Interaction of waves with non-colinear currents

The present paper reports on a study of the interaction of a current-free monochromatic surface wave field with a wave-free uniform current field in a three-dimensional flow frame. The wave and the current fields are not necessarily collinear with each other. The formulation of the wave-current field is done under the assumption of irrotational and inviscid flow. We have developed the three dimensional expressions describing the characteristics of the combined flow in terms of mass, momentum and energy transport conservation. These equations are found efficient to describe the sought-for combined wave-current field. The parameters describing the wave-current field after the interaction are the surface disturbance amplitude and length, mean water depth, mean current-like parameter and direction of the combined flow, which would be calculated from a set of equations that satisfy conservation of mean mass, momentum and energy flux and a dispersion relation on the free surface before and after the interaction. The results are shown in terms of relative changes in wave heights and lengths, current-like parameters and final directions obtained for the combined wave-current field with respect to current-free wave and wave-free current pre-interaction parameters.     

Effect of vertically logarithmic steady currents on shallow surface waves

The combined wave-current flow has been solved by researchers by assuming wave over either depthwise constant or linear current profile. Some complicated nonlinear current profiles have also been considered to simulate various shear currents. We consider a nonlinear current vertically logarithmic in nature and examine its interaction with a periodic surface wave. The Navier-Stokes equations for incompressible flow are solved for the current part and by using periodic boundary conditions. The effect of logarithmic current on wave components is assessed. The corresponding celerity and dispersion equation yields a close-form solution for the shallow-wave approximation. Several comparative trends between wave-only, wave with log current, and wave with constant current for the wave following/opposing these currents have been discussed. The flow properties of the first order are presented which can be applicable to the real inland and coastal flows, where progressive waves are ubiquitous over a depthwise logarithmic current. The work is further extended to the second-order semiempirical wave component by using past experimental data on the wave spectrum of combined flow. Published in Morskoi Gidrofizicheskii Zhurnal, No. 3, pp. 20–40, May–June, 2008.     

波流共同作用下海底人工边坡动态响应分析

为了研究波流共同荷载作用下开挖基槽附近海床动态响应和液化破坏情况,提出一个二维耦合计算模型,采用雷诺时均纳维-斯托克斯（RANS）方程描述波浪运动情况,通过设定侧边界条件实现稳定流场。海床部分通过求解Biot固结方程,得到波流荷载下海床中的应力和位移情况。将模型计算结果与水槽试验数据和解析解进行比较,验证了波流模型和海床模型的有效性。在此模型基础上,分析得到了开挖之后海床新的应力和固结状态。同时,通过参数分析得到了波流耦合情况下波浪形态的变化,以及海流对海床液化情况和孔压情况的影响。最后,通过线性回归计算得到最大液化深度与流速的拟合关系曲线。计算结果可用于判断基槽开挖后不规则海床的液化情况,对相关研究和实际工程具有一定参考意义。     

长兴岛海区波流相互作用数值模拟研究

波和流是近岸海区的主要动力因素。应用二维潮流数学模型和最新第三代近岸海浪模式SWAN,建立了非结构网格下二维情况近岸波流耦合作用数学模型。时间离散采用欧拉向前格式,空间离散采用有限体积法显式格式。通过将波浪场及潮流场进行迭代耦合计算,实现了对波流共同作用下波浪场和潮流场的数值模拟。将模型应用于矩形海湾实验和李孟国数模实验等理想地形以及大连长兴岛海区实际复杂地形算例,并用现场实测资料对计算结果进行验证,结果表明:耦合结果与实测结果吻合良好,并且要优于未耦合的结果。     

西北太平洋浪流相互作用对有效波高的影响研究

西北太平洋强流区会对海浪的特征和分布产生显著的影响,尤其是研究台风过程中海流与海浪的相互作用具有重要的研究意义。本文以ROMS海洋模式和SWAN海浪模式为基础,构建了浪流耦合模式系统,对2013年10月6-17日间的台风“丹娜丝”、“百合”、“韦帕”过程中西北太平洋浪流相互作用中海流对有效波高的影响进行了研究。通过对比模式模拟有效波高与浮标观测资料,发现耦合后的有效波高比非耦合结果更接近观测值,耦合模式中海流的存在对有效波高的分布有明显的影响。研究表明,特别是在有效波高峰值处,海流引起的有效波高增大最大可达1 m。海浪浪向及流向的空间分布以及中国近海浮标处浪向与流向的时间序列表明,流向与浪向反向时,海流的影响造成有效波高增大;二者同向时,有效波高减小。海流对有效波高的调整会沿着海浪传播的方向传播相当一段距离。在西北太平洋的海浪场计算中,引入海流的耦合模式计算结果对改善强流区海浪预报具有重要意义,并且海流的模拟精度对于高精度的海浪预报非常重要。     

波-流联合作用场中流的等效作用研究

针对波-流相互作用问题中的流速沿水深非线性分布的水流处理方法问题,提出了“等效均匀流”概念和相应理论,使非线性分布的水流作用等效为相应的均匀流作用,从而使问题大大简化.无论是二维顺、逆流问题还是三维波一流斜交折射问题,非均匀流都可以基于本文方法和理论予以近似处理,以采用等效均匀流概念计算的小尺度垂直桩桩的波一流联合作用力计算为例,对该理论和方法的应用作了初步的探讨和验证.     

Longitudinal dispersion in wave-current-vegetation flow

The flow, turbulence, and longitudinal dispersion in wave-current flow through submerged vegetation are experimentally examined. Laboratory experiments are carried out by superimposing progressive waves on a steady flow through simulated submerged vegetation. The resultant wave-current-vegetation interaction shows strong interface shear with increase in the velocity due to the wave-induced drift. The increase in turbulence in the region of vegetation is found to be about twice higher than in the no-wave case due to the additional mixing by wave motions. Solute experiments are conducted to quantify the wave-current-vegetation longitudinal dispersion coefficient (WCVLDC) by the routing method and by defining length and velocity scales for the wave-current-vegetation flow. An empirical expression for the WCVLDC is proposed. Although the increase in vertical diffusivity is observed as compared with bare-bed channels, the shear effect is stronger, which increases the value of the WCVLDC. The study can be a guideline to understand the combined hydrodynamics of waves, current, and vegetation and quantify the longitudinal dispersion therein. Published in Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 50–67, January–February, 2009.     

A simple analytical model for surface water waves on a depth-varying current

A perturbation analysis is presented in which a series of small amplitude regular waves co-exist with an arbitrarily sheared current, U(z). Assuming that the current velocity is weak, i.e. U(z)/c=O(ε), the solution is extended to O(ε²), where c is the phase velocity and ε=ak the wave steepness. This provides a first approximation to the non-linear wave-current interaction, and allows simple explicit solutions for both the modified dispersion relation and the water-particle kinematics to be derived. These solutions differ from the existing irrotational models commonly used in design and, in particular, highlight the importance of the near-surface vorticity distribution. These results are shown to be in good agreement with laboratory data provided by Swan et. al. [J. Fluid Mech (2001, in press)]. Perhaps more surprisingly, good agreement is also achieved in a number of strongly non-linear wave-current combinations, where the results of the present analytical solution are compared with a fully non-linear numerical wave-current model.     

浪、潮、风暴潮联合作用下的底应力效应

运用建立的二维非线性浪,潮和风暴耦全模式分析了波流相互作用下的底应力及其对耦合波浪场和流场的影响。由渤海的两次强寒潮过程的数值实验表明,在波流相互作用下,底应力明显增大,增大的底应力对波浪场影响甚微,但将明显改变水位和流速的大小,这种影响在近岸浅水区更加显著。     

波浪对潮流能水轮机性能测试影响的实验研究

随着潮流能开发利用技术日趋成熟,对其测试工作也提出了更高的要求。然而,在潮流能装置性能测试中,波流相互作用的影响往往被忽略,导致测试结果不准确。为了研究波流相互作用对测试的影响方式与程度,采用物理模型试验的方法,对垂直轴潮流能发电装置模型进行了试验研究。通过分析波流作用下装置的扭矩、转速及发电功率,发现波流与发电装置耦合作用明显,相比不存在波浪影响的情况下,叶轮的转动、主轴的扭矩都变得不规则,启动流速变小,同时,扭矩、转速及发电功率的瞬时值显著增大。测试结果表明,波流相互作用对装置性能测试影响显著,平均影响程度约10%,研究结果为今后潮流能发电装置性能测试标准的制定和完善提供了参考和依据。     

大尺度圆柱墩群周围的波流场的数值模拟

本文对波流共同作用下大尺度圆柱墩群周围的波流场进行了数值研究。利用波浪弥散关系的迭代计算求得波向与流向的夹角以及波浪的相对频率。流场通过求解浅水环流方程得到,波浪场通过求解含流的缓坡方程得到,通过二者的迭代计算得到大尺度圆柱墩群周围的波流场的耦合解。用有限元法建立了数值模型,并将本文的计算数据与试验数据以及其他学者计算数据进行了比较,结果较为合理。     

Numerical study of wave and longshore current interaction

Wave and longshore current interaction was examined based on the numerical models.In these models,water waves in the presence of longshore currents were modeled by parabolic mild slope equation,and wave breaking induced longshore currents were modeled by shallow water equation.Water wave provided the radiation stress gradients to drive current.Wave and longshore current interactions were considered by cycling the wave and longshore current models to a steady state.The experiments for regular and irregular breaking wave induced longshore currents by Hamilton and Ebersole（2001） and Reniers and Battjes（1997） were simulated.The numerical results indicate that the present models are effective for simulating the interaction of wave and breaking wave induced longshore currents,and the numerically simulated longshore current at wave breaking point considering wave and longshore current interaction show some disagreement with those neglecting the wave-current interaction,and the breaking wave induced longshore current effect on wave transformation is not obvious.     

港珠澳大桥青州航道桥桥墩基础冲刷试验研究

桥墩基础冲刷是桥梁毁坏的重要因素,是桥梁基础设计的关键指标之一。目前国内外对于桥墩基础在复杂动力条件下冲刷深度的研究常采用物理模型试验方法,利用正态系列模型方法,在波流水槽中研究了水流、潮流和波流共同作用下青州航道桥索塔基础周围流态变化和局部冲刷特征。研究结果表明,桥墩最大冲刷深度和冲淤范围与水流流速、桥墩轴线与水流夹角和波浪等因素有关;在潮流最大流速和恒定流流速一致情况下,桥墩局部冲刷深度达到平衡后,将会达到与恒定流基本一致的最大冲深;波流共同作用下的最大冲刷深度比恒定流增加10%左右。设计桥墩形状在100年一遇水流和波浪共同作用下桥墩基础局部最大冲刷深度为13.7 m。     

黄河三角洲区域的波流相互作用数值分析

将三维水动力-生态模式COHERENS与第三代波浪模式SWAN结合起来,采用该耦合模式数值计算了黄河三角洲的波浪特征波高与特征周期情况,从而探讨水流和波动水位对波浪特征波高和特征周期计算结果的影响。总的说来特征波高、特征周期、流速的计算结果与观测值吻合得较好,说明了COHERENS模式和SWAN模式相结合而成的波流耦合模式能够较好地计算黄河三角洲地区的流场与浪场情况。研究这些动力因素的机制和时空变化规律,对于研究海岸、河口的泥沙运动,海岸侵蚀的机理,合理开发利用自然资源,防止海洋灾害具有十分重大的意义。     

Forces on a single pile caisson in breaking waves and current

The effect of breaking and steep non-breaking waves on a vertical pile such as found in minimal caisson structures in the Gulf of Mexico shallow water environment was studied in a wave tank testing. The waves generated were both regular and irregular. The irregular waves were of Bretschneider type. In some tests current was combined in the direction of waves. Specially steep waves in the recorded wave profile were chosen for the analysis of wave forces. It was observed that the forces on the caisson at the wave frequency due to breaking waves were no higher in general than those in nonbreaking steep waves. The drag coefficients in waves alone were much higher than those in a combined wave-current field. The wave-current drag coefficients approached those found in the steady current alone.     

内波对风浪中短波波面斜率分布的影响

在小风速条件下,分层水中,水下运动物体所产生的内波,通过改变表面流场,使得风浪中的短波波面斜率分布发生了改变。由此,可以通过观察表面风浪中短波波面斜率分布的变化,识别出水下运动物体的移动轨迹     

波流联合作用下深水铰接塔平台的组合共振

研究了深水铰接塔平台在波流联合作用下的组合共振特性。将平台顶部工作单元简化为集中质量,塔柱和浮力仓简化为均匀直杆,建立了铰接塔平台运动分析模型。考虑海流和波浪对平台的作用,应用Morison公式计算铰接塔平台瞬时位置所受水动力,依据拉格朗日原理建立了铰接塔平台的强非线性运动方程。分别考虑波浪作用和波流联合作用,采用数值计算方法,计算了高400m、塔柱直径15m的浮力塔平台的多种组合共振响应。研究表明,波浪作用下平台将出现2vm＋vn组合共振,波流联合作用下平台将出现vm＋vn组合共振、2vm＋vn组合共振。     

Short-term variations and influencing factors of suspended sediment concentrations at the Heisha Beach,Guangdong, China

Knowledge of sediment variation processes is essential to understand the evolution mechanism of beach morphology changes. Thus, a field measurement was conducted at the Heisha Beach, located on the west coast of the Zhujiang River(Pearl River) Estuary, to investigate the short-term variation in suspended sediment concentrations(SSCs) and the relationship between the SSC and turbulent kinetic energy, bottom shear stress(BSS), and relative wave height. Based on extreme event analysis results, extr...     

A swell model of the German Bight

A numerical model is presented, which investigates the contribution of wave-induced currents to the tidal residual circulation in the German Bight. The momentum transfer, by swell decaying to the mean circulation, is calculated including wave-current interaction without refraction. The model couples deep-water and shallow-water energy dissipation mechanisms such as wave attenuation and wave breaking. The model computes wave set-up, wave set-down and a longshore current as well. The pure wave-induced circulation is calculated, and also the residual circulation due to the interaction between waves and tide. The results suggest that the wave-induced currents can be neglected for the calculation of transport of near-surface pollutants.     

CALCULATION OF WAVE-CURRENT FORCE ON ISOLATED PILE

By means of photography the author has investigated the mechanism of wave and current motion to measure simultaneously orbital path, velocity and acceleration of water particles. This new experimental system consists of a camera, a special light source, an intermittent exposure unit and a chemical liquid tracer.On the basis of theoretical analysis of combined effects of current and wave and the results of experiments, a model of total wave and current velocity is provided to calculate wave-current forces on a pile according to Morison's Formula. The calculated results from three different sets of wave and current data have been compared with experimental data and they are found in excellent agreement.