共查询到20条相似文献，搜索用时 15 毫秒
1.
Kern E. Kenyon 《Journal of Oceanography》2006,62(6):923-927
Surface gravity waves are commonly observed to slow down and to stop at a beach without any noticeable reflection taking place.
We assume that as a consequence the waves are continuously giving up their linear and angular momenta, which they carry with
them, along with energy, as they propagate into gradually decreasing mean depths of water. It takes a force to cause a time
rate of decrease in the linear momentum and a torque to produce a time rate of decrease in the angular momentum. Both a force
and a torque operate on the shoaling waves, due to the presence of the sloping bottom, to cause the diminution of their linear
and angular momenta. By Newton’s third law, action equals reaction, an equal but opposite force and torque are exerted on
the bottom. No other mechanisms for transferring linear and angular momenta are included in the model. Since the force on
the waves acts over a horizontal distance during shoaling, work is done on the waves and energy flux is not conserved. Bottom
friction, wave interaction with a mean flow, scattering from small-scale bottom irregularities and set-up are neglected. Mass
flux is conserved, which leads to a shoreward monotonic decrease in amplitude consistent with available swell data. The formula
for the time-independent force on the bottom agrees qualitatively with observations in seven different ways: four for swell
attenuation and three for sediment transport on beaches. Ardhuin (2006) argues against a mean force on the bottom that is
not hydrostatic, mainly by using conservation of energy flux. He also applies the action balance equation to shoaling waves.
Action is a difficult concept to grasp for motion in a continuum; it cannot be easily visualized, and it is not really necessary
for solving the shoaling wave problem. We prefer angular momentum because it is clearly related to the observed orbital motion
of the fluid particles in progressive surface waves. The physical significance of wave action for surface waves has been described
recently by showing that in deep water action is equivalent to the magnitude of the wave’s orbital angular momentum (Kenyon
and Sheres, 1996). Finally, Ardhuin requires that there be a significant exchange of linear momentum between shoaling waves
and an unspecified mean flow, although the magnitude and direction of the exchange are not predicted. No mention is made of
what happens to the orbital angular momentum during shoaling. Mass flux conservation is not stated. 相似文献
2.
Fabrice Ardhuin 《Journal of Oceanography》2006,62(6):917-922
In a recent paper, Kenyon (2004) proposed that the wave-induced energy flux is generally not conserved, and that shoaling
waves cause a mean force and torque on the bottom. That force was equated to the divergence of the wave momentum flux estimated
from the assumption that the wave-induced mass flux is conserved. This assumption and conclusions are contrary to a wide body
of observations and theory. Most importantly, waves propagate in water, so that the momentum balance generally involves the
mean water flow. Although the expression for the non-hydrostatic bottom force given by Kenyon is not supported by observations,
a consistent review of existing theory shows that a smaller mean wave-induced force must be present in cases with bottom friction
or wave reflection. That force exactly balances the change in wave momentum flux due to bottom friction and the exchange of
wave momentum between incident and reflected wave components. The remainder of the wave momentum flux divergence, due to shoaling
or wave breaking, is compensated by the mean flow, with a balance involving hydrostatic pressure forces that arise from a
change in mean surface elevation that is very well verified by observations. 相似文献
3.
Kern E. Kenyon 《Journal of Oceanography》1997,53(1):89-92
The effects of the gravity torques acting on the angular momentum of surface gravity waves are calculated theoretically. For
short crested waves the gravity torque is caused by the force of gravity on the orbiting fluid particles acting down the slopes
of the crests and troughs and in the direction parallel to the crests and troughs. The gravity torque tries to rotate the
angular momentum vectors, and thus the waves themselves, counterclockwise in the horizontal plane, as viewed from above, in
both hemispheres. The amount of rotation per unit time is computed to be significant assuming reasonable values for the along-crest
and trough slopes for waves in a storm area. The gravity torque has a frequency which is double the frequency of the waves.
For long crested waves the gravity torque acts in the vertical plane of the orbit and tries to decelerate the particles when
they rise and accelerate them when they fall. By disrupting the horizontal cyclostrophic balance of forces on the fluid particles
(centrifugal force versus pressure force) the gravity torque accounts qualitatively for the three characteristics of breaking
waves: that they break at the surface, that they break at the crest, and that the crest breaks in the direction of wave propagation. 相似文献
4.
Low-frequency waves in the surf and swash zones on various beach slopes are discussed using numerical simulations. Simulated surface elevations of both primary waves and low-frequency waves across the surf zone were first compared with experimental data and good agreement found. Low-frequency wave characteristics are then discussed in terms of their physical nature and their relationship to the primary wave field on a series of sea bottom slopes. Unlike primary waves, low-frequency wave energy increases towards the shoreline. Low-frequency waves in the surf and swash are a function of incident waves and the sea bottom slope and hence the saturation level of the surf zone. Wave energy on a gently sloping beach is dominated by low-frequency waves while primary waves play a significant role on a steep beach. Low-frequency wave radiation from the surf zone on a given beach depends on primary wave frequency and beach slope. However, a very poor correlation was found between surf similarity parameter and low-frequency wave radiation. 相似文献
5.
海岸沙坝近底悬移质通量实验研究 总被引：1，自引：0，他引：1
为了研究海岸沙坝的产生和演化机理,对不规则波和波群作用下沙坝上方的近底悬移质通量进行了实验研究。分析了短波、长波和平均水流对悬移质通量的影响。结果表明:各种波况下平均水流和长波的作用始终使泥沙向离岸方向输移,而短波的作用使泥沙向岸方向运动;平均水流引起的泥沙输移始终占主要成分,长波的次之。不规则波情况下平均水流的影响较规则波的情况相对较弱,三种成分对泥沙输运的贡献属于同一量级。波群情况下长波的影响随着波浪群性的增强而加大,短波的不明显,而平均水流的影响则随着波浪群性的增强而减弱。 相似文献
6.
In the recent paper by Tai-Wen Hsu, John R.-C. Hsu, Wen-Kai Weng, Swun-Kwang Wang, and Shan-Hwei Ou (Coastal Engineering, 53, 865–877, 2006), the authors derived theoretical formulations for calculating the wave setup and setdown induced by obliquely incident waves on a beach. The derivation of an expression for setdown contains errors which would lead to an imbalance in longshore momentum flux outside the surfzone. We correct their derivation and give results in terms of the radiation stress concept in a general case including an oblique wave incidence. We also point out that the correct form of wave setdown is important to describe the zero-net force in the momentum balance outside the surfzone. 相似文献
7.
Physical models of submerged partial revetment structures were built on natural beach sand with a diameter of 0.35 mm and specific gravity of 2.63. The armor units, the diameter and specific gravity of which varied in the range of 8.5–67.95 mm and 1.81–2.77 respectively, were placed only on wave breaking areas. A series of experiments has been conducted on the conditions of different armor units and different wave characteristics using regular waves and irregular waves. Based on the experimental data, the effects of wave height, wave period, diameter and specific gravity of armor units, water depth in the channel, and wave types on static damage of given structures are assessed. Some empirical formulas have been suggested through regression analysis to describe static stability and stability number of submerged partial revetment structures under pure regular waves, pure irregular waves, and regular–irregular waves. The suggested formulas compared with Van der Meer’s (1988) formulas and some differences have occurred because of differences among revetment types and test conditions; therefore, proposed formulas give reasonable results for the test conditions used. 相似文献
8.
《Coastal Engineering》2006,53(7):545-555
In the paper, the three-dimensional structure of the wave-induced momentum flux in irrotational waves propagating over a two-dimensional, irregular bathymetry is analyzed. The expansion method developed by de Vriend and Kitou [de Vriend, H.J., Kitou, N., 1990a. Incorporation of wave effects in a 3D hydrostatic mean current model. Delft Hydraulics Report H-1295. de Vriend, H.J., Kitou, N., 1990b. Incorporation of wave effects in a 3D hydrostatic mean current model. Proc. 22nd Int. Coast. Eng. Conf. ASCE, 1005–1018.] for unidirectional waves has been extended to derive expressions for velocity components in three-dimensional waves over sloping bottom. The vertical wave-induced momentum flux resulting from this solution has been shown to be vertically-varying (contrary to the 2D-V case) and to act as a counterbalance for the vertical variability of the other wave forcing terms in the momentum equations. Thus, the total wave forcing remains depth-invariant, but—contrary to the ‘traditional’ solution based on the radiation stress concept—it does not depend explicitly on the direction of wave propagation and is a simple function of gradients of wave energy and water depth only. One of the most important consequences of this fact is the lack of the longshore-current-generating force in the case of non-dissipative waves approaching a shore with a bottom profile uniform in the along-shore direction. To illustrate the meaning of the new solution, the wave forcing due to waves approaching a barred beach has been analysed in detail. Also, the present solution has been shown to give the same results as the one obtained by extending of the approach by Rivero and Arcilla [Rivero, F.J., Arcilla, A.S., 1995. On the vertical distribution of 〈ũw˜〉. Coast. Eng. 25, 137–152.] to three dimensions. 相似文献
9.
植被斜坡岸滩海啸波消减数值模拟研究 总被引：1，自引：0，他引：1
An explicit one-dimensional model based on the shallow water equations(SWEs) was established in this work to simulate tsunami wave propagation on a vegetated beach. This model adopted the finite-volume method(FVM)for maintaining the mass balance of these equations. The resistance force caused by vegetation was taken into account as a source term in the momentum equation. The Harten–Lax–van Leer(HLL) approximate Riemann solver was applied to evaluate the interface fluxes for tracing the wet/dry transition boundary. This proposed model was used to simulate solitary wave run-up and long-periodic wave propagation on a sloping beach. The calibration process suitably compared the calculated results with the measured data. The tsunami waves were also simulated to discuss the water depth, tsunami force, as well as the current speed in absence of and in presence of forest domain. The results indicated that forest growth at the beach reduced wave energy loss caused by tsunamis. A series of sensitivity analyses were conducted with respect to variable parameters(such as vegetation densities, wave heights, wave periods, bed resistance, and beach slopes) to identify important influences on mitigating tsunami damage on coastal forest beach. 相似文献
10.
在波浪和水流的作用下,泥沙在不同时间尺度下的运动会引起沙滩的冲淤演变,对海岸资源有重要的影响。因此,了解沙滩季节性演变规律,并采取针对性的防护措施,是近岸沙滩亟须解决的问题。目前,现场观测是研究沙滩剖面冲淤演变的重要方法,通过沉积物组成、岸滩坡度及波浪动力的时空变化,了解沙滩剖面的变化特性,对于沙滩管理和海岸保护具有十分重要的意义。基于2017年9月—2019年11月在荣成楮岛南岸沙滩每个月采集一次的剖面数据,以及波浪动力数据,分别探究了沙滩在不同时间尺度下的变化特征,并对沙滩变化特征与波浪动力因素的相关性进行了探讨。研究发现：楮岛南岸沙滩形态变化具有较强的季节性特征,春季沙滩比较稳定;夏季沙滩受台风影响侵蚀严重,但在风暴过后的短时间内,沙滩泥沙恢复较快;冬季沙滩恢复速度逐渐减缓并趋于稳定。在夏季和冬季期间,波能流密度的向岸分量对楮岛南沙滩的演变产生重要作用,而且波能流密度向岸分量的均值（选取数据采集前15 d的波浪条件参与计算）与沙滩体积的相关性最好,并给出了两者的线性拟合公式。 相似文献
11.
低频长波对港湾共振、泥沙输运、波浪爬高与越浪等过程有重要影响。采用非静压模型SWASH模拟了不规则波在浅滩上的传播及破碎过程,重点探讨了滩顶短波破碎程度对低频波能演变的影响。模拟结果显示,当滩顶短波处于临界破碎状态时,低频波能流沿浅滩持续增长,浅滩对低频长波的放大效应（滩后与滩前低频波能流之比）显著;当滩顶短波轻微破碎、破波仅发生在外破波区时,低频波能流的沿滩增长率进一步变大;当滩顶短波剧烈破碎、破波延续到内破波区时,低频波能流沿滩先增长而后转为衰减,滩后放大率较临界破碎时明显减小。研究结果表明,浅滩顶部水深改变了短波破碎程度,进而影响低频长波的演化过程,浅滩上长波总体增长率随滩顶水深的减小呈现先增大后减小的规律,在短波轻微破碎时最大。 相似文献
12.
利用大型水槽设计了在由深水到近岸不同坡度处海浪在变浅作用下诱导产生的长周期重力波的实验。正态随机海浪在深水生成并沿斜坡向浅水传播,记录了不同水深处波面高度随时间的变化过程并进行统计分析和谱分析。实验数据分析结果表明,长周期重力波的能量随着水深的变浅而增高,其谱锋频率位于0.2~0.3fp附近,这里fp是深水正态海浪过程的谱峰频率。长周期重力波的能量与入射波的能量比与波面高度分布的偏度密切相关。进一步分析了两种波动的能量谱峰值比和波面高度分布偏度的相关关系,获得了经验关系,为预测近岸浅水长周期重力波提供了科学依据。 相似文献
13.
利用涌浪影响下短时段内的冲流带滩面高频高程数据和碎波带波流资料,在奇异谱分析(SSA)的基础上,对比研究了不同形态滩面的冲淤变化趋势、趋势分布形状、冲淤变化周期和冲淤变化强度,以及同一条剖面不同桩点间各因素间的变化关系;用交叉谱方法探索了每分钟滩面高频冲淤变化与碎波带长重力波间的作用关系。分析结果表明,滩角韵律地形引起的冲流分流作用促进了滩脊向滩谷的泥沙转运,冲流带滩面存在明显的长重力波频段的周期性冲淤振动,滩面冲淤振动强度由滩面下部向上部递减,碎波带长重力波对滩面高频冲淤变化起重要作用。 相似文献
14.
We consider steady, slowly varying water waves propagating on a steady current over a gently sloping bed, so-called current depth refraction. All expressions are correct to second order in wave amplitude. Formulating the energy equation for the fluctuating motion in terms of wave action (wave energy divided by intrinsic angular frequency) results in an expression, where the dissipative term is strikingly similar to wave action itself. It is simply the ‘extra’ dissipation (per unit area) caused by the fluctuating motion (i.e. total dissipation minus the effect of current acting on total mean bed shear stress) divided by the intrinsic angular frequency. We call it ‘wave action dissipation’. An inconsistency in Phillips' (1977) book is pointed out. A new formula for the calculation of wave amplitudes along rays is set forth. 相似文献
15.
Surf zone dynamics simulated by a Boussinesq type model. Part I. Model description and cross-shore motion of regular waves 总被引：2，自引：0，他引：2
This is the first of three papers on the modelling of various types of surf zone phenomena. In this first paper, part I, the model is presented and its basic features are studied for the case of regular waves. The model is based on two-dimensional equations of the Boussinesq type and it features improved linear dispersion characteristics, possibility of wave breaking, and a moving boundary at the shoreline. The moving shoreline is treated numerically by replacing the solid beach by a permeable beach characterized by an extremely small porosity. Run-up of nonbreaking waves is verified against the analytical solution for nonlinear shallow water waves. The inclusion of wave breaking is based on the surface roller concept for spilling breakers using a geometrical determination of the instantaneous roller thickness at each point and modelling the effect of wave breaking by an additional convective momentum term. This is a function of the local wave celerity, which is determined interactively. The model is applied to cross-shore motions of regular waves including various types of breaking on plane sloping beaches and over submerged bars. Model results comprise time series of surface elevations and the spatial variation of phase-averaged quantities such as the wave height, the crest and trough elevations, the mean water level, and the depth-averaged undertow. Comparisons with physical experiments are presented. The phaseaveraged balance of the individual terms in the momentum and energy equation is determined by time-integration and quantities such as the cross-sectional roller area, the radiation stress, the energy flux and the energy dissipation are studied and discussed with reference to conventional phase-averaged wave models. The companion papers present cross-shore motions of breaking irregular waves, swash oscillations and surf beats (part II) and nearshore circulations induced by breaking of unidirectional and multidirectional waves (part III). 相似文献
16.
A three-dimensional, multi-level model was used to study the energy dissipation of semidiurnal internal Kelvin waves due to their interaction with bottom topography. A simplified topography consisting of a channel with an additional shallow bay was used to clarify the wave’s scattering process. When the first mode semidiurnal internal wave given at an open boundary arrives at the bay mouth, higher-mode internal waves are generated at a step bottom of the bay mouth. As a result, the energy of the first mode internal Kelvin wave is effectively decayed. The decay rate of the internal Kelvin wave depends on both the width and length of the additional bay. The maximum decay rate was found when a resonance condition occurs the bay, that is, the bay length is equal to a quarter of wave length of the first mode internal wave on the shallow region. The decay rate in the wide bay cases is higher than that in a narrow case, due to a contribution from the scattering due to the Poincare wave that emanates from the corners of the bay head. The decay rate with the additional bay is 1.1–1.8 times that of the case without the additional bay. The decay rate due to the scattering process is found to be of the same order as that of the internal and bottom friction. 相似文献
17.
18.
The boundary layer characteristics beneath waves transforming on a natural beach are affected by both waves and wave-induced
currents, and their predictability is more difficult and challenging than for those observed over a seabed of uniform depth.
In this research, a first-order boundary layer model is developed to investigate the characteristics of bottom boundary layers
in a wave–current coexisting environment beneath shoaling and breaking waves. The main difference between the present modeling
approach and previous methods is in the mathematical formulation for the mean horizontal pressure gradient term in the governing
equations for the cross-shore wave-induced currents. This term is obtained from the wave-averaged momentum equation, and its
magnitude depends on the balance between the wave excess momentum flux gradient and the hydrostatic pressure gradient due
to spatial variations in the wave field of propagating waves and mean water level fluctuations. A turbulence closure scheme
is used with a modified low Reynolds number k-ε model. The model was validated with two published experimental datasets for normally incident shoaling and breaking waves
over a sloping seabed. For shoaling waves, model results agree well with data for the instantaneous velocity profiles, oscillatory
wave amplitudes, and mean velocity profiles. For breaking waves, a good agreement is obtained between model and data for the
vertical distribution of mean shear stress. In particular, the model reproduced the local onshore mean flow near the bottom
beneath shoaling waves, and the vertically decreasing pattern of mean shear stress beneath breaking waves. These successful
demonstrations for wave–current bottom boundary layers are attributed to a novel formulation of the mean pressure gradient
incorporated in the present model. The proposed new formulation plays an important role in modeling the boundary layer characteristics
beneath shoaling and breaking waves, and ensuring that the present model is applicable to nearshore sediment transport and
morphology evolution. 相似文献
19.
通过波浪水槽实验,开展不同类型波浪作用下的沙质岸滩演化规律研究工作。本次实验研究不考虑比尺,采用1:10与1:20组成的复合沙质斜坡对岸滩进行概化,选取规则波和椭圆余弦波两种典型波浪作用,对波浪的传播、变形和破碎、上爬、回落过程以及波浪作用前后沙质岸滩床面地形进行了观测,探讨波浪作用下沙质岸滩剖面演化规律。本文实验工况中,规则波作用下,岸滩剖面呈现出沙坝剖面和滩肩剖面,椭圆余弦波作用下的岸滩剖面均呈滩肩形态,发现岸滩剖面形态不仅与波浪作用类型、强度、周期等因素相关,还与波浪破碎的强度等因素有关。通过对实验过程中现象的进行观察和分析,引入了卷破波水舌冲击角的概念。对波浪卷破破碎后形成的水流挟沙运动与岸滩剖面形态的关系进行定性分析,对水舌冲击角与Irribarren参数之间的关系进行定量分析,基于Irribarren参数与岸滩剖面形态的关系初步建立了波浪作用下沙质岸滩剖面形态判别关系式。通过本文实验结果和前人实验结果对趋势线进行拟合,求得其判别系数,判别式能够较好地划分淤积型岸滩、侵蚀型岸滩及过渡型岸滩三种岸滩形态。 相似文献
20.
文章基于长乐海滩前滨剖面的实测波浪数据, 通过统计分析以及谱分析的方法, 探讨了潮汐过程中长乐海滩波浪参数及耗能过程的变化规律。结果表明, 观测期间内波浪以混合浪为主, 各测点谱型较宽, 存在多峰振荡现象。向岸传播过程中, 波能耗散的形式为窄频域向宽频域转变, 能量分布趋于分散, 高频波能减小, 低频波能反而有所上升, 波浪破碎后生成长重力波。破波带内的能量衰减与波浪传播距离具有良好的相关性, 破碎波能在破波带内大约衰减了98.3%。潮汐水位对波浪具有明显的调制作用。入射波能随潮汐水位的增加而有所增加, 且水位越高, 入射波能分布越分散。破波带内的有效波高和潮汐水位具有显著的正相关关系。潮汐过程中固定测点的波谱变化与波浪沿剖面的波谱变化具有明显的相似性。 相似文献