孤立波作用下珊瑚礁海岸附近流动特性研究

该文通过基于大涡模拟的三维数值模型研究了孤立波作用下珊瑚礁海岸附近的流动特性,考虑了两种礁坪水深的情况,通过物理模型实验对比验证了礁面上自由液面的空间与时间变化以及流速的时间变化,并运用数值结果进一步分析了流场和涡量场的沿礁变化规律。结果表明:该数值模型能合理地模拟不同礁坪水深下孤立波的浅水变形、破碎和滚波的运动以及波生流的变化。波浪破碎时礁坪上水流由亚临界流向超临界流转变,随后流速沿礁衰减。泻湖内的流速变化不再显著,波浪破碎伴随着强烈的水体涡动,涡动随着滚波的沿礁衰减而逐渐耗散,泻湖中的涡动几乎可以忽略不计。礁坪水深的增大显著降低了礁坪上的涡动强度。     

规则波对大直径群桩作用的数值模拟研究

多桩柱结构在海洋工程中应用广泛,大直径群桩效应使得桩柱所受到的波浪力与单桩大为不同。首先使用基于势流理论开发的三维水动力分析程序DIFFRACT计算了单个圆柱和双圆柱所受到的波浪力,通过与相应解析解的对比验证了数值结果的准确性。进一步分析了大尺度多桩柱结构在规则波中所受的波浪力。群桩间的水动力相互作用使桩群中每个圆柱所受的波浪力存在多个峰值,其最大值可达单个圆柱所受波浪力的2.30倍,并且最大波浪力圆柱的位置受桩群布置的影响。     

椭圆余弦波作用下沙纹床面附近涡流运动特性

沙纹床面附近的涡动分离及其运动过程显著影响床沙的输运。该文采用Open FOAM开源程序包建立基于原始Navier-Stokes方程的三维数值模型,使用VOF方法追踪自由液面,利用k-ε湍流模型捕捉复杂的涡流运动,对波浪作用下沙纹床面附近涡流运动特性进行研究。结果表明,受沙纹床面的影响,波浪呈现非线性特征,波高增加、波峰尖锐,且相位有所滞后;一个波周期内涡动首先产生于沙纹背浪侧,并沿背水坡抬升至沙纹峰以上,继而向上游移动;上溯至最大位置后,在下一个波周期影响下转向下游移动直至完全耗散;受分离涡的影响,近底层流场极不稳定,但整体上一个波周期内逆波向流作用较大,这与涡流显著的上溯趋势相同;涡动上溯的最大水平距离ΔX随λ/a的增大而减小,而最大垂向距离ΔZ则无明显变化;上溯过程中旋涡中心点处的湍动能呈现减小趋势,其中ωt=150°之前减小速率较快而后有所减缓。     

孤立波作用下岸滩剖面变化成因的水动力数值分析

该文基于Open FOAM开源程序包建立波浪数值水槽,对孤立波在斜坡上的水动力特性进行模拟。运用实验数据验证了数学模型的精度和可靠性,进一步研究岸滩剖面变化的成因,并分析冲刷区不同位置泥沙颗粒所受水流冲量的变化规律,发现地形冲刷变化与水流的冲量作用为正相关,回落过程中水流冲量大于上爬过程,因而冲刷主要发生在回落过程。探讨淤积区泥沙颗粒的受力特征,发现由于水跃过程中漩涡作用,中层水流的泥沙颗粒出现向上受力,泥沙颗粒由底部回落水流向上部水流转移,水跃后期泥沙颗粒受力方向为向岸向下,岸滩最大淤积位置出现在水跃中水体涡量最大时的临近向岸区域。     

用三维时变雷诺方程模型模拟小尺度组合桩柱上的波浪力

该文以雷诺时均的Navier-Stokes方程为控制方程，用k-ε模型来封闭湍流模型，采用VOF方法来跟踪波动自由表面，建立了三维数学模型。然后对波浪与小尺度孤立柱的相互作用过程进行了数值模拟，得到了时变的波浪力，然后用实验资料进行了验证，并且和Morison方程的计算结果进行了比对。然后利用验证过的模型模拟了三维波浪场中两个不同间距的纵向排列的小尺度桩柱上所受的波浪力，得到了两个桩柱的干扰系数和间距的关系。计算方法和计算结果对此类结构物的设计施工有一定的参考价值。     

内孤立波环境下柱体的受力特性

针对以往孤立波对柱体作用研究多只针对柱体的整体受力开展,少有研究精细获取柱体不同部位受力特性的问题,借助三维大涡模拟(LES)数值波浪水槽,通过提取柱周流场及压强分布,得到柱体所受压差阻力及黏滞力的垂向分布,对柱体在孤立波环境中的受力特性进行了分析,并采用多元线性回归分析,构造综合影响参数分析了柱体受力特性,构建了柱体受力系数经验表达式。结果表明:上下层水体中方柱所受压差阻力约分别为圆柱的1.5倍和3.5倍;作用于柱体上的黏滞力比压差阻力小1或2个数量级,可忽略流体的黏性效应;综合影响参数与相对波幅正相关,与上下水深比负相关。     

错置双柱式桥墩三维流场及水流力特征研究

错置双柱式桥墩在桥梁工程中广泛存在,错置双柱式圆柱三维绕流以及水流力特征值得深入研究。该文采用ANSYS Fluent数值模拟软件,考虑自由液面影响,对典型等直径45°错置双柱桥墩在不同柱间间距下的三维流场以及水流力特征等进行了研究,研究结果表明:柱间间距为2D时,两柱后漩涡沿顺流方向拉伸严重,Z1柱处漩涡规律性脱落不明显,Z2柱后有漩涡规律脱落,且Z2柱阻力均值、阻力振幅及升力振幅均大于Z1柱;Z1柱周向自由液面高度变化较小,Z2柱周向自由液面分布近似关于沿顺流方向过Z2柱心的直线对称,Z2柱两侧自由液面高度也会随漩涡结构的发展而出现波动。Z1柱周向压强分布波动较小,Z2除受底部边界及自由液面影响较大的截面外,各截面压强波动也较小。文章还进一步研究了L/D增大后,各柱阻力系数、升力系数、漩涡脱落频率和斯特劳哈尔数等水流力参数的变化特点。     

基于CIP法的波物相互作用强非线性数值模拟

极端波浪环境作用下,浮体易发生上浪拍击等强非线性现象,这一问题也是波浪与浮体相互作用研究的难点之一。该文基于高阶CIP(Constrained Interpolation Profile)法,采用THINC(Tangent of Hyperbola for Interface Capturing)数值技术精确捕捉自由液面,建立了二维多相流强非线性数值水槽模型。通过模拟线性波和孤立波的生成、传播过程,对该模型的收敛性、稳定性及造波性能进行了全面的验证与分析。利用该数值模型模拟和分析了极端波浪对浮体的强非线性作用。     

三孤立波的斜坡爬高特征

该文采用推板式造波机和改进的Goring造波方法在波浪水槽中生成了由三个等波高孤立波组成的波列,首先在坡度为1/10的斜坡上进行了多个孤立波连续爬高的实验研究。实验测量了等波高双孤立波和三孤立波在等水深波浪水槽中传播和在斜坡上的爬高过程,给出了沿程多点浪高仪测量的波面时间序列和高速摄像记录的水线在斜坡上爬高与回落过程影像。分析了来波相对波高和无量纲波峰间距对每个孤立波爬高放大系数的影响。在基于RANS方程和VOF方法的数值波浪水槽中,模拟了三孤立波爬高过程,给出了最大爬高与破碎特征。实验和数值模拟结果表明,孤立波在斜坡上回落时会产生强劲的回流水流,该反向流动导致后随孤立波破碎,消耗波动能量,使得后随孤立波的爬高放大系数明显小于没有回落水流影响的首个孤立波的爬高放大系数。当孤立的波峰间较大时,若来波相对波高较小,后两个的孤立波爬高基本相同;若来波相对波高较大时,第三个孤立波的爬高大于第二个孤立波的爬高。     

孤立波与不同淹没深度水平圆柱体的相互作用

用基于时变雷诺方程和方程为基础的数学模型模拟了孤立波与近海不同淹没深度水平圆柱的相互作用过程,其中自由表面的跟踪采用了分段线性近似的VOF方法.结果表明：当圆柱靠近水底时,尤其是在圆柱与底部海床有较小缝隙时,圆柱底部附近的涡旋较强;而圆柱靠近水面时,水面附近的涡旋较强,圆柱越靠近水面,圆柱背浪面一侧的水面附近产生的涡对越多.     

A 3-D numerical study of solitary wave interaction with vertical cylinders using a parallelised particle-in-cell solver

This paper aims to provide a better understanding of the interaction between solitary waves and vertical circular cylinders. This is achieved via process based numerical modelling using the parallel particle-in-cell based incompressible flow solver PICIN. The numerical model solves the Navier-Stokes equations for free-surface flows and incorporates a Cartesian cut cell method for fluid-structure interaction. Solitary waves are generated using a piston-type wave paddle. The PICIN model is first validated using a test case that involves solitary wave scattering by a single vertical cylinder. Comparisons between the present results and experimental data show good agreement for the free surface elevations around the cylinder and the horizontal wave force on the cylinder. The model is then employed to investigate solitary wave interaction with a group of eleven vertical cylinders. The wave run-up and wave forces on the cylinders are discussed.     

非淹没双直立圆柱系统波浪爬升的数值模拟

波浪爬升是近海构筑物和海洋平台结构设计中的重要参数。全面掌握波浪的爬升特性有利于结构的安全保证和优化。采用有限元方法建立了求解Berkhoff缓坡方程的数值模型，并计算了非淹没单个直立圆柱周围的波高分布，计算结果与解析解吻合很好。以非淹没双直立圆柱为研究对象，探讨了圆柱间距对波浪爬升的影响。结果表明:上游圆柱周围的波高分布曲线波动较大，但最大相对波高和最小相对波高的发生位置基本与单个圆柱的情况相同；当圆柱间距为1/4波长的奇数倍时，最小相对波高明显减小，圆柱肩部出现第二峰值；而当圆柱间距为1/4波长的偶数倍时，最小相对波高则明显增加，圆柱肩部出现第二谷值。下游圆柱周围的波高分布曲线与单个圆柱的情况相似，但波高相对较小。     

NUMERICAL STUDY OF MULTIDIRECTIONAL FOCUSING WAVE RUN-UP ON A VERTICAL SURFACE-PIERCING CYLINDER

In this article,a numerical model based on improved Boussinesq equations and the Finite Element Method(FEM)with unstructured triangular elements is proposed and verified by experimental results for the focusing wave group interaction with a vertical surface-piercing cylinder.The multidirectional focusing waves with different directional spreading parameters and their interaction with a vertical surface-piercing cylinder are numerically simulated.The directional spreading parameter influences the wave form,that is,a wider directional spreading would induce a narrower wave form in space.The wave run-up on the cylinder increases with the increase of the wave directional spreading parameter,but when the parameter is greater than 30-40,the wave run-up changes only slightly and the influence of the directional spreading can be neglected.A larger diameter cylinder may have a larger wave run-up at the front face.But at the back side,it is other way round.     

Run-up of non-breaking double solitary waves with equal wave heights on a plane beach

The evolution and run-up of double solitary waves on a plane beach were studied numerically using the nonlinear shallow water equations(NSWEs) and the Godunov scheme. The numerical model was validated through comparing the present numerical results with analytical solutions and laboratory measurements available for propagation and run-up of single solitary wave. Two successive solitary waves with equal wave heights and variable separation distance of two crests were used as the incoming wave on the open boundary at the toe of a slope beach. The run-ups of the first wave and the second wave with different separation distances were investigated. It is found that the run-up of the first wave does not change with the separation distance and the run-up of the second wave is affected slightly by the separation distance when the separation distance is gradually shortening. The ratio of the maximum run-up of the second wave to one of the first wave is related to the separation distance as well as wave height and slope. The run-ups of double solitary waves were compared with the linearly superposed results of two individual solitary-wave run-ups. The comparison reveals that linear superposition gives reasonable prediction when the separation distance is large, but it may overestimate the actual run-up when two waves are close.     

变水深下孤立波对直立大圆柱的绕射

本文以平均速度势表示的Boussinesq方程为控制方程,采用文献[1]中所提出的谱方法,研究孤立波在变水深下对直立大圆柱的绕射。通过数值方法求得圆柱所受到的波浪力系数,讨论水深变化对圆柱波浪力系数的影响。     

NUMERICAL SIMULATION OF SOLITARY WAVE RUN-UP AND OVER-TOPPING USING BOUSSINESQ-TYPE MODEL

In this article,the use of a high-order Boussinesq-type model and sets of laboratory experiments in a large scale flume of breaking solitary waves climbing up slopes with two inclinations are presented to study the shoreline behavior of breaking and non-breaking solitary waves on plane slopes.The scale effect on run-up height is briefly discussed.The model simulation capability is well validated against the available laboratory data and present experiments.Then,serial numerical tests are conducted to study the shoreline motion correlated with the effects of beach slope and wave nonlinearity for breaking and non-breaking waves.The empirical formula proposed by Hsiao et al.for predicting the maximum run-up height of a breaking solitary wave on plane slopes with a wide range of slope inclinations is confirmed to be cautious.Furthermore,solitary waves impacting and overtopping an impermeable sloping seawall at various water depths are investigated.Laboratory data of run-up height,shoreline motion,free surface elevation and overtopping discharge are presented.Comparisons of run-up,run-down,shoreline trajectory and wave overtopping discharge are made.A fairly good agreement is seen between numerical results and experimental data.It elucidates that the present depth-integrated model can be used as an efficient tool for predicting a wide spectrum of coastal problems.     

非淹没刚性植被影响下孤立波在岸滩上的爬高

为探究海岸刚性植被对海啸波的削弱效应,通过物理模型试验和数值模拟研究了孤立波与不同坡度岸滩上非淹没刚性植被的相互作用问题。物理模型试验在波浪槽中进行,测试了不同的入射波波高、植被密度和岸滩坡度对孤立波爬高的影响,并运用物理模型试验数据校核改进后的Boussinesq方程,得到植被的拖曳力系数。结果表明:拖曳力系数随植被密度的增大而增大,随坡度增大而减小;植被后的无量纲透射波高和无量纲岸滩爬高随着无量纲的入射波高的增大而减小,随着植被密度的增大而减小;当岸滩坡度增大时,无量纲透射波高增大而无量纲爬高并无显著差异。最后根据回归分析得出了岸滩爬高与相对入射波高、植被密度和岸滩坡度的幂函数型经验关系式。     

AN EXPERIMENTAL OBSERVATION OF A SOLITARY WAVE IMPINGE-MENT,RUN-UP AND OVERTOPPING ON A SEAWALL

A sequence of laboratory experiments using solitary waves was performed to model the effect of leading form of three types of tsunamis(a bore,an impinging wave and an overtopping wave)on a seawall on a sloping beach.The wave evolution process,impinging pressure along the seawall surface,total overtopping discharge behind the seawall and the maximum run-up height on the rear slope were measured and compared.Laboratory data were employed to re-examine relevant empirical formulae in the literature.The effect of the presence of the seawall in reducing maximum run-up height using the present setup was briefly discussed.The present data can be used for calibrating numerical and mathematical models.     

Application of artificial neural network to calculation of solitary wave run-up

The prediction of solitary wave run-up has important practical significance in coastal and ocean engineering,but the calculation precision is limited in the existing models.For improving the calculation precision,a solitary wave run-up calculation model was established based on artificial neural networks in this study A back-propagation(BP)network with one hidden layer was adopted and modified with the additional momentum method and the auto-adjusting learning factor.The model was applied to calculation of solitary wave run-up.The correlation coefficients between the neural network model results and the experimental values was 0.9965.By comparison with the correlation coefficient of 0.9635,between the Synolakis formula calculation results and the experimental values,it is concluded that the neural network model is an effective method for calculation and analysis of solitary wave run-up.