海岸植物消浪机理与减低波浪冲高的试验研究和数值模型开发

Coastal vegetation has the capability of dissipating wave energy, protecting shoreline, and stabilizing seabed. However, the interaction between coastal vegetation and waves is very complex due to large variation in both vegetation properties and wave characteristics. The mechanism of wave dissipation by coastal vegetation is poorly understood, and there are limited studies of the vegetation effects on reducing wave runup on slopes. In order to further investigate the vegetation effects on wave attenuation and gain more detailed knowledge of turbulent flow properties within coastal vegetation, a series of well-controlled laboratory experiments will be conducted in this study. Through the analysis of the experimental data, the rate of wave attenuation will be quantified as a function of vegetation characteristics such as vegetation stem diameter, stiffness, planting density, geometry, and relative submergence as well as wave conditions such as incident wave height and period. Also, the relative contributions of vegetation stems and canopy in reducing wave energy will be examined. The wave forces on vegetation will be measured and analyzed to obtain the formulas of drag force and inertial force coefficients and to uncover the wave dissipation mechanism within vegetation domain. The characteristics of wave runup on vegetated slope will be explored as well. At the same time, a robust three-dimensional numerical model for turbulent free surface flows will be developed for simulation of wave-vegetation interaction. At last, based on the numerical results, experimental data, and field observations, a design criterion and assessment formulation on the most effective planting method will be proposed.

实践表明，海岸植物能有效地消能减浪与固滩护岸。但由于海岸植物种类繁多，波浪特性多变，植物与波浪相互作用的水动力过程十分复杂，目前人们对植物消浪的详细机制还不够了解，对植物降低波浪在岸坡上的爬高特性也缺乏系统研究成果。本项目拟结合系列水槽模型试验与理论数值分析，对植物的消浪特性进行深入系统的研究，建立植物属性（如植株大小与枝干刚度、种植密度和方式、淹没度等）、波浪特性（如波高、周期等）与波高衰减率的定量关系，确定植物树干和树冠在不同波浪条件下对消能减浪的贡献比例，获得植物阻力系数与惯性系数的计算公式；分析植株间水流紊动精细结构，揭示植物消能减浪的内在机制；研究波浪在有植被岸坡上的冲高过程，探索防浪林内波浪传播、破碎与衰减特性。开发可模拟植物与波浪相互作用的三维自由面紊流数值模型；在模型试验与数值模拟的基础上，结合现场观测，提出能满足工程安全要求的海岸植物科学种植方法。

海岸植物能够有效的衰减海岸区波浪能量，从而发挥固岸护滩的作用。本项目通过水槽试验与数值模拟手段研究了植物区内部的消浪机理，探讨了不同波浪特性与植物特性对于波浪衰减的影响。首先，我们试验研究了明渠水流与植物区相互作用，发现在某些特定流速下水槽中会产生横向驻波，这种横向驻波是由于植物杆后部漩涡脱落造成的，而横向驻波的频率也与漩涡脱落频率相接近。随后，我们开展了孤立波在植物区的衰减的实验研究，发现水深一定时，入射波高越大，植物区总的波高衰减率越大；而波高水深比一定时，淹没度越大，植物区总的波高衰减率越小。然后，这些测得的实验数据被用于验证新开发的能够模拟植物区内部紊流特性的数值模型，该模型还经过了前人发表的数据的验证。随后，这个经过验证的模型被用于探讨淹没度对于波高衰减的影响，我们发现淹没度超过一定数值后，波高衰减不再受淹没度的影响。