随机波浪下泰勒离散系数的时域解

利用Wolk提出的粒子追踪方程,通过等分频率法划分不规则波谱,利用MATLAB做粒子运动模拟计算,得到无因次化泰勒离散系数K/D随时间t变化的曲线;通过与Huang等得到的P-M谱的泰勒离散系数K/D计算结果比较证明了本计算方法的可靠性。采用该方法研究了不规则波条件下,波序列(同一谱型不同波面序列)和谱型(谱峰周期、有效波高、谱峰升高因子)对波浪离散系数的影响;计算结果表明:同一谱型不同波序列对泰勒纵向离散系数稳定值和稳定时间无影响;不规则波谱峰周期越大,纵向离散系数K/D越小,稳定时间越短;有效波高越大,纵向离散系数K/D越大,稳定时间越长;谱峰升高因子越大,泰勒离散系数K/D越大,稳定时间越长;与规则波相比,不规则波的泰勒离散系数K/D的值略小10%~30%。     

波浪场中浓度输移扩散Stokes漂移效应的欧拉描述

为了说明波浪场中浓度输移扩散Stokes漂移效应的欧拉描述方法,采用欧拉方法推导了波浪场中波浪周期平均的浓度输移扩散方程,其对流项是由波浪速度的波动和物质浓度的波动相互作用而产生,所含的对流速度恰是Stokes漂移速度。由此说明,波浪场中浓度扩散问题的Stokes漂移效应可以自动的由欧拉法来考虑,所得到的Stokes漂移效应与拉格朗日描述的结果是等价的。为了进一步说明这一问题,将粒子追踪法的拉格朗日描述的Stokes漂移速度与欧拉法的结果进行了对比,二者是一致的。研究中也数值求解了线性波浪场中σ坐标下浓度扩散方程,将浓度的Stokes漂移、浓度分布和粒子追踪法的结果进行了对比,以证明欧拉描述和拉格朗日描述两种方法的等价性。研究中也根据实验结果对实际波浪场中Stokes漂移效应所引起的浓度漂移进行了讨论,解释了物理模型实验中的观察到的波浪场中浓度漂移现象。     

随机波浪作用下海洋平台主动控制的时滞补偿研究

基于预测控制理论，研究了适用于海洋平台的时滞补偿控制算法。该方法借助于随机波浪力的近似公式和卡尔曼滤波原理，推导出了随机波浪力向前一步预测公式，同时采用卡尔曼滤波方程，实现了对状态向量向前一步预测。利用随机波浪力及状态向量的实时在线预测公式，推导出最优控制力向前一步预测的表达式。在此基础上，发展了不仅适用于反馈控制系统而且适用于前馈-反馈控制系统的时滞补偿算法。采用一典型海洋平台为数值算例，计算结果表明，该方法在一定时滞范围内对海洋平台主动控制中时滞的补偿效果是显著的。     

随机波浪下遥控潜水器强非线性耦合空间运动与缆索安全性研究

模拟了带有脐带缆的潜水器(ROV)的强非线性流体动力学性能,由于ROV的前进速度与其它方向的运动速度为同一数量级,与传统的潜艇有重要的区别。潜艇中常用的按前进航速线性化处理的技术不能有效地用于潜水器,必须保留其运动方程中尽可能多的非线性项进行模拟。潜器本体的运动模型必须考虑为六自由度,脐带缆的运动必须考虑为三维运动。中继平台的运动幅值,可能会接近甚至超过水面船的运动幅值,这会增加ROV进出坞的困难。缆力对流速比对水面波浪更敏感、对垂向激励比水平激励更敏感。即使是随机波浪激励,深水吊索张力也会具有一定的周期性。近水面时这种周期性消失,两端张力趋于同步。     

随机波浪作用下黑泥湾冲淤演变的数值模拟

近岸海域潮流、波浪动力条件复杂,单纯考虑潮流输沙对底床冲淤演变的影响可能存在较大的偏差。基于局地较长时期海浪场统计特征,将随机波浪因子引入底床冲淤演化模拟研究中,采用ECOMSED模式进行了不同波浪动力条件影响下黑泥湾海域冲淤演化的数值模拟,并与现场观测资料进行了比较,取得了较好的结果。结果表明,黑泥湾及附近海域存在较稳定的N—S向潮余流,这在整体上是本区泥沙输运的重要影响因素;湾内海域基本处于冲淤动态平衡,冲淤格局与其地形、海流流速和波浪场分布有关,楮岛周围与镆铘岛东面近岸海域以侵蚀为主,镆铘岛南部近岸以淤积为主;随机波浪要素的引入对冲淤演变模拟结果有较大的影响,引入波浪要素后的模拟的结果与海图更为接近。     

随机波浪中畸形波在三维岛礁地形上的试验研究

在试验水池中,开展了波浪在岛礁地形上演化问题的研究。首先在实验水池中建立了西太平洋某岛礁地形的模型,然后采用改进的JONSWAP谱,由造波机产生不同周期、波高的随机波浪。试验中观察到了不同类型畸形波生成的过程及不同波面形态的畸形波。对偏度、峰度及水深与畸形波要素H_m/H_s（H_m表示波列中的最大波高, H_s为有效波高）的关系进行了详细的分析,同时,对畸形波波高H_fr与偏度的关也进行了分析。通过对试验结果分析,发现峰度与畸形波要素i>H_m/H_s呈正相关, H_fr增大时相应的偏度也会呈现增大的趋势。此外,水深的变化剧烈时（如斜坡、海山位置）有助于畸形波的发生。     

随机波浪作用下底层水沙运动的试验研究

通过一系列室内水槽试验,对规则波与不规则波浪荷载作用下的粉土质海床内的孔隙水压力、底层悬沙浓度以及底层水体流速的变化进行了比较分析。结果表明:波浪荷载的能量分布对床土的响应强度有着重要影响,尤其低频(大周期)部分的影响尤为强烈;随着超孔隙水压力累积,进而影响到底层悬沙浓度的变化;悬沙颗粒的结构和性质同样随着水动力的变化而变化,不同强度的水动力通过影响颗粒的絮凝特性而影响到悬沙颗粒的沉降和悬浮。另外,随机波浪所伴随的较强的非线性作用同样影响着悬浮体的絮凝与解体,这大大加剧了细颗粒沉积物的悬浮、运动的复杂性。     

随机波浪作用下座床式大直径薄壁圆筒防波堤的动力分析空间模型

随机波浪作用下座床式大直径薄壁圆筒防波堤的动力运动过程分为:摇摆、摇摆—小滑移运动和摇摆—大滑移运动三种运动模态,引入了控制侧向滑移的阻滑板—弹簧—阻尼器运动模型,建立了相应的动力分析空间模型。在大型有限元软件ANSYS中利用参数化设计语言APDL进行二次开发实现其空间模型,并把此空间模型计算结果与文献[1]中建立的平面模型计算结果比较,获得了一些有价值的结论,表明了本模型和方法对随机波浪荷载作用下大直径薄壁圆筒防波堤动力响应的数值模拟的可行性和有效性。     

Effect of Stokes drift on upper ocean mixing

Stokes drift is the main source of vertical vorticity in the ocean mixed layer. In the ways of Coriolis - Stokes forcing and Langmuir circulations, Stokes drift can substantially affect the whole mixed layer. A modified Mellor-Yamada 2. 5 level turbulence closure model is used to parameterize its effect on upper ocean mixing conventionally. Results show that comparing surface heating with wave breaking, Stokes drift plays the most important role in the entire ocean mixed layer, especially in the subsurface layer. As expected, Stokes drift elevates both the dissipation rate and the turbulence energy in the upper ocean mixing. Also, ilffluence of the surface heating, wave breaking and wind speed on Stokes drift is investigated respectively. Research shows that it is significant and important to assessing the Stokes drift into ocean mixed layer studying. The laboratory observations are supporting numerical experiments quantitatively.     

全球Stokes 漂流的时空分布特征研究

利用海浪模式WWIII(Wave Watch III)2008年的模拟结果对海面Stokes漂流、Stokes输运、Stokes深度以及全球Langmuir数的年平均分布特征和季节平均分布特征分别进行了详细的研究与分析。结果表明,海面Stokes漂流和Stokes输运均呈现高纬度偏大的特征,以南极绕极流海域最为突出。全球大部分海域Stokes漂流影响深度在20 m以内,呈现大洋东部偏大,西部偏小的分布特征。全球大部分海域的混合作用是剪切不稳定性和Langmuir湍效应并存的状态,甚至有些海域是以Langmuir湍效应为主。因此,在进行大尺度的海洋数值模拟时,应该考虑波浪导致的混合效应。     

The influence of Stokes drift on oil spills: Sanchi oil spill case

Spilled oil floats and travels across the water’s surface under the influence of wind, currents, and wave action. Wave-induced Stokes drift is an important physical process that can affect surface water particles but that is currently absent from oil spill analyses. In this study, two methods are applied to determine the velocity of Stokes drift, the first calculates velocity from the wind-related formula based upon a one-dimensional frequency spectrum, while the second determines velocity directly from the wave model that was based on a two-dimensional spectrum. The experimental results of numerous models indicated that: (1) oil simulations that include the influence of Stokes drift are more accurate than that those do not; (2) for medium and long-term simulations longer than two days or more, Stokes drift is a significant factor that should not be ignored, and its magnitude can reach about 2% of the wind speed; (3) the velocity of Stokes drift is related to the wind but is not linear. Therefore, Stokes drift cannot simply be replaced or substituted by simply increasing the wind drift factor, which can cause errors in oil spill projections; (4) the Stokes drift velocity obtained from the two-dimensional wave spectrum makes the oil spill simulation more accurate.     

Stokes漂对上层海洋温度变化影响的数值研究

The impact of Stokes drift on the mixed layer temperature variation was estimated by taking into account an advective heat transport term induced by the Stokes drift in the equation of mixed layer temperature and using the oceanic and wave parameters from a global ocean circulation model （HYCOM） and a wave model （Wave Watch III）. The dimensional analysis and quantitative estimation method were conducted to assess the importance of the effect induced by the Stokes drift and to analyze its spatial distribution and seasonal variation characteristics. Results show that the contribution of the Stokes drift to the mixed layer temperature variation at mid-to-high latitudes is comparable with that of the mean current, and a substantial part of mixed layer temperature change is induced by taking the Stokes drift effect into account. Although the advection heat transport induced by the Stokes drift is not the leading term for the mixed layer temperature equation, it cannot be neglected and even becomes critical in some regions for the simulation of the upperocean temperature.     

On the effects of wave drift on the dispersion of floating pollutants

The movement of floating pollutants such as oil slicks on the surface of the sea is due to a number different factors, among which wave drift is certainly significant.In principle, it has been known since Stokes' time that a floating particle is subject to the movement caused by the orbital motion of water particles and that an average drift velocity results because the trajectories are not closed. In the past, however, this effect was often either disregarded or simply included with the surface wind induced current. In recent times the difference between the two effects has been conceptually clarified, so that the average wave drift in random one-dimensional seas has been the object of research and the results are now included in most handbooks and models for oil slick forecasting.Due to the chaotic nature of the wave field, however, the drift also causes floating substances to disperse, and this phenomenon is a much more neglected area of research. Recent work by Bovolin et al. [IAHR Congress, 1997] and Sobey and Barker [J. Coast. Res. 13 (1997)] has brought the subject to attention, and computational tools can now be made to quantify the effect and to verify when and how it should be taken into consideration in oil slick accident practise.The work presented in this paper is based on random simulation of the wave induced Eulerian velocity field in a directional sea, by making use of standard offshore wave directional models and on the ensemble averaging of floating particles trajectories in order to compute the spatial dispersion.     

表面波浪对海洋上层混合的作用

A new three-dimensional numerical model is derived through a wave average on the primitive N-S equations, in which both the＂Coriolis-Stokes forcing＂ and the＂Stokes-Vortex force＂ are considered. Three ideal experiments are run using the new model applied to the Princeton ocean model （POM）. Numerical results show that surface waves play an important role on the mixing of the upper ocean. The mixed layer is enhanced when wave effect is considered in conjunction with small Langmuir numbers. Both surface wave breaking and Stokes production can strengthen the turbulent mixing near the surface. However, the influence of wave breaking is limited to a thin layer, but Stokes drift can affect the whole mixed layer. Furthermore, the vertical mixing coefficients clearly rise in the mixed layer, and the upper ocean mixed layer is deepened especially in the Antarctic Circumpolar Current when the model is applied to global simulations. It indicates that the surface gravity waves are indispensable in enhancing the mixing in the upper ocean, and should be accounted for in ocean general circulation models.     

Stokes波的谱特性分析

应用理论推导及数值计算方法，对Stokes随机波的谱特性进行了分析。首先将波面方程，海水质点水平速度用一阶波面分量的非线性组合表示，应用平稳随机高阶短的降阶计算法则，得到了波面方程及海水质点水平速度与一阶波面分量的自相关函数之间的关系，从而确定了Stokes随机波浪的波浪谱密度及海水质点水平速度和加速度谱密度，进而求得有关波浪要素的均方根值。文章还应有数值计算方法，分析了波浪基本参数对均方根值的影响。     

Spectral analysis of Stokes waves

The spectral properties of Stokes waves are shown in this paper by theoretical and numerical methods. This is done by expressing wave profiles and velocities of water particles as nonlinear combinations of the first order component of wave profiles. Under the assumption of the first order wave profiles being zero mean Gaussian processes, the relationship between autocorrelation functions of wave profiles and velocities of water particles and the first order component of wave profiles is established using the nonlinear spectral analysis. The spectral densities of nonlinear random waves, the velocities and accelerations of water particles are then obtained. Numerical computations are carried out to analyze the effect of fundamental parameters of waves. The results indicate that wave height is the most sensible parameter to the root mean squares related and wave depth is the least sensible one of all.