共查询到19条相似文献，搜索用时 703 毫秒
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溶质暂态存储是岩溶地下水溶质运移过程中的普遍现象。为揭示岩溶管道与裂隙介质间溶质暂态存储机制,本文构建室内管道-裂隙物理模型,开展集中补给条件下的定量示踪试验,运用双区对流弥散模型实现溶质运移过程模拟。研究表明:随着集中补给水动力条件的增强,裂隙暂态存储水量呈线性增加趋势,溶质穿透曲线由单峰型向双峰型转变;管道和裂隙中的平均流速呈负相关关系,溶质在管道和裂隙中的滞留时间差决定了穿透曲线的形态;溶质暂态存储引发了穿透曲线的拖尾效应和双峰现象,对岩溶地下水溶质运移过程具有重要的控制作用。 相似文献
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基于CFP的岩溶管道流溶质运移数值模拟研究 总被引：2，自引：0，他引：2
多重岩溶含水介质的复杂性导致岩溶地下水流动及溶质运移的数学模拟成为地下水研究难点之一。为了探讨岩溶多重含水介质中地下水流溶质运移特征,文章构建了管道流CFP水流模型和MT3DMS溶质运移三维耦合数值模型。在阐述管道流CFP和MT3DMS基本原理的基础上,通过建立水文地质概念模型算例（1个落水洞、4个直管道）,探讨岩溶管道水流及溶质运移规律,分析讨论不同水文地质参数对浓度穿透曲线的影响。研究结果表明:管道流CFP模型能够刻画岩溶管道与基岩裂隙水流交换特征,MT3DMS模型能够模拟穿透曲线的拖尾现象,符合实际岩溶区特征。随着水力梯度、管道直径及管道渗透系数增大,孔隙度减小,浓度曲线峰值越大,峰值到达时间越快,浓度穿透曲线越对称。得出结论:耦合CFP水流模型和MT3DMS溶质运移模型能够刻画岩溶管道流溶质运移规律,为研究岩溶复杂介质污染物运移特征提供一种思路和途径。 相似文献
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岩溶区地下水数值模拟研究进展 总被引：2，自引：2，他引：0
岩溶含水介质的不均一性导致岩溶地下水流动、溶质运移和热量迁移的数学模拟研究成为地下水模拟的难点。本文综述了岩溶区地下水流模拟的几种方法,重点阐述了等效多孔介质法、双重连续介质法和三重介质法的定义、发展过程和适用范围,并回顾了这几种方法的研究成果。从等效多孔介质法到三重介质法,模拟精度不断提高,适用范围也逐渐由大区域实际问题向小区域理论研究过渡。介绍了溶质运移模拟和热迁移模拟的研究方法及实例。溶质运移模拟以对流弥散方程为基础,其中尺度效应是溶质运移模拟的重点研究问题;热量迁移模拟应考虑地下热水密度变化对地下热水运动的影响。溶质运移模拟和热量迁移模拟往往是将迁移模型和已经调试成功的地下水流动模型相耦合,从而达到模拟溶质及热量迁移的目的。由于溶质运移和热量迁移的复杂性,现阶段水流模型多数处于等效多孔介质模型阶段。综合理论及实际应用,指出精确刻画裂隙及管道和注重基础数学算法是岩溶水数值模拟进步的关键。 相似文献
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为探讨化学物质在土石混合介质中的运移过程和机理,采用饱和稳态流下的Cl-1混合置换试验,测定水流和溶质运移过程,分析土石混合介质的溶质穿透曲线特征及碎石组成和含量对运移过程的影响。选用CXTFIT2.1的平衡和物理非平衡对流弥散模型,对参数弥散系数D和滞留因子R进行反求。结果显示:不同土石比的D变异较大:0.258~22.31 cm2/h。R的波动范围为0.6~1.54;碎石含量影响土石介质的溶质运移过程表现为平均孔隙流速、弥散系数、弥散度均与土石比成负指数的幂函数关系。对碎石粒径与溶质运移参数进行相关分析发现,小粒径的碎石含量增加,则孔隙流速和弥散系数有减少的趋势,而大于10 mm的碎石有利于溶质的运移。通过土石介质的非反应性阴离子的混合置换试验研究,可以为非均一介质中化学物质运移提供参考。 相似文献
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山东淄博市大武水源地裂隙岩溶水中污染物运移的数值研究 总被引：11，自引：0，他引：11
在分析研究淄博市大武水源地裂隙岩溶含水层的水力性质和污染物运移特征的基础上 ,对裂隙岩溶水的水头和污染物运移进行数值研究。目前国内外对裂隙岩溶水进行数值计算时 ,通常用等价多孔介质模型 ,但裂隙岩溶介质和多孔介质有很大不同。裂隙岩溶介质的储水和导水空间为裂隙网络 ,导水系数大 ,地下水的实际平均流速比孔隙水大得多 ,但给水度和贮水系数小。当用等价多孔介质模型进行模拟时应考虑这些特点。对于污染物运移的模拟 ,要同时求解水头方程和对流弥散方程 ,可采用MODFLOW和MT3D软件进行模拟。研究区裂隙岩溶水水头的数值计算表明 ,等效多孔介质模型水头的拟合误差能满足国标GB/T144 97- 93的要求。各时段地下水水量均衡计算的精度也满足要求。对流弥散方程的数值计算 ,由于Peclet数高达 95 .6 7,对流占绝对优势 ,可能存在数值弥散和数值振荡 ,因而采用多种方法进行了比较。对于同一问题 ,同时采用上游有限差分法 (UFDM) ,混合的欧拉拉格朗日方法 (特征线法MOC、改进特征线法MMOC和混合特征线法HMOC) ,总变异消减法(TVD)进行计算 ,并比较其结果。结果表明 ,混合特征线法 (HMOC)和总变异消减法 (TVD)比较适合于对流占优势的运移问题计算。由于渗透系数K和有效孔隙度θ对溶质运移结果的影响很大 ,? 相似文献
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为了研究岩溶管道中溶潭对溶质运移的影响,在实验室内构建水箱-管道系统,在不同管道结构和水流条件下进行定量示踪实验并得到相应的穿透曲线(BTCs);采用Qtracer2软件分析溶质运移参数,采用滞后系数R分析实验结果与一维经典对流弥散方程解析解之间的差别。实验结果显示:随着水箱数量的增加,示踪剂(NaCl)峰值质量浓度逐渐降低,弥散系数和弥散度逐渐增加,穿透曲线拖尾逐渐增长,表明水箱的瞬态存储使溶质运移滞后;与不对称水箱相比,对称水箱BTC拖尾较长;峰现时间随着不对称水箱数量的增多明显滞后;出口流量增加时,弥散度减小,BTC拖尾变短。一维经典对流弥散方程解析解仅对单管道最大流量条件下的BTC拟合较好,对流量较小的单管道和水箱-管道系统的BTC拟合较差,需研究适用的模型解释其拖尾现象。 相似文献
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岩溶管道溶质运移的尺度效应研究对穿透曲线的正确解译非常重要,但目前针对单一弯曲管道中溶质运移尺度效应的研究仍比较缺乏。文章将岩溶管道和溶潭分别概化为透明软管和水箱,基于前期建立的水箱-管道系统(简称“管道系统”),在水箱下游设置不同长度的弯曲管道,通过示踪试验研究管道运移尺度对穿透曲线的影响,并采用暂时存储模型模拟试验曲线。结果表明：(1)随着水箱下游管道长度的增加,峰值质量浓度逐渐缓慢降低,穿透曲线上升段斜率无明显变化,穿透曲线拖尾逐渐缩短,表明运移管道长度增加对溶质运移的影响大于下游管道弯曲;(2)穿透曲线偏度系数、后段溶质羽穿透时间和溶质羽穿透时间与管道系统长度呈良好的负线性相关关系(R2>0.96);(3)当对称和不对称水箱管道系统长度分别增加至154.5 m和164.3 m时,偏度系数接近0,穿透曲线分布接近对称;(4)弥散系数、存储区截面积和交换系数与管道系统长度呈良好的负线性相关关系,当对称和不对称水箱管道系统长度分别增加至159.9 m和178.1 m时,存储区截面积接近0,水箱导致的溶质运移滞后效应基本消失。研究结果对野外岩溶管道穿透曲线的... 相似文献
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从地质角度出发,采用Visual MODFLOW软件,针对不同水力梯度、弥散度和渗透系数等4种工况,通过模拟污染物运移特征,分析了悬挂式PRB几何尺寸对水文地质参数的敏感性。其分析结果表明:水力梯度越大,导水门越厚,悬挂式PRB的埋深越浅;弥散度越大,PRB的深度和宽度越大;渗透系数越大,导水门越厚。 相似文献
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DNAPLs本身的化学性质、裂隙的几何性质以及泄漏条件等影响重非水相流体（DNAPLs）在裂隙介质中的运移和分布。针对DNAPLs的运移规律研究多集中在孔隙介质和单裂隙中,在随机网络裂隙中的研究较少。本研究生成随机网络裂隙是基于蒙特卡罗方法,运用像素扫描识别并输出裂隙的坐标和宽度,然后采用PetraSim模拟四氯乙烯(PCE)在随机网络裂隙中的运移,探讨裂隙宽度空间变异性和泄漏条件（包括泄漏速率和泄漏位置）对DNAPLs运移的影响。数值模拟结果表明:DNAPLs的空间展布和运移路径受裂隙宽度空间变异性影响,随着网络裂隙中裂隙宽度空间变异性增大,出现优势通道,DNAPLs运移的速率加快,DNAPLs的质心位置和饱和度空间分布发生明显变化;DNAPLs的运移速率和空间展布受泄漏速率影响,泄漏速率越大,DNAPLs运移速率越快,模型底部蓄积的DNAPLs的饱和度越大,DNAPLs的空间展布也越大;同一网络裂隙中,泄漏位置不同,导致DNAPLs的运移路径及分布范围不同,不同的泄漏位置重力方向裂隙空间变异性不同,导致DNAPLs运移路径和空间展布各不相同。研究结果可以丰富裂隙介质中DNAPLs运移机理研究,为裂隙介质中DNAPLs污染修复提供模型参考。 相似文献
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Fracture networks play a more significant role in conducting fluid flow and solute transport in fractured rock masses, comparing with that of the rock matrix. Accurate estimation of the permeability of fracture networks would help researchers and engineers better assess the performance of projects associated with fluid flow in fractured rock masses. This study provides a review of previous works that have focused on the estimation of equivalent permeability of two-dimensional (2-D) discrete fracture networks (DFNs) considering the influences of geometric properties of fractured rock masses. Mathematical expressions for the effects of nine important parameters that significantly impact on the equivalent permeability of DFNs are summarized, including (1) fracture-length distribution, (2) aperture distribution, (3) fracture surface roughness, (4) fracture dead-end, (5) number of intersections, (6) hydraulic gradient, (7) boundary stress, (8) anisotropy, and (9) scale. Recent developments of 3-D fracture networks are briefly reviewed to underline the importance of utilizing 3-D models in future research. 相似文献
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In fractured-rock aquifers, the geometric and hydraulic properties of the fractures commonly have a dominant influence on transport. Tracer tests are often used to estimate directly the gross transport properties of a fractured rock mass. The prospects for understanding characteristics of the heterogeneities in a fractured porous medium were explored from evidence provided by tracer experiments. The approach was to simulate flow and transport on a large set of prescribed fracture networks in a two-dimensional homogeneous permeable medium, thus generating synthetic tracer test data. The fracture orientation, aperture, spacing and network geometry were systematically altered from one case to the next. A classification scheme was devised for the tracer breakthrough curves using principal component analysis and this classification was linked to the fracture pattern properties. Even under highly simplified and controlled conditions, quite different fracture patterns can produce very similar breakthrough curves. The classification scheme thus demonstrates that a single breakthrough curve cannot reveal the fracture geometry with any precision. However, the scheme provided a methodology for rejecting geometric properties that do not belong to the fracture pattern under investigation, thus reducing the uncertainty in fracture geometry. 相似文献
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Tao Chen Christoph Clauser Gabriele Marquart Karen Willbrand Thomas Hiller 《Hydrogeology Journal》2018,26(6):1903-1916
Upscaling permeability of grid blocks is crucial for groundwater models. A novel upscaling method for three-dimensional fractured porous rocks is presented. The objective of the study was to compare this method with the commonly used Oda upscaling method and the volume averaging method. First, the multiple boundary method and its computational framework were defined for three-dimensional stochastic fracture networks. Then, the different upscaling methods were compared for a set of rotated fractures, for tortuous fractures, and for two discrete fracture networks. The results computed by the multiple boundary method are comparable with those of the other two methods and fit best the analytical solution for a set of rotated fractures. The errors in flow rate of the equivalent fracture model decrease when using the multiple boundary method. Furthermore, the errors of the equivalent fracture models increase from well-connected fracture networks to poorly connected ones. Finally, the diagonal components of the equivalent permeability tensors tend to follow a normal or log-normal distribution for the well-connected fracture network model with infinite fracture size. By contrast, they exhibit a power-law distribution for the poorly connected fracture network with multiple scale fractures. The study demonstrates the accuracy and the flexibility of the multiple boundary upscaling concept. This makes it attractive for being incorporated into any existing flow-based upscaling procedures, which helps in reducing the uncertainty of groundwater models. 相似文献
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对交叉裂隙渗流传质特性的定量描述是研究整个裂隙网络渗透传质特性的基础。为真实模拟水流及溶质在三维交叉裂隙中的运移过程,首先通过三维轮廓仪获取天然岩石裂隙表面的形貌数据,再应用三维重构技术生成相应的三维交叉裂隙模型,随后求解Navier-Stokes方程,假定溶质运移满足Fick定律,模拟水流和溶质在三维交叉裂隙中的运移过程。通过对比粗糙裂隙模型与平行平板模型的模拟结果发现：粗糙度对流体的分布及流动状态存在显著的影响;不同进、出口工况下的流体流动及溶质运移状态亦表明：裂隙交叉的几何形貌会显著地影响溶质混合行为。这些结果表明,目前被广泛采用的平行平板模型在评估岩体内特别是交叉口的物质运移特性时将导致较大的偏差,在将来的研究中有必要针对裂隙交叉口的几何特征建立修正的模型以提高评估的准确性。 相似文献
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R. Lalehzari S. H. Tabatabaei M. Kholghi 《International Journal of Environmental Science and Technology》2013,10(6):1367-1376
Groundwater quantity and quality modeling is one approach for optimal use of available water resources in arid and semiarid regions. This study was conducted to simulate flow treatment and nitrate transport on Shahrekord aquifer using three-dimensional solute transport model and geographical information system. Hydraulic conductivity, specific yield and recharge values in flow simulation process and effect molecular diffusion coefficient, longitudinal dispersivity and distribution coefficient in quality model were calibrated. 120 water samples during July 2007 to June 2008 were collected monthly from 10 wells and measurements of nitrate were carried out. The results show that the developed model is successfully used to simulate flow path and nitrate transport in saturated porous media. The highest values of nitrate occur along Bahram–Abad village and the surroundings. The groundwater quality in the area represents a complex system, which is affected by different factors of pollution, such as urban wastewater and leaching of agricultural lands. 相似文献
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Sven Follin Lee Hartley Ingvar Rhén Peter Jackson Steven Joyce David Roberts Ben Swift 《Hydrogeology Journal》2014,22(2):313-331
The large-scale geological structure of the crystalline rock at the proposed high-level nuclear waste repository site at Forsmark, Sweden, has been classified in terms of deformation zones of elevated fracture frequency. The rock between deformation zones was divided into fracture domains according to fracture frequency. A methodology to constrain the geometric and hydraulic parameters that define a discrete fracture network (DFN) model for each fracture domain is presented. The methodology is based on flow logging and down-hole imaging in cored boreholes in combination with DFN realizations, fracture connectivity analysis and pumping test simulations. The simulations suggest that a good match could be obtained for a power law size distribution where the value of the location parameter equals the borehole radius but with different values for the shape parameter, depending on fracture domain and fracture set. Fractures around 10–100 m in size are the ones that typically form the connected network, giving inflows in the simulations. The report also addresses the issue of up-scaling of DFN properties to equivalent continuous porous medium (ECPM) bulk flow properties. Comparisons with double-packer injection tests provide confidence that the derived DFN formulation of detailed flows within individual fractures is also suited to simulating mean bulk flow properties and their spatial variability. 相似文献
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多孔介质渗透系数的空间尺度效应研究进展 总被引：6，自引：1，他引：5
多孔介质渗透系数的空间尺度问题是一个与地下流体运动和溶质运移的数值模拟密切相关的应用性课题,广泛的应用需求和新的计算方法使其成为近年的热门课题之一。它涉及到相互联系的两个方面：①非均质介质场渗透系数空间尺度行为的分析与模拟;②将局部测量尺度下的试验参数转化为数值模拟网格尺度下的参数输入值的升尺度（ｕｐｓｃａｌｉｎｇ）方法和计算模型。首先介绍了该课题在概念上的拓展及其物理含义,进而以方法为主线,对这一领域具有代表性的研究成果进行了分类和评述,讨论了该课题的研究对地下水流和溶质运移的模拟分析乃至整个多孔介质流体运动研究的意义。 相似文献
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In natural rock masses, the shapes of three‐dimensional (3‐D) blocks cut by arbitrary fracture networks may be very complex. Owing to the geometric complexity and difficulty of mesh discretization of 3‐D blocks and fracture facets, explicit consideration of fracture networks in flow analysis of fractured porous medium (FPM) is very challenging. Using the numerical manifold method based on independent covers (NMMIC), an FPM flow model was proposed that can deal with very complex 3‐D fracture networks. In this paper, the convergence of NMMIC was first demonstrated. The theoretical basis of the arbitrary refinement of computational meshes was proven. Moreover, three peculiarities of NMMIC meshes, that is, arbitrary shape, arbitrary connection, and arbitrary refinement of independent covers, were concluded. Finally, some two‐dimensional (2‐D) tunnel flow examples were analyzed and the numerical results were compared with the analytical results. 3‐D examples with complex fracture distributions were also analyzed. In addition, the computational scale of the developed program was tested by increasing the number of computational elements. The results show that our model can accurately analyze the groundwater flow of rocks surrounding tunnels with complex fracture distributions. 相似文献