CAREER:On the Coupled Nature of Highly-Flexible Plates Subjected to Fluid Loads: An Exploration of Structural Response and Reconfiguration

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The swimming motion of rays in the ocean involves the flapping of two flexible fins. As a result of the fins changing shape, the surrounding flow field is altered. Another example of this type of fluid-structure interaction is that of seagrass. In a current, the seagrass will flex and become streamlined with the flow. These flexible structures cause a net reduction in drag. This project takes inspiration from these two examples with its goal being to identify how the flow field changes as a result of the shape reconfiguration of a highly flexible plate near an air-water interface. Drag reduction will also be demonstrated by actively controlling the plate stiffness. The results of this work have the potential to improve propulsion methods and mixing processes. Another component of this project includes an annual summer educational program for middle school students, complete with small table-top experiments. Local undergraduate and high school students will also have an opportunity to participate in this research.The goal of this research project is to understand the fluid-structure interaction of a highly flexible plate near a free surface. Scaling laws will need to be developed to explain the reduction in drag coefficient due to the reconfiguration of the plate in the proximity of the free surface. These scaling laws will be achieved primarily through experimentation and compared with theory and simulation. Particle image velocimetry measurements will yield velocities and pressures. Stereoscopic digital imaging and high-speed photography will be used to measure plate deflections at the water-structure interface. Pressure and force sensors on the plate will measure fluid loads. A new method based on measurements of the water-contact line along with theory will allow for the prediction of the pressure on the plate without artificially stiffening the plate with traditional pressure transducers. The project will advance our understanding of flow around a highly flexible plate due to: 1) the influence of the free-surface, 2) vertical oscillatory motion, i.e. flow around the body that periodically changes directions, 3) the combination of vertical oscillatory motions and forward speed, and 4) active control of the plate stiffness to attain pre-defined flow conditions. By leveraging active and passive structural reconfigurations, drag can potentially be reduced on undulatory propulsors and vessels.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.