A three-dimensional theory for the development and migration of deep sea sedimentary waves

A perturbation model is presented for a velocity field of a bottom current flowing over a sinusoidal topography or an obstacle. The model extends existing theory by taking into account the three-dimensional Coriolis vector and an initial horizontal velocity vector at any orientation. One possible mechanism of the development of sedimentary waves in the vicinity of an obstacle by an arbitrarily oriented initial horizontal current is analyzed in detail. Space-stationary fluid particle oscillations are initiated on the downstream side of an obstacle, which can result in sedimentary waves. The model shows that their wavelength depends on latitude, water depth, obstacle width and orientation as well as the initial current direction and intensity. The model defines intervals for current velocities normal to the wave crest, for which the sedimentary waves grow (or are destroyed) or migrate in a certain direction. Information derived from bathymetric and seismic surveys, such as wavelength, height, orientation and migration direction of mudwaves, can be used to calculate the velocity component across the wave crest and to estimate the current direction, as is demonstrated for an example from the Argentine Basin (Project MUDWAVES, Site 5).     

深海布放缆不同材料属性下应力波自由传播频率特性影响研究

在频域对深海布放缆系统内应力波自由传播特性进行了分析。在布放缆数学建模时使用了哈密顿原理,并在建模时考虑布放缆的曲率。计算过程中保留了缆绳曲率与其弧长坐标之间的非线性关系,并最后得到了其上传播的应力纵波与应力横波的特性。通过计算得到布放缆属性和缆绳内竖直张力等参数对缆绳内自由传播频率特性的影响曲线。结果表明,这些因素对自由传播应力波的频率关系、色散关系、相速度与群速度影响显著。对于应力纵波,整个频域可被两个截止频率与一个行波截止频率分成四个区域。除了通频带之外,在低频时亦存在抑止带和行波抑止带。应力纵波仅能在通频带中以行波形式传播,而应力横波则可以在所有频率范围内以行波形式传播。     

热带气旋下海浪对大气向海洋输入的动量和能量的影响

海浪不仅决定着海洋表面的粗糙度,由热带气旋引起的海浪,还通过其发展演化控制着大部分的海气之间的动量和能量传递。本文采用热带气旋观测数据IBTrACS和海浪模式WW III的模拟结果探究了热带气旋下海浪对大气向海洋输入的动量和能量的影响。结果发现,近30 a热带气旋的强度约每10 a增加 1 m/s,但移速没有明显变化。热带气旋的强度越大,从大气输入到海浪和从海浪输入到海流中的动量之差和能量之差也越大。由于热带气旋的风场和海浪场都有较强的不对称性,海气动量差和能量差也表现出非均匀分布：动量差较大的区域在热带气旋移动方向的后方,能量差的最大值则分布在右后象限,且二者均为左前方比较小。逆波龄与动量差和能量差呈高度正相关,相关系数约为0.95,说明波越年轻吸收的动量和能量越多。气旋移速越快逆波龄越大,且热带气旋移动速度与动量差和能量差呈正相关,相关系数在0.8以上。因此,海浪影响着大气向海洋输入的动量和能量的分布和大小,在以后关于海洋边界动力学和热力学的研究中,考虑海浪的演化可能会使结果更加准确。     

Pipeline breakout from sea floor under wave action

The vertical stability of a submarine pipeline laid half-buried on the sea floor under wave action is studied. As the wave-induced lifting force acts to detach the pipe from the sea floor, mud suction resistance will be developing at pipe-soil interface, acting to hold the pipe in place. This couples the pipe equilibrium with the seabed response which is modelled as a poroelastic media, following the formulation of Biot. Conditions for pipe detachment or breakout from the sea floor are investigated for typical seawave, pipe, and seabed parameters. A general power law will describe the slow quasistatic breakout of the pipe. In the case when the forcing wave period is much shorter than the quasistatic breakout time, the response function of the coupled pipe-seabed system will involve weak nonlinear terms of higher harmonics. The possibilities for resonating the system in such case are examined by including the inertia of the pipe in the analysis.     

Dynamic behavior of offshore spar platforms under regular sea waves

Many innovative floating offshore structures have been proposed for cost effectiveness of oil and gas exploration and production in water depths exceeding one thousand meters in recent years. One such type of platform is the offshore floating Spar platform. The Spar platform is modelled as a rigid body with six degrees-of-freedom, connected to the sea floor by multi-component catenary mooring lines, which are attached to the Spar platform at the fairleads. The response dependent stiffness matrix consists of two parts (a) the hydrostatics provide restoring force in heave, roll and pitch, (b) the mooring lines provide the restoring force which are represented here by nonlinear horizontal springs. A unidirectional regular wave model is used for computing the incident wave kinematics by Airy’s wave theory and force by Morison’s equation. The response analysis is performed in time domain to solve the dynamic behavior of the moored Spar platform as an integrated system using the iterative incremental Newmark’s Beta approach. Numerical studies are conducted for sea state conditions with and without coupling of degrees-of-freedom.     

Spectral evolution of surface waves in a deep sea due to the effect of wave-wave interactions

The wave-wave kinetic equation for surface gravity waves in a deep sea is solved numerically, using the Runge-Kutta technique. Spectral evolution of waves resulted only from their being non-linear, with no wave generation and decaying taking place. To perform computations the JONSWAP-type frequency spectra and a variety of angular wave spectra were used. The angular spectrum of waves turned out to be stable. The frequency spectrum differed from the JONSWAP spectrum in that it had a high-frequency part, which was not similar to the Phillips spectrum. The form of the high-frequency spectral slope was determined as a result of spectral evolution and proved to have the form of the ‘−6’ law. Translated by Vladimir A. Puchkin.     

波浪作用下孤立砂球稳定性条件研究

波浪作用下大块石稳定性条件的研究,不仅是泥沙运动力学急待发展的内容之一,也是抛石工程合理化设计的重要问题。在收集大量国内外有关研究资料的基础上,分析了在波浪作用下大块石的受力状况,得出当大块石处于失稳临界状态时,其所受失稳应力与其自身有效容重和其当量直径乘积的比值是雷诺数、斯特鲁哈尔数及块石水下休止角的函数。为排除块石形状和块石间相互支撑形式不规则等干扰因素的影响,采用固定钢圈支撑孤立水泥砂球,在波浪槽中进行试验研究。根据试验资料,在斯特鲁哈尔数大于10的条件下,验证了当沙粒雷诺数达到105以后Shields曲线出现跳跃的事实。     

台风背景下海浪对海表流场和海表温度的影响

海浪作为海-气界面中重要的物理过程,对海洋上混合层的近表面分布具有重要作用。本文以台风"威马逊"和"麦德姆"为背景,基于FVCOM耦合模式模拟了台风浪及上层海洋的响应过程,探讨了海浪对海表流场和海表温度的影响。结果表明耦合模式能够较准确地模拟出有效波高,台风过境后海表流场在海浪的作用下反映出与台风相对应的气旋性特性,改变的流场量级可达0.4 m/s;海表温度出现不同程度的下降,最大降温约4℃,最大降温中心与流场变化区域相对应,且降温区相对台风路径呈显著的"右偏性"。最大降温滞后台风中心过境2 d左右,恢复时间一般超过10 d,与实况相吻合。     

Dispersal of droplets over breaking wind waves under the direct action of wind

This paper describes the dispersal of droplets over breaking wind waves under the direct action of wind, based on a comparison between the actual distribution of droplet velocity and the wind field measured in a wind-wave tank (reference wind speed 16 m sec^–1). The velocity distribution of droplets with a diameterd>0.81 mm over breaking wind waves was measured by Koga (1981). In this paper the wind field over breaking wind waves is measured by a flow visualization technique using styrofoam flakes as a tracer. The comparison allows a clear interpretation of droplet movement over the wave profile, and shows that the horizontal movement of the droplets ofd>0.81 mm is approximately determined by acceleration by the wind while their vertical movement is determined by acceleration due to gravity. These observations offer some support for the dispersion model proposed by Koga and Toba (1981).     

Nonlinear coupled dynamic response of offshore Spar platforms under regular sea waves

Many innovative floating offshore structures have been proposed for cost effectiveness of oil and gas exploration and production in water depths exceeding one thousand meters in recent years. One such type of platform is the offshore floating Spar platform. The Spar platform is modelled as a rigid body with six degrees-of-freedom, connected to the sea floor by multi-component catenary mooring lines, which are attached to the Spar platform at the fairleads. The response dependent stiffness matrix consists of two parts (a) the hydrostatics provide restoring force in heave, roll and pitch, (b) the mooring lines provide the restoring force which are represented here by nonlinear horizontal springs. A unidirectional regular wave model is used for computing the incident wave kinematics by Airy’s wave theory and force by Morison’s equation. The response analysis is performed in time domain to solve the dynamic behavior of the moored Spar platform as an integrated system using the iterative incremental Newmark’s Beta approach. Numerical studies are conducted for sea state conditions with and without coupling of degrees-of-freedom.     

Propagation of passive impurities in the northwest part of the Black Sea under the action of cyclones moving to the north

We perform the theoretical analysis of the turbulent diffusion of impurities in the sea in the presence of long waves. The role of generators of long-wave motions is played by moving cyclonic baric formations. At the initial time, the zone of pollution is specified in the form of a spot of a passive substance localized near the Karkinitskii Bay in the Black Sea. The results of our investigations enable us to estimate the contribution of long waves to the process of diffusion of the spot of impurity depending on the trajectory of motion of the cyclonic formation. It is shown that, under the action of waves induced by the cyclone, the maximum concentration in the spot decreases more rapidly only for a certain period of time. Moreover, we observe a northwest displacement of the spot specified by the structure of the wave field.Translated from Morskoi Gidrofizicheskii Zhurnal, No. 4, pp. 3–18, July–August, 2004.     

On incipient motion of silt-sand under combined action of waves and currents

Sediment incipient motion is a fundamental issue in sediment transport theory and engineering practice. Silt has transitional behavior between cohesive and non-cohesive sediment and its incipient motion is still poorly understood. This study aims to find an expression for incipient motion from silt to sand from a unified perspective and analysis. From the analysis of forces, using the derivation method for the Shields curve, an expression for sediment incipient motion is proposed for both silt and sand under conditions of combined waves and currents. The differences and similarities in the sediment motion threshold were analyzed under the effects of waves and currents, and fine and coarse sediment. The Shields number was revised by introducing the cohesive force and additional static water pressure, which indicates that this study could be seen as an extension of the Shields curve method for silt. A number of experimental datasets as well as field data were used to verify the formula. The effect of bulk density on fine sediment was discussed and tested using experimental data.     

深水管道S型铺设监测研究

目前,深水管道S型铺设取得了优异的铺设成果,逐渐成为深水海底管道铺设的重要方法,但其铺设环境复杂,上弯段管道与托管架动态接触,现有分析手段无法有效模拟。同时,S型铺设关键设备的设计技术还不成熟,没有相应的设计规范。首先对深水管道S型铺设开展监测研究,提出了深水管道S型铺监测方案,最后利用实验室模型实验验证了该方案的可行性,可以为深水S型铺设关键设备的设计提供必要的设计数据。     

Stoneley waves,Lopez Island noise,and deep sea noise from 1 to 5 Hz

The Lopez Island OBS Intercomparison Experiment provided a data set of sufficient spatial density to allow study of the propagation of shot-generated Stoneley waves as well as ambient background noise. The Stoneley waves were observed propagating at velocities of 20 to 50 m s^-1, Phase velocities were determined by fitting peaks in the frequency wave number spectrum. Group velocities were calculated by narrowly filtering the data and determining the arrival time of the peak in the frequency packet. Particle displacement plots illustrate the surface wave character of these waves. The analysis of the ambient background noise failed to produce a clearly defined dispersion curve yet it did allow bounds to be placed on the phase velocities (20 to 50 m s^-1). The data were modeled using eleven layers overlying a half-space. The results indicated that the top 7 m of the sediment column at Lopez Island is best approximated by two zones. In the upper zone there is a fairly rapid change of shear velocity with depth. This zone overlies a region in which the shear velocity gradient is much lower. Deep ocean background noise recorded by University of Washington ocean bottom seismometers was also examined. Although insufficient data precluded any velocity analysis, definite similarities exist between these data and noise data observed at Lopez Island.Hawaii Institute of Geophysics Contribution No. 1174.     

海浪的条件特征周期

在海浪波面高度为正态分布的假定下,导出一种以给定波高为条件的条件周期概率密度函数.与风浪槽中测量数据比较,结果表明,在窄谱情况下此概率密度函数与实验室风浪的实际符合良好.根据此密度函数定义了3种条件特征周期,并导出它们与平均周期的关系式.根据这些关系对有关海洋工程上的一些问题作了解释和讨论.     

Experimental investigation on the dynamic response of a moored wave energy device under regular sea waves

This paper attempts to provide a better understanding of the hydrodynamic behaviour of a floating multi-resonant oscillating column wave energy device which combines the concept of a floating breakwater and a wave energy device. Experiments were conducted on a 1:20 scale model of the floating wave energy device moored by six mooring lines to study the dynamics of the device under regular waves for various scopes. The effect of non-dimensionalized wave frequency parameter on the motion response and mooring force are reported and discussed in detail in this paper.     

Numerical modeling of wind waves generated by tropical cyclones using moving grids

A version of the WAVEWATCH III wave model featuring a continuously moving spatial grid is presented. The new model option/version is intended for research into wind waves generated by tropical cyclones in deep water away from the coast. The main advantage of such an approach is that the cyclones can be modeled with spatial grids that cover much smaller areas than conventional fixed grids, making model runs with high spatial resolution more economically feasible. The model modifications necessary are fairly trivial. Most complications occur due to the Garden Sprinkler effect (GSE) and methods used to mitigate it. The basic testing of the model is performed using idealized wind fields consisting of a Rankine vortex. The model is also applied to hurricane Lili in the Gulf of Mexico in October 2002. The latter application shows that the moving grid approach provides a natural way to deal with hurricane wind fields that have a high-resolution in space, but a low resolution in time. Although the new model version is originally intended for tropical cyclones, it is suitable for high-resolution modeling of waves due to any moving weather pattern.     

Experimental investigation of breaking criteria of deepwater wind waves under strong wind action

The present study describes an experimental investigation of breaking criteria of deepwater wind waves under strong wind action. In a wind wave flume, waves were generated using different wind speeds and measured at different locations to obtain wave trains of no, intermittent, or frequent breaking. Water particle movement and free surface elevation were measured simultaneously using a PIV system and a wave gauge, respectively. For wind waves, not all the waves measured at a fixed location are breaking waves, and the breaking of a larger wave is not guaranteed. However, the larger the wave height, the larger the probability of breaking. In order to take as many breaking waves as possible for the cases of frequent breaking, we used the waves whose heights were close to the highest one-tenth wave height. The experimental results showed that the geometric or kinematic breaking criteria could not explain the occurrence of breaking of wind waves. On the other hand, the vertical acceleration beneath the wave crest was close to the previously suggested limit value, −0.5g, when frequent breaking of large waves occurred, indicating that the dynamic breaking criterion would be good for discriminating breaking waves under a strong wind action.     

孤立波作用下植物带消浪效果影响因素分析

近岸植物带能有效削弱波浪作用,植物带消浪影响因素分析对布置护岸工程、维护岸线稳定有重要意义。在模型实验基础上,探究相对波高、模型相对宽度、模型相对高度和体积分数对透射系数的影响。设置波浪水槽试验,研究孤立波在不同水深、入射波高及植物排布方式等组合条件下对植物消浪效果的影响。采用遗传编程法得出各复杂度下的透射系数计算公式,并分析各参数在方程中的表现情况,发现遗传编程能定性给出参数的敏感度。相比于非线性回归拟合结果,遗传编程方法得到的函数关系更加精确。采用人工神经网络方法进一步分析与验证各影响因素对植物消浪效果的影响程度,结果表明人工神经网络得出的结果与遗传编程方法相近,体积分数对消浪效果起主导作用。