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. Zemlyanukhin; A. V. Bochkarev Pages: 408 - 414 Abstract: A quasi-hyperbolic equation is derived that simulates the axisymmetric propagation of bending waves in a cylindrical shell, which interacts with a nonlinearly elastic medium. With the correct asymptotic procedure, the study of a wave process reduces to analysis of a nonlinear Schrödinger equation. It is established that the development of modulation instability requires a “soft” nonlinearity of the medium surrounding the shell. Operating modes that allow the propagation of stable light envelope solitons are revealed. PubDate: 2018-07-01 DOI: 10.1134/s1063771018040139 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:O. V. Rudenko; C. M. Hedberg Pages: 422 - 431 Abstract: The phenomenon of “wave resonance” which occurs at excitation of traveling waves in dissipative media possessing modular, quadratic and quadratically-cubic nonlinearities is studied. The mathematical model of this phenomenon is the inhomogeneous (or “forced”) equation of Burgers type. Such nonlinearities are of interest because the corresponding equations admit exact linearization and describe real physical objects. The presence of “accompanying sources” (traveling with the wave) on the right-hand side of the inhomogeneous equations ensures the inflow of energy into the wave, which thereafter spreads throughout the wave profile, flows to emerging shock fronts, and then dissipates due to linear and nonlinear losses. As an introduction, the phenomenon of wave resonance in ideal and dissipative media is described and physical examples are given. Exact expressions for nonlinear steady-state wave profiles are derived. Non-stationary processes of wave generation, spatial “beating” of amplitudes with different relationship between the speed of motion of the sources and the natural wave velocity in the medium are studied. Resonance curves are constructed that contain a nonlinear shift of the absolute maxima to the “supersonic” region. The features of the resonance in each of the three types of nonlinearity are discussed. PubDate: 2018-07-01 DOI: 10.1134/s1063771018040127 Issue No:Vol. 64, No. 4 (2018)

Authors:S. N. Antonov Pages: 432 - 436 Abstract: A new acousto-optic deflector with a wide angular scanning range and a high diffraction efficiency has been studied. The device uses an additional deflector, which allows the angle of incidence of the input beam to be adjusted in order to fulfill the Bragg phase–matching condition over the entire scanning range of the main deflector. The characteristics of an anisotropic two-crystal deflector based on paratellurite crystals have been measured. It has been established experimentally that the operating bandwidth of the device is 32 MHz for a diffraction coefficient no less than 90%, which determines a light beam scanning angle of 50 mrad. PubDate: 2018-07-01 DOI: 10.1134/s1063771018040012 Issue No:Vol. 64, No. 4 (2018)

Authors:O. P. Bychkov; G. A. Faranosov Pages: 437 - 452 Abstract: The use of high-bypass-ratio engines in civil aviation has resulted in the occurrence of an additional noise source associated with noise of interaction between a jet and an airplane wing. A theoretical model is proposed for predicting the characteristics of interaction noise based on the near-field parameters for an isolated jet. The required near-field characteristics were obtained experimentally in the AC-2 anechoic chamber of the Central Aerohydrodynamic Institute (TsAGI) using a system of azimuthal microphone arrays. Noise in the far-field zone was also measured for both an isolated jet and a jet with a closely located plate simulating a wing. The results of comparing the directivities and spectra of interaction noise obtained using the proposed model and measured experimentally are in good agreement. PubDate: 2018-07-01 DOI: 10.1134/s1063771018030041 Issue No:Vol. 64, No. 4 (2018)

Authors:H. X. Li; C. H. Tao; G. Goloshubin; C. Liu; S. H. Shi; G. N. Huang; H. Zhang; J. Zhang; X. F. Zhang Pages: 453 - 458 Abstract: A modified Biot/Squirt flow model was developed. The difference between MBISQ and BISQ models is the expression for the porosity differential. Numerical analysis shows that the acoustic dispersion predicted by MBISQ is much higher than by BISQ. Investigations of the effects of permeability, viscosity, and squirt flow length on velocity and attenuation indicate that the behavior of MBISQ agrees with that of the BISQ model. The result of sediment acoustic inversion based on MBISQ was more reasonable than the result of BISQ model. PubDate: 2018-07-01 DOI: 10.1134/s1063771018040061 Issue No:Vol. 64, No. 4 (2018)

Authors:V. A. Zverev Pages: 459 - 471 Abstract: Recent processing of earlier obtained experimental data has revealed two phenomena making it possible to obtain necessary and sufficient conditions for detecting a forward scattering signal with the best efficiency. The location object should intersect one of the rays connecting the emitter and the receiver without touching the water surface. This is the basis of the first phenomenon: significant (more than 100-fold) compression of the detected signal. The second phenomenon is that the noise background surrounding the detected signal is a type of noise formed by an uneven bottom relief. This noise does not generate false alarms and is physically similar to speckle noise in optics. It is demonstrated that additive noise is primarily formed by signals scattered by a rough lake surface and that this noise is weakly suppressed when detecting the useful signal; however, it can be eliminated by imparting directivity to the illuminating signal source. All other noise is completely suppressed. PubDate: 2018-07-01 DOI: 10.1134/s1063771018040140 Issue No:Vol. 64, No. 4 (2018)

Authors:Yu. V. Petukhov; V. G. Burdukovskaya Pages: 472 - 478 Abstract: We consider the patterns manifested during the formation of the spatial intensity distribution of an acoustic field excited by a vertical array in a deep-water oceanic waveguide with an underwater sound channel open to the surface and an acoustically transparent bottom. The study focuses on the dependence of the spatial divergence of multimode beams on the angle of compensation of an array emitting a tone signal. It is established that if the size of the array aperture significantly exceeds the optimal size, then at a certain angle of compensation appreciably differing from zero, a multimode beam forms with minimal diffraction divergence even in the absence of bending points and smooth extrema of the dependence of the length of the ray cycle on the ray parameter. PubDate: 2018-07-01 DOI: 10.1134/s1063771018040103 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)

Authors:A. A. Abdrashitov; E. A. Marfin; D. V. Chachkov; V. M. Chefanov Pages: 492 - 502 Abstract: An experimental study of the generation of pressure fluctuations in a well acoustic emitter with nozzles of various shapes has been carried out. The effect of a smooth nozzle inlet section on the generation amplitude, the optimum jet length, and the outlet diameter has been studied. The formation of a region of reverse currents connecting to the cavity in the nozzle between the channel wall and the jet periphery has been considered. A significant increase in the generation amplitude produced at the smooth nozzle inlet and the formation of a uniform velocity profile in the nozzle channel have been observed. PubDate: 2018-07-01 DOI: 10.1134/s1063771018030016 Issue No:Vol. 64, No. 4 (2018)

Authors:V. F. Kopiev; I. V. Khramtsov; M. Yu. Zaytsev; E. S. Cherenkova; O. Yu. Kustov; V. V. Palchikovskiy Pages: 503 - 510 Abstract: A technique for studying the aeroacoustic parameters of vortex rings with various diameters in an anechoic chamber is developed. The motion trajectories of vortex rings produced by a piston generator with nozzles with various exit diameters are studied. Spectral analysis of the noise of vortex rings for various distances from nozzles with various diameters is carried out. For the first time, the dependences of the fundamental radiation frequency on the time of a ring’s motion are obtained in dimensionless form. The data on noise from turbulent vortex rings confirm the conclusion that sound from rings with different diameters and velocities is emitted by the same mechanism. PubDate: 2018-07-01 DOI: 10.1134/s1063771018040097 Issue No:Vol. 64, No. 4 (2018)

Authors:I. V. Khramtsov; O. Yu. Kustov; E. S. Fedotov; A. A. Siner Pages: 511 - 517 Abstract: Numerical simulation of acoustic processes with an interferometer at high acoustic pressure levels is one of the ways to noise reduction processes using samples of sound-absorbing structures (SAS). In the course of research, an SAS sample consisting of a single Helmholtz resonator of circular shape was used. Studies were conducted at sound pressure levels of 110, 130, 140, and 150 dB. Results obtained with the interferometer with normal wave incidence were taken as a basis. In the calculations, systems of linearized and complete Navier–Stokes equations were used. The results obtained with the linearized Navier–Stokes equations make it possible to determine the acoustic characteristics of the sample for linear modes of operation with sufficient accuracy. The complete system of Navier–Stokes equations, taking into account compressibility, allowed good qualitative and quantitative agreement with the experiment at high acoustic pressure levels. PubDate: 2018-07-01 DOI: 10.1134/s1063771018040073 Issue No:Vol. 64, No. 4 (2018)

Abstract: The paper studies the dependence of the potential noise immunity of a detection system and noise immunity of a detection system with an interference compensator on the array parameters, angular signal position and local noise, the degree of correlation of distributed noise and spectral densities of the signal power, noise, and interference. The gain in noise immunity of the detection system when the optimal spatial filter is used with respect to the use of an interference compensator is estimated as a function of the degree of correlation of distributed noise and the power of random amplitude–phase errors of the weight coefficients of the array. PubDate: 2018-05-01 DOI: 10.1134/S1063771018030089

Abstract: Sound propagation in monodisperse emulsions with arbitrary volume concentrations is studied theoretically using a cell model. It is assumed that emulsion cells are bounded by thin and imponderable rigid shells allowing realization of the minimum energy dissipation principle with viscous acoustic losses. Solutions covering many particular cases and wide parameter and variable ranges have been obtained. These solutions are suitable for studying acoustic properties of emulsions and suspensions, marine sediments, fogs, and smoke, as well as elastoviscous materials with solid or liquid inclusions, etc. Sound propagation and absorption in emulsions and suspensions are considered in more detail. The experimental data in the literature is compared. PubDate: 2018-05-01 DOI: 10.1134/S1063771018030090

Abstract: We present the methods and results of numerical experiments studying the low-frequency sound propagation in one of the areas of the Arctic shelf with a randomly inhomogeneous gas-saturated bottom. The characteristics of the upper layer of bottom sedimentary rocks (sediments) used in calculations were obtained during a 3D seismic survey and trial drilling of the seafloor. We demonstrate the possibilities of substituting in numerical simulation a real bottom with a fluid homogeneous half-space where the effective value of the sound speed is equal to the average sound speed in the bottom, with averaging along the sound propagation path to a sediment depth of 0.6 wavelength in the bottom. An original technique is proposed for estimating the sound speed propagation in an upper inhomogeneous sediment layer. The technique is based on measurements of acoustic wave attenuation in water during waveguide propagation. PubDate: 2018-05-01 DOI: 10.1134/S1063771018030053

Abstract: A mathematical model is proposed for a Kirchhoff–Love-type nonlinear elastic cylindrical shell surrounded by an elastic medium and containing a viscous incompressible liquid. The model is used to analyze wave processes both analytically and numerically. On the basis of the proposed computational algorithm, a software package is developed, which makes it possible to plot diagrams and to obtain numerical solutions to Cauchy problems with initial conditions taken in the form of exact solutions to dynamic equations of shells in the absence of the liquid. PubDate: 2018-05-01 DOI: 10.1134/S106377101803003X

Abstract: Nonlinear evolution of a standing acoustic wave in a spherical resonator with a perfectly soft surface is analyzed. Quadratic approximation of nonlinear acoustics is used to analyze oscillations in the resonator by the slowly varying amplitude method for the standing wave harmonics and slowly varying profile method for the standing wave profile. It is demonstrated that nonlinear effects may lead to considerable increase in peak pressure at the center of the resonator. The proposed theoretical model is used to analyze the acoustic field in liquid drops of an acoustic fountain. It is shown that, as a result of nonlinear evolution, the peak negative pressure may exceed the mechanical strength of the liquid, which may account for the explosive instability of drops observed in experiments. PubDate: 2018-05-01 DOI: 10.1134/S1063771018030144

Abstract: The paper considers active wave processes in changes in the lumina of cylindrical hollow organs. A mathematical model is proposed for autowave transport of the internal contents of an organ based on mechanochemical interactions. The self-organization of changes in the shapes of organs are discussed in application to lymphatic vessels of living organisms. PubDate: 2018-05-01 DOI: 10.1134/S1063771018030107