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1.
含水层非均质性的刻画是模拟地下水中污染物运移的关键。以渗透系数为研究对象,构建了综合集合卡尔曼滤波方法、有效电阻率模型与地下水运移模型的同化框架,通过融合地球物理观测数据与污染物浓度观测数据来推估渗透系数的空间分布。基于理想算例,验证了该同化框架刻画含水层非均质渗透系数场的有效性,并针对不同初始参数信息与观测类型对比了耦合与非耦合水文地球物理方法的适用性。研究结果表明:基于集合卡尔曼滤波方法同化多种类型的观测数据,可有效地推估非均质参数空间分布。当初始信息较准确时,耦合方法的参数推估精度更高;初始信息存在偏差时,非耦合方法有更好的同化效果。由于非耦合方法计算成本较低且对初始信息缺失时适用性更强,在实际应用中可先基于非耦合方法初步估计参数,再利用耦合方法进一步提高参数推估精度。融合多种类型观测数据可有效提高参数推估效果。 相似文献
2.
为弥补当前河岸带水热交换模拟对土体非均质传热考虑不足的缺陷,在饱和-非饱和渗流及多孔介质传热理论基础上,引入土体有效导热系数模型,构建考虑土体非均质传热的河岸带水热耦合模型。结合COMSOL软件的特点,给出河岸带水热耦合模型的实现方法及求解流程,并通过河岸带温度和水位原型观测资料验证和对比分析不同有效导热系数模型下河岸带水热耦合模型的模拟效果。结果表明：与传统不考虑土体非均质传热方法相比,该模型能够较好地反映河岸带水热交换过程。此外,基于Johansen有效导热系数模型的河岸带水热耦合模型模拟效果表现最佳,模拟结果与前人试验结果一致。研究成果可为河岸带水热交换及污染物迁移过程的深入研究提供技术支撑。 相似文献
3.
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... 相似文献
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重质非水相有机污染物(DNAPL)泄漏到地下后,其运移与分布特征受渗透率非均质性影响显著。为刻画DNAPL污染源区结构特征,需进行参数估计以描述水文地质参数的非均质性。本研究构建了基于集合卡尔曼滤波方法(EnKF)与多相流运移模型的同化方案,通过融合DNAPL饱和度观测数据推估非均质介质渗透率空间分布。通过二维砂箱实际与理想算例,验证了同化方法的推估效果,并探讨了不同因素对同化的影响。研究结果表明:基于EnKF方法同化饱和度观测资料可有效地推估非均质渗透率场;参数推估精度随观测时空密度的增大而提高;观测点位置分布对同化效果有所影响,布置在污染集中区域的观测数据对于参数估计具有较高的数据价值。 相似文献
6.
针对防洪保护区溃堤及漫堤洪水演进数值模拟面临复杂计算域、河道-防洪保护区洪水耦合作用等问题,建立了基于侧向联解的一维-二维耦合水动力学模型.通过构造并求解Riemann问题实现一维-二维模型耦合,有效克服了基于堰流公式的传统方法难以处理模型间动量交换的缺点,也避免了堰流公式中流量系数选取的不确定性;提出了时间步长自适应匹配方法,解决了一维模型和二维模型时间步长不一致问题.算例研究表明,该模型可有效模拟河道-防洪保护区耦合系统中漫堤洪水和具有任意溃口形状的溃堤洪水演进过程,具有较好的推广应用价值. 相似文献
7.
包气带作为"四水转化"的关键带,在地下水流与溶质运移模拟中起着重要作用。VSF是一款基于MODFLOW-2000开发的用于模拟非饱和-饱和带水分变化和运移过程的数值模拟程序。本文首先介绍了VSF程序的设计原理与结构,并重点介绍了VSF区别于MODFLOW-2000的用以概化非饱和带水分运移和边界条件设置的子程序包模块,包括Richards方程渗流(REF)、浸润面(SPF)、地表滞水(PND)、地表蒸发(SEV)和植物根区蒸散发(RZE)等子程序包。本文以REF、SPF、PND和SEV等子程序包为例,将VSF与MODFLOW-2000耦合应用于一个非饱和-饱和带水流运移过程的模拟算例。结果表明,VSF可与MODFLOW耦合实现饱和带水位与非饱和带饱和度的同步计算,并能刻画模型中单元格饱和状态的变化过程,其多种实用的边界条件可提供较为全面的模拟条件,是模拟实际包气带-饱和带耦合问题的有效工具。 相似文献
8.
为了更好地把握溃坝洪水风险,减小因溃坝洪水而造成的人员生命和财产损失,建立了基于Godunov格式的一维、二维溃坝水流耦合数学模型。一维溃坝水流模型采用HLL格式的有限体积法求解,二维溃坝水流模型采用基于非结构网格的Roe格式离散求解,在一维、二维模型的链接处采用重叠计算区域的方法实现一维模型和二维模型之间的水力要素信息交换。经弯道溃坝算例和断面突变溃坝算例验证,该耦合模型具有良好的可靠性和适用性,验证后的耦合模型为大尺度的溃坝水流数值模拟打下了基础。 相似文献
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通过将经典时间分数阶对流-弥散方程的等待时间分布函数的尾部修改为指数型,推导出了改进时间分数阶对流-弥散方程,并提出有效的时空算子分裂数值求解方法。对两个理想算例和一个实际算例进行计算,结果表明,改进的时间分数阶对流-弥散方程继承了时间分数阶对流-弥散方程能模拟穿透曲线幂率型拖尾分布的优点,还可模拟穿透曲线尾部由幂率型转换到指数型的过程;特征时间λ、分数阶指数γ和两相容量比例系数β共同决定了运移行为。改进的新模型可以区分非均质介质中流动相和非流动相中的溶质浓度, 更细微地模拟非Fick溶质运移行为。 相似文献
11.
Konrad Miotliński 《Aquatic Geochemistry》2008,14(2):117-131
The reactive transport modeling of a complicated suite of reactions apparent in the aquifer during the application of N-containing
fertilizers is reported. The unconfined sandy aquifer can be subdivided into an oxic zone which contains groundwater with
oxygen and nitrate and an anoxic zone characterized by elevated iron and sulfate concentrations in groundwater. Oxygen and
nitrate are being reduced by pyrite and organic matter that commonly apparent in the aquifer. The oxidation of pyrite is modeled
using the local equilibrium approach, whereas decomposition of organic matter, with the adoption of kinetic approach. The
system is buffered by dissolution of aluminum and iron oxides. The modeling process is a two-step procedure. First, the processes
are modeled in the one-dimensional (1D) column using PHREEQC code. Subsequently, the calibrated and verified data were copied
and used in two-dimensional (2D) PHAST model. Prior to the performance of reactive transport modeling operations with PHAST,
a reliable flow model was executed. Finally, predictions are made for the distribution of water chemistry for the year 2008.
Model predicts that sulfate derived from the ongoing pyrite oxidation is reduced by the dissolved organic carbon at the higher
depth and forms pyrite by the reaction with iron. The results of this study highlight the importance of understanding the
interplay between the transport and chemical reactions that occur during the input of nitrate to the aquifer. Reactive transport
modeling incorporating the use of a newly developed code PHAST have proved to be a powerful tool for analyzing and quantifying
such interactions. 相似文献
12.
In this article, an approach for the efficient numerical solution of multi-species reactive transport problems in porous media
is described. The objective of this approach is to reformulate the given system of partial and ordinary differential equations
(PDEs, ODEs) and algebraic equations (AEs), describing local equilibrium, in such a way that the couplings and nonlinearities
are concentrated in a rather small number of equations, leading to the decoupling of some linear partial differential equations
from the nonlinear system. Thus, the system is handled in the spirit of a global implicit approach (one step method) avoiding
operator splitting techniques, solved by Newton’s method as the basic algorithmic ingredient. The reduction of the problem
size helps to limit the large computational costs of numerical simulations of such problems. If the model contains equilibrium
precipitation-dissolution reactions of minerals, then these are considered as complementarity conditions and rewritten as
semismooth equations, and the whole nonlinear system is solved by the semismooth Newton method. 相似文献
13.
The Simpevarp area is one of the alternative sites being considered for the deep geological disposal of high level radioactive waste in Sweden. In this paper, a coupled regional groundwater flow and reactive solute transport model of the Simpevarp area is presented that integrates current hydrogeological and hydrochemical data of the area. The model simulates the current hydrochemical pattern of the groundwater system in the area. To that aim, a conceptual hydrochemical model was developed in order to represent the dominant chemical processes. Groundwater flow conditions were reproduced by taking into account fluid-density-dependent groundwater flow and regional hydrogeologic boundary conditions. Reactive solute transport calculations were performed on the basis of the velocity field so obtained. The model was calibrated and sensitivity analyses were carried out in order to investigate the effects of heterogeneities of hydraulic conductivity in the subsurface medium. Results provided by the reactive transport model are in good agreement with much of the measured hydrochemical data. This paper emphasizes the appropriateness of the use of reactive solute transport models when water-rock interaction reactions are involved, and demonstrates what powerful tools they are for the interpretation of hydrogeological and hydrochemical data from site geological repository characterization programs, by providing a qualitative framework for data analysis and testing of conceptual assumptions in a process-oriented approach. 相似文献
14.
This paper presents an approach conducive to an evaluation of the probability density function (pdf) of spatio-temporal distributions
of concentrations of reactive solutes (and associated reaction rates) evolving in a randomly heterogeneous aquifer. Most existing
approaches to solute transport in heterogeneous media focus on providing expressions for space–time moments of concentrations.
In general, only low order moments (unconditional or conditional mean and covariance) are computed. In some cases, this allows
for obtaining a confidence interval associated with predictions of local concentrations. Common applications, such as risk
assessment and vulnerability practices, require the assessment of extreme (low or high) concentration values. We start from
the well-known approach of deconstructing the reactive transport problem into the analysis of a conservative transport process
followed by speciation to (a) provide a partial differential equation (PDE) for the (conditional) pdf of conservative aqueous
species, and (b) derive expressions for the pdf of reactive species and the associated reaction rate. When transport at the
local scale is described by an Advection Dispersion Equation (ADE), the equation satisfied by the pdf of conservative species
is non-local in space and time. It is similar to an ADE and includes an additional source term. The latter involves the contribution
of dilution effects that counteract dispersive fluxes. In general, the PDE we provide must be solved numerically, in a Monte
Carlo framework. In some cases, an approximation can be obtained through suitable localization of the governing equation.
We illustrate the methodology to depict key features of transport in randomly stratified media in the absence of transverse
dispersion effects. In this case, all the pdfs can be explicitly obtained, and their evolution with space and time is discussed. 相似文献
15.
结合化学反应方程式,并应用多孔多相介质溶混污染物输运过程的数值模型,对多孔多相介质中含均相/非均相化学反应传质过程进行了数值模拟。化学反应主要包含均相快速/慢速和非均相快速/慢速等5种化学反应过程,溶质输运行为的控制机制主要考虑对流、扩散及降解、吸附等。基于原有的隐式特征线Galerkin离散化的有限元方法,求解模型控制方程的边值初值问题,求解过程中把均相化学反应物质中按照反应物和生成物分开,非均相反应物质按照固相和液相分开,对均相反应物及非均相液相物质浓度耦合求解,而均相生成物和非均相固相物质独立求解。使方程组按照其不同类型进行分类,同时可减少未知数的个数。对于含有非线性内状态变量的右端项进行迭代求解。数值例题结果验证了所提出的数值方法的有效性、计算精度和稳定性。 相似文献
16.
Gour-Tsyh Yeh Yilin Fang Fan Zhang Jiangtao Sun Yuan Li Ming-Hsu Li Malcolm D. Siegel 《Computational Geosciences》2010,14(1):149-170
Subsurface contamination problems of metals and radionuclides are ubiquitous. Metals and radionuclides may exist in the solute
phase or may be bound to soil particles and interstitial portions of the geologic matrix. Accurate tools to reliably predict
the migration and transformation of these metals and radionuclides in the subsurface environment enhance the ability of environmental
scientists, engineers, and decision makers to analyze their impact and to evaluate the efficacy of alternative remediation
techniques prior to incurring expense in the field. A mechanistic-based numerical model could provide such a tool. This paper
communicates the development and verification of a mechanistically coupled fluid-flow thermal-reactive biogeochemical-transport
model where both fast and slow reactions occur in porous and fractured media. Theoretical bases, numerical implementations,
and numerical experiments using the model are described. A definition of the “rates” of fast/equilibrium reactions is presented
to come up with a consistent set of governing equations. Two example problems are presented. The first one is a reactive transport
problem which elucidates the non-isothermal effects on heterogeneous reactions. It also demonstrates that the rates of fast/equilibrium
reactions are not necessarily greater than that of slow/kinetic reactions in the context of reactive transport. The second
example focuses on a complicated but realistic advective–dispersive–reactive transport problem. This example exemplifies the
need for innovative numerical algorithms to solve problems involving stiff geochemical reactions. It also demonstrates that
rates of all fast/equilibrium reactions are finite and definite. Furthermore, it is noted that a species-versus-time curve
cannot be used to characterize the rate of homogeneous fast/equilibrium reaction in a reactive transport system even if one
and only one such reaction is responsible for the production of this species. 相似文献
17.
Peter C. Lichtner 《Geochimica et cosmochimica acta》1985,49(3):779-800
A time-space continuum model for transport of hydrothermal fluids in porous media is presented which provides for simultaneous, reversible and irreversible chemical reactions involving liquids, gases and minerals. Homogeneous and heterogeneous reactions are incorporated in the model in a similar fashion through source/sink terms added to the continuity equation. The model provides for moving reaction fronts through surfaces of discontinuity across which occur jump discontinuities in the various field variables satisfying generalized Rankine-Hugoniot relations. Reversible reactions including aqueous complexing, oxidation-reduction reactions, mineral precipitation and dissolution reactions and adsorption are explicitly accounted for by imposing chemical equilibrium constraints in the form of mass action equations on the transport equations. This is facilitated by partitioning the reacting species into primary and secondary species corresponding to a particular representation of the stoichiometric reaction matrix referred to as the canonical representation. The transport equations for the primary species combined with homogeneous and heterogeneous equilibria result in a system of coupled, nonlinear algebraic/partial differential equations which completely describe the evolution of the system in time. Spatially separated phase assemblages are accommodated in the model by altering the set of independent variables across surfaces of discontinuity. Constitutive relations for the fluid flux corresponding to primary species are obtained describing transport of both neutral and charged species by advection, dispersion and diffusion. Numerical implementation of the transport equations is considered and both explicit and implicit finite difference algorithms are discussed. Analytical expressions for the change in porosity and permeability with time are obtained for an assemblage of minerals reacting reversibly with a hydrothermal fluid under quasi-steady state conditions. Fluid flow is described by Darcy's law employing a phenomenological expression relating permeability and porosity. Finally an expression for the local retardation factor of solute species is derived for the case of advective transport in a single spatial dimension which accounts for the effects of homogeneous and heterogeneous equilibria including adsorption on the rate of advance of a reaction front. The condition for the formation of shock waves is given. 相似文献
18.
Modeling reactive transport in porous media, using a local chemical equilibrium assumption, leads to a system of advection–diffusion
PDEs coupled with algebraic equations. When solving this coupled system, the algebraic equations have to be solved at each
grid point for each chemical species and at each time step. This leads to a coupled non-linear system. In this paper, a global
solution approach that enables to keep the software codes for transport and chemistry distinct is proposed. The method applies
the Newton–Krylov framework to the formulation for reactive transport used in operator splitting. The method is formulated
in terms of total mobile and total fixed concentrations and uses the chemical solver as a black box, as it only requires that
one be able to solve chemical equilibrium problems (and compute derivatives) without having to know the solution method. An
additional advantage of the Newton–Krylov method is that the Jacobian is only needed as an operator in a Jacobian matrix times
vector product. The proposed method is tested on the MoMaS reactive transport benchmark. 相似文献
19.
In the framework of safety assessment studies for geological disposal, large scale reactive transport models are powerful inter-disciplinary tools aiming at supporting regulatory decision making as well as providing input to repository engineering activities. Important aspects of these kinds of models are their often very large temporal and spatial modelling scales and the need to integrate different non-linear processes (e.g., mineral dissolution and precipitation, adsorption and desorption, microbial reactions and redox transformations). It turns out that these types of models may be computationally highly demanding. In this work, we present a Lagrangian-based framework, denoted as FASTREACT, that aims at solving multi-component-reactive transport problems with a computationally efficient approach allowing complex modelling problems to be solved in large spatial and temporal scales. The tool has been applied to simulate radionuclide migration in a synthetic heterogeneous transmissivity field and the results have been successfully compared with those obtained using a standard Eulerian approach. Finally, the same geochemical model has been coupled to an ensemble of realistic three-dimensional transport pathways to simulate the migration of a set of radionuclides from a hypothetical repository for spent nuclear fuel to the surface. The results of this modelling exercise, which includes key processes such as the exchange of mass between the conductive fractures and the matrix, show that FASTREACT can efficiently solve large-scale reactive transport models. 相似文献
20.
A new approach is proposed for incorporating solid solution reactions into mass conservation equations describing reaction paths in both closed and open systems. The method is applicable to problems involving advective, dispersive, and diffusive transport in a porous medium. By representing the continuously variable solid solution composition with a discrete set of stoichiometric solids that span composition space, combined with a kinetic formulation of their rates of reaction, a self-determining spatial and temporal evolution of the solid solution concentration and composition is obtained. It is demonstrated that equilibrium of an aqueous solution with a stoichiometric solid derived from a solid solution corresponds to equilibrium of the solid solution itself if and only if equilibrium of the stoichiometric solid is stable. One advantage of this approach is that it is unnecessary to introduce any additional compositional variables to represent the solid solution. Discretization may be over the entire range of composition space, or over some subset depending on the system. A major consequence of the kinetic discrete-composition solid solution representation is that modeling solid solutions is similar to modeling pure mineral phases with the exception of a weighting factor applied to reaction rates of stoichiometric solids corresponding to a common solid solution. With this approach, precipitation leads to a discrete zonation of the solid solution that approximates the continuous variation in composition expected for the actual solid solution. The approach is demonstrated for a hypothetical ideal and non-ideal binary solid solution AxB1−xC for a reaction path formulation and reactive transport involving advection and diffusion. 相似文献