共查询到20条相似文献，搜索用时 15 毫秒
1.
T. Senjuntichai S. Mani R.K.N.D. Rajapakse 《Soil Dynamics and Earthquake Engineering》2006,26(6-7):626-636
This paper considers time-harmonic vertical vibration of an axisymmetric rigid foundation embedded in a homogeneous poroelastic soil. The soil domain is represented by a homogeneous poroelastic half space that is governed by Biot's theory of poroelastodynamics. The foundation is subjected to a time-harmonic vertical load and is perfectly bonded to the surrounding half space. The contact surface can be either fully permeable or impermeable. The dynamic interaction problem is solved by employing an indirect boundary integral equation method. The kernel functions of the integral equation are the influence functions corresponding to vertical and radial ring loads, and a ring fluid source applied in the interior of a homogeneous poroelastic half space. Analytical techniques are used to derive the solution for influence functions. The indirect boundary integral equation is solved by using numerical quadrature. Selected numerical results for vertical impedance of rigid foundations are presented to demonstrate the influence of poroelastic effect, foundation geometry, hydraulic boundary condition along the contact surface and frequency of excitation. 相似文献
2.
The basic formulation for the mutual coupling between grounded circuits in the presence of a vertical conductor is used to examine the full electromagnetic and induced polarization response for a homogeneous half-space model. Both interfacial polarization at the steel/electrolyte boundary and induced eddy currents in the casing are accounted for in the analysis. It is shown that for mild steel casings the eddy currents, hitherto neglected, play an important role because of their strong frequency dependence. Calculated curves of the appar- ent complex resistivity as a function of frequency show that the overall response can be influenced by the state of corrosion at the surface of the casing. 相似文献
3.
PETER FURNESS 《Geophysical Prospecting》1993,41(6):779-790
Two methods for computing spontaneous mineralization potentials in the region external to the source body are reviewed. The first of these is a long-established technique in which the causation is assumed to be a distribution of simple current source on the boundary of the mineralization. The second is a more recent technique which assumes a surface distribution of current dipole moment (double layer) along the boundary of the source body. The former technique is a special case of a more general spontaneous potential (SP) model in which the source is a density of current dipole moment (current polarization) distributed throughout the mineralization. As far as the potentials in the region external to the source body are concerned this current polarization can be simply related to an equivalent double layer source function, i.e. the potential discontinuity produced over the boundary of the mineralization by an equivalent double layer model. This simple relationship suggests an integral equation technique for the exact numerical solution of boundary value problems appropriate to the polarization model for spontaneous mineralization potentials. The technique is applied to exploring the justification of interpreting mineralization self-potentials by the traditional approach. 相似文献
4.
A new experimental method using a finite soil model with no special treatement on its boundaries is employed for soil-structure intration problems to simulate the semi-infinitenesss of the actual soil medium. The present method utlizies the characteristics of transient response to an impluse load to obtain the impedance functions and effective input motions for surface and embedded foundations. This technique is applicable to a linear elastic system whose impulse response decreases to a small enough value before observing the reflected waves. The experimentally obtained impedance functions and effective input motions are compared with those obtained by the direct boundary integral equation method and the hybrid approach. Good agreement between the xperimental and analytical results validates the present method as well as the accuracy of the numerical tools. 相似文献
5.
6.
Haiming Zhang Xiaofei Chen College of Earth Sciences Graduate University of Chinese Academy of Sciences Beijing China School of Earth Space Sciences University of Science Technology of China Hefei China 《地震学报(英文版)》2009,(1)
In this study, we preliminarily investigated the dynamic rupture process of the 1999 Chi-Chi, Taiwan, earthquake by using an extended boundary integral equation method, in which the effect of ground surface can be exactly included. Parameters for numerical modeling were carefully assigned based on previous studies. Numerical results indicated that, although many simplifications are assumed, such as the fault plane is planar and all heterogeneities are neglected, distribution of slip is still consistent roug... 相似文献
7.
8.
9.
Roland Klees 《Surveys in Geophysics》1993,14(4-5):419-432
The Boundary Element Method (BEM), a numerical technique for solving boundary integral equations, is introduced to determine the earth's gravity field. After a short survey on its main principles, we apply this method to the fixed gravimetric boundary value problem (BVP), i.e. the determination of the earth's gravitational potential from measurements of the intensity of the gravity field in points on the earth's surface. We show how to linearize this nonlinear BVP using an implicit function theorem and how to transform the linearized BVP into a boundary integral equation using the single layer representation. A Galerkin method is used to transform the boundary integral equation using the single layer representation. A Galerkin method is used to transform the boundary integral equation into a linear system of equations. We discuss the major problems of this approach for setting up and solving the linear system. The BVP is numerically solved for a bounded part of the earth's surface using a high resolution reference gravity model, measured gravity values of high density, and a 50 50 m2 digital terrain model to describe the earth's surface. We obtain a gravity field resolution of 1 1 km2 with an accuracy of the order 10–3 to 10–4 in about 1 CPU-hour on a Siemens/Fujitsu SIMD vector pipeline machine using highly sophisticated numerical integration techniques and fast equation solvers. We conclude that BEM is a powerful numerical tool for solving boundary value problems and may be an alternative to classical geodetic techniques. 相似文献
10.
系统地论述了大地电磁三维交错采样有限差分数值模拟算法实现过程中交错网格剖分、积分公式离散化、边界条件、方程组求解、三维张量阻抗的计算等内容. 由于提出了简洁的边界条件，采用了解大型系数矩阵方程组的双共轭梯度稳定解法，所实现的三维交错采样有限差分数值模拟算法具有迭代收敛稳定、计算精度高、速度快等特点. 通过两个理论模型的计算结果检验了算法的正确性和计算精度. 所实现的三维交错采样有限差分数值模拟算法为研究三维反演问题奠定了基础. 相似文献
11.
本文提出了一种基于非结构化网格的海洋电磁有限单元正演算法.为了回避场源奇异性,文中选用二次场算法,将背景电阻率设置为水平层状且各向异性,场源在水平层状各向异性介质中所激发的一次场通过汉克尔积分得到.基于Coulomb规范得到二次矢量位和标量位所满足的Maxwell方程组,通过Galerkin加权余量法形成大型稀疏有限元方程,采用不完全LU分解(ILU)预条件因子的quasi-minimum residual(QMR)迭代解法对有限元方程进行求解得到二次矢量位和标量位;进而,利用滑动平均方法得到二次矢量位和标量位在空间的导数,由此得到二次电磁场;通过一维模型对算法的可靠性进行验证,与此同时,针对实际复杂海洋电磁模型,比较有限元模拟结果与积分方程模拟结果,进一步验证算法精度.若干计算结果均表明,文中算法具有良好的通用性,适用于井中电磁、航空电磁,环境地球物理等非均匀且各向异性介质中的电磁感应基础研究. 相似文献
12.
Review on localized boundary integral equation:Discrete wavenumber method for 2D irregular layers 
下载免费PDF全文
下载免费PDF全文 The pioneer study of simulating the wave field in media with irregular interface belongs to Aki and Larner.Since that many numerical methods on the subject have been developed,such as pure numerical techniques,ray method and boundary method.The boundary method based on boundary integral equation is a semi-analytical method which is suitable to modeling wave field induced by irregular border.According to the property of the applied Green's function the boundary methods can be sorted into space domain boundary method and wavenumber domain boundary method.For both of them it is necessary to solve a large equation,which means much computation is needed.Thus,it is difficult for the boundary methods to be applied in simulating wave field with high frequency or in large range.To develop a new method with less computation is meaningful.For this purpose,localized boundary integral equation,i.e.,discrete wavenumber method is proposed.It is rooted in the Bouchon-Campillo method,an important wavenumber domain boundary method.Firstly the force on interface is separated into two parts:one is on flat part and the other on irregular part of the interface.Then Fourier transform is applied to identify their relation,the unknown distributes only on irregular part.Consequently computation efficiency is dramatically improved.Importantly its accuracy is the same as that of Bouchon-Campillo. 相似文献
13.
14.
基于稳定电流场的基本方程、三维区域满足的边值问题以及相应的变分问题,研究了三维起伏地形条件下电阻率的有限单元数值模拟算法. 离散积分区域时,以三棱柱为最小研究单元,推导了含有地形特征信息的三线性插值型函数以及单元刚度矩阵. 采用变带宽、一维数组方式只存储稀疏刚度矩阵中非零元素,能够节约内存. 利用Cholesky分解法只分解一次大型稀疏矩阵,通过回代可以求出方程组的全部解,当求解有多个供电点的测深问题时可以缩短计算时间. 模型计算表明,在水平层状介质模型上,三维计算结果与解析解或二维数值解十分吻合,计算精度满足误差要求. 在二维山脊上的二极剖面或三维山谷上的中间梯度剖面上,其三维计算结果与相应模型的土槽实验结果或边界元法计算结果也非常接近. 相似文献
15.
R. N. EDWARDS 《Geophysical Prospecting》1984,32(5):955-969
The cross-hole variant of the magnetometric resistivity (MMR) method requires two bore holes in the vicinity of a conductive target. In the first, two fixed current electrodes are located, one above the other. They are linked to a low frequency current source by cables, the whole system forming a vertical current bipole. In the second, a sensitive coil measures the axial magnetic field as a function of depth. For a uniform earth, if both holes are vertical, the measured component vanishes by symmetry. However, the presence of a local conductor channels the current and causes an anomalous magnetic component which is interpreted to indicate the position, shape and relative conductance of the target. Mineral deposits are often lamellar in form. The conductive disc is the simplest bounded lamella for which MMR responses may be computed. It is excited by a single current source on its axis. The second source and the surface of the earth are assumed to be far away, a valid assumption for down-hole measurements. The numerical method introduces a new integral equation describing the interaction of current dipoles located in the plane of the disc. The equation is solved analytically for a disc of infinite radius, a layer, and the result is compared with a corresponding known boundary value solution. The computed radial current in the disc and the magnetic field generated by it are described in terms of a current channelling number. The magnitude of the computed field is of the order of one nanoTesla for a typical mining problem. 相似文献
16.
E. MUNDRY 《Geophysical Prospecting》1984,32(1):124-131
For the calculation of geoelectrical model curves for a two-dimensional resistivity distribution, the potential equation is transformed by means of a Fourier cosine transform into a two-dimensional Helmholtz equation containing the separation parameter λ. The numerical solution of this equation for different values of λ for an irregular grid is obtained using the method of finite differences combined with the method of overrelaxation. The method by which derivatives are replaced by finite differences turned out to be very important, especially for high resistivity contrasts. After testing several methods designed to deal with any type of resistivity distribution, a method of discretization similar to that used by Brewitt—Taylor and Weaver (1976) for magnetotelluric modeling for H polarization was found the best. Examples are given of model curves for Schlumberger soundings over a vertical fault covered by overburden. The incorrect use of horizontal-layer models leads to erroneous interpretations that are more complex than the real subsurface situations. 相似文献
17.
Peter Furness 《Geophysical Prospecting》1999,47(3):393-409
A useful analysis of the mise-à-la-masse problem can be made by considering a perfectly conducting orebody in a piecewise uniform conducting earth. While the use of a perfect conductor is clearly an idealization of the true geological conditions it provides several advantages for the present purpose.
The electric field associated with the above model can be expressed in terms of a surface integral of the normal potential gradient over the boundary of the conductor, where the normal gradient satisfies a well-posed Fredholm integral equation of the first kind. This integral equation formulation remains unchanged when the conductor is arbitrarily located in the conducting earth, including the important case when it crosses surfaces of conductivity discontinuity. Moreover, it is readily specialized to the important case of a thin, perfectly conductive lamina.
Consideration of the boundary value problem relevant to a conductive body fed by a stationary current source suggests that under certain circumstances, equivalent mise-à-la-masse responses will result from any perfect conductor confined by the equipotential surfaces of the original problem. This type of equivalence can only be reduced by extending the potential measurements into or on to the conductor itself.
This ambiguity in the interpretation of mise-à-la-masse surveys suggests a simple if approximate integral solution to the mise-à-la-masse problem. The solution is suitable for modelling the responses of perfect conductors and could possibly be used as the basis of a direct inversion scheme for mise-à-la-masse data. 相似文献
The electric field associated with the above model can be expressed in terms of a surface integral of the normal potential gradient over the boundary of the conductor, where the normal gradient satisfies a well-posed Fredholm integral equation of the first kind. This integral equation formulation remains unchanged when the conductor is arbitrarily located in the conducting earth, including the important case when it crosses surfaces of conductivity discontinuity. Moreover, it is readily specialized to the important case of a thin, perfectly conductive lamina.
Consideration of the boundary value problem relevant to a conductive body fed by a stationary current source suggests that under certain circumstances, equivalent mise-à-la-masse responses will result from any perfect conductor confined by the equipotential surfaces of the original problem. This type of equivalence can only be reduced by extending the potential measurements into or on to the conductor itself.
This ambiguity in the interpretation of mise-à-la-masse surveys suggests a simple if approximate integral solution to the mise-à-la-masse problem. The solution is suitable for modelling the responses of perfect conductors and could possibly be used as the basis of a direct inversion scheme for mise-à-la-masse data. 相似文献
18.
S. SPITZ 《Geophysical Prospecting》1981,29(4):578-588
The induction problem for an inhomogeneous two-dimensional conductor presenting a vertical contact between two media of diverse conductivities is considered. The general solution of the Helmholtz equation in the atmosphere is constructed for a simple induction mechanism. It is found that in the E-polarization case the anomalous field behavior in the boundary region and beyond differs from the generally assumed one. The conclusion of this paper is that the boundary conditions widely utilized in numerical computations have to be modified. 相似文献
19.
Membrane polarization occurs in sediments with different surface area of capillaries (pores) and is regarded as a slow type of polarization. This phenomenon is the foundation of the well known methods of induced polarization (IP): time domain and frequency domain induced polarization. The characteristic parameters of induced polarization which are required for studying physical properties of rocks are measured in the laboratory. Data measured in the laboratory confirmed the distinctions of IP processes at time-on and time-off. Additionally linear dependence of voltage and applied current is not always observed. This paper presents the first step of studying: theoretical consideration for time-on and mathematical modeling of membrane polarization, ion concentrations of electrolyte in the pores of different models of pores space, and arising voltage. The problem of concentration of ions along the pores can be solved using the diffusion equation with specified initial and boundary conditions. Reduced boundary conditions for time-on show that transient concentrations at the boundaries are linear with time. It allows obtaining the analytical solution for this equation. Mathematical modeling has been performed for different combinations of pores. It is shown that if electrical current flows from the pores with greater transfer numbers to the pores with smaller transfer numbers, an excess of ions will be observed at this boundary. If the difference of transfer numbers is negative, there is a decrease in the concentration of ions at the vicinity of the boundary. This decrease will continue until the concentration at this boundary reaches zero. In this case the galvanic chain will be interrupted and electrical current flowing through the sample does not penetrate to this cell. The duration of the process of ions distribution in the pore and time of blockage t 0 is proportional to the radii of contacted pores and inversely proportional to the transfer number difference and square of the current flowing through this cell. It was shown by both laboratory measurement and field processes that induced polarization relates to low porous rocks with small transfer number differences. 相似文献
20.
Earth medium is not completely elastic, with its viscosity resulting in attenuation and dispersion of seismic waves. Most viscoelastic numerical simulations are based on the finite-difference and finite-element methods. Targeted at viscoelastic numerical modeling for multilayered media, the constant-Q acoustic wave equation is transformed into the corresponding wave integral representation with its Green’s function accounting for viscoelastic coefficients. An efficient alternative for full-waveform solution to the integral equation is proposed in this article by extending conventional frequency-domain boundary element methods to viscoelastic media. The viscoelastic boundary element method enjoys a distinct characteristic of the explicit use of boundary continuity conditions of displacement and traction, leading to a semi-analytical solution with sufficient accuracy for simulating the viscoelastic effect across irregular interfaces. Numerical experiments to study the viscoelastic absorption of different Q values demonstrate the accuracy and applicability of the method. 相似文献