Ultrasonic wave propagation in rare-earth monochalcogenides

The ultrasonic attenuation in thulium monochalcogenides TmX (X=S, Se and Te) has been studied theoretically with a modified Mason’s approach in the temperature and range 100 K to 300 K along 〈100〉, 〈110〉 〈111〉 crystallographic directions. The thulium monochalcogenides have attracted a lot of interest due to their complex physical and chemical characteristics. TmS, TmSe and TmTe are trivalent metal, mixed valence state, and divalent semiconductor, respectively. Coulomb and Born-Mayer potential is applied to evaluate the second- and third-order elastic constants. These elastic constants are used to compute ultrasonic parameters such as ultrasonic velocities, thermal relaxation time, and acoustic coupling constants that, in turn, are used to evaluate ultrasonic attenuation. A comparison of calculated ultrasonic parameters with available theoretical/experimental physical parameters gives information about classification of these materials.      

Acoustic wave propagation in bent thin-walled wave guides

Theoretical analysis of sound wave propagation in structures indicates considerable amplitude reduction during transmission through a bent joint, while some build-up can be observed in front of the bend. Every type of transmitted wave (longitudinal and flexural in plane frames) is found to combine with other forms of sound propagation as a result of the deflection of the axis of the wave guide. The screening effect of the bend, in solids with arbitrary viscoelastic properties, is evident even under highly simplified assumptions, such as compatibility and equilibrium. By solving several practical problems, the attenuation due to folding of the structure is compared to the damping effect of the material, with the conclusion that the former contribution is the larger of the two. A pair of examples of insulation analysis of structures is worked out, and the results yield the particle velocity—the first step in determining the radiation pattern. The influence of dense columns in walls, of beams in plates, and of coupling effects in bent structures are examined.     

Acoustic wave propagation in high-pressure system

Recently, substantial attention is paid to the development of methods of generation of pulsations in high-pressure systems to produce pulsating high-speed water jets. The reason is that the introduction of pulsations into the water jets enables to increase their cutting efficiency due to the fact that the impact pressure (so-called water-hammer pressure) generated by an impact of slug of water on the target material is considerably higher than the stagnation pressure generated by corresponding continuous jet. Special method of pulsating jet generation was developed and tested extensively under the laboratory conditions at the Institute of Geonics in Ostrava. The method is based on the action of acoustic transducer on the pressure liquid and transmission of generated acoustic waves via pressure system to the nozzle. The purpose of the paper is to present results obtained during the research oriented at the determination of acoustic wave propagation in high-pressure system. The final objective of the research is to solve the problem of transmission of acoustic waves through high-pressure water to generate pulsating jet effectively even at larger distances from the acoustic source. In order to be able to simulate numerically acoustic wave propagation in the system, it is necessary among others to determine dependence of the sound speed and second kinematical viscosity on operating pressure. Method of determination of the second kinematical viscosity and speed of sound in liquid using modal analysis of response of the tube filled with liquid to the impact was developed. The response was measured by pressure sensors placed at both ends of the tube. Results obtained and presented in the paper indicate good agreement between experimental data and values of speed of sound calculated from so-called "UNESCO equation". They also show that the value of the second kinematical viscosity of water depends on the pressure.     

Acoustic wave propagation in liquid helium II

Elsewhere [1], using the framework of multipolar continuum mechanics, the authors have discussed a possible alternative to the two-fluid theories for liquid helium 11 and showed that, in the case when the fluid is assumed to be incompressible, second sound waves exist in both the stationary and rotating fluid. Here the constitutive theory presented in the paper cited is extended to include the effects of compressibility and viscosity and a study of these effects on the propagation of small-amplitude waves. 1t is found that the qualitative predictions agree with the experimental observations in helium II.     

Acoustic wave propagation in two-phase heterogeneous porous media

The propagation of an acoustic wave through two-phase porous media with spatial variation in porosity is studied. The evolutionary wave equation is derived, and the propagation of an acoustic wave is numerically analyzed in application to marine sediments with various physical parameters.     

声波在球状准周期多层介质中的传播

运用转移矩阵方法研究了声波在准周期球形多层介质中的传播，与周期性结构比较它具有不同结构的通带和禁带，且随介质层数的增加声波衰减速度变慢。声波透射系数还随介质厚度的改变发生周期性的变化。     

Acoustic wave propagation in fluid metamaterial with solid inclusions

Acoustic wave propagation in a composite of water with embedded double-layered silicone resin/silver rods is considered. Approximate values of effective dynamical constitutive parameters are obtained. Frequency ranges of simultaneous negative constitutive parameters are found. Localized surface states on the interface between metamaterial and “normal” material are found. The Doppler effect in metamaterial is considered. The presence of anomalous modes is shown.     

Acoustic wave propagation in a binary mixture of inviscid fluids

Linearized equations governing the thermo-mechanical behaviour of a binary mixture of inviscid fluids are derived. Restrictions which are sufficient for the equations to have a unique solution are imposed on some of the material constants. The propagation of plane harmonic waves of small amplitude in the mixture is examined and the inequalities are shown to ensure a physically reasonable response. As an application of the theory properties of acoustic waves in a binary mixture of ideal gases are evaluated numerically.     

High pressure structural phase transition in uranium monochalcogenides

The pressure induced phase transition in uranium monochalcogenides, UX (X = S, Se, and Te) is studied by two-body potential approach. It is found that US, USe and UTe undergo a structural phase transition from NaCl (B1) type to CsCl (B2) type at 78.5, 21 and 9.5 GPa, respectively, which is in good agreement with the recent experimental data. In addition, second-order elastic constants (SOECs) (C ₁₁, C ₁₂ and C ₁₄) have been calculated which can be used to establish the nature of the forces in these materials. The present study shows that the considered two-body potential model can be used to predict the phase transition pressure in UX compounds provided the strength and hardness parameters in B1 and B2 phases are different.     

Acoustic propagation from a spiral wave front source in an ocean environment

A spiral wave front source generates a pressure field that has a phase that depends linearly on the azimuthal angle at which it is measured. This differs from a point source that has a phase that is constant with direction. The spiral wave front source has been developed for use in navigation; however, very little work has been done to model this source in an ocean environment. To this end, the spiral wave front analogue of the acoustic point source is developed and is shown to be related to the point source through a simple transformation. This makes it possible to transform the point source solution in a particular ocean environment into the solution for a spiral source in the same environment. Applications of this transformation are presented for a spiral source near the ocean surface and seafloor as well as for the more general case of propagation in a horizontally stratified waveguide.     

Acoustic wave propagation through the boundary between a liquid and the Heusler ferromagnetic alloy

Incidence of an acoustic wave upon a plane boundary between a liquid and a ferromagnetic crystal is considered. The ferromagnet is the Ni_2+x+y Mn_1−x Ga_1−y Heusler alloy with a shape memory, which is in the region of the premartensite or martensite phase transition in temperature. The directions of propagation and polarization and the amplitudes of the reflected and transmitted quasilongitudinal and quasitransverse waves in the (110) plane of the crystal are determined. Starting from a certain critical angle of incidence, a longitudinal wave in the crystal becomes inhomogeneous and gliding along the boundary with an accompanying surface oscillation. In the vicinity of the phase transition point, this wave may be radiated into the crystal bulk. Proceeding from the experimental data by Trivisonno for ultrasonic velocities and absorption in a Ni₂MnGa crystal, numerical estimates are obtained for the aforementioned acoustic effects.     

Electromagnetic wave propagation with negative phase velocity in regular black holes

We discuss the propagation of electromagnetic plane waves with negative phase velocity in regular black holes. For this purpose, we consider the Bardeen model as a nonlinear magnetic monopole and the Bardeen model coupled to nonlinear electrodynamics with a cosmological constant. It turns out that the region outside the event horizon of each regular black hole does not support negative phase velocity propagation, while its possibility in the region inside the event horizon is discussed.     

Stress wave propagation in A1 single crystals

Transmitted wave profiles are presented for A1 single crystals that were loaded along crystallographic directions [100], [110] and [111] by a stress wave of the amplitude 1·85 GPa. The experiments were carried out with the Hopkinson Split Bar Technique. The observed wave profiles strongly depend on the specimen length. The constitutive relation of elastic-plastic-relaxing solid was proposed for the interpretation of obtained results. Mechanical properties can then be inferred by comparing observed rates of decay with theoretical models of stress relaxation.     

Acoustic shock wave propagation in a heterogeneous medium: a numerical simulation beyond the parabolic approximation

Numerical simulation of nonlinear acoustics and shock waves in a weakly heterogeneous and lossless medium is considered. The wave equation is formulated so as to separate homogeneous diffraction, heterogeneous effects, and nonlinearities. A numerical method called heterogeneous one-way approximation for resolution of diffraction (HOWARD) is developed, that solves the homogeneous part of the equation in the spectral domain (both in time and space) through a one-way approximation neglecting backscattering. A second-order parabolic approximation is performed but only on the small, heterogeneous part. So the resulting equation is more precise than the usual standard or wide-angle parabolic approximation. It has the same dispersion equation as the exact wave equation for all forward propagating waves, including evanescent waves. Finally, nonlinear terms are treated through an analytical, shock-fitting method. Several validation tests are performed through comparisons with analytical solutions in the linear case and outputs of the standard or wide-angle parabolic approximation in the nonlinear case. Numerical convergence tests and physical analysis are finally performed in the fully heterogeneous and nonlinear case of shock wave focusing through an acoustical lens.     

A phase regulated back wave propagation technique for geoacoustic inversion

An inversion method based on the concept of back wave propagation (BWP) is described in this paper for estimation of geoacoustic parameters from acoustic field data. A phase-regulation technique is introduced to increase the sensitivity of the method for geoacoustic model parameters having low sensitivity. The case of data consisting of signal plus additive noise is also addressed. It is shown theoretically that the sensitivity can be increased by a factor alpha using the phase regulation procedure, and that the spatial resolution of signal energy that is concentrated by BWP at the known source position is increased when a increases. This result suggests an effective criterion for use in the inversion, based on the spatial distribution of signal energy around the true source location. The basis for the criterion is the spatial variance of the back-propagated pressure field in a window around the known source location. A multistep search process is proposed to avoid using a complicated multidimensional search process. Inversion results from both simulations and experimental data are given. The real data were taken from the Pacific Shelf experiment carried out in shallow water off the West Coast of Vancouver Island in the Northeast Pacific Ocean.     

Acoustic propagation in the subsurface sound channel

Experimental data obtained in the kilohertz frequency band for the sound propagation in the subsurface channel formed by the wind-caused mixing of subsurface waters are discussed. The data were obtained in different years in the northeastern region of the Atlantic Ocean, where the subsurface waters down to the depths of 40–70 m are mixed by both wind waves and the swell that arrives from distant ocean areas. The hydrological conditions in the subsurface waters of this region are characterized by a good reproducibility. The spatial structure of the sound field and the attenuation of sound propagating in the subsurface channel are analyzed. The origin of the additional attenuation (in comparison with the absorption in sea water) is discussed. The data of our experiments are compared with those obtained by other experimenters and with the calculations performed using the computer code by Avilov. The necessity of improving the computer codes to allow for the scattering of sound beyond the channel under the influence of the swell, whose parameters are unrelated to the wind regime at the experimental site, is emphasized.     

Simulation of extended phase screens in problems of optical wave propagation through the atmosphere

Turbulent medium in problems of optical wave propagation through the atmosphere is usually nodeled as a set of statistically independent plane screens with a random two-dimensional field of phase progress. In this paper, we develop methods for the formation of nonperiodic phase screens infinitely extended in a certain direction, which are required in problems of dynamic simulation of wave propagation. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 1, pp. 21–34, January 2006.