Oscillations of a Modeled Mangrove-Root for Energy Harvesting and Hydrodynamics Characterization

A one-degree-of-freedom vortex induced vibration (VIV) was investigated to measure the energy extracted from oscillations of the mangrove roots. A mangrove root was modeled as a vertical cylinder (Cyl), submerged in a water tunnel, pivoted at its top by a thin steel plate. This enhance transverse oscillations, perpendicular to the water flow. Three plates thickness were used to simulate diverse root’s rigidity. A generator was attached to the Cyl and the voltage was measured. The oscillation amplitude (OA) of the Cyl tip was recorded with HS camera and 2-D PIV measurements were made. The Cyl was still for low water velocities, then OA increase very fast reaching a maximum, and decrease until a very low value. Contrary, frequency of the OA was always increasing with water velocity. Similar behavior was found for all rigidities, but the critical values also increase with rigidity. The rms voltage follows similar tendency than OA with a maximum of 28 mV for the case of maximum rigidity. The analysis of downstream vortex shedding data extracted from PIV will be used to correlate with mechanical energy conversion of the root and with the electrical energy. This analysis of VIV correlated with oscillations will be fundamental for future bio-inspired energy harvesting devices.