Acoustical Physics最新文献

The article presents the results of a study of the acoustic parameters of a vocal source and the dynamics of the glottis area under terrestrial gravity and weightlessness. Vocal source pulses are found by inverse filtering of the speech signal using the linear prediction method. The glottis area function is determined as the solution to the inverse problem for the equation of airflow through the glottis. The extrema of the vocal excitation impulse and its integral, as well as the extrema of the glottal area function and its time derivative, are calculated. The temporal relationships between these extrema are determined in speech tests recorded under gravity and weightlessness. Four cosmonauts participated in the speech experiments. The effect of weightlessness on the probability distribution of the calculated parameters was determined. The quantitative indicators of these discrepancies depend on the speaker and the phonetic composition of the speech tests.

This paper presents an experimental setup designed to measure stress-strain relationships in solid material samples and reports on the results obtained using it. The setup provides for the acoustic measurements under tension-compression and torsion strains across a broad range of frequencies and amplitudes. The amplitude-dependent variation in sound velocity is determined from changes in the time-of-flight of a probing ultrasonic pulse during low-frequency dynamic loading. Measurement data of the stress-strain relationships of a Berea sandstone specimen have been presented. Power-law dependencies of hysteretic nonlinearity and nonlinear acoustic attenuation on frequency were experimentally established. The agreement between these findings and previously published results from independent studies has been confirmed the accuracy of the measurements. Finally, a qualitative explanation has been proposed for the observed frequency-dependent behaviors.

It is shown that the algorithm used in sonic boom modeling, based on linear interpolation of the potential of a discontinuous solution to the Hopf equation, can in some cases lead to significant errors. The causes of these errors are analyzed, and an algorithm free of these errors is proposed using an exact expression for the potential with piecewise linear initial data in the Hopf equation. It is demonstrated that the proposed algorithm makes it possible to construct a solution with high accuracy even in the case of very complicated initial conditions. The results of applying the proposed algorithm are compared with the data from numerical calculations performed using an iterative algorithm of the shock-capturing scheme. It is shown that the proposed algorithm avoids the smoothing of solutions typical of shock-capturing schemes and significantly accelerates the calculations due to the absence of time step restrictions.

In an ecologically sensitive region—the Ural River Delta Nature Reserve near the Caspian Sea shelf—simultaneous measurements of underwater and airborne noise from a Griffon BHT130 hovercraft were conducted. The measurements were designed to assess the potential negative impact of hovercraft noise on the fish and birds of the reserve. In addition to determining sound pressure levels, a gradient-type vector receiver, formed by four spatially spaced hydrophones, was used to estimate the absolute particle velocity levels of underwater noise. Such measurements are an important part of underwater noise research, as a significant proportion of fish perceive sound as particle vibrations. Simultaneous recording of underwater and airborne noise allowed us to evaluate their mutual correlation. The resulting correlation between the underwater and airborne noise levels from the hovercraft can be used to simplify the estimation of the upper limit of underwater noise based on the measured airborne noise levels. The measured and estimated maximum underwater noise levels of the hovercraft were significantly lower than those of conventional submersible motor-driven vessels, making the hovercraft an attractive alternative for operation in areas with particularly high requirements for permissible levels of anthropogenic noise impact in the aquatic environment.

Abstract—An approach is proposed for the physical realization of a perfectly matched layer (PML) at the open end of a waveguide is proposed. In addition, the paper proposes an extension of the concept of a physically realizable PML to suppress dispersive distortions: it is demonstrated that adapting PML principles enables the synthesis of a dispersionless interference PML antenna.

Sound source identification based on the temporal realization of the signal is a pressing problem for various practical applications, ranging from speech recognition to vibration defect diagnostics. This paper proposes a classification algorithm based on modern convolutional neural networks. The input data is a log-mel spectrogram obtained by multitaper processing—a power spectrum estimation method that uses orthogonal windows (tapers) to suppress noise components and improve the information content of features. Multitaper processing allows one to estimate the power spectral density of a stationary ergodic random process using a finite segment of its realization. The mel scale is a psychophysical pitch scale that simulates human perception. This paper presents a description of the algorithm and its validation using river navigation data collected using a directional sound source—a microphone located in the focal plane of a parabolic reflector. Model training is evaluated depending on the amount of data, and the performance of various convolutional networks is compared.

When solving problems in industrial and medical acoustics, it is necessary to know the elastic and dissipative parameters of the used materials, which are determined by the phase velocities and absorption coefficients of acoustic waves. In this work, a pulse-echo double through-transmission method in oblique incidence has been used to measure the phase velocities and absorption coefficients of longitudinal and shear acoustic waves in materials. The polycarbonate, plexiglass, nylon, and Teflon plates have been used as the samples under study. A setup has been designed consisting of a piezoelectric transducer serving as a transmitter and receiver, a flat reflector positioned parallel to the transducer surface, and a plane-parallel sample under study mounted in a rotating device between the transmitter and reflector. The reflector allows the beam to be reversed so that it entirely passes the same path backward as it did forward, i.e., without displacement, returning to the transmitter. When the beam is obliquely incident on the plate, two refracted waves are generated in the latter, namely, longitudinal and shear one separated by arrival time. By separating these components in the received signal and performing their spectral analysis, the frequency dependences of the phase velocities and absorption coefficients of the longitudinal and shear waves have been measured with high accuracy.

The paper considers the problem of suppressing the noise of local sources of interference in sonar active mode. Three adaptive algorithms for spatial–frequency–time processing of signals from a multielement antenna array—the compensation algorithm, the standard Capon algorithm, and the Capon algorithm with limited levels of the major eigenvalues—are investigated in terms of their noise immunity for detecting echo signals. According to the simulation results, the compensation algorithm provides the highest noise immunity when using both a tone and an chirp probe signal. This algorithm allows for the suppression of noise from intense local sources of interference, including when the angular distance between the directions of arrival of the echo signal and the interference source signal is less than the width of the receiving antenna’s radiation pattern.

The exact solutions for rays and ray tube areas in a standard atmosphere made it possible to formulate a criterion for sonic boom focusing on the ground in supersonic turn mode, as well as to calculate the caustic–ground intersection line width in acceleration mode in elementary functions. The dichotomy method was used as the basis for simple algorithms to calculate the caustic–ground intersection lines (focusing lines) arising in the acceleration and supersonic turn modes of a supersonic passenger aircraft. The dependence of the geometry of the focusing lines on the main flight trajectory parameters has been investigated. In acceleration mode, these parameters are flight altitude and acceleration, and in the case of supersonic turn, flight altitude, Mach number, and trajectory curvature radius. The focusing lines “stabilization” effect with increasing acceleration in acceleration mode and Mach number in supersonic turn mode has been observed. It has been established that flight altitude has a significantly smaller effect on the focusing lines shape than other trajectory parameters.

Using numerical simulation, error estimates for acoustic methods of distance measurement to underwater vehicles in the southern part of the Kara Sea have been obtained. Trains of soliton-like internal waves (IWs), which may occur on the acoustic path between an acoustic beacon and an underwater vehicle equipped with a navigation sound receiver, are considered the primary factor determining the errors in such measurements. According to experimental data, the amplitude of solitons in a train in the study area can reach several tens of meters, with the phase front width of the IWs exceeding 10 km. It is demonstrated that these hydrodynamic disturbances can lead to measurement errors of up to hundreds of meters, depending on the direction of propagation of the IW train: along or across the acoustic path.