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

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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.