Abstract
Tidal energy has the potential for future electricity generation to be widely used in intercostal areas during the rise and fall of tides. Inspired by mangrove roots, we designed a novel device to harvest hydrokinetic energy from tidal currents. This device consists an oscillating cylinder, partially submerged in a flow of water and an electric generator composed of a fixed magnet and a coil attached to the cylinder pivoted at its top by a thin flexible steel plate. This energy harvesting system is considered as one-degree-of-freedom vortex-induced vibration (VIV). The oscillation amplitude of the cylinder tip was recorded with a high-speed camera and 2-D PIV measurements were made to explore the hydrodynamic interaction within the devices for Reynolds numbers ranging from 200 to 1500 (based on cylinder diameter) consistent with biological velocity in tidal flows. We analyzed the kinematics as well as the power generation of the device for different stiffness of the plate. We observed that the cylinder was unmoved for low water velocities; however, by increasing the flow velocity the oscillations increase and reached a maximum value; similar fashion was observed for all stiffness. It was found that for a specific range of reduced velocity (0 < Ur < 3.5) the device worked in its optimal range in which the amplitude of oscillations and the efficacy of the system reach the highest values. This analysis of VIV correlated with oscillations will be fundamental for future bio-inspired energy harvesting devices. These renewable energy devices could have applications to power small actuators or sensors to monitor coastal infrastructure.
