SOME PROPERTIES OF FAR FIELD PATTERNS OF ACOUSTIC WAVES IN AN INHOMOGENEOUS MEDIUM

In this paper, by using functional analysis and integral equation method, we obtain some results about the properties of far field of acoustic waves in an inhomogeneous medium. And we also discuss some ill-posed inverse scattering problems by Tikhonov regularization method.

Propagation of plane waves in poroviscoelastic anisotropic media

This study discusses wave propagation in perhaps the most general model of a poroelastic medium. The medium is considered as a viscoelastic, anisotropic and porous solid frame such that its pores of anisotropic permeability are filled with a viscous fluid. The anisotropy considered is of general type, and the attenuating waves in the medium are treated as the inhomogeneous waves. The complex slowness vector is resolved to define the phase velocity, homogeneous attenuation, inhomogeneous attenuation, and angle of attenuation for each of the four attenuating waves in the medium. A non-dimensional parameter measures the deviation of an inhomogeneous wave from its homogeneous version. An numerical model of a North-Sea sandstone is used to analyze the effects of the propagation direction, inhomogeneity parameter, frequency regime, anisotropy symmetry, anelasticity of the frame, and viscosity of the pore-fluid on the propagation characteristics of waves in such a medium.

Seismic reflection and transmission coefficients of a single layer sandwiched between two dissimilar poroelastic solids

The seismic reflection and transmission characteristics of a single layer sandwiched between two dissimilar poroelastic solids saturated with two immiscible viscous fluids are investigated. The sandwiched layer is modeled as a porous solid with finite thickness. The propagation of waves is represented with potential functions. The displacements of particles in different phases of the aggregate are defined in terms of these potential functions. Due to the presence of viscosity in pore fluids, the reflected and transmitted waves are inhomogeneous in nature, i.e., with different directions of propagation and attenuation. The closed-form analytical expressions for reflection and transmission coefficients are derived theoretically for appropriate boundary conditions. These expressions are calculated as a non-singular system of linear algebraic equations and depend on the various parameters involved in this non-singular system. Hence,numerical examples are studied to determine the effects of various properties of the sandwich layer on reflection and transmission coefficients. The essential features of layer thickness, incident direction, wave frequency, liquidsaturation and capillary pressure of the porous layer on reflection and transmission coefficients are depicted graphically and discussed. The analysis shows that reflection and transmission coefficients are strongly associated with incident direction and various properties of the porous layer.

Fast and accurate analysis of electromagnetic scattering from targets situated in dielectric half space

Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based on derivation of dyadic Green＇s functions in this environment. The coupling is divided into nearby region and well-separated region by grouping. The Green＇s function can be divided into two parts： primary term and reflected term. In the well-separated region, the two terms are both expressed as Sommerfeld integral, which can be accelerated by deforming integral path and taking interpolation and extrapolation. For the nearby region, the direct Sommerfeld integral makes the filling of impedance matrix time-expensive. A tabulation and interpolation method is applied to speed up this process. This infinite integral is pre-computed in sampling region, and a two-dimensional table is then set up. The impedance elements can then be obtained by interpolation. Numerical results demonstrate the accuracy and efficiency of this algorithm.

The characteristics of variation in inhomo geneity of temporalspatial distribution of short to imminent precursors before strong earthquakes

C_v is used in this paper to describe the variation in inhomogeneity of spatial and temporal distribution of precur sors. The inhomogeneous variation in the spatial and temporal distribution of the anomalies in water radon and electromagnetic waves before M_s≈6 earthquakes in northern North China is analyzed in detail. Results show that before a moderate to strong earthquake, the distribution of anomalies in water radon and electromagnetic waves changes inhomogeneously, i.e., C_v increases significantly. The inhomogeneity in spatial distribution of short-to- imminent precursors increases before a strong earthquake, which may relates to the enhancement of crustal strain field. The research will not only help us to know more about the process of seismogeny and to improve practical earthquake prediction, but also blaze a new way to do earthquake prediction with present precursor data.

Study of inhomogeneous and heterogeneous ultrasonic waves in kidney stones

Renal calculi are inhomogenous, heterogeneous and complex in nature. There is a large variation in their chemical composition due to food habits of patients and hence geography of the inhabitants in different parts of the world. Ultrasonic studies are made to investigate various physical and other constants of such renal calculi. A double-probe through transmission technique is used to study various propagation parameters. The ultrasonic waves displayed on cathode-ray oscilloscope are complex and complicated in nature. Complete analysis of such wave patterns is given in the present study. The data reported would help in the design of an u ltrasonic lithotripter.

Fast Inhomogeneous Plane Wave Algorithm for Homogeneous Dielectric Body of Revolution

To solve the electromagnetic scattering problem for homogeneous dielectric bodies of revolution(BOR),a fast inhomogeneous plane wave algorithm is developed.By using the Weyl identity and designing a proper integration path,the aggregation and disaggregation factors can be derived analytically.Compared with the traditional method of moments(MoM),both the memory and CPU time requirements are reduced for large-scale homogeneous dielectric BOR problems.Numerical results are given to demonstrate the validity and the efficiency of the proposed method.

Ellipticity of motion of particle in field of inhomogeneous plane wave

The elliptic motion of particle in the fields of the inhomogeneous plane wavs that are generated on a liquid thermoviscoelastic solid interface is studied.. Calculations show that the ellipticity of the motion of Particle is related to the incident angle that the homogeneous plane wave incidents upon the interface. The influeree of viscous properties of solid on the ellipticity of particle's motion is small and shows near the critical angles of longitudinal and transversal wavs. Under the incidence at Rayleigh angle, the change of the ellipticity of motion of the particle is periodic in the wake of its Rayleigh wavelength and its elliptic locus is couoter clockwise and clockwise rotation periodically.

The progress in the verification of key technologies for floating structures near islands and reefs

In 2019 a Scientific Research&Demonstration Platform was deployed near islands and reefs in South China Sea by a joint research group of 7 institutes and universities in China.It is a simplified small model of a two-module semi-submersible-type VLFS.The test on site has continued for more than one and half years since then for long-term observations to validate the developed key technologies for design and behavior predictions of floating structures deployed near islands and reefs.An integrated information system was set up to continuously collect and inspect the data of the encountered waves,structure responses,connector forces,mooring line forces,anti-corrosion status of the platform,the performance efficiencies of a floating breakwater nearby and a wave energy converter attached on the breakwater.In this paper,the status of the on-site measurements and validations of the key technologies are briefly described.

The influence of rock anisotropy on elliptical-polarization state of inhomogenously refracted P-wave

This paper discusses the influence of the anisotropy parameters on elliptical-polarization of the inhomogenously refracted P-wave induced at VTI-media interface.For this refracted P-wave,we have derived,the equations of the elliptical-polarization trajectory.Following the elliptical-polarization trajectory,we calculated the effects of the rock anisotropic-parameters on the polarization state,with a Poincare-sphere-like representation,for several varying media parameters.It is noted that the size,shape and initial phase angle of the elliptical-polarization trajectory are all depending the anisotropy media,as well as on the incident-angle.We expect that the findings from this paper would be applied to practical applications of seismic exploration.

A sweeping preconditioner for Yee＇s finite difference approximation of time-harmonic Maxwell＇s equations

This paper is concerned with the fast iterative solution of linear systems arising from finite difference discretizations in electromagnetics. The sweeping preconditioner with moving perfectly matched layers previously developed for the Helmholtz equation is adapted for the popular Yee grid scheme for wave propagation in inhomogeneous, anisotropic media. Preliminary numerical results are presented for typical examples.