Sound diffraction on an elastic spheroidal shell

Object and purpose of research. This paper obtains solutions and performs estimations of characteristics of sound reflection and scattering by ideal and elastic bodies of various shapes (analytical and non-analytical) near media interface, or underwater sonic channel, or in a planar waveguide with a solid elastic bottom. Materials and methods. The harmonic signals are investigated with the method of normal waves based on the phase velocity of signal propagation, and impulse signals related to the energy transfer are studied using the method of real and imaginary sources and scatterers based on the group velocity of propagation. Main results. The scattered sound field is calculated for ideal spheroids (elongated and compressed) at fluid – ideal medium interface. The spectrum of a scattered impulse signal is calculated for a body placed in a sonic channel. First reflected impulses are found for an ideal spheroid in a planar waveguide with anisotropic bottom. Conclusion. In the studies of diffraction characteristics of bodies at media interfaces it was found that the main contribution to scattered field is given by interference of scattered fields rather than interaction of scatterers (real or imaginary). It is shown that at long distances the spectral characteristics of the channel itself have a prevalent role. When impulse sound signals in the planar waveguide are used, it is necessary to apply the method of real and imaginary sources and scatterers based on the group velocity of sound propagation.

Using the Kirchhoff integral for approximate calculation of angular characteristics of sound scattering by elastic shells of nonanalytical form

Предложен новый приближенный метод расчета угловых характеристик рассеяния звука на упругих телах неаналитической формы при различных геометрических параметрах стыкуемых фрагментов аналитической формы. Метод базируется на использовании интегральной формулы Кирхгофа и известных строгих решениях задач дифракции звука на упругих аналитических телах. Совместное использование методов динамической теории упругости и разделения переменных с помощью потенциалов Дебая и «типа Дебая» позволяет получить решения задач дифракции звука на изотропных оболочках неаналитической формы, составленных из компонентов сфероидальной, цилиндрической и сферической форм. Вычислены и проанализированы угловые характеристики рассеяния при различных волновых размерах, геометрических и физических параметрах оболочек. Применение рассматриваемого метода имеет особенно актуально в диапазонах низких и средних звуковых частот, где упругие тела являются эффективными рассеивателями звука, что повышает вероятность определения их индивидуальных признаков. A new approximate method for calculating the angular characteristics of sound scattering on elastic bodies of non-analytical form for various geometric parameters of the joined fragments of the analytical shape we proposed. The method they based on the use of the Kirchhoff integral formula and well-known rigorous solutions of sound diffraction problems on elastic analytical bodies. The combined use of methods of the dynamic theory of elasticity and separation of variables using Debye potentials and "Debye type" potentials allows us to obtain solutions to problems of sound diffraction on isotropic shells of non-analytical form composed of components of spherical, cylindrical and spherical forms. Angular scattering characteristics are calculated and analyzed for various wave sizes, geometric and physical parameters of the shells are calculated. The application of this method is particularly relevant in the low and medium sound frequency ranges, where elastic bodies are effective sound diffusers, which increases the probability of determining their individual characteristics.

Analytical representation of hydrophone complex frequency response

The problem of analytical representation of hydrophone complex frequency response based on a model consisting of an advance line and a minimum-phase part, which describing the effect of sound diffraction and resonance properties of an active element, is considered. Algorithms are proposed for approximating the hydrophone complex frequency response by a fractional-rational function of the complex variable according to the data of the hydrophone amplitude-frequency and/or phasefrequency responses. Examples of the application of these algorithms for processing experimental frequency characteristics of hydrophones are given.

Determination of the hydrophone phase-frequency response by its amplitude-frequency response

One of the tasks of the COOMET 786/RU/19 pilot comparisons is to check the correctness of the hydrophone model proposed in VNIIFTRI, consisting of an advance line and a minimum-phase part, including the effect of sound diffraction and resonance properties of the active element. This model makes it possible to use the Hilbert transform to obtain the phase-frequency response from the amplitude-frequency response as well as for inverse operation. The results of measuring experiments performed using facilities of the State Primary Standard GET 55-2017 are presented. For many practical tasks, it is not necessary to obtain the phase-frequency response for an acoustic center of the receiver. It is enough to determine the shape of the phase-frequency response using much less laborious methods. The question of which of the characteristics is expedient to determine during calibration - for an acoustic center, or for a point on the surface of an active element, deserves a discussion among specialists performing acoustic measurements.

Acoustic Monitoring of Anomalous Stressed Zones, Determination of their Positions, Surfaces, Evaluation of Catastrophic Risk.

<p>Self-organization is not a universal property of matter, it exists under certain internal and external conditions and this is not associated with a special class of substances. The study of the morphology and dynamics of migration of anomalous zones associated with increased stresses is of particular importance in the development of deep deposits, complicated by dynamic phenomena in the form of mountain impacts. An important tool for this study is geophysical exploration. To describe the geological environment in the form of an array of rocks with its natural and technogenic heterogeneity, one should use its more adequate description, which is a discrete model of the medium in the form of a piecewise inhomogeneous block medium with embedded heterogeneities of a lower rank than the block size. This nesting can be traced several times, i.e. changing the scale of the research, we see that heterogeneities of a lower rank now appear in the form of blocks for heterogeneities of the next rank. A simple averaging of the measured geophysical parameters can lead to distorted ideas about the structure of the medium and its evolution. We have analyzed the morphology of the structural features of disintegration zones before a strong dynamic phenomenon. The introduction of the proposed integrated passive and active geophysical monitoring into the mining system, aimed at studying the transient processes of the redistribution of stress-strain and phase states, can help prevent catastrophic dynamic manifestations during the development of deep-seated deposits. Active geophysical monitoring methods should be tuned to a model of a hierarchical heterogeneous environment. Iterative algorithms for 2-D modeling and interpretation for sound diffraction and a linearly polarized transversal elastic wave on the inclusion with a hierarchical elastic structure located in the J-th layer of the N-layer elastic medium are constructed. The case is considered when the inclusion density of each rank coincides with the density of the containing layer, and the elastic parameters of inclusion of each rank differ from the elastic parameters of the containing layer.<br><br></p>

Diffraction of sound waves by a lined cylindrical cavity

In this paper, diffraction of sound waves through a lined cavity is analyzed rigorously. The inner–outer surfaces of the cavity and the base of the cavity are coated with three different absorbing linings. By using the Fourier transform technique in conjunction with the Mode-Matching method, the related boundary value problem is formulated as a Wiener–Hopf equation. In the solution, two infinite sets of unknown coefficients are involved that satisfy two infinite systems of linear algebraic equations. Numerical solution of this system is obtained for various values of the parameters of the problem. The graphical results are also presented which show that how efficiently the sound diffraction can be reduced by selection of problem parameters.