Acoustical Physics最新文献

Chuprov’s interference invariant (II) well describes the properties of a sound field in shallow water. However, the question of how applicable Chuprov’s II concept is to deep water, where the patterns of sound field decay with distance are more complex has been insufficiently studied. Therefore, the authors studied the II properties in the near and far fields of acoustic illumination, as well as in the shadow zone. A new definition of the invariant was proposed and studied, and its characteristics were compared with Chuprov’s II as a function of distance, reception and emission depths, and summer or winter propagation conditions. The new invariant is called the phase-energy invariant (PEI), since orthogonal components of the phase gradient are used to describe the spatial sound energy distribution. The stability of the new invariant, its independence on different influencing factors, and its natural change with distance from zero to one are shown. It has been established that in winter conditions, at almost all distances, the PEI is equal to unity, and the II does not have stable values and varies jumpwise over a very wide range. In summer conditions, in the shadow zone, with increasing distance, the PEI increases, just like the II, from close to zero to one. In the near and far fields of acoustic illumination, the PEI is approximately equal to unity, and the II in these zones, both in summer and winter, is characterized by unlimited oscillations, caused by division by a value close to zero. It is shown that the definition of PEI is valid both in single-mode waveguides and in free unbounded space with a dispersive medium.

The information content of the parameters of a spectral voice source model in an automatic voice identity recognition problem is studied. For the voice parameters, the identity recognition error was 20.8%; using these parameters together with the pitch period reduced the error to 13.8%. Lastly, the combined use of the spectral model parameters with the pitch period and mel-frequency cepstral coefficients provided the highest accuracy (the recognition error was 1.2%).

Features of Rayleigh scattering by a solid particle at a small distance compared to the wavelength from an impenetrable plane boundary are revealed. The choice of the Green’s function in the integral representation of the Helmholtz equation makes it possible to reduce integration only over the particle surface and eliminate the contribution of the interface surface. When expanding over a small wave parameter, a well-known approach is used, making it possible to represent the solution of a given order as the sum of a potential function and a component expressed in terms of lower-order approximations. The potential component is found, expressed in terms of solid irregular harmonics centered on the particle and its mirror image. The vibrational velocity of the center of a particle and the scattering amplitude are determined. In the lowest order of the wavenumber, the scattering amplitude is expressed in terms of the monopole and dipole components.

The low-frequency (74 kHz) shear elasticity of the homologous series of normal hydrocarbons (alkanes) is studied using acoustic resonance. The shear modulus and mechanical loss tangent are measured, and the relaxation frequency and effective viscosity are calculated. The dependences of these parameters on homologue viscosity are established. It is shown that the mechanical loss tangent of all studied liquids is less than 1, demonstrating that the relaxation frequency is below the experimental frequency.

The acoustic characteristics of barriers with a T-shaped profile are studied by finite element simulation. It has been found that the sound reduction efficiency of this barrier is related not only to diffraction, but also to sound interference at the leading and trailing edges of the barrier. It is shown that the sound interference at the trailing edge of the barrier, in contrast to the sound interference at the leading edge, affects the sound field only at short distances from the rear surface of the barrier. The influence of the sound frequency and geometrical dimensions of the barrier on these processes is analyzed.

A method is proposed for solving the inverse problem of reconstructing acoustic wave sources from field measurements on some surface using wavefront reversal in the particle dynamics method. In this method, the studied medium is represented as a set of interacting particles (material points or solid bodies), for which classical equations of motion are written. The paper considers the representation of a medium as a set of particles in a body-centered cubic crystal lattice. The case of a linear dependence of the force of attraction of particles on distance is considered. The advantage of this approach is the ability to take into account wave propagation in arbitrarily inhomogeneous media using a single numerical model. The possibility of visualizing two spherical acoustic wave sources in water behind an obstacle has been demonstrated numerically and experimentally, despite the presence of transverse waves in the considered model of a solid body; their influence is negligible in this case. The method was tested experimentally on a soundproof screen with an aperture simulating a sound-emitting object of complex shape. A wave from a point source of short pulses passes through the aperture. Using a receiving acoustic sensor mounted on a two-dimensional scanner, the spatiotemporal distribution of sound vibrations on the water surface was measured. By processing the data using wavefront reversal in the particle model, the image of the aperture in the soundproof screen was reconstructed.