Simultaneous one-dimensional water flow and mass transport of conservative solutes in porous media

Three variations of the Galerkin finite element method are used for the numerical solution of the one-dimensional, vertical water flow and mass transport equations in variably saturated porous media. The final result is a system of differential equations with derivatives depending only on time, which are approximated by a relationship leading to a second-order accuracy. Examples of two different soil types (clay loam and sandy) are presented to verify the accuracy of the numerical schemes. In these examples, saltwater is allowed to be infiltrated into the soil profile with different boundary conditions on the soil surface (Neuman or Dirichlet type). In some cases, the infiltration of saltwater is followed immediately by salt-free water.     

层状土壤条件下地下滴灌水氮运移模型及应用

基于土壤水分运动的动力学方程和溶质运移的对流-弥散方程,考虑地下滴灌灌水器流量随时间的变化,建立了层状土壤地下滴灌施用硝酸铵(NH4NO3)条件下水氮运移的数学模型。利用均质砂土(S)、均质壤土(L)、上砂下壤(SL)和砂土夹层(LSL)四种土壤的试验数据对模型进行了验证。结果指出,考虑土壤中灌水器流量随时间变化可稍改善土壤含水率和硝态氮的模拟精度。利用验证后的数学模型研究了灌水器流量(1.1、1.75和2.6L/h)、灌水器与犁底层相对位置对地下滴灌水氮分布的影响,模拟结果表明灌水器流量对含水率分布的影响不明显,但灌水器流量的增大可明显增加20~40cm土层硝态氮含量;灌水器与犁底层相对位置对水氮分布影响显著,灌水器位于犁底层中(埋深25cm)土壤表层干土层较薄、水氮向下运移深度较小,有利于减小土壤蒸发和避免水氮淋失。     

泰安市岩溶水环境系统模拟分析

作者运用有限单元法，根据变化的历史开采布局和污染演化趋势，建立了水量水质耦合模型，对岩溶水资源进行了数值模拟评价。在此基础上，以现状开采量和历史水质污染的演化趋势为基次，对未来10年的岩溶水水位水质进行了预测，预测结果表明：在2010年，部分地区的氯离子浓度超出了饮用水标准，大部分地区的总硬度严重超标。     

Numerical simulation of shallow-water flooding using a two-dimensional finite volume model

A 2-D Finite Volume Model (FVM) is developed for shallow water flows over a complex topography with wetting and drying processes. The numerical fluxes are computed using the Harten, Lax, and van Leer (HLL) approximate Riemann solver. Second-order accuracy is achieved by employing the MUSCL reconstruction method with a slope limiter in space and an explicit two-stage Runge-Kutta method for time integration. A simple and efficient method is introduced to deal with the wetting and drying processes without any correction of the numerical flux term or the source term. In this new method, a switch of alternative schemes is used to compute the water depths at the cell interface to obtain the numerical flux. The model is verified against benchmark tests with analytical solutions and laboratory experimental data. The numerical results show that the model can simulate different types of flood waves from the ideal flood wave to cases over complex terrains. The satisfactory performance indicates an extensive application prospect of the present model in view of its simplicity and effectiveness.     

区域农田土壤水和氮素行为的模拟

本文以华北平原为研究区域,根据第二次全国土壤普查资料,应用地理信息系统的方法(ARC/INFO),研究了土壤类型的区域分布,并得出了以72个典型土壤剖面为代表的华北平原土壤类型分布的概化图。通过对作物生长发育参数、土壤和气候资料的简化处理,将土壤水、热、氮联合模拟模型应用于区域农田土壤水、氮素行为的模拟计算。结果表明,通过模型计算与地理信息系统相结合,便于评价不同水氮管理、不同降雨年型条件下区域农田土壤水、氮素行为。通过以中等水氮处理为例的计算,评价了不同降雨年型所得到的水分利用效率(WUE)和氮素利用效率(NUE).区域内WUE明显在干旱年型下最高,湿润年型下最低,而NUE的规律相似但不太明显。各指标在区域上分布有一定的规律,与气候分异和土壤类型分异密切相关。     

再生水回用于景观水体氮营养盐对叶绿素a和藻密度的影响研究

再生水回用于景观水体是否会带来严重的生态风险,尚需广泛而深入的研究。以北京市某再生水厂出水为研究对象,人工配制各浓度梯度的营养盐,试验研究补给再生水后景观水体水质指标的变化,重点考察氮营养盐(氨氮、硝酸盐氮)对叶绿素a和藻密度的影响情况。试验结果表明叶绿素a和藻密度主要受水体中氮磷比和磷酸盐浓度的影响,与单独的硝酸盐氮浓度增加并无直接的关系。当磷酸盐浓度保持在1mg/L以下,氨氮浓度在4mg/L以下,硝酸盐氮浓度在16mg/L以下,将再生水一次性补给景观水体是可行的,不会产生藻类暴发。     

非饱和土壤中吸附性溶质运移的基本方程和参数结构

本文应用随机场的谱分析方法，研究了吸附性溶质在非饱和，非均匀土体中运动时平均浓度所遵循的基本方程。当非饱和水分运动以重务为主要作用力时，设经对数变换后的土壤饱和渗透系数，吸附系数和α参数为正态平稳随机场，求得了宏观弥散度的解析表达式。研究结果表明，宏观散度由三部分组成，分别来源于非饱和渗透系数的自相关函数，非饱和渗透系数吸附参数的互相关函数，以及吸附参数的自相关函数。     

某厂区防渗工程地下水数值模拟

根据某厂区的水文地质条件,在建立水文地质数学模型的基础上,运用有限差分数值计算软件对该厂区地下水的渗流规律进行数值分析,并运用其跟踪模拟子模块对该厂区地下水的水质点进行了粒子示踪模拟。通过研究区埋设的孔隙水压力计测试成果的验证,该模型模拟结果与厂区地下水渗流场的实际情况较为吻合,即厂区地下水会从西北部地区向西南部和南部的梅坝溪及东北部的下道湖溪渗流。模型可用于该厂区地下水动态模拟和预测,及污染物运移途径研究,可以为厂区的防渗工程提供可靠依据。     

地下滴灌条件下水热运移数学模型与验证

基于土壤水、热运动基本方程,结合地下滴灌水分运动特点,建立了地下滴灌水热运移数学模型。利用HYDRUS-2D软件对模型进行了求解,并用田间实测数据进行验证。模拟和验证结果表明,模型对地下滴灌条件下的土壤水分和土壤温度运移变化动态的模拟效果较好,该水热运移数学模型可以用来监测和调控作物生长所需的土壤水、热环境条件。模拟值和实测值的结果对比表明,上层土壤的水分和温度的模拟值较下层土壤值差异较明显,且数值波动大,主要原因是上层土壤易受到土壤蒸发和大气温度剧烈波动的影响。     

桥渡壅水对河道水位流场影响二维数值模拟

采用Simple算法建立了一套河道平面二维水流数学模型.针对桥渡壅水问题,提出了两项措施来进行桥墩的概化:①局部地形修正,主要通过增加桥墩所在节点的河底高程来反映桥墩对河道过水面积的压缩效果;②局部糙率修正,主要通过加糙来反映桥墩的阻水作用.通过对工程问题的计算验证其效果,选取赣江神岗山-井冈山拟建的阳明大桥长约7.5 km的河段作为计算河段.地形采用2000年实测河道地形图.计算网格采用边界层坐标系下河道拟贴体正交网格.网格节点数为73×70个,计算结果较好地反映了建桥前后桥墩附近水位流场的变化情况,说明桥墩概化较为合理.     

流域水沙资源优化配置理论与模型及其在黄河下游的应用

本文在分析流域水沙资源利用现状、水沙灾害性及水沙优化配置必要性的基础上,构建了流域水沙资源联合多目标优化配置理论框架,它由河床演变均衡稳定理论和水沙资源联合多目标优化配置理论组成,进而建立了流域水沙资源优化配置数学模型,该模型包括河床演变均衡稳定模型和水沙资源多目标优化配置模型两个子模型。应用模型计算分析了黄河下游主河槽的均衡稳定断面尺寸和输水输沙优化的临界指标,提出了强化非恒定流调水调沙、调控含沙量60～100kg/m3之间的不利水沙条件等改善小浪底水库调度运用的措施,并进一步提出了黄河下游水沙资源多目标优化配置的模式, 应用模型计算分析了不同水沙条件的水沙资源优化配置方案,为黄河下游河道的科学治理提供了新的思路。     

Appraisal and optimization of agricultural water use in large irrigation schemes: I. Theory

A new approach on the functioning of an irrigation scheme has been presented. A mathematical representation of the irrigation system based on measured system properties, such as losses due to percolation and to poor management, in only a part of the system is used. This mathematical representation is termed an equivalent irrigation network. The merit of this approach is that it reduces the number of required streamflow measurements.When water amounts are measured for a number of paths in the irrigation network, so-called path efficiencies are obtained. The path efficiency is a measure of the amount of water lost along the way. The numerical model that simulates the operation of the irrigation system is based on the path efficiencies. This simulation model in turn is used to calculate different objective functions, corresponding with different optimization goals, like uniform water distribution, minimum groundwater extraction, minimum cost of water supply.This paper gives the theoretical background of the approach. The application to an actual irrigation scheme will be discussed in a second paper.     

冰期河流弯道冰水动力学行为研究

以黄河什四份子弯道为研究对象,基于2019-2020年度的凌情监测影像及现场试验数据,分析了河流弯道冰水动力学行为特征。结果表明:上宽下窄的河道形态是造成弯道卡冰的主要原因,流凌-封河阶段,弯顶节点工程对水流的顶托作用促进了上游回流区的形成;受弯道离心力作用,河冰聚集于河道凹岸一侧,并在回流区堆积形成冰桥,从而缩小了断面过冰面积,河道逐渐封冻;弯顶下游流速大且来冰量少,形成清沟,主流向河中发展;冰塞堆积于弯顶上游凹岸主河槽内,水流被挤压至凸岸非冰塞区,弯道主流易位;在稳封期,河道冰水动力特征基本不再变化,在解冻开河期,凸岸非冰塞区流速较大,主流区冰盖优先解冻且沿主流输移,回流区冰盖最后消融,河道主流逐渐恢复至畅流阶段,整体呈复归式。     

Implications of effluent discharge from a proposed wastewater treatment plant on coastal water quality in the upper gulf of Thailand

Abstract

The paper deals with the assessment of the change in coastal water quality due to effluent discharge from a wastewater treatment plant through an outfall in the Upper Gulf of Thailand. A hydrodynamic and water quality modeling approach is used to predict the water quality level in the vicinity of the outfall when the effluent discharge and concentration levels are specified. With the continuation of effluent discharge for a one‐year period, the concentration levels of coliform bacteria and nutrients increase significantly in the vicinity of the outfall. These inferred states of seawater quality would pose hygiene risks for green mussel cultivation and affect the ecosystem due to high nutrient enrichment and eutrophication. Recommendations for improvement are put forward keeping a balance between social, economic, and engineering considerations.     

一二维联解潮流数学模型在防洪评价中的应用

针对单纯使用一维或二维数学模型难以准确高效模拟大型涉水工程对水域影响的问题,通过利用一、二维联解潮流数学模型,在珠江口某港区码头工程附近使用二维模型,对该区域流场和流速变化范围进行模拟,其余水域采用一维模型模拟。结果表明,工程对珠江东四口门及工程周边水域水位、流速、河道潮量及分流比、潮排、潮灌、排涝等影响不大。结论认为,一、二维数学模型联解计算可以用于大型工程,尤其是海域内大型工程的防洪评价计算,并能够得出较为可靠的计算结果。     

Development and application of a eutrophication water quality model for river networks

The Preissmann implicit scheme was used to discretize the one-dimensional Saint-Venant equations, the river-junction-fiver method was applied to resolve the hydrodynamic and water quality model for river networks, and the key issues on the model were expatiated particularly in this article. This water quality module was designed to compute time dependent concentrations of a series of constituents, which are primarily governed by the processes of advection, dispersion and chemical reactions. Based on the theory of Water Quality Analysis Simulation Program （WASP） water quality model, emphasis was given to the simulation of the biogeochemical transformations that determine the fate of nutrients, in particular, the simulation of the aquatic cycles of nitrogen and phosphorus compounds. This model also includes procedures for the determination of growth and death of phytoplankton. This hydrodynamic and water quality model was applied to calculate two river networks. As illustrated by the numerical examples, the calculated water level and discharge agree with the measured data and the simulated trends and magnitudes of water quality constituents are generally in good agreement with field observations. It is concluded that the presented model is useful in the pollutant control and in the determination of pollutant-related problems for river networks.     

Simulation of water allocation and salt movement in the root zone

This paper is concerned with the simulation of the water allocation and salt movement in the root zone of a particular crop. A mathematical model of four ordinary differential equations is developed. The model performs water balance and salt balance in unsaturated and saturated regions of the root zone. It is a lumped input and lumped parameter conceptual model, which considers the average soil moisture and salt concentration in the root zone. The equations are solved numerically over the time period of the growing season. Precipitation and irrigation water are treated as inputs.The analyzed results indicate that, for the shallow water table case, the water table elevation has an important effect on the soil moisture depletion dynamics of the unsaturated zone. An appreciable amount of water from the saturated zone is transferred through capillary rise to the unsaturated zone particularly in the case of sandy loam soils. It was found that the water table elevation varies significantly during the growing season.The salt movement simulation indicates a salt concentration build up in the unsaturated zone during the growing season. Contours of equal crop yield reduction as a function of the unsaturated zone initial salt concentration and the irrigation water salt concentration are obtained.The model was tested with data from the Mashtul Pilot Area in Egypt and its performance was satisfactory.     

太仓浏家港围滩工程对河道影响的二滩潮流数模计算与分析

采用水深平均二维非恒定潮流数学模型，在经过３个潮次调试和验证计算合理的基础上，计算并论证了太仓浏家港同滩工程对上、下游河道防洪及流场的影响，为该工程可行性研究提供了初步论证依据。计算与分析表明：在代表潮次的潮流条件下，太仓围滩对潮位的最大影响值小于３５ｃｍ，围滩后流速影响达±１０ｃｍ／ｓ的区域集中于围滩四周约１ｋｍ范围之内．     

基于黏聚裂纹模型的混凝土断裂过程扩展有限元法模拟

为了解决混凝土材料的断裂问题,采用扩展有限元法结合黏聚裂纹模型对混凝土非线性断裂力学行为进行模拟。在黏聚裂纹模型中,裂纹附近应力场没有奇异性,因此,基于四结点四边形单元构造了一种新的黏聚裂纹模拟的扩展有限元位移模式,并采用符号函数对所有的开裂单元(包括裂纹贯穿单元和裂尖单元)进行加强。采用类似于"弧长法"的方案求解非线性控制方程。结果表明:该加强策略解决了裂尖单元裂纹两边应力不等的问题,其裂尖位置任意,且混合单元处理方便。通过数值模拟混凝土Ⅰ型和混合型断裂问题,将模拟结果与参考解及试验结果进行比较,误差均在5%以内,验证了该方法的可靠性。该方法采用统一的符号函数进行加强,编程更为方便。     

需水胁迫下的流域"三生"用水系统演化分析

生态用水和社会经济用水的竞争状况使得研究水资源短缺地区流域“三生”用水系统演化状况,以及有效进行流域“三生”用水系统的调控十分必要。从宏观角度出发,本文提出了构建流域主要指标为状态变量下的“三生”用水系统演化模拟模型,并利用模型进行演化趋势预测的分析思路。以蓟运河流域为例,构建了人口数量、人均GDP、生态系统指数以及生态用水比例为状态变量的“三生”用水系统演化模型。通过定量模拟,表明若不加以调控,该流域最终将走向生态失衡、经济停滞的恶性局面。由参数设置对调控方案进行分析,提出了提高生态用水比例、控制经济增长速度、提高用水效率和积极进行生态建设对策,为实现蓟运河流域的“三生”用水系统可持续发展服务。