Acoustical Physics最新文献

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.

A low-order model of quadrupole sound sources in a turbulent jet has been developed using the acoustic analogy method. Multimicrophone acoustic measurements of jet sound radiation are used to estimate the model parameters and validate it. Based on measurements carried out in different zones of the sound field, estimates of the size of the effective localization region of sound sources are made and the boundaries of the zone of dominance of quadrupole sound radiation over pseudo-sound fluctuations are determined. The proposed model can be used in practical estimates of the spectral and correlation characteristics of the far and near sound field of the jet.

Multidimensional optimization algorithms were used to numerically solve the problem of determining the minimum number of compensating monopole sources located in free space on two spherical surfaces surrounding the primary source, providing a given value of suppression of its integral radiation level.

The article presents a study of the acoustic field of the propeller, including at the resonance frequencies of its blades. The study is based on a computational and experimental approach with the combined use of numerical and experimental physical modeling. The article shows the importance of taking into account the elastic resonances of the propeller in the design, demonstrates the methods of physical and numerical modeling used, which provide high accuracy in determining the resonance frequencies of the blades in water and in air. Using the example of two propeller models made of different materials, the effect of the Q-factor on the levels and type of radiation spectrum is experimentally demonstrated.

Under laboratory conditions, experimental verification of the developed algorithms for reconstructing low-contrast bottom layers during their coherent sensing was carried out. The algorithms use parametric models for generating signals reflected from a layered half-space in the form of a set of elastic layers. To solve the problem at the Department of Acoustics of Nizhny Novgorod State University, an experimental setup was created for the formation, emission, and reception of high-resolution sound pulses reflected from a set of elastic layers placed in a tank of water. The experimental study showed the possibility of using the coherent sensing method for layered media with relatively similar acoustic parameters. Processing of the data obtained resulted in good agreement between the developed computational model of probing acoustic pulse signals reflected from a layered bottom and the physical modeling data. It is shown that analysis of the plane of the geoacoustic parameters of a specific problem using the developed numerical model makes it possible to assess the capabilities of a promising method for coherent diagnostics of low-contrast bottom layers.