极端条件下复合式海堤越浪过程的水动力学特性研究

Wave overtopping against a sea dike belongs to one of the complicated flows with the free surface of large deformation and breaking, which is the major factor inducing the failure of sea dikes. For the sea dikes of composite profile, the overtopping flow dynamics over sea dikes in regular waves and irregular waves is studied experimentally and numerically. Time-resolved PIV is applied to study overtopping flow on a sea dike with a composite profile in regular waves. For the PIV measurements, fluorescent tracer particles are applied in combination with an optical filter, in order to remove the reflections of the laser lightsheet by the bubbles induced by breaking and air entrainment in the overtopping flow. For a visualization of the global flow dynamics, the laser beam is expanded and used to illuminate the entire sea dike crest and overtopping flow structure. The velocity fields of the overtopping flows are analyzed and discussed for the unsteady flow with the free surface, which will serve as the benchmarks for validation of numerical simulation of overtopping flows against the typical sea dikes. The numerical wave flume is developed to simulate the overtopping flows against a composite sea dike with armor units in waves. Through improving efficiency of the numerical wave flume, it is capable to handle with the hydrodynamic flows with two different scales in terms of the armor unit and the wave length. The changes of the layer thicknesses and the maximum velocities of the overtopping flows at different locations on the dike crest and the landward slope are obtained. Discussions are focused on the mechanism of spatial and temporal evolution of the overtopping flows on the sea dike crest and the landward slope for the cases of different combination of tidal level and incoming wave. It is challenging to develop the PIV based measuring approach and numerical model of overtopping with violent deformation and breaking of the free surface against sea dikes. The hydrodynamic characteristics of overtopping flows could be used to evaluate the safety of the sea dikes when overtopping appears.

海堤越浪往往伴随着自由表面大变形、破碎、飞溅和越堤流动等复杂流动现象，是导致海堤失效的主要动力因素。本项目以大潮和风浪作用下复合式海堤的越浪流动作为研究对象，发展基于高速PIV的海堤越浪流动结构的精细测量方法，获得海堤越浪波浪水槽实验的瞬时流场信息，建立越浪流态的基准实验数据库，给出越浪流流速分布特征。完善可消除二次反射的数值波浪水槽，实现可精确刻画护面块体形状和摆放方式的海堤越浪数值模拟方法。以复合式海堤为对象，进行系统的实验测量和数值模拟，揭示复合式海堤在典型高潮位和风浪作用下的越浪流动结构的变化规律，建立越浪流基本参数的工程计算公式。本项目的研究成果不仅对波浪与海岸结构物的相互作用研究具有重要的学术价值，而且可应用于极端高潮位和超强台风作用下海堤的安全性评估。

海堤越浪往往伴随着自由表面大变形、破碎、飞溅和越堤流动等复杂流动现象，是导致海堤失效的主要动力因素。本项目采用理论分析、数值模拟与物理模型实验相结合的方法对典型海堤的越浪过程流体动力特征进行了系统深入的研究。主要创新性研究成果有：在大型波浪水槽中实现了海堤越浪过程越堤流的PIV测量，获得了孤立波作用下越堤流流场特征；在国际上率先提出了基于解析松弛方法和流函数波理论的大波高规则波的数值造波技术，成功消除造波边界的二次反射，建立了适合海堤断面越浪过程模拟的基于水气两相流动模型的数值波浪水槽；通过数值模拟与物理实验，进一步完善并确认斜坡堤越浪过程中越堤流的水动力学特征，认为越堤流在堤顶流动时其最大厚度沿程按指数规律减小，而最大速度流则先减小后增大,并进一步给出了堤顶最大流速与越浪量之间的关系；以复合式海堤为对象，进行了系统的实验测量和数值模拟，揭示复合式海堤在典型高潮位和风浪作用下越浪量和越堤流动特征的变化规律。此外，本项目研究并发展了大变形自由表面流动与破碎波的两相SPH数值模型，并可进一步应用于设有护面块体的海堤越浪过程。在本项目执行过程中，密切结合上海地区重要海堤达标工程和新海堤建设，应用建立的数值模拟与实验测量方法对超强台风作用下海堤越浪量的预测及其控制策略开展了研究，为上海化学工业区海堤等重点工程建设提供了技术支撑。