Том 70, № 5 (2024)

A one-dimensional nonlinear problem of parametric generation of low-frequency radiation is considered in the case of a pulsed high-frequency initial excitation capable of forming shock fronts in the wave profile. A numerical algorithm for solving the Burgers equation in the time domain using a Godunov-type shock-capturing scheme is developed. Examples of the propagation of model frequency-modulated signals with different envelope shapes at different ratios of nonlinear and dissipative effects, which limit the interaction length of pump waves are considered. Examples of waveforms and spectra evolution during self-demodulation of a high-frequency pump signal are given, with self-demodulation manifesting at shorter distances in strongly nonlinear propagation regimes due to additional attenuation of the wave energy at shock fronts. It is shown that the efficiency of low-frequency radiation generation increases in shockwave propagation modes.

The propagation of slit shear waves in the quasi-symmetric structure of piezoelectrics of the 4mm symmetry class has been theoretically investigated. It has been shown that taking into account the unequal level of losses and amplification in piezoelectrics leads in the shear wave spectrum either to an intersection, or to a touch, or to a convergence of two modes at the point of their degeneracy (singular point). It is established that the intersection of the mode spectra occurs only in the case of equal loss and gain values (PT is a symmetric structure). Based on this, it is concluded that by the nature of the spectra near a singular point, it is possible to determine the level of imbalance of gain and loss in piezoelectric waveguides. As in the case of a purely PT-symmetric structure, the frequency dependence of the amplitude at an exceptional point of a quasi PT-symmetric structure (with a fairly small difference in loss and gain levels) has a very narrow peak, which opens up the possibility of creating hypersensitive sensors based on them. Thus, it is demonstrated that even with unequal levels of loss and gain in piezoelectrics (quasi PT-symmetric structure), it is possible to obtain a structure with all the properties of a PT-symmetric structure.

The article considers the possibility of using a non-destructive spectral-acoustic method for quantitative control of the porosity of Kh12MF steel samples obtained by hot isostatic pressing. The results of studies of samples obtained at different stages of hot isostatic pressing in the range of residual porosity from 0% to 9% are presented. The control technique is based on the analysis of acoustic structural noise parameters. Various methods of measuring parameters of structural noise are analyzed from the point of view of sensitivity and measurement error of the used informative parameters of structural noise. Clarified calculation algorithms for determining the parameters of structural noise are proposed, and the results of their experimental verification are presented. The obtained results can serve as a basis for developing an engineering method for assessing the degree of porosity of the material of parts and structural elements obtained by hot isostatic pressing, under operating conditions.

The effect of lateral asymmetry in the radiation pattern of a propeller installed near the wing is studied. Within the framework of a simplified theoretical model of the propeller loading noise and its shielding by a half-plane, as well as using numerical modeling of the interaction of the propeller with a flat finite plate, it is shown that when the propeller and the scattering surface are close to each other, a significant lateral asymmetry of the propeller tonal noise emission in the far field appears. The mechanism of this effect, which accompanies the symmetrical sound directivity of the propeller itself and the symmetry of the scatterer (wing), is associated with the phased summation of the sound field emitted directly by the propeller and the secondary sound field generated on the surface of the wing due to the scattering of disturbances (mainly hydrodynamic) created by the propeller on the leading edge of the wing. Thus, the study demonstrated that the presence of lateral asymmetry in the noise radiation pattern inherent in propeller-driven aircraft is a consequence of the interaction of the propellers and closely spaced wings.

A method for rapid estimations of supersonic civil aircraft sonic boom characteristics in standard atmosphere is proposed. The piece-wise linearity of the temperature profile and the absence of atmospheric wind allow to completely reduce the problem on the geometry of the propagation of sonic boom waves to an algebraic form. For acoustic pressure, an exact solution is formulated on the basis of the approach of nonlinear geometric acoustics. The dependence of the geometry of the sonic boom waves propagation on the parameters of the aircraft cruise flight is analyzed. Under the conditions of the third seminar SBPW (Sonic Boom Prediction Workshop) 2020, ground overpressure signatures from the X-59 demonstrator were calculated.

In work the results of the analysis of experimental data allowing to reveal behavior of parameters of fluctuation of the design at change of amplitude of acoustic pressure with the concept of conductivity of acoustic vibration entered into consideration are provided. The nonlinear behavior of the vibration response of the design of different compartments of the rocket and segments of panels when loading by their field of acoustic pressure is confirmed. The general patterns of nonlinearity are found, in the particular it is shown that conductivity tends to lowering with the growth of acoustic loading close generally to the power function.

The paper presents the results of an experiment on the assessment of subjective indicators of acoustic perceptibility by pedestrians (experts) of a vehicle approaching at a constant speed (TS) and some conclusions. Subjective indicators of perceptibility were defined as the distance between the vehicle and the expert, at the moment when the expert heard (recorded) the sound of an approaching car, as well as the time of the car's approach to the expert at that moment. Subjective indicators of perceptibility are compared with the objective parameters of car noise measured by the method of UN Regulation No. 138 — the sound pressure level, its frequency response, as well as the sound level. The study is motivated by the problem of traffic safety of electrified vehicles with low noise, which include, in particular, electric cars, electric scooters and electric scooters. This article publishes the first results of a research paper devoted to the problem of increasing the perceptibility of low-noise vehicles for pedestrians without damaging the acoustic ecology of cities and suburbs.

The properties of speech bursts of closure are studied using the material of a database of 39 speakers containing single-digit and multi-digit numerals with parallel recording of signals on a telephone handset and a directional microphone. Speech burst detection is performed by a short-term and long-term detector of spectral-temporal inhomogeneities, as well as a detector of the similarity measure of the eigenfunctions of the consonant burst spectrum and the current spectrum of the speech burst. The probability of the presence of a voiced or voiceless closure is estimated in the spaces of the amplitude spectrum and the spectrum of the group delay by the ratio of energy in the high and low frequency ranges. The place of articulation of a back-lingual consonant affects the probability distributions of the duration of the interval between the onset of a speech burst and the onset of a vowel, the frequency of the peak with maximum amplitude in the high-frequency region, the ratio of the energy in the high- and low-frequency region of the speech burst spectrum, and the similarity measures of the eigenfunctions of the consonant burst spectrum and the current spectrum of the speech burst.

The current state of the Acoustic Journal Archive is presented with a description of its English-language part. The prospects for the development of the Archive are discussed in connection with the discrepancy between the contents of the journal and its English-language version, “Acoustical Physics”. The “Open Access” trend in access to scientific literature, which has become widespread, is commented on.