SENSITIVITY STUDY OF THE EFFECTS OF WAVE-INDUCED VERTICAL MIXING ON VERTICAL EXCHANGE PROCESSES

The hydrodynamic model COHERENS-SED, developed by the present authors through introducing wave-enhanced bottom stress, wave dependent surface drag coefficient, wave-induced surface mixing, SWAN to COHERENS, is modified to account for wave-induced vertical mixing. The COHERENS-SED model can also be used for one-dimensional, two-dimensional, three-dimensional current and salinity calculations. One-dimensional model and three-dimensional model are used to study the effects of the wave-induced vertical mixing. The horizontal current velocity profiles obtained by the model are in good agreement with the analytical velocity profiles under the same input conditions. Numerical results show that higher wave height would generally generate larger vertical eddy viscosity and lower horizontal velocity. The results for fresh water in Yellow River Delta show that the wave-induced vertical mixing increases the momentum of fresh water transferring ability downwards to seabed and salt water's mixing with upper fresh water. Fresh water flume length is compressed considerably.     

波浪辐射应力理论的应用和研究进展

回顾波浪辐射应力张量的概念，前人的研究成果表明微幅波的辐射应力理论是符合实际的．综述波浪辐射应力理论在海洋流体动力学中的应用，分析该理论在研究近岸流的形成、波浪增水和波浪减水、沿岸流流速的沿程分布、破波带内底部反向流的速度分布、河口海岸泥沙运动、海岸碎波拍和波流相互作用等问题中的应用．总结波浪辐射应力的研究进展，包括考虑有限振幅波和不规则波的辐射应力场以及微幅波辐射应力张量沿水深分布的研究，指出辐射应力张量沿水深分布的研究可以为探讨近岸水动力环境的垂直结构以及完善波流相互作用三维数学模型提供理论基础．为深入考察波浪辐射应力张量沿水深分布情况，提出进一步研究的思路．     

Three-dimensional unstructured modelling of wave-induced circulation over a plane and irregular beach

Nearshore currents have a complicated circulation structure over a beach due to the mutual interaction between waves and currents. To investigate the wave-induced circulation over a beach, a three-dimensional unstructured model accounting for the combined actions of waves and currents is established. The wave distribution over the beach is computed by a wave model and the depth-dependent wave radiation stresses with the surface roller are employed in the hydrodynamic model. The present model takes the mixing coefficients and the bottom shear stress under waves and currents into account. To evaluate the three-dimensional unstructured model, the laboratory experiments over a plane and irregular beach are used to test the performance of the model. The undertow over a plane beach is well reproduced and the vertical variability is captured. The performance of the model over an irregular beach is well displayed in the reproduction of pairs of counter-rotating primary circulations at the embayment troughs. Meanwhile, the secondary circulations are observed in the swash zone. The model captures the circulation systems over a beach and the circulation structures of the wave-induced currents are well exhibited.     

Littoral drift by alongshore flow at Visakhapatnam – East Coast of India

The littoral drift in the surf zone of Visakhapatnam has been evaluated using simulated longshore current. In this study we examined littoral processes, driven by longshore currents using a set of numerical models (Mike-21 modeling system). Deepwater waves as they approach shallow water dissipate energy and the water from the broken waves flow parallel to the shoreline known as longshore current. In order to simulate the current from wave breaking, offshore wave data for the period 1995–2004, have been collected from British Meteorological Office (BMO), UK. Waves having an annual exceedance of 20% are allowed to propagate to nearshore using a nearshore spectral wind-wave model from predominant directions. The wave-induced radiation stress obtained from wave model then formed the basis for simulating the longshore current and associated sediment transport. The results of these simulations show the pattern of longshore flow and sedimentation. The net annual discharge at selected coastal stretches is estimated and presented. It has been inferred from the study that the sediment transport for the coast is of the order of 0.4–0.6 million m³/year.     

Study of wave induced radiation stress and vertical mixing in the Yellow River runoff diffusion

The purpose of this paper is to study the role of wave induced radiation stress and vertical mixing in the Yellow river runoff diffusion in vertical profile. Firstly, only using a hydrodynamical model to simulate river runoff at yellow river estuary area, and then using a coupled model also to simulate yellow river runoff by introducing vertically varied radiation stress or wave induced vertical mixing. Under condition of only tide existing, river runoff diffused far away from coastal near water surface. When considering vertically varied wave radiation stress, the velocity increased and river runoff flowed near estuary not go into the sea. When considering wave induced vertical mixing, the surface velocity decreased and the value of velocity became to be uniformed. So the function of radiation stress and vertical mixing induced by wave is different.

     

ANALYTICAL SOLUTION OF WAVE-INDUCED SEEPAGE PRESSURE ACTING ON THE BASE OF BREAKWATER

The wave loads acting on a breakwater resting on seabed include not only the waveforce from the wave field around the structure but also the wave-induced seepage pressure actingon the base of breakwater.The latter is also a circumstance load which can not be neglected inengineering design.This paper presents a closed-form analytical solution of wave-induced seep-age pressure acting on the base of breakwater resting on an infinite-depth porous elastic seabed.Based on the Biot's consolidation theory,the soil deformation and the compressibility of pore wa-ter are considered.The water wave pressure on sea bottom is determined by the linear waterwave theory.The numerical results of uplifting force and moment caused by the wave-inducedseepage pressure are given and the influences of soil deformation and pore water compressibilityon the calculation results are discussed.     

波浪作用下海床液化的数值分析

较大的风浪会使海床发生液化,波浪引起的海床液化问题是海岸及近海工程必须要考虑的关键问题之一。当海床内部土骨架的有效应力转移给孔隙水压力进而变为零时,土体将丧失剪切强度出现液化现象。基于Biot固结理论,利用软件FLAC,分析波浪作用下海床的动力响应,可推出波浪作用下海床最大液化深度,同时也可以得出波浪作用下海床液化的过程,即孔隙水压力上升、土层液化、液化后土层下沉压缩以及孔隙水压力消散,所得结果较好地反映了波浪作用下海床液化的规律。     

DISTRIBUTION OF WAVE-INDUCED EXCESS MOMENTUM FLUXES OVER DEPTH AND APPLICATION TO THREE-DIMENSIONAL NUMERICAL MODELING OF WAVE-CURRENT INTERACTIONS

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波-流共同作用下令仃洋三维盐度数值模拟

为了研究伶仃洋内盐度的输移运动规律,建立了三维斜压盐度数学模型。模型考虑了径流、潮流及波浪场作用下的盐度输运,波浪的影响通过三维辐射应力和波一流共同作用底应力反映。采用平面正交曲线坐标和垂向σ坐标对复杂边界和地形进行了较好的拟合,方程采用守恒有限差分法离散,并采用内外模式分裂技术求解,水平动量方程的求解采用了“预测”、“校正”相结合的方法以保证内外模式所求流速值的一致性。应用枯水期伶仃洋大规模同期实测的水位、流速和盐度资料对模型进行了验证,计算值与实测值吻合较好,表明了模型对伶仃洋水流、盐度运动规律模拟的可靠性。     

近岸波浪及沿岸流数值模拟研究

利用抛物型缓坡方程计算波浪场,并以波浪辐射应力为近岸动力因素,建立深度平均的二维近岸流的控制方程。运用该近岸流方程,对美国Santa Barbara Leadbetter海岸波浪斜向入射所产生的波浪场及波浪破碎所形成的沿岸流进了数值模拟,其中抛物型缓坡模型采用Crank-Nicolson格式进行数值离散,近岸流方程采用ADI差分格式离散。与现场实测资料的对比表明,无论考虑或不考虑波浪非线性因子,模拟结果与实测结果均吻合良好。     

波浪作用下缓坡近岸海域沿岸流分布影响因素分析

本文研究了均匀岸坡地形条件下．规则波及不规则波浪作用下缓坡近岸海域沿岸流的分布规律。采用数学模型与物理模型相结合，分析了波浪要素，地形坡度等因素对沿岸流分布的影响。提出了表征沿岸流分布特征参数的经验公式。研究结果表明，缓坡近岸海域，波浪作用下沿岸流的分布主要受到入射波浪波高、入射角度及地形坡度的影响。不规则波浪作用下沿岸流的速度分布相对平缓。     

波浪作用下淤泥质底床泥体输移

建立了用于模拟波浪运动的水体引起底床软泥层振荡并导致泥体输移的垂向二维数值模型。该水-泥模型中应用了一个半经验的非线性的淤泥流变模型,该流变模型表达了淤泥体在循环剪切外力(波浪)作用下其应变及应变率与应力关系的显著的滞后回线特征。数值处理技巧上,为提高数值格式对水-泥界面附近流动的分辨力,较好地再现界面附近速度梯度大的流动特点,垂向网格方法是在水-泥界面的两侧区域均采用对数网格。模型验证是通过计算水波波高衰减率和底床软泥体输移速度,并与有关的实验测量数据进行比较。     

Wave-induced flow and its influence on ridge erosion and channel deposition in Lanshayang channel of radial sand ridges

Very limited modeling studies were available of the wave-induced current under the complex hydrodynamic conditions in the South Yellow Sea Radial Sand Ridge area（SYSRSR）. Partly it is due to the difficulties in estimating the influence of the waveinduced current in this area. In this study, a coupled 3-D storm-surge-wave model is built. In this model, the time-dependent varying Collins coefficient with the water level method（TCL） are used. The wave-flow environment in the Lanshayang Channel（LSYC） during the ＂Winnie＂ typhoon is successfully represented by this model. According to the modelling results, at a high water level（HWL）, the wave-induced current similar to the long-shore current will emerge in the shallow area of the ridges, and has two different motion trends correlated with the morphological characteristics of the ridges. The wave-induced current velocity could be as strong as 1 m/s, which is at the same magnitude as the tidal current. This result is verified by the bathymetric changes in the LSYC during the ＂Matsa＂ typhoon. Thus, the wave-induced current may be one of the driven force of the ridge erosion and channel deposition in the SYSRSR. These conclusions will help to further study the mechanism of the ridge erosion and channel deposition in the SYSRSR.     

Application of SWAN+ADCIRC to tide-surge and wave simulation in Gulf of Maine during Patriot's Day storm

The southern coast of the Gulf of Maine in the United States is prone to flooding caused by nor'easters. A state-of-the-art fully-coupled model, the Simulating WAves Nearshore(SWAN) model with unstructured grids and the ADvanced CIRCulation(ADCIRC) model, was used to study the hydrodynamic response in the Gulf of Maine during the Patriot's Day storm of 2007, a notable example of nor'easters in this area. The model predictions agree well with the observed tide-surges and waves during this storm event. Waves and circulation in the Gulf of Maine were analyzed. The Georges Bank plays an important role in dissipating wave energy through the bottom friction when waves propagate over the bank from offshore to the inner gulf due to its shallow bathymetry. Wave energy dissipation results in decreasing significant wave height(SWH) in the cross-bank direction and wave radiation stress gradient, which in turn induces changes in currents. While the tidal currents are dominant over the Georges Bank and in the Bay of Fundy, the residual currents generated by the meteorological forcing and waves are significant over the Georges Bank and in the coastal area and can reach 0.3 m/s and 0.2 m/s, respectively. In the vicinity of the coast, the longshore current generated by the surface wind stress and wave radiation stress acting parallel to the coastline is inversely proportional to the water depth and will eventually be limited by the bottom friction. The storm surge level reaches 0.8 m along the western periphery of the Gulf of Maine while the wave set-up due to radiation stress variation reaches 0.2 m. Therefore, it is significant to coastal flooding.     

基于抛物型缓坡方程模拟近岸波流场

波浪向近岸传播的过程中由波浪破碎等效应所形成的近岸波流场是近岸缓坡区域重要的环境动力因素之一。本文基于近岸波浪传播的缓坡模型对近岸波浪场及近岸波浪斜向入射破碎后所产生的沿岸波流场进行了数值模拟。考虑到波浪向近岸传播中局部复杂区域波向不易确定，计算时直接从波浪辐射应力定义出发，采用抛物型缓坡方程所给出的辐射应力公式来计算波浪产生的辐射应力，在此基础上耦合近岸波流场数学模型对近岸波浪破碎形成的波流场进行了数值模拟研究，结果表明本文的数值模型是有效的。     

不规则波辐射应力的精确解与近似解

波浪辐射应力是波生沿岸流乃至近岸流的主要驱动力。波浪辐射应力的计算将直接关系到沿岸流的大小及其水动力特性。不规则波相对规则波更能反应实际海洋中的波浪运动,因此不规则波作用下辐射应力的计算将更能体现实际沿岸流中的波浪驱动力。通过推导给出不规则波辐射应力计算的精确解与近似解,并对两种计算方法进行了分析比较,在此基础上进一步用波生沿岸流试验结果对近似计算方法中的波能计算进行了验证。结果表明窄谱情况下,不规则波辐射应力的近似计算方法已有较好的精度,可节省大量的计算时间,从而提高计算效率,但精确计算方法更能准确反应各时刻各位置辐射应力的波动状况。     

Wave interaction with a floating rectangular box near a vertical wall with step type bottom topography

Diffraction of water waves by a floating structure near a wall with step type bottom topography is investigated under the two-dimensional small amplitude wave theory. Full solution of the problem under the potential flow approach is obtained by using the matched eigenfunction expansion method. The wave-induced forces on the structure and on the wall are studied for different water depth ratios, dimension of the structure and the distance of the wall from the structure.

     

波浪和水流对大直径圆柱的共同作用力

本文将波流共同对圆柱作用的速度势分成合模势（无自由表面的绕流速度势）、流兴波势和非定常波势三部分。忽略小量的流兴波势，考虑合模势对非定常波势的影响，用直接边界元法求出非定常波势，从而求出波流共同对圆柱的作用力，提出了沿流线的自由表面条件和波流共同作用下散射波的幅射条件。文中给出了波流对大直径圆柱作用力曲线，可供工程设计使用，适用条件是相对水深ｄ／Ｌ＞０．１５，相对流速Ｕ／ｃ＜０．２。     

波浪加速度不对称性对海床液化的影响

为研究加速度不对称波浪作用下的海床响应特征,基于Biot多孔弹性介质理论建立了波浪作用下海床响应数学模型,采用水槽实验数据对模型进行了验证。通过引入加速度不对称波浪压力边界条件的计算方法,模拟分析了波浪加速度不对称性对海床内部孔隙水压力、有效应力以及土体液化的影响。结果表明,波浪加速度不对称性会引起海床表层正向孔压幅值的显著衰减,使孔压的空间分布变得偏斜,减小了液化深度和宽度,使海床液化区域变得窄而浅。     

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。