枢纽下游河床冲刷深度和水位降落估算方法

通过清水冲刷水槽试验,在探索非恒定输沙及床沙调整等规律的基础上,结合沙量平衡原理,建立了一种枢纽下游河床冲刷深度和水位降落的计算模式。洪峰过程可以概化为一种恒定的"当量流量",深槽冲刷以枯水边界作为脱离体,可将该模式延伸于天然河道。能够计算冲刷过程及终期河床冲刷纵剖面和不同流量下的水位降落。     

波流作用的近岸圆柱局部床面侵蚀

波浪流对近岸浅水带床面作用强烈,该区域结构物局部床面侵蚀显著,潜存致灾威胁。用三维数值方法研究了瞬态孤立波作用下非黏性沙海床上的近岸圆柱体局部冲刷规律,分析了波浪流冲刷的3类主要影响要素,讨论了近岸地形条件影响下的波流冲刷深度。研究认为,表征浅水波流特征和柱体尺度的无量纲数Urp与KC数存在非独立关系,二者均能分别反映波流冲刷的主要规律;表示泥沙运动的力学参数Shields数在波流动床条件下仍对柱体局部冲刷有贡献;近岸地形通过床面坡度对波破碎的增强及堤岸挡墙对波浪的反射,都会影响到局部冲刷。     

间歇性波浪扰动下河口底泥中磷释放特性研究

作为反映河流、海洋水体受污历史的载体,河口底泥在污染达到一定程度时易在海洋动力作用下释放沉积其中的污染物,影响水体水质。为了明确秦皇岛近岸海域内污源染,量化波浪扰动下底泥释放对水质的影响,该研究以波流水槽为动力试验设备,选取秦皇岛污染最严重的河流之一大蒲河的河口底泥为研究对象,试验研究河口底泥在间歇性波浪扰动下磷的释放特性。总磷在波浪扰动下的释放可分为浓度迅速增加的初期和浓度随时间线性增加的稳定期两个阶段,浓度随波高增大而升高,且在波高大于8 cm时与浊度呈显著正相关。溶解性总磷受浓度梯度和波浪引起的孔隙水压力影响向上覆水体迁移扩散,随时间呈小幅增加。总磷在波浪扰动初期的释放强度为2.00×10~(-3)–8.75×10~(-3) mg/m2/s,是稳定期释放强度0.50×10-4–2.25×10~(-4) mg/m~2/s的18–40倍,且两个阶段的释放强度均随波高呈指数增长。当波浪强至起动底泥,原先的泥水界面释放转为底泥起动悬浮释放,水体中颗粒态磷取代溶解态磷成为磷的主要赋存形态。间歇性波浪扰动静置期,颗粒态磷的吸附沉降使得水体中总磷浓度和颗粒态磷的比例大幅降低。     

Clear-water scour depth below underwater pipelines

The paper presents (1) a semi-theoretical model for the computation of maximum clear-water scour depth below underwater pipelines in uniform sediments under steady flow and (2) an experimental investigation on the influence of upward seepage on clear-water scour depth below underwater pipelines.Based on the “image method” of the potential flow theory for the flow through the gap between a circular pipeline and the scoured bed, a theoretical model is presented for the computation of maximum scour depth below underwater pipelines in clear-water condition considering the wall correction. Also, a simple theoretical calculation, that involves Chiew's (1991) [Chiew, Y.M., 1991. “Prediction of maximum scour depth at submarine pipelines.” J Hydraul Eng 117(4), 452–466] gap flow curve, is proposed to estimate the maximum scour depth considering the wall correction. The computed results agree satisfactorily with the experimental data. In addition, the potential predictors of the maximum scour depth given by different researchers are compared with the experimental data.The result of an experimental investigation on the scour depth below pipelines under the influence of upward seepage through the bed sediment is presented. In general, the scour depth below pipelines with upward seepage is smaller than that without seepage. There exists a critical value of the ratio of seepage velocity to main flow velocity that corresponds to a minimum scour depth.     

挟沙水流床面冲刷深度试验研究

在清水冲刷粗化层极限冲刷深度研究的基础上,结合室内概化水槽试验,探讨了挟沙水流床面冲刷问题。不同来沙条件下床面冲刷深度水槽试验观测成果表明,随着上游单宽加沙率的增加,挟沙水流床面冲刷深度减小,挟沙水流相对冲刷深度与相对来沙条件呈线性变化趋势。参考爱因斯坦推移质输沙率公式,建立了一个能够综合反映来水来沙条件以及床面条件的床面冲刷深度计算公式。该公式计算值与试验实测值吻合良好。     

海啸波引起的近岸房屋局部冲刷试验

基于波浪水槽,分别考虑独栋和房屋群两种情况,开展海啸波引起的近岸房屋局部冲刷试验研究,分别建立了独栋房屋情况下相对最大冲刷深度与海啸波相对越顶高度关系式和房屋群情况下局部最大冲刷深度与海啸波波高、房屋宽度、房屋高度、房屋数量、房屋间的中心间距的关系式。试验结果表明在海啸波越顶水流产生的水跌以及海啸波通过房屋时产生的扰流共同作用下,房屋周围,特别是海侧会产生明显的局部冲刷坑;回落水流水跌是局部冲刷坑产生的主要因素,扰流是次要因素。所建立的关系式揭示了最大局部冲刷深度与海啸波、房屋尺寸、房屋布局的内在联系。     

不规则波作用下墩柱周围局部冲刷研究

对相对柱径较大（0．15〈D／L〈0．5）的圆柱式结构物在不规则波作用下周围的局部冲刷情况，进行了多组试验研究，系统地研究了不规则波作用下圆柱周围地形的变化规律，试验中分别考虑了波浪的波高、周期、水深、泥沙粒径及圆柱直径等因素对圆柱周围局部冲刷地形的影响，分析了圆柱周围冲淤地形形成的机理，特别是对床面泥沙粒径因素进行了详细分析，认为波浪作用下圆柱周围冲刷深度与床面粒径并不成反比关系，而是在d50=0．18mm附近最小，在此基础上提出了不规则波作用下圆柱周围最大冲刷深度及其发生位置的计算公式。     

射流冲刷平衡深度研究

本文通过水槽实验和理论分析,研究了在水流速度低、泥沙易淤积的区域引入平面冲击射流对消除泥沙淤积的影响。实验观测了射流局部达到冲刷平衡时,最大冲刷深度随射流喷口高度、喷口宽度、喷口流速、横流流速及泥沙特性变化的规律。由泥沙起动理论和平面射流运动规律,建立了射流冲刷平衡深度计算式。用不同性质的泥沙和采用不同射流喷口宽度、不同喷口高度的射流冲刷实验资料对建立的计算公式进行了验证,计算结果与实验资料吻合良好。     

泥石流坝后侵蚀坑内部边坡规律实验研究

侵蚀坑内部边坡的大小决定着侵蚀坑的形态和发展,研究侵蚀坑内部边坡的变化规律可为合理估算冲刷范围提供依据.通过室内水槽实验观测,侵蚀坑纵剖面坑内坡度总体表现为上游坡较下游坡陡,并且随着水槽原始坡度以及沟床组成物质的变化而变化.对于具有相同级配的粘性砂和无粘性砂,粘性砂的侵蚀坑坑内坡度较无粘性砂的要陡.定义侵蚀坑上下游出口与其最深点连线的倾角为侵蚀坑坑内上下游坡度,通过对实验数据进行回归分析,建立了侵蚀坑坑内坡度与泥沙的水下休止角以及沟床原始纵坡之间的定量关系.     

海啸波作用下植被区海堤局部冲刷试验

近年来频发的海啸造成了沿岸建筑物周围剧烈的冲刷,而植物具有很好的减小海啸灾害的作用。采用PVC圆管概化模拟刚性植物,选取孤立波模拟海啸波,通过改变入射波高、植物带长度和密度、堤顶出水高度,研究植物对海啸波作用下海堤局部冲刷的影响,建立了海堤堤前冲刷坑、淤积沙坝、冲淤平衡点相对水平位置的尺度与植物带的长度和密度、波高、堤顶出水高度、泥沙比重以及岸滩坡度之间的关系式。试验结果表明:植物对海堤局部冲淤变化产生显著影响,植物带使得堤后近岸侧相对最大冲刷深度显著减小,堤前离岸侧冲刷位置由原堤脚处前移至植物带所在位置,冲刷范围大幅增加;堤前冲淤面积受入射波高和植物因素的共同影响,在同一植物模型下,冲刷坑面积和淤积沙坝面积都随入射波高的增大而增加;适当增大植物带密度,优化植物分布方式,可有效减弱海啸波对海堤的冲刷危害。     

Experimental study on wave-current structure around a pneumatic breakwater

A model of a pneumatic breakwater comprised of perforated pipes placed on a wave flume bottom and connected to a piston-type air compressor is installed in a wave flume. Ascending air bubbles form an aerial barrier which dissipates wave energy and reduces the height of transmitted waves. The model is exposed to regular waves with fixed parameters, and its properties are modified by changing the amount of air supplied to the pipes. Particle Image Velocimetry and Acoustic Doppler Velocimetry methods are employed to measure a wave-current velocity field in the close vicinity of a submerged aerial barrier used as a breakwater. The measurements are supported by free-surface elevation registration in order to evaluate the effectiveness of the pneumatic breakwater in damping waves and to identify processes responsible for wave energy dissipation. Basing on the measurements, the performance of the pneumatic breakwater in different wave conditions is analysed. The results indicate that the dissipation of energy inside a region of a turbulent flow induced by ascending air bubbles may be considered the main mechanism of wave energy attenuation by pneumatic breakwaters.     

Engineering application of submerged water jets for sediment removal in a tidal riverbed

Sediment deposition problems have attracted the interest of engineers and researchers. Several experimental studies have been conducted on scour depth using turbulent jets. However, field observation and monitoring have rarely been reported. This study aimed to eliminate sediments on a tidal riverbed using a prototype device, which consisted of a set of submerged vertical water nozzles and submerged horizontal air nozzles. The effectiveness of the water jet in sediment removal during spring and neap tides was evaluated. The quantitative relationships of dimensionless parameters, such as (1) the relative sediment scour volume versus the number of flows from the jet exit, (2) the relative sediment scour volume versus the relative scour depth, and (3) the relative scour size versus the relative jet intensity, were analyzed. The results showed that the freshwater flowing to the sea affected the sediment scour volume during the falling cycle of spring tides. In contrast, the rising cycle of spring tides retarded the freshwater flow, resulting in a decrease in the sediment scour volume. A steep water surface slope accelerated the river flow and further influenced the cross-flow current around the study area. As a result, a highly diffusive turbulent flow was produced, causing suspended sediments to be rapidly removed from the scour hole center. An increase in the number of flows from the jets led to intensified diffusion of turbulent energy into the flow. The rapidly varying water depth caused jet energy to be dissipated before approaching the riverbed, and it significantly affected the scour process during the spring-tide period. The proposed equations can be used to estimate the scour volume, scour size, and re-suspended sediments in tidal rivers within defined ranges of parameters.     

桥墩振动对其局部冲刷的影响

为了探究桥墩振动对其局部冲刷的影响,以圆柱型桥墩为例,开展了不同泥沙底床条件下的振动桥墩局部冲刷水槽试验。结果表明,在振动载荷下,对于中值粒径分别为14.42μm、31.75μm和85.92μm的细颗粒底床,当振动强度从0增大至3.72,最大冲刷深度和最大冲刷半径均随之增大;中值粒径为14.42μm的泥沙底床最大冲刷深度增幅最大达910%,且粒径越大,增幅越小。对于中值粒径为260μm的粗颗粒底床,当振动强度从0增至2.31,最大冲刷深度降低了37.50%,而最大冲刷半径增加了38.37%。因此,桥墩的振动对其局部冲刷有着重要影响,且对细颗粒底床和粗颗粒底床的影响不同。桥墩振动导致有黏性的细颗粒泥沙发生流变从而加剧了其局部冲刷;而无黏性的粗颗粒泥沙受到振动作用而加密,其局部冲刷削弱。提出了考虑桥墩振动的局部冲刷深度计算公式,其理论计算值与实测值相对误差在±20%的数据达87.5%,能够为涉水桥梁基础埋深的设计提供更合理的计算依据。     

垂直射流冲刷砂床的喷嘴间距试验研究

疏浚工程中常利用射流进行河道清淤和冲砂施工。为探究喷嘴间距对射流冲刷的影响,开展了一系列不同靶距、速度和间距的双喷嘴冲刷粗砂、中砂砂床试验,分析了冲刷坑形、冲坑深度和冲坑截面积的变化特性,得到了各工况下的最优喷嘴间距L_B和不利喷嘴间距L_N。结果表明,对于同一粒径砂床,改变靶距和速度冲刷时的L_B和L_N值变化较小,而与粗砂砂床相比,冲刷中砂砂床时的L_B和L_N值均有所增加。研究成果可供疏浚工程中射流系统设计作为参考。     

基于Flow-3D的水平射流冲刷泥沙数值模拟

为了模拟分析闸口水平射流对下游泥沙冲刷的全过程,基于水工模型试验,采用Flow-3D软件中的泥沙冲刷模型结合RNG模型和FAVOR方法,进行了水平射流冲刷固定底板下游泥沙的模拟试验。根据原水工模型条件,结合模型试验结果,对冲刷过程中的水面线、流速分布、冲坑深度和堆丘高度进行了对比分析。结果显示,数值模拟与原试验结果中水面线和流速分布吻合度很高,冲刷过程中的冲坑深度与堆丘的高度也很接近。分析了冲刷过程中的泥沙运动,模拟了不同粒径泥沙的冲刷过程并将结果进行对比,发现达到冲刷平衡阶段时冲坑深度与堆丘高度随泥沙粒径的增大而减小,该结论符合理论分析,证明该软件中泥沙模型可用于物理试验中的有关变量分析。     

波流作用下淹没圆柱局部冲深影响因素分析

淹没圆柱在海洋工程中运用广泛,局部冲刷对此类建筑物的安全有较大影响。为掌握该类型建筑物在波流作用下的冲刷特性,在波流水槽内开展了一系列试验研究。试验将圆柱模型安装在波流水槽中部的沙槽内,沙槽内铺设中值粒径0.22 mm的无黏性沙,形成平底海床。试验中圆柱处于淹没情况,改变入射波流条件,观测多种波流作用下,不同高度淹没圆柱周围的局部冲刷深度发展过程,分析了多种无量纲参数对局部冲刷深度的影响。结果表明:当KC数不变时,冲刷深度s/D随着相对流速U_cw和Fr的增大而增大,当Fr增大到一定程度时(Fr>0.80),冲刷深度s/D趋于稳定; U_cw在固定范围内时,冲刷深度s/D随KC数的增加而增加,增长速率逐渐变慢; 引入淹没因子K_s,得到了淹没圆柱与非淹没圆柱的冲刷深度计算关系式。     

太湖长兜港固体悬浮物再悬浮的室内模拟

定量研究浅水湖泊动力扰动与沉积物再悬浮的关系,目前仍是湖泊研究中的难点之一。实验利用再悬浮发生装置,对太湖长兜港沉积物风浪扰动进行室内模拟,建立扰动强度与有效波高之间的关系,定量分析风浪对太湖水体中悬浮物的影响及固体悬浮物在水体中的垂向分布,初步得出风浪对太湖沉积物扰动深度一般在毫米级的结论。     

含沙水流挑流消能对卵石河床冲刷的试验研究

本文通过室内浑水模型试验,探讨了卵石床质河流上泄水建筑物挑流消能对河床的局部冲刷问题。试验结果表明:浑水水流的单宽流量大小、含沙量的多少以及含沙粒径的变化都对冲刷坑深度有一定的影响。本文就浑水冲刷特性问题,与清水挑流消能作了对比,提出了一些初步认识。     

Impacts of ice cover on local scour around semi-circular bridge abutment简

The presence of ice cover in winter can significantly change the flow field around bridge abutments, which can also cause a different local scour pattern. To investigate the impacts of ice cover, results from a recent flume experiments were presented. Smooth and rough ice covers were created to investigate the impacts of ice cover roughness on the scour geometry around the semi-circular abutment. Three bed materials were used, with 50D s of 0.58 mm, 0.50 mm, 0.47 mm respectively. Scour volume and scour area were calculated. It was found that the maximum scour depth was located 75o inclined to the flume wall. Under rough ice cover, the scour area and scour depth were the largest. An empirical equation on the maximum scour depth was also developed.     

Log‐Vane Scour in Clear Water Condition

Log‐Vane is a grade‐control structure of common use to stabilize river bed and river banks. The purpose of this paper is to study the scour phenomena downstream of Log‐Vanes in straight rivers. The main goal is to obtain design equations to determine the main scour parameters and the scour morphology. All the experiments have been carried out in a horizontal channel and in clear water conditions. Log‐Vanes made of wood, with different heights and vane angles, were tested. Different hydraulic conditions including densimetric Froude numbers, water drops and tail water values were tested. Results show that the tail water depth is an important variable to determine the maximum scour depth. The vane angle results to be an important parameter to predict the scour parameters. Dimensional analysis allows to derive design equations useful to estimate the maximum scour depth, maximum length of the scour and maximum height and length of the dune. Copyright © 2014 John Wiley & Sons, Ltd.