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。当水下柔性体在流体表面附近操作时，其接近空气-水界面可引起自由表面变形。为了了解这种变形对物体动力学的影响，本项目将研究物体结构动力学与周围流体动力学之间的耦合所起的作用。近地表能量采集器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其性能。此外，近表面机器人设计者可以受益于理解流体-结构-表面相互作用的基本原理，这可以促进扩展其使命范围，从检测和绘制污染水溢出表面，到监视沿海地区，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，这些活动将激励和吸引人们进入工程和科学学科，从马萨诸塞州东南海岸的K-12学童到研究生，通过课堂讲座，基于项目的学习模块，和游戏为基础的推广活动。这项研究的目标是系统地调查流体结构，空气-水界面附近的柔性膜的表面相互作用。通过一组水洞实验，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，流体-结构-表面的相互作用的柔性薄膜在轴向流中放置在不同的淹没高度近表面将进行研究。特别感兴趣的是研究不稳定性的发生，任何可能的流致振动响应的发生，以及尾流中的膜涡动力学。比较将与经典的颤振响应观察到的柔性薄膜放置在均匀的流，远离自由表面。接下来，一个基于能量的降阶非线性模型的近表面柔性膜将开发耦合其非线性结构动力学与三维流场信息，通过TR-PTV测量获得。将采用一种数学算法，结合微分求积法的高阶有限元求解方法，求解完全耦合的偏微分运动方程。该研究结果有望影响科学研究界和社会，为我们提供了一个详细的了解，在自由表面附近的柔性薄膜的流体弹性行为，在广泛的可能的操作环境。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.