Vol 69, No 3 (2023)

The propagation of bending waves in a plate resting on a two-parameter elastic foundation is considered. In contrast to the classical Kirchhoff model, the mathematical model used here takes into account not only the kinetic and potential energies of bending vibrations, but also the kinetic energy due to the inertia of rotation of the plate elements during bending. The dispersion equation, phase velocity, energy transfer velocity, and energy characteristics of waves propagating in the plate are analyzed depending on the ratio of the coefficients determining the shear and compression stiffness of the elastic foundation. Conditions are found under which waves with phase and group velocities having opposite directions (frequently called “backward” waves), can exist in the plate. It is demonstrated that such waves significantly change the behavior of the energy flux. In addition, relations are found that relate the kinematic and average energy characteristics of the waves.

The article presents the results of studying the reflection of an intense acoustic beam from stepped structures. The case of high Reynolds numbers is considered, when a sawtooth wave profile formed in the incident beam, and an obstacle in the form of a step was located normal to the acoustic axis and behind the discontinuity coordinate. When reflected from the obstacle, the acoustic beam incident on it splits into two parts, between which there is a path difference, specified by the stepped structure itself. The experiment focused on obstacles that create a path difference between the two parts of the beam during reflection, equal to 0, λ/3, λ/2, λ, etc. A broadband membrane hydrophone was used to record the shape of the profile of nonlinear waves of the incident and reflected acoustic beams at an arbitrary spatial point. This made it possible to analyze the evolution of the beam shape with increasing distance from the obstacle, as well as to study its transverse structure. The effect of doubling the characteristic frequency of a signal as an acoustic beam is reflected from a stepped structure is shown, which creates a path difference of λ/2 between the two parts of the reflected beam. It is demonstrated that the dynamics of nonlinear effects in intense beams reflected from stepped structures is similar to the transformation of the profile of acoustic waves generated by dual-frequency pump signals.

The scattering of a plane sound wave by a spherical interface between two liquid or gaseous media is simulated. The influence of heat conductivity and viscosity is taken into account; the results of G. Kirchhoff’s classical work on sound propagation in a viscous and heat-conducting medium are used. A spherical surface can have any wave dimension. The results are compared with the field scattered by a solid sphere, which is an ideal heat conductor.

It is demonstrated that exposing petroleum disperse systems to ultrasound significantly decreases their viscoelastic properties. The operating parameters of exposure of high-viscosity oil to ultrasound were experimentally determined in order to reduce its effective viscosity and pour point. The results of pilot tests of the developed ultrasound module indicate that exposing high-viscosity oil to ultrasound in flow mode can significantly upgrade existing technology for transporting high-viscosity oil.

The article studies the acoustic characteristics of Russian speech under conditions of multitalker babble noise and manifestation of the Lombard effect in the context of auditory analysis of a complex scene. We have compared the spectral characteristics of stressed vowels [a], [u], [i] in words uttered by six women in completely quiet conditions and against a background of diotically presented multitalker babble noise at a level of 60 dB, imitating polyphony. In noise conditions, versus quiet, we obtained an increase in voice fundamental frequency (F0) and the first formant (F1) for all identified vowels. No overall pattern in changes in the second formant (F2) was found. When the vowel [i] was spoken in noise conditions, F2 decreased in all speakers; when vowels [u] and [a] were pronounced, it could have both decreased and increased. Thus, in general, the nature of the revealed changes in the spectral characteristics of the vowels of Russian speech in noise conditions corresponded to the features of Lombard speech for a number of European and Asian languages. For the first time, an inversely proportional relationship between F0 of a speaker in quiet conditions and its changes in noise conditions: the higher F0 in quiet conditions, the less its increase on a noise background . The revealed spectral changes reflect the processes of adaptive articulation correction aimed at highlighting the speaker’s voice and increasing the intelligibility of his speech against the background of multitalker babble noise.

Laser Doppler vibrometry is actively used in experimental studies because of its noncontact measurement technique. When using a stationary laser to measure the vibrations of rotating bodies and Fourier transform to process the results of such measurements, a problem arises, associated with a decrease in the frequency resolution of the spectra with increasing rotation rate of the body. As a result, at sufficiently high rotation rates, closely spaced discrete components may cease to be resolved. This paper proposes a method for solving such a problem using the least squares method. The operability of this processing method has been demonstrated on experimental data.

The causes of acoustic noise occurring during braking of electric vehicles, in particular, in the metro, were analyzed. The spectrum of such noise was measured, and it is shown that high-frequency discrete tones are excited by braking resistors, applied for electrodynamic braking of electric vehicles. Three proposed mechanisms of electromechanical interaction in a Fecral plate, which is a braking resistor element, were considered: the Ampère force and linear and nonlinear magnetostriction. It was shown that predominant odd harmonics indicate the presence of a significant piezomagnetic effect and the inverse effect of linear magnetostriction in the Fecral alloy. A phenomenological approach was used to calculate the piezomagnetic tensor elements for Fecral. Calculations by the finite element method showed that asymmetric cuts introduced into the plate may significantly decrease intensity of acoustic vibrations excited by the braking resistor.

An improved pulsed correlation gas flowmeter with clamp-on sensors for measuring gas flows in pipes has been created and studied. Such devices operate by measuring vortex motion velocity in a turbulent flow. The problems of isolating a weak useful signal that has passed through a gas against a background of interference from signals propagating along the pipe wall are discussed. A schematic of a correlation flowmeter with pulsed probing and the possibility of automatic search for a useful signal against a noise background is proposed. The operation of the flowmeter is demonstrated against the background of pipe wall vibrations and liquid droplets in the flow.

Curves of equal loudness for sounds of different frequencies and auditory frequency responses are discussed. It is shown that curves of equal loudness do not describe the auditory frequency response and are applicable only to tonal signals. The auditory frequency response can adapt to the sound spectrum. For music, a broadband frequency response is formed; for speech, a frequency response with low-frequency suppression is used.