岸坡植被水域椭圆余弦波传播模拟及分析

Numerical study for conical wave propagation in slope vegetation waters

  • 摘要: 基于扩展型强非线性Boussinesq水波方程,通过在动量方程中引入植被应力项来考虑植被对波浪的作用,建立了近岸植被水域波浪传播运动的数值模型。将植被场中随机波浪传播的数值模拟结果与物理试验数据进行比较,吻合良好,并在对模型进行验证的基础上,模拟和分析了水平二维岸坡植被区域椭圆余弦波的传播变形。针对波浪爬坡,破碎,增减水以及波生流进行分析,结果表明,随着水深变浅,波高逐渐变大;当波高增大到临界点时破碎,植被区波高明显比无植被区衰减得更快;相比远离岸线的植被,破碎区植被对波高衰减更显著,而且不会出现二次破碎;与无植被区域相比,植被区域波相速度和波长较小,局部产生比较明显的折射效应;植被位于破碎区时,由于植被的耗能作用,近岸区域波浪增水显著减小;植被对近岸环流具有显著影响,植被边缘出现强近岸环流和大尺度旋涡;破碎区内分布的植被作用下离岸流分布均匀,流速较小,分布范围比较大;植被区域距离岸线越远,产生的涡旋尺度越大,植被末端的离岸流也越剧烈。

     

    Abstract: The numerical model for wave propagation in vegetation water was developed based on fully nonlinear Boussinesq equation in which the drag force due to vegetation was added. The model was verified by comparing between the numerical and experimental results for wave propagation in vegetation waters. The numerical results are in line with flume experiments. Then the model was used to test waves propagating through a finite patch of vegetation at the bank slope. An analysis is conducted to understand shoaling, breaking and wave-induced current by aquatic vegetation. It is found that the wave height in the vegetated zone is attenuated more rapidly than in the adjacent unvegetated region, which is induced by the damping effects of the vegetation. Compared with the vegetation away from the shoreline, the vegetation affects more on attenuation in the surf zone, no secondary crushing occuring. And wave phase speed and wave length of the broken wave are also decreased in the vegetated region compared to the unvegetated region, which leads to refraction effects bending wavecrests towards the patch in the exterior region. When vegetation is located in inthe surf zone, the wave setup is significantly reduced. In the outer part of the vegetation patch(close to the breaker line), the wave setup is relatively larger. The vegetation has a significant effect on the nearshore circulation, and the nearshore circulation and the large-scale vortex appear on the edge of the vegetation. The distribution of the offshore flow in shore is uniform, the flow velocity is small and the distribution range is relatively large. The farther the vegetation area is from the shoreline, the larger the vortex scale is, and the more intense the offshore flow is.

     

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