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1.
Large Eddy Simulation for Wave Breaking in the Surf Zone 总被引：1，自引：0，他引：1
BAI Yuchuan BAI Yuchuan JIANG Changbo SHEN Huanting 《中国海洋工程》2001,(4):541-552
In this paper, (he large eddy simulation method is used combined with the marker and cell method to study the wave propagation or shoaling and breaking process. As wave propagates into shallow water, the shoaling leads lo the increase of wave height, and then at a certain position, the wave will be breaking. The breaking wave is a powerful agent for generating turbulence, which plays an important role in most of the fluid dynamic processes throughout the surf zone, such as transformation of wave energy, generation of near-shore current and diffusion of materials. So a proper numerical model for describing the turbulence effect is needed. In this paper, a revised Smagorinsky subgrid-scale mode! is used to describe the turbulence effect. The present study reveals that the coefficient of the Smagorinsky model for wave propagation or breaking simulation may be taken as a varying function of the water depth and distance away from the wave breaking point. The large eddy simulation model presented in this pape 相似文献
2.
《Coastal Engineering》2006,53(4):311-318
The extended mild-slope equations of Suh et al. [Suh, K.D., Lee, C., Park, W.S., 1997. Time-dependent equations for wave propagation on rapidly varying topography. Coastal Eng., 32, 91–117] and Lee et al. [Lee, C., Kim, G., Suh, K.D., 2003. Extended mild-slope equation for random waves. Coastal Eng., 48, 277–287] are compared analytically and numerically to determine their applicability to random wave transformation. The geometric optics approach is used to compare the two models analytically. In the model of Suh et al., the wave number of the component wave with a local angular frequency ω is approximated with an accuracy of O(ω − ω¯) at a constant water depth, where ω¯ is the carrier frequency of random waves. In the model of Suh et al., however, the diffraction effects and higher-order bottom effects are considered only for monochromatic waves, and the shoaling coefficient of random waves is not accurately approximated. This inaccuracy arises because the model of Suh et al. was derived for regular waves. In the model of Lee et al., all the parameters of random waves such as wave number, shoaling coefficient, diffraction effects, and higher-order bottom effects are approximated with an accuracy of O(ω − ω¯). This approximation is because the model of Lee et al. was developed using the Taylor series expansion technique for random waves. The result of dispersion relation analysis suggests the use of the peak and weighted-average frequencies as a carrier frequency for Suh et al. and Lee et al. models, respectively. All the analytical results are verified by numerical experiments of shoaling of random waves over a slightly inclined bed and diffraction of random waves through a breakwater gap on a flat bottom. 相似文献
3.
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
4.
Several levels of increasing complexity of transferring wave information from offshore to nearshore have been studied to quantify their influence on extreme beach erosion estimates. Beach profiles which have been monitored since 1976 were used to estimate extreme beach erosion and compared to predictions. Examination of the wave propagation assumptions revolves around two types of offshore to nearshore transfer: excluding or including wave breaking and bottom friction. A second complication is whether still water level variations (ocean tide plus storm surge) are included.The inclusion of various combinations of wave propagation processes other than shoaling and refraction in the wave transfer function changes on the extreme erosion distribution tail through lowering estimates above one year return period. This brings the predicted tails closer to the observations, but does not capture the upper limit of storm demand implied by the extensive beach profile data set. Including wave breaking has a marked effect on probabilistic estimates of beach erosion. The inclusion of bottom friction is less significant. The inclusion of still water level variability in the wave transfer calculation had minimal impact on results for the case study site, where waves were transferred from offshore to water at 20 m depth. These changes were put into perspective by comparing them to changes resulting from limiting beach erosion by adjusting the statistical distributions of peak wave height and storm duration to have maximum limits. We conclude that the proposed improvements on wave transformation methods are as significant as limiting wave erosion potential and worth including. 相似文献
5.
The interaction between the liquid sloshing in a rectangular tank equipped inside the barge and the barge responses has been investigated through a comprehensive experimental program. The barge was subjected to both regular and random wave excitations under beam sea condition. Three relative fill levels (hs/l) with liquid fill depth (hs) to length of tank (l) ratio of 0.163, 0.325 and 0.488 were considered. In addition, the barge responses of equivalent dry weight condition corresponding to each fill level were measured to understand the influence of sloshing. While the excitation wave frequency equals to first mode natural sloshing frequency, a noticeable decrease in the sway response has been observed. However, the effect of sloshing oscillation on the heave response is insignificant. A split up of roll resonance was observed for the aspect ratio of 0.163 due to the coupling effect of roll motion and sloshing. 相似文献
6.
A fully nonlinear Boussinessq-type model with several free coefficients is considered as a departure point. The model is monolayer and low order so as to simplify numerical solvability. The coefficients of the model are here considered functions of the local water depth. In doing so, we allow to improve the dispersive and shoaling properties for narrow banded wave trains in very deep waters. In particular, for monochromatic waves the dispersion and shoaling errors are bounded by ~ 2.8% up to kh = 100, being k the wave number and h the water depth. The proposed model is fully nonlinear in weakly dispersive conditions, so that nonlinear wave decomposition in shallower waters is well reproduced. The model equations are numerically solved using a fourth order scheme and tested against analytical solutions and experimental data. 相似文献
7.
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
8.
9.
This paper provides an approach by which the scour depth below pipelines in shoaling conditions beneath non-breaking and breaking random waves can be derived. Here the scour depth formula in shoaling conditions for regular non-breaking and breaking waves with normal incidence to the pipeline presented by Cevik and Yüksel [Cevik, E. and Yüksel, Y., (1999). Scour under submarine pipelines in waves in shoaling conditions. ASCE J. Waterw., Port, Coast. Ocean Eng., 125 (1), 9–19.] combined with the wave height distribution including shoaling and breaking waves presented by Mendez et al. [Mendez, F.J., Losada, I.J. and Medina, R., (2004). Transformation model of wave height distribution on planar beaches. Coast. Eng. 50 (3), 97–115.] are used. Moreover, the approach is based on describing the wave motion as a stationary Gaussian narrow-band random process. An example of calculation is also presented. 相似文献
10.
A three-dimensional time-domain potential flow model is developed and applied to simulate the wave resonance in a gap between two side-by-side rectangular barges. A fourth-order predict-correct method is implemented to update free surface boundary conditions. The response of an up-wave barge is predicted by solving the motion equation with the Newmark-β method. Following the validation of the developed numerical model for wave radiation and diffraction around two side-by-side barges, the influence of up-wave barge motion on the gap surfaceresonance is investigated in two different locations of the up-wave barge relative to the back-wave barge at various frequencies. The results reveal that the freely floating up-wave barge significantly influences the resonance frequency and the resonance wave amplitude. Simultaneously, the up-wave barge located in the middle of the back-wave barge leads to a reduction in the resonance wave amplitude and motion response when compared with other configurations. 相似文献
11.
This paper builds on the work of Masselink [Masselink, G., 1993. Simulating the effects of tides on beach morphodynamics. J. Coast. Res. SI 15, 180–197.] on the use of the residence times of shoaling waves, breaking waves and swash/backwash motions across a cross-shore profile to qualitatively understand temporal beach behaviour. We use a data set of in-situ measurements of wave parameters (height and period) and water depth, and time-exposure video images overlooking our single-barred intertidal measurement array at Egmond aan Zee (Netherlands) to derive boundaries between the shoaling zone, the surf zone and the swash zone. We find that the boundaries are functional dependencies of the local relative wave height on the local wave steepness. This contrasts with the use of constant relative wave heights or water levels in earlier work. We use the obtained boundaries and a standard cross-shore wave transformation model coupled to an inner surf zone bore model to show that large (> 5) relative tide ranges (RTR, defined as the ratio tide range–wave height) indicate shoaling wave processes across almost the entire intertidal profile, with surf processes dominating on the beach face. When the RTR is between 2 and 5, surf processes dominate over the intertidal bar and the lower part of the beach face, while swash has the largest residence times on the upper beach face. Such conditions, associated with surf zone bores propagating across the bar around low tide, were observed to cause the intertidal bar to migrate onshore slowly and the upper beach face to steepen. For RTR values less than about 2, surf zone processes dominate across the intertidal bar, while the dominance of swash processes now extends across most of the beach face. The surf zone processes were now observed to lead to offshore bar migration, while the swash eroded the upper beach face. 相似文献
12.
基于非静压单相流模型NHWAVE建立了高精度二维数值波浪水槽,采用日本2011年实测真实海啸波型系统研究了海啸波在岛礁上传播变形的规律,并且分析了波高、礁坪淹没水深和礁前斜坡坡度等因素对孤立波和真实海啸传播变形的影响。结果表明,相比孤立波,类海啸波的波长明显大于孤立波波长,在测点处引起的水面变化持续时间更长,同等波高情况下真实海啸波型比孤立波能够携带更多的能量,与岛礁的相互作用也更为复杂,在礁坪上形成的淹没水深约为孤立波的两倍。礁前斜坡坡度和礁坪淹没水深均对类海啸波的反射和透射系数有显著影响。随着礁前斜坡坡度的增加,反射系数和透射系数均逐渐增加。随着礁坪淹没水深的增加,反射系数逐渐减小,而透射系数逐渐增大。但是,反射系数和透射系数均随着入射波高的增加而逐渐减小。 相似文献
13.
《Coastal Engineering》2001,42(3):219-239
This paper describes an adaptive quadtree-based 2DH wave–current interaction model for evaluating nearly horizontal wave-induced currents in the surf-zone. The model accounts for wave breaking, shoaling, refraction, diffraction, wave–current interaction, set-up and set-down, mixing processes (turbulent diffusion), bottom frictional effects, and movement of the land–water interface at the shoreline. The wave period- and depth-averaged governing equations, which conserve mass, momentum, energy and wave action, are discretised explicitly by means of an Adams–Bashforth second-order finite difference technique on adaptive hierarchical staggered quadtree grids. Grid adaptation is achieved through seeding points distributed according to flow criteria (e.g. local current gradients). The model is verified for nearshore circulation at a sinusoidal beach and nearshore currents at a multi-cusped beach. Reasonable agreement is obtained with experimental data from da Silva Lima [da Silva Lima, S.S.L., 1981. Wave-induced Nearshore Currents. PhD Thesis, Department of Civil Engineering, University of Liverpool] and Borthwick et al. [Borthwick, A.G.L., Foote, Y.L.M., Ridehalgh, A., 1997. Nearshore measurements at a cusped beach in the UK Coastal Research Facility, Coastal Dynamics '97, Plymouth, 953–962]. The modelling approach presented herein should be useful in simulating nearshore processes in complicated natural coastal domains. Of particular value is the local grid enrichment capability, which permits refined modelling of important localised flow behaviour such as rip currents and surf-zone circulation systems. 相似文献
14.
A modified Boussinesq-type model is derived to account for the propagation of either regular or irregular waves in two horizontal dimensions. An improvement of the dispersion and shoaling characteristics of the model is obtained by optimizing the coefficients of each term in the momentum equation, expanding in this way its applicability in very deep waters and thus overcoming a shortcoming of most models of the same type. The values of the coefficients are obtained by an inverse method in such a way as to satisfy exactly the dispersion relation in terms of both first and second-order analyses matching in parallel the associated shoaling gradient. Furthermore a physically more sound way to approach the evaluation of wave number in irregular wave fields is proposed. A modification of the wave generator boundary condition is also introduced in order to correctly simulate the phase celerity of each input wave component. The modified model is applied to simulate the propagation of breaking and non-breaking, regular and irregular, long and short crested waves in both one and two horizontal dimensions, in a variety of bottom profiles, such as of constant depth, mild slope, and in the presence of submerged obstacles. The simulations are compared with experimental data and analytical results, indicating very good agreement in most cases. 相似文献
15.
Lou Jing P.V. Ridd C.L. Mayocchi M.L. Heron 《Estuarine, Coastal and Shelf Science》1996,42(6):787-802
Waves propagating from deep water into shallow coastal areas produce oscillatory currents near the sea bottom. The magnitude of these currents depend upon the period and amplitude of the incoming waves, and the dissipation mechanism such as wave breaking and bottom friction. Field experiments in a gently shoaling bay, i.e. Cleveland Bay, Northern Australia, showed that there is a broad band of water at around 6 m depth, where the benthic surge velocities are maximum. Both further inshore and offshore, the bottom velocities were less than at 6 m depth, contrary to the normal expectation that the velocities should increase as the water becomes shallower. A new and computationally efficient wave model was developed and was able to reproduce experimental results for waves above 50 cm wave height, but not for small waves (wave height about 30 cm). One implication of this higher band of benthic surge velocities may be to produce high water turbidities in this region. Turbidity data from Cleveland Bay is consistent with this hypothesis. 相似文献
16.
XIE Ming-xiao ZHANG Chi YANG Zhi-wen LI Shan LI Xin GUO Wei-jun ZUO Shu-hua 《海洋工程》2017,31(5):549-558
A process-based 3D numerical model for surfzone hydrodynamics and beach evolution was established. Comparisons between the experimental data and model results proved that the model could effectively describe the hydrodynamics, sediment transport feature and sandbar migration process in the surfzone with satisfactory precision. A series of numerical simulations on the wave breaking and shoaling up to a barred beach were carried out based on the model system. Analyzed from the model results, the wave-induced current system in the surfzone consists of two major processes, which are the phase-averaged undertow caused by wave breaking and the net drift caused by both of the nonlinear wave motion and surface roller effect. When storm waves come to the barred beach, the strong offshore undertow along the beach suppresses the onshore net drift, making the initial sandbar migrate to the seaside. Under the condition of calm wave environment, both the undertow and net drift flow to the shoreline at the offshore side of the sandbar, and then push the initial sandbar to the shoreline. The consideration of surface roller has significant impact on the modeling results of the sandbar migration. As the roller transfer rate increases, the sandbar moves onshore especially under the storm wave condition. 相似文献
17.
建立了同时考虑波致雷诺应力和时均水平压强梯度影响的二阶波浪边界层数学模型,模型计算得到的浅化波浪层流边界层内瞬时流速剖面、振荡速度幅值和时均流速剖面均与水槽实验数据吻合较好,在此基础上探讨了浅化波浪边界层流速分布特性及其影响机制。随着波浪的浅化变形,边界层内时均流速剖面"底部向岸、上部离岸"的变化特征越来越明显。这是二阶对流项引起的波致雷诺应力和离岸回流引起的时均水平压强梯度共同作用的结果,在床面附近由波致雷诺应力占主导作用并趋于引起向岸流动,在上部区域由时均水平压强梯度占主导作用并趋于引起离岸流动。 相似文献
18.
Kern E. Kenyon 《Journal of Oceanography》2004,60(6):1045-1052
Freely propagating surface gravity waves are observed to slow down and to stop at a beach when the bottom has a relatively gentle upward slope toward the shore and the frequency range of the waves covers the most energetic wind waves (sea and swell). Essentially no wave reflection can be seen and the measured reflected energy is very small compared to that transmitted shoreward. One consequence of this is that the flux of the wave’s linear momentum decreases in the direction of wave propagation, which is equivalent to a time rate of change of the momentum. It takes a force to cause the time rate of change of the momentum. Therefore, the bottom exerts a force on the waves in order to decrease the momentum flux. By Newton’s third law (action equals reaction) the waves then impart an equal but opposite force to the bottom. In shallow (but finite) water depths the wave force per unit bottom area is calculated, for normal angle of incidence to the beach, to be directly proportional to the square of the wave amplitude and to the bottom slope and inversely proportional to the mean depth; it is independent of the wave frequency. Constants of proportionality are: 1/4, the fluid density and the acceleration of gravity. Swell attenuation near coasts and some characteristics of sand movement in the near-shore region are not inconsistent with the algebraic structure of the wave force formula. Since the force has a depth variation which is significantly faster than that of the dimensions of the particle orbits in the vertical direction, the bottom induces a torque on the fluid particles that decreases the angular momentum flux of the waves. By an extension of Newton’s third law, the waves also exert an equal but opposite torque on the bottom. And because the bottom force on the waves exists over a horizontal distance, it does work on the waves and decreases their energy flux. Thus, theoretically, the fluxes of energy, angular and linear momentum are not conserved for shoaling surface gravity waves. Mass flux, associated with the Stokes drift, is assumed to be conserved, and the wave frequency is constant for a steady medium. 相似文献
19.
Feng Weibing Hong Guangwen
Ph. D Student Hohai University Nanjing .
Professor Hohai University Nanjing 《中国海洋工程》1995,(1)
An analytic-numerical solution of wave transformation in shoaling water is presented in this paper. The analytical expression for wave heights along the wave rays is derived in consideration of the combined effect of water depth shoaling, the wave refraction and the sea bottom friction. The wave rays (orthogonals) are calculated by a fourth order Runge-Kutta algorithm and the wave crest lines are computed by an iteration procedure. The numerical results are compared with analytical solution for a special case of parallel- straight contour shore and field data, and comparisons show that the proposed mathematical model and computation method are very useful and convenient for engineering application. 相似文献
20.
This paper presents new laboratory experiments carried out in a supertank (300 m × 5 m × 5.2 m) of breaking solitary waves evolution on a 1:60 plane beach. The measured data are employed to re-examine existing formulae that include breaking criterion, amplitude evolution and run-up height. The properties of shoreline motion, underwater particle velocity and scale effect on run-up height are briefly discussed. Based on our analyses, it is evidently found that there exist five zones during a wave amplitude evolution course on the present mild slope. A simple formula which is capable of predicting maximum run-up height for a breaking solitary wave on a uniform beach with a wide range of beach slope (1:15–1:60) is also proposed. The calculated results from the present model agree favorably with available laboratory data, indicating that our method is compatible with other predictive models. 相似文献