Predictive Models for Wave Damping by Flexible Aquatic Vegetation

水生植被提供了许多自然利益，包括保护海岸线免受风暴和侵蚀，提供栖息地和改善水质。波浪可以从河床上踢起沉积物，造成侵蚀，使水浑浊，并增加水中的污染物。植被减少了波浪运动，防止沉积物被扬起。然而，植被的这种好处不能纳入湖泊和沿海管理计划，因为没有准确的方法来预测植被减少波浪运动。该项目将开发一个模型，根据植被的特征（包括几何形状、大小和灵活性）来预测植被对波浪能的减少。有了这个新模型，工程师和流域管理人员将能够评估不同的植被恢复方案，以保护海岸线和减少导致水质差的侵蚀事件。本实验室研究探讨了灵活的植被和波浪之间的相互作用，以建立预测模型，植被对波浪能量耗散的影响。灵活的植被弯曲响应流，这种重新配置改变植被阻力。重新配置的影响可以用有效设备长度le来描述，有效设备长度le是刚性设备的长度，其赋予与重新配置的柔性设备相同的流体动力学阻力。在初步研究中，PI？他的实验室为具有简单带状形态的个体植物（淡水和咸水鳗草）开发了比例定律，可以预测水流和波浪中的阻力。这项新的研究将扩展到植物群落（草甸），水流和波浪相结合的条件，以及更复杂形态的植物（例如伊乐藻和眼子菜）。具体而言，本研究将开发模型来预测植物的几何和生物力学特性，电流和波场参数的LE，并将演示如何有效长度可以用来预测波能耗散在波浪和波流条件组合的草甸。实验将在一个长24米、深60厘米的水槽中进行，水槽中装有桨式造波机。最初，模型叶片将由低（LDPE）和高（HDPE）密度聚乙烯制成。随后的实验将考虑使用活体植物和3D打印模型的更复杂的形态。单个叶片的运动将通过数字成像来捕获，并且将使用潜水式力传感器来测量隔离的和草地内的单个叶片上的力。速度场将采用声学多普勒测速仪和PIV测量。波能的耗散将根据波振幅的纵向衰减来估计，波振幅的纵向衰减将使用电阻式水面计来测量。该项目将有助于对流体-柔性-结构相互作用的基本理解，这与许多工程主题有关，例如被动能量收集装置和柔性表面的流动控制。与地球系统相关，本项目将开发一个统一的模型，用于预测不同形态的植物和相关现场条件范围内的波浪消散。

Aquatic vegetation provides many natural benefits, including the protection of shorelines from storms and erosion, the provision of habitat, and the improvement of water quality. Waves can kick up sediment from the bed causing erosion, making the water cloudy and adding pollutants to the water. Vegetation reduces wave motion and keeps sediment from being kicked up. However, this benefit of vegetation cannot be incorporated into lake and coastal management plans, because there is no accurate method for predicting the reduction of wave motion by vegetation. This project will develop a model for predicting the reduction of wave energy from vegetation based on the characteristic of the vegetation, including geometry, size and flexibility. With this new model, engineers and watershed managers will be able to assess different scenarios of vegetation restoration for their potential to protect shorelines and to reduce erosion events that drive poor water quality. This laboratory study explores the interaction between flexible vegetation and waves to develop predictive models for the impact of vegetation on wave energy dissipation. Flexible vegetation bends in response to flow, and this reconfiguration alters the vegetation drag. The impact of reconfiguration can be described in terms of an effective plant length, le, which is the length of rigid plant that imparts the same hydrodynamic drag as the reconfigured flexible plant. In a preliminary study, the PI?s lab developed scaling laws for individual plants with simple strap morphology (fresh and saltwater eelgrass) that predict the drag in current and in waves. This new study will extend the scaling laws to communities of plants (meadows), to conditions with combined currents and waves, and to plants of more complex morphology (e.g. Elodea and Potamogeton). Specifically, this study will develop models to predict le from plant geometric and biomechanical properties, and current and wave-field parameters, and will demonstrate how the effective length can be used to predict the wave energy dissipation over a meadow in waves and in combined wave-current conditions. The experiments will be carried out in a 24m-long and 60cm-deep water channel with a paddle wavemaker. Initially, model blades will be constructed from low (LDPE) and high (HDPE) density polyethylene. Later experiments will consider more complex morphologies using both live plants and 3-D printed models. The motion of individual blades will be captured with digital imaging, and the forces on individual blades in isolation and within a meadow will be measured with a submersible force transducer. The velocity field will be measured with acoustic Doppler velocimetry and PIV. The dissipation of wave energy will be estimated from the longitudinal decay of wave amplitude, which will be measured using resistance-type water surface gages. This project will contribute fundamental understanding to fluid-flexible-structure interaction, which is relevant to many engineering topics, e.g. passive energy-harvesting devices and flow-control with flexible surfaces. Relevant to earth systems, this project will develop a unified model for predicting wave dissipation due to plants of different morphology and across the range of relevant field conditions.