共查询到16条相似文献，搜索用时 420 毫秒
1.
一个或多个异常体的识别与区分及边界的确定是电磁法探测中提高分析精度的难点。本文利用基于电场的矢量有限元开展了复杂模型三维倾子响应及感应矢量研究。实感应矢量对电流聚集方向的指向性与分析频率的趋肤深度及介质的相对电性大小有关,通过这种指向性能有效地判定异常体的上界面和多个不同性质异常体的存在,但难以对下界面进行判定;虚感应矢量反映了感应电流(涡流)的流动方向,不同电阻率的地质体其感应电流的大小和方向不同,利用虚感应矢量的旋转方向、中心轴及分析频率的探测深度可有效地确定异常体的中心和上下界面。虚感应矢量相对于趋肤深度具有反映更大探测深度的能力,能有效地显示深部异常体对感应电流大小和方向的影响。数值模拟结果表明:虚感应矢量对异常体的识别与区分优于传统的电阻率和倾子参数。 相似文献
2.
在二维地电模型中,大地电磁测深倾子资料可以很好地反映地电构造的水平非均匀性,特别是在解释垂直或者倾斜板状体的空间分布情况时,可以起到十分重要的作用,在实际应用中可以用来寻找断裂,判断其走向、倾向、埋深和规模。应用有限单元法分别对水平、垂直和倾斜的板状模型进行正演模拟,该算法采用矩形网格内进一步三角形细化的方式剖分模型,通过三角形网格提高了对倾斜接触面的近似程度,同时增加计算量不明显,然后计算出倾子的实部、虚部和振幅的资料。研究结果表明:倾子响应对介质电性水平不均匀反映十分灵敏,特别是对横向低阻异常体,同时对异常体的位置和埋深也有清楚的显示。 相似文献
3.
利用有限单元法模拟二维MT倾子响应 总被引：1，自引：0，他引：1
在二维地电模型中,考虑到大地电磁测深(MT)倾子响应依赖于横电(TE)模式的数值模拟问题,笔者采用矩形网格单元和双二次插值对MT的倾子响应进行求解。首先,给出了二维地电条件下的边值问题和变分问题,并通过有限单元法对模型进行单元剖分、插值、积分和整体合成;其次,通过求解复系数方程组得到了每个节点的电场值;最后,采用差分方法求得电场沿横向和垂向的偏导数值,从而计算出二维MT的倾子响应。通过对2个二维地电模型的倾子响应进行数值模拟,获得了倾子响应的实部、虚部和振幅,结果很好地反映了不均匀体的横向分布情况。 相似文献
4.
在二维地电模型中,倾子资料作为大地电磁测深实测资料之一,能够很好地反映地下介质在水平方向的不均匀性,可以作为复杂地质构造的表征.这里采用矩形网格单元的双二次插值有限元法对MT的倾子响应进行正演模拟,通过对异常体在不同条件下倾子数值的分析,结果表明,倾子异常的幅值不仅与上覆层的电导率、厚度以及观测频率有关,还与水平非均匀界面两边介质电导率的对比度,以及地下介质尺寸的大小有关.因为倾子响应的异常幅值很小,在实际观测中由于受到多方面的干扰,且地下异常体的几何不规则性,于是倾子响应的异常也是诸多情况的综合反映.通过对倾子影响因素的分析,可以更加准确地利用倾子资料进行地质解释. 相似文献
5.
张量CSAMT一维数值模拟分析 总被引：1，自引：0，他引：1
研究一维张量CSAMT张量阻抗和倾子向量的变化特征,首先应用快速汉克尔变换法,计算准静态条件下x方向电偶极子在柱坐标系中电磁场各分量的数值解,由对称理论得出y方向电偶极子的电场和磁场值;然后,再利用二个源定向,基于张量阻抗关系式,建立六个线性方程,得到张量阻抗和倾子向量,设计理论地电模型,进而对其进行分析。这些工作不仅可以为二维/三维张量CSAMT数值模拟提供对比,而且还可以为张量CSAMT资料解释提供一定的帮助。 相似文献
6.
研究一维张量CSAMT张量阻抗和倾子向量的变化特征,首先应用快速汉克尔变换法,计算准静态条件下x方向电偶极子在柱坐标系中电磁场各分量的数值解,由对称理论得出y方向电偶极子的电场和磁场值;然后,再利用二个源定向,基于张量阻抗关系式,建立六个线性方程,得到张量阻抗和倾子向量,设计理论地电模型,进而对其进行分析。这些工作不仅可以为二维/三维张量CSAMT数值模拟提供对比,而且还可以为张量CSAMT资料解释提供一定的帮助。 相似文献
7.
8.
ZTEM(Z轴倾子电磁法)是一种天然场源的频率域航空电磁法,其特点是磁场垂直分量在空中机载平台测量,磁场水平分量在地面的固定基站测量,具有勘探深度大、速度快、成本低、覆盖面积大等技术优势。本文实现了ZTEM二维有限差分正演和二维非线性共轭梯度(NLCG)反演算法。研究对象是倾子资料,反演过程中通过解"拟正演"问题来避开雅克比矩阵的直接计算。通过理论模型合成数据反演试算,验证了ZTEM倾子资料二维NLCG反演算法的稳定性与可靠性。与大地电磁(MT) TE模式阻抗资料反演结果进行对比,发现在异常体横向边界的约束方面,ZTEM倾子反演比MT阻抗反演更具优越性。 相似文献
9.
10.
11.
We present the results of the analysis of experimental data of synchronous observations of variations in the electric and magnetic fields as well as acoustic oscillations in the surface zone of the Earth compared with variations in the meteorological parameters. We demonstrate the synchronous variations in these fields and atmospheric parameters. We revealed, for the first time, not only synchronous but also advancing manifestations of the geomagnetic field perturbations. We introduce a new parameter: the inverse magnetic tipper whose variations during atmospheric perturbations are clearly manifested compared with the variations in the magnetic tipper. 相似文献
12.
岩体的块体结构和结构面网络模型生成,是进行各种力学分析和场分析的基础。详细研究了有限结构面进行复杂块体切割的过程,提出了相应的算法,并采用C++语言编写了相应的程序。为描述块体切割后的复连通特性,在块体数据结构中添加了有向壳的概念。结构面可以为简单的凸多边形,也可采用形态更加复杂的凹多边形。通过面-面求交线、交线环路搜索形成有向环、有向环包含关系分析形成有向面、有向面拓扑搜索形成有向壳和有向壳包含关系分析形成块体等过程,将有限结构面分别与各块体进行切割运算,形成进行块体切割的一般方法。在切割过程中将得到的有向环,有向面、有向壳和块体分别进行拓扑有效性校核,满足要求后得到最终的块体和结构面网络模型。选取4个算例来验证该方法的可行性。计算结果表明,该方法可以对复杂块体进行有效地切割,结构面可以选择包括凹形面在内的复杂多边形,方法具有普遍意义。 相似文献
13.
电磁测深法视电阻率定义问题的研究 总被引：17，自引：2，他引：17
本文首先提出电法勘探中视电阻率定义的基本原则,并以此为依据讨论了MT法、TEMS法及FEMS法中各种视电阻率定义的优缺点,提出了改进办法.研究发现,MT法利用面阻抗实部或在时间域中给出的视电阻率是很有效的定义方法,能很好地区分良导层,而面阻抗虚部定义的视电阻率效果最差.对TEMS法来说,利用视电阻率全区定义较通常的远区或近区近似定义更有效.研究还表明,由磁场时间导数定义的全区视电阻率有时出现多解性甚至无解,而利用磁场本身定义的视电阻率是很有效的.对FEMS法,进行了类似的全区视电阻率定义问题讨论,虽然取得的结果不如TEMS法理想,但比起目前常用的大、小感应数条件下定义的视电阻率响应还是有一定效果.文中对电磁测深法中出现的视电阻率响应曲线的假极值效应进行了物理解释. 相似文献
14.
Reflection–transmission matrix method for the consolidation of a multilayered saturated soil 
下载免费PDF全文
下载免费PDF全文 The consolidation of the layered saturated soil is an important issue in civil engineering and has been investigated extensively during the past decades. In this study, based on the Biot's theory, the reflection–transmission matrix (RTM) method for treating the layered saturated soil under axisymmetric consolidation is developed. To decouple the governing equations of the Biot's theory, the McNamee displacement functions are introduced, and the general solution for the saturated soil is obtained using the Laplace and Hankel transforms. In order to develop the RTM method for the layered saturated soil, based on the obtained general solution, the static wave vector corresponding to the state vector of the saturated soil and the transform matrix relating the aforementioned two vectors are defined. Also, the transfer matrices corresponding to the two vectors are introduced, and the representations of the RTMs for the static wave vector of the saturated soil are presented. As the state vector, static wave vector, and the transform matrix relating the two vectors are all defined in the global coordinate system, the RTMs obtained in this study thus have a reasonable physical meaning. By using the RTMs for the layered saturated soil, the solutions for the layered saturated soil subjected to external sources are derived. Comparison of results due to the proposed RTM method with some existing results and results due to the transfer matrix method validates the developed RTM method. Some numerical results are obtained based on the proposed RTM method for the layered saturated soil. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
15.
Dae S. Young 《Mathematical Geology》1987,19(6):467-479
Geostatistics is extended to the spatial analysis of vector variables by defining the estimation variance and vector variogram in terms of the magnitude of difference vectors. Many random variables in geotechnology are in vectorial terms rather than scalars, and its structural analysis requires those sample variable interpolations to construct and characterize structural models. A better local estimator will result in greater quality of input models; geostatistics can provide such estimators: kriging estimators. The efficiency of geostatistics for vector variables is demonstrated in a case study of rock joint orientations in geological formations. The positive cross-validation encourages application of geostatistics to spatial analysis of random vectors in geoscience as well as various geotechnical fields including optimum site characterization, rock mechanics for mining and civil structures, cavability analysis of block cavings, petroleum engineering, and hydrologic and hydraulic modelings. 相似文献
16.
The Kapuskasing Structural Zone (KSZ) reveals a section through the Archean lower crustal granoblastic gneisses. Our new paleomagnetic data largely agree with previous work but we show that interpretations vary according to the choices of statistical, demagnetization and field-correction techniques. First, where the orientation distribution of characteristic remanence directions on the sphere is not symmetrically circular, the commonly used statistical model is invalid [Fisher, R.A., Proc. R. Soc. A217 (1953) 295]. Any tendency to form an elliptical distribution indicates that the sample is drawn from a Bingham-type population [Bingham, C., 1964. Distributions on the sphere and on the projective plane. PhD thesis, Yale University]. Fisher and Bingham statistics produce different confidence estimates from the same data and the traditionally defined mean vector may differ from the maximum eigenvector of an orthorhombic Bingham distribution. It seems prudent to apply both models wherever a non-Fisher population is suspected and that may be appropriate in any tectonized rocks. Non-Fisher populations require larger sample sizes so that focussing on individual sites may not be the most effective policy in tectonized rocks. More dispersed sampling across tectonic structures may be more productive. Second, from the same specimens, mean vectors isolated by thermal and alternating field (AF) demagnetization differ. Which treatment gives more meaningful results is difficult to decipher, especially in metamorphic rocks where the history of the magnetic minerals is not easily related to the ages of tectonic and petrological events. In this study, thermal demagnetization gave lower inclinations for paleomagnetic vectors and thus more distant paleopoles. Third, of more parochial significance, tilt corrections may be unnecessary in the KSZ because magnetic fabrics and thrust ramp are constant in orientation to the depth at which they level off, at approximately 15-km depth. With Archean geothermal gradients, primary remanences were blocked after the foliation was tilted to rise on the thrust ramp. Therefore, the rocks were probably magnetized in their present orientation; tilting largely or entirely predates magnetization. 相似文献