Authors:T. I. Belyankova; V. V. Kalinchuk Pages: 245 - 259 Abstract: Characteristic features of wave field formation caused by a surface source of harmonic vibration in a prestressed functionally graded layer are investigated. It is assumed that the elastic moduli and the density of the material vary with depth according to arbitrary laws. The initial material of the medium is represented by a model hyperelastic material with third-order elastic moduli. The boundary-value problem for a set of Lamè equations is reduced to a set of Cauchy problems with initial conditions, which is solved by the Runge–Kutta–Merson method modified to fit the specific problem under study. Considering shear vibrations of a functionally graded layer as an example, effects of the type of its inhomogeneity, variations in its properties, and nature of its initial stressed state on the displacement distribution in depth are investigated. Special attention is paid to characteristic features of displacement localization in a layer with an interface-type inclusion near critical frequencies. A direct relation between the inhomogeneous layer structure and the type of displacement localization in depth is demonstrated. It is found that the role of initial stresses and variations in material parameters considerably increases in the vicinities of critical frequencies. PubDate: 2017-05-01 DOI: 10.1134/s1063771017030046 Issue No:Vol. 63, No. 3 (2017)

Authors:S. N. Gurbatov; M. S. Derybin; D. A. Kas’yanov; V. V. Kurin Pages: 260 - 269 Abstract: The paper considers the degenerate parametric interaction of an intense acoustic pumping beam and a weak signal beam at the subharmonic. The use of a special emitter system with independent signal emission at the harmonic and subharmonic made it possible to study the features of nonlinear interaction both for different amplitude levels and arbitrary phase relations of the fields at these frequencies. Just as predicted in the theory, the experiment showed that signal amplification at the subharmonic hardly occurs at all. It is shown that the use of odd field harmonics, which are absent for a zero amplitude of the signal wave, makes it possible to substantially increase the efficiency of isolating a weak signal wave. The interaction of beams for large and small acoustic Reynolds numbers of the signal wave is studied. PubDate: 2017-05-01 DOI: 10.1134/s1063771017020063 Issue No:Vol. 63, No. 3 (2017)

Authors:S. G. Mikhailov; O. V. Rudenko Pages: 270 - 274 Abstract: We study experimentally the behavior of a nonlinear element, a light plate pressed to the opening in the cavity of an acoustic resonator. Measurements of field oscillations inside and outside the cavity have shown that for large amplitudes, they become essentially anharmonic. The time dependences of displacement of the plate with increasing amplitude of the exciting voltage demonstrates a gradual change in the shape of vibrations from harmonic to half-period oscillation. A constant component appears in the cavity: rarefaction or outflow of the medium through the orifice. We construct a theory for nonlinear oscillations of a plate taking into account its different elastic reactions to compression and rarefaction with allowance for monopole radiation by the small-wave-size plate or radiation of a plane wave by the plate. We calculate the amplitudes of the harmonics and solve the problem of low-frequency stationary noise acting on the plate. We obtain expressions for the correlation function and mean power at the output given a normal random process at the input. PubDate: 2017-05-01 DOI: 10.1134/s1063771017030101 Issue No:Vol. 63, No. 3 (2017)

Authors:V. I. Babii Pages: 275 - 287 Abstract: Decentralization of the standards base in measuring the speed of sound in liquids by expressing the speed of sound in fractions of the speed of light in vacuum is considered. A method to take into account the diffraction effects by measuring the speed of sound in the case of a constant acoustic wavelength and binding the absolute speed of sound values to the calculated thermodynamic values obtained by the nonacoustical method when the adiabatic compressibility is equal to the isothermal one is proposed. Errors of the reproducibility of the unit of the speed of sound in water using the proposed method are estimated. PubDate: 2017-05-01 DOI: 10.1134/s1063771017030034 Issue No:Vol. 63, No. 3 (2017)

Authors:A. A. Karabutov; N. B. Podymova Pages: 288 - 296 Abstract: The influence of the volumetric porosity of isotropic metal-matrix composite materials, which are reinforced with ceramic microparticles, on the dispersion of the phase velocity of longitudinal acoustic waves is investigated. For this purpose, the method of broadband acoustic spectroscopy with a laser source of ultrasound and piezoelectric detection of nanosecond ultrasonic pulses is used. Composite samples based on a silumin matrix with added silicon carbide (SiC) microparticles in different mass concentrations (3.8–15.5%) were investigated. As the concentration of SiC particles in a sample increases, its porosity that is determined using the hydrostatic-weighing method also increases. The simultaneous increase in the filler concentration and porosity leads to the appearance of a dispersion of the phase velocity of longitudinal acoustic waves in the sample within the frequency range of 3–25 MHz. The obtained empirical relationship between the relative change in the phase velocity and the sample porosity can be used to obtain a proximate quantitative estimate of the bulk porosity of the isotropic metal-matrix composite materials. PubDate: 2017-05-01 DOI: 10.1134/s106377101703006x Issue No:Vol. 63, No. 3 (2017)

Authors:Kapil Dev Tyagi; Arun Kumar; Rajendar Bahl; Karmjeet Singh Pages: 297 - 301 Abstract: This paper presents the results of field experiments done for the measurement of attenuation constant and speed of sound in the snow medium. The field experiments were conducted at two locations corresponding to relatively dry and wet snow. The main objective of our method is to overcome the potential limitations of the other methods. There are two major concerns: one is sound signal leakage and the other is the measurement need to be done within a same layer of snowpack. The ref lections from the boundaries will affect the measurements. In our experiments the transducers are kept far from the snowpack boundaries, so that there will be no likelihood of strong ref lected signals from the boundaries. These issues have not been addressed by the other researchers. This work adds to the measurement results of the attenuation constant and speed of sound in snow that are available in the research literature. It is found that sound signal attenuation greatly depends on the frequency of sound signal and wetness of snow. PubDate: 2017-05-01 DOI: 10.1134/s1063771017030113 Issue No:Vol. 63, No. 3 (2017)

Authors:I. V. Bobrovskii; M. S. Rybina; V. D. Melent’ev; V. P. Yagotinets Pages: 302 - 308 Abstract: The paper presents the results of experimental research on a multichannel underwater acoustic communications system that increases the digital information rate by aggregate frequency signals under deepsea conditions with multipath signal propagation. Quantitative estimates of information reception quality under various types of interference are given. PubDate: 2017-05-01 DOI: 10.1134/s1063771017030058 Issue No:Vol. 63, No. 3 (2017)

Authors:O. A. Godin; B. G. Katsnelson; Jixing Qin; M. G. Brown; N. A. Zabotin; Xiaoqin Zang Pages: 309 - 320 Abstract: This paper investigates a novel approach to processing records of ambient noise in the ocean that are measured concurrently in spatially separated locations. The approach is a synthesis of two well-known phase-coherent signal processing techniques. At the first stage of processing, an approximation to the transient acoustic Green function is found by the method of noise interferometry. At the second stage, the approximate Green function is time reversed and back propagated from the location of one of the receivers, thereby producing a focus in the vicinity of the other receiver. Unlike the earlier work, measurements at just two points (rather than vertical array measurements) are used when the sound-propagation range is large compared to the ocean depth. The requirement for optimal focusing of the back-propagated field is shown to lead to extraction of estimates of the unknown physical parameters of the waveguide and, hence, to passive acoustic remote sensing of the ocean. PubDate: 2017-05-01 DOI: 10.1134/s1063771017020038 Issue No:Vol. 63, No. 3 (2017)

Authors:G. N. Kuznetsov; A. N. Stepanov Pages: 321 - 330 Abstract: We study the applicability of the reciprocity principles in an underwater waveguide for the vector-scalar fields of multipole sources. We show analytically and numerically that multipole sources are divided into two groups according to this principle: in the first group, the sound pressure field and the horizontal projections of the vibration velocity vectors satisfy the reciprocity principle, while the vertical projections of these vectors do not. In the second group, the pressure and the horizontal projections of the vibration velocity vector do not satisfy the reciprocity principle, while their vertical projections do. We establish that the phase gradients and angles of arrival of signals in the vertical plane do not satisfy the reciprocity principle for the vector-scalar fields of volumetric sources with arbitrary directivity in the vertical plane. PubDate: 2017-05-01 DOI: 10.1134/s1063771017030083 Issue No:Vol. 63, No. 3 (2017)

Authors:A. I. Mashoshin Pages: 331 - 337 Abstract: Using theoretical analysis and mathematical modeling, we study the dependence of the number of maxima in the correlation function of a wideband signal, whose parameters are related to the source coordinates, on the hydroacoustic conditions, the parameters of the receiver, and the signal/noise ratio. PubDate: 2017-05-01 DOI: 10.1134/s1063771017030095 Issue No:Vol. 63, No. 3 (2017)

Authors:B. M. Salin; O. N. Kemarskaya; P. A. Molchanov; M. B. Salin Pages: 338 - 345 Abstract: The paper considers the problem of backscattering of sound waves by near-surface volumetric inhomogeneities under conditions of intense wind waves. We calculate the expected share of the scattered signal spectrum based on the given wind-wave intensity and the depth distribution of volumetric inhomogeneities. For deep ocean conditions in the frequency range of 500–1000 Hz for a pulse duration of 10 s, we measure the levels and shape of the reverberation spectrum for time delays from 20 to 100 s. Comparison of the measured and calculated reverberation spectra has shown their good coincidence. PubDate: 2017-05-01 DOI: 10.1134/s1063771017020105 Issue No:Vol. 63, No. 3 (2017)

Authors:V. S. Averbakh; V. V. Bredikhin; A. V. Lebedev; S. A. Manakov Pages: 346 - 358 Abstract: The paper presents the results of experimental research into the nonlinear acoustic properties of carbonate rocks depending on saturation. The linear acoustic properties of the same sample depending on saturation were presented earlier in Physical Acoustics. The previously obtained data point to the isotropy of the material, which makes it possible to restrict analysis to only two vibration modes. Responses for finite deformations were measured for the longitudinal and shear modes of an isotropic sample, which made it possible to analyze the nonlinear properties of macroscopic deformations with a change in volume and pure displacement. A heretofore unknown feature of the response was revealed for finite deformation values; it is related to the occurrence of a jumplike transition from classical nonlinearity to a hysteresis type of nonlinearity. As well, the deformation amplitude corresponding to the transition depends on fluid saturation. We studied the slow relaxation that occurs after long-term excitation of a sample with a deformation amplitude on the order of 10−6. Data are presented on relaxation for deformation from pure displacement and deformation with a change in volume, which made it possible to isolate features related to the type of deformation and to compare the obtained data with the earlier published theoretical model. These data are compared with the results of other research groups. PubDate: 2017-05-01 DOI: 10.1134/s1063771017030022 Issue No:Vol. 63, No. 3 (2017)

Authors:Shi-da Xu; Yuan-hui Li; Jian-po Liu Pages: 359 - 367 Abstract: An acoustic emission (AE) testing of rock cracking was performed under uniaxial loading conditions by precut varisized circular holes in selected brittle granites. Based on AE-source location technique and AE-theory for moment tensor analysis, rules of the temporal–spatial evolution of micro-cracks in different failure mechanisms were explored and types of micro-cracks were analyzed as well. The results revealed that the micro-cracks are uniquely easy to generate in the positions where stress are concentrated. Tensile fractures are easy to form on the roof and floor of a circular hole, while shear fractures are easy to be found on both sides. The locations of initial cracks generated around the holes in the loading process are the direction or vertical direction of maximum principle stress. Macroscopic crack orientation agrees with the direction of maximum principle stress approximately. As the size of circular opening increases and the relative size of pillar decreases, shear cracks are dominant with the percentage more than 45%, tension cracks are fewer, accounted for less than 40% of the total events, and mixed-mode cracks represent a minimum proportion, despite the decrease of percentage of shear cracks. The findings of this work can serve for supporting design of tunnel or roadway to avoid collapse. PubDate: 2017-05-01 DOI: 10.1134/s1063771017030137 Issue No:Vol. 63, No. 3 (2017)

Authors:I. V. Andronov Pages: 133 - 140 Abstract: High-frequency diffraction of a plane acoustic wave incident at a small angle to the axis of a narrow hyperboloid of revolution is considered. By the parabolic equation method in spheroidal coordinates, the leading term of field asymptotics in the near-surface boundary layer is constructed in the form of an integral involving Whittaker functions. Difficulties associated with its calculation are considered. Results obtained for the field at the surface of a perfectly rigid hyperboloid are presented. They reproduce the predicted high-frequency diffraction effects. PubDate: 2017-03-01 DOI: 10.1134/s1063771017010018 Issue No:Vol. 63, No. 2 (2017)

Authors:A. V. Bochkarev; A. I. Zemlyanukhin; L. I. Mogilevich Pages: 148 - 153 Abstract: A new generalized sixth-order nonintegrable equation is derived to model axisymmetric longitudinal wave propagation in an inhomogeneous cylindrical shell interacting with a nonlinear elastic medium. Exact soliton-like solutions to this equation are constructed with allowance for geometric and physical nonlinearities, both individually and in combination. PubDate: 2017-03-01 DOI: 10.1134/s1063771017020026 Issue No:Vol. 63, No. 2 (2017)

Authors:Gaurav Sharma; Sushil Kumar; Vivek Singh Pages: 159 - 167 Abstract: The potentiality of a phoxonic crystal for sensing of biodiesel in a binary mixture of diesel and biodiesel is theoretically investigated. Using the transfer matrix method, the transmission of acoustic and optical waves through a periodic one-dimensional crystal of Si–SiO2 layers is studied. A pass band is created in the band gap region by introducing a cavity in the considered one-dimensional crystal structure. This pass band can also be considered as a defect mode, and it is found that its position is highly dependent on mole concentration of binary mixture of biodiesel and diesel present in the cavity. The sensitivity of the sensor for a binary mixture of biodiesel and diesel in the cavity with various mole concentrations is estimated. Simulated results provide a valuable guidance for designing a phoxonic crystal sensor consisting of a defect layer. PubDate: 2017-03-01 DOI: 10.1134/s1063771017020117 Issue No:Vol. 63, No. 2 (2017)

Authors:A. E. Isaev; A. S. Nikolaenko; I. V. Chernikov Pages: 175 - 184 Abstract: The paper considers a method for suppressing the reverberant distortions of an underwater sound receiver signal during receiver calibration in a laboratory water tank. The method is based on using the water tank transfer function, which is a complex frequency-dependent coefficient that establishes, for the point of signal reception, the relation between the sound pressures in the reverberant sound field of the water tank and in the free sound field. The procedure for experimentally obtaining the water tank transfer function is considered. Examples of suppressing reverberant distortions during noise and pulse sound reception are presented. PubDate: 2017-03-01 DOI: 10.1134/s1063771017020075 Issue No:Vol. 63, No. 2 (2017)

Authors:N. P. Mel’nikov; V. P. Elistratov Pages: 196 - 203 Abstract: The paper presents the spatial variability of cavitation thresholds and some hydrological and hydrochemical parameters of seawater in the interfrontal zone of the Pacific Subarctic Front, in the Drake Passage, and in the equatorial part of the Pacific Ocean, measured in the near-surface layer to a depth of 70 m. PubDate: 2017-03-01 DOI: 10.1134/s1063771017010092 Issue No:Vol. 63, No. 2 (2017)

Authors:Jiake Li; Xiaodong Chen; Yi Wang; Yifeng Shi; Daoyin Yu Pages: 229 - 236 Abstract: A generalized sidelobe canceler (GSC) approach is proposed for medical ultrasound imaging. The approach uses a set of adaptive weights instead of traditional non-adaptive weights, thus suppressing the interference and noise signal of echo data. In order to verify the validity of the proposed approach, Field II is applied to obtain the echo data of synthetic aperture (SA) for 13 scattering points and circular cysts. The performance of GSC is compared with SA using boxcar weights and Hamming weights, and is quantified by the full width at half maximum (FWHM) and peak signal-to-noise ratio (PSNR). Imaging of scattering point utilizing SA, SA (hamming), GSC provides FWHMs of 1.13411, 1.68910, 0.36195 mm and PSNRs of 60.65, 57.51, 66.72 dB, respectively. The simulation results of circular cyst also show that GSC can perform better lateral resolution than non-adaptive beamformers. Finally, an experiment is conducted on the basis of actual echo data of an ultrasound system, the imaging result after SA, SA (hamming), GSC provides PWHMs of 2.55778, 3.66776, 1.01346 mm at z = 75.6 mm, and 2.65430, 3.76428, 1.27889 mm at z = 77.3 mm, respectively. PubDate: 2017-03-01 DOI: 10.1134/s1063771017020087 Issue No:Vol. 63, No. 2 (2017)

Authors:V. N. Kostin; D. Yu. Filatenkov; Yu. A. Chekasina; O. N. Vasilenko; E. D. Serbin Pages: 237 - 244 Abstract: We study how the conditions of excitation and detection influence the magnetoacoustic emission (MAE) parameters of ferromagnets. For a large group of metal ferromagnet samples differing in physical properties and dimensions, the dependence of the MAE amplitude on the frequency of the remagnetizing field has a similar nonmonotonic character. In all probed cases, the maximum of the amplitude corresponds to a field frequency of 3–5 Hz. The decrease in the MAE amplitude for a subsequent increase in the frequency of the alternating field is related to the action of eddy currents. It is shown that the size of the field corresponding to the MAE maximum, which for a given time dependence of the remagnetizing field can be determined by the time shift in an oscillogram, can be a new parameter of the structuroscopy of ferromagnets. PubDate: 2017-03-01 DOI: 10.1134/s1063771017010055 Issue No:Vol. 63, No. 2 (2017)