Thermodynamic compatible model of microfractured porous media and Stoneley waves

Nonstationary theory of two-velocity continuum describing the propagation of acoustic waves inmicrofractured porousmedia is based on general physical principles: the first law of thermodynamics, the conservation laws, the kinematic relationships in the metric tensor and the Galilean principle of relativity. As a physical application, the theory of the Stoneley wave in microfractured porous media is developed. The simulation results are compared with the results of physical measurement of the Stoneley wave parameters in the boreholes. It is shown that an additional fluid transport through fractures makes it possible to satisfactorily correlate the experimental and theoretical data. In general, the developed theory is a nonlinear physical model of fluid dynamics in fractured porous media.     

Excitation mechanisms and dispersion characteristics of guided waves in multilayered cylindrical solid media

This paper first reviews a method of simulating the propagation characteristics of guided waves in multilayered coaxial cylindrical elastic solid media. Secondly, this method is used to investigate the properties of the guided waves for the ultrasonic long-range non-destructive evaluation techniques for rockbolts. To do so, the special case of non-leaky guided modes in open waveguides is considered. The method explains how the complex dispersion function is converted into a real function: hence the bisection technique can be employed to search for all the real roots. The model is used to (i) characterize the low dispersion range and anomalous dispersion of normal and Stoneley modes and (ii) analyze the excitation mechanisms of guided waves from axisymmetric and non-axisymmetric acoustic sources. The results are used to select suitable excitation frequency ranges associated with dominant modes with large amplitudes, low dispersion, and distinguishable propagation velocities to reduce signal distortion. The results suggest the lowest order flexural mode, excited by a radial force source, has potential to be used in practice. Also, the highly dispersive Stoneley mode propagating along a cylindrical interface is defined and distinguished from the normal mode using two properties, velocity high-frequency asymptotes and amplitude distributions along the radial direction.     

Shear-horizontal transverse-electric seismoelectric waves in cylindrical double layer porous media

The shear-horizontal(SH) waves excited by the shear source in a borehole are easy to analyze due to the simple waveform. The borehole-side structures make the formation properties discontinuous. We consider a cylindrical double layer structure and study the borehole shear-horizontal and transverse-electric(SH-TE) seismoelectric waves. We first derive the expressions of the basic field quantities, and simulate the acoustic field and electric field using the real axis integral method. Compared with the wave fields of an infinitely homogeneous porous medium outside the borehole, the cylindrical layered structure makes the multi-mode cylindrical Love waves and their accompanying electric fields excited.Next, in order to study the interface response law of the inducing electric fields, we use the secant integral method to calculate the interface converted electromagnetic waves and analyze the causes of each component. It is found that an interface response occurs each time the SH wave impinges the interface in the layered porous medium. The results show that the SH-TE mode has a potential application for borehole-side interface detection in geophysical logs.     

Radiation of surface Stoneley waves by distributed force sources acting at the solid earth-atmosphere interface

Using the Fourier transform, we find an integral solution describing the excitation of seismoacoustic waves in the solid Earth and the atmosphere by time-dependent forces arbitrarily distributed over the interface between the media. The solid Earth and the atmosphere are modeled by an isotropic solid half-space and a homogeneous gaseous half-space, respectively. Depending on the types of the excited surface and bulk waves, classification of the corresponding force distributions is performed. In the case of harmonic sources, an expression for the period-averaged radiated power of the Stoneley wave is obtained. For arbitrary time dependence of the forces, we find an expression describing the the Stoneley-wave energy radiated during the entire time of the source operation. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 7, pp. 624–637, July 2007.     

The effect of curvature on Stoneley waves

The effect of curvature is investigated for plane waves propagating in the circumferential direction along concave and convex cylindrical surfaces, and at the interface of a circular cylindrical inclusion in smooth or bonded contact with an unlike infinite medium. The waves propagate with an arbitrary, but generally large number of circumferential modes. These problems reduce to Rayleigh and Stoneley waves in the limit as the curvature vanishes. Dispersion relationships are presented for each case.     

Leaky Stoneley waves at a moving interphase boundary

The possibility of the existence of a leaky Stoneley wave at a uniformly moving interphase boundary defined as a jump in the acoustic parameters of an isotropic elastic medium is discussed. It is shown that the motion of the interphase boundary exerts dissimilar effects on the orientation of the wave normals of partial waves forming the Stoneley wave, and this results in different Doppler shifts of the frequencies of the partial waves in the laboratory frame of reference.     

Stoneley (interfacial) waves between two magneto-electro-elastic half planes

We investigated the propagation properties of Stoneley waves between two magneto-electro-elastic half planes. Magneto-electro-elastic materials are assumed to possess hexagonal (6 mm) symmetry. Twenty-five sets of magneto-electrical interface conditions were adopted and generalized frequency equations were derived and solved numerically. It was found that, for each set of interface conditions, existing Stoneley waves are always non-dispersive. Numerical results further show that material properties have a significant effect on both the number and velocity of Stoneley waves, and that, although different magneto-electrical interface conditions could influence the existence of Stoneley waves, they have no effect on wave velocities.     

弱界面固体附层媒质中的类Rayleigh波

当半无限大固体媒质上有一层固体附加层时表面波是频散的。由界面的“准弹簧”模型,本文导出了有各向同性固体附加层时半无限大各向同性均匀媒质中弱界面情况下的类Rayleigh波的特征方程。文中给出了典型复合结构具有刚性联接界面、滑移联接界面和弱界面时类 Rayleigh波的色散曲线,分析了界面刚度系数对类 Rayleigh波传播速度的影响。数值计算的结果表明选择合适的参数可以由低频超声类Rayleigh进行涂层结构界面特性的无损评价。     

Weak cylindrical gravitational waves

A study is made of the linearized Einstein equations without right-hand side on the background of a flat metric in cylindrical coordinates. General solutions are obtained by an expansion with respect to irreducible representations of the group of cylindrical symmetry. The solutions are investigated with allowance for additional conditions imposed on the physicogeometrical quantities, a monad choice being made of the frame of reference in the Chronometrie and kinemetric gauges.     

Radiative transfer in cylindrical media

A numerical method for the solution of the radiative transfer equation in a circularly symmetric, cylindrical region is developed. The transfer equation is formulated as a second-order differential equation resulting in a set of tridiagonal difference equations. This form is particularly well suited to line formation and energy balance calculations using the complete linearization method. Several numerical examples are presented.     

Excitation of Rayleigh and Stoneley surface acoustic waves by distributed seismic sources

Using the integral Fourier-transform technique, we obtain a solution in integral form to the problem of excitation of elastic waves in a homogeneous isotropic solid half-space and the bordering homogeneous gas by the time-dependent forces which are arbitrarily distributed in a solid over the plane parallel to the interface of the media. Different configurations of the force sources are analyzed from the viewpoint of excitation of different types of seismoacoustic waves. Expressions for the time-averaged radiated powers of the Stoneley wave at the gas–solid interface and the Rayleigh wave at the solid–vacuum interface as well as analytical expressions for the Rayleigh wave displacements, which are valid for large distances from the source, are obtained for the harmonic dependence of forces on time. Excitation of a Rayleigh wave by the point sources oriented vertically, i.e., along the normal to the surface of elastic half-space, and horizontally, i.e., parallel to this surface, is analyzed in detail. Analytical expressions for the Rayleigh-wave radiated power are obtained. The dependences of these powers on the source orientation and depth are derived. It is shown that the Rayleigh-wave radiated power decreases with distance between the point of the force application and the boundary and turns to zero for a source depth of about 17.5% of the wavelength of the transverse wave in the case of a horizontally oriented subsurface source and a medium with identical Lamé parameters λ and μ. This power increases and reaches a relative maximum when the source depth becomes equal to about 42.4% of the wavelength of the transverse wave and then exponentially falls off as the source depth increases. This maximum is about 5.5% of the surface-source radiated power.     

Optical absorption tunability and local electric field distribution of gold-dielectric-silver three-layered cylindrical nanotube

The effects of inner nanowire radius, shell thickness, the dielectric functions of middle layer and surrounding medium on localized surface plasmon resonance (LSPR) of gold-dielectric-silver nanotube are studied based on the quasi-static approximation. Theoretical calculation results show that LSPR of gold-dielectric-silver nanotube and LSPR numbers can be well optimized by adjusting its geometrical parameters. The longer wavelength of $\left|\omega_{-}^{-}\right\rangle$ mode takes place a distinct red-shift with increasing the inner nanowire radius and the thickness of middle dielectric layer, while a blue-shift with increasing outer nanotube thickness. The physical mechanisms are explained based on the plasmon hybridization theory, induced charges and phase retardation. In addition, the effects of middle dielectric function and surrounding medium on LSPR, and the local electric field factor are also reported. Our study provides the potential applications of gold-dielectric-silver nanotube in biological tissues, sensor and related regions.     

Finite element model for waves guided along solid systems of arbitrary section coupled to infinite solid media

The Semi-Analytical Finite Element (SAFE) method is becoming established as a convenient method to calculate the properties of waves which may propagate in a waveguide which has arbitrary cross-sectional shape but which is invariant in the propagation direction. A number of researchers have reported work relating to lossless elastic waves, and recently the solutions for nonpropagating waves in elastic guides and for complex waves in viscoelastic guides have been presented. This paper presents a further development, addressing the problem of attenuating waves in which the attenuation is caused by leakage from the waveguide into a surrounding material. This has broad relevance to many practical problems in which a waveguide is immersed in a fluid or embedded in a solid. The paper presents the principles of a procedure and then validates and illustrates its use on some examples. The procedure makes use of absorbing regions of material at the exterior bounds of the discretized domain.     

Dispersion characteristics of transverse surface waves in piezoelectric coupled solid media with hard metal interlayer

The propagation of transverse surface waves in a piezoelectric layer/metal substrate system with one or multiple hard metal interlayer(s) is investigated analytically. The general dispersion equations for the existence of the waves are obtained in a simple mathematic form for class 6 mm piezoelectric materials. The presence of a hard metal interlayer can not only get rid of the undesired mode appearing in the case without an interlayer but shorten the existence range of the phase velocity within which a nonleaky but dispersive mode exists. The effects of the hard interlayer on the phase velocity can be used to manipulate the behavior of the waves and has implications in acoustic wave devices.     

Plane and cylindrical shock waves in magnetogasdynamics

Summary The Chisnell-Chester-Whitham method has been used to study the propagation of diverging plane and cylindrical shock waves through an ideal gas in the presence of a magnetic field having only constant axial and azimuthal components, simultaneously for both weak and strong cases. By assuming an initial density distribution ϱ₀ = ϱ′r ^−W , where ϱ′ is the density at the plane/axis of symmetry andw is a constant, the analytical expressions for shock velocity and shock strength have been obtained. The expressions for the pressure, the density and the particle velocity immediately behind the shock have been derived for both the cases.

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Riassunto Il metodo di Chisnell-Chester-Whitham è stato usato per studiare la propagazione di onde d’urto divergenti cilindriche e piane attraverso un gas ideale in presenza di un campo magnetico che ha solo componenti costanti assiali e azimutali, contemporaneamente per casi deboli e forti. Assumendo una distribuzione di densità iniziale ϱ₀ = ϱ′r ^−W , dove ϱ′ è la densità al piano/asse di simmetria ew è una costante, si sono ottenute le espressioni analitiche per la velocità d’urto e la forza d’urto. Le espressioni per la pressione, la densità e la velocità delle particelle immediatamente dopo l’urto sono state determinate per entrambi i casi.

     

Guided waves in anisotropic media

This paper investigates the propagation of electromagnetic waves in a dielectric anisotropic medium containing conducting planes. A plane and rectangular waveguide is considered for certain particular cases of the orientation of the principal axis of the anisotropic medium relative to the waveguide coordinates. The dispersion equations for the propagation constants are deduced.In conclusion we thank D. A. Dobrotin for his advice.