Acoustical Physics最新文献

The propagation of a Rayleigh-type surface acoustic wave (SAW) along the free boundary of a layered half-space with a smooth change in its elastic parameters horizontally is considered analytically and numerically. The change in amplitude of the SAW for the transition of a wave from a single-layer system to a single-layer, single-layer to two-layer, and two-layer to two-layer system depending on the elastic parameters, as well as the length of the sounding wave, is calculated. It is shown that as it propagates, the amplitude of SAW decreases with an increase in the velocity of longitudinal waves and density of the medium, and with an increase in the velocity of transverse waves in the medium, the SAW amplitude can both increase and decrease. The change in the SAW amplitude associated with a change in the longitudinal wave velocity is stronger; therefore, this parameter should be taken into account in applied methods. It is shown that the magnitude of the dominant wavelength depends on both the geometric and elastic parameters of the system.

The article considers the possibility of using a nondestructive 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 residual porosity range 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 study presents the results of an analysis of experimental data that make it possible to reveal the behavior of the parameters of fluctuation in design during a change in acoustic pressure amplitude with the concept of conductivity of acoustic vibration. 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 particular, it is shown that conductivity tends to lower with growth in acoustic loading that is generally close to a power function.

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 the evolution of waveforms and spectra in a process of 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 wave energy at shock fronts. It is shown that the efficiency of low-frequency generation increases in shockwave propagation regimes.

The use of cellular materials with the geometry of triply periodic minimal surfaces (TPMS) is proposed for the creation of durable cellular materials with controlled acoustic characteristics. Homogeneous unit cells with the primitive, diamond, FRD and gyroid topologies with different porosities were developed, and their acoustic parameters were determined. Using the semiphenomenological Johnson–Champoux–Allard–Lafarge–Pride model, the sound absorption capacity of materials with this geometry was estimated. It was shown that by varying the size of the unit cell and thickness of the sample, it is possible to control the acoustic characteristics and average sound absorption coefficient in the range from 0.2 to 0.8. The reliability of the calculations was confirmed experimentally using additively manufactured samples. The results demonstrate the potential of using TPMS for creating materials with controlled pore geometry to achieve predictable sound absorption characteristics.

The effect of lateral asymmetry in the radiation pattern of a propeller installed near a wing is studied. Using a simplified theoretical model of propeller loading noise and its shielding by a half-plane, as well as 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, significant lateral asymmetry of propeller tonal noise radiation in the far field occurs. The mechanism underlying this effect, which accompanies the symmetrical noise directivity of the propeller itself and the symmetry of the scatterer (wing), is associated with the phased summation of the sound field radiated directly by the propeller and the secondary sound field generated on the surface of the wing due to scattering of perturbations (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 aircraft is a consequence of the interaction between propellers and closely spaced wings.