海岸带柔性植被环境下波浪动力衰减的数值模拟方法与机理研究

Vegetation in coastal wetland plays an important role in attenuating wave and protecting embankments. Most coastal area of Jiangsu Province covers high-density flexible vegetation under the action of wind wave which the movement mechanism is complex. Different from the rigid vegetation, the flexible vegetation will oscillate periodically under the effect of wave, and the group movement of high-density flexible vegetation is affected by each other. Therefore, the numerical simulation of the dynamic attenuation of the vegetation is also relative difficult. There are obvious differences between the flexible vegetation and the rigid vegetation in the mechanism on wave attenuation. Based on deeper research, the law of the dynamic attenuation of wind wave by the numerical simulation method is of great academic significance and application value for disaster prevention and mitigation. In this paper, in order to clarify the attenuation theories and provide a theoretical basis for artificial construction of vegetation revetment, a numerical module for wave attenuation under coastal flexible vegetation has been established. And a coupling model of interaction of wave and the flexible has been set up, taking the group movement of flexible vegetation into consideration. This thesis mainly work as follows: 1）Wave attenuation mechanism under the action of single flexible water grass and the establishment of numerical module. 2）Wave attenuation mechanism under the action of group flexible vegetation and the establishment of numerical module. 3）Coupling and validation of numerical module of wave attenuation. 4）Analysis of dynamic response of wave propagation under flexible vegetation. Based on theoretical analysis and numerical simulation, this project provides powerful technical supports for disaster prevention and mitigation in coastal zone.

海岸潮滩植被对消浪及护滩有重要作用，以江苏沿海植被为例，多为密度较高的柔性植被。不同于刚性植被，柔性植被在波浪作用下会周期性的摆动，同时高密度柔性植被的群体运动会互相影响，因此对柔性植被在波浪作用下动力衰减的数值模拟也相对困难。柔性植被与刚性植被在消浪效果及机制上有明显区别，深入的研究柔性植被对风浪的动力衰减的数值模拟及其规律，对沿海防灾减灾具有重要的学术意义和应用价值。本项目旨在建立柔性植被作用下波浪衰减数值模块，构建考虑柔性植被的群体运动条件下，波浪和柔性植被相互作用的耦合模型，阐明柔性植被对波浪的衰减原理，为人工建造植被护岸提供理论基础。本项目的研究内容包括：单根柔性植被作用下波浪衰减机理及数值模块的建立、群体柔性植被作用下波浪衰减机理及数值模块的建立、波浪衰减数值模块的耦合及验证、波浪传播过程对柔性植被的响应规律研究。项目成果预期可为我国海岸防灾减灾提供理论和技术支持。

海洋强国战略与生态文明建设已对我国海岸灾害防护工作提出了新的更高要求。因同时具有生态效益与护岸作用，植被消浪已成为海岸工程的前沿课题。目前植被消浪研究已取得了较好发展，但仍主要局限于刚性假设。. 本项目（1）构建了近岸浅水区波浪作用下柔性植被受力运动数学模型，提出了XBeach相位解析波浪模型中柔性植被消浪作用的计算方法；揭示了波浪作用下单根柔性植物受力和运动特性，阐明了波浪要素和柔性植被特性对波浪衰减的影响规律。（2）量化研究了植被对波高的衰减能力，分析了植被带波高衰减的影响参数，并分别建立了刚性和柔性植被消浪作用下的阻力系数半经验公式。（3）提出了波流共同作用下淹没柔性植被运动与消浪模拟方法，阐明了波流共同作用下柔性植被动力特性，揭示了波流共同作用下柔性植被消浪规律。（4）对影响柔性植被固沙岸滩冲刷演变的波浪、植被相关因素进行了逐项分析，揭示了柔性植被固沙岸滩演变规律。. 研究结果表明：（1）柔性植被可显著衰减波高以及波浪增水，相对淹没度、波高、波周期、拖曳力系数和植被弹性模量对柔性植被受力运动具有显著影响。同时，提高植被分布密度、增加植被区域长度或者增大植被弹性模量可显著提高波高衰减率。（2）在刚性阻力系数和邱卡数相关性的基础上，进一步考虑植被相对高度和波浪波陡系数对刚性阻力系数的影响，对刚性阻力系数的拟合公式进行了改进。建立并拟合了柔性植被的刚度和振荡系数与波浪衰减的阻力系数半经验公式。（3）邱卡数和流速比可对植被最大水平力、植被顶端摆幅和顶端最大水平位移产生显著非线性影响。此外，同向水流可增强或减弱柔性植被消浪。（4）规则波波高、周期以及水深等波浪要素，以及植被高度、分布密度、弹性模量等植被参数可对柔性植被固沙岸滩冲刷产生显著影响。. 项目研究成果可完善植被消浪模拟理论及方法，丰富波浪基础理论，并为我国新型海岸防护工程措施提供科学依据。