STUDY ON THE EFFECT OF SEDIMENT MOTION ON TRANSPORT TRANSFORMATION OF HEAVY METAL POLLUTANTS

By combining laboratorial experiments,theoretical analysis and mathematical model,theeffect of sediment motion on transport-transformation of heavy-metal pollutants is studied. (1)Previous studies on adsorption-desorption of heavy-metal pollutants by sedimentparticles are systematically summarized.Based on this summary,subjects that need to be furtherstudied are put forward. In rivers most heavy-metal pollutants concentrate on sediment particles.In order tocontrolling water pollution aused by heavy-metal pollutants following topics should beemphasized:studies on the effect of suspended matter and deposit on transport-transformation of

Incipient sediment motion in vegetated open-channel flows predicted by critical flow velocity

Incipient sediment motion plays a key role in scouring and bed load transport. However, the incipient sediment motion in the vegetated open-channel flows has yet to be fully understood. This study aims to quantify the critical conditions of the sediment particle movement in the presence of emergent and submerged vegetation. A new formula of the critical flow velocity was proposed to predict the incipient sediment motion based on the force balance equation of a sediment particle and the assumption that the velocity distribution in the bed roughness boundary layer fits the logarithmic law. Analysis of the derived formula revealed that the critical flow velocity for incipient sediment motion decreases with the increase in vegetation density. The proposed formula agrees well with the experimental data in the literature, thereby implying that the critical flow velocity can effectively quantify the incipient sediment motion in the vegetated open channel flows.

Incipient motion of sediment in presence of submerged flexible vegetation

The presence of submerged vegetation on river beds can change the water flow structure and alter the state of sediment motion. In this study, the incipient motion of sediment in the presence of submerged flexible vegetation in open channels was investigated in a laboratory experiment. The vegetation was simulated with flexible rubber cylinders arranged in parallel arrays. The effect of the vegetation density, water depth, and sediment grain size on the incipient motion was investigated. The experimental results indicate that the incipient motion velocity of sediment increases as the vegetation density decreases and the water depth and sediment grain size increase. With flexible plants, the incipient motion velocity of sediment is lower than it is without vegetation, and is larger than it is with rigid vegetation. A general incipient motion velocity equation was derived, which can be applied to both flexible and rigid vegetation conditions.

Incipient Motion of Sediment Under Currents

Summarized in the paper are the author's studies on incipient motion of sediment in recent 40 years. In addition to the forces of gravity, drag and lift, the cohesive force and the additional static pressure are important for fine particles. The relations between three stages of incipient motion are defined by use of instantaneous velocity. Formulas for initial velocity and critical shear stress are given and overall verified by the author's and others' experimental data.

Sedimentation motion of sand particles in moving water(Ⅰ):The resistance on a small sphere moving in non-uniform flow

In hydraulics,when we deal with the problem of sand particles moving relative to the surrounding water,Stokes'formula of resistance has usually been used to render the velocity of sedimentation of the particles.But such an approach has not been proved rigorously,and its accuracy must be carefully considered.In this paper,we discuss the problem of a sphere moving in a non-uniform flow field,on the basis of the fundamental theory of hydrodynamics.We introduce two assumptions:i)the diameter of the sphere is much smaller than the linear dimension of the flow field,and ii)the velocity of the sphere relative to the surrounding water is very small.Using these two assumptions,we solve the linearized Navier-Stokes equations and equations of continuity by the method of Laplace transform,and finally we obtain a formula for the resistance acting on a sphere moving in a non-uniform flow field.

Rheological Properties and Incipient Motion of Cohesive Sediment in the Haine Estuary of China

The Haihe cohesive sediment, which is typical in China, is studied systematically for its basic physical and incipient motion properties. Following the requirements of dredging works in the Haihe Estuary, cohesive sediment samples were taken from three locations. Laboratory experiments were conducted to determine the rheological properties of these samples and to examine the incipient motion of the cohesive sediment. It is found that the cohesive sediment has an obvious yield stress tau(b), which increases with the mud density in a manner of an exponential function, and so does the viscosity parameter eta. The cohesive sediment behaves like a Bingham fluid when its density is below 1.38 similar to 1.40 g/cm(3), and when denser than these values, it may become a power-law fluid. The incipient motion experiment also revealed that the incipient velocity of the cohesive sediment increases with die density in an exponential manner. Therefore, the incipient motion is primarily related to the density, which is different from the case for non-cohesive sediment in which the incipient motion is con-elated with the diameter of sand particles instead. The incipient motion occurs in two different ways depending on the concentration of mud in the bottom. For sufficiently fine particles and a concentration lower than 1.20 g/cm(3), the cohesive sediment appears as fluidized mud, and the incipient motion is in the form of instability of an internal wave. For a higher concentration, the cohesive sediment appears as general quasi-solid-mud, and the incipient motion can be described by a series of extended Shields curves each with a different porosity for newly deposited alluvial mud.

Shear velocity criterion for incipient motion of sediment

The prediction of incipient motion has had great importance to the theory of sediment transport. The most commonly used methods are based on the concept of critical shear stress and employ an approach similar, or identical, to the Shields diagram. An alternative method that uses the movability number, defined as the ratio of the shear velocity to the particle＇s settling velocity, was employed in this study. A large amount of experimental data were used to develop an empirical incipient motion criterion based on the movability number. It is shown that this approach can provide a simple and accurate method of computing the threshold condition for sediment motion.

Sedimentary structure of the western Bohai Bay basin and other basins in North China revealed by frequency dependent P-wave particle motion

High-resolution seismic models of sediment basins are critical inputs for earthquake ground motion prediction and petroleum resource exploration.In this study we employed a newly developed technique that utilizes the frequency-dependent nonlinear P-wave particle motion to estimate sedimentary structure beneath the Bohai Bay basin.A recent study suggests that the delay of the P wave on the horizontal component relative the vertical component and its variations over frequency are caused by interference of the direct P wave with waves generated at the sediment base.The frequency-dependent delay time can be used to constrain sediment thickness and seismic velocity beneath recording stations.We measured the particle motions of teleseismic P waves recorded by 249 broadband stations of the North China Array,which covers the western Bohai Bay basin and its surrounding areas.We found that the P waves of 90 stations inside the Bohai Bay basin and other local basins within the Taihang and Yanshan mountain ranges exhibit significant frequency-dependent nonlinear particle motions,and used the particle motion data to invert the sediment thickness(Z0)and surface S-wave velocity(β0).The estimated sediment thickness inside the Bohai Bay Basin varies from 1.02 km to 3.72 km,with an average of 3.20 km,which roughly agrees with previous active source studies.

Incipient Motion of Bed Load Sediment and Its Application in the Three Gorges Hydro Project

A formula for the calculation of critical shear stress of non-uniform sediment was developed by on river bed has been established while considering the relative degree expose of grains.The values of the Coeffi- cients in the formula have been obtained.The formula has been verified with prototype observation data, flumes data of both nature and lightweight sand.The computed results fully reflect the characteristics of thresh- old motion of non-uniform sediment.The result have been used in some physical mo...

Distribution of Time-Averaged Suspended Sediment Concentration Due to Waves

According to the mechanism of sediment suspension under waves, namely, the main reason of sediment suspension changes from the turbulent mixing in the bottom boundary layer to the periodic motion of the water particle near the free water surface, a three-layer model of sediment concentration distribution due to waves is presented along the whole water depth based on the concept of the finite mixing length. 1he determination of the parameters in the model is discussed and an empirical formula is suggested. Comparisons between the calculated results and the measurements indicate that the resuits of the model agree well with the data from both the large and small scale flume experiments.

生物碎屑砂运动特性研究进展

生物碎屑砂是海洋沉积物的重要组成部分,运动特性是研究其沉积过程的关键。从生物碎屑砂的特性出发,归纳出形状和内孔隙这2个对泥沙运动产生影响的主要特性。分别从沉降、起动和岸滩演变的实验研究出发,剖析了生物碎屑砂特性对泥沙运动特性产生的影响。现有研究只探究了形状对单颗粒生物碎屑砂运动的影响,缺乏对群颗粒运动的探讨。受限于研究手段,缺少讨论内孔隙特性对生物碎屑砂运动产生的影响。未来应结合海洋水动力条件,综合考虑生物碎屑砂形状和内孔隙特性,开展生物碎屑砂运动特性研究,量化生物碎屑砂特性产生的影响,将成果运用于实际,预测生物碎屑沉积环境中的岸滩地貌演变。

An Investigation of Stochastic Nature of Bed Load Motion in Chuanjiang River

Bed Load Motion and its transport rate is one of the basic issues in river dynamics.In this paper, the authors discussed the stochastic nature of bed load motion in Chuanjiang River in details.Chungjiang lies in the upstream reach of Yangtze River.Its stochastic nature is shown in the following four aspects.Firstly, even though all the conditions are the same,due to the fluctuation of the flow,the bed load discharge and the location and width of sediment transport belts are different.Secondly,during the ...

恒定流作用下泥沙垂向相对暴露度试验研究

基于泥沙三维受力分析,探讨垂向相对暴露度对单颗粒泥沙起动的影响,推导考虑垂向相对暴露度影响的单颗粒泥沙起动流速公式。通过概化单颗粒泥沙起动试验测量数据,明确泥沙起动公式中的上举力系数与拖曳力系数。研究结果表明,上举力系数和拖曳力系数与水流条件和颗粒粒径有关,在恒定流作用下垂向相对暴露度增大导致拖曳力系数和上举力系数增大。当垂向相对暴露度到达一定数值后,拖曳力系数与上举力系数均有逐渐减小的趋势。相同泥沙粒径情况下,单颗粒泥沙起动流速随着垂向相对暴露度的增加而增加。垂向相对暴露度不仅改变单颗粒泥沙所受力臂大小,且改变了作用在单颗粒泥沙上的流速大小,影响了泥沙的起动。

光滑床面上智能泥沙颗粒弱起动过程试验研究

为揭示泥沙起动的微观力学机制,通过在圆球中植入无线陀螺仪传感器制作智能泥沙颗粒,进行明渠水槽起动试验,结合视觉测量技术,实时采集颗粒位移、速度、加速度、角速度等高频数据,研究不同来流流速对粗颗粒泥沙弱起动过程影响的动力机制。试验发现,粗颗粒泥沙起动是一个平动和转动叠加的复杂动力过程,呈现出绕流脱涡激励下的横流向和顺流向摆动及周期性转动等运动模式,具体模式和颗粒雷诺数密切相关,试验工况中,颗粒雷诺数为386时横流向摆动现象最显著。基于测量数据,进一步分析了颗粒起动过程中的冲量和动能特性。

典型城市江段岸滩植被生长对河道行洪及泥沙起动影响研究

水生植被广泛生长于河流和湖泊的浅滩区域,在发挥自身生态功能的同时,也对河道行洪和泥沙输移有重要影响。本研究基于野外天然河道植被调查,采用二维浅水动力学数值模拟定量评估了长江干流武汉段汉口江滩南荻–芦苇群落大规模扩张对漫滩流量下河道水沙输移的影响:在植被阻水作用下,植被区上游水位最大壅高幅度达0.04 m左右;植被区内流速减幅在0.3~1.2 m/s,主流区流速增幅为0.04~0.3 m/s。水动力变化进而改变了泥沙起动情况,近岸植被区形成了一条狭长的泥沙起动减弱带,起动粒径最大减小了5 mm;而主流区的起动粒径有所增大,增幅在3~10 mm之间。研究成果可提高对天然河道尺度下植被水沙动力学的认识,并为生态河道防洪设计提供理论参考。

无黏性非均匀沙的参数自适配起动切应力计算方法

非均匀沙起动条件的确定是研究非均匀沙输移的关键。工程实际应用中有修正法和等效粒径法两种,两种方法中含有的参数率定需要已知分组沙起动切应力测定值,且取值依赖率定数据集。基于两种方法在理论上计算的分组沙起动切应力相等思想,结合吴伟明提出的修正法与王涛提出的等效粒径方法,将两种方法中含有的率定参数作为自适配参数,通过函数拟合确定,拟合适配过程不依赖分组沙起动切应力数值。实践检验表明,通过自适配确定参数可以提高泥沙起动切应力计算方法的适用范围,精度更高。成果可以为非均匀沙起动条件计算提供新思路。

东海舟山群岛海域表层沉积物运移特性

通过潮流和表层沉积物粒度参数等实测资料,对舟山群岛海域表层沉积物的运移趋势、净输运通量以及起动流速进行了初步分析。结果表明,舟山群岛对研究区表层沉积物分布影响明显;舟山群岛海域表层沉积物整体由湾口向外海输运,平均日单宽输沙通量由杭州湾内向外海迅速减小;从杭州湾向外海,泥沙起动越来越难,单纯潮流对表层沉积物再悬浮作用相对较弱。

两相流分离鳃泥沙运动轨迹及加速滑移的力学分析

利用高速摄像技术捕捉分离鳃中泥沙运动的图像,对两相流分离鳃内部水沙运动进行测试,描绘了分离鳃流场概化图像,证明分离鳃内有异重流现象发生。通过对分离鳃鳃片上的泥沙进行力学分析,推导出泥沙在鳃片上的运动轨迹,研究了泥沙的沉降特性,并给出泥沙沉降条件与结构设计参数β之间的关系,从力学分析的角度论证了前期物理试验中得出的结构优化参数的合理性。

振荡流底层拟序结构及其与泥沙相互作用研究

湍流拟序结构与泥沙及床面相互作用的机理,是目前国内外泥沙学术界研究的热点领域。本文针对单向流和振荡流底边界层的湍流拟序结构与泥沙相互作用研究状况进行了综述,重点论述了振荡流底边界层湍流研究的概况与今后需要开展的重点研究内容。

河口泥沙研究的进展

作者通过大量的文献调研 ,评述了国内外学者在河口泥沙运动的基本理论、数值模型等方面的研究工作和成果 ,结合近年来作者关于河口水流结构、盐淡水混合以及泥沙输运的研究工作 ,提出加强对河口泥沙非恒定运动过程、河口最大浑浊带形成机理及其与河口拦门沙演化关系研究的必要性 。