Predictive Models for Wave Damping by Flexible Aquatic Vegetation

水生植被提供许多自然益处，包括保护海岸线免受风暴和侵蚀、提供栖息地和改善水质。海浪会从河床上掀起沉积物，造成侵蚀，使水变得浑浊，并向水中添加污染物。植被可以减少波动，防止沉积物被掀起。然而，植被的这种好处不能纳入湖泊和海岸管理计划，因为没有准确的方法来预测植被减少波浪运动。本项目将根据植被的特征，包括几何形状、大小和灵活性，开发一个模型来预测植被的波能减少。有了这个新的模型，工程师和流域管理人员将能够评估不同的植被恢复方案，以了解它们保护海岸线和减少导致水质差的侵蚀事件的潜力。这项实验室研究探索了柔性植被与波浪之间的相互作用，以开发植被对波浪能量耗散影响的预测模型。灵活的植被因水流而弯曲，这种重新配置改变了植被的阻力。重新配置的影响可以用有效植物长度LE来描述，该长度是刚性植物的长度，它提供与重新配置的柔性植物相同的水动力阻力。在一项初步研究中，皮？S实验室为具有简单条带形态的单个植物(新鲜和咸水鳗草)开发了比例定律，可以预测水流和波浪中的阻力。这项新的研究将把比例定律扩展到植物群落(草甸)、水流和波浪组合的条件，以及更复杂形态的植物(例如伊洛迪亚和波塔莫格顿)。具体地说，这项研究将建立模型，根据植物的几何和生物力学特性，以及水流和波场参数来预测LE，并将演示如何使用有效长度来预测波浪和波流组合条件下草甸上的波浪能量耗散。这些实验将在一条24米长、60厘米深的水道中进行，并配有桨形造波机。最初，模型叶片将由低密度聚乙烯(LDPE)和高密度聚乙烯(HDPE)制造。稍后的实验将考虑使用活植物和3-D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捕获，单独的叶片和草地内的单个叶片上的力将通过潜水式力传感器测量。速度场采用声学多普勒测速仪和PIV进行测量。波浪能量的耗散将根据波幅的纵向衰减来估计，而波幅的纵向衰减将使用阻力型水面计来测量。这个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，该项目将开发一个统一的模型，用于预测不同形态和相关野外条件范围内的植物引起的波浪耗散。

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.