Modeling of the Turbulence in the Water Column under Breaking Wind Waves

Past studies have shown that there is a wave-enhanced, near-surface mixed-layer in which the dissipation rate is greater than that derived from the “law of the wall”. In this study, turbulence in water columns under wind breaking waves is investigated numerically and analytically. Improved estimations of dissipation rate are parameterized as surface source of turbulent kinetic energy (TKE) for a more accurate modelling of vertical profile of velocity and TKE in the water column. The simulation results have been compared with the experimental results obtained by Cheung and Street (1988) and Kitaigorodskii et al. (1983), with good agreement. The results show that the numerical full model can well simulate the near-surface wave-enhanced layer and suggest that the vertical diffusive coefficients are highly empirical and related to the TKE diffusion, the shear production and the dissipation. Analytical solutions of TKE are also derived for near surface layer and in deep water respectively. Near the surface layer, the dissipation rate is assumed to be balanced by the TKE diffusion to obtain the analytical solution; however, the balance between the dissipation and the shear production is applied at the deep layer. The analytical results in various layers are compared with that of the full numerical model, which confirms that the wave-enhanced layer near the surface is a diffusion-dominated region. The influence of the wave energy factor is also examined, which increases the surface TKE flux with the wave development. Under this region, the water behavior transits to satisfy the classic law of the wall. Below the transition depth, the shear production dominantly balances the dissipation. This revised version was published online in August 2006 with corrections to the Cover Date.     

风廓线雷达结合RASS反演湍流耗散率的方法

为探索反演湍流耗散率的最优方法,促进湍流规律和机理研究以及相关方法的业务化应用,文章根据风廓线雷达和无线电-声探测系统的探测原理,选取实例数据,通过虚温计算的布维频率和大气湍流引起的谱宽反演湍流耗散率。研究结果表明:该方法较为有效和简便,适用于加装无线电-声探测系统的风廓线雷达;湍流耗散率并不完全随高度增加而递减,而存在某高度层内湍流较强的现象;湍流耗散率与大气稳定度相互影响。     

Investigation of the Energy Balance in the Water–Air Boundary Layer under the Conditions of Developing Wind Waves

We present the results of the analysis of the energy balance in a wind–water system under the conditions of developing waves. Our investigation is based on the use of the experimental data obtained in a water channel and taken from the literature. We propose an expression for the energy balance between the air flow and wavy water surface based on the data of simultaneous measurements of the vertical wind profiles and drift currents and the parameters of waves for various fetches and indifferent density stratification.     

Comparison Study on Wind Input and Whitecapping Dissipation Expressions in Numerical Simulation of Typhoon-Generated Waves

In order to investigate the effect of wind input and whitecapping dissipation on the simulation of typhoon-waves, three experiments are conducted with the latest version of SWAN (Simulating WAves Nearshore) model.The three experiments adopt the Komen, Janssens, and Westhuysen expressions for wind input and whitecappingdissipation, respectively. Besides the above-mentioned source terms, other parameterization schemes in these experiments are the same. It shows that the experiment with the Westhuysen expression result in the least simulationerrors while that with the Janssens expression has the most. The results from the experiments with Komen and Westhuysen expressions show that the differences in significant wave height (SWH) have good correlation with thedifferences in dissipation energy caused by whitecapping. This indicates that the whitecapping dissipation sourceterm plays an important role in the resultant differences of the simulated SWH between the two experiments.     

近地层风廓线与垂直湍流强度关系研究

通过改进Prandtl 混合长理论,得出近地层风廓线形式     

Features of Profiles for Currents,Momentum Flux,and a Turbulence Dissipation Rate in Wind-Wave Channel

Izvestiya, Atmospheric and Oceanic Physics - Vertical profiles of the mean horizontal currents U(z), the vertical momentum fluxes τ(z), and the turbulence kinetic-energy dissipation rates (TKE...     

Comparison Study on Wind Input and Whitecapping Dissipation Expressions in Numerical Simulation of Typhoon Generated Waves

In order to investigate the effect of wind input and whitecapping dissipation on the simulation of typhoon-waves, three experiments are conducted with the latest version of SWAN （Simulating WAves Nearshore） model. The three experiments adopt the Komen, Janssens, and Westhuysen expressions for wind input and whitecapping dissipation, respectively. Besides the above-mentioned source tems, other parameterization schemes in these experiments are the same. It shows that the experiment with the Westhuysen expression result in the least simulation errors while that with the Janssens expression has the most. The results from the experiments with Komen and Westhuysen expressions show that the differenees in significant wave height （SWH） have a good correlation with the differences in dissipation energy caused by whiteeapping. This indicates that the whitecapping dissipation source term plays an important role in the resultant differences of the simulated SWH between the two experiments.     

深水风浪的风区指数律

对已有根据观测提出的幂函数形式风浪成长关系进行了分析。发现这些风浪成长关系在消去无因次风区后一致地与3／2指数律相协调，尽管它们原来存在较大的不协调性。发现Jeffreys，Sverdrup和Munk以及Platit的风能输入源函数在谱积分意义下具有相似性，而Tsikunov，Hasselmann和Phillips的破波耗散源函数在谱积分意义下也具有相似性，尽管这些源函数的原始形式和物理背景显著地不同。利用有效波能量平衡方程，将3／2指数律和发现的风能输入及破波耗散源函数相似性相结合，提出了深水风浪随风区成长的分式指数律，以得到的分式指数律拟合已有基于观测提出的风浪成长关系提出了半经验的风浪成长关系，与已有观测数据符合。     

风浪对众包测深数据的精度影响分析

针对当前众包测深数据精度难以掌控导致其难以应用的现状,通过构建船舶横摇姿态计算模型,分析了风浪这一重要海洋环境因素对众包测深数据精度的影响程度,得出了众包测深数据的推荐风浪条件和最低要求风浪条件。实验结果表明:①风浪等级增大,各测深点水深测量偏差随之加大,符合《海道测量规范》测深限差要求的测深点数量也随之减少,且在海底倾斜越严重的海域,表现更加明显;②3级风2级浪条件下的众包测深数据可满足限差要求;4级风3级浪时众包测深数据在不同海底倾斜程度下,满足限差要求的数据量不一样;5级以上风4级以上浪在海底倾斜程度超过7.5°时多数测深点不能满足限差要求。     

自升式钻井平台风载荷试验研究

对于自升式钻井平台而言,风载荷在所有环境载荷中比重最大。现行规范在计算平台风载荷时主要采用面积投影法,不考虑各构件之间的空气动力学干扰的影响,导致计算结果偏于保守,不利于结构的优化设计。本文以CIMC自主研发的122m水深自升式钻井平台为例,对其于在位状态和迁航状态的风载荷进行风洞试验研究,并与规范计算结果进行对比验证。结果表明,试验结果要小于规范计算,空气动力学干扰和升力作用的影响不可忽略。     

风生近惯性波的传播和耗散综述

近惯性波广泛存在于全球海洋,对海洋中的能量级联非常重要。风输入海洋的近惯性能量在海洋中是如何传播和耗散的,能量在海洋中如何划分,一直是受到高度关注的话题。本文简要综述了风生近惯性波在海洋中的传播和耗散过程,包括影响近惯性波传播的因素,比如β效应、中尺度涡度、台风尾流和近惯性波自身的波数特征等;近惯性波在风暴等强天气过程下的传播方式;近惯性波在混合层中衰减时间尺度的模拟;近惯性能量在海洋中的分配以及现有研究中还未解决的问题。本文拟为今后的近惯性波研究提供一些思路,进一步促进近惯性波机制和模拟等方面研究的深入开展。     

海浪资料的平滑和海浪谱谱矩估计

基于海浪谱估计理论，按谱估计方法导出了离散波面记录平滑处理后的谱形式，并计算了由各阶谱矩表示的谱宽度。指出平滑后的离散波面记录产生了新的随机过程，它们和原离散波面记录的内部结构和外部特征是完全不同的。但高阶矩表示的无因次谱宽度，即ε5=√1-m5^2/m4m6,ε7=√1-m7^2/m6m8几乎不受平滑（N=2，N=3）的影响，和原始谱的对应值相吻合。通过离散波面记录求导处理得波面速度谱，与理论转换得速度谱结果几乎完全一致。     

Growth of Wind Waves with Fetch in the Sea of Japan under Winter Monsoon Investigated Using Data from Satellite Altimeters and Scatterometer

By using wind vector fields observed by the NASA Scatterometer (NSCAT) and significant wave heights observed by the TOPEX/POSEIDON and European Remote Sensing Satellite-2 (ERS-2) altimeters, one-dimensional fetch growth of wind waves has been investigated under conditions of strong wind and high waves caused by the East Asian winter monsoon in the Sea of Japan. The evolution of fetch-limited wind waves can be observed by the altimeters along their ground tracks. The fetch is estimated by using vector wind fields observed by NSCAT. The derived growth characteristics of wind waves are compared with empirical relationships between the non-dimensional fetch and significant wave height proposed by previous studies. Good agreement is discernible with Toba's fetch graph formula normalized by the friction velocity, while Wilson's well-known formula normalized by the wind speed at a height of 10 m tends to underestimate the wave height under such severe conditions of high wind and very long fetch. This discrepancy is explained by the wind-speed dependence of the drag coefficient. A simple correction to Wilson's formula for the high wind conditions is proposed and compared with the observed data.     

Shelf Waves in the Great Australian Bight Based on Satellite Altimetry Data

Izvestiya, Atmospheric and Oceanic Physics - In this study we analyze shelf waves in the Great Australian Bight using satellite altimetry data. The phase velocity of the first mode of topographic...     

Efficient Generation of Freak Waves in Laboratory

In the present study,Kriebel's method is improved to generate freak waves in laboratory.The improved method superposes a random wave train with two transient wave trains to simulate freak wave events in a wave tank.The freak waves are more nonlinear than what generated with Kriebel's method of the same energy.It can also generate freak waves to satisfy all the qualifications of the adopted definition with less energy than Kriebel's and can hardly influence the significant wave height.     

基于最优插值法的Argo数据网格化实验

利用最优插值数据同化方法对Argo资料进行了网格化实验,得到了与WOA05较为一致的结果,验证了最优插值法对Argo资料网格化的有效性,并为加快开发制作适用于海洋模式和数据分析的Argo网格化数据集打下了很好的基础。     

Mass Transport in a Thin Layer of Bi-Viscous Mud Under Surface Waves

The mass transport in a thin layer of non-Newtonian bed mud under surface waves is examined with a two-fluid Stokes boundary layer model. The mud is assumed to be a bi-viscous fluid, which tends to resist motion for small-applied stresses, but flows readily when the yield stress is exceeded. Asymptotic expansions suitable for shallow lluid layers are applied, and the second-order solutions for the mass transport induced by surface progressive waves are obtained numeri-cally. It is found that the stronger the non-Newtonian behavior of the mud, the more pronounced intermittency of the flow. Consequently, the mass transport velocity is diminished in magnitude, and can even become negative (i. e. , oppo-site to wave propagation) for a certain range of yield stress.     

Numerical Modeling of Wave-Enhanced Turbulence in the Oceanic Upper Layer

A coupled model of air-wave-sea interaction is modified based on a new roughness formulation and the latest data. The model parameters for aerodynamic roughness from below (ARB) and wave-dependent roughness from above (ARA, z _0a ) are assumed equal. The combined roughness is assumed to be a function of friction velocity, gravity, air and seawater densities, and wave age (c _w ). The model is used in a study of wave-enhanced turbulence under breaking waves to predict turbulent dissipation (), ARA, and drag coefficient (C _d ). Both waves and shear production are considered as sources of ocean turbulent energy. The atmospheric part of the model is used only to specify a correct condition at the interface. Numerical experiments are performed to study the -distribution, z _0a and C _d , and to compare with data. The major achievement is model verification using all available data. The first full application of this model is in conjunction with an ocean circulation model in a coupled circulation-wave system. Simulations show that the -distribution is strongly dependent on local wind-forced wave heights. For each wind and wave state there is a particular wave-dependent depth that is verified by data. The comparison shows that the model predicted agrees well with the observed of the z ^–4 law distribution of Gargett (1989). Simulations also show that waves have an important role in causing to differ from the classical wall-layer theory and z _0a , with a value of 0.30 for the empirical constant a _a . The model-predicted , z _0a , C _d and C _gd agree well with data.     

风浪槽内风浪外频谱谱形的一些特征

利用实验室风浪槽内测得的波面序列资料估计风浪外频谱。通过与实测风浪内频谱的比较,研究实测风浪外频谱的谱形特征,探讨海浪外频谱与内频谱的相似性问题。此外,还检验一种理论海浪外频谱。     

Estimates of Turbulence Intensity and Power Density of an Asymmetric Tidal Current under Wind Forcing Variability

Izvestiya, Atmospheric and Oceanic Physics - A high-frequency (1.2 MHz) four-beam Acoustic Doppler Current Profiler moored on the seabed has been used for direct turbulence measurements in a tidal...