Numerical study on influence of vegetation on bed shear stress under coastal waves
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摘要: 本文基于OpenFOAM建立三维波浪数值水槽，模拟计算植被水域波浪作用下的床面切应力，分析了入射波高、植被密度、植被淹没高度、水流对植被水域波浪作用下床面切应力的影响。结果表明：纯波时，由于植被的阻水作用，植被水域床面切应力沿程衰减，其衰减程度与入射波高、植被密度及植被淹没高度呈现正相关；与纯波时相比，在波浪和同向流共同作用下正向床面切应力幅值增大，负向床面切应力幅值减小；弱水流对植被水域床面切应力的大小及分布无明显影响；强水流时，床面切应力在植被水域先增大后逐渐减小并在植被水域后显著降低。Abstract: To analyze the effects of wave height, vegetation density, submerged height of vegetation and current on the bed shear stress at vegetation zones, a three-dimensional wave-current numerical flume is established based on OpenFOAM in this study. The results show that the bed shear stress attenuates along the vegetation zones because of the blocking effect of vegetation, and the decay rate is positively correlated with the wave height, vegetation density and submerged height of vegetation. Compared with pure wave, the amplitude of positive bed shear stress increases and the amplitude of negative bed shear stress decreases under the condition of combined wave-current flows. The weak current has no obvious effect on the size and distribution of the bed shear stress at vegetation zones. In the case of strong current, the bed shear stress increases at vegetation zones and suddenly decreases after the vegetation zones.
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Key words:
- coastal vegetation /
- wave /
- bed shear stress /
- OpenFOAM
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图 1 考虑植被外形扰动的模拟结果
Fig. 1 Simulation results considering the disturbance of vegetation shape
图 4 理论值与模拟值对比（工况1）
Fig. 4 Comparison between theoretical and simulated values (case 1)
图 5 理论值与模拟值对比（工况2）
Fig. 5 Comparison between theoretical and simulated values (case 2)
图 10 不同流速下床面切应力变化
Fig. 10 Variation of bed shear stress under different current velocity
图 11 不同工况下植被水域最大床面切应力分布
Fig. 11 Distribution of maximum bed shear stress in vegetation zones under different conditions
图 12 不同流速下最大床面切应力衰减率
Fig. 12 Decay rate of maximum bed shear stress at different current velocities
表 1 经验系数取值
Tab. 1 Default values for the closure coefficient
经验系数 ${C_\mu }$ ${C_{\varepsilon 1}}$ ${C_{\varepsilon 2}}$ ${\sigma _\varepsilon }$ ${\lambda _2}$ ${\sigma _t}$ 值 0.09 1.44 1.92 1.3 0.05 0.85 
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表 2 植被及波浪参数
Tab. 2 Parameters of vegetation and waves
工况 波高/
m周期/
s水深/
m流速/
（m·s−1）植被
杆径/m植被
高度/m植被水域
长度/m植被密度/
(stem·m−2)1 0.04 1.5 0.3 0 0.005 0.6 5 560 2 0.04 1.5 0.3 0.186 0.005 0.6 5 560
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表 3 验证工况参数
Tab. 3 Parameters of verification conditions
工况 波高/m 周期/s 水深/m 波浪水质点振幅/m 边界层雷诺数 1 0.05 1.5 0.4 0.022 2 103.68 2 0.1 1.5 0.4 0.045 8 414.72 3 0.15 2 0.54 0.092 26 769.86
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表 4 模拟工况参数
Tab. 4 Parameters of numerical simulation conditions
工况 波高/m 周期/s 水深/m 流速/
(m·s−1)植被高
度/m植被水域
长度/m植被密度/
(stem·m−2)1 0.05 1.5 0.4 0 0.6 5 560 2 0.1 1.5 0.4 0 0.6 5 560 3 0.15 1.5 0.4 0 0.6 5 560 4 0.1 1.5 0.4 0 0.6 5 149 5 0.1 1.5 0.4 0 0.6 5 2 228 6 0.1 1.5 0.4 0 0.1 5 560 7 0.1 1.5 0.4 0 0.2 5 560 8 0.1 1.5 0.4 0 0.3 5 560 9 0.05 1.5 0.4 0.01 0.6 5 560 10 0.05 1.5 0.4 0.02 0.6 5 560 11 0.05 1.5 0.4 0.04 0.6 5 560 12 0.05 1.5 0.4 0.063 0.6 5 560 13 0.05 1.5 0.4 0.08 0.6 5 560 14 0.05 1.5 0.4 0.103 0.6 5 560 15 0.05 1.5 0.4 0.155 0.6 5 560 16 0.05 1.5 0.4 0.2 0.6 5 560 17 0.1 1.5 0.4 0.02 0.6 5 560 18 0.1 1.5 0.4 0.062 0.6 5 560 19 0.1 1.5 0.4 0.103 0.6 5 560 20 0.1 1.5 0.4 0.155 0.6 5 560 21 0.1 1.5 0.4 0.2 0.6 5 560 22 0.1 1.5 0.4 0.3 0.6 5 560
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