孤立波作用下珊瑚礁海岸附近流动特性研究

Study on flow characteristics over coral reefs under solitary waves

该文通过基于大涡模拟的三维数值模型研究了孤立波作用下珊瑚礁海岸附近的流动特性,考虑了两种礁坪水深的情况,通过物理模型实验对比验证了礁面上自由液面的空间与时间变化以及流速的时间变化,并运用数值结果进一步分析了流场和涡量场的沿礁变化规律。结果表明:该数值模型能合理地模拟不同礁坪水深下孤立波的浅水变形、破碎和滚波的运动以及波生流的变化。波浪破碎时礁坪上水流由亚临界流向超临界流转变,随后流速沿礁衰减。泻湖内的流速变化不再显著,波浪破碎伴随着强烈的水体涡动,涡动随着滚波的沿礁衰减而逐渐耗散,泻湖中的涡动几乎可以忽略不计。礁坪水深的增大显著降低了礁坪上的涡动强度。

A three-dimensional numerical model was developed based on the Large Eddy Simulation(LES) method to study the flow characteristics over coral reef under the action of solitary waves with two reef-flat water depths examined.Numerical model was validated by the laboratory experiments in view of the spatial and temporal variations of the free-surface elevation as well as the temporal variation of the velocity across the reef profile. The variations of flow and vorticity fields across the reef were further analyzed by the numerical simulations. Results show that the numerical model can reasonably reproduce the processes of wave shoaling, breaking, bore propagation and wave-driven current under both two reef-flat water depths. The current associated with breaking waves on the reef flat transfers from the subcritical to supercritical flow, and it then decays along the reef. The flow variation in the lagoon is not obvious. Wave breaking is accompanied by a strong vortex motion of water. The vortices gradually dissipate along the reef profile with the damping of prorogating bore, and they are almost negligible in the lagoon. With the increasing of reef-flat water depth, the strength of vortex motion is significantly reduced.