Acoustical Physics最新文献

For a low-frequency sound signal propagating in a horizontally inhomogeneous waveguide in shallow water, the influence of a fluctuating interface between the water layer and fluid bottom sediments was studied based on statistical modeling using the cross-sectional method. The modeling was carried out for hydrological conditions in many situations corresponding to the shallow shelf zones of the Russian Arctic seas. A specific feature of these water areas is the presence of an almost homogeneous water layer on poorly consolidated bottom sediments with various characteristics, including a high degree of gas saturation. The dependence of the average intensity of the sound signal and its individual modes on the parameters of the problem has been studied: the characteristic scale of fluctuations of the interface and impedance of this interface, which determines its penetrable properties. It is shown that the influence of bathymetric fluctuations on the average intensity of acoustic modes has its own characteristics versus the influence of random volumetric inhomogeneities of the sound speed in the water layer and sediments, established earlier. Thus, bottom roughness of a relatively small scale leads, on average, to increased attenuation of a sound signal when propagating in a waveguide, and this can occur at relatively short distances from the source. An increase in the reflectivity of a rough bottom boundary weakens the effect of increased sound attenuation so that for typical values of sound speed in the bottom, attenuation at distances of 10–20 km from the source differs little from that for an undisturbed horizontal boundary.

A modification of Dean’s method is proposed for determining the impedance in the case of a nonuniform sound field on the front and bottom surfaces of a resonator. Instead of acoustic pressures in Dean’s formula, the modification uses the coefficients of eigenfunctions, which correspond to a uniform acoustic pressure distribution on the front and bottom surfaces of the resonator. The eigenproblem is solved by the finite element method; the coefficients of the eigenfunctions are found by the least squares method. At the current stage of research, the full-scale experiment has been replaced by numerical simulation in a linear formulation of sound propagation in an impedance tube with normal wave incidence with a honeycomb resonator attached to it. The inhomogeneity of the pressure field over the cross section of the resonator is created from the different positions of holes in the resonator face plate. The study is done for a different number of acoustic pressure measurement points at the bottom of the resonator. Calculations show that the proposed method is efficient and provides good agreement with the straight method for determining impedance. However, the possibilities of using modification of Dean’s method in full-scale measurements are limited, because accurate resonator impedance determination requires a large number of measurement points.

One source of modern aircraft engine noise is the fan, which is especially noticeable during takeoff at high angular rotation speeds. In such modes, supersonic flow around the fan blades occurs, which leads to the formation of shock waves that propagate upstream until they exit the engine duct. As a result, specific noise is emitted into the front hemisphere, consisting of a number of harmonics that are multiples of the fan rotation frequency. The paper analyzes this effect using a simple model of the propagation of a system of shock waves. An energy approach is used to demonstrate that a system of shock waves with shocks of equal amplitude attenuates the most rapidly.

Recognition by adults of the psychoneurological state of children with autism spectrum disorders (ASD), n = 35, and typically developing (TD) children, n = 47, aged 5–14 years, was studied. A perceptual analysis was carried out, in which adult native Russian speakers (auditors) took part, n = 206. For perceptual analysis, test sequences (audio tests) were created containing words and phrases of children with ASD and TD children, selected from spontaneous speech recordings. The auditors were faced with the problem of determining the psychoneurological state of a child based on auditory perception: typical–atypical development. A spectrographic analysis of the speech material of children with ASD and TD children was carried out. The phrases of children with ASD are characterized by a lower speech rate compared to the phrases of TD children, as well as fewer words, longer duration of stressed and unstressed vowels in words, higher values of the frequency of the fundamental tone in the phrase, word, and stressed and unstressed vowels.

New protocols have been developed of biological tissue volumes with shock-wave bursts using trajectories uniformly filled with discrete foci within a given volume. Each focus was sonicated with a millisecond-long pulse, which immediately generated a single thermal lesion. In developing the most advantageous irradiation protocols, the effect of the source peak power at a constant time-averaged value, the distance between single foci, and geometry of the outer contour of the trajectory on the shape, volume, and thermal ablation rate was analyzed. It is shown that for an arbitrary geometry of the outer contour of a single-layer trajectory, the most advantageous is the saturation mode of the shock front amplitude at the array focus using a trajectory with a spatial step 1.5 times greater than the transverse size of the single lesion. To obtain thermal ablation volumes on the order of cubic centimeters, protocols have been suggested with layer-by-layer irradiation of tissue, which make it possible to accelerate the thermal ablation process by 2.5 times compared to protocols used in clinical practice. The advantage of the proposed protocols that use the shock-wave exposure is the ability to generate localized and predictable thermal lesion without using MRI temperature monitoring.

Numerical simulation of the aeroacoustic characteristics of a supersonic jet issuing from a Laval nozzle into space at rest at the design condition (Mach number M = 2) was carried out. The results of calculations using the large eddy simulation (LES) method are presented. The mean and fluctuation characteristics of the flow in the jet, as well as the characteristics of the jet noise in the far field, including its azimuthal composition, were obtained. The calculation results are compared with experimental data, and their satisfactory agreement is shown. It is concluded that there are various mechanisms of noise generation in the considered jet.