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Numerical study on vertical structures of undertow inside and outside the surf zone
作者姓名:ZHANGChi  WANGYigang  ZHENGJinhai
作者单位:ZHANG Chi,ZHENG Jinhai(State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China);WANG Yigang(Key Laboratory of Coastal Disaster and Prevention of Ministry of Education, Hohai University,Nanjing 210098, China) 
基金项目:The National Natural Science Foundation of China under contract No 50979033;;the Program for New Century Excellent Talents in University of China No NCET-07-0255;;the Special Fund of State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering under contract No 2009585812
摘    要:Nearshore shoaling and breaking waves can drive a complex circulation system of wave-induced currents. In the cross-shore direction, the local vertical imbalance between the gradient of radiation stress and that of pressure due to the setup drives an offshore flow near the bottom, called ‘undertow’, which plays a significant role in the beach profile evolution and the structure stability in coastal regions. A 1DV undertow model was developed based on the relationship between the turbulent shear stress and t...

关 键 词:垂直结构  暗流  数值研究  冲浪  水平剪应力  能量平衡方程  流模型  流通系统
收稿时间:2008/10/15 0:00:00
修稿时间:5/5/2009 12:00:00 AM

Numerical study on vertical structures of undertow inside and outside the surf zone
ZHANGChi,WANGYigang,ZHENGJinhai.Numerical study on vertical structures of undertow inside and outside the surf zone[J].Acta Oceanologica Sinica,2009,28(5):103-111.
Authors:ZHANG Chi  WANG Yigang and ZHENG Jinhai
Institution:1.State Key Laboratory of Hydrology-Water Resources and Hydraulic Engineering, Hohai University, Nanjing 210098, China2.Key Laboratory of Coastal Disaster and Prevention of Ministry of Education, Hohai University, Nanjing 210098, China
Abstract:Nearshore shoaling and breaking waves can drive a complex circulation system of wave-induced currents. In the cross-shore direction, the local vertical imbalance between the gradient of radiation stress and that of pressure due to the setup drives an offshore flow near the bottom, called 'undertow', which plays a significant role in the beach profile evolution and the structure stability in coastal regions. A 1DV undertow model was developed based on the relationship between the turbulent shear stress and the gradient of horizontal current velocity. A shear stress boundary condition at the wave trough level derived from the momentum balance equation combined with a no-slip condition at the sea bed were applied to solve the vertical structure of undertow. The turbulent eddy viscosity was assumed to be relevant to the breaking energy dissipation and linearly distributed over depth. The wave characteristics as inputs for the present model were obtained by solving an extended wave energy balance equation incorporating the surface roller effect. Numerical results showed generally good agreements with three series of experimental data for various bathymetries and wave conditions. Comparisons indicated that the formula proposed in this paper for the shear stress at wave trough level could reasonably improve the modeled undertow profiles especially outside the surf zone and a little distance shoreward of the breaking point, and revealed that the model performs well in simulating both vertical and horizontal distributions of undertow and is capable of providing hydrodynamic forcing for the cross-shore sediment transport.
Keywords:undertow  surf zone  numerical model  shear stress  
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