Том 71, № 4 (2025)

For an Euler Bernoulli beam and a thin inextensible half-ring, it is shown that their Green's function for normal forces and displacements can be zero in the presence of dissipative losses. The beam and the half-ring are considered in two versions: with a simple support and movable seal at the ends. Solutions exist in wide frequency bands. For a half-ring with a movable seal, there are solutions for which the frequency derivative of the Green's function is close to zero with a frequency-independent loss tangent. A vibration isolator in the form of a closed ring with four supports arranged at points corresponding to one of these solutions will have both theoretically infinite vibration isolation at one frequency and large vibration isolation in a wide band of neighboring frequencies.

Many real liquids contain solid inclusions of various sizes in addition to the liquid phase itself. These inclusions influence the propagation of acoustic waves. Such parameters of acoustic waves as absorption and speed of sound propagation depend on the size and concentration of particles. For some multicomponent systems, acoustic parameters can be described quite well within the framework of the theory proposed by Urick. In this work, the dependences of absorption coefficient and sound velocity for agarose gel suspension with talc particles and for suspensions with silica particles are obtained. Experimental attenuation spectra in different suspensions were compared with theoretical calculations of the Urick model. Dependences of acoustic absorption and sound velocity on concentration in suspensions with different particle sizes were obtained. The comparison results showed that the Urick model satisfactorily describes the absorption in various suspensions at particle concentrations φ < 20%.

The study theoretically evaluated the possibilities of using ray-tracing and diffraction-based methods to aberration correction, which are used in noninvasive neurosurgery for focusing high-intensity ultrasound through the skull bones at various depths in the human brain. The analysis is based on using head computed tomography (CT) data of skulls with various geometric characteristics from an anonymized set of eight patients. A mosaic 1 MHz phased array shaped as a spherical bowl with radius of curvature and diameter of 200 mm, and absolutely dense filling of the surface with 256 elements, was considered as the transducer. In the ray-tracing method, aberration correction was carried out by calculating the phase shift along the rays emanating from the target point to the centers of the elements. In the diffraction-based method, a combination of the Rayleigh integral and a pseudospectral numerical method for solving the wave equation in an inhomogeneous medium, implemented in the k-Wave software package, was used for aberration correction and ultrasound focusing simulations. It is shown that the strongest field distortions are observed for skulls with more pronounced variations of bone thickness. The diffraction-based method allows for increasing the focusing efficiency, as well as performing correction at shallower depths in the brain compared to the ray-based method.

The paper presents the results of the calculation of sound diffraction on screens of various shapes, performed using the Finite Element Method (FEM) developed by the authors in the Bubnov–Galerkin formulation. The calculations were verified on problems that have an exact solution (diffraction on a cylinder, on a segment, and on a sphere), and the results of the experimental validation of the calculations of sound diffraction on a rectangular screen, performed using the Maximum Length Sequence Method, are also presented. The article was prepared based on the materials of the report at the 10th Russian conference “Computational experiment in aeroacoustics and aerodynamics”, September 16–21, 2024, Svetlogorsk, Kaliningrad region, http://ceaa.imamod.ru/.

Results of numerical investigation of the effect of clocking, which is circumferential indexing of rotor or stator blade rows, on tone noise of the first two booster stages of turbofan engine low pressure compressor are presented. Calculations are performed for several relative positions of both rotor blade rows and stator blade rows. The computational model under consideration includes a row of rotor blades of the fan, rows of rotor blades and rows of stator blades corresponding to the first two booster stages and also row of inlet guide vanes of the booster. The stages have identical numbers of rotor blades and stator blades. A task is to obtain the power of noise radiation and directivity diagrams for most intensive tones at operational conditions = 58%. The investigation is performed using a method of multistage turbomachine tone noise calculation in frequency domain. The method is capable to model a change of relative position of blade rows without any manipulations with computational grid. The results of calculations show, that the clocking of rotor blade rows can change the power of radiation from inlet by 4 dB. The clocking of stator blade rows has negligible influence on the total power of noise radiation from inlet, though for some circumferential modes the power can change by more than 5 dB. The article was prepared based on the materials of the report at the 10th Russian conference “Computational experiment in aeroacoustics and aerodynamics”, September 16–21, 2024, Svetlogorsk, Kaliningrad region, http://ceaa.imamod.ru/.

Nowadays, the solution of applied problems of seismic exploration and ultrasonic non-destructive testing is accompanied by the use of computer simulation. This poses a challenge for scientists to develop new modifications of numerical methods that allow increasing the accuracy of calculations while minimizing the cost of computing resources. Unlike numerical methods on unstructured computational grids, the use of Chimera computational grids (or superimposed ones, or adaptive ones) also allows describing boundaries and contact boundaries of arbitrary shape, but at the same time spending less RAM and time on calculations. This is especially important in connection with the active use of neural networks for solving inverse problems, since when generating training samples, both the accuracy of modeling and the speed of calculations and the amount of RAM spent are important. The paper considers and compares various modifications of the grid-characteristic method on Chimera computational grids. Examples of test calculations are given.

The aim of this study is to investigate the manifestation of emotional states in the speech of typically developing (TD) adolescents and adolescents with intellectual disabilities (ID). Emotional speech from 25 adolescents was analyzed during the reading of nonsense texts in the emotional states of “joy — neutral — sadness — anger — fear”. Spectrographic analysis of children's speech was conducted using the software “Cool Edit Pro 2.0”. The following parameters were measured: duration; pitch values (F0); minimum (F0min) and maximum (F0max) pitch values; pitch range values (F0max–F0min); intensity values for the phrase, stressed word, and stressed vowel. A perceptual experiment involving 10 adult listeners was conducted. Differences in acoustic characteristics of emotional speech were identified between TD and ID adolescents: word and vowel duration; minimum pitch values for words and vowels. According to the results of the perceptual experiment, TD adolescents demonstrated a better ability to express sadness and anger in their voice compared to adolescents with ID.

The problems of acoustic physics describing the propagation of acoustic effects or associated flows rely on the equations of hydroaeromechanics, in particular, on the Navier–Stokes equations containing the vector Laplacian of the velocity of a liquid or gaseous medium. One of the most commonly used coordinate systems is spherical one. The paper discusses a fundamental misprint in “Fluid mechanics” by L.D. Landau and E.M. Lifshitz (Course of Theoretical Physics, Volume VI), which has been replicated up to the 6th revised edition of 2021, and which also made it into the English version of the Course published by Pergamon. It concerns the Navier-Stokes equation in spherical coordinates (15.21), which describes the r-component of the vector Laplacian. A typo migrates to secondary publications and can complicate theoretical studies related to the application of the Navier–Stokes equations, which the author of this note has personally encountered. The r-component of the vector Laplacian is derived in detail from general principles to show what the corresponding Navier–Stokes equation should look like and that the typo is indeed present. In addition, more compact equivalent forms of the Navier–Stokes equations in spherical coordinates are proposed.