| Tartalmi leírás: |
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.
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