基于系列模型试验的波流共同作用下单桩冲刷及防护措施研究

冲刷问题是导致海洋环境中桩基础损毁的重要因素之一,极细沙在波流环境下具有"易冲易淤"的特点,以往针对极细沙底床的基础冲刷研究比较少见,采用系列模型试验的方法,针对极细沙海床在波流共同作用下的桩基础冲刷深度及防护措施效果展开研究,并将试验结果与前人经验公式计算结果进行比较。研究结果表明:波流作用下冲刷坑由圆桩两侧向桩前后发展,桩后冲刷深度较小,且当波流动力条件较强冲刷坑形态发展为水滴型。试验在K_c=3.11,相对速率U_(cw)=0.53条件下,采用系列模型延伸法得到原形桩基冲刷深度约为其直径2倍。沙被防护效果较好,试验未观察到圆桩周围产生冲刷破坏。在使用经验公式计算时,应综合考虑经验公式的适用范围与实际情况之间的差别,并分析其对冲刷结果可能带来的影响趋势。     

长江口岸直水道鳗鱼沙心滩头部守护工程局部冲刷系列水槽试验研究

为维持长江口岸直水道下段目前较为有利的滩槽格局,将在鳗鱼沙心滩头部建造护滩守护工程,需要研究守护工程周边的最大冲刷深度,以确定边缘压石宽度与重点防护部位。采用1∶100与1∶200的系列水槽试验研究护滩工程周围的局部冲刷深度,试验结果表明:局部可能最大冲深6.0 m左右,结果可应用于工程设计。     

海上多边形筒形基础局部冲刷数值模拟研究

基于CFD方法建立海上风电基础三维冲刷数值模型，研究单向流作用下海上风电基础局部冲刷特性。首先，通过所建立数值模型计算1:20比尺下的海上风电筒形基础的局部冲刷深度和尾涡绕流，并与相同比尺下的物理模型试验进行对比，结果吻合较好。进而，针对实际海况下的多边形筒形基础开展原型尺寸下的局部冲刷数值模拟，得到了冲刷平衡状态下多边形筒形基础周围各测点冲刷深度时程曲线和床面等高线，研究结果可为类似海上风电基础周围冲刷防护提供技术参考和工程借鉴。     

粉沙质海岸上栈桥桩基的波流冲刷试验

以现场天然沙为试验床质，利用系列模型，采用不规则波与潮流相结合的方式，对江苏LNG接卸站陆连岛栈桥桩基周围的冲刷情况。进行了系统试验。     

波浪作用下局部冲刷群桩动力特性试验研究

利用模型试验对深水桥墩群桩基础进行研究。用摇摆式造波装置施加波浪荷载,基于典型的冲刷坑形态,通过开挖桩周土体模拟不同的冲刷深度,探讨不同冲刷深度下桩基在波浪荷载作用下的动力反应。作为对比,同样进行了同参数下的单桩平行试验。研究结果表明:随着冲刷深度的增加,桩基础的自振频率逐渐降低,桩顶加速度和位移幅值呈增大趋势。桩基动力响应同时受水深的影响——随着水深的增大,位移和加速度也有所增加。在实际工程设计中,应该考虑桩基冲刷受损程度和水文条件的综合影响。     

波流共同作用下大型桥墩周围局部冲刷实验研究

桥墩周围局部冲刷深度是跨海大桥基础设计的重要参数。采用系列模型试验方法,对具体工程大型桥墩在水流和波流共同作用下的局部冲刷分别进行研究,提出了冲刷坑形态和最大冲刷深度,供工程设计参考。同时,通过单向水流和波浪 水流两种情况冲深结果比较,指出在预测波流共同作用下的大型桥墩局部冲深时,不应将两种动力条件进行简单的迭加,而应具体问题具体分析。     

东海大桥桥墩冲刷防护工程护底结构稳定性试验研究

东海大桥是上海国际航运中心洋山深水港工程的重要组成部分。据实测显示,自大桥建成后,部分桥墩周围发生了明显的局部冲刷现象,最大冲刷深度已达到或稍超出设计时预估的冲刷深度。为确保桥梁安全运营,对桥墩实施防护工程是非常必要的。文章采用物理模型试验方法,研究了波浪和水流组合作用下典型桥墩防护方案护底结构稳定性。研究结果表明:100 a重现期波浪(H_s=5.12 m,T=10.5 s)与最大可能流速(1.98 m/s)共同作用下,对底床形成有效防护需要25 000个钩连体,对于混凝土联锁块软体排方案,需要辅助压脚结构,其中网箱石笼结构的受力性能好,材料利用率高。     

海上风电场风机桩基局部冲刷计算

建设海上风电场时,风机所处的环境十分复杂,在风、浪、流等要素的影响下,风机桩基周围会出现冲刷坑,而风机桩基的局部冲刷深度是工程设计的重要参数.采用胜利埕岛油田海洋平台桩基局部冲刷现场观测资料,对常用的两个桩基局部冲刷经验公式进行验证,并对拟建的风电场工程风机桩基的局部冲刷深度进行计算,计算结果具有一定的参考价值.     

桩基挡板透空堤与潜堤消浪特性数值计算研究

为改善港内水域平稳度,本文采用Fluent软件建立桩基挡板透空堤与潜堤的数值波浪水槽联合模型,在设计高水位及2年一遇波浪组合下,计算潜堤断面尺度(坡比、堤顶宽度、堤身高度)和潜堤位置变化的120组试验工况,研究潜堤的消浪特性,得到潜堤位于距透空堤1/6波长位置与潜堤高度2.5 m能够改善水域平稳度,满足堤后H4%波高均小于0.6 m。     

粉沙质海床上人工岛周围波流冲刷试验

以现场天然沙为试验床质，利用系列模型，采用不规则波与潮流相结合的方式，对江苏LNG接卸站人工岛周围的冲刷情况，进行了系统试验。试验研究了波浪、潮流在不同组合情况下人工岛周围海底的泥沙冲淤变化，得出冲刷段和淤积段的分布及其强度，同时还对相应的防冲刷工程措施进行了研究。     

淤泥质海床上人工岛水流冲刷试验

港珠澳大桥人工岛局部冲刷是大桥工程设计亟待解决的关键技术问题。在现场资料分析与物理模型验证的基础上,采用正态系列模型延伸法,在潮汐宽水槽中研究了淤泥质海床上人工岛周围流态变化和局部冲刷的发展过程。研究结果表明,在洪季大潮情况下,东、西人工岛最大冲深分别为10.3 m和9.0 m,冲刷坑集中在岛桥结合部和隧道防护段及防撞墩附近;最大冲刷深度与人工岛的几何形状、流速、工程水域的沙土特性以及水深等相关,冲刷坑的平面形态则与岛型、水流夹角、涨落潮流速差以及潮流历时有密切关系。     

潮汐河段桥墩局部冲刷深度的试验研究

随着公路延伸到潮汐河道和近海海港,在桥梁设计中需要对潮汐河段桥墩的局部冲刷深度进行分析。在动床模型试验中使用了典型的潮汐水流条件和3种代表性的模型沙。使用拍照和测量记录下冲刷坑的形态和深度变化过程,得到了潮汐河段桥墩的冲刷过程,将潮流冲刷的深度与恒定流的深度进行比较,得出不同条件下冲刷深度的折减系数为0.75~0.92,建议以涨落急最大流速代替恒定流流速作为计算的标准,试验结果还表明泥沙粒径小于0.15 mm条件下的公式计算结果与试验结果有差别,建议对公式进行修正。     

Experimental investigation on scour development and scour protection for offshore converter platform

Local scour around the offshore converter platform caused by current and wave will lead to the instability of foundation. A series of experiments are performed to investigate the scour development and scour protection of the offshore converter platform. The development and evolution characteristics of the local scour around the gravity based structure foundation under the actions of current flow and wave are analyzed. The results show that the edge scour mainly occurs at the lateral sides of the platform and the scour pits are symmetrical about the centerline of the platform in the streamwise flow direction. The scour depth around the gravity based structure increases with the increase of flow velocity. The inclination and collapse of the platform is observed at α = 90° and U₀ = 0.25 m/s. The sand ripples are observed around the gravity based structure under the wave action, and the scour depth increases with the increase of wave height and wave period. Based on the comparisons of different scour protection methods, the combined bionic grass-geotextile-riprap protection has the best scour protection efficiency for the offshore converter platform.     

Comparison of Scour and Flow Characteristics Around Circular and Oblong Bridge Piers in Seepage Affected Alluvial Channels

The present study examines scour geometry and turbulent flow characteristics around circular and oblong piers in alluvial channel with downward seepage. Experiments were conducted in plane sand bed of non-uniform sand under no seepage, 10% seepage and 15% seepage conditions. Scour depth at oblong pier is significantly lesser than the scour depth at circular one. However, the scour depth at both piers reduces with downward seepage. The measurements show that the velocity and Reynolds stresses are negative near the bed at upstream of piers where the strong reversal occurs. At downstream of oblong pier near the free surface, velocity and Reynolds stresses are less positive; whereas, they are negative at downstream of circular pier. The streamline shape of oblong pier leads to reduce the strength of wake vortices and consequently reversal flow at downstream of pier. With application of downward seepage turbulent kinetic energy is decreasing. The results show that the wake vortices at oblong pier are weaker than the wake vortices at circular pier. The strength of wake vortices diminishes with downward seepage. The Strouhal number is lesser for oblong pier and decreases with downward seepage for both oblong and circular piers.     

受渗流影响的冲积河道中圆型和矩形桥墩受腐蚀情况和流动特性比较（英文）

The present study examines scour geometry and turbulent flow characteristics around circular and oblong piers in alluvial channel with downward seepage. Experiments were conducted in plane sand bed of non-uniform sand under no seepage, 10% seepage and 15% seepage conditions. Scour depth at oblong pier is significantly lesser than the scour depth at circular one.However, the scour depth at both piers reduces with downward seepage. The measurements show that the velocity and Reynolds stresses are negative near the bed at upstream of piers where the strong reversal occurs. At downstream of oblong pier near the free surface, velocity and Reynolds stresses are less positive; whereas, they are negative at downstream of circular pier. The streamline shape of oblong pier leads to reduce the strength of wake vortices and consequently reversal flow at downstream of pier. With application of downward seepage turbulent kinetic energy is decreasing. The results show that the wake vortices at oblong pier are weaker than the wake vortices at circular pier. The strength of wake vortices diminishes with downward seepage.The Strouhal number is lesser for oblong pier and decreases with downward seepage for both oblong and circular piers.     

海南岛西南海域泥沙特征及地形演变

基于水文泥沙测验及遥感影像资料分析海南岛西南海域泥沙特征,采用不同沿岸输沙公式对比计算海域的波浪沿岸输沙量,采用多年实测地形数据研究岸滩的演变规律。结果表明:海域内含沙量大潮大于小潮,但总体上悬沙含量较低;研究海域内径流对输沙影响较为有限,但受沿岸波流输沙的影响相对较大;而海区的悬移质颗粒比较均匀,颗粒较细;沿岸段波浪沿岸输沙能力净输沙方向均为自南向北,年净输沙能力在6.72万~13.31万m~3;岸滩演变的主要动力是波浪、波生沿岸流和潮流共同作用导致东方市所辖岸线的变化总体以自然冲淤变化为主,但冲淤强度有限,变化幅度不大。     

Experimental study on the width of the turbulent area around bridge pier

At present, the method of calculating the turbulent flow width around the bridge pier is not given in the "Standard for Inland River Navigation" (GB50139-2004) in China, and the bridge designer usually increases the bridge span in order to ensure the navigation safety, which increases both of the structural design difficulty and the project investments. Therefore, it is extremely essential to give a research on the turbulent flow width around the bridge pier. Through the experiments of the fixed bed and the mobile bed, the factors influencing the turbulent flow width around the bridge pier have been analyzed, such as the approaching flow speed, the water depth, the angles between the bridge pier and the flow direction, the sizes of bridge pier, the shapes of the bridge pier, and the scouring around the bridge pier, etc. Through applying the dimension analytic method to the measured data, the formula of calculating the turbulent flow width around the bridge pier is then inferred.     

Effect of downward seepage on turbulent flow characteristics and bed morphology around bridge piers

In this work, experimental investigations have been pursued to analyse the influence of downward seepage on the turbulent characteristics of flow and corresponding changes in vortex structure around circular bridge pier in alluvial channel. Experiments were conducted in sand bed channel with circular piers of different sizes for no seepage, 10% seepage and 20% seepage cases. The measurement of turbulent flow statistics such as velocity and Reynolds stresses is found to be negative within the scour hole at upstream of the pier whereas application of downward seepage retards the reversal of the flow causing a decrement in the velocity and Reynolds stresses. Higher Reynolds shear stress prevails at the downstream side because of the production of wake vortices. Contribution of all bursting events to the total Reynolds shear stress production has been observed to increase with downward seepage. The analysis of integral scale suggest that size of eddies increases with seepage, which is responsible for increase in particle mobility. Initially rate of scouring is more which abatements gradually with expanding time as well as with the increased of downward seepage. Presence of downward seepage reduces the depth and length of vortex and shifts towards downstream side of the pier.