Blowing the Top on Parametric Resonance: Relief Valve Control for the Stabilisation of an OWC Spar Buoy

• Published in: Volume 9: Ocean Renewable Energy
• Main Authors: Davidson, Josh, P. F. Gomes , Rui, Galeazzi, Roberto, C. C. Henriques , João
• Format: Article in Journal/Newspaper
• Language: English
• Published: The American Society of Mechanical Engineers (ASME) 2020
• Subjects: Arctic
• Online Access: https://orbit.dtu.dk/en/publications/599c53de-2fc9-46bd-b846-8538284424e6; https://doi.org/10.1115/OMAE2020-19128

An active control method, to suppress the onset of pitch/roll parametric resonance on an oscillating water column (OWC) spar buoy, is proposed in this paper, which utilises a pressure relief valve at the top of the OWC air chamber. The paper examines the hypothesis that by opening the relief valve, to reduce the air chamber pressure difference and to decouple the dynamics of the spar buoy and the OWC within, the natural pitch/roll frequencies of the system will be shifted, allowing parametric resonance to be cancelled when its onset is detected. The paper reports on experiments, performed to test the stated hypothesis, with a small-scale model OWC spar buoy in a wave flume. Two configurations are considered and tested in a range of monochromatic waves (1) fully closed air chamber; (2) fully open chamber. The results partially confirm the hypothesis, demonstrating that the occurrence of parametric resonance observed for certain wave frequencies when the chamber is closed does not occur when the chamber is open. However, the change in the natural pitch/roll frequencies between the two configurations is very small, and parametric resonance occurs in both confurations for waves with twice this frequency.