Flow and transport simulation of Madeira River using three depth-averaged two-equation turbulence closure models

This paper describes a numerical simulation in the Amazon water system, aiming to develop a quasi-three-dimensional numerical tool for refined modeling of turbulent flow and passive transport of mass in natural waters. Three depth-averaged two-equation turbulence closure models, , , and , were used to close the non-simplified quasi-three-dimensional hydrodynamic fundamental governing equations. The discretized equations were solved with the advanced multi-grid iterative method using non-orthogonal body-fitted coarse and fine grids with collocated variable arrangement. Except for steady flow computation, the processes of contaminant inpouring and plume development at the beginning of discharge, caused by a side-discharge of a tributary, have also been numerically investigated. The three depth-averaged two-equation closure models are all suitable for modeling strong mixing turbulence. The newly established turbulence models such as the model, with a higher order of magnitude of the turbulence parameter, provide a possibility for improving computational precision.     

基于流固耦合的垃圾污染物运移模型及模拟

基于流固耦合和溶质运移理论，建立了垃圾渗滤液有机污染物运移耦合模型，用SOM法对所建的模型进行数值求解，利用该数值模型对垃圾渗滤液在地下水中迁移行为进行模拟，预测了污染物浓度的时空分布特征，对耦合、非耦合模拟结果结合实际监测数据进行对比，并对污染晕的大小、分布范围进行了数值模拟分析。结果表明，耦合模型模拟的污染物浓度变化趋势与监测值基本吻合，从而验证了耦合模型的可靠性和实用性。     

填海工程背景下半岛地下水流场及污染物运移的数值模拟分析

以古雷半岛为例,基于GMS地下水数值模型探索海砂填海(情景一)、海砂+黏土填海(情景二)、黏土填海(情景三)这三种填海情景对研究区地下水流场及污染物运移的影响。结果表明:(1)研究区在填海背景下地下水水位整体抬升,水位上升幅度由小到大依次为情景一、情景二、情景三,最高升幅达4.78m。(2)不同填海情景下的地下水流场差异在填海区的黏土区域最为明显,情景二、情景三与情景一的地下水水位差最大值分别为4.44 m和8.20m。(3)在仅考虑物理作用的情况下,三种填海情景下污染物运移均呈现以水平运移为主、垂向运移为辅的特点。(4)相较于污染物运移基本相同的情景一与情景二,预测时间30a时,水平方向上情景三污染物迁移面积、迁移速率分别下降23.07%、18.89%;垂向上污染物主要积聚于第一层含水层,情景三观测井在第一层含水层的污染物浓度为情景一(或情景二)的5.87倍。说明采用低渗透性黏土填海对于污染物运移具有一定的阻滞作用。     

二维强非均质含水层中水力传导度空间变异对污染物迁移的影响

对于介质的非均质性相对较小的情况，可将水力传导度对数(lnK) 的空间分布概化为正态分布的统计均匀随机场。而对于强非均质介质，lnK的空间分布可表征为其增量遵从Levy稳定分布的非平稳随机场。本研究假设二维承压含水层内面积为128m x 128 m的研究区域中,在(10m,64m)处瞬时注入浓度为1000 mg/L的污染物：利用改进的连续随机增加（successive random additional, SRA) 方法生成含水层lnK增量具有Levy稳定分布的统计特征的随机场；采用Monte-Carlo数值实验方法并结合MODFLOW与MT3DMS分别模拟研究区域内水流和溶质迁移过程，分析水力传导度强变异性对污染羽状物浓度空间矩及宏观弥散的影响。结果表明：Levy指数a决定lnK的空间分布形状，宽度参数C则影响lnK的取值范围；污染羽的质心位置(一阶矩)与C、a的大小无关；C越大、a 越小，污染羽形状越不规则，污染羽状物的扩散范围(二阶矩)越大；且a 越小，污染羽状物具有明显的拖尾现象；纵向宏观弥散度随时间呈幂函数递增趋势。     

河渠分汊处流量与污染物分配

本文建立了一个深度平均的水环境全场紊流模型,将流场与浓度场耦合求解以确定流场和浓度场的分布,通过数值积分得出分流比与污染物分配比。对分汊河渠不规则边界的处理,本文提出了一种新方法:区域坐标系统法。应用上述数学模型和数值方法,本文对河渠分汊点上游存在岸边排放口时分汊河段的流场和浓度场进行了计算,并着重讨论了对称分汊情况下分汊角、排放口入射动量对汊道分流比和污染物分配比的影响。所得计算结果与作者的实验资料符合较好。在此基础上,对不对称分汊情况下流量及污染物的分配也进行了初步探讨。     

基于隐格式水动力模型的庄河养殖海域污染物运动轨迹的数值模拟

基于非结构四叉树矩形网格,建立了近岸海域深度平均二维隐格式水动力数学模型,通过耦合拉格朗日粒子追踪法和粒子云团随机走动原理计算水体污染物的运动轨迹。水动力数学模型采用有限体积方法离散方程,使用Rhie-Chow的动量插值方法对同位网格不合理的压力波加以抑制,并使用SIMPLEC程式导出水位校正方程。通过对"工"字型理想海湾的水动力、风与流共同作用下正方形海湾的油膜输移及扩散状况进行模拟验证后,将该模型应用于计算北黄海庄河养殖海域的水动力特性以及污染物在海中的输移过程和运动轨迹,最后给出该海域模拟期间的污染物运移规律。研究结果对庄河养殖海域的水环境管理有重要的意义。     

DISTRIBUTIONS OF FLOW RATE AND CONTAMINANT IN RIVER OR CHANNEL DIVERSION

Based on numerical modelling for two-dimensional flow in which the density ofeffluent is different from that of environment,the flow and concentration fields are couplinglysolved.Through numerical integration the flow rate and contaminant distributions with differentangles and different momentum of effluent can be obtained.The results given in this paper couldbe a base for quantitative estimation in hydraulic engineering design and assessment and planningof water quality.     

含污染物的环流非充分发展弯道湍流数值模拟

本文建立了可模拟弯道中含污染物湍流的三维部份抛物型代数应力模型，以４５°弯道为例，针对左右两岸分别泄放污染物的环流非充分发展弯道流进行了计算，对所得的水流结构及污染物浓度分布进行了分析，结果充分反映出环流非充分发展弯道流中水流结构及污染浓度分布的特点。     

非定常浅水流动中热水对流—扩散过程的数值模拟

本文从深度平均的连续、动量和热输运方程出发,应用深度平均的k-ε湍流模式,对非定常浅水明渠流动中侧向排入热水形成的速度场和温度场作了数值模拟。在定常情况下,本文的计算结果表明:当水深较浅或热水排放动量较大时,放弃“刚盖假设”对于提高预计精度是必要的。非定常情况的计算结果与采用准定常假设的计算结果作了比较。这一比较表明:即使以最大主流速度定义的Strouhal数很小,在憩流前后的一段时间内,流动非定常性对速度场和温度场的影响仍是显著的。     

Experimental investigation on diffusive contaminant release from permeable sediment layer under unidirectional unsteady flow

The interfacial diffusive contaminant（phosphorus） release from permeable sediment layer into overlying water column under a unidirectional unsteady（periodic） flow condition was experimentally measured and analyzed. The experimental results indicate that the gross diffusive contaminant release rate is substantially enhanced as compared to that under a steady flow condition, and this enhancement trend is much more pronounced in an immediate release stage. The interfacial diffusive contaminant release rate tends to increase with the increasing flow velocity, decreasing period and augmenting amplitude for the case of the unsteady flow. The additional interfacial diffusive contaminant release under the unsteady flow condition may be related to the hydrodynamic response of the diffusive boundary layer to the flow unsteadiness of the overlying water, depending upon not only the periodic thickness variation of the diffusive boundary layer immediately above the sediment-water interface modulated by the temporal flow velocity of the overlying water column but also the intensified turbulent mixing between the overlying water and the pore-water within the superficial sediment layer induced by an alternate acceleration/deceleration fluctuation during each period.     

Numerical research for contaminant release from un-suspended bottom sediment under different hydrodynamic conditions

Contaminant release from bottom sediments in rivers is one of the main problems to study the environmental hydrodynamics. Contaminant will release into the overlying water column under different hydrodynamic conditions through pore-water in sediment, the release mechanism can be roughly divided into convection diffusion, molecular diffusion and adsorption/desorption. In this article, phosphorus was as a typical contaminant with sorption. Through theoretical analysis of the contaminant release, according to different particle-sized and hydraulic conditions, the mathematics model of contaminant release can be established by the coupled Navier-Stokes equation, Darcy equation, solute transport equation and adsorption/desorption equation. Then that model was verified by flume experiment. Numerical studies show that, under different velocity, the instantaneous concentration of convection diffusion is about 6 times to 50 times larger than that of molecular diffusion during initial stages. The concentration of molecular diffusion is about 1 times to 4 times larger than to that of convection diffusion during late stages. Through analysis, the diffusive boundary layer near the interface can be obtained. In addition, the release will increase with particle size decreasing, and the release will be influenced much more by the size change when the particle size is relatively big under different velocity.     

地下水污染物迁移可靠性分析的小生境混合遗传算法

在地下水污染物迁移问题中,考虑水动力弥散系数及测量误差的不确定性因素对浓度估计可靠性的影响,采用小生境混合遗传算法,对地下水污染物迁移的可靠性进行探讨,并在可靠性条件下进行污染浓度正反问题分析,为地下水环境保护和调控提供更多的决策依据。分析结果表明,小生境混合遗传算法在地下水污染物迁移问题的可靠性分析中具有可行性和有效性。     

陆源污染对伶仃洋水质影响的数值模拟

引入环境水力学数学模型，利用二维ADI法进行数值模拟，对伶仃洋水域的潮流运动和污染迁移扩散展开了研究，并成功地进行了验证计算。为河口的治理开发和伶仃洋的生态环境保护，提供了较好的数学模型。     

闸坝调控下重污染河流污染物迁移规律研究

以沙颍河槐店闸为研究对象,构建了闸坝调控作用下二维水动力-污染物迁移模型,根据试验获取的数据对模型进行率定和检验。结果表明:闸坝的存在对河流水环境系统具有一定负面影响,但是合理的闸坝调控能够改善河流水质,减小突发性水污染事故发生的概率;该模型可以有效地模拟计算闸坝调控作用下污染物的迁移过程。     

Numerical research on the mechanism of contaminant release through the porous sediment-overlying water interface

After the pollutant discharged into the river or lake has been reduced, the release of the contaminant from the sediment to the overlying water may cause the river and lake be contaminated again. On the condition that the overlying water flow does not lead to sediment suspension, numerical researches are carried out for the mechanism of contaminant release through the sedimentoverlying water interface. The overlying water flow is calculated as turbulence. The sediment is regarded as isotropic homogeneous porous medium, therefore the seepage field in the porous sediment layer is obtained by solving Darcy＇s equations. Coupled two dimensional steady flows of the overlying water and the pore water in the sediment are calculated. Based on the flow fields obtained, the unsteady contaminant solute transportation process in the pore water in the sediment and the overlying water is numerically simulated, as the shapes of the sediment-overlying water interface are flat or periodic triangular respectively. Numerical results show that the exchange of the pore water and the overlying water is an important factor which decides the release flux of the contaminant from the sediment to the overlying water. The pressure distribution produced by the overlying water flow along the sedimentoverlying water interface, as it is not flat, may induce the seepage of the pore water in the sediment and through the sedimentoverlying water interface, which may increase the release flux of the contaminant from the sediment to the overlying water.     

生物降解处理地下有机污染物的模型研究

本文综合多学科的研究结果，阐明了多孔介质中有机污染物和细菌微生物运动的形式，规律及其相互作用。采用二重孔隙介质模型，给出在裂隙含水层中建立其运动方程组与推导孔隙及裂隙交界面上交换关系的原则。以好氧菌及厌氧菌共存系统为例，得出具体的控制方程系统和交换关系式，并进行了数值模拟，得到了有用的结果。     

不同条件下矩形沙坑影响的数值模拟对比研究

应用有限体积法建立了河道平面二维水流泥沙数学模型并将模型应用于典型河段的计算,验证了模型的计算精度.设置了不同来水来沙条件和沙坑几何边界条件,将本模型应用于几种工况的理想矩形河道中矩形沙坑影响模拟研究,计算表明采砂对河道的正常演变产生影响,影响结果与离沙坑的距离、沙坑的深度和面积大小以及来水来沙情况等因素有关.初步分析了在采沙规划中可控制采沙影响后果的措施.     

盐龙湖表面流人工湿地底泥氧化层对污染物释放的影响

为了解盐城市盐龙湖表面流人工湿地底泥氧化层理化性质,探讨其对底泥氮、磷及有机物释放过程的影响,在测定底泥理化性质的基础上进行了室内静态柱状试验。结果表明:盐龙湖表面流人工湿地长期运行后在底泥表层形成了厚度为1 cm、呈棕黄色、无明显臭味、含水率低、TP含量高、TOC和TN含量低的氧化层;氧化层对于底泥中污染物的释放特征影响显著(P0.05),对内源污染的控制具有一定的正面作用;无氧化层试验组上覆水中TN、NH_3-N和COD的平均质量浓度分别比有氧化层试验组高9.5%、30.8%和3.5%;在湿地的实际管理中,不宜对湿地进行疏浚,如疏浚则疏浚深度应达到健康层。     

Experimental study on the effects of sediment size and porosity on contaminant adsorption/desorption and interfacial diffusion characteristics

The joint effects of the sediment size and porosity on the contaminant adsorption/desorption and interfacial diffusion characteristics were experimentally investigated. The adsorption of Phosphorus (P) on the natural and artificial sediment suspensions was measured with respect to the P adsorption isotherms and kinetics in the experiment. The obtained adsorption isotherms for different grain-sized sediment suspensions fit well with the Langmuir equation, dependent on the initial aqueous concentration and sediment content. The P kinetic adsorption behaviors for cohesive fine-grained and non-cohesive coarse-grained sediment suspensions clearly show the size-dependent feature. On the other hand, the P kinetic release feature of a porous sediment layer is affected by not only the direct desorption of the uppermost sediments, but also the diffusivity in the pore-water within the underlying sediment layer, characterized by the sediment size and porosity, respectively. Furthermore, the temporal contaminant release from the permeable sediment layer into the overlying water column increases with the increasing flow velocity, while this enhancement in mediating the interfacial diffusion flux is somewhat insignificant in an immediate release stage, largely due to the resistance of the diffusive boundary layer on the hydrodynamic disturbance.     

Impact of consolidation pressure on contaminant migration in clay liner

Consolidation deformation occurs in clay liners under the self-weight of wastes at a simple garbage dump or dredged sediment dump, which leads to a decrease in the porosity. However, the migration of contaminants in clay liners is influenced by the porosity. Thus, the impact of consolidation deformation of clay liners on the migration of contaminants cannot be ignored. Based on Biot’s consolidation theory, the contaminant migration theory, and consideration of the three kinds of migration mechanisms of convection, diffusion, and adsorption, a one-dimensional migration model of contaminants in deforming porous media was established, and the finite difference method was adopted to obtain the numerical solutions for an established initial-boundary value problem. The impact of consolidation pressure on the migration law of a contaminant was studied. The results show that, regardless of adsorption modes, different consolidation pressures have similar impacts on the migration law of the contaminant. Namely, over a certain migration time, the greater the consolidation pressure is, the smaller the migration depth of the contaminant. The results also show that, while the migration time increases, the impact of a certain increment of consolidation pressure on the variation of contaminant concentration with the depth increases gradually and, while the migration depth increases, the impact of a certain increment of consolidation pressure on the variation of the contaminant concentration with time increases gradually.