Design and test of a new marine energy harvesting device

• Main Author: Anjali Vishwanathan
• Other Authors: Tang Hui
• Format: Final Year Project
• Language: English
• Published: 2013
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/54057
• Institution: Nanyang Technological University

Vortex-induced vibrations (VIVs) are a well-studied phenomenon for a single elastically mounted rigid circular cylinder free to oscillate in the transverse direction. When an additional cylinder is added downstream, the flow and vortex dynamics change. This project attempts to broaden the research into the study of VIVs for two identical elastically mounted rigid cylinders free to oscillate in transverse direction. The amplitude ratio and frequency ratio are measured for different spacing ratios, s/D from 1.5 to 4, in steps of 0.5. The proximity wake interference region, which is where the downstream cylinder lies, is studied in this project. Tests are conducted at high Reynolds numbers (compared to previous studies at lower Reynolds number, Re < 10^4) ranging from 26,000 to 60,000 for two cylinders of diameters 60mm and 100mm at low mass ratios, m* = 1.30, 1.55 and 2, across velocity ratios of U* = 5 - 14. The effect of the downstream cylinder was to widen the synchronisation range of VIVs. Steadily increasing frequency ratio across the range of velocity ratio was observed, irrespective of the spacing ratio. The amplitudes of VIVs for both the cylinders were higher than that of an isolated single cylinder for all spacing ratios. Effects of free surface and bottom boundary were observed for the experiments and thus peak amplitude ratio and frequency ratio could not be ascertained. An energy conversion setup, similar to a linear generator, to harness the energy of VIVs of a single cylinder was implemented. A peak-to-peak open circuit voltage of 3.5 V was obtained for a water velocity of 0.45m/s. The frequency of the voltage obtained was nearly twice the cylinder vibration frequency. The maximum power output that was obtained across a load resistor of 5.6 MΩ was 0.72 microwatts for 0.45m/s water velocity.