the action of longitudinal forces, while in the second case, destabilization takes place. The critical value of the mean pressure is determined. The dynamic modes of plate deformation under a sharp increase and decrease in pressure are analyzed. In the first case, vibrations with increased frequency are excited, while in the second case, the excited vibrations have a reduced frequency compared to the natural frequency of the unloaded plate. For deep evacuation, an exponential increase in deflection with time is observed. A method for solving the problem for complex pressure changes has been developed. PubDate: 2018-09-01 DOI: 10.1134/s1063771018050032 Issue No:Vol. 64, No. 5 (2018)

Authors:D. G. Kovzel’ Pages: 612 - 623 Abstract: —The article presents a new modification to a measuring–recording apparatus developed at the Il’ichev Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, to monitor anthropogenic noise levels on the northeastern shelf of Sakhalin Island. The functional possibilities of the original devices, modules, and software are described. The main device of the apparatus is the Shelf-2014 underwater bottom station, which records acoustic pressure variations in the 2–15 000 Hz frequency range. For operation in real time, the station is supplemented with a telemetry buoy. The Iridium satellite network serves as the buoy’s data transmission channel. Software at a shore post makes it possible to view the acoustic conditions in real time. The coordinates and technical status of bottom stations and buoys are controlled automatically. An operator receives on-screen notification when the parameters go beyond the permissible limits. The modified apparatus was tested on the shelf of the Sea of Japan. PubDate: 2018-09-01 DOI: 10.1134/s1063771018050044 Issue No:Vol. 64, No. 5 (2018)

Authors:D. V. Leonov; N. S. Kulberg; A. I. Gromov; S. P. Morozov; A. V. Vladzimirskiy Pages: 624 - 636 Abstract: The proposed ultrasound imaging mode allows detection of objects, which essentially differ in their scattering properties from the surrounding tissues and liquids. The objects in question are primarily microcalcifications, renal and urinary stones. Our previous study has shown that the Doppler signals from these objects have two components common for echoes from solid mineral inclusions. They can be in superposition with the blood and noise signals. One of these two mineral-related components is characterized by cavitation, the other – by elastic vibrations of the object presumably caused by acoustic radiation force. According to statistical and energy parameters, these components differ from each other, as well as from noise and blood echoes. The article proposes a practical method for identifying signals with mineral-related components. This method is the base for the novel diagnostic visualization mode specifically designed for the mineral inclusions detection with ultrasound. PubDate: 2018-09-01 DOI: 10.1134/s1063771018050068 Issue No:Vol. 64, No. 5 (2018)

Authors:P. A. Popov; A. A. Igolkin; E. V. Shakhmatov Pages: 637 - 642 Abstract: Problems of a decrease in acoustic loads on complex-shaped objects within a cylindrical shell are encountered frequently in practice. A good example is adjustment of a space vehicle to an assembly protection unit of a carrier rocket. This study presents a mathematical model for determining acoustic loads acting on an object and depending on the factor of acoustic energy absorption by surfaces. As a result, the spectra of the root-mean-square levels of the acoustic pressure have been obtained as functions of the area of a shell surface coated with a sound-absorbing material, as well as the area of an object beneath it. PubDate: 2018-09-01 DOI: 10.1134/s1063771018050081 Issue No:Vol. 64, No. 5 (2018)

Authors:L. R. Yablonik Pages: 643 - 650 Abstract: —The proposed method is based on the Biot theory of wave propagation in porous saturated elastic media. To simplify the cumbersome full calculation procedure, specific features of typical fibrous porous materials are used: a large density and moderate stiffness of the elastic frame in comparison to air. In this case, the transfer properties of an elastic porous layer are represented by two second-order matrices, which characterize sound transfer by airborne and frame-borne waves. Combined with the boundary conditions, such a representation in standard schemes makes it possible to form a single transfer matrix for the layer, by considering it a linear four-pole that relates the pressures and normal velocity components at the inlet and exit. When calculating the sound insulation of a multilayer structure, the formed matrix of the elastic porous layer is introduced via a cofactor into a chain of second-order transfer matrices determined by the other layers. Examples and comparative calculations are presented that demonstrate the high correspondence of the method’s results to the full calculation data. PubDate: 2018-09-01 DOI: 10.1134/s106377101805010x Issue No:Vol. 64, No. 5 (2018)

Authors:D. D. Zakharov Pages: 387 - 401 Abstract: A combined asymptotical and iteration method is used to study dispersion curves for the case of dynamic bending of isotropically layered plates. Based on the explicit limit formulation of dispersion equation, asymptotics of roots are derived in closed form for large values of root moduli. The influence of elastic and geometric parameters of layers are analyzed. The existence of critical values of geometric parameters that correspond to change of the type of asymptotics is demonstrated. The errors of asymptotics are estimated, and an iterative method is proposed for calculating the exact values of roots in statics. A low-frequency long-wave asymptotics of complex dispersion curves is derived; its accuracy is the higher the lower the frequency and the greater the number of the curve are. It is also proved that each complex curve has a long flat segment, the length of which increases simultaneously with the number of curve. The dispersion curves themselves are also calculated by another specific iterative procedure. The fundamental bending mode is analyzed together with its purely imaginary sister. The existence of the additional purely imaginary curve at low frequency is proved. Examples of calculating the static roots and the dispersion curves for subcritical and supercritical values of geometrical parameters are presented, and the efficiency of the algorithm is estimated. PubDate: 2018-07-01 DOI: 10.1134/s106377101803017x Issue No:Vol. 64, No. 4 (2018)

Authors:A. L. Gray; O. V. Rudenko Pages: 402 - 407 Abstract: The observed nonclassical power-law dependence of the amplitude of the second harmonic wave on the amplitude of a harmonic pump wave is explained as a phenomenon associated with two types of nonlinearity in a structurally inhomogeneous medium. An approach to solving the inverse problem of determining the nonlinearity parameters and the exponent in the above-mentioned dependence is demonstrated. To describe the effects of strongly pronounced nonlinearity, equations containing a double nonlinearity and generalizing the Hopf and Burgers equations are proposed. The possibility of their exact linearization is demonstrated. The profiles, spectral composition, and average wave intensity in such doubly nonlinear media are calculated. The shape of the shock front is found, and its width is estimated. The wave energy losses that depend on both nonlinearity parameters—quadratic and modular—are calculated. PubDate: 2018-07-01 DOI: 10.1134/s1063771018040048 Issue No:Vol. 64, No. 4 (2018)

Authors:A. I. Korobov; N. V. Shirgina; A. I. Kokshaiskii; V. M. Prokhorov Pages: 415 - 421 Abstract: The paper presents results from experimental studies on the influence of loading–unloading processes on the mechanical, linear, and nonlinear properties of the strain-hardening polycrystalline aluminum alloy AMg6 (Rus). The stress–strain curve is measured for AMg6 samples under high-cycle loading–unloading up to fracture of a sample. The microhardness of the sample is measured before and after its fracture. It has been found that the loading–unloading process leads to strain hardening of the AMg6 alloy. The influence of strain hardening of AMg6 on its linear and nonlinear elastic properties is studied by an ultrasonic method. To study the nonlinear elastic properties for different domains of the loading curve, we used the Thurston–Brugger method and spectral method by studying the efficiency of second acoustic harmonic generation. The experimental results are discussed. PubDate: 2018-07-01 DOI: 10.1134/s1063771018030119 Issue No:Vol. 64, No. 4 (2018)

Authors:Yu. V. Petukhov; E. L. Borodina; V. G. Burdukovskaya Pages: 479 - 491 Abstract: The paper considers the regular patterns that can be manifested in the behavior of the invariant of the spatial–frequency interference structure of an acoustic field in oceanic waveguides that are homogeneous and inhomogeneous along a track. Using the WKB and adiabatic approximations, an analytic expression is obtained for the invariant that, when certain conditions are fulfilled, reduces to the well-known classical expression independent of the mode numbers, their parity, or the emission frequency. It has been established that the approximate classical expression for the invariant correctly describes the slope of interference lines only in ranges of variation in the grazing angles of modes where the dependence of the cycle length of their corresponding Brillouin waves on the ray parameter is quite smooth and monotonic. The paper studies the formation of the spatial–frequency interference structure of an acoustic field propagating from a shallowwater isovelocity waveguide to a relatively deep-water waveguide with a near-surface sound channel. PubDate: 2018-07-01 DOI: 10.1134/s1063771018030132 Issue No:Vol. 64, No. 4 (2018)