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Simulation of subsurface heterogeneity is important for modeling subsurface flow and transport processes. Previous studies have indicated that subsurface property variations can often be characterized by fractional Brownian motion (fBm) or (truncated) fractional Levy motion (fLm). Because Levy-stable distributions have many novel and often unfamiliar properties, studies on generating fLm distributions are rare in the literature. In this study, we generalize a relatively simple and computationally efficient successive random additions (SRA) algorithm, originally developed for generating Gaussian fractals, to simulate fLm distributions. We also propose an additional important step in response to continued observations that the traditional SRA algorithm often generates fractal distributions having poor scaling and correlation properties. Finally, the generalized and modified SRA algorithm is validated through numerical tests. 相似文献
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西准噶尔包古图地区地层火山岩锆石LA-ICP-MS U-Pb年代学研究 总被引：24，自引：11，他引：13
包古图地区位于西准噶尔东南部,区内出露地层主要为石炭系太勒古拉组、包古图组和希贝库拉斯组,为一套巨厚的半深海相-大陆坡相火山-火山碎屑沉积建造。这套地层的时代归属和地层层序长期以来一直存在争议。本文报导了包古图地区实测地层剖面,并从太勒古拉组玄武岩和包古图组及希贝库拉斯组凝灰岩中分别选出锆石,进行了LA-ICP-MS U-Pb年代学研究,获得206Pb/238U加权平均年龄分别为357.5±5.4Ma、332.1±3.0Ma和336.3±2.5Ma。由此确定这套地层属于早石炭世的杜内阶到维宪阶,由下到上依次为太勒古拉组、包古图组和希贝库拉斯组。 相似文献
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Subgrid modeling of some type is typically used to account for heterogeneity at scales below the grid scale. The single-domain model (SDM), employing field-scale dispersion, and the dual-domain model (DDM), employing local hydrodynamic dispersion and exchange between domains having large hydraulic conductivity contrasts, are well-known examples. In this paper, the two modeling approaches are applied to tritium migration from the H-area seepage basins to a nearby stream--Fourmile Branch--at the Savannah River Site. This location has been monitored since 1955, so an extensive dataset exists for formulating realistic simulations and comparing the results to data. It is concluded that the main parameters of both models are scale-dependent, and methods are discussed for making initial estimates of the DDM parameters, which include mobile/immobile porosities and the mass exchange coefficient. Both models were calibrated to produce the best fit to recorded tritium data. When various attributes of the dataset were considered, including cumulative tritium activity discharged to Fourmile Branch, plume arrival time, and plume attenuation due to closure of the seepage basins in 1988, the DDM produced results superior to the SDM, while causing no unrealistic upgradient dispersion. A sensitivity analysis showed that only the DDM was able to accurately produce both the instantaneous activity discharge and cumulative activity with a single parameter set. This is thought to be due to the advection-dominated nature of transport in natural porous media and the more realistic treatment of this type of transport in the DDM relative to the SDM. 相似文献
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An Examination of Scale-Dependent Dispersion Coefficients 总被引：1，自引：0，他引：1