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1.
In this paper, 3D steady‐state fluid flow in a porous medium with a large number of intersecting fractures is derived numerically by using collocation method. Fluid flow in the matrix and fractures is described by Darcy's law and Poiseuille's law, respectively. The recent theoretical development presented a general potential solution to model the steady‐state flow in fractured porous media under a far‐field condition. This solution is a hypersingular integral equation with pressure field in the fracture surfaces as the main unknown. The numerical procedure can resolve the problem for any form of fractures and also takes into account the interactions and the intersection between fractures. Once the pressure field and then the flux field in fractures have been determined, the pressure field in the porous matrix is computed completely. The basic problem of a single fracture is investigated, and a semi‐analytical solution is presented. Using the solution obtained for a single fracture, Mori‐Tanaka and self‐consistent schemes are employed for upscaling the effective permeability of 3D fractured porous media. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

2.
The thermodynamic approach (mean field theory) of Strässler and Kittel has been applied to rationalize a large body of experimental work on magnetite. A single long-range order parameter suffices to describe the entropy of the Verwey transition, the Seebeck coefficient, and the resistivity of Fe3O4. The parametrization scheme yields results consistent with two regimes. For Fe3(1?δ)O4 with δ <δc～0.0039 a first order Verwey transition is encountered, consistent with a nondegenerate ground and doubly degenerate excited state. For δ>δc the transition is second-order, consistent with two doubly degenerate states. These features may be conveniently visualized by mapping the equilibrium free energy constraint into a cusp catastrophe, one of several elementary ones in Thom's classification scheme.  相似文献   

3.
近年来冻结施工方法越来越多地使用在城市土木工程施工中,但由于受冻土冻结理论基础的缺失和研究方法的局限,长时间以来人们对冻结法的设计始终没有找到较为理想的方案,参数变量选取遇到很大困难,同时在施工阶段没有较为标准统一的技术规范参照,使得该工法的实际应用往往出现工程量浪费、施工混乱和工程质量无保障等情况,而其中冷冻管直径是主要影响参数。通过同轴管土体冻结试验的研究,采用不同直径的冷冻管进行冻结试验,利用Fluent模型分析冻结过程的温度场分布规律,确定了最优冷冻管管径的选择方法,为冻结法的设计及施工提供依据。  相似文献   

4.
A mechanism for the acceleration of electrons in the ionosphere of Io due to the moon's motion through the Jovian magnetic field and the presence of Io's ionosphere is considered. Attention is drawn to the important role of the anisotropic conductivity of the ionosphere, which results in the formation of a longitudinal (with respect to the planetary magnetic field) component of the charge-separation electric field. Owing to this anisotropy, the electric field induced by the motion of Io, Ei, produces in Io's ionosphere not only a Pedersen electrical current along Ei but also a Hall current that is approximately perpendicular to the moon's surface in the “upstream” and “downstream” parts of the ionosphere. However, this current cannot be closed through the surface, leading to the formation of a powerful charge-separation field in Io's ionosphere. This field has a component parallel to the magnetic field, with an amplitude comparable to that of the induced electric field. Electron runaway along the magnetic field is also considered, and the occurrence of “active longitudes” and preferred locations for the sources of decametric radio emission in the northern hemisphere of Jupiter are interpreted. The characteristic energies and fluxes of the accelerated electrons injected into Io's flux tube are estimated. The energy of these electron fluxes is sufficient to produce the electromagnetic radiation observed from Io's magnetic tube.  相似文献   

5.
In the Goiás Alkaline Province, in central Brazil, some mafic–ultramafic alkaline bodies crop out, such as Morro do Engenho Complex (ME), whereas other intrusive bodies are completely covered by Quaternary sediments, such as A2 body, and can only be defined by their magnetic and gravity responses. The bodies give rise to strong gravity and magnetic anomalies. We inverted the gravity and magnetic data to estimate 3D density and magnetic intensity contrasts. The gravity inversion reveals that ME and A2 intrusions, totally emplaced in the upper crust, have maximum depths of about 10 and 6 km, respectively. The estimated density contrast distribution indicates a NE–SW preferential direction for ME intrusive body. Since the remnant magnetization is very important in the area, we inverted the magnetic data, testing two hypotheses: only induced field and induced plus remnant magnetizations. The results of the inversion using only induced field could not explain the observed magnetic field, which was about 1000 nT larger than the calculated one. Induced plus remnant field inferred from wandering polar path fitted the observations. 3D magnetic inversions when remnant magnetization was included recover deeper and thinner bodies compared with gravity inversion. The inverted bodies have spherical shapes which are more consistent with the model of magmatic chambers instead of plug intrusions.  相似文献   

6.
The Rapid Inversion of 3-D Potential Field and Program Design   总被引：1，自引：0，他引：1  
The application of three-dimensional inversion of gravity and magnetic fields is very important not only in geophysical researches, but also in the study of geological structures. A formula of potential field in frequency-domain, developed by Parker in 1973, can be used as a rapid and effective algorithm in gravity and magnetic inversion. The technique has been improved then by Oldenburg, Sprenke, Feng and others.In addition to a brief introduction of Parker's algorithm and its applications, this paper includes the following five parts: basic computational techniques, inversion of single layer, convergence and constraints, simultaneous inversion for density and topography as well as inversion of multilayers. The authors present relevant practical iterative formulas and its varieties when density distribution varies with depth in linear or exponential relation. In order to maintain computation stability and speed up iteration convergence, some approaches are taken in the program design, for instance shifting lower interface of the studied layer, inverting corrections of topography, reducing grid boundary effects and utilizing low-pass filter. With the consideration of the nonuniqueness of the inversion, a method of using seismic data to constrain the range ofpossible models is discussed. It is pointed out that the density variation generates less effects than those of topography on the spectrum of gravity anomaly in second order. Therefore density contrast and topography can be inverted simultaneously by an alternative weighting iteration. By analogy, the inversion of multilayer model can be done in the above procedure. An approach of model decomposition is useful in the computation of multilayer model. The techniques discussed in the present paper for gravitational field are also valid for magnetic field.  相似文献   

7.
The bonded discrete element model (DEM) is a numerical tool that is becoming widely used when studying fracturing, fragmentation, and failure of solids in various disciplines. However, its abilities to solve elastic problems are usually overlooked. In this work, the main features of the 2D bonded DEM which influence Poisson's ratio and Young's modulus, and accuracy when solving elastic boundary value problems, are investigated. Outputs of numerical simulations using the 2D bonded DEM, the finite element method, a hyper elasticity analysis, and the distinct lattice spring model (DLSM) are compared in the investigation. It is shown that a shear interaction (local) factor and a geometric (global) factor are two essential elements for the 2D bonded DEM to reproduce a full range of Poisson's ratios. It is also found that the 2D bonded DEM might be unable to reproduce the correct displacements for elastic boundary value problems when the represented Poisson's ratio is close to 0.5 or the long-range interaction is considered. In addition, an analytical relationship between the shear stiffness ratio and the Poisson's ratio, derived from a hyper elasticity analysis and applicable to discontinuum-based models, provides good agreement with outputs from the 2D bonded DEM and DLSM. Finally, it is shown that the selection of elastic parameters used the 2D bonded DEM has a significant effect on fracturing and fragment patterns of solids.  相似文献   

8.
The effects of a large coronal mass ejection (CME) on a solar coronal streamer located roughly 90° from the main direction of the CME propagation observed on January 2, 2012 by the SOHO/LASCO coronograph are analyzed. Radial coronal streamers undergo some bending when CMEs pass through the corona, even at large angular distances from the streamers. The phenomenon resembles a bending wave traveling along the streamer. Some researchers interpret these phenomena as the effects of traveling shocks generated by rapid CMEs, while others suggest they are waves excited inside the streamers by external impacts. The analysis presented here did not find convincing arguments in favor of either of these interpretations. It is concluded that the streamer behavior results from the effect of the magnetic field of a moving magnetic flux rope associated with the coronal ejection. The motion of the large-scale magnetic flux rope away from the Sun changes the surrounding magnetic field lines in the corona, and these changes resemble the half-period of a wave running along the streamer.  相似文献   

9.
Astronomy Reports - The orientation parameter effect of a hot Jupiter’s intrinsic dipole magnetic field on the flow structure in an extended gaseous (ionospheric) envelope of the planet is...  相似文献   

10.
城市人口分布空间自相关的功率谱分析   总被引：13，自引：0，他引：13  
从理论上可以证明标准的城市人口密度负指数距离衰减模型本质上是一种空间相关函数，基于这种思想对Clark模型进行Fourier变换，可以导出城市人口密度的幂次频谱分布，且功率谱指数理应为β=2±。负指数与幂指数的这种变换关系暗示了城市地理系统简单与复杂的辩证关系。借助中国杭州市4年的人口普查资料转换的平均人口密度分布数据对上述推论进行检验，发现β渐进式趋近于2但并不约等于2。将β值进一步换算为人口过程的分维D和Hurst指数H，结果表明：城市人口具有长程负相关作用，但这种空间作用显示明确的局域化倾向。目前的城市形态演化模拟几乎无一例外地引入了长程作用，根据杭州人口分布的局域化特征，有关地理长程作用的假设和应用有必要重新探讨。  相似文献   

11.
The employed method of 3D gravity modeling is based on calculation of the gravity effects of the main density boundaries of the lithosphere, subtraction of these effects from the observed gravity field, and the subsequent conversion of the residual gravity anomalies first to the Moho depth and then to the total thickness of the Earth's crust and the thickness of its consolidated part. On the modeling, we also took into account the gravity effects due to an increase in the sediment density with increasing sediment depth and a rise of the top of the asthenosphere beneath the mid-ocean Gakkel Ridge. The resulting 3D models of the Moho topography and crustal thickness are well consistent with the data of deep seismic investigations. They confirm the significant differences in crustal structure between the Eurasian and Amerasian Basins and give an idea of the regional variations in crustal thickness beneath the major ridges and basins of the Arctic Ocean.  相似文献   

12.
Geo-electric anomalies are generated during the process of stress accumulation and release associated with earthquakes. However, the mechanism of these anomalies remains equivocal. Based on the analysis of thermoelectric characteristics of semiconductor minerals of the earth’s deep crust such as graphite, ferrosilicon alloy, magnetite etc., we perform finite element analysis to evaluate the principles governing the thermoelectric power generated by minerals and rocks. The results show that graphite, ferrosilicon alloy and magnetite all exhibit Seebeck effect and can be superimposed. And the thermo-electric field can be enhanced with the activation temperature increases, the content of thermoelectric minerals increases, the size of aggregates increases, and the spacing of thermoelectric minerals grains decreases. Seismogenic processes would generate a similar thermal gradient. The natural semiconductor minerals in this thermal field show a thermoelectric effect, forming a thermoelectric field that interferes with the background electric field. This study indicates that thermoelectric effect may have an important influence on the formation of geoelectric field.  相似文献   

13.
Reliable recognition of Electric Earthquake Precursors (EEP) is mainly prevented by disturbances of magnetotelluric (MT) origin, making EEP's interpretation difficult. However, assuming that EEP's are not accompanied by a significant magnetic anomaly, the MT disturbances can be reduced by applying the method of residual electric field calculations. In the present work, we present a Dynamic Neural Network (DNN) based prediction procedure. A DNN is employed to predict the behaviour of an ellectrotelluric time series with ultimate objective its application to earthquake prediction using electric precursors. To achieve such a goal, a learning phase is necessary, during which the synaptic weights of the DNN are adjusted according to an appropriate update law so as to minimize an error signal. Then the method proceeds to the prediction phase, where using the weight values resulted at the end of the learning phase the DNN predicts, the actual signal accurately. The proposed approach is applied to measured electrotelluric data.  相似文献   

14.
The experiment on verification of existence of new type of physical interaction suggested by N.A.Kozyrev was performed. The experimental setup included two types of detectors measuring the self-potentials of the electrodes in marine water and the dark current of the photomultiplier. Both detectors were protected from known sources of classical effects. Natural time variations of the potentials and the dark currents were recorded in period range 1 minute — 1 year. Number of new effects was discovered: correlation of the potentials with the dark current and the potential on another distant setup; advanced reaction of the potentials on the Earth magnetic field; nonlocal reaction of the potentials on the environmental temperature with retarded, instantaneous and advanced lag; relation of the potentials with the sudden ionospheric disturbances. Interpretation of this effects on the base of developed Kozyrev's idea on the active properties of time is rather successful.  相似文献   

15.
赵晓东  周国庆  别小勇 《岩土力学》2010,31(6):1817-1821
为获取加载过程中结构-冻土界面温度场的时空分布规律,采用红外热辐射成像技术对模型桩-冻土界面上红外辐射温度场的产生、发展及其演变过程进行了试验研究。结果表明：模型桩在加载直至滑移过程中,桩-冻土界面处存在红外辐射温升现象;桩-冻土界面发生滑移前,红外热图上低温区域在密度和范围上均逐渐减小,距离冻土试样表面不同深度D处温升幅度?T和影响宽度W随时间而逐渐增加,但相同时刻?T和W随深度D的增加而减小;桩-冻土界面发生滑移后,红外热图上的高温区成带状分布,并趋于贯通,最大温升幅度?Tmax和温升影响的最大宽度Wmax随深度D的增加呈线性减小规律。研究结果可为红外热辐射成像技术应用于冻土地区结构-冻土界面温度场测试提供参考。  相似文献   

16.
A detailed, systematic experimental and theoretical study was conducted to investigate the effect of pressure on equilibrium D/H fractionation between brucite (Mg(OH)2) and water at temperatures from 200 to 600°C and pressures up to 800 MPa. A fine-grained brucite was isotopically exchanged with excess amounts of water, and equilibrium D/H fractionation factors were calculated by means of the partial isotope exchange method. Our experiments unambiguously demonstrated that the D/H fractionation factor between brucite and water increased by 4.4 to 12.4‰ with increasing pressure to 300 or 800 MPa at all the temperatures investigated. The observed increases are linear with the density of water under experimental conditions. We calculated the pressure effects on the reduced partition function ratios (β-factor) of brucite (300-800 K and P ≤ 800 MPa) and water (400-600°C and P ≤ 100 MPa), employing a statistical-mechanical method similar to that developed by Kieffer (1982) and a simple thermodynamic method based on the molar volumes of normal and heavy waters, respectively. Our theoretical calculations showed that the reduced partition function ratio of brucite increases linearly with pressure at a given temperature (as much as 12.6‰ at 300 K and 800 MPa). The magnitude of the pressure effects rapidly decreases with increasing temperature. On the other hand, the β-factor of water decreases 4 to 5‰ with increasing pressure to 100 MPa at 400 to 600°C. Overall D/H isotope pressure effects combined from the separate calculations on brucite and water are in excellent agreement with the experimental results under the same temperature-pressure range. Our calculations also suggest that under the current experimental conditions, the magnitude of the isotope pressure effects is much larger on water than brucite. Thus, the observed pressure effects on D/H fractionation are common to other systems involving water. It is very likely that under some geologic conditions, pressure is an important variable in controlling D/H partitioning.  相似文献   

17.
This paper presents an analysis of the rocking vibrations of a rigid cylindrical foundation embedded in poroelastic soil. The foundation is subjected to time‐harmonic rocking excitation and is perfectly bonded to the surrounding soil. The soil underlying the foundation base is represented by a homogeneous poroelastic half‐space, whereas the soil along the side of the foundation is modeled as an independent poroelastic stratum composed of a series of infinitesimally thin layers. The behavior of the soil is governed by Biot's poroelastodynamic theory. The contact surface between the foundation base and the poroelastic soil is assumed to be smooth and either fully permeable or impermeable. The dynamic interaction problem is solved by employing a simplified analytical method. Some numerical results for the nondimensional rocking dynamic impedance and nondimensional angular displacement amplitude of the foundation are presented to show the effect of nondimensional frequency of excitation, poroelastic material parameters, hydraulic boundary condition, depth ratio and mass ratio of the foundation. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

18.
Thomson's formulas (1872) that give the position of the magnetic centre of a magnet and the first results on the global geomagnetic field were sufficient to show that the source of this field had a disymmetry in the equatorial plane. To confirm this with Schmidt's (1934) explicit formulas giving the position of the optimal eccentric dipole, numerical calculus was necessary. To obtain their relatively simple formulas, Thomson and Schmidt used lengthy algebra that was avoidable.  相似文献   

19.
2-D and 3-D densities of fractures are commonly used in mining safety design, natural gas and oil production in fractured reservoirs, and the characterization of subsurface flow and transportation systems in fractured rocks. However, many field data sets are collected in 1-D frequency (f) (e.g., scanlines and borehole data). We have developed an ARC/ INFO-based technology to calculate fracture frequency and densities for a given fracture network. A series of numerical simulations are performed in order to determine the optimal orientation of a scanline, along which the maximum fracture frequency of a fracture network can be obtained. We calculated the frequency (f) and densities (both D1 and D2) of 36 natural fracture trace maps, and investigated the statistical relationship between fracture frequency and fracture density D1, i.e. D1=1.340f+ 0.034. We derived analytical solutions for converting dimensional density (D1) to non-dimensional densities (D2 and D3) assuming that fracture length distribution f  相似文献   

20.
An independent approach, based on a power law relation interconnecting the lead time of precursory signals and the stress drop of forthcoming earthquake, confirms the reported evidence that the observed magnetic field anomaly and consequently, according to Maxwell’s laws, electric field anomaly prior to Mw 6.3 Aquila earthquake in 2009 exhibit features of criticality. Precisely, by inserting the data from Aquila earthquake in this power law, we get an exponent α = 0.329, which is in excellent agreement with previously found ones and falls within the range values (0.3–0.4) for critical exponents for fracture. This fact implies that upon the initiation of the observed magnetic field anomaly and the associated electric signal prior to Aquila earthquake, the prefocal area enters into a critical stage where nonlinear dynamic processes, typical behaviour of a system close to criticality, prevail.  相似文献   

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