共查询到20条相似文献，搜索用时 15 毫秒
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仿用反射地震法处理MT资料反演的理论探讨 总被引：1，自引：0，他引：1
本文讨论了电法勘探中电磁波场在水平层状介质中的传播特征,重点讨论它与地震波在水平层状介质中的传播特征在数学形式上的相似性,同时利用反射地震学中的脉冲响应概念来构建电法勘探中的伪脉冲函数响应.所恢复的伪脉冲响应是由一些离散脉冲函数组成,脉冲幅度与分层介面的波场反射系数和透射系数有关.本文采用拟合最小二乘法同时进行代数联合迭代(SIRT)跟踪的方法解决了欠定方程在其范数约束条件下的求解问题.并把该方法应用于一维多层导电体模型中,证实了伪脉冲理论的可靠性与实用性. 相似文献
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研究了横观各向同性饱和土地基在地表动力荷载作用下的三维瞬态响应。基于饱和多孔介质的三维Biot波动理论,利用Laplace变换,建立圆柱坐标系下横观各向同性饱和土的波动方程;解耦波动方程后,根据算子理论,并借助Fourier展开和Hankel变换技术,得到瞬态荷载作用下,饱和土介质的土骨架位移和应力、孔隙水相对位移和孔隙水压力的一般解;利用一般解,给出横观各向同性饱和地基在地表集中荷载激励下的瞬态Lamb问题的解答。数值算例结果表明,采用各向同性饱和介质的动力学模型,不能准确描述具有明显各向异性特性的饱和土地基的瞬态动力特性。 相似文献
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给出了适用于全空间层状模型偶极子源格林函数的去奇异性广义描述技术。过源平行于层界面设置一个虚界面,使相邻层界面限制的区域中电磁矢量势函数可以分解为TE模式和TM模式标量势函的叠加,且它们都满足齐次Helmhlotz方程,相应的解可以通过叠加上行波和下行波函数得到。源的奇异性被耦合到切向电磁场所满足的不连续边界条件上,并通过反射系数所描述的振幅递推关系延拓到其他任意层中,实现了全空间任意位置格林函数的计算。该思路被应用到VED源激发的海洋电磁模型数值模拟中,计算结果很好地反映了电磁场在海洋模型中的传播过程,验证了该技术思路的正确性。 相似文献
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Luz Angélica Caudillo-Mata Eldad Haber Christoph Schwarzbach 《Computational Geosciences》2017,21(5-6):963-980
In order to reduce the computational cost of the simulation of electromagnetic responses in geophysical settings that involve highly heterogeneous media, we develop a multiscale finite volume method with oversampling for the quasi-static Maxwell’s equations in the frequency domain. We assume a coarse mesh nested within a fine mesh that accurately discretizes the problem. For each coarse cell, we independently solve a local version of the original Maxwell’s system subject to linear boundary conditions on an extended domain, which includes the coarse cell and a neighborhood of fine cells around it. The local Maxwell’s system is solved using the fine mesh contained in the extended domain and the mimetic finite volume method. Next, these local solutions (basis functions) together with a weak-continuity condition are used to construct a coarse-mesh version of the global problem. The basis functions can be used to obtain the fine-mesh details from the solution of the coarse-mesh problem. Our approach leads to a significant reduction in the size of the final system of equations and the computational time, while accurately approximating the behavior of the fine-mesh solutions. We demonstrate the performance of our method using two 3D synthetic models: one with a mineral deposit in a geologically complex medium and one with random isotropic heterogeneous media. Both models are discretized using an adaptive mesh refinement technique. 相似文献
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《Russian Geology and Geophysics》2007,48(7):575-580
An inverse solution to the 1D wave equation is obtained using the spectral Laguerre transform to find the distribution of wave velocities at some point of the medium. The problem is solved as optimization in which the function of Laguerre harmonics is minimized by the conjugate gradient or Newton’s algorithms.Reported are velocities of a wave defined by a stepwise constant function. The accuracy of the inverse solution for the Laguerre harmonics is investigated against the approximation accuracy in the boundary problem. The accuracy and efficiency of the Laguerre method are compared to those in the Fourier method. 相似文献
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A fully coupled meshfree algorithm is proposed for numerical analysis of Biot’s formulation. Spatial discretization of the governing equations is presented using the Radial Point Interpolation Method (RPIM). Temporal discretization is achieved based on a novel three-point approximation technique with a variable time step, which has second order accuracy and avoids spurious ripple effects observed in the conventional two-point Crank Nicolson technique. Application of the model is demonstrated using several numerical examples with analytical or semi-analytical solutions. It is shown that the model proposed is effective in simulating the coupled flow deformation behaviour in fluid saturated porous media with good accuracy and stability irrespective of the magnitude of the time step adopted. 相似文献
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探地雷达是利用超高频脉冲电磁波探测地下介质分布的一种浅层地球物理勘探方法,探地雷达超高频、宽频带脉冲电磁波在地下有耗介质中的衰减特性是一个十分复杂的过程。本文从电磁波传播的麦克斯韦方程出发,较为系统地研究和分析了雷达脉冲电磁波在有耗介质中传播的衰减特性,对研究雷达脉冲电磁波在地下有耗介质中的传播机制有指导意义。 相似文献
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基于Zienkiewicz提出的非饱和多孔介质波动理论,考虑两相流体和固体颗粒的压缩性以及惯性、黏滞和机械耦合作用,采用半解析的方法获得了一类典型边界条件下单层非饱和多孔介质一维瞬态响应解。首先推导出无量纲化后以位移表示的控制方程,并将其写成矩阵形式;然后,将边界条件齐次化,求解控制方程所对应的特征值问题,得到了满足齐次边界条件的特征值和相对应的特征函数。根据变异系数法并利用特征函数的正交性,得到了一系列仅黏滞耦合的关于时间的二阶常微分方程及相应的初始条件。在此基础上,运用精细时程积分法给出了常微分方程组的数值解。最后,通过若干算例验证了结果的正确性并探讨了单层非饱和多孔介质一维瞬态动力响应的特点。该方法可推广应用于其他典型的边界条件。 相似文献
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井间电磁波层析成像中的高精度时间域正演计算 总被引：1，自引：0，他引：1
为提高井间电磁波层析成像的分辨率, 正演计算中需保持较高的计算精度.本文正演计算中采用时间域伪谱(PSTD) 法模拟井间电磁波的传播.该算法在时间域有限差分(FDTD) 法的基础上采用快速傅立叶变换(FFT) 计算麦克斯韦方程中的空间导数.该算法除了具备时间域有限差分法的优点外, 在计算条件完全相同的情况下, 计算精度明显高于时间域有限差分法.时间域伪谱法的正演计算为井间电磁波高分辨率层析成像奠定了重要基础. 相似文献
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在考虑横观各向同性含液饱和多孔介质固体骨架和流体可压缩性以及固体骨架的黏弹性特征下,基于横观各向同性含液饱和多孔介质u-w形式的三维动力控制方程,以固相位移u、液相相对位移w为基本未知量,综合运用Laplace变换、双重Fourier变换等方法,在直角坐标系下通过引入中间变量,将六元2阶动力控制方程组化为两组各含4个未知变量的常微分方程组,给出了直角坐标系下横观各向同性含液饱和多孔介质三维黏弹性动力反应的积分形式一般解;作为理论推导的验证,通过引入初始条件和边界条件,对横观各向同性含液饱和多孔介质半空间黏弹性瞬态反应问题进行了求解。解答的退化验证表明,所推导的理论解是正确的。 相似文献
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We present a uniform asymptotic solution (UAS) for a displacement discontinuity (DD) that lies within the middle layer of a three‐layer elastic medium in which relative shear deformation between parallel interfaces is controlled by linear springs. The DD is assumed to be normal to the two interfaces between the elastic media. Using the Fourier transform method we construct a leading term in the asymptotic expansion for the spectral coefficient functions for a DD in a three‐layer‐spring medium. Although a closed‐form solution will require a solution in terms of an infinite series, we demonstrate how this UAS can be used to construct highly efficient and accurate solutions even in the case in which the DD actually touches the interface. We compare the results using the Green's function UAS solution for a crack crossing a soft interface with results obtained using a multi‐layer boundary element method. We also present results from an implementation of the UAS Green's function approach in a pseudo‐3D hydraulic fracturing simulator to analyze the effect of interface shear deformation on the fracture propagation process. These results are compared with field measurements. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
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Analytical layer element solutions for deformations of transversely isotropic multilayered elastic media under nonaxisymmetric loading 总被引：1，自引：0，他引：1
This paper presents the analytical layer element solutions for deformations of transversely isotropic elastic media subjected to nonaxisymmetric loading at an arbitrary depth. The state vectors for the nonaxisymmetric problem are deduced through the substitution of the Hu Hai‐chang solutions into the basic equations for the transversely isotropic elastic media. From the state vectors, the analytical layer element of a single layer is obtained in the Hankel transformed domain. The analytical layer element is an exact and symmetric stiffness matrix whose elements are without positive exponential functions, which can not only simplify the calculation but also improve the stability of computation. On the basis of the continuity conditions between adjacent layers, the global stiffness matrix is obtained by assembling the interrelated layer elements. The solutions for the multilayered elastic media in the transformed domain are obtained by solving the algebraic equation of the global stiffness matrix, which satisfies the boundary conditions. The actual solutions in the physical domain are further obtained by inverting the Hankel transform. Finally, some cases are analyzed to verify the solutions and evaluate the influences of the transversely isotropic character and stratified character of the media on the load–displacement responses. The numerical results show that the variations of the elastic properties between layers have a great effect on the displacements of the multilayered media. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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A novel numerical method based on the finite element approach is established for the zero current method approach for calculating multi-species ionic diffusion. The proposed numerical method uses the direct calculation of the coupled set of equations in favor of the staggering approach. A one-step truly implicit time stepping scheme is adopted together with an implementation of a modified Newton–Raphson iteration scheme for search of equilibrium at each considered time step calculation. Results from the zero current case are compared with existing results from the solutions of the more general Gauss’ law method. 相似文献
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Existing solutions for analyzing one-dimensional (1-D) consolidation of unsaturated soil are only derived to cater to two extreme drainage conditions (fully drained and undrained). This study presents a new explicit solution for 1-D consolidation of unsaturated soil with semi-permeable drainage boundary. Based on the assumptions of two independent stress variables and the governing equations proposed by Fredlund, the eigenfunction expansion method is adopted to develop an explicit analytical solution to calculate excess pore-water and pore-air pressures in an unsaturated soil when it is subjected to external loads. The developed general solutions are expressed in terms of depth, z, and time, t. For the semi-permeable drainage boundary, eigenvalues and eigenfunctions in the space domain are developed. The technique of Laplace transform is used to solve the coupled ordinary differential equations in the time domain. The newly derived explicit solution is verified with the existing semi-analytical method in the literature, and an excellent agreement is obtained. Compared with the semi-analytical solution, the newly derived analytical solution is more straightforward and explicit so that this solution is relatively easier to be implemented into a computer program to carry out a preliminary assessment of 1-D consolidation of unsaturated soil. 相似文献
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An approximate analytical solution has been established for the well known Richards’ equation for unsaturated flow of transports in soils. Despite the importance of Richards’ equation in geotechnical and geoenvironmental applications, most solutions to the problem are generally based on numerical methods often having limitations in application. It is therefore advantageous to explore analytical solutions to the problem. The proposed solution is based on homotopy analysis method (HAM). The method is superior over traditional perturbation techniques in a sense that it is not dependent on the assumption of a small parameter as the initial step. Several simple cases have been explored to describe the application of HAM to Richards’ equation. The results obtained by HAM are also compared with existing solutions to demonstrate the accuracy of the proposed method. 相似文献
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This study introduces the prediction of probabilistic settlements with the uncertainty in the spatial variability of Young’s modulus to illustrate the preliminary development of a spectral stochastic meshless local Petrov–Galerkin (SSMLPG) method. Generalized polynomial chaos expansions of Young’s moduli and a two-dimensional meshfree weak–strong formulation in elasticity are combined to derive the SSMLPG formulation. Because of the local and truly meshless nature, the SSMLPG method is more computationally efficient than available stochastic numerical methods. Two examples further show that SSMLPG-based predictions remain sufficiently accurate even in case of scattered nodes. Therefore, the SSMLPG method can be a valuable alternative for solving stochastic boundary-value problems. 相似文献
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电偶源频率电磁测深三维地电模型有限元正演 总被引：9，自引：1，他引：8
在有源变频测深(包括可控源音频大地电磁测深CSAMT)的三维有限元正演中,应用了吸收边界条件和边元有限元算法,计算精度为3%左右,基本上可满足电偶极源三维地电模型情况下频率电磁测深响应特征的分析。同时由于广义变分概念的引入,可使泛函的变分原理应用于有耗媒质电磁场问题。 相似文献