Abstract: The results of the numerical simulation and experimental study of an entirely piezoceramic cylindrical resonator to generate sonoluminescence are presented. The data on the origin and study of single- and multibubble sonoluminescence in a water–air system are presented. It is shown that in a piezoelectric resonator sonoluminescence occurs under electric voltages, whose values of are one order of magnitude less than in resonators of other types. PubDate: 2020-05-01

Abstract: The experimental study results of acoustic radiation generation via zero–refraction–index periodic structures are presented. The frequency dependences of refraction indices for structures in an acoustic frequency range are constructed based on the previous data in a microwave range. The measurements showed that, in a frequency range, where the refraction index changes sign, acoustic radiation is focused and has a narrow directivity pattern. Attention is drawn towards research trends that indicate where these structures may be useful. PubDate: 2020-05-01

Abstract: The article considers the problem of sound absorption by a monopole in a room with perfectly hard walls. The radiation impedance of a monopole in the form of a piston built into one of the walls was found. The impedance of the monopole is calculated that ensures the maximum damping constant of the room first natural resonance. It is shown that in the general case, a monopole with an impedance chosen in a certain way absorbs sound more efficiently than a Helmholtz resonator. The proposed approach can be used to design active sound absorption systems for small rooms. PubDate: 2020-05-01

Abstract: Collisions of two pulsed signals in a medium with modular (M) nonlinearity and a special relaxation law are investigated. The processes are described by an integro-differential equation, the kernel of which is nonzero in a finite time interval. It is believed that within this interval, the “memory of the medium” is constant, but outside it, it vanishes. For this model, the analysis is reduced to solving a simple differential-difference equation, whereas the volume of computations is significantly reduced. The phenomena accompanying pulse collisions of are described: nonlinear mutual attenuation, annihilation, and signal broadening with time. The effect of the signal parameters and properties of the medium on these processes is explained. The collision of two modular solitons described by the Korteweg–de Vries M-equation is considered. It is shown that, by using this model, the interaction may differ from the usual behavior of solitons, revealing an analogy with elastic particle interaction. PubDate: 2020-05-01

Abstract: Algorithms are realized for localizing vibration activity sources in complex mechanoacoustic systems using finite element modeling. For the case of one source, the localization method was used in the least squares form applied to the first eigenvector of the sample correlation matrix. It is shown that frequency summation can significantly increase the localization accuracy in this case. Considerable attention is paid to assessing the number of simultaneously operating vibration sources and the possibility of correctly localizing them. The efficiency of two source localization methods was compared: the maximum likelihood method calculated for a single source and the MUSIC (Multiple Signal Classification) method specially modified for this problem. It is shown that the modified MUSIC method is more efficient in solving the localization problem with two sources compared to the maximum likelihood method calculated for a single source. It is noted that the maximum likelihood method calculated for two or more sources cannot be applied because of the too high computational complexity. PubDate: 2020-05-01

Abstract: The effect of anomalous transparency on the passage of sound from water to air is considered. A mathematical model is used to calculate the coefficient of pressure transmission through the water–air interface taking into account the influence of inhomogeneous plane waves. The features of the acoustic field in air are shown for an underwater source located at a distance from the media interface smaller than the wavelength. The theoretical dependences of the pressure transmission coefficient on the wave distance from the source to the interface are given. The conditions and methods for measuring the coefficient of transmission of spherical waves through a planar interface are described. The experimental dependences of the pressure transmission coefficient on the radiation frequency and depth of the source are presented. Oscillograms of acoustic signals transmitted from water to air are shown. PubDate: 2020-05-01

Abstract: The article describes an experimental facility for studying and testing sound-absorbing linings made of acoustic metamaterials designed to reduce the noise generated by a source in a finite waveguide. The main focus is on the features of acoustic field formation in a waveguide and its emission from the open ends. The article centers on the results of a study of how different facility parameters influence the efficiency of linings. The large influence of the parameter “type of source” on the lining efficiency has been revealed and investigated for the first time. It is rigorously defined, and the physical mechanism of its influence on the efficiency is described. Conditions are formulated under which the efficiency of a sound-absorbing lining measured on the experimental facility will be equal to or close to its efficiency measured on a real object. It is shown that one of the most important conditions is the coincidence of types of acoustic sources used in the facility with a real one. The results obtained are useful in designing efficient sound-absorbing linings, as well as in creating experimental facilities for their development and testing. PubDate: 2020-05-01

Abstract: The noise of the main rotor of a helicopter in hover and horizontal flight modes is numerically simulated. To calculate the acoustic characteristics caused by the nonstationary load on the blades, a software package is used, validated with experimental data in hover mode. A hybrid calculation method is used, according to which the near field is calculated first, followed by the acoustic characteristics in the far field. In the near field, the values of the field parameters near the rotating blade are found by direct solution of the unsteady Euler equations in a noninertial coordinate system. To calculate the far field, the integral Ffowcs Williams–Hawkings method is applied using permeable control surfaces enclosing the blade. PubDate: 2020-05-01

Abstract: For low-frequency multipole sources of various orders in a Pekeris waveguide, we have obtained and studied the dependences that determine the change in the structure and magnitude of interference maxima of the vector–scalar signal components with varying frequencies; waveguide, receiver, and source depths; and distances between them. Approximating expressions are found that, for different waveguide depths and source and receiver locations, are consistent with the exact decay laws of these field components in these zones. It is shown that the dependences of the fields of all multipoles based on the characteristics of the amplitude–phase structure are divided into two large groups. PubDate: 2020-05-01

Abstract: Total radiation force on a spherical levitating object, which is placed between a single axis acoustic levitator, is obtained using finite element simulation. Variation in the total radiation force on the spherical levitating object with respect to the position of the object between the driver and the reflector is studied in resonance as well as non-resonance condition. Simulation results are verified with experimental results available in the literature. Further, a parametric study has been performed on the radius of curvature of driver and reflector. Three different cases have been considered. (1) Curved driver surface with flat reflector surface. (2) Curved reflector surface with flat driver surface. (3) Both driver and reflector having curved surfaces. It is observed that the case with both driver and reflector surfaces being curved results in maximum radiation force on the spherical levitating object. The values of radius of curvature for maximum radiation force for all three cases are also obtained. Total radiation forces for all three cases (with optimum value of radius of curvature) as well as the flat surfaced driver-reflector arrangement are compared. PubDate: 2020-05-01

Abstract: Problems about vibrations of an orthotropic layer with a cylindrical cavity with an arbitrary transverse cross section under the action of a load applied on its surface are considered. In the case of cavities with a small relative size, an asymptotic approach to the calculation of fields is proposed. An estimate of the applicability area of the asymptotic approach in comparison with the method of boundary integral equations, as well as a comparison with the solution obtained based on the Born approximation are presented. PubDate: 2020-05-01

Abstract: A method for analyzing the structural inhomogeneity and optical properties of colloids is experimentally realized. The method uses the dependence of the time profile of the optoacoustic signal excited in the studied medium on the light absorption and extinction coefficients in this medium. As the tested colloid solutions, water- and kerosene-based magnetic fluids with a volume magnetite concentration of 0.35–3.5% were studied. The increase in the extinction coefficient in magnetic fluids by the increase in depth was observed. The relative variation in the extinction coefficient depends on the concentration of magnetite particles, properties of the carrier fluid, and the acoustic boundary type. The relationship between the particle concentration and optical properties of the magnetic fluid allows this method to be used for determining the volume concentration of magnetite in the fluid. PubDate: 2020-05-01

Abstract: — By analyzing references, one can obtain interesting information about the kind of research that is being performed, what approaches exist, information about scientists working in a field of interest, the institutions where such research is being carried out, and journals that reflect this information. Citation issues are discussed in the Akusticheskii Zhurnal articles. An analysis of the cited literature showed that with the advent of the Internet, the depth of citation increased, as did the reduced half-life of articles. Attention is drawn to references to Akusticheskii Zhurnal (hereafter – Acoustics or AJ) itself. An analogy is drawn with the statement of academician V.L. Ginzburg that our scientists do not receive the Nobel Prize “primarily due to their colleagues: Soviet physicists,” who, as it turns out, do not really nominate their compatriots. The same can be attributed to the inadequate impact factor of Acoustics, which is decreased by the authors themselves. The issues of information support in the field of Russian-speaking acoustics are discussed. PubDate: 2020-05-01

Abstract: The concept of a dynamically self-similar structure (dynamic fractal) is introduced, consisting in the similarity of the dynamic parameters of the cell generatrices. Elastic wave propagation in unbranched dynamically self-similar structures is investigated. It is shown that such structures are equivalent in frequency to a periodic structure with additional fixation; however, the nature of wave propagation in them significantly differs. A dynamic fractal can feature both attenuated waves and waves that increase along the length of the structure; the intensity of wave attenuation is stronger than in a periodic structure. PubDate: 2020-05-01

Abstract: The article presents results of numerical simulation and experimental studies of elastic wedge wave propagation in cylindrical wedges with positive and negative curvature in the 100–600 kHz frequency range. It is shown that wedge waves in such structures have dispersion and their localization at the edge of the wedge is stronger than that of straight wedges. The results of a study for cases where the inner surface of the wedge is bounded by fluids with different viscosities (water, SAE 10W-30 motor oil, 86% glycerol aqueous solution) are presented. PubDate: 2020-05-01

Abstract: The main factors affecting the spatial characteristics of surface noise fields are changes in sound speed and sea surface boundary perturbations due to mesoscale ocean phenomena and wind-induced noise, respectively. This study derived the surface noise cross-spectral density sensitivity kernel for sound speed changes and local boundary perturbations and analyzed their effects on cross-spectral density. Numerical results show that the sound speed perturbations of any position in the entire observation plane changes the surface noise cross-spectral density function in surface noise with finite frequency. The cross-spectral density between two receivers in the vertical direction is the most sensitive to the sound speed changes of the region between two receivers. Additionally, the influence depends on the relationship between the wavelength of sound wave and the distance of two receivers. Scattering on the surface boundary perturbation would lead to fluctuations in the cross-spectral density function. When the boundary perturbation along the horizontal direction is distant from two receivers, the cross-spectral density sensitivity kernel for surface scattering oscillates, and the influence of boundary perturbation on the cross-spectral density function gradually weakens. Finally, the period of the cross-spectral density sensitivity kernel oscillations is a half wavelength of the sound wave. PubDate: 2020-05-01

Abstract: The article presents a numerical study of the formation of the amplitude response in a free surface from simultaneous scattering of Rayleigh waves and vertically incident longitudinal waves by an embedded contrast velocity inclusion. It has been established that the significant presence of body waves in a microseismic field does not fundamentally change the result of the microseismic sounding method, which is based on the notion of the overwhelming contribution of the fundamental mode of a Rayleigh wave to the formation of the Earth’s microseismic field. Cases are considered when a microseismic signal at the same frequency is modeled only by the fundamental mode of the Rayleigh wave, only by a vertically incident longitudinal wave, and by both types of waves simultaneously. Variants of inhomogeneities with different dimensions and velocity properties are considered. The analysis was performed in a (λ, r)-space, in analogy with reconstruction of the structure of the geological setting in the microseismic sounding method, where λ is the wavelength of the fundamental Rayleigh mode and r is the coordinate on the Earth’s surface. PubDate: 2020-03-01

Abstract: A method of control for an ordered group of particles that levitate in an ultrasonic field and structures of rectilinear segments is proposed. An ultrasonic field in air at a frequency of 40 kHz and particles whose dimensions are less than a quarter of a wavelength or thin cylindrical objects with diameters of less than a quarter of a wavelength are considered. The ultrasonic field is formed using four phased arrays of radiators that are placed oppositely on lateral faces of a rectangular parallelepiped. The radiators form a distribution of the standing wave field in the plane, which provides levitation of particles in a rectangular grid in a plane layer. With the use of numerical simulation and experimentally, it has been shown that the obtained distribution is stabilized and the particles remain immobile at local minimums of the Gor’kov potential. Moreover, regulation of the phase difference of opposite radiators provides controlled motion of a group of particles in a horizontal plane and a change in the focusing plane of side radiators provides controlled motion of a group of particles along the vertical plane. It has been shown experimentally that not only small particles but also structures assembled of rectilinear segments whose length is much greater than the wavelength can levitate in this field distribution. PubDate: 2020-03-01

Abstract: The authors have carried out a systematic study of the accuracy in the impedance eduction of liners in “interferometer with flow” rigs in the absence of grazing flow. A method is proposed for determining the confidence interval of sound pressure measurements for such a rig. The analytical model of sound propagation in a rectangular duct in the presence of impedance transitions, previously proposed by the authors and described with the Wiener–Hopf method, is experimentally confirmed. A method is developed and implemented for impedance eduction of liners in the absence of flow, based on an analytical method that takes into account the passage of sound modes through the impedance transition. PubDate: 2020-03-01

Abstract: Aiming at the problem of high complexity and poor real-time performance of the traditional minimum variance (MV) algorithm, a low-complexity minimum variance algorithm combined with power method is proposed. Firstly, the echo data is transformed into beam domain by discrete cosine transform and the dimension reduction parameter is determined according to the data of scanning lines. Secondly, the maximum eigenvalue and corresponding eigenvector of sample covariance matrix are obtained by the power method to reduce the complexity of eigenvalue decomposition. Finally, by ignoring low-energy echo signal, the inversion of covariance matrix can be simplified to construct a new weighted vector, which can reduce the complexity of MV. The Field II simulation results show that the proposed algorithm has better resolution, contrast ratio and efficiency than the traditional MV algorithm, and outperforms the minimum variance algorithm based on eigenvalue decomposition (ESBMV) in resolution and efficiency. PubDate: 2020-03-01