Vertical flow structure during Sandy Duck: observations and modeling
Vertical flow structure during Sandy Duck: observations and modeling
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DOI：
10.1016/j.coastaleng.2004.02.001
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发表时间：
2004-05
影响因子：
4.4
通讯作者：
A. Reniers;E. Thornton;T. Stanton;J. Roelvink
中科院分区：
文献类型：
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作者：
A. Reniers;E. Thornton;T. Stanton;J. Roelvink
在沙鸭现场试验期间，对时间平均的跨岸和近岸水流的垂直分布进行了观测，并与模型预测进行了比较，以评估控制水流行为的参数。测量是由8个双分量海流计组成的垂直堆叠获得的，最低和最高的传感器分别位于床上方O(0.1)m和O(2.7)m处。在破浪条件下的观测表明，最大回流速度出现在水柱的下部，这与实验室的观测结果一致。在冲浪区以外的非破碎条件下，最大回流速度更接近水面，这也与实验室的结果一致。与以往的观测结果类似，测得的沿岸流速度剖面在不破碎条件下呈对数分布，在破碎条件下变得更加均匀。流动垂直结构的模型描述包括风应力、波应力、压力梯度、湍流涡粘性和波边界层的存在。该模式采用抛物线形函数描述中、下边界层内湍流涡粘性的垂直分布。在产生湍流的区域，即在破碎波的情况下靠近地面和在底部边界层内，涡粘性增强。通过最小化模型测量误差，得到了破碎引起的湍流涡粘性和底摩擦力的估计值。如果正确地模拟了波浪变换和相关的质量通量，并采用抛物线型涡粘性分布，则使用湍流涡粘性和底摩擦力的校正表达式所作的预报与观测结果基本一致。使用分段恒定的涡流粘度分布通常会导致测量结果与模型结果之间的一致性降低。
Observations of the vertical distribution of time-averaged cross-shore and alongshore flows during the Sandy Duck field experiment are compared with model predictions to assess the parameters governing the flow behaviour. The measurements were obtained with a vertical stack of eight two-component current meters, with the lowest and highest sensor at, respectively O(0.1) and O(2.7) m, above the bed. Observations under breaking wave conditions within the surfzone show that the maximum return flow velocities occur in the lower part of the water column, consistent with laboratory observations. Under non-breaking conditions outside the surfzone the maximum return flow velocities are observed closer to the water surface, again in line with laboratory results. Analogous to previous observations the measured longshore current velocity profiles are logarithmic under non-breaking conditions and become more depth-uniform under breaking conditions. The model description of the vertical structure of the flow includes the presence of wind stresses, wave stresses, pressure gradients, turbulent eddy viscosity and a wave boundary layer. The model utilizes parabolic shape functions to describe the vertical distribution of the turbulent eddy viscosity in the middle layer and within the bottom boundary layer. Eddy viscosity is enhanced in regions where turbulence is produced, i.e. near the surface in the case of breaking waves and within the bottom boundary layer. Estimates of the wave-breaking-induced turbulent eddy viscosity and bottom friction are obtained by minimizing the model–measurement discrepancies. Predictions utilizing calibrated expressions for both the turbulent eddy viscosity and bottom friction are in general agreement with the observations, provided the wave transformation and associated mass flux are modeled correctly and a parabolic eddy viscosity distribution is used. Using a piecewise constant eddy viscosity distribution generally results in a degrading of the agreement between measurements and model results.