波浪要素对水平圆柱杆件水动力系数影响研究

通过试验研究了波浪要素对水平固定圆柱杆件水动力系数的影响。试验利用垂直杠杆原理,提取了杆件在波浪下的水平受力历时曲线,基于改造的莫里森方程,计算了不同波浪要素下的水动力系数C_D和C_M取值。定义分析了新的波高参数KH,周期参数KT和雷诺数Re对水动力系数的影响。研究表明,整体拟合法与四点拟合法获得的水动力系数在数值上差异不大。KH、KT及Re均对水动力系数的取值有较显著影响:1)随着波高KH的增大,C_D、C_M整体呈幂指数衰减,且C_M的衰减更为迅速;2)随着波周期KT的增大,C_D、C_M整体亦呈衰减趋势;3)相同波高条件下,C_M随Re数增大而增大,而C_D值相对稳定。最后给出了波浪条件下水动力系数C_D和C_M的经验计算公式。     

波浪作用下中上层浮鱼礁动力响应数值模型建立方法

人工浮鱼礁型式多样，适应水深范围广，优化锚泊方式可规模化建设浮鱼礁群，是海洋中上层生境构建的重要手段。中上层浮鱼礁投放于近海，属于海岸工程范畴，抗浪性能是其结构设计的关键。根据有限单元法和集中质量点法，详细阐述和推导了中上层浮鱼礁各构成组件连接位置处点或单元的相互耦合受力和运动处理方法，以及浮鱼礁出水条件的判别方法和水质点速度、加速度的修正方法。建立的波浪作用下三维浮鱼礁动力响应数值模型与其在波浪水槽中的物理模型试验对比，验证了数值模型的正确性。最后建立了一种新型锚泊方式的浮鱼礁动力响应数值模型，分析了浮鱼礁摆动角度、锚绳拉力、网衣系缚点总拉力的历时变化。研究结果可为中上层浮鱼礁优化结构形状和搭配浮体、配重提供判断依据。     

基于单方向阻尼源项的数值消波方法

采用边界条件造波法与人工阻尼消波法开展波浪数值模拟时,存在自由面抬升现象,导致波浪模拟精度略有损失。为解决上述问题,提出了一种基于单方向阻尼源项的数值消波方法,通过采用VOF模型在大、小两种波陡条件下开展波浪数值模拟进行了验证,并进一步研究了阻尼系数与密度依赖性对波浪模拟精度的影响。结果表明,单方向阻尼源项能够显著降低平均自由面高度,有效抑制平均自由面抬升,进而提高波浪模拟精度。阻尼系数及密度依赖性的优取值与波陡条件有关,且阻尼系数的影响大于密度依赖性。     

礁坪上波浪传播的数值模拟

本文基于具备间断捕捉能力的二阶全非线性Boussinesq数值模型,对规则波和随机波在礁坪地形上的传播变形进行了数值模拟。该模型采用高阶有限体积法和有限差分方法求解守恒格式的控制方程,将波浪破碎视为间断,同时采用静态重构技术处理了海岸动边界问题。重点针对礁坪上波浪传播过程中的波高空间分布和沿程衰减,礁坪上的平均水位变化,以及波浪能量频谱的移动和空间差异等典型水动力现象开展数值计算。将数值结果与实验结果对比,两者吻合情况良好,验证了模型具有良好的稳定性,具备模拟破碎波浪和海-岸动边界的能力,能较为准确地模拟波浪在礁坪地形上的传播过程中发生的各种水动力现象。     

浅水浮式风机基础水动力特性及波浪荷载的CFD数值分析

采用计算流体动力学(CFD)方法对OC4-DeepCwind半潜式风机基础在30～100 m水深下的水动力特性和非线性波浪荷载进行了研究。基于验证的数值波浪水池,通过结构自由衰减运动及规则波下浮式基础的幅值响应算子(RAO)计算,分析了浮式风机基础的结构动力特性及水动力特性随水深的变化规律,研究了浅水条件下非线性波浪荷载特征。研究结果表明,随着水深的减小,风机基础结构垂荡固有周期略有增大,垂荡和纵摇的阻尼比均呈现逐渐增大的趋势;与黏性流理论计算结果相比,势流结果在浅水波浪工况下对垂荡和纵摇RAO存在显著低估;在浅水波浪作用下,风机基础所受波浪荷载的三倍波频成分占比可超过5%,体现了浅水条件下波浪与结构之间较强的非线性作用。     

波浪增减水的实用数学模型及其数值模拟

提出了一种模拟近岸区波浪增减水的实用数学模型.首先采用考虑波能损失的抛物型缓坡方程数值模拟波浪破碎引起的波浪复振幅变化,接着根据计算得到的波浪复振幅,采用一种新的辐射应力公式计算辐射应力分量,然后采用深度平均方程计算波浪破碎产生的增减水.采用该模型对规则波和不规则波破碎引起的增减水进行了数值模拟,数值模拟结果与实验结果吻合良好,表明该模型可有效模拟近岸区由于波浪破碎引起的增减水.     

基于SPH-ALE方法的浮力摆水动力数值模拟

基于光滑粒子流体动力学-任意拉格朗日欧拉(SPH-ALE)方法建立二维数值波浪水槽,在控制方程中引入近似黎曼解替代人工黏性,采用排斥力边界条件防止流体粒子穿透固边界,采用指数型衰减函数设置海绵层以消除水槽末端的波浪反射。应用所建立的数值模型对规则波传播及其与浮力摆摆板的相互作用进行了水动力数值模拟,结果表明:文中SPH-ALE模型能够较精确地模拟波浪传播,合理地复现波浪与浮力摆摆板相互作用的物理过程。     

作用于小尺度方柱上的正向波浪力

基于扩展的Morison方程和实验研究,深入分析了方柱在波浪(规则波及随机波)与水流场中的正向力受力特性,并对其水动力系数C_d及C_m随KC数和方柱迎浪方向变化的关系进行了详细的探讨,有关成果对工程实际有参考价值。     

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。     

考虑植物影响的波浪和波生流迭加条件下水动力特性数值模拟研究

海岸湿地是近海地区重要的生态系统,由于潮流、波浪尤其是非连续水流与植被的相互作用,导致该海域的水动力环境复杂多变。本文发展了一个深度平均二维波流耦合数学模型,模拟湿地海域波浪和波生沿岸流的运动特性。水动力模型中植物拖曳力作为源项放入动量方程中,在波浪作用量平衡方程增加波能耗散项用于解释水生植物对波浪产生的阻力作用。在动态耦合模型中,波浪模型为潮流模型提供波浪辐射应力、波高、波浪周期等数据信息,潮流模型为波浪模型提供计算的水位和流速,可以达到双向动态耦合。本文发展的波流耦合模型通过三个实验室试验数据加以验证,计算结果和实验数据吻合较好,在波浪、波生流和植物迭加条件下,所建模型能够有效地模拟波浪、沿岸流等不同现象。     

基于类海啸波型的岛礁水动力特性数值模拟研究

基于非静压单相流模型NHWAVE建立了高精度二维数值波浪水槽,采用日本2011年实测真实海啸波型系统研究了海啸波在岛礁上传播变形的规律,并且分析了波高、礁坪淹没水深和礁前斜坡坡度等因素对孤立波和真实海啸传播变形的影响。结果表明,相比孤立波,类海啸波的波长明显大于孤立波波长,在测点处引起的水面变化持续时间更长,同等波高情况下真实海啸波型比孤立波能够携带更多的能量,与岛礁的相互作用也更为复杂,在礁坪上形成的淹没水深约为孤立波的两倍。礁前斜坡坡度和礁坪淹没水深均对类海啸波的反射和透射系数有显著影响。随着礁前斜坡坡度的增加,反射系数和透射系数均逐渐增加。随着礁坪淹没水深的增加,反射系数逐渐减小,而透射系数逐渐增大。但是,反射系数和透射系数均随着入射波高的增加而逐渐减小。     

Study of irregular wave run-up over fringing reefs based on a shock-capturing Boussinesq model

This paper presents the results of a parametric study of irregular wave run-up over fringing reefs using the shock-capturing Boussinesq wave model Funwave-TVD to better understand the role of fringing reefs in the mitigation of wave-driven flooding. Laboratory experiments were newly performed with a typical fringing reef profile and typical hydrodynamic conditions to validate the model. Experimental data shows irregular wave run-ups are dominated by the low-frequency motions and confirms the run-up resonant phenomenon over the back-reef slope, which has been revealed in previous numerical studies. It is demonstrated that irregular wave evolution and run-up over fringing reefs are reasonably reproduced by the present model with a proper grid size. However, the infragravity run-up height and highest 2% run-up height over the back-reef slope are under-predicted due to the underestimation of the infragravity wave height over the reef flat. The validated model was then utilized to model irregular wave transformations and run-ups under different conditions. Through a series of numerical experiments, the effects of key hydrodynamic and reef geometry parameters, including the reef flat width, water depth over the reef flat, fore-reef slope angle and back-reef slope angle, on the irregular wave run-up were investigated. Variations of spectral components of irregular wave run-ups were examined to better understand the physical process underlying the effect of each parameter.     

Numerical investigation of tsunami-like wave hydrodynamic characteristics and its comparison with solitary wave

Solitary waves have been commonly used as an initial condition in the experimental and numerical modelling of tsunamis for decades. However, the main component of a tsunami waves acts at completely different spatial and temporal scales than solitary waves. Thus, use of solitary waves as approximation of a tsunami wave may not yield realistic model results, especially in the coastal region where the shoaling effect restrains the development of the tsunami wave. Alternatively, N-shaped waves may be used to give a more realistic approximation of the tsunami wave profile. Based on the superposition of the sech²(*) waves, the observed tsunami wave profile could be approximated with the N-shaped wave method, and this paper presents numerical simulation results based on the tsunami-like wave generated based on the observed tsunami wave profile measured in the Tohoku tsunami. This tsunami-like wave was numerically generated with an internal wave source method based on the two-phase incompressible flow model with a Volume of Fluid (VOF) method to capture the free surface, and a finite volume scheme was used to solve all the governing equations. The model is first validated for the case of a solitary wave propagating within a straight channel, by comparing its analytical solutions to model results. Further, model comparisons between the solitary and tsunami-like wave are then made for (a) the simulation of wave run-up on shore and (b) wave transport over breakwater. Comparisons show that use of these largely different waveform shapes as inputs produces significant differences in overall wave evolution, hydrodynamic load characteristics as well as velocity and vortex fields. Further, it was found that the solitary wave uses underestimated the total energy and hence underestimated the run-up distance.     

基于格子Boltzmann方法的斜坡堤越浪数值模拟研究

准确确定越浪量对于斜坡堤设计有重要意义。利用格子Boltzmann方法(LBM),并采用主动吸收式速度入口造波、出流边界消波、VOF方法追踪自由表面以及静态Smagorinsky模型模拟紊流运动,建立二维数值波浪水槽,对光滑斜坡堤上规则波与不规则波越浪进行数值模拟。模拟结果与试验值及其他数值模型结果比较表明,二维LBM数值波浪水槽具有模拟斜坡堤越浪的能力,但对于破碎较为剧烈的越浪过程模拟,该模型还存在一定的不足,未来可从提高自由表面模型精度等方面进一步改善其性能。     

聚焦波作用下平面网衣结构的水动力特性研究

由于沿海区域的限制以及愈加严重的环境污染,渔业养殖正从近海走向深远海。深远海海域的海况更加恶劣,给养殖装备的设计与性能评估带来新的挑战。为解决该问题,对极端波浪与养殖装备网衣结构的相互作用开展研究。基于waves2Foam建立数值波浪水池,极端波浪模拟采用基于NewWave理论的聚焦波模型,网衣结构模拟采用多孔介质模型,并通过与Morison模型计算的网衣受力等效分析,获得多孔介质模拟网衣结构阻力系数的直接估计方法。然后将多孔介质模型嵌入waves2Foam中,开展聚焦波与网衣结构相互作用的数值模拟,同时开展水槽试验,验证数值模拟的准确性。基于数值模拟结果,系统地分析了不同网衣密实度及不同波浪参数下网衣结构的升阻力特性以及网衣结构对波浪场的扰动规律。研究表明：聚焦波波峰幅值和网衣密实度对网衣结构的升阻力影响较大,且升力峰值出现在阻力为0的时刻;网衣结构对聚焦波的时空演化特性有影响,改变了聚焦波波形。     

Solitary wave interactions with an array of two vertical cylinders

This paper addresses a numerical investigation of nonlinear waves interactions with an array of two surface-piercing vertical cylinders and the corresponding nonlinear hydrodynamic loads on each individual cylinder. The primary interest of this study is concentrated on the problem of three-dimensional scattering of solitary waves by cylinder arrays and the nonlinear interactions between scattered waves. The theoretical model adopted for simulation is the generalized Boussinesq two-equation model. The boundary-fitted coordinate transformation and multiple-grid technique are utilized here to simplify the computation domain and to facilitate the applications of the boundary conditions on the cylinder surfaces. The velocity potential, free-surface elevation and subsequent evolution of the scattered wave field are numerically evaluated. The hydrodynamic forces on each cylinder during wave impact are also determined. A study of the sheltering effect by the neighboring structures on wave loads is conducted. It is found that the presence of the neighboring cylinder has shown significant influence on the wave loads and the scattering of the primary incident waves. For two transversely arranged cylinders, the transverse force coefficient increases as the separation distance decreases.     

圆形数值波浪水池斜向和多向入射波浪模拟研究

为了研究斜向入射波浪,基于三维不可压缩两相流模型,开发了一套圆形数值波浪水池数值模型。在圆形波浪水池中,通过源项造波法成功生成了任意入射方向的波浪,并且利用人工摩擦项模拟阻尼区以数值耗散反射波浪。模型基于嵌入式多块网格体系,采用FVM法(finite volume method)离散Navier-Stokes方程,VOF法(volume of fluid)追踪自由水面。试验结果表明,斜向入射波浪的模拟结果与理论值基本一致,圆形波浪水池在模拟斜向入射波浪时,有效区域的面积较传统波浪水池显著增大,而且有效区域受波浪入射角度的影响也较小。同时,通过叠加多列斜向入射波浪,模拟出了多向交叉波列,并通过与理论结果对比,发现其具有较高的精度。     

Application of VOF in Calculating Wave Energy Loss due to Spilling Breaker

- A large amount of experimental analysis and systematical theoretical calculation has been done by the authors to solve the problem of wave transformation and breaking, considering the effect of both current and topography, but only the wave energy loss due to spilling breaker in the surf zone has been discussed in this paper. Based on test result analysis and calculation with the Stream Function Wave Theory, the wave velocity field at breaking points has been obtained, and it is used to calculate the wave heights after breaking by the VOF (Volume of Fluid) method, in which the governing equations are continuity equation and Navier-Stokes Equation for imcompressible fluids. In the present paper, the improved VOF technique is used to calculate the wave heights of stable regular waves after breaking. Results fit the test data well, which shows that the VOF method is suitable to numerical simulation of regular waves after breaking. Besides, the breaker coefficient B of regular waves in the bore model is a