核素在资江河道泥沙中的迁移模型

大量现象和研究成果都表明核素以泥沙颗粒为载体进行迁移转化．本文运用环境科学、水力学、泥沙工程学基本原理．巧妙结合MATLAB数学工具和数学方法,创造性地提出了一维非稳态瞬时排放核素的迁移转化模型,并与连续排放核素的情况进行了对比．     

深海采矿船附近海底重金属迁移过程数值模拟

本文以水相和泥沙相核素的物理迁移为基础,分析深海采矿船附近海底重金属的迁移扩散、吸附解析和悬移沉降等作用,结合水力学、泥沙动力学等方程,建立了重金属迁移转化的整体模型和分相模型,并利用差分算法对模型进行求解,最后结合实验测定和实测资料给出的模型相关参数,运用MATLAB软件对重金属的迁移进行图像模拟,直观地反映重金属浓度的变化过程.     

河口海岸泥沙数学模型研究

导出了风浪和潮流共同作用下的悬沙输移方程式和扶沙能力公式,建立了河口海岸平面二维泥沙数学模型.验证表明,此模型可以较好地模拟风浪和潮流作用下河口海岸区含沙量分布场和海底冲淤变化,为研究和解决河口海岸工程中的泥沙问题提供了新手段.     

土壤重金属复合污染整体模型研究

在重金属迁移建模研究成果的基础上,考虑土壤对重金属的吸附特性,推导出土壤重金属复合污染物迁移转化整体模型.为求解该模型,分别引进Langmuir等温竞争吸附模型与土壤水分迁移模型.最后,以重金属Zn和Cd为例,数值模拟其在土壤中的垂向迁移过程,并利用MATLAB画出相关图形.     

我国多沙河流一些中小型水库的泥沙处理

我国北方有许多含沙量较高的河流,中小型水库的淤积问题严重.实践表明:多沙河流水库在调节迳流的同时,必须考虑调节泥沙,否则水库会很快被泥沙淤废而失去调节迳流的作用,此外,排出水库的浑水如何处理也是个重要问题,若处理不当,势将导致下游河道或水库的严重淤积。我国科技人员与广大群众相结合,通过实践、认识、再实践、再认识,逐步摸索到一套合理调节水、沙,并结合下游引洪淤灌的水库泥沙处理办法,既减缓了水库淤积,又利用了水沙资源,促进了农业生产.本文介绍了这方面的经验.主要内容有河流水文泥沙特征、水库淤积概况、水库防淤排沙措施及出库浑水的利用技术等。     

泥沙的群体沉降速度

本文讨论了在浓度很高时候,泥沙的群体沉降速度.作者认为所谓泥沙的群体沉降速度问题从物理本质来说并不是真正的沉降速度问题,而是水在泥沙和水所组成的胶团形成的多孔介质中的渗流问题,也就是水流经这种多孔介质所形成的问题.作者根据这样的认识,写出了泥沙群体沉降速度的数学表达式,并且和黄委会水科所测量得到的实验数据进行了比较.比较的结果是令人满意的.     

矿区土壤中含水率及重金属迁移转化的数值模拟

本文基于由连续性方程和达西定律所推出的土壤中水分运动基本方程,以一维垂向水分方程为研究对象,构造稳定收敛的有限差分格式,运用MATLAB数学工具,对地面饱水情况下土壤水分运动的一维垂向方程进行了数值模拟,得到了土壤中水分的迁移规律;同时,综合考虑对流扩散作用以及土壤对重金属的吸附解吸作用,利用非饱和土壤中重金属离子迁移转化模型,对锌离子在矿区土壤中的迁移转化进行了数值模拟,展示了锌离子在矿区土壤中的浓度分布规律．     

中子活化示踪沙技术的研究

本文选取铱(Ir)作为信号元素,采用化学吸附标记的方法制作示踪沙,应用中子活化分析方法检测泥沙中信号元素的含量,依据信号元素的运动特征判断泥沙的运移规律.该方法克服了流明沙技术及放射性示踪沙技术的缺点,并能真实地模拟天然泥沙的运动特性,是一种先进的泥沙运动观测技术.在天津港进行的国内首次实际应用试验中取得了预期效果.     

再生水补给河流的水质模糊风险评价

采用再生水进行河流补给,对河流生态系统健康产生直接或潜在的危害.探讨河流水环境系统的不确定性,基于忽略弥散的一维河流水质模型,建立了再生水补给影响下的河流水质模型,选用三角模糊数来描述和处理水环境风险评价.应用结果表明,所建模型对于河流水质模拟与风险评价具有很好的适用性和稳定性.     

泥沙对水的相对速度和含沙浓度对脉动速度的影响

本文从流体动力学的基本理论出发,讨论了泥沙运动理论中的三个基本问题.(1)泥沙在湍性水流中对水的相对速度.(2)水流挟带泥沙以后脉动速度的改变.(3)泥沙在二维渠道均匀定常流动中含沙量的垂直分布和通常的扩散理论的修正.按照我们理论分析的结果,发现和通常水力学及河道动力学中常用的表达式有一些出入.     

Coupled consolidation and contaminant transport model for simulating migration of contaminants through the sediment and a cap

Capping contaminated sediments in waterways is an alternate remediation technique to dredging and is typically much cheaper than dredging. When cap material is placed on top of contaminated sediment, it has both a short-term and long-term hydraulic impact on the underlying sediment. A numerical model of consolidation, based on a nonlinear finite strain theory for a consolidating fine-grained sediment bed was developed. The nonlinear equation of consolidation was solved in a material (or reduced) coordinate using an explicit finite difference numerical scheme. An one-dimensional advection–diffusion equation with sorption and decay was solved on a convective coordinate using a finite volume total variation diminishing (TVD) scheme for the contaminant concentration within the consolidating sediment. The contaminant transport model was coupled with the consolidation model. The time and space varying porosities, permeabilities, and advective velocities computed by the consolidation model were linked to the transport model at the same time level. A number of benchmark tests that are relevant to the consolidation of a fine-grained sediment were designed and tested. The relative contribution of consolidation-induced transient advective velocities on the migration of a contaminant during consolidation was also investigated. The coupled model performance was validated by simulating the transport of hazardous chemicals under consolidation in a confined aquatic disposal (CAD) site in the Lower Duwamish Waterway, Seattle.     

鱼咀及丁坝对长江口航道分流分沙的影响

利用水平二维水流、盐度、泥沙数学模型研究了长江口航道整治工程(一期)实施前后,航道的分水分沙特点,重点讨论了束水丁坝的长度、潜堤的方向对航道分流比、分沙比的影响．数值模拟结果表明,双导堤工程减少了航道的分沙量,这有利于维护航道的畅通,但同时也使航道的分流比减小．航道分流分沙比的改变可通过调整各水工建筑物的布置或尺寸来实现．与束水丁坝长度的影响相比,鱼咀工程潜堤方向的改变对航道分流分沙比的影响更大．     

Man-made plutonium in freshwater and marine environments

Significant concentrations of plutonium isotopes are found in lake and coastal marine sediments accumulating at rates of 1–5 mm/yr. The activity levels of^{239, 240}Pu range between 0·7–3·3 dpm/g for post 1960 sediments. The measured and the calculated integrated activities of²³⁹Pu in the lake sediments are in agreement. This suggests that plutonium is chemically reactive in freshwater environments and it is removed to sediments from the water column shortly after its injection. A delay of about three years has been observed between the peak of plutonium fallout and its incorporation in the varved sediment from Santa Barbara basin. Based on this observation the mean size of particles transporting plutonium to the basin sediments is estimated to be about three microns. The usefulness of plutonium isotopes as a tracer nuclide for estimating sedimentation rates for the last two decades have been evaluated.     

Advection of methane in the hydrate zone: model,analysis and examples

A two‐phase two‐component model is formulated for the advective–diffusive transport of methane in liquid phase through sediment with the accompanying formation and dissolution of methane hydrate. This free‐boundary problem has a unique generalized solution in L¹; the proof combines analysis of the stationary semilinear elliptic Dirichlet problem with the nonlinear semigroup theory in Banach space for an m‐accretive multi‐valued operator. Additional estimates of maximum principle type are obtained, and these permit appropriate maximal extensions of the phase‐change relations. An example with pure advection indicates the limitations of these estimates and of the model developed here. We also consider and analyze the coupled pressure equation that determines the advective flux in the transport model. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrodynamic interaction in suspended sediment distribution of open channel turbulent flow

In the present study, a theoretical model is proposed to predict the vertical distribution of suspended sediment in open channel turbulent flow. We derive our mathematical model based on the six prominent hydrodynamic mechanisms, which are upward sediment flux due to the turbulent diffusion, downward gravitational settling of the sediment, hindered settling phenomenon, secondary current, fluid induced lift force on the suspended particles and the gradient of Reynolds normal stress of the suspended sediment. The importance of the hydrodynamics is described by the changes of suspended sediment concentration profile in terms of the particle-flow interaction caused by those mechanisms. We also address the significance of the co-existence of those mechanisms for estimating the suspended sediment concentration profile. The present model agrees satisfactorily with a wide spectrum of experimental data in available literature. Unlike the previous researchers, we select a broad range of previously published models of vertical sediment concentration distribution for comparison analysis, and the proposed model shows better prediction accuracy which is confirmed by error analysis.     

Mathematical modelling of bottom evolution by particle deposition and resuspension

A two-dimensional numerical model for the evolution of a bottom due to particle deposition and resuspension by a fluid flow is here presented. A computational fluid dynamic approach is used to calculate the flow field and a Lagrangian particle tracking technique is applied to solve the dispersed phase. The evolution of the lower boundary is simulated taking into account the mass conservation of the solid phase and the geotechnical properties of the granular material. The model is characterized by two important features. First, fluid dynamics are coupled with the bottom evolution due to particle deposition and resuspension. This permits to use the model to simulate complex flow fields as well as complex time-evolving geometries. Second, the dispersed phase is calculated by a Lagrangian approach, which retains the discrete information of the individual particles of the granular bottom which may be of interest for some industrial processes (coating) and environmental flows (sediment stratification). First consistency checks have been performed for some deposition and resuspension test cases with fluid at rest. The model has also been tested by comparison with a physical experiment of deposition inside a cavity. Finally, as an example of possible applications of industrial and environmental interest, the model has been applied to investigate particle deposition in rectangular cavities and the evolution of a sand heap by a fluid flow.     

Transient wave propagation in a one dimensional partially saturated poroelastic column

Based on the theory of mixtures, a dynamic three phase model for partially saturated poroelasticity is established. This model is applied to a one-dimensional unsaturated poroelastic column and an analytical solution in the Laplace domain is deduced. By using the Convolution Quadrature Method, the solution in the time domain is obtained. Using some widely distributed porous materials as rock, soil and sediment, the wave propagation behavior in terms of displacement and pore pressure is examined. By neglecting the viscosity of the fluid, assuming very large fluid permeabilities, the second and third compressional waves are identified. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A model of multiphase flow and transport in porous media applied to gas migration in underground nuclear waste repository

We prove existence of solutions for a new model of two compressible and partially miscible phase flow in porous media, applied to gas migration in an underground nuclear waste repository. This model, modeling fully and partially water saturated situations, consist of a coupled system of quasilinear parabolic partial differential equations. We seek a new set of variables in order to obtain a system which belongs to the class of equations considered by Alt and Luckhaus such that it would be possible to use their existence theorem. A simulation of a numerical test case is performed in order to numerically demonstrate the ability of this model to take in account the appearance of one phase. To cite this article: F. Smaï, C. R. Acad. Sci. Paris, Ser. I 347 (2009).     

Pattern formation and modulation in a hyperbolic vegetation model for semiarid environments

This paper presents analytical and numerical investigations of pattern formation and modulation in a one-dimensional hyperbolic extension of the Klausmeier reaction–diffusion–advection vegetation model for semiarid environments. The hyperbolicity of the model is shown to provide an additional degree of freedom which can be used to modify the dynamical response of the system away from the parabolic limit as well as to reproduce qualitatively the experimental data. Results of linear stability analysis reveal the possibility to modulate, almost separately, the main pattern features (wavelength and uphill migration speed) by acting on two independent parameters: the slope steepness and the characteristic velocity. Moreover, a possible justification of the mechanism underlying the uphill migration of the patterns is suggested in terms of the phase shift between the spatial distributions of vegetation biomass and water. The hyperbolicity of the system has also facilitated the search for a class of exact solutions, via the differential constraint method, for a hyperbolic vegetation model whose kinetic terms are more general than Klausmeier’s ones and whose applications are potentially broad.