CAREER: Fluid-Structure-Surface Interactions of Flexible Bodies at the Air-Water Interface

了解水下柔性体（如用于能量收集的近表面阵列或近表面机器人）中流体-结构-表面相互作用的基本原理将为广泛的应用提供新的科学见解。当一个水下柔性体在流体表面附近工作时，它靠近空气-水界面会引起自由的表面变形。为了了解这种变形对机体动力学的影响，该项目将研究机体结构动力学与其周围流动的流体动力学之间的耦合所起的作用。能量收集器近表面阵列的设计是一个很好的应用例子，其中可以利用相互作用来提高它们的性能。此外，近地表机器人的设计者可以从了解流体-结构-表面相互作用的基本原理中受益，这可以促进扩大其任务范围，从探测和绘制地表污染水泄漏，到沿海地区的监测，再到海上结构健康监测。该提案中的科学努力与教育活动相结合，将通过课堂讲座、基于项目的学习模块和基于游戏的外展活动，从马萨诸塞州东南海岸的K-12学生到研究生，激发和吸引人们进入工程和科学学科。本研究的目的是系统地研究空气-水界面附近柔性膜的流固-表面相互作用。通过一系列水洞实验、高速成像技术和体积高分辨率时间分辨粒子跟踪测速（TR-PTV）测量，研究了轴向流动中近地表不同淹没高度下柔性膜的流固面相互作用。特别感兴趣的是研究不稳定性的开始，任何可能的流诱导振动响应的发生，以及薄膜尾迹中的涡动力学。比较将与经典颤振响应观察到的柔性薄膜放置在均匀流动，远离自由表面。接下来，通过将柔性膜的非线性结构动力学与通过TR-PTV测量获得的三维流场信息耦合，建立基于能量的近表面柔性膜的降阶非线性模型。结合微分求积法的高阶有限元解法的数学算法将被用于求解完全耦合的运动偏微分方程。这一发现为我们提供了在各种可能的操作环境中接近自由表面的柔性薄膜的流体弹性行为的详细理解，预计将影响科学研究界和社会。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Understanding the fundamentals of fluid-structure-surface interactions in underwater flexible bodies (like near surface arrays for energy harvesting or near surface robots) will provide new scientific insights for a broad range of applications. When an underwater flexible body operates near the surface of the fluid, its proximity to the air-water interface can cause free surface deformations. To understand the effect of such deformations on the dynamics of the body, this project will investigate the role played by the coupling between the structural dynamics of the body and the hydrodynamics of its surrounding flow. The design of near surface arrays of energy harvesters is an excellent example of an application where the interaction can be utilized to improve their performance. Moreover, near surface robot designers can benefit from understanding the fundamentals of fluid-structure-surface interactions that can facilitate expanding their mission envelope, ranging from detecting and mapping polluted water spill on the surface, to surveillance of coastal zones, to offshore structural health monitoring. The scientific endeavors in this proposal are integrated with educational activities that will inspire and attract people to engineering and science disciplines, from K-12 schoolchildren in the Southeast Coast of Massachusetts to graduate students through classroom lectures, project-based learning modules, and game-based outreach activities.The goal of this research is to systematically investigate the fluid-structure-surface interactions of flexible films near the air-water interface. Through a set of water tunnel experiments, high speed imaging techniques, and volumetric high-resolution time-resolved particle tracking velocimetry (TR-PTV) measurements, fluid-structure-surface interactions of a flexible film in axial flow placed at varying submerged heights near surface will be studied. Of particular interest are studying the onset of instability, occurrence of any possible flow-induced vibration response, and vortex dynamics in the wake of the film. Comparisons will be made with classical flutter responses observed for flexible films placed in uniform flow, distant from the free surface. Next, an energy-based reduced-order nonlinear model of the near-surface flexible film will be developed by coupling its nonlinear structural dynamics with three-dimensional flow field information, obtained through TR-PTV measurements. A mathematical algorithm incorporating higher-order finite element solution approach of Differential Quadrature Method will be used to solve the fully coupled partial differential equations of motion. The findings are expected to impact the scientific research community and society by providing us with a detailed understanding of fluidelastic behavior of flexible films in proximity of free surface in a wide range of possible operational environments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.