孤立波作用下破碎区单圆柱附近流动特性数值研究

为了合理分析孤立波作用下破碎区单圆柱附近的水流结构以及圆柱受力特性,该文利用OpenFOAM开源程序求解基于Navier-Stokes方程的三维数值模型,该模型采用S-A IDDES湍流模型,使用修正的VOF方法捕捉自由液面。研究发现,该数值模型能合理捕捉到孤立波与圆柱相互作用过程中复杂的液面形态变化;圆柱附近自由液面沿柱面呈三维分布,上爬过程的柱前雍高显著大于回落过程的柱后雍高;回落过程中柱前形成的尾涡在强度和范围上大于上爬过程中柱后形成的尾涡;圆柱表面的动水压强随水深的增长呈近似线性增长,最大值位于上爬过程中最大雍高时刻的迎浪点位置;圆柱所受的波浪力与柱面附近自由液面雍高历时相符,且上爬过程圆柱受到的波浪力明显大于回落过程。     

Finite element analysis of second order wave radiation by a group of cylinders in the time domain

A finite element based numerical method is employed to analyze the wave radiation by multiple or a group of cylinders in the time domain. The nonlinear free surface and body surface boundary conditions are satisfied based on the perturbation method up to the second order. The first- and second-order velocity potential problems at each time step are solved through a Finite Element Method (FEM). The matrix equation of the FEM is solved through iteration and the initial solution is obtained from the result at the previous time step. The three-dimensional (3-D) mesh required is generated based on a two-dimensional (2-D) hybrid mesh on a horizontal plane and its extension in the vertical direction. The hybrid mesh is generated by combining an unstructured grid away from cylinders and two structured grids near the cylinder and the artificial boundary. The fluid velocity on the free surface and the cylinder surface are calculated by using a differential method. Results for various configurations including the cases of two cylinders and four cylinders and a group of eighteen cylinders are obtained to show the joint influences of cylinders on the first- and second-order waves and forces, including the effects of spacing ratios and wave frequency on the second order waves and the mean force, in particular.     

计算域中存在直立岛式结构物时波浪传播的数值模拟

针对计算域中存在直立岛式结构物的复连通区域，提出了岛体边界条件，利用缓坡方程建立了在计算域中存在直立岛式结构物时波浪传播的数值模拟模型。模型适用于变水深水域问题，克服了解析解只能适用于等水深水域的不足。直立圆柱和无穷小厚度岛式防波堤周围波浪传播的数值算例表明，数值解与解析解吻合良好，说明所建立的数值模拟模型能有效地模拟复连通区域内的波浪传播。矩形固定式防波堤周围波浪场的数值模拟说明该模型对工程实际有较强的适应性。     

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.     

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。     

聚焦波浪与直立圆柱作用的数值模拟

基于Fluent平台建立了可用于波浪传播模拟的数值计算水槽,利用不同波浪参数的线性规则波模拟分析了网格尺度L/Δx对产生波浪质量的影响,确定数值水槽的网格划分尺度,并验证了阻尼消波的有效性。在此基础上,用模拟频谱的方法对聚焦波浪的传播进行了数值模拟,通过数值模拟与物理试验不同位置处的聚焦波波面和聚焦点下水质点速度时间过程线对比,验证了模拟频谱方法数值计算的有效性。进一步对聚焦波浪与直立圆柱的作用进行了数值模拟,数值模拟聚焦波面过程、聚焦波浪水质点速度、圆柱周围波浪波动过程、圆柱上所受的波压力等,并与试验结果进行了对比,数值计算结果与试验结果吻合很好,验证了所建立的数值水槽的有效性。对聚焦波波面和压力特征值进行了误差分析,并分析了误差的产生原因,为进一步研究聚焦波浪与工程结构物的作用奠定基础。     

大型海洋结构物的非线性绕射效应

本文在空间上应用面源法,在时间域上应用步进法,数值处理了三维物体与非线性波浪的相互干扰,研究了结构物的非线性绕射效应。首先,作为比较,求解了正弦波列和孤立波绕射垂直桩柱的情形。接着,进一步求解了大振幅波浪绕射固定在自由面上的大型浮动码头的工程实例。结果表明,非线性波浪绕射力与线性结果,有一定的差别。有时,尽管从总体效应来看,这种差别不十分明显,但从上浪、出水和波的爬高以及局部应力等局部效应来看,这种差别可能很明显。     

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。     

非线性波浪绕射问题的数值计算

本文给出非线性波浪绕射问题的计算模型,并用时间步进和边界元法求解。该模型能适用于严重非线性情形,且能满足初始条件和辐射条件。作为对该模型的检验,我们对孤立波绕过穿刺水面的直立圆柱的算例进行了计算,并同Isaacson的解析解、李宝元的差分解进行了比较,结果吻合很好。此外我们还用数值方法同时模拟造波机造波和求该波与直立圆柱的相互作用。结果表明,数值波浪水池能够以尽可能短的暂态过程,模拟波浪与物体的相互作用,提供良好的初始条件。数值波浪水池还能用于任意水深、任意水底形状下的相互作用问题。本文的计算模型和算法具有机时省,计算稳定的优点。     

LOCAL SCOUR AROUND A LARGE-SCALE VERTICAL CIRCULAR CYLINDER DUE TO COMBINED WAVE-CURRENT ACTION

The local scour around a large scale vertical circular cylinder due to combined wave-current action was experimentally and numerically studied in the present paper. Experiments were carried out to research the affect of the wave height, current velocity and the diameter of the cylinder on the scour process. The topography near the cylinder in various cases during scour was measured. The cylinder diameter affects the distribution of scour and deposition area. The maximum scour depth increases evidently when the current velocity increases, The maximum scour depth does not increase after the wave height retains a certain value. A numerical model using a finite element method for simulating the scour process was established. And the numerical results agree well with the measured data. The numerical model is more applicable in the case of large-scale cylinders.     

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。     

Numerical simulation of three-dimensional breaking waves and its interaction with a vertical circular cylinder

Wave breaking plays an important role in wave-structure interaction. A novel control volume finite element method with adaptive unstructured meshes is employed here to study 3-D breaking waves. The numerical framework consists of a "volume of fluid" type method for the interface capturing and adaptive unstructured meshes to improve computational efficiency. The numerical model is validated against experimental measurements of breaking wave over a sloping beach and is then used to study the breaking wave impact on a vertical circular cylinder on a slope. Detailed complex interfacial structures during wave impact, such as plunging jet formation and splash-up are captured in the simulation, demonstrating the capability of the present method.     

Transmission of solitary waves through slotted barriers: A laboratory study with analysis by a long wave approximation

Economic and long-term social impacts of tsunami waves, as shown in the 2004 Indian Ocean tsunami, have been devastating. In addition to the passive measures such as the tsunami early warning systems, active protective measures such as tsunami breakwaters and tsunami-resistant buildings are also necessary. Slotted barriers are low cost structures that can be very effective in reducing the transmitted energy of long waves. In this study, the transmission of tsunami waves, with the leading wave being modeled by a solitary wave, through slotted barriers in the form of a row of circular cylinders is studied experimentally. The results are also analyzed by a method based on long wave approximations. It is found that the spacing between two adjacent cylinders is one of the main factors that control the transmission of solitary waves through slotted barriers. Reflection coefficients and the reduction of drag force on coastal structures protected by slotted barriers are also discussed in the paper.     

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。     

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。     

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。     

有限深两层流体中水波与水平圆柱潜体的相互作用

研究了有限深两层流体中表面波模态和内波模态的水波与水平圆柱潜体的相互作用问题。在线性势流理论框架内,建立了两种模态入射波作用下,水平圆柱体绕射势的多极展开求解理论。基于所建立的求解模型,对作用在圆柱体上的波浪力进行了数值计算分析,并且与均匀流中情况进行了比较。结果表明了,在入射波的某个频率范围内,流体的分层效应对圆柱体波浪力的影响是不可忽略的。同时,对流域内的绕射速度矢量场进行了数值分析。     

Numerical study of the wave-induced slamming force on the elastic plate based on MPS-FEM coupled method

Slamming is the phenomenon of structure impacting the water surface. It always results in the extremely high load on the structure. This paper is mainly concerned with the slamming force caused by the wave-plate interaction. In this paper, the process of solitary wave impacting onto the horizontal plate is simulated with the help of the moving particle semi-implicit and finite element coupled method(MPS-FEM). The MPS method is adopted to calculate the fluid domain while the structural domain is solved by FEM method. In the first series of simulations, the profiles of the solitary waves with various amplitudes, which are generated in the numerical wave tank, are compared with the theoretical results. Thereafter the interaction between the solitary waves and a rigid plate is simulated. The effects of wave amplitude, as well as the elevation of the plate above the initial water level, on the slamming force are numerically investigated. The calculated results are compared with the available experimental data. Finally, the interactions between the solitary waves and the elastic plate are also simulated. The effects of the structural flexibility on the wave-induced force are analyzed by the comparison between the cases with elastic and the rigid plate.     

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.     

直墙前直立圆柱纵荡问题的研究

应用镜像原理，将直墙前单个圆柱的纵荡问题转化为双柱在静水中的相向振荡问题，应用速度势的特征展开法，建立了直墙前垂直圆柱纵荡问题的解析解。通过数值计算研究了圆柱与直墙间距离大小、水深等因素对附加质量和辐射阻尼的影响。计算结果表明，直墙前圆柱上的附加质量和辐射阻尼明显不同于开敞水域中单柱纵荡的情况，且随着波数的变化发生振荡。