Predictive Models for Wave Damping by Flexible Aquatic Vegetation

柔性水生植被的波浪阻尼预测模型

基本信息

批准号：
1659923
负责人：
Heidi Nepf
金额：
$ 44.08万
依托单位：
Massachusetts Institute of Technology
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-02-15 至 2022-01-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1659923&HistoricalAwards=false
关键词：
Predictive Models Wave Damping Flexible

项目摘要

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.

水生植被提供了许多自然效益，包括保护海岸线免受风暴和侵蚀、提供栖息地以及改善水质。波浪会将沉积物从河床上卷起，造成侵蚀，使水体浑浊，并向水中添加污染物。植被可以减少波浪运动并防止沉积物被卷起。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对波浪运动的减少。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）来预测植被波浪能的减少。通过这个新模型，工程师和流域管理者将能够评估不同的植被恢复方案，以了解其保护海岸线和减少导致水质恶化的侵蚀事件的潜力。本实验室研究探讨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。灵活的植被会随着水流而弯曲，这种重新配置会改变植被阻力。重新配置的影响可以用有效设备长度 le 来描述，它是赋予与重新配置的柔性设备相同的水动力阻力的刚性设备的长度。在一项初步研究中，PI 的实验室为具有简单带状形态的单个植物（淡水和咸水鳗草）制定了比例定律，可以预测水流和波浪中的阻力。这项新研究将把尺度法则扩展到植物群落（草地）、水流和波浪相结合的条件以及形态更复杂的植物（例如伊乐藻和眼子菜）。具体来说，本研究将开发模型来根据植物几何和生物力学特性以及电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组合波中草地上的波浪能量耗散- 当前情况。实验将在一条长24m、深60cm、配有桨式造波机的水道中进行。最初，模型叶片将由低密度聚乙烯 (LDPE) 和高密度聚乙烯 (HDPE) 制成。后续实验将使用活体植物和 3D 打印模型来考虑更复杂的形态。将通过数字成像捕获各个叶片的运动，并使用潜水力传感器测量孤立的和草地内各个叶片上的力。速度场将通过声多普勒测速仪和 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，波幅的纵向衰减将使用电阻式水面计进行测量。该项目将有助于对流体-柔性结构相互作用的基本理解，这与许多工程主题相关，例如。被动能量收集装置和柔性表面的流量控制。与地球系统相关，该项目将开发一个统一的模型，用于预测不同形态的植物和各种相关现场条件引起的波耗散。