Finite Difference Approach on Magnetohydrodynamic Stratified Fluid Flow Past Vertically Accelerated Plate in Porous Media with Viscous Dissipation

This study intends to evaluate the influence of temperature stratification on an unsteady fluid flow past an accelerated vertical plate in the existence of viscous dissipation.It is assumed that the medium under study is a grey,non-scattered fluid that both fascinates and transmits radiation.The leading equations are discretized using the finite differencemethod(FDM).UsingMATLABsoftware,the impacts of flowfactors on flowfields are revealed with particular examples in graphs and a table.In this regard,FDM results show that the velocity and temperature gradients increase with an increase of Eckert number.Furthermore,tables of the data indicate the influence of flow-contributing factors on the skin friction coefficients,and Nusselt numbers.When comparing constant and variable flow regimes,the constant flow regime has greater values for the nondimensional skin friction coefficient.This research is both innovative and fascinating since it has the potential to expand our understanding of fluid dynamics and to improve many different sectors.

Application of CPD in Analyzing EM Field in Stratified Media with an Uniform Plane Wave Slanted Through

The Counter-Propagation Deduction (CPD) method suggested by the authors is a new one for analyzing electromagnetic (EM) field in stratified media. The mechanism or the method is briefly introduced, and the rield in a layered medium in the presence or slant incidence of a perpendicularly or parallelly polarized electric wave is investigated. Some illustrative examples show that the method is capable of providing the direct mathematic expressions of the fields in an arbitrary layer, and is convenient for numerical evaluation through an unified program, irrespective of the number of medium layers.

Predicting suitability of different scale-dependent dispersivities for reactive solute transport through stratified porous media

In this paper,the behavior of breakthrough curves(BTCs) for reactive solute transport through stratified porous media is investigated.A physical laboratory model for layered porous media was constructed,in which thin layer of gravel was sandwiched in between two thick layers of natural soil.Gravel layer and natural soil layers were hydraulically connected as single porous continuum.A constant source of tracer was connected through gravel layer and elucidated at different sampling points in the direction of flow.Flexible multiprocess non-equilibrium(MPNE) transport equation with scale-dependent dispersivity function was used to simulate experimental BTCs of reactive solute transport through layered porous media.The values of equilibrium sorption coefficient and other input parameters were obtained experimentally.The simulation of BTC was performed using MPNE model with scale-dependent dispersivity.The simulation of different scale-dependent dispersivities was then compared and it was found that for field scale of estimation of dispersivity,asymptotic and exponential dispersivity functions performed better.In continuation to the comparison of simulated BTCs obtained using different models,spatial moment analysis of each aforesaid scale-dependent dispersivity model was also done.Spatial moment analysis provides the information related to mean solute mass,rate of mass travel,and mean plume dispersion.Linear and constant dispersivities showed higher variance as compared to asymptotic and exponential dispersion functions.This supports the field applicability of asymptotic and exponential dispersivity functions.The BTCs were also found to elucidate a nonzero concentration with time,which was clearly affected by physical non-equilibrium.In natural condition,such information is required in effective aquifer remediation process.

Analysis of wave propagation on human body based on stratified media model

Human body communication(HBC) is a promising near-field communication(NFC) method emerging in recent years. But existing theoretical models of HBC are too simple to simulate the wave propagation on human body. In this work, in order to clarify the propagation mechanism of electromagnetic wave on human body, a surface waveguide HBC theoretical model based on stratified media cylinder is presented. A numerical model analyzed by finite element method(FEM) is used for comparing and validating the theoretical model. Finally, results of theoretical and numerical models from 80 MHz to 200 MHz agree fairly well, which means that theoretical model can characterize accurate propagation mechanism of HBC signal. Meanwhile, attenuation constants derived from two kinds of models are within the range from 1.64 to 3.37, so that HBC signal can propagate effectively on human body. The propagation mechanism derived from the theoretical model is useful to provide design information for the transmitter and the modeling of the propagation channel in HBC.

A STUDY ON EM SCATTERING OF A TWO-DIMENSIONAL INHOMOGENEOUS STRUCTURE BURIED IN STRATIFIED MEDIA

The TM-polarized electromagnetic scattering problem of a two-dimensional inho-mogeneous structure buried in lossy stratified media is presented. Analysis work consists of two parts mainly, derivation of the Green’s function of a filament buried in lossy stratified media and constitution of the electric field integral equation of the equivalent current caused by the differences between the inhomogeneities and the stratified media. Based on these works, illustrative numerical results are given to model inhomogeneous underground tubes in lossy stratified media, and to describe the scattering field affected by different factors such as permittivity distribution, dimension, and buried depth of the inhomogeneities and so on.

Frequency related localisation of harmonic elastic waves in stratified welds

The paper presents a computational model for elastic waves in a structured weld adjacent to the free surface of an elastic solid. The main emphasis is on the interaction of waves with the micro-structure of the weld. Effects of localisation and channeling of waves are addressed. A model of a grain structure within the weld is also considered.

Parameter Inversions of Multi-Layer Media of Mars Polar Region with Validation of SHARAD Data

HF (high frequency) radar sounder technology has been developed for several missions of Mars surface/subsurface exploration. This paper presents a model of rough surface and stratified sub-surfaces to describe the multi-layer structure of Mars polar deposits. Based on numerical simulation of radar echoes from rough surface/stratified interfaces, an inversion approach is developed to obtain the parameters of Polar Layered Deposits, i.e. layers thickness and dielectric constants. As a validation example, the SHARAD radar sounder data of the Promethei Lingula of Mars South Polar region is adopted for parameters inversion. The result of stratification is also analyzed and compared with the optical photo of the deep cliff of Chasma Australe canyon. Dielectric inversions show that the deposit media are not uniform, and the dielectric constants of the Promethei Lingula surfaces are large, and become reduced around the depth of 20 m - 30 m, below where most of the deposits are nearly pure ice, except a few thin layers with a lot of dust.

Recursive algorithm and accurate computation of dyadic Green's functions for stratified uniaxial anisotropic media

A recursive algorithm is adopted for the computation of dyadic Green＇s functions in three-dimensional stratified uniaxial anisotropic media with arbitrary number of layers. Three linear equation groups for computing the coefficients of the Sommerfeld integrals are obtained according to the continuity condition of electric and magnetic fields across the interface between different layers, which are in correspondence with the TM wave produced by a vertical unit electric dipole and the TE or TM wave produced by a horizontal unit electric dipole, respectively. All the linear equation groups can be solved via the recursive algorithm. The dyadic Green＇s functions with source point and field point being in any layer can be conveniently obtained by merely changing the position of the elements within the source term of the linear equation groups. The problem of singularities occurring in the Sommerfeld integrals is efficiently solved by deforming the integration path in the complex plane. The expression of the dyadic Green＇s functions provided by this paper is terse in form and is easy to be programmed, and it does not overflow. Theoretical analysis and numerical examples show the accuracy and effectivity of the algorithm.

The modeling analysis of microwave emission from stratified media of non-uniform lunar cratered terrain surface for Chinese Chang-E1 observation

In China's first lunar exploration project,Chang-E 1,the multi-channel (3.0,7.8,19.35,37 GHz) microwave radiometers were aboard the satellite,with the purpose of measuring microwave brightness temperature from lunar surface and surveying the global distribution of lunar regolith layer thickness,and global evaluation of 3He content.To analyze the modeling of microwave radiative transfer from three-layered media of lunar surface,some factors,such as the cratered lunar surface roughness,scattering of regolith particulate medium with temperature profile,are discussed.Based on the statistics of the lunar cratered terrain and using Monte Carlo (MC) method,the cratered lunar surfaces are numerically generated.The triangulated network is utilized to divide the undulated lunar surface into discrete triangle meshes with the size 10 m as a digital surface topography.The reflectivities of each plane mesh are calculated,and the average reflectivity for all MC-realized lunar surfaces is obtained.It is found that under the spatial resolution of 30 km×30 km of Chang-E 1 radiometer observation,the lunar surface can be well modeled as a flat surface.It makes the predominance of the parameters,such as the regolith layer thickness and stratified structures,to be studied.Using the radiative transfer equation of stratified media with dense scatterers,the scattering coefficient of the regolith particulate medium is found negligible,and the emission is mainly governed by the absorptive property of the medium.Brightness temperature of multi-layered media,i.e.lunar soil,regolith layer with temperature profile and underlying rock media,are derived and calculated,and relevant main factors to affect the modeling and emission simulation are analyzed.

New method for wave radiation and propagation in anisotropic stratified media

A matrix-exponent method is proposed to treat wave radiation and propagation in anisotropic stratified media. By using matrix-exponent formulations, the present method is elegant for expressions and reliable for computations. As an example, the method is used to calculate the ELF excitation of the Earth-ionosphere waveguide by an equivalent dipole resulting from heating the lower ionosphere with modulated HF waves.

Full Waveform Inversion Method for Horizontally Inhomogeneous Stratified Media

Full waveform inversion method is an approach to grasp the physical property parameters of un- derground media in geotechnical nondestructive detection and testing field. Using finite-diference time domain(FDTD) method for elastic wave equations, the full-wave field in horizontally inhomogeneous stratified media for elastic wave logging was calculated. A numerical 2D model with three layers was computed for elastic wave propagation in horizontally inhomogeneous media. The full waveform inversion method was verified to be feasible for evaluating elastic parameters in lateral inhomogeneous stratified media and showed well accuracy and conver- gence. It was shown that the time cost of inversion had certain dependence on the choice of starting initial model. Furthermore, this method was used in the detection of nonuniform grouting in the construction of immersed tube tunnel. The distribution of nonuniform grouting was clearly evaluated by the S-wave velocity profile of grouted mortar base below the tunnel floor.

地铁杂散电流场的有限元模拟

为了研究地铁杂散电流场的分布规律及其影响范围,建立二维地铁杂散电流场数学模型,采用伽辽金有限单元法进行求解,根据有限元控制方程编制求解程序。对存在解析解的圆环域恒定电位场的模拟计算结果表明,该数学模型和计算程序是合理的可行的。对均匀介质、成层介质的地铁杂散电流场模拟计算结果表明:从地铁隧道到周围地下环境的电位都是非线性衰减的;距离地铁隧道越远,杂散电流强度越小;加大地铁隧道附近区域的电阻可以减小地铁杂散电流的影响范围。本文有限元模拟计算结果可作为确定杂散电流防护范围、定量评价地铁杂散电流对周围地下环境影响程度的依据。

横观各向同性层状场地的动力边界条件

采用横观各向同性层状弹性体模拟场地土 ,对该场地底部采用了三种不同的边界 :固定边界、阻尼边界及半空边界。推导了这三种边界条件的公式 ,并且给出了它们进入离散化后的 Rayleigh波与 L ove波的代数特征方程方法。然后 ,计算了场地在三种边界条件下对垂直及水平简谐集中荷载的位移响应 ,并与理论解进行了比较 ,指出了它们的适用范围。

瞬变电磁场的波场变换研究

通过对不同条件下层状介质模型瞬变电磁场数据的波场变换、分析，提高了对瞬变电磁场波场变换物理意义的认识，并总结出若干有价值的规律。指出这种通过数学方法变换出的波场，不仅在形式上满足波动方程，而且在导电介质中也存在“传播”现象，在“传播”过程中，当遇到电性分界面时，也存在“反射”和“透射”。这些结论为在瞬变电磁法中，正确合理地引入地震处理解释方法提供了重要的理论依据。

水平层状非均质横向同性地层中阵列多分量感应测井响应的快速计算

应用模式匹配算法研究建立水平层状非均质横向同性地层中多分量感应测井响应的快速算法.首先,利用Fourier级数展开法将多分量感应响应的数值模拟转化为三个轴对称问题,并利用电阻率径向导数的奇异表达式,引入两个附加奇异微分算子,用于描述柱状分界面上的积累面电荷对共面线圈系电磁响应的影响.然后通过模式匹配算法求解轴对称问题,得到水平层状非均质横向同性地层中多分量感应磁场的半解析解以及测井响应计算方法,最后通过数值模拟结果对该算法进行检验并进一步考察阵列多分量感应仪器的响应特征.

横观各向同性层状场地在SH波入射时共振特性

采用横观各向同性 (以下简称TI)层状弹性体模拟半空间之上的场地土 .首先推导了在入射SH波时TI弹性体界面上透射角的计算公式 ,然后利用笔者推得的在入射平面SH简谐波时TI弹性土层的刚度矩阵及TI层状场地的响应计算公式 ,计算了典型TI层状场地在SH简谐波入射时的频响函数 .计算表明 ,在入射角度较小时 ,场地的横、竖向模量比越大 ,则共振频率越低 ,而共振幅值越高 .

层状介质中大斜度井感应测井响应计算新方法

针对大斜度井环境中的测井响应计算问题,感应测井仪器发射源简化为一系列的磁偶极子,将其在层状地层中产生的电磁场分解成彼此独立的横电波(TE)和横磁波(TM),得到层状地层电磁场含有Bessel函数的解析解。引进高斯积分方法来计算无穷复数域的Bessel函数积分,方便地解决了这类积分问题。根据此方法计算并分析了当前常用的1503型双感应仪器在大斜度井中的测井响应特征,为正确认识和评价大斜度井感应测井资料提供重要依据。

层状介质弹性参数反演问题研究综述

地震波动方程反问题的研究具有重要的理论意义和实践意义．由于高维波动方程反演问题理论研究的困难和巨大的计算量，层状介质弹性参数反演研究在数学界和地球物理学界引起了广泛的关注．经过前人近三十年的努力，一维声波方程的单参数反演理论已趋成熟，并已逐步实用化．基于矢量波动方程的多参数反演、非脉冲响应对应的反问题是层状介质弹性参数反演需要进一步深入研究的问题．

半空间电场型并矢格林函数及其数值计算

从均匀介质中偶极子的辐射场出发,通过谱域展开,推导出半空间的电场型并矢格林函数谱域积分(索末菲尔德积分)形式的完整表达,包括场点与源点处于同侧或异侧时对应的格林函数,重点讨论了场点和源点在垂直方向重合时的结果及其物理解释,排除了一般表达式在场源横向距离为零时会出现奇异性的问题。通过严格的数值积分方法计算半空间分界面的场分布来对公式的正确性进行了检验。

圆柱分层介质中格林函数的完整求解 Ⅰ:场型格林函数

完整、详细地推导了圆柱分层介质中由z、φ和ρ方向电偶极子产生的电场、磁场的谱域、空域格林函数,从而为利用矩量法准确分析圆柱共形微带天线提供了理论基础。另外,在文献[2-6]的基础上提出了一种稳定性好的快速计算圆柱分层介质格林函数的数值分析方法。数值计算结果说明了本文公式的正确性及改进后方法的优越性。