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171.
岩溶坝区透水参数的随机模型 总被引:1,自引:0,他引:1
岩溶坝区的渗透特性受高应力场的作用,使其固有的非均质各向异性更趋复杂,采用确定性的方法不能准确的描述其本质特性。本文在对岩溶坝区透水性随机场进行分析的基础上,提出了渗透随机性的数学描述。考察岩溶坝区主要的两场作用,即渗流与应力场的耦合。基于Taylor随机有限元建立了渗流应力耦合的随机微分方程格式,并对耦合随机模型反演求解渗透参数提出了思路。 相似文献
172.
The purpose of this research was to study the complexity of the energization of the ring current during a geomagnetic storm, produced during southern Bz(IMF) by the injection of plasma sheet ions, accelerated by enhanced convective electric fields. This model assumes that the plasma sheet is continuously populated by H+ from the sun and the ionosphere, and sporadically by ionospheric O+, making the ring current a coupled system whose energy can hardly be expressed analytically. When Bz(IMF) turns north, the ring current becomes uncoupled, and the energy decays exponentially if the storm is weak, or can be expressed as a combination of exponentials during strong storms representing the quick decay of O+ and the slower decay of H+, as has been shown. 相似文献
173.
Study on coupling between deep and shallow structures of Xingtai area and some significant questions
IntroductionIn order to gain a clear idea of the deep tectonic environment of Xingtai earthquake area,three wide-angle deep seismic renectionlrefraction profiles have been conducted through the are4they are Yuanshi--Ji'nan profile, Renxian--Wuqing profile and Tat' an--LongyaM inzhou profi I e.The Yuanshi--Ji'nan profile passes through the epicenter of the Ms=7.2 main shock andTat' ~ongyaO--X inzhou profi ie passes through the ep icenter of the Ms=6. 8 earthquake. Duringthe "Eighth Five-… 相似文献
174.
At times of strong solar wind forcing such as those that produce major magnetic storms, the region 1 current system dominates over the Chapman–Ferraro current system in mediating the transfer of force between the solar wind and the terrestrial system. The global force balance can be broken into two components, one involving the high-altitude part of the region 1 current system that is in contact with the solar wind (labeled here the HRS) and the other involving the low-altitude part of the region 1 current system that lies in the ionosphere (the LRS). Both communicate their J×B force to the geomagnetic dipole via a gradient in the magnetic field that they generate. In the HRS case the force acts to push the dipole away from the sun. This is the region 1 analog of the Chapman–Ferraro mechanism for transmitting the solar wind's force to the Earth. However, in the LRS case, the force (which is much stronger than in the HRS case) acts to push the dipole toward the sun, seemingly paradoxically. The LRS balances the ‘paradoxical’ sunward force on the dipole with an opposite force on the atmosphere. This paper uses MHD simulations to demonstrate the presence of both the normal force-transmitting gradient generated by the Chapman–Ferraro and the counter-Chapman–Ferraro gradient in the magnetic field generated by the region 1 current system. 相似文献
175.
176.
177.
The common-ray approximation eliminates problems with ray tracing through S-wave singularities and also considerably simplifies
the numerical algorithm of the coupling ray theory for S waves, but may introduce errors in travel times due to the perturbation
from the common reference ray. These travel-time errors can deteriorate the coupling-ray-theory solution at high frequencies.
It is thus of principal importance for numerical applications to estimate the errors due to the common-ray approximation applied.
The anisotropic-common-ray approximation of the coupling ray theory is more accurate than the isotropic-common-ray approximation.
We derive the equations for estimating the travel-time errors due to the anisotropic-common-ray (and also isotropic-common-ray)
approximation of the coupling ray theory. The errors of the common-ray approximations are calculated along the anisotropic
common rays in smooth velocity models without interfaces. The derivation is based on the general equations for the second-order
perturbations of travel time. 相似文献
178.
Marcos E. C. Bernardes Mark A. Davidson Keith R. Dyer Ken J. George 《Ocean Dynamics》2006,56(3-4):186-197
The main objective of this paper is to address the principal mechanisms involved in the medium-term (order of months to years) morphodynamic evolution of estuaries through the application of a process-based numerical modelling. The Teign estuary (Teignmouth, UK) is the selected site. The system is forced by the macrotidal semi-diurnal tide in the English Channel and is perturbed to a minor extent by high river discharge events (freshets). Although waves have a definite influence on the adjacent coastal area, Wells (Teignmouth Quay Development Environmental Statement: Changes to Physical Processes. Report R.984c:140. ABP Marine Environmental Research Ltd., Southampton, 2002b) suggested that swell waves do not enter the estuary. Hence, wave effects are neglected in this study, as only tides and the river discharge are taken into account. The sediment grain size is highly variable, but mainly sandy. Within the frame of the COAST3D project (), four bathymetric surveys of the adjacent coastal area were carried out at a nearly weekly intervals. The outer estuary and the adjacent coastal area were also surveyed every 6 months as part of the COASTVIEW project (). Based on these data and on continuously measured parameters, such as water level, waves, wind and river discharge, numerical modelling of the morphodynamic processes can be tested. To replicate the morphological changes in the medium-term within a feasible simulation time, forcing conditions are reduced through the use of an input reduction method (called ensemble technique). In this study, simulations are based on the coupling between Telemac-2D and its non-cohesive sediment transport module, Sisyphe (version 5.3 for both modules). Three different sediment transport formulae were tested: (1) Engelund and Hansen (A monograph on sediment transport in alluvial streams, 3rd edn. Technological University of Denmark, Copenhagen, 1967) including the modifications proposed by Chollet and Cunge (J Hydraul Eng 17(1):1–13, 1979); (2) Bijker (Mechanics of sediment transport by the combination of waves and current. In: Design and reliability of coastal structures. 23rd international conference on Coastal Engineering, pp 147–173, 1968) and (3) Soulsby (Dynamics of Marine Sands. A manual for practical applications. HR Wallingford, Wallingford, p 142, 1997) modified version of van Rijn [J Hydraul Eng 110(10):1431–1456, 1984a, J Hydraul Eng 110(11):1613–1641, 1984b] formulation. Both a qualitative (i.e. visual comparison) and a quantitative tool [Brier Skill Score (BSS); described in Sutherland et al. in Coast Eng 51:917–939, 2004b] are applied to assess the similarity of simulations when compared to model predictions and observations. Tests confirmed the reliability and time efficiency of the ensemble technique, since it reproduced very well the results of a reference run, a computation based on the observed boundary conditions. For the spring-neap cycle modelled, the BSS was of 0.91 (a perfect modelling would have a BSS of 1), with a reduction in the simulation time on the order of 80%. For the 6-month-period simulation, results were also excellent: BSS=0.92 and a computer time reduction of 85%. In principle, this method has the advantage of being applied to any process-based numerical model. 相似文献
179.
H. Greiner-Mai J. Hagedoorn L. Ballani I. Wardinski D. Stromeyer R. Hengst 《Studia Geophysica et Geodaetica》2007,51(4):491-513
We investigate the temporal behaviour of the axial component of the electromagnetic core-mantle coupling torque that is associated
with the poloidal part of the geomagnetic field observable at the Earth surface. For its computation, we use different models
of the geomagnetic field, expanded into spherical harmonics (Wardinski and Holme, 2006; Sabaka et al., 2004), and the mantle
conductivity. The geomagnetic field, which we have to know at the core-mantle boundary for the associated computations, will
be inferred from the field at the Earth surface by the non-harmonic field continuation through a conducting mantle shell.
The aims of this investigation are (i) to check how sensitive is the computation of the torque with respect to the different
geomagnetic field models, (ii) to check its dependence on the spherical harmonic degree n, and (iii) to determine the difference
between the mechanical torque derived from the observed length-of-day variations (atmospheric influence subtracted) and the
poloidal electromagnetic torque in dependence on the assumed conductivity. To use the non-harmonic field continuation for
the torque calculation and to obtain an insight into the influence of the different geomagnetic field models on the EM torques
are the major aspects of this paper.
grm@gfz-potsdam.de 相似文献
180.
L. E. Sjöberg 《Journal of Geodesy》2007,81(5):345-350
This study emphasizes that the harmonic downward continuation of an external representation of the Earth’s gravity potential
to sea level through the topographic masses implies a topographic bias. It is shown that the bias is only dependent on the
topographic density along the geocentric radius at the computation point. The bias corresponds to the combined topographic
geoid effect, i.e., the sum of the direct and indirect topographic effects. For a laterally variable topographic density function,
the combined geoid effect is proportional to terms of powers two and three of the topographic height, while all higher order
terms vanish. The result is useful in geoid determination by analytical continuation, e.g., from an Earth gravity model, Stokes’s
formula or a combination thereof. 相似文献