双重介质模型研究现状——裂隙-孔隙含水层的数学模型

和多孔介质中流体运动规律研究所得到的进展相比,裂隙介质中流体运动规律的研究仍处于发展阶段。近年来,由于裂隙含水层试验资料的解释,核废料及有毒化学废料的地质处理,海水入侵以及裂隙油田开发的需要,引起了人们对裂隙介质中流体运动规律研究的极大兴趣,本文介绍了描述裂隙含水层水力特性的双重介质模型的理论、方法及应用范围。文中所介绍的四种模型可以根据实际的地质—水文地质条件直接应用于裂隙-孔隙含水层试验的解释。     

岩溶区地下水数值模拟研究进展

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。      

连续时间随机游动理论模拟多孔介质中溶质运移的研究进展

近年来,基于连续时间随机游动(Continuous Time Random Walk, CTRW)理论所建立的模拟非均质多孔介质中溶质运移的方法已在大量的数值实验、室内实验、野外实验中得到了广泛的验证,为非均质多孔介质中的溶质运移行为提供了一种有效的模拟方法。简述了提出和发展CTRW的研究背景、基础理论以及与经典的对流-弥散方程等其他模拟方法的关系,综述了该理论在模拟溶质运移中的发展和应用,分析了实际应用中的关键问题,并展望了将其进一步发展应用于模拟反应性溶质运移的前景。     

宏观各向异性多孔介质中流体变形及溶质运移

为深入探究含水层中多孔介质的不规则形态和分布对于地下水流场及溶质运移的作用,根据沉积环境中已被发现的倾斜交叉分层地质单元结构,人为构造多孔介质双层交叉鱼骨结构,使其形成宏观各向异性水力传导特征,通过数值模拟研究该结构及其空间位置对于流场和溶质运移的影响。研究发现:宏观各向异性多孔介质引发了螺旋状流动,导致流线的拉伸和折叠,使得溶质羽发生不规则变形,显著提升了非反应性溶质的稀释程度;宏观各向异性结构和溶质羽在三维空间中的垂向相对位置对于溶质运移具有显著影响。     

多孔介质渗流力学理论研究现状及发展趋势

多孔介质广泛存在于地下岩土结构、工程材料、生物体中,由于多孔介质微结构的复杂性,多孔介质渗流问题受到广泛关注。总结介绍了多孔介质渗流理论在国内外的研究现状,对多孔介质的描述、渗流问题的研究方法以及多孔介质中溶质运移、热量运移以及数值模型等方面的研究进展作了评述,并就多孔介质渗流理论在环境、农业、生态等领域的应用与发展方向提出看法。     

基于图像法的多孔介质双分子反应溶质运移模拟

采用图像分析法确定溶质浓度,以硫酸铜和EDTA二钠作为双分子反应物,在多孔介质模型中开展了不同粒径(1.52.0,2.53.0,3.54.0 mm)和流量(1.0,1.5,2.0 mL/s)下反应性溶质运移实验,探讨了应用不完全混合的对流弥散模型(IM-ADRE)对双分子反应溶质运移的模拟和预测,并进行了参数敏感性分析。结果表明:图像分析法可准确获取多孔介质中显色反应性溶质的浓度,灰度值与浓度的决定系数R²大于0.96;用IM-ADRE模型能够准确预测双分子反应性溶质硫酸铜和EDTA二钠在3种不同多孔介质中的运移过程,误差低于3.71%;实验条件的改变对IM-ADRE模型参数D、m和β₀的影响显著,说明模型参数依赖于环境条件,其变化规律需要根据实际环境条件进一步率定,便于IM-ADRE模型的进一步推广应用。     

多孔介质粒径变异系数对污染物运移的影响

多孔介质污染物运移对于明晰地下水污染很重要,但在多孔介质中粒径变异系数(coefficientofvariation,COV)对内部微观孔隙结构中污染物运移过程影响的研究还存在不足.为此,基于随机算法,提出了一种不同COV且孔隙度一致的多孔介质几何模型构建方法,通过对Navier-Stokes(N-S)方程和对流-扩散方程(advection-diffusion equation,简称ADE)进行耦合求解得到多孔介质地下水流场及污染物浓度场,引入克里斯琴森均匀系数,定量评价流场流速分布的均匀性,基于MIM(mobile and immobile)模型和ADE模型分析耦合求解得到的穿透曲线特征.结果表明：随着粒径COV的增大,流场流速分布的不均性增强,MIM模型中的溶质流动区域占比β、无量纲传质率α^*均增大;MIM模型拟合优度高于ADE模型,且随COV增大,ADE模型的拟合全局误差Ei逐步增大.总体上,粒径COV控制了溶质流动区域和非流动区域的大小及其之间的溶质交换强度,造成了多孔介质内部溶质运移的“非费克”行为,使得ADE模型的误差逐步增大,对于较大COV的多孔介...     

岩体粗糙单裂隙渗流及溶质运移研究

与多孔介质相比,裂隙介质中的渗流、溶质运移要复杂得多,许多学者在这方面进行了深入的研究,他们在模型的建立、求解、验证等方面都取得很大突破,但仍有许多难点没有解决。着眼于粗糙单裂隙开度变化的实质特性,将原有裂隙介质渗流、溶质运移方程进行修改,建立粗糙单裂隙渗流、溶质运移数学模型,并进行数值模拟。     

裂隙岩体地下水溶质运移的尺度问题

核废料的安全贮存、地下污染的预测控制等目前面临的许多重大问题要求对大尺度裂隙岩体地下水溶质运移问题进行研究,然而裂隙岩体地下水溶质运移问题的尺度效应给这项研究带来了极大的挑战.本文介绍了裂隙岩体地下水溶质运移的多尺度概念模型及其物理和数学模拟方法,并探讨了模拟尺度与观测尺度、预测尺度、裂隙介质尺度之间的关系及尺度效应的分形特征.     

潜水带中的水盐传输及其对土壤改良的意义

研究溶质在多孔介质中的运移规律,在许别工程技术和生产部门有重大意义。盐渍化土壤的改良就与此问题有关。近年来,已有不少学者对这个问题作了研究,但由于数学处理的困难性,模型解大多都是采用数值解法,仅在几个简单情况下得到了解析解。並且,主要还只是讨论承压水域中的问题。水流的非承压性,介质的吸附作用等因素,就更使问题复杂化,     

LNAPL在二维含水介质中运移规律的研究

为研究LNAPL(轻质非水相液体)污染物在均匀含水介质中的运移规律,本文建立微元模型推导出LNAPL在均匀含水介质中的对流--弥散方程。针对不同的介质模型,对二维对流--弥散方程运用差分法进行数值模拟,求其数值解。分析LNAPL污染物的运移特征,得出在均匀介质和非均匀层状介质中运移规律:LNAPL污染物在含水介质中的运移规律遵循对流--弥散方程,介质的弥散系数是影响LNAPL污染物运移的主要因素。     

Comparison Between Analytical and Numerical Methods in Evaluating the Pollution Transport in Porous Media

Contaminant transport modelling in environmental engineering is generally conducted to evaluate the potential impact of contaminant migration on the subsurface environment or for interpreting tracer tests or groundwater quality data. In the past few decades a number of mathematical models have been established for evaluating the migration of pollution as indicated in the literature. This paper presents a comparison between a number of analytical and numerical models in evaluating pollution transport in soils. Three analytical models and a finite element model developed in this research are used for comparing four numerical examples under different conditions. Four cases of advection dominated problem with line source boundary, advection dominated problem with semi-line source boundary, advection–dispersion–sorption problem with line source boundary and advection–dispersion–sorption problem with semi-line source are considered. Based on the results the best analytical model that has a higher accuracy is recommended for practical applications.     

One‐dimensional contaminant transport through a deforming porous medium: theory and a solution for a quasi‐steady‐state problem

Contaminant migration through soil is usually modelled mathematically using the dispersion–advection equation. This type of model finds application when planning the remediation of contaminated land, predicting the movement of polluted groundwater and designing engineered landfills. Usually the analysis assumes that the porous media through which the contaminant migrates is stationary. However, the construction of landfills on clay soils means that the soil beneath the landfill will undergo time‐dependent deformation as the soil consolidates. To date, there are no published data on the effect a deforming porous media may have on contaminant transport beneath a landfill; indeed, there appears to be no theory of contaminant migration through a deforming soil. In this paper, a one‐dimensional theory of contaminant migration through a saturated deforming porous media is developed based on a small and large strain analysis of a consolidating soil and conservation of contaminant mass. By selection of suitable parameters, the new transport equation reduces to the familiar one‐dimensional dispersion–advection equation for a saturated soil with linear, reversible, equilibrium controlled sorption of the contaminant onto the soil skeleton. Analytic solutions to a quasi‐steady‐state contaminant transport problem for a deforming media are presented, and a preliminary assessment made of the potential importance of soil deformation on the results of a contaminant migration analysis. Copyright © 2000 John Wiley & Sons, Ltd.     

Experimental and Modelling Approaches for the Assessment of Chemical Impacts of Leachate Migration from Landfills: A Case Study of a Site on the Triassic Sandstone Aquifer in the UK East Midlands

Current risk-based methods for assessing the effects of landfill leachate migration on groundwater resources are conservative and generalised. Cost-effective and practical strategies are required which can robustly determine the potential for contaminant attenuation on a site-specific basis. In this paper laboratory column experiments and reactive transport modelling are evaluated as a combined approach for assessing the chem’ical impact of leachate migration in the Triassic Sandstone aquifer. The results are compared with field data for a landfill in the East Midlands. Columns of aquifer sandstone were flushed sequentially with groundwater, followed by acetogenic or methanogenic leachate to simulate chemical interactions occurring during leachate loading episodes. The key contaminants in leachate (NH₄, heavy metals, organic fractions) were attenuated by ion exchange, redox reactions, sorption and degradation. These processes produce a consistent hydrochemical signature which may help identify the extent of leachate migration in the aquifer. The laboratory results largely replicate those found in the field system, and the behaviour of inorganic contaminants during leachate flushing of the aquifer columns can be described by the reactive transport model. The experimental and modelling approach presented represents a powerful tool for risk assessment and prediction of leachate contaminant fate at unlined and lined landfills.     

Pharmaceuticals and personal care products transference-transformation in aquifer system

Pharmaceuticals and personal care products (PPCPs) are a new kind of contaminant widely existing in the surface water and groundwater environment. In recent years, PPCPs have been received widely attention from many researchers. The migration and transformation of PPCPs are mainly photolysis, biodegradation, adsorption and hydrolysis in aquifer environment. The influencing factors of PPCPs migration include PPCPs' own physical and chemical properties, types and contents of organic matter, pH, lithology, geotechnical structure and the thickness of vadose zone, etc. At present, the research of PPCPs in China is still in the primary stage, especially on the contaminant in aquifer system. Therefore, the research in this field needs to be further strengthened.     

弥散尺度效应的试验研究进展及展望

水动力弥散尺度效应问题是地下水中污染物运移研究的重要内容,针对国内外的弥散尺度效应研究,分别从室内和野外两个方面对弥散尺度效应试验研究进行综述。统计了室内试验各影响因素产生弥散尺度效应所占的比例,并根据表格数据分析造成弥散尺度效应的原因。最后,提出弥散尺度效应的试验研究展望:(1)验证弥散尺度效应的存在性;(2)研究弥散尺度效应的产生机理;(3)弥散尺度效应的定量化研究。     

MT3D-通用的三维地下水污染物运移数值模型

定量研究污染物在地下水中的运移过程通常采用数值模拟方法。MT3D是一套基于有限差分方法的污染物运移模拟软件，近年来在国外水文地质和水环境模拟等领域的研究中已经得到较为广泛的认可。MT3D比较全面地考虑了污染物在地下水中的对流、弥散和化学反应等过程，可以灵活处理各种复杂的源汇项和边界条件，能够准确模拟承压、无压和越流含水层中的污染物运移过程。MT3D具有模块化的程序结构、灵活的求解方法以及全面的模拟功能，非常适合实际问题的研究，值得在国内推广使用。     

佳木斯市地下水水量水质模型

佳木斯市是一个以开采地下水为主要供水水源的城市.本文根据当地的水文地质条件,建立了佳木斯市的地下水的水量水质模型.用有限元法求解水量模型进行地下水资源评价.用特征有限元法求解水质模型进行地下水污染预测,该方法在求解对流一弥散方程时能有效地消除数值弥散和数值振荡,精度较高.为使该方法付诸实施,文中也提出了当利用特征有限元法求解时确定运动水质点所属单元的方法.     

IAHS/AGU symposium on groundwater contamination

Papers presented at a two-day jointly sponsored IAHS/AGU symposium on groundwater contamination are briefly summarized. This international symposium was held 11–12 May, 1989, in Baltimore, Maryland. Presentations encompassed recent research developments in three general areas: abiotic and biotic processes governing contaminant transport; aquifer rehabilitation; and the influence of agricultural practices and nonpoint sources on aquifer quality. Contributions offered an interesting mixture of theoretical, mathematical, laboratory, and field studies. In the first session, transport processes explored ranged from dispersion and fingering to nonequilibrium sorption, metals complexation, and bacteria migration. The use of optimization modeling in the design of remediation strategies was the focus of another session. Here theoretical studies were presented alongside case histories of aquifer rehabilitation. In a final session, a number of models for agricultural management were described. These presentations were complemented by case studies of actual aquifer degradation resulting from land-use and management practices.     

A self-adapting model for assessing hazardous environmental releases

Simulation results are presented by using an h-adaptive mass consistent finite element method (FEM) coupled with a Lagrangian particle transport technique (LPT) for dispersion associated with hazardous atmospheric releases. A three-dimensional wind field is first constructed from the adaptive FEM model. Lagrangian particles that define the contaminant dispersion are then produced with the LPT scheme, employing a random walk/stochastic approach. The application of FEM permits flow patterns with irregular geometries to be easily simulated, while the LPT permits contaminant particle dispersion patterns to be quickly depicted. The hybrid model is fast, runs on PCs, and appears well suited for emergency response dispersion predictions and assessment.