Characterization of a Mangrove-Like System for Tidal Energy Harvesting: Effect of root and path diameter.*

Tidal energy is a potential source of renewable energy for many coastal locations in the US. However, many of the conventional devices to convert hydrokinetic energy to electrical energy are not necessarily apt in these locations. Inspired by mangrove roots - a tree that is abundant along the tidal stream in tropical and sub-tropical areas, we designed a novel device to harvest hydrokinetic energy from tidal currents. This device consists of one or multiple oscillating cylinders, partially submerged in the water and an electric generator composed of fixed magnets and a winding. A steel plate provides a restoring spring force for the system. The device was tested in a recirculating water tunnel for different cylinder diameters, array sizes and flow speeds. The kinematics and the voltage output were measured for the different conditions. The flow downstream the model was measured using Particle Image Velocimetry. In general, the device starts to oscillate at a critical flow speed and reach a maximum velocity until the motion decreases. The maximum amplitude oscillation and voltage output tend to increase with larger cylindrical diameters and when the cylinders were closer to each other. The power performance and wake structure are also compared.