波浪作用下柔性草本植物受力特性研究

草本盐沼植物广泛分布于海岸带形成滨海湿地系统, 这些滨海湿地具有生态、旅游、养殖及减灾等多方面价值. 草本植物的消浪作用在海岸稳固和沿海防灾减灾等方面发挥了重要作用. 已有植物消浪研究通常过度简化, 将植物视为刚性圆柱并依赖于调节经验拖曳力系数来提高预测准确度, 对柔性植物与波浪的相互作用机理研究还很欠缺. 草本植物通常由多片柔性叶片和一根柔性相对较小的杆茎组成. 在波浪作用下, 植物的叶片与杆茎产生不同程度的动态变形以及相互作用, 从而改变波浪与植物间的相对运动速度, 使得柔性植物受力特性十分复杂. 本文采用简单柔性结构物受力尺度定律计算单片叶片和单根杆茎受力, 并用遮蔽系数量化叶片与杆茎间相互作用引起的叶片受力降低程度, 提出了波浪作用下柔性草本植物动态受力计算公式. 与单片叶片、单根杆茎和既有叶片又有杆茎的模型植物及真实植物样本测量受力比较表明, 本文提出的植物受力模型可较好地预测植物最大受力及植物受力随波浪周期的变化情况. 

WAVE-INDUCED FORCE ON FLEXIBLE MARSH PLANTS

Salt marshes are common features in coastal regions and forming eco-rich wetlands. These wetlands provide ecosystem services, tourism and fishery benefits, as well as coast protection. Salt marshes can dissipate wave energy, which enhances coastal stability and protects the shoreline from storms and small tsunami waves. Previous wave damping predicting methods are usually oversimplified by modeling plants as rigid cylinders. Further, these studies strongly depend on the adjustment of empirical drag coefficient, while a knowledge gap exists between the mechanism of flexible plant-wave interaction. A marsh plant usually consists of multiple flexible leaves and a less flexible central stem, both the geometric and flexibility of the leaves and the stem affect the drag on the full plant. Under waves, the leaves and the stem reconfigure to different degrees at different speeds. The dynamic response of plant elements reduces the relative velocity between the wave and the plant. Further, the leaves and the stem interact with one another, making the characteristics of wave-induced plant force highly complicated. Build on the force scaling law for a simple plant element, such as a flat leaf or a cylindrical stem, we proposed a simple equation to predict the drag on plants with both leaves and stem. The force on the full plant is the sum of the force on the leaves and the force on the stem. The force on a representative leaf and the stem were estimated by the force scaling law. The force due to all the leaves was estimated by the force on the representative leaf using a sheltering coefficient, which accounts for the drag reduction in the leaves due to the interaction between the leaves and the stem. The model predicted maximum drag and the drag force over the wave period agreed well with the experiment measured drag force on an individual leaf, an individual stem, and model and live plants with both leaves and stem.