Authors:A. F. Sobolev; M. A. Yakovets Pages: 625 - 636 Abstract: Exact solutions to problems of the propagation of acoustic modes in lined channels with an impedance jump in the presence of a uniform flow are constructed. Two problems that can be solved by the Wiener- Hopf method—the propagation of acoustic modes in an infinite cylindrical channel with a transverse impedance jump and the propagation of acoustic modes in a rectangular channel with an impedance jump on one of its walls—are considered. On the channel walls, the Ingard–Myers boundary conditions are imposed and, as an additional boundary condition in the vicinity of the junction of the linings, the condition expressing the finiteness of the acoustic energy. Analytical expressions for the amplitudes of the transmitted and reflected fields are obtained. PubDate: 2017-11-01 DOI: 10.1134/s1063771017060148 Issue No:Vol. 63, No. 6 (2017)

Authors:L. N. Magdich; V. I. Balakshy; S. N. Mantsevich Pages: 645 - 651 Abstract: The effect of the electronic tuning of the acoustic resonances in an acousto-optic mode-locking device of a laser is investigated theoretically and experimentally. The problem of the excitation of a Fabry–Perot acoustic resonator by a plate-like piezoelectric transducer (PET) is solved in the approximation of plane acoustic waves taking into consideration the actual parameters of an RF generator and the elements for matching the PET to the generator. Resonances are tuned by changing the matching inductance that was connected in parallel to the transducer of the acousto-optic cell. The cell used in the experiment was manufactured from fused silica and included a lithium niobate PET. Changes in the matching inductance in the range of 0.025 to 0.2 μH provided the acoustic-resonance frequency tuning by 0.19 MHz, which exceeds the acoustic- resonance half-width. PubDate: 2017-11-01 DOI: 10.1134/s1063771017060094 Issue No:Vol. 63, No. 6 (2017)

Authors:A. I. Belov; G. N. Kuznetsov Pages: 652 - 659 Abstract: The paper presents the results of an experimental study of spatial attenuation of low-frequency vector-scalar sound fields in shallow water. The experiments employed a towed pneumatic cannon and spatially separated four-component vector-scalar receiver modules. Narrowband analysis of received signals made it possible to estimate the attenuation coefficients of the first three modes in the frequency of range of 26–182 Hz and calculate the frequency dependences of the sound absorption coefficients in the upper part of bottom sediments. We analyze the experimental and calculated (using acoustic calibration of the waveguide) laws of the drop in sound pressure and orthogonal vector projections of the oscillation velocity. It is shown that the vertical projection of the oscillation velocity vector decreases significantly faster than the sound pressure field. PubDate: 2017-11-01 DOI: 10.1134/s1063771017050037 Issue No:Vol. 63, No. 6 (2017)

Authors:G. N. Kuznetsov; A. N. Stepanov Pages: 660 - 672 Abstract: We obtain, and compare with exact solutions, the approximate analytic relations that determine, for increasing distance, irregularities of attenuation in the regular sound pressure components and orthogonal projections of the oscillation velocity vectors of low-frequency signals formed in a waveguide by various multipoles. We show that the mentioned field characteristics essentially depend on the type of multipole, the distance between the source and receivers, and the specific features of the received scalar or vector field components. It is established that the approximating dependences agree well with the exact laws of attenuation in the field and, despite the variety of dependences, they are divided into three compact groups with uniform characteristics. PubDate: 2017-11-01 DOI: 10.1134/s1063771017060082 Issue No:Vol. 63, No. 6 (2017)

Authors:V. F. Kopiev; M. Yu. Zaytsev; V. I. Vorontsov; S. A. Karabasov; V. A. Anikin Pages: 686 - 698 Abstract: The aeroacoustic characteristics of a helicopter rotor are calculated by a new method, to assess its applicability in assessing rotor performance in hovering. Direct solution of the Euler equations in a noninertial coordinate system is used to calculate the near-field flow around the spinning rotor. The far-field noise field is calculated by the Ffowcs Williams–Hawkings (FW–H) method using permeable control surfaces that include the blade. For a multiblade rotor, the signal obtained is duplicated and shifted in phase for each successive blade. By that means, the spectral characteristics of the far-field noise may be obtained. To determine the integral aerodynamic characteristics of the rotor, software is written to calculate the thrust and torque characteristics from the near-field flow solution. The results of numerical simulation are compared with experimental acoustic and aerodynamic data for a large-scale model of a helicopter main rotor in an open test facility. Two- and four-blade configurations of the rotor are considered, in different hover conditions. The proposed method satisfactorily predicts the aerodynamic characteristics of the blades in such conditions and gives good estimates for the first harmonics of the noise. That permits the practical use of the proposed method, not only for hovering but also for forward flight. PubDate: 2017-11-01 DOI: 10.1134/s1063771017060070 Issue No:Vol. 63, No. 6 (2017)

Authors:Liu Yang; Jun Huang; Mingxu Yi; Chaopu Zhang; Qian Xiao Pages: 699 - 710 Abstract: A numerical study of a high efficiency propeller in the aerodynamic noise generation is carried out. Based on RANS, three-dimensional numerical simulation is performed to obtain the aerodynamic performance of the propeller. The result of the aerodynamic analysis is given as input of the acoustic calculation. The sound is calculated using the Farassat 1A, which is derived from Ffowcs Williams–Hawkings equation, and compared with the data of wind tunnel. The propeller is modified for noise reduction by changing its geometrical parameters such as diameter, chord width and pitch angle. The trend of variation between aerodynamic analysis data and acoustic calculation result are compared and discussed for different modification tasks. Meaningful conclusions are drawn on the noise reduction of propeller. PubDate: 2017-11-01 DOI: 10.1134/s1063771017060033 Issue No:Vol. 63, No. 6 (2017)

Authors:A. N. Rybyanets; A. V. Nasedkin; S. A. Shcherbinin; E. I. Petrova; N. A. Shvetsova; I. A. Shvetsov; M. A. Lugovaya Pages: 737 - 743 Abstract: Through the developed technique, the finite-element optimization and the experimental validation of the construction and parameters of low-frequency bimorph piezoelectric transducers designed for the diagnostics and activation of oil wells are carried out. PubDate: 2017-11-01 DOI: 10.1134/s1063771017060124 Issue No:Vol. 63, No. 6 (2017)

Authors:G. T. Adamashvili Pages: 517 - 523 Abstract: A theory of acoustic self-induced transparency of a two-component vector soliton for a generalized Love wave is constructed. The three-layer system contains a resonance transition layer with paramagnetic impurity atoms or quantum dots. It is shown that, under these conditions, a vector soliton of the generalized Love wave can be formed. It oscillates at the sum and difference frequencies in the vicinity of the carrier wave frequency. Explicit analytical expressions for the parameters of a nonlinear surface acoustic wave are presented. The parameters depend on the elastic properties of the contacting media, the resonance transition layer, and the transverse structure of the wave. Numerical calculations are carried out for the three-layer Al2O3/ZnO/SiO2 system. The significant difference between the two-component vector soliton and singlecomponent soliton is shown. PubDate: 2017-09-01 DOI: 10.1134/s1063771017050013 Issue No:Vol. 63, No. 5 (2017)

Authors:A. A. Eremin; E. V. Glushkov; N. V. Glushkova; R. Lammering Pages: 562 - 569 Abstract: Theoretical and practical aspects of applying time reversal of elastic waves to localize a source of oscillations or a defect are considered in problems of active ultrasonic monitoring of thin-walled metal structures. Backward reradiation of a time-reversed signal is implemented using a computer model based on a semianalytical integral approach. The proposed algorithm is verified experimentally on aluminum samples excited by piezoelectric wafer active sensors. The results corroborate the possibility of reliably determining of the position and size of the load application region and a local inhomogeneity with a relatively small number of signal measurement points on the sample surface. PubDate: 2017-09-01 DOI: 10.1134/s1063771017050050 Issue No:Vol. 63, No. 5 (2017)

Authors:A. G. Petrov; S. Z. Shkundin Pages: 604 - 609 Abstract: The derivation of a formula for the time during which a sound signal propagates between two given points A and B in a stationary gas flow is considered. It is shown that the gas flow changes the signal reception time by a quantity proportional to the consumption, regardless of the detailed velocity profile. The difference between the reception time of signals from point B to the point A and vice versa is proportional to air consumption with high accuracy. It is shown that the relative error of the obtained formula does not exceed the squared maximum Mach number in the gas flow. This allows measurement of the consumption of gas moving in a mine with an arbitrary stationary subsonic velocity field. PubDate: 2017-09-01 DOI: 10.1134/s1063771017040091 Issue No:Vol. 63, No. 5 (2017)

Abstract: Using the spectral solution to the evolutionary Burgers equation, we have numerically simulated the propagation of intense random acoustic waves in a nondisperse medium. We have solved the problem of reconstructing the initial signal spectrum using the measured spectral and bispectral characteristics of the received signal on short tracks. PubDate: 2017-11-01 DOI: 10.1134/S1063771017060021

Abstract: We consider a recently developed method to analyze the angular structure of pulsed acoustic fields in an underwater sound channel. The method is based on the Husimi transform that allows us to approximately link a wave field with the corresponding ray arrivals. The advantage of the method lies in the possibility of its practical realization by a vertical hydrophone array crossing only a small part of the oceanic depth. The main aim of the present work is to find the optimal parameter values of the array that ensure good angular accuracy and sufficient reliability of the algorithm to calculate the arrival angles. Broadband pulses with central frequencies of 80 and 240 Hz are considered. It is shown that an array with a length of several hundred meters allows measuring the angular spectrum with an accuracy of up to 1 degree. The angular resolution is lowered with an increase of the sound wavelength due to the fundamental limitations imposed by the uncertainty relation. PubDate: 2017-11-01 DOI: 10.1134/S1063771017060100

Abstract: The laws of sound decay in a cubic room, one wall of which is absorbing and the other scattering, are obtained. It is shown that under certain conditions, sound decay in a room occurs nonexponentially and the shape of the decay curve depends on the scattering coefficient of the walls. This makes it possible to suggest a method for measuring the scattering coefficient by the analysis the decay curve when the walls have sound-scattering materials and structures. Expressions are obtained for approximating the measured decay curve, and the boundaries of the method’s applicability are determined. PubDate: 2017-11-01 DOI: 10.1134/S1063771017050062

Abstract: Experimental results of studying low-frequency (74 kHz) shear elasticity of polymer liquids by the impedance method (analogous to the Mason method) are presented. A free-volume thick liquid layer is placed on the horizontal surface of a piezoelectric quartz crystal with dimensions 34.7 × 12 × 5.5 cm. The latter performs tangential vibrations at resonance frequency. The liquid layer experiences shear strain, and shear waves should propagate in it. From the theory of the method, it follows that, with an increase in the layer thickness, both real and imaginary resonance frequency shifts should exhibit damped oscillations and tend to limiting values. For the liquids under study, the imaginary frequency shift far exceeds the real one, which testifies to the presence of bulk shear elasticity. PubDate: 2017-11-01 DOI: 10.1134/S1063771017050025

Abstract: The paper discusses the results of an experiment conducted in the Sea of Japan in March 2016 on an acoustic track 194 km long under winter hydrological conditions. We have studied the most complex case of propagation of pulse pseudorandom signals from the shelf into shallow water during vortex generation on the acoustic track. Analysis of the experimentally obtained pulse characteristics have shown that the maximum first approach of acoustic energy recorded at all points agrees well with the calculation. This testifies to the fact that at a given reception depth, the first to arrive are pulses that have passed in the near-surface sound channel over the shortest distance and at small angles close to zero. We propose a technique for calculating the mean sound velocity on the track from satellite monitoring data on the surface temperature, which makes it possible to rely on the successful application of the results obtained in acoustic ranging and navigation problems. PubDate: 2017-11-01 DOI: 10.1134/S1063771017060112

Abstract: The Biot theory is used to study the properties of acoustic waves in fluid-saturated porous media with large porosity values. Materials are considered for which a large elasticity modulus of the matrix (skeleton) is comparable in size to the large fluid pore saturation modulus. PubDate: 2017-11-01 DOI: 10.1134/S1063771017060045

Abstract: In order to study the response characteristics of infrasound in coal samples under the uniaxial loading process, coal samples were collected from GengCun mine. Coal rock stress loading device, acoustic emission tested system and infrasound tested system were used to test the infrasonic signal and acoustic emission signal under uniaxial loading process. The tested results were analyzed by the methods of wavelet filter, threshold denoise, time–frequency analysis and so on. The results showed that in the loading process, the change of the infrasonic wave displayed the characteristics of stage, and it could be divided into three stages: initial stage with a certain amount infrasound events, middle stage with few infrasound events, and late stage gradual decrease. It had a good consistency with changing characteristics of acoustic emission. At the same time, the frequency of infrasound was very low. It can propagate over a very long distance with little attenuation, and the characteristics of the infrasound before the destruction of the coal samples were obvious. A method of using the infrasound characteristics to predict the destruction of coal samples was proposed. This is of great significance to guide the prediction of geological hazards in coal mines. PubDate: 2017-11-01 DOI: 10.1134/S1063771017060057

Abstract: Numerical implementation of the two-dimensional functional-analytical Novikov–Agaltsov algorithm is considered and its possibilities are discussed. This algorithm is intended for reconstructing combined scalar-vector inhomogeneities describing spatial distributions of the speed of sound, absorption, and vector flow field. The results of the numerical simulation of the algorithm in the single- and multifrequency probing modes are presented. The obtained results illustrate an acceptable accuracy and interference resistance of the obtained estimates, which illustrates the application prospects of the algorithm in practical problems of acoustic tomography. PubDate: 2017-11-01 DOI: 10.1134/S1063771017060136

Abstract: This paper presents a method for measuring the thickness and velocities of body waves and the density of an isotropic layer by a pulse scanning acoustic microscope. The method is based on recording the microscope signal as a function of the displacement magnitude of the focused ultrasonic transducer along its axis perpendicular to the sample surface and on the decomposition of the recorded 2D spatiotemporal signal into the spectrum of plane pulse waves. The velocities of the longitudinal and transverse waves and the layer’s thickness are calculated from the relative delays of the components of the spectrum of plane waves reflected from the surfaces of the layer and the density is computed by the amplitudes of these components. An experimental investigation of a test sample in the form of a glass plate carried out in the 50-MHz range shows that the error in measuring the thickness and velocities of body waves does not exceed 1% and the density measurement error does not exceed 10%. PubDate: 2017-11-01 DOI: 10.1134/S106377101706015X

Abstract: Community noise of a hypothetical medium-range airplane equipped with open-rotor engines is assessed by numerical modeling of the aeroacoustic characteristics of an isolated open rotor with the simplest blade geometry. Various open-rotor configurations are considered at constant thrust, and the lowest-noise configuration is selected. A two-engine medium-range airplane at known thrust of bypass turbofan engines at different segments of the takeoff–landing trajectory is considered, after the replacement of those engines by the open-rotor engines. It is established that a medium-range airplane with two open-rotor engines meets the requirements of Chapter 4 of the ICAO standard with a significant margin. It is shown that airframe noise makes a significant contribution to the total noise of an airplane with open-rotor engines at landing. PubDate: 2017-11-01 DOI: 10.1134/S1063771017060069