港珠澳大桥岛桥结合跨箱梁波浪力试验研究

通过三维物理模型系列试验,对港珠澳大桥工程西人工岛、岛桥结合跨进行模拟。试验测量了不同波浪入射角度、波高、波周期以及梁底净高等影响因子下的岛桥结合跨箱梁所受的浮托力和水平力,分析了受力随波陡、相对梁底作用高度以及波浪入射角度的变化规律。研究表明,在一定条件下箱梁浮托力和水平力,随波陡的增大而减小,随梁底相对作用高度的增加而增大,波浪入射方向的影响主要表现为与箱梁沿波浪传播方向的有效长度相关。由于岛桥结合跨的特殊性,改进的Douglass公式并不适用于岛桥结合跨箱梁受力的计算。通过主要影响因子的量纲分析,建立针对岛桥结合跨箱梁浮托力和水平力的计算公式。研究成果可为今后同类工程以及数值模拟提供借鉴与参考。     

矩形人工岛波浪爬高的数值模拟

本文基于线性绕射理论,提出了采用波源分布法计算矩形人工岛上波浪爬高的数值模型.在三种入射波向(α=0°、45°、90°)下进行数值计算,所得到的结果与整体模型试验的实测结果进行了比较,二者吻合较好.表明波源分布法是确定波浪爬高的一个有效方法,可为人工岛工程设计提供可靠的高度参数.     

不同因素对人工岛波浪绕射影响研究

为研究人工岛尺度变化和波浪方向分布对人工岛绕射波浪的影响,基于MIKE21-BW模型应用数值方法模拟人工岛波浪绕射过程。数值结果与Briggs等的物理试验结果的对比表明两者吻合较好,验证了模型的适用性。在规则波条件时,圆形人工岛绕射波浪的数值结果与线性波浪绕射理论解基本一致;采用该模型分别模拟了6种尺度的圆形人工岛、单向不规则波和9种方向分布θ_(max)、4种谱峰周期条件时绕射波浪分布情况。分析结果表明,圆形人工岛绕射系数随着尺度的增加,掩护区绕射系数随之减小;θ_(max)在10°~45°范围内,随着θmax的增大,绕射系数随之增大,θ_(max)在45°~75°内绕射系数变化较小;随着谱峰周期的增加,绕射系数随之增大。研究成果既为相关规范的完善提供了基础,也为相关工程设计提供了参考。     

礁面大糙率存在下孤立波传播变形及爬高实验研究

本文采用圆柱体阵列来模拟珊瑚礁面的大糙率,通过波浪水槽实验研究礁面糙率对孤立波传播变形及岸滩爬高的影响。结果表明,粗糙礁面的存在显著削弱了礁坪上孤立波的首峰和礁后岸滩反射造成的次峰,同时降低了波浪在珊瑚礁面的传播速度;垂直于岸线方向沿礁相对波高随着入射波增大而减小,随着礁坪水深的增大而增大,粗糙礁面上波高沿礁的衰减更为显著;礁前斜坡的无量纲反射波高随无量纲入射波高的变化与礁坪水深有关,当入射波高足够大时其趋于常值,粗糙礁面略微增大了礁前斜坡的反射;无量纲透射波高和岸滩爬高随着无量纲入射波高的增大而减小,特别是礁坪水深较大时更为显著,粗糙礁面时的无量纲岸滩爬高相对于光滑礁面平均减小46%;通过回归分析得出了同时适合于光滑和粗糙礁面的预测孤立波岸滩爬高的经验关系式。     

波浪爬高

本文论述了斜面坡度、波陡、堤前水深对规则波爬高的影响。认为可以用伊里巴伦数I_r来区分堤前波浪运动形态的变化。利用本次室内模型试验的数据,得到了斜坡和陡墙上的波浪爬高曲线以及斜坡上波浪爬高计算公式。     

龙口市人工岛周边海域波浪场和水动力场的数值模拟

为了科学的分析离岸人工岛群对周边海岸动力的影响,本文以龙口市人工岛为例,运用MIKE21数值模拟软件建立了龙口离岸人工岛及附近海域的水动力模型和波浪模型,根据波浪的生成、成长和传播原理,针对最有可能形成较大波浪的W、WNW、NW三个方向,采用频率为0.5%(重现期为200a)的高潮位叠加频率为0.5%(重现期为200a)的W、WNW和NW向风作用下的波浪场和水动力场进行数值模拟研究,给出了高潮位条件下人工岛周边不同波向对应的有效波高和最大波高值,以及最大流速和流向数据,可为人工岛群的地坪标高确立和防浪建筑物的布设提供科学依据。     

不同尺度人工岛波浪绕射系数的研究

为研究人工岛沿波浪传播方向尺度变化对绕射系数的影响,本文基于MIKE21-BW模型,数值模拟研究了入射波为不规则波时人工岛尺度不同对其绕射系数的影响。通过数值结果与Briggs物理模型试验结果进行了对比,结果吻合较好,验证了模型在研究波浪绕射问题上的适用性。在未考虑结构物沿波浪传播方向尺度对绕射系数的影响时,将数值结果与《海港水文规范》(JTS145-2-2013)规范结果比对,结果差异较小;本文采用上述模型模拟了结构物沿波浪传播方向7种不同尺度时的波浪绕射情况,分别是0.5Ls,Ls,2Ls,3Ls,4Ls,5Ls及6Ls,通过对不同尺度时的波浪绕射系数变化的分析,得到结果:结构物尺度在0.5Ls~2Ls范围内时,绕射系数随着结构物尺度的增大而变大;结构物尺度在3Ls~6Ls范围内时,绕射系数随着结构物尺度的增大而减小;在人工岛岛壁附近和其掩护区内绕射系数变化较明显;人工岛结构物尺度变化对绕射系数值有影响。文中给出了不同尺度人工岛绕射系数等值线图,可为工程设计中绕射波高确定提供参考。     

岛屿地形下的核电厂护岸防洪设计研究

对国内第一个岛屿地形下核电厂的护岸防洪设计进行了研究,提出直立式护岸结构方案以满足核电厂防洪和避让毗邻海岛的要求。在波浪数值模拟计算结果基础上,开展了波浪整体物理模型试验、波浪局部整体物理模型试验和波浪断面物理模型试验,对护岸的越浪量和结构稳定性进行了优化验证。研究结果表明,岛屿地形下,波浪破碎和波能集中导致护岸堤身坡脚处波高增大,须加高挡浪墙和优化挡浪墙结构型式;在相同的越浪量标准下,采用直立堤结构相对斜坡堤结构对应的护岸挡浪墙的高程须明显加高;利用部分海岛地形斜坡高地作为厂区护岸一部分时,原状海岛地形斜坡高地处的波浪爬高效应明显,须加高邻近护岸挡浪墙的高程。     

运用DSAS和SMC分析人工岛建设对岸线变化的影响

海南岛东郊椰林人工岛建设于砂质海岸外,对海岸线变化有非常大的影响。选取5景遥感影像,运用DSAS数字岸线分析系统分析人工岛建设前后岸线变化,同时利用SMC模拟系统分析人工岛建设前后水动力变化情况,用于分析研究泥沙运移趋势。结果表明人工岛建设后,该海岸西段人工岛与陆地之间海域波浪场明显减弱,而沿岸流则由人工岛建设前的自东向西,变为人工岛建设后后两股沿岸流在岛体后方相汇,利于此处泥沙堆积。通过岸线变化分析,人工岛建设之后西段岸线受人工岛的遮蔽由侵蚀转变为淤积,最大淤积速率可达70m/a,形成现在向海凸出沙嘴,最终将演化为连岛沙坝,东段岸线接受不到岛体的庇护则仍表现为侵蚀状态。     

波浪在有平台的斜坡上的爬高

本文在海堤模型试验研究的基础上,分析了平台宽度和平台高程对波浪爬高的影响,得出了具有平台斜坡上波浪爬高的经验计算式。     

Linear irregular wave generation in a numerical wave tank

In the design of any floating or fixed marine structure, it is vital to test models in order to understand the fluid/structure interaction involved. A relatively inexpensive method, compared to physical model testing, of achieving this is to numerically model the structure and the wave conditions in a numerical wave tank. In this paper, a methodology for accurately replicating measured ocean waves in a numerical model at full scale is detailed. A Fourier analysis of the measured record allows the wave to be defined as a summation of linear waves and, therefore, Airy's linear wave theory may be used to input the wave elevation and associated water particle velocities. Furthermore, a structure is introduced into the model to display the ability of the model to accurately predict wave–structure interaction. A case study of three individual measured waves, which are recorded at the Atlantic marine energy test site, off the west coast of Ireland, is also presented. The accuracy of the model to replicate the measured waves and perform wave–structure interaction is found to be very high. Additionally, the absolute water particle velocity profile below the wave from the numerical model is compared to a filtered analytical approximation of the measured wave at a number of time-steps and is in very good agreement.     

Reflection and diffraction of internal solitary waves by a circular island

We have investigated the reflection and diffraction of first-mode and second-mode solitary waves by an island, using a three-dimensional nonhydrostatic numerical model. The model domain consists of a circular island 15 km in diameter in an ocean 300 m deep. We use prescribed density anomalies in an initially motionless ocean to produce highly energetic internal solitary waves; their subsequent propagation is subject to island perturbations with and without the effect of earth’s rotation. In addition to reflected waves, two wave branches pass around the island and reconnect behind it. Island perturbations to the first-mode and second-mode waves are qualitatively similar, but the latter is more profound because of the longer contact time and, in the presence of earth’s rotation, the scale compatibility between Rossby radius of the second baroclinic mode and the island diameter. Without earth’s rotation, reflected and diffracted waves are symmetrical relative to the longitudinal axis passing through the island center. With earth’s rotation, the current following the wave front veers to the right due to Coriolis deflection. For a westward propagating incoming wave, the deflection favors northward wave propagation in the region between the crossover point and the island, shifting the wave reconnection point behind the island northward. It also displaces the most visible part of the reflected waves to the southeast. In the presence of earth’s rotation, a second-mode incoming wave produces island-trapped internal Kelvin waves, which are visible after the passage of the wave front.     

Simulation of Random Waves and Associated Laminar Bottom Shear Stresses

This work presents a new approach for simulating the random waves in viscous fluids and the associated bottom shear stresses. By generating the incident random waves in a numerical wave flume and solving the unsteady two-dimensional Navier-Stokes equations and the fully nonlinear free surface boundaiy conditions for the fluid flows in the flume, the viscous flows and laminar bottom shear stresses induced by random waves axe determined. The deterministic spectral amplitude method implemented by use of the fast Fourier transform algorithm was adopted to generate the incident random waves. The accuracy of the numerical scheme is confirmed by comparing the predicted wave spectrum with the target spectrum and by comparing the nanlerical transfer function between the shear stress and the surface elevation with the theoretical transfer function. The maximum bottom shear stress caused by random waves, computed by this wave model, is compared with that obtained by Myrhaug＇ s model （1995）. The transfer function method is also employed to determine the maximum shear stress, and is proved accurate.     

An Irregular Wave Maker of Active Absorption with VOF Method

A numerical irregular wave flume with active absorption of re-reflected waves is simulated by use of volume of fluid （VOF） method. An active ＇absorbing wave-maker based on linear wave theory is set on the left boundary of the wave flume. The progressive waves and the absorbing waves are generated simultaneously at the active wave generating-absorbing boundary. The absorbing waves are generated to eliminate the waves coming back to the generating boundary due to reflection from the outflow boundary and the structures. SIRW method proposed by Frigaard and Brorsen （1995） is used to separate the incident waves and reflected waves. The digital filters are designed based on the surface elevation signals of the two wave gauges. The corrected velocity of the wave-maker paddle is the output from the digital filter in real time. The numerical results of regular and irregular waves by the active absorbing-generating boundary are compared with the numerical results by the ordinary generating boundary to verify the performance of the active absorbing-generator boundary. The differences between the initial incident waves and the estimated incident waves are analyzed.     

潜堤后高阶自由谐波的研究

基于高阶边界元方法的完全非线性数值水槽模型模拟潜堤地形上波浪的传播变形,通过与实验值进行比较,考察数学模型的正确性.采用两点法分离得到堤后高倍频自由波来研究入射波参数、水深对堤后高倍频自由波的影响.研究发现:基频波、二阶和三阶自由波幅值分别与入射波波幅成线性、二次和三次函数关系,基频波幅值基本不随波浪周期变化,而二阶和...     

Tests and Applications of An Approach to Absorbing Reflected Waves Towards Incident Boundary

If the upstream boundary conditions are prescribed based on the incident wave only, the time-dependent numerical models cannot effectively simulate the wave field when the physical or spurious reflected waves become significant. This paper describes carefully an approach to specifying the incident wave boundary conditions combined with a set sponge layer to absorb the reflected waves towards the incident boundary. Incorporated into a time-dependent numerical model, whose governing equations are the Boussinesq-type ones, the effectiveness of the approach is studied in detail. The general boundary conditions, describing the down-wave boundary conditions are also generalized to the case of random waves. The numerical model is in detail examined. The test cases include both the normal one-dimensional incident regular or random waves and the two-dimensional oblique incident regular waves. The calculated results show that the present approach is effective on damping the reflected waves towards the incident wave boundary.     

Implementation and modification of a three-dimensional radiation stress formulation for surf zone and rip-current applications

Regional Ocean Modeling System (ROMS v 3.0), a three-dimensional numerical ocean model, was previously enhanced for shallow water applications by including wave-induced radiation stress forcing provided through coupling to wave propagation models (SWAN, REF/DIF). This enhancement made it suitable for surf zone applications as demonstrated using examples of obliquely incident waves on a planar beach and rip current formation in longshore bar trough morphology (Haas and Warner, 2009). In this contribution, we present an update to the coupled model which implements a wave roller model and also a modified method of the radiation stress term based on Mellor (2008, 2011a,b,in press) that includes a vertical distribution which better simulates non-conservative (i.e., wave breaking) processes and appears to be more appropriate for sigma coordinates in very shallow waters where wave breaking conditions dominate. The improvements of the modified model are shown through simulations of several cases that include: (a) obliquely incident spectral waves on a planar beach; (b) obliquely incident spectral waves on a natural barred beach (DUCK'94 experiment); (c) alongshore variable offshore wave forcing on a planar beach; (d) alongshore varying bathymetry with constant offshore wave forcing; and (e) nearshore barred morphology with rip-channels. Quantitative and qualitative comparisons to previous analytical, numerical, laboratory studies and field measurements show that the modified model replicates surf zone recirculation patterns (onshore drift at the surface and undertow at the bottom) more accurately than previous formulations based on radiation stress (Haas and Warner, 2009). The results of the model and test cases are further explored for identifying the forces operating in rip current development and the potential implication for sediment transport and rip channel development. Also, model analysis showed that rip current strength is higher when waves approach at angles of 5° to 10° in comparison to normally incident waves.     

Wave Forces Acting on Vertical Walls

Regular and irregular wave forces acting on vertical walls are studied by a previously developed numerical model. The computed wave forces are compared with the available experimental data to verify the numerical model, and satisfactory agreements are obtained. The variation of wave forces with incident angles and the shape of simultaneous pressure distribution are investigated, and the comparisons between numerical results and Goda＇ s predictions are also carried out. It is concluded that the maximum wave forces acting on the unit length of vertical wall is often induced by the obliquely incident waves instead of normally incident waves, while Goda＇ s formula may be inapplicable for oblique wave incidence. The shape of simultaneous pressure distribution is not significantly influenced by incident angles, and it can be favorably predicted by Goda＇ s formula. When regular wave heights are taken as the same as irregular wave height H1%, the irregular wave forces Ph. 1% are slightly larger than regular wave forces in most cases.