射流冲刷沙床初始阶段的SPH方法数值模拟

针对射流移动清淤时短时间内的冲刷效果问题,采用无网格光滑粒子动力学方法(SPH),对平面垂直淹没射流冲刷沙床的初始阶段进行了模拟计算。探讨了SPH中淹没环境和沙土材料的建立方法,研究了射流冲刷初始阶段动态冲坑深度的发展趋势,分析了射流速度对冲坑深度发展的影响。结果表明:采用SPH方法可以有效地模拟射流冲刷的过程;在初始阶段,冲坑深度随时间线性增加,而且随着射流速度的增加,坑深增加的速率加快。本文研究可为探讨疏浚射流破土效果提供数值方法参考。     

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。     

Effect of side slope of main channels on formation and penetration of scour hole in confluences

In an open‐channel confluence, deep scour holes and depositional point bars are usually formed due to high bed‐shear stresses and secondary circulations. In the present study, presuming the effectiveness of channel geometry on the flow dynamics at the confluence, some variables including different side slope angles of the main channel (θ = 45°, 60°, 75°, 90°), lateral to downstream discharge ratio (Q_r), and downstream densimetric Froude number (Fr_g3) were experimentally studied under clear‐water condition for the confluence angle α = 90°. According to the results, the increase of θ led to a greater penetration of scour hole across the main and tributary channels, whereas a little scour development was observed along those channels. Meanwhile, an increase in Q_r and Fr_g3 caused further scouring, but their effects on the dimensions of scour hole diminished with increase of θ. Thus, with increase of Q_r from 0.194 to 0.552, the mean penetration rate of scour hole to all directions for θ = 45°, 60°, 75°, and 90° was obtained 42.8%, 32.4%, 25%, and 20.5%, respectively. In addition, considering the effect of θ, Q_r, and Fr_g3, some empirical relationships were obtained for estimating the penetration length of scour hole. The derived relationships show that Fr_g3 plays more important role on the dimensions of scour hole than θ.     

Laboratory Investigation of Stilling Basin Slope Effect on Bed Scour at Downstream of Stepped Spillway: Physical Modeling of Javeh RCC Dam

Stepped spillway and stilling basin are one of the most important energy dissipation structures. Eventhough, most of energy dissipated by these structures, but in skimming flow, the upstream flow motion is nonaerated and the residual energy capable to destroyed structures during floods. In this study, effect of stilling basin slope on bed scour, downstream of Javeh dam was investigating. Experiments performed in hydraulic structures laboratory of the University of Kerman with six different discharges (5, 7, 13, 17, 25 and 30 l/s.m) and five various stilling basin slope (0.02, 0.01, 0, ?0.01 and???0.02). The parameters such as maximum scour depth (d_s), flow velocity (in three point), water depth on upstream and downstream of stepped spillway and stilling basin, the distance of the maximum scour depth to sill (L_s) and the gheometery of scour hole measured. Result shown that when stilling basin slopes was 0.02, the average of maximum relative scour depth, 47% Increased and in ?0.02, 52.2% Decreased. In addition, the distance of maximum scour depth until stilling basin increased by increasing and decreased by decreasing the stilling basin slope.

     

差动式挑流消能冲坑深度初探

从能量损失的途径出发,把挑流能量损失过程分成4个阶段,并引入流速修正系数,修正无能量损失情况下求出的流速,从而得到入水前的水流流速。在得到冲坑内的能量损失后,由单位体积消能率来推算水体体积。再用几何方法求得水体最大冲刷深度,从而得到冲坑深度。     

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。     

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。     

Effect of synthetic fibers on resisting scour caused by horizontal jet

Given that the development of scour downstream of hydraulic structures increases the risk of structural damage, it is important to find cost-effective and environmental approaches to reduce this risk. This study aimed to experimentally evaluate the effect of synthetic fibers on the scour profile downstream of a sluice gate with a rigid apron. Experiments were performed with the same Froude number and with different weight percentages of synthetic fibers on both non-cohesive and cohesive sediments. One uniform sand was used as the non-cohesive sediment, and three different cohesive sediments were prepared by mixing different percentages of kaolinite soil with the used sand. The scouring experiments showed that the presence of synthetic fibers did not considerably affect the scour hole dimension in non-cohesive sediments. Evaluation of the scour in the cohesive sediments in silty sand (SM) texture found that an increase in the percentage of silt reduced the scour hole dimensions. The effect of synthetic fibers on scour of SM-texture-based sediments was also investigated, and the results showed that increasing the percentage of synthetic fibers decreased the scour hole dimensions. In addition, the cohesive sediments in SM texture did not have a similar non-dimensional scour profile, and the presence of synthetic fibers did not significantly affect the scour hole.     

圆柱桥墩局部冲刷机理试验研究

为进一步探索圆柱桥墩局部冲刷机理,分别从桥墩附近水流流速分布特性、桥墩冲刷特性以及冲刷与流速相互关系对圆柱桥墩顺水流向不同布置方式的局部冲刷水力学特征进行了模型试验研究.结果表明:两排10桥墩顺水流(桥墩轴向与水流方向夹角分别为90°,60°,30°,0°)均匀布置时,桥墩轴向与流向夹角越小,流速在桥墩上下游紊动越小,对下游影响范围越大,且流速越大,冲刷深度和范围越大.顺水流布置0°夹角时,冲刷程度最小,在相同流量下,冲刷稳定历时最短;垂直布置(90°夹角)时,冲刷程度最严重,所需冲刷稳定历时最长,且随着流量的增大,桥墩墩前冲刷坑最深位置逐渐向水槽中间偏移.     

Effect of abutment aspect ratio on clear‐water scour in floodplains

Scour around abutments is recognized as one of the main reasons of bridge foundations failure. This paper presents the experimental results of the effects of abutment width and length on the scour development up to its equilibrium condition around 45° wing‐wall setback abutments in a compound channel. The developing scour hole characteristics are tested for three different lengths and widths at different time intervals until its equilibrium scour conditions. The findings showed that the abutment width has a profound effect on the characteristics of the scour hole, contradicting the results of previous studies. Generally, an increase in the relative abutment width leads to a reduction in the scour depth and width. However, the scour length, area, and volume initially increase with an increase in the relative abutment width, L_c/y_f , from 1.33 to 10.67, where L_c is the abutment width and y_f is the floodplain flow depth, and then these characteristics decrease significantly with a much wider abutment, L_c/y_f , from 10.67 to 21.33. Overall, the effects of the abutment width on abutment scour should be accounted. To this end, empirical equations are proposed to predict the scour hole characteristics. Scour data from previous studies are also used to compare with the proposed equations.     

射流作用下不同沙床动态冲坑变化规律的试验研究

基于泥沙动力学和射流冲刷理论,对粗沙沙床和中沙沙床在某一流速下进行不同靶距的淹没射流实验,通过高速摄像机捕捉动态冲坑在短时间内的发展变化,分析了在前10s和前1s内的坑深发展规律。并将前1s等分成24个时间段分析其细微变化。结果表明:冲坑深度在前10s内基本呈对数规律发展;射流冲刷刚开始时中沙沙床冲坑深度的发展趋势有时滞后于粗沙沙床;冲坑深度随时间有先增加后减小的趋势,在此流速下存在一个最优靶距。此实验的研究成果在疏浚工程施工作业时具有一定的参考价值。     

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。     

裸露穿河管道在压重块保护下的冲刷特性

水流冲刷引起河床变形的不确定性对水下穿越管道的安全运行造成威胁.为了探究裸露穿河管道在压重块保护措施下的冲刷特性,通过水槽模型试验,研究压重块长度、压重块布置间距、水流流速、河道水深等因素对管道周围河床地形和冲刷深度的影响.试验结果表明:水下穿越管道在压重块保护措施下的冲刷过程可分为冲刷坑形成、压重块迎流侧悬空、管道迎...     

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。     

水库坝前冲刷漏斗形态三维水沙数学模型研究

利用"动刚盖法"处理自由表面边界,结合水库坝前水沙运动规律导出坝前局部床面泥沙边界条件及泄流初期河床滑塌变形的判别条件,通过坐标变换建立坐标系下水库坝前冲刷漏斗形态三维水沙数学模型.分别利用正向和侧向底孔泄流条件下冲刷漏斗水槽试验资料对模型进行验证.模拟结果表明,不同泄流方式下底孔附近三维水流结构、横断面、纵剖面及平面形态特征等均与实测资料基本一致,模型关于自由表面边界、近底泥沙交换条件、河床纵坡、横坡滑塌处理是合理的.     

头屯河水库坝前冲沙漏斗及泄空冲沙的初步探讨

介绍了河流上建造水库形成淤积的原因及水库淤积的形态和特性,进而引入了水库排沙的一些方法,并描述了头屯河水库在没有进行泄空冲沙前的淤积形态及相关特征。研究和分析了坝前冲沙漏斗的形态及特征,其中包括冲刷坑深度和水下休止角等漏斗特征的确定。并根据这些淤积形态和漏斗特征,以及水库实际冲刷的形态和过程,建立了溯源冲刷的物理图形,找出适合溯源冲刷纵向冲刷长度估计的计算公式,并对头屯河水库冲刷长度进行了验证。     

Large-scale experimental study on scour around offshore wind monopiles under irregular waves

The Keulegan-Carpenter (KC) number is the main dimensionless parameter that affects the local scour of offshore wind power monopile foundations. This study conducted large-scale (1:13) physical model tests to study the local scour shape, equilibrium scour depth, and local scour volume of offshore wind power monopiles under the action of irregular waves with different KC numbers. Systematic experiments were carried out with the KC number ranging from 1.0 to 13.0. With a small KC number (KC < 6), and especially when the KC number was less than 4, the scour mainly occurred on both cross-flow sides of the monopile with a low scour depth. When the KC number exceeded 4, the shape of the scour hole changed from a fan to an ellipse, and the maximum scour depth increased significantly with KC. With a large KC number (KC > 6), the proposed method better predicted the equilibrium scour depth when the wave broke. In addition, according to the results of three-dimensional terrain scanning, the relationship between the local equilibrium scour volume of a single offshore wind power monopile and the KC number was derived. This provided a rational method for estimation of the riprap redundancy for monopile protection against scour.     

泥沙粒径及射流速度对沙床冲刷的影响

射流冲刷在众多疏浚工程中应用广泛并发挥了重要作用,对其开展深入研究很有必要。基于Eulerian二相流模型和k-ε湍流模型,以粒径为0.04~0.23 mm的沙床为研究对象,进行了二维垂向淹没射流冲刷沙床的数值模拟,研究了粒径和射流速度对沙床冲刷的影响。结果表明,在研究的粒径范围内,最大冲刷深度和悬浮泥沙体积与流速成正相关,与粒径成负相关,且流速的影响更大。     

桥墩局部冲刷动态模拟及不同截面的冲刷特性

为了获得桥墩局部冲刷随时间的演变过程,探讨不同截面桥墩的冲刷特性,采用计算流体动力学软件FLUENT的自定义函数功能和动网格更新技术,考虑湍流涡增强效应的床面剪应力和坡度影响的临界剪应力,得到床面的输沙率,通过输沙率与床面高程的变化关系实现床面地形随时间的动态变化,并利用泥沙坍塌的调整来克服床面坡度超过泥沙休止角造成的模拟失真及数值不稳定。结果表明:局部冲刷最大深度、冲坑形态及流场结构的模拟结果与试验结果较为吻合;在最大墩宽一致的情况下,流线形桥墩的冲坑深度比圆柱形桥墩降低约45%,比尖角形桥墩降低约40%,冲坑范围也有所下降。     

阿尔塔什坝前冲刷漏斗模型试验研究

在水利工程设计中,水库坝前冲刷漏斗形态、大小及相应的水沙流动特性直接关系到泄水建筑物的正常运行。根据阿尔塔什水库坝前模型试验,对坝前冲刷漏斗形态进行了研究,总结了不同运行工况下纵、横向漏斗变化规律,提出保持发电洞"门前清"的泄流流量及其对应的冲沙历时。与类似工程试验结果对比表明,本试验结果合理可行,可供设计参考。