共查询到18条相似文献，搜索用时 187 毫秒
1.
为探讨含水层非均质性不同刻画方法对地下水流和溶质运移预测的影响,基于非均质含水层砂箱实验,分别用传统等效均质模型、克立金插值和水力层析刻画含水层渗透系数场,并探讨了先验信息对水力层析结果的影响.将不同方法估算的渗透系数场用以预测地下水流和溶质运移过程,以此判断不同方法估算结果的优劣,分析含水层非均质性对地下水流和溶质运移的影响.结果表明:与克立金插值法相比,水力层析法可以更好地刻画含水层非均质性,较准确地预测地下水流和溶质运移过程;钻孔岩心渗透系数样本值作为先验信息可以提高水力层析法估算结果的精度;传统等效均质模型无法准确预测地下水流和溶质运移过程.含水层非均质性的增强将导致溶质污染羽分布形态和运移路径的空间变异性增强,并且优势通道直接决定溶质的分布及运移路径. 相似文献
2.
随机水文地质学方法,较传统的确定性方法而言,是解决非均质含水层中水流和溶质运移问题的一种更为合理的手段。据以往研究,假设渗透系数场遵循对数正态分布,利用直接傅立叶变换方法来生成渗透系数随机场。应用基于随机理论的蒙特卡罗方法,来研究渗透系数的空间变异性对污染物运移结果的影响。实例研究表明,污染物在含水层中运移过程中污染羽的展布范围(二阶矩)随着渗透系数空间变异方差的增大而扩大,而污染羽在空间上的质心位置(一阶矩)基本不受方差的影响,仅取决于渗透系数随机场的均值大小。另外还分析了污染羽在各点的浓度变化方差和变异系数分别随渗透系数变异方差的变化状况。 相似文献
3.
地下水数值模拟是目前定量研究地下水水量和水质的重要手段。使用基于随机理论的MonteCarlo方法来进行地下水数值模拟。这种方法能较好地考虑水文地质参数的空间变异性。主要将MonteCarlo方法和确定性模型模拟方法的模拟结果在渗透系数场、水头场、速度场和浓度场等方面进行了比较。结果表明:在模拟三维非均质含水层中的溶质运移问题时,充分考虑了含水层渗透系数空间变异性的MonteCarlo法比确定性方法更为有效,模拟精度提高了很多,且对模拟误差及误差来源有合理的数学解释。 相似文献
4.
探讨了将蒙特卡罗(Monte Carlo)方法应用于多尺度非均质含水层中溶质运移模拟的方法。所研究的含水层由两种具有不同渗透系数统计特征的多孔介质所组成,每一种多孔介质是非均质的,且其渗透系数场符合平稳假设,而整个模拟区的渗透系数是非平稳的。Monte Carlo方法要求参数是平稳的,因此,分别对两种多孔介质产生若干随机渗透系数场后,用两种方法进行组合,并进行溶质运移的模拟计算。通过对计算结果的分析,综合考虑计算精度、计算时间等因素,得出了处理多尺度非均质多孔介质中溶质运移问题的较好方法。 相似文献
5.
基于不同地质统计方法的渗透系数场对污染物运移的影响 总被引：1，自引：0，他引：1
渗透系数场的空间变异性是影响污染物运移结果的决定因素,而地质统计方法是解决渗透系数空间变异性的主要技术手段。本文利用野外场地实测数据,采用普通克里格法和指示克里格法、顺序高斯模拟法和顺序指示模拟法四种地质统计方法,插值估测和模拟再现随机渗透系数场,进而对比研究四种渗透系数场对大尺度污染物运移的影响。研究结果表明,污染羽的质心位置（一阶矩）主要由渗透系数的平均值来决定;污染羽在空间上的展布范围（二阶矩）主要受渗透系数空间变异方差的影响;条件模拟克服了估计法的平滑效果,较好地再现真实曲线的波动性,渗透系数（ lnK）估计方差与污染羽空间二阶矩随着条件模拟次数的增加而减小,并且顺序指示模拟程度更加明显。 相似文献
6.
考虑参数空间变异性的非饱和土坡可靠度分析 总被引：2，自引：0，他引：2
在考虑多个土体参数空间变异性的基础上,提出了基于拉丁超立方抽样的非饱和土坡稳定可靠度分析的非侵入式随机有限元法。利用Hermite随机多项式展开拟合边坡安全系数与输入参数间的隐式函数关系,采用拉丁超立方抽样技术产生输入参数样本点,通过Karhunen-Loève展开方法离散土体渗透系数、有效黏聚力和内摩擦角随机场,并编写了计算程序NISFEM-KL-LHS。研究了该方法在稳定渗流条件下非饱和土坡可靠度分析中的应用。结果表明：非侵入式随机有限元法为考虑多个土体参数空间变异性的非饱和土坡可靠度问题提供了一种有效的分析工具。土体渗透系数空间变异性和坡面降雨强度对边坡地下水位和最危险滑动面位置均有明显的影响。当降雨强度与饱和渗透系数的比值大于0.01时,边坡失效概率急剧增加。当土体参数变异性或者参数间负相关性较大时,忽略土体参数空间变异性会明显高估边坡失效概率。 相似文献
7.
针对确定性模型难以描述含水层非均质空间分布的问题,提出基于随机理论的地下水环境风险评价方法。以矩形场地地下水污染风险评价为例,采用蒙特卡罗法生成大量渗透系数随机场,模拟含水层参数各种可能的非均质空间分布,在此基础上建立场地地下水流模型与溶质运移模型,分别计算污染物在地下水中的迁移转化情况。统计大量随机模拟中污染事故发生的频率,当模拟次数足够多时,污染频率收敛于污染概率,污染风险即通过污染概率体现出来。该方法将模型参数设为满足一定分布特征的随机变量,避免了确定性方法得出的武断的评价结果,可为工厂的选址、水源地的选址等工作提供科学指导。 相似文献
8.
9.
分数微分对流-弥散方程(FADE)是模拟溶质迁移问题的新理论,但应用FADE来模拟溶质迁移时能否克服弥散的尺度效应尚待验证。利用长土柱实验资料结合FADE的解析解拟合推求FADE的弥散系数,并分析其与尺度之间的相关关系。研究结果表明,FADE的弥散系数具有随尺度增大而增大的现象,且均质土柱中FADE的弥散系数尺度效应小于非均质土柱中弥散系数尺度效应。在均质土柱中,弥散系数与尺度之间成指数相关关系,在非均质土柱中,弥散系数与尺度之间成幂相关关系。考虑了弥散系数分别与迁移时间和迁移距离呈线性递增两种相关关系,进而分别构建了3种考虑弥散尺度效应的FADE模型,并提出了求解的差分方法。利用上述3种考虑弥散尺度效应的FADE来模拟和预测不同空间位置处的溶质迁移过程。结果表明,对均质土柱中的溶质迁移可得到较好的模拟结果;对于非均质土柱,其模拟结果与实测结果仍然存在一定的差异。 相似文献
10.
针对非等温分布条件下由土工膜(geomembrane,简称GMB)+土工复合膨润土衬垫(geosynthetic clay liner,简称GCL)+压实黏土衬垫(compacted clay liner,简称CCL)组成的3层复合衬垫中有机污染物一维瞬态运移问题,考虑了对流、扩散、机械弥散、吸附、降解和热扩散等因素,建立了相应的数学模型。该模型可考虑扩散系数和渗透系数等参数随温度变化。利用有限差分法,获得了该模型的数值解。通过将所建模型计算结果分别与试验结果、已有解析模型计算结果和COMSOL软件计算结果进行对比,验证了所建模型的正确性。基于所定义的击穿时间tb,以甲苯作为代表性有机污染物分析和讨论了不同因素对运移行为的影响。结果表明：(1)非等温分布条件会使渗透系数、扩散系数和线性吸附系数等参数发生变化,其中渗透系数和扩散系数的变化会加快运移过程,尤其是扩散系数,而线性吸附系数的变化会减慢运移速率;(2)复合衬垫上部和底部温度差ΔT的增大会使击穿时间tb减小,底部运移通量Jb增大;当ΔT为0、10、20、30、40 ... 相似文献
11.
Ronggao Qin Yanqing Wu Zengguang Xu Derrick Xie Chi Zhang 《Hydrogeology Journal》2013,21(6):1235-1246
The combined influence of dip angle and adsorption heterogeneity on solute transport mechanisms in heterogeneous media can be understood by performing simulations of steady-state flow and transient transport in a heterogeneous aquifer with dipping anisotropy. Reactive and non-reactive contaminant transport in various types of heterogeneous aquifer is studied by simulations. The hydraulic conductivity (K) of the heterogeneous aquifer is generated by HYDRO_GEN with a Gaussian correlation spectrum. By considering the heterogeneity of the adsorption distribution coefficient (K d), a perfect negative correlation between lnK and lnK d is obtained by using the spherical grains model. The generated K and K d are used as input to groundwater flow and transport models to investigate the effects of dipping sedimentary heterogeneity on contaminant plume evolution. Simulation results showed that the magnitude of the dip angle strongly controls the plume evolution in the studied anisotropic and heterogeneous aquifer. The retarded average pore-water velocity (v/R) of the adsorption model significantly controls the horizontal spreading of the plume. The bottom plume is intensively retarded in the zones between the dipping lenses of lower hydraulic conductivity and the no-flow bottom boundary. The implications of these findings are very important for the management of contaminated heterogeneous aquifers. 相似文献
12.
Stochastic analysis of the effect of spatial variability of diffusion parameters on radionuclide transport in a low permeability clay layer 总被引：1，自引：0，他引：1
Most studies that incorporate subsurface heterogeneity in groundwater flow and transport models only analyze and simulate the spatial variability of hydraulic conductivity. Heterogeneity of the other flow and transport parameters are usually neglected. This approach is often justified, but there are, however, cases in which disregarding the heterogeneity of the other flow and transport parameters can be questionable. In low permeability media, for instance, diffusion is often the dominant transport mechanism. It therefore seems logical to incorporate the spatial variability of the diffusion parameters in the transport model. This study therefore analyses and simulates the spatial variability of the effective diffusion coefficient and the diffusion accessible porosity with geostatistical techniques and incorporates their heterogeneity in the transport model of a low permeability formation. The formation studied was Boom clay (Belgium), a candidate host rock for the deep geological disposal of high-level radioactive waste. The calculated output radionuclide fluxes of this model are compared with the fluxes calculated with a homogeneous model and a model with a heterogeneous hydraulic conductivity distribution. This analysis shows that the heterogeneity of the diffusion parameters has a much larger effect on the calculated output radionuclide fluxes than the heterogeneity of hydraulic conductivity in the low permeability medium under study. 相似文献
13.
在地下水污染模拟预报中,弥散参数是很难确定的一个模型参数。因实验室小尺度弥散规律一般不能用于大尺度弥散过程,而野外示踪试验却耗资大、周期长,限制了其实用性。文中利用随机数值模拟手段、基于随机理论的蒙特卡罗方法及序贯高斯模拟技术来生成渗透系数随机场,并研究渗透系数对数场的方差、相关长度以及变异函数类型在不同尺度上对纵向弥散度的影响,进而建立纵向弥散度与随机分布渗透系数场的方差和相关长度的统计定量关系,并与Gelhar理论计算结果进行比较。数值模拟结果表明,经过一定迁移距离后纵向弥散度与随机分布渗透系数对数场的方差和相关长度具有良好的线性统计关系,与Gelhar理论公式表达的关系类型类似。但对于较大的方差,纵向弥散度模拟结果明显大于Gelhar理论计算值,而对于较大相关长度在迁移距离不很大时,纵向弥散度模拟结果明显小于Gelhar理论计算值。本研究可为野外大尺度地下水污染预报模型中水动力弥散参数的确定提供方法借鉴。 相似文献
14.
Stochastic analysis of the effect of heterogeneity and fractures on radionuclide transport in a low-permeability clay layer 总被引：1，自引：0，他引：1
Deep low-permeability clay layers are considered as safe environments for disposal of high-level radioactive waste. In Belgium,
the Boom Clay is a candidate host rock for deep geological disposal. In this study, we analyze the effects of fractures and
spatially variable hydraulic conductivity on radionuclide migration through the clay. Fracture geometry and properties are
simulated with Monte Carlo simulation. The heterogeneity of hydraulic conductivity is simulated by direct sequential co-simulation
using measurements of hydraulic conductivity and four types of secondary variables. The hydraulic conductivity and fracture
simulations are used as input for a transport model. Radionuclide fluxes computed with this heterogeneous model are compared
with fluxes obtained with a homogeneous model. The output fluxes of the heterogeneous model differ at most 8% from the homogeneous
model. The main safety function of the Boom Clay is thus not affected by the fractures and the spatial variability of hydraulic
conductivity. 相似文献
15.
Retention of surface-modified nanoscale zero-valent iron (NZVI) particles in the porous media near the point of injection has been reported in the recent studies. Retention of excess particles in porous media can alter the media properties. The main objectives of this study are, therefore, to evaluate the effect of particle retention on the porous media properties and its implication on further NZVI particle transport under different flow conditions. To achieve the objectives, a one-dimensional transport model is developed by considering particle deposition, detachment, and straining mechanisms along with the effect of changes in porosity resulting from retention of NZVI particles. Two different flow conditions are considered for simulations. The first is a constant Darcy’s flow rate condition, which assumes a change in porosity, causes a change in pore water velocity and the second, is a constant head condition, which assumes the change in porosity, influence the permeability and hydraulic conductivity (thus Darcy’s flow rate). Overall a rapid decrease in porosity was observed as a result of high particle retention near the injection points resulting in a spatial distribution of deposition rate coefficient. In the case of constant head condition, the spatial distribution of Darcy’s velocities is predicted due to variation in porosity and hydraulic conductivity. The simulation results are compared with the data reported from the field studies; which suggests straining is likely to happen in the real field condition. 相似文献
16.
Leslie Smith 《Mathematical Geology》1981,13(1):1-21
The spatial variability in porosity, hydraulic conductivity, compressibility, and various grain size fractions is analyzed for several sets of samples from the Quadra Sand. This unit is a well-sorted, medium grained, horizontally stratified sand with relatively few silt or gravel interbeds. Both random and uniformly spaced sample plans are used. The heterogeneity of the flow parameters is characterized by frequency histograms and their estimated moments, by their sample autocorrelation functions, and the estimated power spectra. Emphasis is placed on the nature of the spatial dependence between neighboring values of the flow parameters. A nearest neighbor stochastic process model is fit to the data to consider its adequacy in describing the spatial dependence within the porosity and hydraulic conductivity sequences. Even though the Quadra Sand is relatively uniform, a fairly complex spatial structure is observed. A simple monotonically decaying autocorrelation function may not adequately represent the spatial continuity. Statistical anisotropy is observed in both the extent of the spatial autocorrelation and in its functional form. Results show the importance of scale in constructing a probability model to describe the spatial variability. 相似文献
17.
Influence of temporal fluctuations and spatial heterogeneity on pollution transport in porous media 总被引：1，自引：1，他引：0
The combined influence of temporal fluctuations and spatial heterogeneity on non-reactive solute transport mechanisms in porous media can be understood by performing simulations of steady and unsteady flow and transport in heterogeneous media. The study focuses on issues such as the degree of heterogeneity, correlation length, separation of the combined effects of temporal and spatial variations, and ergodicity conditions under unsteady flow conditions. It is shown that the effect of temporal variations on solute transport is masked by the strong effect of spatial heterogeneity. There is no obvious difference in plume shape between steady and unsteady flow conditions; the first and the second spatial moments of the plume of the unsteady-state flow condition fluctuate around the steady-state flow condition with the same period of oscillations as the input signal at small storage coefficient (S????0.001). At a relatively high standard deviation in hydraulic conductivity and a small storage coefficient, the unsteady flow condition sharpens the temporal variations in macrodispersion coefficients. The magnitude of the longitudinal macrodispersion coefficient under unsteady flow condition is almost doubled at the maximum values. However, the transverse macrodispersion coefficient fluctuates around zero. The Kubo number and Peclet number ranges are 1.2?C64 and 10?C250, respectively. 相似文献
18.
降雨条件下考虑饱和渗透系数变异性的边坡可靠度分析 总被引：1，自引：0，他引：1
土体饱和渗透系数表现为天然的变异性,为此基于Green-Ampt模型建立了考虑饱和渗透系数变异性的降雨入渗物理模型,并藉此模型确定了坡体湿润锋深度和含水率分布。然后结合无限长非饱和土边坡稳定模型得到解析形式的反映边坡稳定性的极限状态函数。采用Monte Carlo法对饱和渗透系数进行随机抽样并最终建立降雨条件下考虑饱和渗透系数变异性的边坡概率分析框架。针对一假想边坡,探讨了饱和渗透系数的变异系数、降雨持时和降雨强度对边坡破坏概率以及破坏发生时间概率分布的影响,结果表明：在降雨初期,边坡的破坏概率随饱和渗透系数变异性的增强而逐渐增加,但随着降雨的持续,破坏概率开始随变异性的增强而显著降低;滑坡最可能发生时间的大小并不受饱和渗透系数变异性的影响,而是直接取决于降雨强度;滑坡最可能发生时间所对应的概率却随变异性的增强而逐渐减小。 相似文献