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191.
192.
193.
M. Poddar 《Pure and Applied Geophysics》1981,119(5):1024-1036
FollowingDmitriev (1960) a rigorous theoretical solution for the problem of scattering by a perfectly conducting inclined half-plane buried in a uniform conductive half-space has been obtained for plane wave excitation. The resultant integral equation for the Laplace transform of scattering current in the half-plane is solved numerically by the method of successive approximation. The scattered fields at the surface of the half-space are found by integrating the half-space Green's function over the transform of the scattering current.The effects of depth of burial and inclination, of the half-plane on the scattered fields are studied in detail. An increase in the depth of burial leads to attenuation of the fields. Inclination introduces asymmetry in the field profiles beside affecting its magnitude. Depth of exploration is greater for quadrature component. An interpretation scheme based on a phasor diagram is presented for the VLF-EM method of exploration for rich vein deposits in a conductive terrain.List of symbols
x, y, z
Space co-ordinates
-
Half-space conductivity
- 0
Free-space permeability
-
Excitation frequency (angular)
-
T
Time
-
h
Depth of the half-plane
-
a
Inclination of the half-plane
-
E
x
x-Directed total electric field
-
E
x
p
x-Directed primary electric field
-
E
xo
p
x-Directed primary electric field atz=0 directly over the half-plane
-
H
y
y-Component of total magnetic field
-
H
y
p
y-Component of primary magnetic field
-
H
y0
p
y-Component of primary magnetic field atz=0 directly over the half-plane
-
H
z
z-Component of total magnetic field
-
H
z
p
z-Component of primary magnetic field
-
J
x
Surface density ofx-directed scattering current
-
G
Green's function
-
k
0,K
Wave numbers
-
u,u
0,u
1,u
2
Functions
-
Space co-ordinate
-
s
Variable in transform domain
-
Variable of integration
-
Normalized scattering current
-
Laplace transform of
-
N
Normalized
- , 0, 1, 2
Functions
-
t
Variable of integration
-
Skin depth
-
H
Total magnetic field
-
H
p
Primary magnetic field
-
H
0
p
Primary magnetic field atz=0 directly over the half-plane
-
M,Q,R,S,U,V
Functions
-
N
1,N
2
Functions 相似文献
194.
The response of a horizontal conducting cylinder embedded in a uniform conducting earth is studied using mathematical models of uniform and line current source excitation for the period range 10 to 104 s. The line current source is located at heights ranging from 100–750 km above the surface of the earth. From the calculated results, it is shown that for periods greater than 103 s the ratioE
x
/H
y
at the surface of the earth for localized fields, such as the auroral and equatorial electrojet normally situated at heights of about 100 km, is considerably different from that for a uniform source. The results presented also show that the magneto-telluric method of geophysical prospecting for ore bodies in regions of the electrojet may not be very practicable for periods exceeding 103 s. 相似文献
195.
An analytical formulation is developed for the resultant electromagnetic field of an oscillating vertical magnetic dipole located over a thin conductive sheet of infinite extent. The sheet is characterized by a conductivity-thickness product or conductance d that may be a function of the horizontal coordinates. The system of integral equations arising in the general formulation is simplified greatly when azimuthal symmetry prevails. Numerical results for a Gaussian variation of d in the radial direction are presented for the case of a symmetrically located source. These results are for the fields at the level of the source dipole over the conductive sheet. It is shown that the quadrature response of the sheet is enhanced when there is rapid variation of the conductance. The null in the resultant wave tilt is also found to be shifted toward the direction of increasing conductance. 相似文献
196.
三维陆地可控源电磁法有限元快速正演的主要瓶颈在于多频率大型稀疏方程组求解问题.本文引入一种基于模型降阶的Krylov子空间投影算法,推导了有限元刚度矩阵的模型降阶形式,构建了频率域传递函数;采用标准正交向量序列,构建一个远远小于有限元刚度矩阵维度的矩阵,该矩阵与频率无关,通过一次模型降阶即可实现多频点有限元方程快速求解.采用基于电场的变分方程,加入散度校正条件,以消除伪解;引入伪δ函数,消除了源点的奇异性,可适用于复杂背景模型三维有限元数值模拟,并为多源的求解奠定了基础;以层状介质模型解析解为标准,通过和基于Pardiso直接求解器的有限元算法(3DFEM)进行比较,模型降阶法计算时间小于前者的1/10,平均相对误差在1.72%,在满足精度要求下,实现了高效率三维有限元数值求解;分别设计了横向高低阻模型和纵向高低阻模型,分析了从近区到远区电场和卡尼亚视电阻率的变化规律,假极值的表现特征,阴影效应的影响等,从而也验证了该算法的正确性.最后,建立了一个地层陷落柱模型,通过模型降阶有限元正演模拟,发现视电阻率断面图在陷落柱上方出现"凹陷",与模型设计吻合,表明该算法对复杂地层模拟具有同样的适用性. 相似文献
197.
电磁辐射"EMOLS"仪观测结果原理及震例 总被引:10,自引:0,他引:10
“九五”期间研制的“EMAOS”电磁辐射仪,其接收原理是按大地电磁测深的原理改进而研制的。选择接收频段为0.01~10Hz,该频段探测深度在0~20km,是浅源地震发生的层位。记录的电磁扰动是在应力场作用下,动电效应产生的电磁场。电场和磁场同时记录增强了信息可信度的判断能力,记录震例表明,异常规律与已有模拟结果基本相同。因此,已总结的模拟记录预报指标等可在数字记录结果中使用。 相似文献
198.
John?H.?SeiradakisEmail author Richard?Wielebinski 《Astronomy and Astrophysics Review》2004,12(4):239-271
This review describes the observational properties of radio pulsars, fast rotating neutron stars, emitting radio waves. After the introduction we give a list of milestones in pulsar research. The following chapters concentrate on pulsar morphology: the characteristic pulsar parameters such as pulse shape, pulsar spectrum, polarization and time dependence. We give information on the evolution of pulsars with frequency since this has a direct connection with the emission heights, as postulated in the radius to frequency mapping (RFM) concept. We deal successively with the properties of normal (slow) pulsars and of millisecond (fast-recycled) pulsars. The final chapters give the distribution characteristics of the presently catalogued 1300 objects.Received: 5 December 2003, Published online: 15 April 2004
Correspondence to: Richard Wielebinski 相似文献
199.
利用烟台WSR—98D雷达产品等资料,分析了2004年6月19日烟台市一次气团风暴的发展过程及其内部风场结构,结果表明:钩状回波中的中气旋是引发气团风暴的主要雷达回波特征。 相似文献
200.
Near‐fault ground motions with forward directivity are characterized by a large pulse. This pulse‐like motion may cause a highly non‐uniform distribution of story ductility demands for code‐compliant frame structures, with maximum demands that may considerably exceed the level of code expectations. Strengthening techniques for multi‐story frame structures are explored with the objective of reducing maximum drift demands. One option is to modify the code‐based SRSS distribution of story shear strength over the height by strengthening of the lower stories of the frame. The modified distribution reduces the maximum story ductility demand, particularly for weak and flexible structures. However, this strengthening technique is less effective for stiff structures, and is almost ineffective in cases in which the maximum demand occurs in the upper stories, i.e. strong and flexible structures. As an alternative, the benefits of strengthening frames with elastic and inelastic walls are evaluated. The effects of adding walls that are either fixed or hinged at the base are investigated. It is demonstrated that strengthening with hinged walls is very effective in reducing drift demands for structures with a wide range of periods and at various performance levels. Wall inelastic behavior only slightly reduces the benefits of strengthening with hinged walls.Copyright © 2004 John Wiley & Sons, Ltd. 相似文献