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1.
本文在时域非线性数值波浪水槽中，研究了不同风速条件下极端波浪的特性。采用推板造波的方式生成非线性波浪，基于Jeffrey遮蔽理论将风压项引入自由面动力学边界条件来模拟风压作用，通过高阶边界元法和混合欧拉-拉格朗日时间步进法来求解初边值问题。通过与已发表的聚焦波群实验结果对比验证了该数值模型的准确性，并研究了风压对极端波浪的最大波高、聚焦位置的偏移和波浪谱的演变等波浪性质的影响。本文进一步在数值波浪水槽中引入均匀水流，来模拟风生流对波浪演变的影响。结果表明，风压的存在会少量增大极端波浪的最大波高，波浪的聚焦和解焦过程伴随着明显的能量传递，并且风生流进一步导致了波浪聚焦位置的偏移。 相似文献
2.
左中道 《海洋学报(英文版)》1986,5(2):195-202
The distribution of wind speed in the easterly in the tropics is not uniform. In the part with large curvature, such as lines of trough and ridge, the wind speed is small, while in the part with small curvature, the wind speed is large. In this paper, these phenomena are expounded with gradient wind equation.Considering the distribution of wind speed, we find the wave speed formula from linearized vorticity and divergence equation. The wave speed is equal to the sum of the Rossby wave speed and a harmonic function for x and t. Its period is about 3.5 days. And it is proved that the disturbance is barotropic instability. The results are caused by interaction between meriodional and zonal disturbances. 相似文献
3.
M.A.C. Teixeira 《Ocean Modelling》2011,36(1-2):149-162
The structure of turbulence in the ocean surface layer is investigated using a simplified semi-analytical model based on rapid-distortion theory. In this model, which is linear with respect to the turbulence, the flow comprises a mean Eulerian shear current, the Stokes drift of an irrotational surface wave, which accounts for the irreversible effect of the waves on the turbulence, and the turbulence itself, whose time evolution is calculated. By analysing the equations of motion used in the model, which are linearised versions of the Craik–Leibovich equations containing a ‘vortex force’, it is found that a flow including mean shear and a Stokes drift is formally equivalent to a flow including mean shear and rotation. In particular, Craik and Leibovich’s condition for the linear instability of the first kind of flow is equivalent to Bradshaw’s condition for the linear instability of the second. However, the present study goes beyond linear stability analyses by considering flow disturbances of finite amplitude, which allows calculating turbulence statistics and addressing cases where the linear stability is neutral. Results from the model show that the turbulence displays a structure with a continuous variation of the anisotropy and elongation, ranging from streaky structures, for distortion by shear only, to streamwise vortices resembling Langmuir circulations, for distortion by Stokes drift only. The TKE grows faster for distortion by a shear and a Stokes drift gradient with the same sign (a situation relevant to wind waves), but the turbulence is more isotropic in that case (which is linearly unstable to Langmuir circulations). 相似文献
4.
5.
Masayuki Tokuda 《Journal of Oceanography》1976,32(3):128-138
The instability of Taylor-Görtler vortices which are expected in the air flow on water waves was studied in part I, under the assumption that the curvature around the crest or the trough of water waves, where the instability was expected to take place first, was constant, namely that the characteristics of the vortices were affected little by the local change of the curvature along the direction of the progress of water waves (the direction ofx-axis) However, the curvature actually varies from positive to negative, or vice versa. In order to study this effect, the instability of Taylor-Görtler vortices is examined with respect to the range of the part of a constant curvature, in the model in which the curvature is positive constant near the trough and negative constant near the crest, and zero in the intermediate regions, respectively. It is shown that as the region of the constant curvature becomes narrower, the instability tends to weaken. For the same example with part I, namely, when the wind of 12.2 m s–1 is blowing over swells of 15 m in wavelength, if the range of constant curvature near the trough is taken as a quarter of one wave length, the critical wave height becomes 0.96 m instead of 0.50 m, and conversely, the wave length and the height of center of the vortex become 11.9 m and 2.1 m instead of 24 m and 3.7 m, respectively.Further, using the energy equations, quantitative estimates are performed of the intensity of the vortices which develop when the wave height of the swell is 1.05 m in the above described example, and also of the influence of the vortices upon the wind profile when the equilibrium state is reached. When the vortices are generated and grow to attain to an equilibrium state interacting with the mean flow, the maximumx-component of velocity in the vortices is about 1.04 m s–1. Consequently, the wind profile undergoes a considerable distortion from the logarithmic one near the level of 2 m height. This distorted wind profile has a form similar to those sometimes observed above the sea surface. 相似文献
6.
基于数值模拟的三维随机海面,从时间域和空间域两个角度对海浪的外观特征和内部结构间的关系进行了研究,得出了一些在工程应用上有参考价值的结果.文章认为,将波面看作是若干随机正弦波叠加的海浪结构模型,用于描述平稳、均匀和窄谱的海况时,其频谱分析结果与外观统计结果基本上是一致的;但是,当海面处于谱宽度较大的风浪或混合浪状态时,一些频谱分析结果必须经过修正才能应用.同一海况下,海面波动的时间过程和沿主波向的空间分布是明显不同的.当海面有突发性大浪时,外频谱能够很好地反映不平稳海况,而频谱则把这种不平稳性平滑了.文章着重讨论了波长和波陡的计算、频谱和外频谱的差异. 相似文献
7.
Masayuki Tokuda 《Journal of Oceanography》1972,28(6):242-253
Taylor-Grörtler vortices are longitudinal vortices resulting from a centrifugal instability. They are generated in the flow having a curved streamline with an increasing velocity in the direction of decreasing curvature.It is shown that the air flow above wind waves and swells also satisfies locally the condition of the centrifugal instability. Numerical calculations indicate the possibility of generation of Taylor-Görtler vortices on the trough of sea waves. For example, when a wind of about 12.2 m/s at 10-m level is blowing over sea waves of the wave length of 15 m like the swell, the critical water wave height beyond which the vortices may be generated is about 0.5 m, and the critical wave length and the height of center of the generated vortices are about 24 m and 3.7 m, respectively. Further, about the relations between the generation of vortices and wind waves, it is shown that the condition of their generation is satisfied at the trough of waves for early stages of the wave generation.In conclusion, it is expected that the Taylor-Görtler vortices change the wind profile along the sea surface, and also, play some part in the growth of wind waves, especially in the formation of their three dimensional structure. 相似文献
8.
Kuniaki Okuda 《Journal of Oceanography》1982,38(5):313-322
Characteristic features of the internal flow field of short wind waves are described mainly on the basis of streamline patterns measured for four different cases of individual wave. In some waves a distinct high vorticity region, with flow in excess of the phase speed in the surface thin layer, is formed near the crest as shown in Part I of this study, but the streamlines are found to remain quite regular even very near the water surface. The characteristics of flow in the high vorticity region are investigated, and it is argued that the high vorticity region is not supported steadily in individual waves but that growth and attenuation in individual waves repeats systematically, without no severe wave breaking. Below the surface vorticity layer a quite regular wave motion dominates. However, this wave motion is strongly affected by the presence of the high vorticity region. By comparing the measured streamline profiles with those predicted from wave profiles by the use of a water-wave theory, it is found that the flow of the wind waves studied cannot be predicted, even approximately, from the surface displacements, in contrast to the case of pure irrotational water waves. 相似文献
9.
G. D. Aburjania 《Izvestiya Atmospheric and Oceanic Physics》2011,47(4):491-502
The generation and further linear and nonlinear dynamics of planetary magnetized Rossby waves (MRWs) in the rotating dissipative ionosphere are studied in the presence of a zonal wind (shear flow). MRWs are caused by interaction with the spatially nonuniform geomagnetic field and are ionospheric manifestations of ordinary tropospheric Rossby waves. A simplified self-consistent set of model equations describing MRW-shear flow interaction is derived on the basis of complete equations of ionospheric magnetohydrodynamics. Based on an analysis of an exact analytical solution to the derived dynamic equations, an effective linear mechanism of MRW amplification in the interaction with nonuniform zonal wind is ascertained. It is shown that operators of linear problems are non-self-adjoint in the case of shear flows, and the corresponding eigenfunctions are nonorthogonal; therefore, the canonically modal approach is of little use when studying such flows; a so-called nonmodal mathematical analysis is required. It is ascertained that MRWs effectively get shear flow energy during the linear stage of evolution and significantly increase (by several orders of magnitude) their energy and amplitude. The necessary and sufficient condition of shear flow instability in an ionospheric medium is derived. Nonlinear self-localization begins with the development of shear instability and an increase in the amplitude, and the process ends with the self-organization of strongly localized isolated large-scale nonlinear vortex structures. Thus, a new degree of freedom and a way for perturbation evolution to occur appear in medium with shear flow. The nonlinear systems can be a pure monopole vortex, a vortex streets, or vortex chains depending of the shape of the sheared flow velocity profile. The accumulation of such vortices in the ionospheric medium can produce a strongly turbulent state. 相似文献
10.
Response of the tropical ocean to a uniform zonal wind is studied numerically and analytically. In addition to the Equatorial Undercurrent and surface westward flows on both sides of the equator, an eastward flow at the pycnocline depth is formed at several degrees latitude in both hemispheres. This subsurface eastward flow first appears in the eastern part of the ocean and extends to the west. Then it gradually decreases in speed, and at a steady state the speed is of the order of 1cm sec–1. The spatial distribution of this subsurface flow is similar to the Subsurface Countercurrent, but the speed is one order smaller than that observed. The obtained thermostad is obscure compared with that observed. Whole of the time evolution produced by a numerical model can be accounted for by linear wave dynamics in a multi-layer model including vertical diffusion and friction. Although diffusion and friction are essential to maintain this subsurface flow, changes in the values of coefficients for vertical viscosity and diffusivity and also in initial density stratification lead only to a minor change in the speed of the subsurface eastward flow. It is concluded that a subsurface eastward flow with speed exceeding 10 cm sec–1 accompanied by a distinctive thermostad structure cannot be explained by linear wave dynamics including vertical dissipation. 相似文献
11.
以Spar型浮式风机为研究对象,研究涡激力对于浮式风机系统运动的影响。对多体动力学软件FAST进行二次开发,加入涡激力的计算接口,实现了在平台涡激、波激、空气动力载荷及系泊联合作用下的Spar浮式风机系统的运动响应的计算。计算了在风、浪、流联合作用下,频率锁定现象发生时,Spar基础的运动响应,分析了风浪下Spar风机运动响应的涡激运动特性,并研究了不同的入流角度的影响。结果表明:考虑涡激力后,Spar基础的横荡运动明显增大;风浪流同向时,风浪的存在会抑制流载荷引起的横荡在涡泄频率的运动;在流与风浪垂直时,会激发Spar基础的更大的纵荡运动响应。 相似文献
12.
We present a case study of low-level wind jets induced in sequence by orographic effects off the Pacific coast of northern
Japan during 7–11 June 2003, and demonstrate that the transition of the wind jets causes areal differences of wave height
variations along the coast. First, we describe evolution and structure of the wind jet by analyzing SeaWinds scatterometer
wind measurements. Under the easterly wind, a strong wind jet formed after passing by Cape Erimo. As the wind shifted to the
southeast, the wind jet started to decay. In turn, the southerly wind along the coast led to another wind jet in the lee of
the easternmost tip of the Sanriku coast. We then identify onsets and decays of the wind jets from time series of wind speed
at meteorological stations. Finally, we demonstrate that the transition of the wind jets has local impacts on wave height
variations. Significant wave heights measured by altimeters were correlated positively with local wind energy, i.e., squares
of wind speeds. Accompanying the wind jet formation/decline, significant differences of wave height variations became marked
among wave observation stations located along the coast at intervals of up to 50 km. 相似文献
13.
The littoral drift rose (LDR) concept is presented herein for improvement in understanding of longshore sediment transport and consequent shoreline processes in areas with smooth (gradually varying) offshore bathymetry extending over a coastal region where the deep water wave climate is reasonably uniform. The concept of the littoral drift rose (LDR) is presented and LDRs are shown to provide insight into coastal evolution and shoreline stability (or instability) for a given region having uniform wave climate. This paper reviews earlier documented applications and work using LDRs and provides an interpretation of earlier findings of shoreline stability using LDRs. Previously known but undocumented findings are also discussed herein which show that the wave climate and hence the LDR can be synthesized into an equivalent LDR developed from one wave component of given magnitude and direction. Practical applications using LDRs are presented, which show that the magnitude and direction of littoral drift throughout a region can be interpreted from limited measured, calculated, or observed data on littoral drift at two locations in the region. 相似文献
14.
An extremely large (“freak”) wave is a typical though rare phenomenon observed in the sea. Special theories (for example, the modulation instability theory) were developed to explain mechanics and appearance of freak waves as a result of nonlinear wave-wave interactions. In this paper, it is demonstrated that the freak wave appearance can be also explained by superposition of linear modes with the realistic spectrum. The integral probability of trough-to-crest waves is calculated by two methods: the first one is based on the results of the numerical simulation of a wave field evolution performed with one-dimensional and two-dimensional nonlinear models. The second method is based on calculation of the same probability over the ensembles of wave fields constructed as a superposition of linear waves with random phases and the spectrum similar to that used in the nonlinear simulations. It is shown that the integral probabilities for nonlinear and linear cases are of the same order of values 相似文献
15.
Yoshiaki Toba Masayuki Tokuda Kuniaki Okuda Sanshiro Kawai 《Journal of Oceanography》1975,31(5):192-198
Wind-wave tunnel experiments reveal, by use of techniques of the flow visualization, that wind waves are accompanied by the wind drift surface current with large velocity shear and with horizontal variation of velocity relative to the wave profile. The surface current converges from the crest to a little leeward face of the crest, making a downward flow there, even though the wave is not breaking. Namely, wind waves are accompanied by forced convections relative to the crests of the waves. Since the location of the convergence and the downward flow travels on the water surface as the crest of the wave propagates, the motion as a whole is characterized by turbulent structure as well as by the nature of water-surface waves. In this meaning, the term of real wind waves is proposed in contrast with ordinary water waves. The study of real wind waves will be essential in future development of the study of wind waves. 相似文献
16.
The study verifies the Black Sea wave model using field data obtained from the Katsiveli research platform. The WAM and mesoscale MM5 and WRF atmospheric models, which are used to calculate the wind field for the wave model, were recently adjusted to the Black Sea region at the Marine Hydrophysical Institute. The results of the work are presented as characteristics of the simulation quality used in world practice in other regions. The scatter index for a significant wave height is 70% in summer and 50% in winter. The values of the scatter index of wave parameters and wind speed appear to be at the same level as in semi-enclosed seas on the northern side of the Mediterranean Sea. It is shown that atmospheric simulation correctly reproduces the interaction between synoptic processes and the mountain range extending alongshore. Error sources in wave simulation are discussed. The most significant drawback is the possibility of mesoscale instability in the atmospheric model without assimilation of observation data within the computational domain. 相似文献
17.
本文采用无海底地形但考虑海洋跃层和剪切背景流的二维非静力准不可压缩方程组的数值模式，开展失稳垂向剪切背景流下线性和非线性对称型海洋内波生成演变的数值实验，并对结果进行分析、比较和讨论。研究结果表明，线性内波强度随积分时间始终呈指数增长，并有内波的对称不稳定；而非线性内波强度则在发展期呈准线性增长，最终进入稳定期。线性增长比非线性增长要快得多，非线性效应具有维稳作用。对该线性和非线性对称型内波，在跃层附近位密度扰动均有大值中心，即其为跃层所俘获，这与实际观测相一致；流函数与位密度扰动两者均有很好配合，位密度扰动的正、负中心分别相应于流函数的上升、下沉运动，表明有从海底向上的斜对流发生，且以跃层为顶盖。对线性内波来说，随积分时间增加，其波形大体不变，其正、负振幅也大体相同，并有符号相反原地增长的两个倾斜环流圈，而在它们之间则有较强倾斜上升流。非线性内波波形随积分时间改变，倾斜环流圈数目也在增加，最终形成负环流强于正环流的结果，并导致流函数、位密度扰动水平梯度剧增，其可视为间断。 相似文献
18.
风场和吞吐流是浅水湖泊运动的主要驱动力,影响着湖区污染物的迁移转化。基于二维非结构网格,构建了乌梁素海水动力模型。通过对比定常风作用下湖流的方向、环流的分布及形式与无风条件下的区别,模拟不同算例吞吐流作用下湖区流速及环流结构的差异,探究了定常风和吞吐流对乌梁素海流场的影响。结果表明:乌梁素海在无风条件下出现大面积的滞流区;风场会增加湖流的流速,影响区域主要在西大滩区、东大滩区及湖区南部明水区,产生明显环流,风场是乌梁素海主要的驱动力; SSW与ENE向风场作用下,典型区域产生的环流位置、形态结构相近,方向相反;吞吐流量的增加会增大湖区整体流速,对湖区流场形态、结构影响较小;定常风条件下,吞吐流量的增加(一定范围)会导致环流强度减弱。研究结果为乌梁素海营养盐、污染物质输移规律研究奠定基础。 相似文献
19.
With all the improvement in wave and hydrodynamics numerical models, the question rises in our mind that how the accuracy of the forcing functions and their input can affect the results. In this paper, a commonly used numerical third-generation wave model, SWAN is applied to predict waves in Lake Michigan. Wind data are analyzed to determine wind variation frequency over Lake Michigan. Wave predictions uncertainty due to wind local effects are compared during a period where wind has a fairly constant speed and direction over the northern and southern basins. The study shows that despite model calibration in Lake Michigan area, the model deficiency arises from ignoring wind effects in small scales. Wave prediction also emphasizes that small scale turbulence in meteorological forces can increase prediction errors by 38%. Wave frequency and coherence analysis show that both models can predict the wave variation time scale with the same accuracy. Insufficient number of meteorological stations can result in neglecting local wind effects and discrepancies in current predictions. The uncertainty of wave numerical models due to input uncertainties and model principals should be taken into account for design risk factors. 相似文献