The analysis on reservoir sediment deposition and downstream river channel scouring after impoundment and operation of TGP

According to the measured data after impoundment and operation of the Three Gorges Reservoir,the reservoir sediment deposition and downstream river channel scouring are described briefly and compared with the research results achieved in the demonstration stage.It is indicated through analysis that the reservoir sediment deposition and downstream river channel scouring during 8-year impoundment and operation are still within the original forecast,so the original forecasting results are feasible.The further observation and comparison should be conducted because the comparison between the observed data and the original forecast is not so sufficient in time and the prototype observation and related research work should be strengthened in the future.

Bed Load Transport Rate in Scouring and Armoring Process of Non-uniform Sediment River Bed

Flume experiments were carried out to study bed load transport rate during rive bed scouring and ar- moring.A theoretical differential equation linking the transport rate to the probability of incipient motion of non-uniform sediment is solved.The transport rate is shown to decrease exponentially with time,according to the theory,which is in good agreement with the experiment data.

黄河泥沙固化材料抗冲特性分析

为了分析黄河泥沙基坝体材料的抗冲刷性能及影响因素,试验研究了固化剂掺量和冲刷时长对黄河泥沙基坝体材料抗冲刷性能的影响规律,并设置了不同固化剂掺量及不同冲刷时长的对照组。本次试验对比不同固化剂掺量及冲刷时长对试块抗冲刷性能的影响,对试验数据进行函数拟合。从拟合后的函数图像分析,随着固化剂掺量的增加,试块的抗冲刷性能提升,但考虑到建设成本问题,固化剂掺量为30%最为符合工程需求。

金沙江向家坝水电站下游河道2020年淤积成因分析

向家坝下游河道泥沙冲淤变化对岸坡稳定及通航具有重要影响,向家坝水电站运行后坝下游河床一直呈冲刷状态,但2020年首次出现淤积。采用输沙法和断面法计算向家坝出库沙量和下游河段泥沙冲淤量,结合气象、水动力及实勘资料,分析向家坝下游2020年淤积成因。研究结果表明:向家坝蓄水后出库年径流量变化不大,出库沙量受上游电站拦沙作用大幅减少,但2020年向家坝下游支流降雨偏丰,支流输沙量大幅增加,产生区域强输沙过程;该年下游各控制站最高水位较历史平均水位均偏高,汛期比降变化不大,水流挟沙能力不足以输送显著增多的泥沙;加上采砂减少和采砂造成的下切幅度较大部位发生回淤。这些原因导致2020年向家坝下游河道产生淤积。

长江中游武汉河段江心洲的差异化冲刷规律

近20 a长江中游分汊河段的江心洲经历了冲刷并发生蚀退,但对微弯河段和顺直河段的江心洲差异化冲刷尚未有清晰认识。选取长江中游武汉河段的白沙洲和天兴洲作为研究对象,采用遥感影像、水文资料及野外调查,分析了白沙洲与天兴洲形态变化及差异化冲刷的原因。结果表明:1989—2020年,白沙洲洲体萎缩将近43.83%,天兴洲洲头浅滩变化较大,整体出露面积相对稳定;白沙洲与天兴洲的归一化植被指数(NDVI)整体较小,洲体植被覆盖空间差异性减小;这2个江心洲枯水期出露面积的变化主要体现在洲头浅滩;位于顺直河段的白沙洲洲头及侧向洲体遭遇冲刷,左侧洲体出现窝崩现象,其主要原因是白沙洲大桥桥墩的壅水与阻流作用;位于微弯河段的天兴洲自三峡工程蓄水后洲头遭受冲刷,2004年洲头守护工程实施和人工抛石有效地抑制了冲刷并实现了促淤作用。因此,江心洲的冲刷差异性主要体现在河段形态、主支汊相对位置和有无守护工程。

海床破坏下的海底管道路由区水动力冲淤特性研究与应用

针对某海底管道路由区人为作业形成的海床破坏区域在水动力作用下发生海底冲淤侵蚀变化问题,在路由区水动力参数观测和海底取样的基础上,研究提出了基于水动力数值模拟分析软件与模型的路由区冲淤特征的分析方法,设计了基于这一工程实际的二维水流-泥沙数学模型,利用管道路由区域实测的水文、地质数据确定了模型的边界条件,有效模拟了不同模型尺度下管道路由区的冲淤状况,经现场实测验证了该方法的正确性与有效性,可为海底管道的保护与运维评估提供技术支持。

床沙级配调整对黄河下游洪水演进的影响

小浪底水库运行以来,进入黄河下游的水沙条件出现了较大变化,受水库清水下泄影响,黄河下游床沙粒径出现了明显的粗化。为了探讨床沙级配粗化对黄河下游洪水演进的影响,本文首先建立了适用于黄河下游的一维水沙耦合数学模型,然后采用花园口至孙口河段2020年4—10月的实测洪水过程对模型进行了验证;其次根据河段床沙粗化特点,并以花园口床沙粗化过程为代表,设计了4组床沙级配作为模拟计算的初始床沙条件;最后采用验证后的模型进行了模拟计算,分析了床沙级配调整对洪水演进的影响。结果表明:床沙级配调整对黄河下游的流量、水位、含沙量、洪水演进时间以及河段冲淤量均有影响,但是对流量影响较小,而水位、含沙量、洪水演进时间与河段冲淤量对床沙级配的改变响应较为敏感。床沙中值粒径d_(50)由0.076 mm(级配1)增至0.242mm(级配4)时,夹河滩断面水位增高0.89 m,花园口至孙口河段冲淤量由冲刷0.679亿m^(3)转变为淤积0.059亿m^(3),冲刷量减幅为109%。研究结果可为新水沙情势下黄河下游河道治理提供借鉴与参考。

Prediction of Scour Depth around Offshore Pipelines in the South China Sea

搜索深度预言近海管道具有到海底的管道工程的设计和构造的大意义。在这份报纸，基于 CFD 软件，流畅的包裹和用户定义功能(UDF ) ，一个 Eulerian 二阶段的模型，包括为水和沉积的联合模型分阶段执行的 Euler-Euler，和为液体的一个狂暴的模型分阶段执行，被采用在管道附近预言 scour 深度。模型被从实验室实验获得的观察数据验证。根据模拟，包括早期的速度的效果，影响 scour 深度的因素等等输送直径和沉积粒子尺寸，被调查。根据各种各样的沉积的早期的速度的公式，同时接近计算在上理论搜索深度在华南海为七个车站的管道被开发，在设计申请的地方，信息是可得到的。

Numerical Simulation of Local Scour Around A Large Circular Cylinder Under Wave Action

A horizontal two-dimensional numerical model is developed for estimation of sediment transport and sea bed change around it large circular cylinder tinder wave action, The wave model is based on an elliptic mild slope equation. The wave-induced current by the gradient of radiation stress is considered and a depth integrated shallow water equation is applied to the calculation of the current. The mass transport velocity and the bed shear stress due to streaming are considered, which are important factors affecting the sediment transport around a structure due to waves, especially in reflective areas. Wave-current interaction is taken into account in the model for computing the bed shear stress. The model is implemented by it finite element method, The results of this model are compared with those from other methods and agree well with experimental data.

Experimental Study of Sediment Incipience Under Complex Flows

Sediment incipience under flows passing a backward-facing step was studied. A series of experiments were conducted to measure scouring depth, probability of sediment incipience, and instantaneous flow velocity field downstream of a backward-facing step. Instantaneous flow velocity fields were measured by using Particle Image Velocimetry (PIV), and an image processing method for determining probability of sediment incipience was employed to analyze the experimental data. The experimental results showed that the probability of sediment incipience was the highest near the reattachment point, even though the near-wall instantaneous flow velocity and the Reynolds stress were both much higher further downstream of the backward-facing step. The possible me- chanisms are discussed for the sediment incipience near the reattachment point.

Bed Load Transport Rates during Scouring and Armoring Processes

Dambreak-induced bed scouring may undermine the foundation of bridge piers and other structures,and that destruction can pose a serious threat.Consequently,this paper aims at exploring the mechanisms of scouring and armoring.Firstly,the incipient velocity for nonuniform sediment particles was studied,and a formula was derived based on the angle of repose of nonuniform sediment.The results showed that the mechanism of incipient motion for sand and fine gravel differed from that for coarse gravel and cobbles.Also,comparison between experimental and field data shows that the results from the proposed formula agree well with those observed for all conditions.Secondly,a birth-death,immigration-emigration Markov process was developed to describe the bed load transport rate associated with scouring and armoring.The comparison between experimental data and computed results shows that our model can predict the bed load transport rate,although there may be some limitations,the chief of which is that there are many variables in the model to be determined through experiment.This makes its application in river engineering inconvenient.

Scour depth beneath a pipeline undergoing forced vibration

This paper studies the coupling effect of the pipeline vibration on the seabed scour. A vertical two- dimensional model is applied to numerically investigate the local scour below a vibrating pipeline with different amplitudes and periods. Using the scour underneath a fixed pipeline as a reference, this paper focuses on the impact of the pipeline vibration on the equilibrium scour depth. Generic relationships are established between the non-dimensional scour depth and the non-dimensional vibrating parameters, i.e., amplitude and frequency. The normalization process takes into account the influences of such parameters as the incoming flow velocity, pipe diameter, and Shields parameter. An empirical formula is proposed to quantify these relationships.

CFD prediction of local scour hole around bridge piers

In order to predict the local scour hole and its evaluation around a cylindrical bridge pier,the computational fluid dynamics(CFD) and theories of sediment movement and transport were employed to carry out numerical simulations.In the numerical method,the time-averaged Reynolds Navier-Stokes equations and the standard k-ε model were first used to simulate the three-dimensional flow field around a bridge pier fixed on river bed.The transient shear stress on river bed was treated as a crucial hydrodynamic mechanism when handling sediment incipience and transport.Then,river-bed volumetric sediment transport was calculated,followed by the modification of the river bed altitude and configuration.Boundary adaptive mesh technique was employed to modify the grid system with changed river-bed boundary.The evolution of local scour around a cylindrical bridge pier was presented.The numerical results represent the flow pattern and mechanism during the pier scouring,with a good prediction of the maximum scour hole depth compared with test results.

荆江河段泥沙冲淤对三峡水库汛期排沙的响应

三峡水库汛期排沙研究大多关注库区的减淤效应,对坝下游河道的冲淤影响尚需进一步研究,对优化水库调度和河道保护利用具有重要意义。以三峡水库下游荆江河段为对象,建立了荆江长河段二维水沙数学模型,并结合实测资料分析,基于三峡水库2018年7月排沙调度,通过设置不同的排沙比(7%~100%),计算分析了荆江河段冲淤对三峡水库排沙比的响应。结果表明:虽然荆江河段全年总体冲刷,但排沙比较大时汛期仍可能淤积,上荆江河段受排沙调度影响相对较大;总体而言,2018年汛期水沙条件下,30%左右的排沙比是荆江河段洪季冲淤的临界点;排沙比提高后,汛期淤积部位大部分为边滩等缓流区,以及弯曲河段凹岸等,主槽仍冲刷,对维护滩槽高差具有积极意义。

Local scour at submarine pipelines

The rapid development of offshore oilfields has increased the number of submarine pipelines being constructed for the transport of crude oil to onshore refineries.Interactions between the pipeline and an erodible bed under the influence of current and waves often lead to local scouring around the structure.When this occurs, the pipeline may be suspended on the seabed resulting in the formation of a span.If the free span is long enough, the pipe may experience resonant flow-induced oscillations,leading to structural failure.This study examines the complex flow-structure-sediment interaction leading to the development of local scour holes around submarine pipelines.It reviews published literature in this area,which primarily is confined to the development of 2- dimensional scour holes.Despite the abundance of such research studies,pipeline-scour in the field essentially is 3-dimensional in nature.Hence,most of these studies have overlooked the importance of the transverse dimension of the scour hole,while emphasizing on its vertical dimension.This clearly is an issue that must be re-examined in light of the potential hazard and environmental disaster that one faces in the event of a pipeline failure.Recent studies have begun to recognize this shortcoming,and attempts have been made to overcome the deficiency.The study presents the state-of-the-art knowledge on local scour at submarine pipelines,both from a 2-dimensional as well as the 3-dimensional perspective.

Scour and Scour Countermeasures at Bridge Sites

This paper examines scour and scour countermeasures at bridge piers and abutments. Abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a floodplain. Notwithstanding this, the mechanism of scour at both piers and abutments is very similar; moreover, the failure mechanisms associated with both armoring and flow-altering countermeasures are not very different. In rivers with a floodplain, abutment scour becomes much more complex. In cases where the abutment ends at or near to the floodplain, it can initiate bank erosion, which clearly is an important erosion problem that is quite distinct from the customary scour at either an abutment in rivers without a floodplain or a pier. For this reason, abutment scour can be very site-specific while pier-scour is more generic in nature. To this end, the ability to identify the type of abutment scour that may form in a particular channel is closely related to an engineer's ability to propose devices for effective scour countermeasure.By summarizing research efforts on using riprap as a pier or abutment countermeasure over the past few decades, this paper highlights the deficiencies of riprap in arresting pier scour. To this end, different failure mechanisms are identified. They are shear failure, winnowing failure, edge failure, bedform-induced failure and bed-degradation induced failure. Each failure mechanism can singly or, more likely, combine to cause the eventual breakdown of the riprap layer. The study shows that a riprap layer is vulnerable to other failure mechanisms even though it is adequately designed against shear failure, rendering it ineffective in arresting scour.

新疆卡拉贝利水库排沙效果试验研究

通过坝区动床泥沙物理模型试验,研究卡拉贝利水库的排沙问题。观测水库排沙运用时的坝前水流形态、沿程流速变化、冲刷漏斗形态,分析不同运用水位和开启不同排沙洞工况的水库排沙效果,并通过敞泄排沙试验探讨水库恢复部分库容的可能性。研究表明,水深与冲沙流量是影响水库排沙的重要因素,相同的冲沙流量下降低水位排沙效率更高。水库应根据上游来水来沙条件、电站运用情况和排沙洞前淤积高程,抓住有利时机,灵活地运用多种方式冲沙。

Experimental Investigation on the Shape and Depth of Local Scour Hole Downstream of the Release Structure

Local scour downstream of the release structure is a critical problem to the safe and stable operation of water resources and hydropower engineering. In order to investigate the shape and depth of the scour hole under the equilibrium state of erosion and deposition downstream of an apron, a group of 16 experiments from the hydraulic similarity model test of Dangka Hydropower Station?was conducted with the non-cohesive sediment of different median particle sizes under different flow rates in this study. The control variable method was?to?study the influence of the flow rate and sediment size on the shape of the scour hole to define the number of experiment times of each test group. The results showed that the plane shape of the scour hole was irregular ellipse or semi-ellipse. The depth and size of the scour hole increased with the increase of the flow rate, and decreased with the increase of the sediment size;?the downstream longitudinal slope ratio of the scour hole increased with the increase of the sediment size. The coefficients of the upstream and downstream slope ratio of the local scour hole were 1/2 to 1/6 and about 1/10, respectively.

滦河下游腰庄段丁坝群水流特性及局部冲刷三维数值模拟

为探究滦河下游丁坝群对水流特性影响及坝头冲刷变化情况,利用Flow 3D建立了滦河下游腰庄段丁坝群三维水沙模型,采用2015年实测数据对模型进行了验证。模拟了5 a一遇和10 a一遇恒定流与非恒定流工况下丁坝群坝头流速分布及局部冲刷。结果表明,丁坝群能够有效减缓水流流速,改善水流对河岸的侵蚀,对滦河下游腰庄河岸起到保护作用。在恒定流条件下,10 a一遇工况较5 a一遇主流最大流速区逐渐偏向右岸,同时受主流冲击的丁坝流速增加约1.7 m/s,其余丁坝流速增加约0.9 m/s。在行洪过程中,受主流冲击的典型丁坝坝头产生了明显的冲刷坑,其中丁坝冲刷坑形态呈沿水流方向的狭长带状。随着重现期的增加,典型丁坝坝头冲刷坑深度增加约1 m,同时丁坝坝头冲刷带开始向上游延伸。研究成果可为丁坝局部冲刷安全分析提供参考。

泥沙突变理论在细颗粒泥沙输沙率中的应用

基于尖点突变理论,针对影响泥沙起动、底床冲刷的主要因素,在不同水流强度下,建立了恒定流下泥沙起动模式,以及沙粒雷诺数、希尔兹数与泥沙冲刷强度的非线性方程,进行了相应的物理模型试验,并将已有试验得到的沙粒雷诺数代入非线性方程,探讨了沙粒雷诺数的大小对非线性方程的影响,将所提公式的计算结果与已有资料进行对比,发现该理论公式的计算值与试验值具有较好的一致性,能基本满足对细颗粒泥沙冲刷强度的预测需求。