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1.
Velocity distributions of waves and currents in the combined flow   总被引:1,自引:0,他引:1  
The theoretical model presented here is designed to predict waves and currents velocity profiles in the combined wave and current motion near a fixed bed. It is also valid for the pure wave motion, because the pure wave motion is only a special case of the combined flow. This model has been derived by using the equation of motion and the eddy viscosity assumptions which are somewhat different from those of former authors. Although the model is simple, the predictions are quite good compared with experimental data from Jonsson and Carlsen (1976) No. 1 and No. 2, Van Doorn (1981) V00RA, V10RA and V20RA, Van Doorn (1982) S00RAL, S10RAL and S20RAL, and Jensen (1989) Test-12 and Test-13.  相似文献   

2.
《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   

3.
A probabilistic model ( -model) was developed to describe the propagation and transformation of individual waves (wave by wave approach). The individual waves shoal until an empirical criterion for breaking is satisfied. Wave height decay after breaking is modelled by using an energy dissipation method. Wave-induced set-up and set-down and breaking-associated longshore currents are also modelled. Laboratory and field data were used to calibrate and verify the model. The model was calibrated by adjusting the wave breaking coefficient (as a function of local wave steepness and bottom slope) to obtain optimum agreement between measured and computed wave height. Four tests carried out in the large Delta flume of Delft Hydraulics were considered. Generally, the measured H1/3-wave heights are reasonably well represented by the model in all zones from deep water to the shallow surf zone. The fraction of breaking waves was reasonably well represented by the model in the upsloping zones of the bottom profile. Verification of the model results with respect to wave-induced longshore current velocities was not extensive, because of a lack of data. In case of a barred profile the measured longshore velocities showed a relatively uniform distribution in the (trough) zone between the bar crest and the shoreline, which could to some extent be modelled by including space-averaging of the radiation force gradient, horizontal mixing and longshore water surface gradients related to variations in set-up. In case of a monotonically upsloping profile the cross-shore distribution of the longshore current velocities is reasonably well represented.  相似文献   

4.
This paper provides a stochastic method by which the random wave-induced scour depth at the trunk section of vertical-wall and rubble-mound breakwaters can be derived. Here the formulas for regular wave-induced scour depth provided by Xie [Xie, S.L., 1981. Scouring patterns in front of vertical breakwaters and their influence on the stability of the foundations of the breakwaters. Report. Department of Civil Engineering, Delft University of Technology, Delft, The Netherlands, September, 61 pp.] for vertical-wall breakwater and Sumer and Fredsøe [Sumer, B.M., Fredsøe, J., 2000. Experimental study of 2D scour and its protection at a rubble-mound breakwater. Coast. Eng. 40, 59–87] for rubble-mound breakwater are used. These formulas are combined with describing the waves as a stationary Gaussian narrow-band random process to derive the random wave-induced scour depth. Comparisons are made between the present method and the Sumer and Fredsøe [Sumer, B.M., Fredsøe, J., 2000. Experimental study of 2D scour and its protection at a rubble-mound breakwater. Coast. Eng. 40, 59–87.] random wave scour data for rubble-mound breakwater, as well as the Hughes and Fowler [Hughes, S.A., Fowler, J.A., 1991. Wave-induced scour predictions at vertical walls. ASCE Proc. Conf. Coastal Sediments vol. 91, 1886–1899] random wave scour data and formula for vertical-wall breakwater. A tentative approach to random wave-induced scour at a vertical impermeable submerged breakwater is also suggested.  相似文献   

5.
A coupled wave–tide–surge model has been established in this study in order to investigate the effect of tides, storm surges, and wind waves interactions during a winter monsoon on November 1983 in the Yellow Sea. The coupled model is based on the synchronous dynamic coupling of a third-generation wave model, WAM-Cycle 4, and the two-dimensional tide–surge model. The surface stress generated by interactions between wind and waves is calculated using the WAM-Cycle 4 directly based on an analytical approximation of the results obtained from the quasi-linear theory of wave generation. The changes of bottom friction factor generated by waves and current interactions are calculated by using simplified bottom boundary layer model. The model simulations showed that bottom velocity and effective bottom drag coefficient induced by combination of wave and current were increased in shallow waters of up to 50 m in the Yellow Sea during the wintertime strong storm conditions.  相似文献   

6.
In recent years, instrumentation for field flow measurements has become more and more sophisticated. In particular, local pressure and velocity are measured at frequency rates up to at least 2 Hz, which gives information on wave energy. The present work describes the methods for partially standing wave measurement in the presence of current by use of coincident measurements of both horizontal velocity and pressure, or vertical velocity. Reflection calculated from either coincident horizontal and vertical velocities or three-gauge methods are compared. They are based on existing experiments carried out in an ocean wave basin for both regular and irregular waves in the presence of current. Applications to field measurements, out of and in the breaking zones are then presented. In the nearshore, coincident horizontal and vertical velocities far from the bottom, and coincident horizontal velocity and pressure close to the bottom give relevant information concerning partially standing waves.  相似文献   

7.
Small amplitude water waves propagating in a medium with a steady non-uniform current are investigated. The non-uniform current is obtained by up- or downwelling through the horizontal bed. A new locally valid velocity potential correct to the second order is derived describing the combined wave–current motion. From this solution expressions for the local evolution of the wave amplitude and the wave number are extracted. These expressions are compared with the results found using the principle of wave action conservation and the linear dispersion relation, and good agreement is found at small distances compared to the wavelength. Unlike earlier works there is no restriction to deep water. The results valid for deep water are found as a special case of the general solution and agree with the solution found by Longuet-Higgins, M.S. and Stewart, R.W. (1961) The changes in amplitude of short gravity waves on steady non-uniform currents. Journal of Fluid Mechanics, 10(4), 529–549. Furthermore, it is shown that the principle of wave action conservation in fact holds for waves propagating in a medium with a steady non-uniform current maintained by up-/downwelling also on finite depth.  相似文献   

8.
It is well known that wave induced bottom oscillations become more and more negligible when the water depth exceeds half the wavelength of the surface gravity wave. However, it was experimentally demonstrated for regular waves that the bottom pressure oscillations at both first and second wave harmonic frequencies could be significant even for incoming waves propagating in deep water condition in the presence of a submerged plate [16]. For a water depth h of about the wavelength of the wave, measurements under the plate (depth immersion of top of plate h/6, length h/2) have shown bottom pressure variations at the wave frequency, up to thirty times larger than the pressure expected in the absence of the plate. In this paper, not only regular but also irregular wave are studied together with wave following current conditions. This behavior is numerically verified by use of a classical linear theory of waves. The wave bottom effect is explained through the role of evanescent modes and horizontally oscillating water column under the plate which still exist whatever the water depth. Such a model, which allows the calculation of the velocity fields, has shown that not only the bottom pressure but also the near bed fluid velocity are enhanced. Two maxima are observed on both sides of the location of the plate, at a distance of the plate increasing with the water depth. The possible impact of such near bed dynamics is then discussed for field conditions thanks to a scaling based on a Froude similarity. It is demonstrated that these structures may have a significant impact at the sea bed even in very deep water conditions, possibly enhanced in the presence of current.  相似文献   

9.
底部切应力作为水动力和泥沙输移模型中的关键参数,对底床泥沙起动、侵蚀淤积速率的研究十分重要。目前基于现场实测流速数据计算底部切应力的理论方法有6种:LP mean法、LP max法、TKE法、TKEW法、RS法和ID法,这些方法都有其特定的适用条件。河口海岸浅水区域水流和波浪作用复杂,遴选合适的方法计算底部切应力非常重要。本文以江苏大丰斗龙港1个观测点(中值粒径为68.56 μm)和上海崇明东滩2个观测点(中值粒径分别为12.89 μm和45.02 μm)为例,利用声学三维高频流速仪ADV (Acoustic Doppler Velocimetry)和波潮仪(RBR wave)进行现场数据采集,分别用6种理论计算方法对底部切应力进行计算,结果表明:(1)LP mean法受到平均流速、仪器探头距离底部床面高度以及波浪强弱的影响,会低估底部切应力;(2)LP max法和TKE法在流速变化幅度较大、波浪作用明显的潮间带浅水环境会高估底部切应力;(3)TKEW法在TKE法的基础上进行了改进,更适用于波浪作用强烈的潮间带浅水环境底部切应力的计算;(4)RS法计算结果受到波浪影响会产生误差,存在较大波浪时,ID法计算结果比RS法计算结果更加可信,但是在水深条件不足时,ID法会高估底部切应力。  相似文献   

10.
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   

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