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101.
Kaili Wang Guanhua Huang 《Advances in water resources》2011,34(6):671-683
The effect of aquifer heterogeneity on flow and solute transport in two-dimensional isotropic porous media was analyzed using the Monte Carlo method. The two-dimensional logarithmic permeability (ln K) was assumed to be a non-stationary random field with its increments being a truncated fractional Lévy motion (fLm). The permeability fields were generated using the modified successive random additions (SRA) algorithm code SRA3DC [http://www.iamg.org/CGEditor/index.htm]. The velocity and concentration fields were computed respectively for two-dimensional flow and transport with a pulse input using the finite difference codes of MODFLOW 2000 and MT3DMS. Two fLm control parameters, namely the width parameter (C) and the Lévy index (α), were varied systematically to examine their effect on the resulting permeability, flow velocity and concentration fields. We also computed the first- and second-spatial moments, the dilution index, as well as the breakthrough curves at different control planes with the corresponding concentration fields. In addition, the derived breakthrough curves were fitted using the continuous time random walk (CTRW) and the traditional advection-dispersion equation (ADE). Results indicated that larger C and smaller α both led to more heterogeneous permeability and velocity fields. The Lévy-stable distribution of increments in ln K resulted in a Lévy-stable distribution of increments in logarithm of the velocity (ln v). Both larger C and smaller α created sharper leading edges and wider tailing edges of solute plumes. Furthermore, a relatively larger amount of solute still remained in the domain after a relatively longer time transport for smaller α values. The dilution indices were smaller than unity and increased as C increased and α decreased. The solute plume and its second-spatial moments increased as C increased and α decreased, while the first-spatial moments of the solute plume were independent of C and α values. The longitudinal macrodispersivity was scale-dependent and increased as a power law function of time. Increasing C and decreasing α both resulted in an increase in longitudinal macrodispersivity. The transport in such highly heterogeneous media was slightly non-Gaussian with its derived breakthrough curves being slightly better fitted by the CTRW than the ADE, especially in the early arrivals and late-time tails. 相似文献
102.
在西安白鹿塬北缘实测了14个黄土自然边坡断面,建立了地质模型,通过采样测试并收集已有的测试资料,获得了各时代黄土地层的物理力学参数,将Morgenstern—Price法稳定性计算公式作为极限状态方程,分别采用Monte—Carlo法和Duncan法进行了边坡稳定的可靠度分析。结果表明:采用Monte—Carlo法和Duncan法得到的14个边坡稳定系数分别为1.11~1.41和1.09~1.33,显示这些边坡处于基本稳定一稳定状态;采用上述两种方法得到的边坡可靠指标分别为0.56~1.79和0.39~1.60,得到的失效概率分别为3.4%~29.0%和5.5%~34.8%,并且共有75%的边坡失效概率大于10%,失效可能性较大。统计结果表明:白鹿塬区边坡的坡高和坡度存在负相关性。低而陡的边坡潜在最危险滑面剪出口较高,失效概率较小;坡高达到50m及以上时,边坡高而缓,剪出口较低,失效概率较大,其中河流下切深,有N2泥岩出露的极高边坡,稳定性最差。Duncan法求解的稳定系数略小于Monte-Carlo法求得的结果,而前者求解的失效概率略大于后者,两种方法计算结果较为接近。由于Duncan法理论简单,计算量小,更宜于在实际工程中应用。 相似文献
103.
104.
105.
岩石质量指标的计算机模拟及其风险分析 总被引:2,自引:0,他引:2
章杨松 《地质灾害与环境保护》2002,13(1):44-47
利用Monte Carlo法在计算机上生成岩体节理网络图,然后建立了模拟计算不同阀值的岩石质量指标RQDt的计算机模拟方法。进一步可作出岩石质量描述图和岩石质量风险分析,分析了岩体中大于10cm的完整岩石的具体分析规律。实例表明,该方法能较全面地描述岩石质量。 相似文献
106.
A MODEL OF INTEGRATED RANDOM INITIAL VALUES AND RANDOM FORCING AND ITS PRELIMINARY EXPERIMENT
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A simple quasi-geostrophic barotropic vorticity equation model is used as the dynamic frame of themodel in this paper.Considering that there are many random errors in model's initial values of meteorolo-gical data,and that it is not perfectly complete about model's physical processes (for example,take no ac-count of the interaction between atmosphere and underlying surface,radiation,etc.),we add the random for-ced term to the model and use the Monte-Carlo method with random initial values.A statistical-dynamicintegrated model is thus built up,and a numerical forecasting experiment of 500hPa monthly mean height fieldof January 1983 has been carried out.The experiment result proves that the forecasting result of the model,considering random forcing and random initial values at the same time,is better than that by the pure dynamicmodel,the random initial value model and the random forced model. 相似文献
107.
Tang Limin Xiao Xi
Lecturer 《中国海洋工程》1997,(2)
During the life of an offshore structure,its structural strength declines due to various kinds ofdamages related to the time factor.In this paper,four major kinds of damages,including damages causedby fatigue,dent,corrosion and marine life,are discussed.Based on these analyses,formulas for theevaluation of the damaged structure reliability are derived.Furthermore the computer program ISM forthe analysis of structural reliability is developed by the use of Advanced First Order Second Moment meth-od and Monte-Carlo Importance Sampling method.The reliability of a turbular joint and a beam are stu-died as numerical examples.The results show that the theory and the analysis method given in this paperare reasonable and effective. 相似文献
108.
109.
R. J. de Meijer F. D. Smit F. D. Brooks R. W. Fearick H. J. Wörtche F. Mantovani 《Earth, Moon, and Planets》2006,99(1-4):193-206
The programme Earth AntineutRino TomograpHy (EARTH) proposes to build ten underground facilities each hosting a telescope.
Each telescope consists of many detector modules, to map the radiogenic heat sources deep in the interior of the Earth by
utilising direction sensitive geoneutrino detection. Recent hypotheses target the core-mantle boundary (CMB) as a major source
of natural radionuclides and therefore of radiogenic heat. A typical scale of the processes that take place at the CMB is
about 200 km. To observe these processes from the surface requires an angular resolution of about 3°. EARTH aims at creating
a high-resolution 3D-map of the radiogenic heat sources in the Earth’s interior. It will thereby contribute to a better understanding
of a number of geophysical phenomena observed at the Earth’s surface. This condition requires a completely different approach
from the monolithic detector systems as e.g. KamLAND.
This paper presents, for such telescopes, the boundary conditions set by physics, the estimated count rates, and the first
initial results from Monte-Carlo simulations and laboratory experiments. The Monte-Carlo simulations indicate that the large
volume telescope should consist of detector modules each comprising a very large number of detector units, with a cross section
of roughly a few square centimetres. The signature of an antineutrino event will be a double pulse event. One pulse arises
from the slowing down of the emitted positron, the other from the neutron capture. In laboratory experiments small sized,
10B-loaded liquid scintillation detectors were investigated as candidates for direction sensitive, low-energy antineutrino detection. 相似文献
110.
Importance Sampling Method in V-Space 总被引:3,自引:0,他引:3
Jin Weiliang
Professor 《中国海洋工程》1997,(2)
Based on the observation of importance sampling and second order information about the fail-ure surface of a structure,an importance sampling region is defined in V-space which is obtained by ro-tating a U-space at the point of maximum likelihood.The sampling region is a hyper-ellipsoid that con-sists of the sampling ellipse on each plane of main curvature in V-space.Thus,the sampling probabilitydensity function can be constructed by the sampling region center and ellipsoid axes.Several exampleshave shown the efficiency and generality of this method. 相似文献