Generation of a double Kelvin wave resulting from the reflection of the Rossby wave by the jump layer

This paper considers the evolution of a spatially-localized divergent Rossby wave field near the depth jump. If the jump magnitude is comparable to the depth, Rossby waves are fully reflected and a double Kelvin wave is then generated. The Rossby waves and the double Kelvin wave are described by the first- and zero-approximation fields of the asymptotic expansion, respectively. Over the characteristic Rossby wave period, the level elevation produced by the double Kelvin wave spreads over an extensive area, theraby making up for the change in the total fluid mass of the Rossby waves.Translated by Vladimir A. Puchkin.     

Analysis of Energy Overshoot of High Frequency Waves with Wavelet Transform

—A study is made on the overshoot phenomena in wind-generated waves.The surface displace-ments of time-growing waves are measured at four fetches in a wind wave channel.The evolution of highfrequency waves is displayed with wavelet transform.The results are compared with Sutherland's. It isfound that high frequency wave components experience much stronger energy overshoot in the evolution.The energy of high frequency waves decreases greatly after overshoot.     

Physical Investigation of Directional Wave Focusing and Breaking Waves in Wave Basin

An experimental scheme for the generation of directional focusing waves in a wave basin is established in this paper. The effects of the directional range, frequency width and center frequency on the wave focusing are studied. The distrihution of maximum amplitude and the evolution of time series and spectra during wave packet propagation and the variation of water surface parameters are extensively investigated. The results reveal that the characteristics of focusing waves are significantly influenced hy wave directionality and that that breaking criteria for directional waves are distinctly different from those for unidirectional waves.     

球坐标系下MASNUM海浪数值模式的建立及其应用

为开展海浪对海洋上混合层的搅拌混合作用及其对海气界面通量的影响等研究,在LAGFD WAM区域海浪数值模式基础上建立了球坐标系下的全球海浪数值模式.重点导出了球坐标系下的海浪能量谱平衡方程及其复杂特征线方程,该组方程包含了背景流场对波动传播的调整、波动沿大圆传播的折射等.数值积分则采用复杂特征线嵌入计算格式.初步数值模拟结果表明,该海浪全球数值模式能够较为精确地刻画海浪的动力过程.     

Modulation of short wind waves by a long surface wave: a mechanism for feedback with an air flow

The paper concentrates on the evolution of a spectrum of short wind waves (SW) along the profile of a long surface wave (LW). Short wave spectral variations are considered in the relaxation approximation. The SW spectrum is modulated by the orbital velocities of long waves and by the variations of wind stress along the LW profile. The latter effect occurs due to wind flux perturbations induced by both the long wave proper and variations of the sea surface roughness induced by the SW modulations. To describe this effect, a feedback mechanism is introduces—the growth of energy of short waves results in the larger roughness of the sea surface, thereby contributing to the local wind stress, which facilitates, in turn, the growth of short waves. With moderate and strong winds being involved, this effect (aerodynamic feedback) is shown to be dominant in the short wave spectrum modulation. The mechanism becomes more efficient with intensification of the wind and decreasing of the long waves' frequency. Results of model calculations are in agreement with the known experimental data. Translated by Vladimir A. Puchkin.     

Comparison of experimental irregular water wave elevation and kinematic data with new hybrid wave model predictions

Surface water wave elevations and kinematics from four unidirectional irregular wave trains, with a Pierson and Moskowitz or JONSWAP random wave spectrum, were measured in the laboratory using resistance wave probes and a laser Doppler anemometer. The wave elevation data, velocity time series, extreme (largest) wave horizontal velocity profiles and extreme wave acceleration fields are compared with the predictions of a new wave kinematics model, named the hybrid wave model. Irregular waves are commonly viewed as the summation of many linear wave components of different frequencies, but more accurate predictions of downstream surface elevations (wave evolution) and wave kinematics are attained by considering the non-linear interactions among wave components. The hybrid wave model incorporates these non-linear wave component interactions, and its wave evolution predictions and kinematics estimates are compared with laboratory measurements in this study. Linear random wave theory, Wheeler stretching and linear extrapolation wave kinematic prediction techniques are also compared. Comparisons between measurements and hybrid wave model estimates demonstrate its improved capability to predict velocity and acceleration fields and wave evolution in two-dimensional irregular waves.     

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.     

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。     

Theoretical and Experimental Study of Breaking Wave on Sloping Bottoms

This paper studies the continuous evolution of breaking wave for the surface water waves propagating on a sloping beach. A Lagrangian asymptotic solution is derived. According to the solution coupled with the wave breaking criteria and the equations of water particles motion, the wave deformation and the continuous wave breaking processes for the progressive water waves propagating on a sloping bottom can be derived. A series of experiments are also conducted to compare with the theoretical solution. The results show that the present solution can reasonably describe the plunging or spilling wave breaking phenomenon.     

基于浮标站和ERA5 再分析资料的浙江沿海台风浪特征分析

为了分析台风影响下浙江沿海风和浪的演变特点，利用浙江省海洋浮标站监测数据和欧洲中期天气预报中心第五代全球气候大气再分析数据（European Centre for Medium-Range Weather Forecasts Reanalysis v5，ERA5），选取2010年以来严重影响浙江的7次台风个例，对台风作用下浙江沿海海面风和浪的演变特点进行分析。结果表明：在台风影响过程中，海浪波型多数呈现混合浪-风浪-混合浪的演变规律；涌浪波型的出现与台风强度及其与浮标站的距离和方位有关，也与海洋潮汐现象紧密相关。台风影响期间，浙江沿海浪高的变化受风速和风向共同作用影响。在风向不变的情况下，持续风速增大对浪高的增大有明显作用；风向的变化也会对浪高变化产生影响，向岸风和离岸风的转变会造成浪高出现剧烈变化。ERA5 再分析资料有效波高在台风浪较大时会呈现偏小的趋势，分析订正后的ERA5 有效波高发现，台风浪有效波高大值区与台风中心位置相关。研究结果可为严重影响浙江沿海的台风浪预报服务提供参考。     

畸形波生成、演化过程研究——波面时间过程随位置的变化

基于完全非线性波浪数值模型,模拟实测畸形波的生成、演化过程,进而分析波面时间过程和畸形波参数的变化规律.研究结果表明:在畸形波形成前、后均可能出现连续的大波和“深谷”现象.在畸形波生成、演化过程中出现的“深谷”和畸形波具有伴生性而非独立异常波浪现象.上述大波、“深谷”和畸形波的连续作用对海洋结构物和船舶造成的潜在威胁可...     

马蹄波波形特征和对圆柱作用实验研究

为了研究真实海洋表面马蹄波特性以及对建筑物的作用,通过物理模型实验研究了马蹄波的波形特征参数以及马蹄波对圆柱体的作用。实验中通过对浪高仪采集的波面升高时间历程曲线进行分析得出了不同水深情况下马蹄波的垂向几何特征,并通过快速傅里叶变换得出了马蹄波波幅谱的特征,研究了马蹄波各组成波波幅沿空间的变化从而得出了圆柱存在对马蹄波演化的影响,同时给出马蹄波绕射形成的波面分布和不同频率谐波在圆柱周围的分布,讨论了马蹄波不同于Stokes波对圆柱作用的特征。结果表明,马蹄波波形受水深影响较大,水深越浅,马蹄波的波面形状越接近椭圆余弦波。圆柱体的存在干扰了马蹄波不稳定的增长,使其在接近圆柱时呈下降趋势,导致不稳定幅值最大值的位置提前并且出现在偏离圆柱迎浪点的侧表面,从而使圆柱受到侧向力的作用。     

Numerical simulation of nonlinear dispersive waves propagating over a submerged bar by IB–VOF model

It is a good test for a numerical model to simulate progressive waves propagating over a submerged bar with a relatively high ratio of slopes. In this paper, the combined IB–VOF model is used to predict nonlinear dispersive waves propagating over a submerged bar with both slopes of 1:2. The predicted free surface elevations are compared with the experimental data and numerical results presented by other researchers. The comparison shows that the IB–VOF model is able to provide satisfactory wave profiles in the shallow water with strong nonlinear effects and in the wave transmitted region with strong wave dispersion in particular. Moreover, the wave evolution behind the submerged bar is described in detail, including the spatial wave profile modulation, spectral analysis of the time-series waves, flow velocity and pressure fields, and kinetic energy distribution. The effect of fluid viscosity on the numerical simulations is also studied, and it is found that the effect on the wave evolution considered in this paper is not significant. Finally, the hydrodynamic force acting on the bar is calculated using the IB–VOF model.     

The influence of bubble clouds on acoustic propagation in the surfzone

High-frequency propagation close to an active surf line is explored with 12and 100-kHz propagation paths together with measurements of bubble clouds, bubble size distributions, and waves. Breaking waves inject massive bubble plumes that are mixed downwards from the roller region by intense turbulence. If these injections follow one another at intervals less than the time taken for the bubbles to rise to the surface, acoustic signals will be continuously blocked, forming an acoustical barrier that effectively inhibits any propagation. Occasionally, waves break seaward of this barrier. In this case, dense bubble clouds are mixed down beneath the air entrainment zone, but there is sufficient time for them to disappear before succeeding breakers, allowing intermittent high-frequency propagation recharge the bubble field. The duration and shape of signal dropouts are then determined by the selective removal of bubbles by buoyancy and dissolution. In addition to turbulence created by the air entrainment process, a lower level of continuous background turbulence may be generated by interaction of residual currents with the wave boundary layer. Our observations illustrate the variable character of acoustic blocking by bubble clouds and serve as a basis for quantitative analysis of these effects with a 2D propagation model coupled to 2D models of bubble cloud evolution and background turbulence     

Nonlinear effects in the process of propagation of internal waves with regard for the turbulent viscosity and diffusion

By the method of asymptotic multiscale expansions in the Boussinesq approximation, we study nonlinear effects observed in the process of propagation of internal waves with regard for the turbulent viscosity and diffusion. We determine the decrement of attenuation of waves and the boundary-layer solutions at the bottom and on the free surface. The wave-induced mean current is found in the second order of smallness in the wave steepness. The coefficients of the nonlinear Schr?dinger equation are obtained for the envelope of the wave packet. It is shown that a weakly nonlinear plane wave is stable under longitudinal modulation in the long-wave limit. If the wavelength is smaller than a certain critical value, then the wave is unstable under modulation.     

Evolution of waves induced by periodic variations of pressure in a bounded basin of variable depth

Within the framework of the linear theory of long waves, we study the evolution of a wave process caused by the action of surface pressure periodically varying in time in a bounded basin of variable depth without vertical walls. We assume that the basin is filled with a homogeneous liquid nonperturbed at the initial time and take into account the action of dissipative forces. We obtain the analytic solution of the posed problem. It is used to perform the detailed analysis of the influence of the dissipative forces and the frequency of perturbing pressure on the characteristics of the process of evolution of waves. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

内波远距离传播演化的实验研究

为了研究内波远距离传播过程中的演化规律,本文采用图像测速法(PIV)分别对内波近场和远场的速度场进行测量。实验中同时采用两台CCD相机对实验区域进行拍摄,根据实验结果对内波能量和垂向模态结构进行计算分析。实验结果表明,在近场区域生成的内波主要表现为内波射线结构。内波射线在经过海表面反射后,其能量在空间上出现非对称结构,能量在加强区域较减弱区增加约15%。在远场,内波射线结构不再清晰,内波主要表现为低模态内波结构。内波射线在反射时能量衰减显著,损失约为50%;低模态内波可以离开内波生成源地远距离传播,传播过程中能量损失较小,在远场传播过程中(第一模态内波半波长的距离)能量损失约20%。低模态内波的传播相速度介于垂向第一模态和第二模态相速度之间。     

An experimental investigation of the velocity field under cnoidal waves over the asymmetric rippled bed

1 IntroductionIn coastal areas a ubiquitous phenomenon is theformation of ripples in the seabed. It is now widelyaccepted that the flow and sediment transport overseabed are vital in relation to erosion, surface wavedissipation and pollution dispersion et…     

浙江东矶列岛海域实测波要素及典型台风浪特征分析

利用东矶列岛海域一年实测波浪资料,统计分析波要素特征,以台风“利奇马”为例,分析台风浪演变过程。结果表明：研究海域年平均有效波高0.88 m,年平均周期4.3 s,年最大波高8.67 m出现在夏季台风“利奇马”影响时。研究海域以轻浪为主,其次是小浪和中浪;常浪向为ESE,次常浪向为E和SE;强浪向为SSE,次强浪向为SE。波浪平均持续时间和波高之间符合指数衰减关系。台风“利奇马”影响期间,最大谱峰56.20 m²/Hz,台风浪谱型以双峰谱为主,台风浪类型经历了涌浪—混合浪—风浪—混合浪—涌浪这一演变过程。     

Analysis of energy characteristics in the process of freak wave generation

The energy characteristics in the evolution of the wave train are investigated to understand the inherent cause of the freak wave generation. The Morlet wavelet spectrum method is employed to analyze the numerical, laboratory and field evolution data of this generation process. Their energy distributions and variations are discussed with consideration of corresponding surface elevations. Through comparing the energy characteristics of three cases, it is shown that the freak wave generation depends not only on the continuous transfer of wave train energy to a certain region where finally the maximum energy occurs, but also on the distinct shift of the converged energy to high-frequency components in a very short time. And the typical energy characteristics of freak waves are also given.