TY - JOUR
TI - Transverse motion instability of a submerged moored buoy
AU - Orszaghova, J
AU - Wolgamot , H
AU - Draper, S
AU - Taylor, R
AU - Taylor, P
AU - Rafiee, A
T2 - Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences
AB - Wave energy converters and other offshore structures may exhibit instability, in which one mode of motion is excited parametrically by motion in another. Here, theoretical results for the transverse motion instability (large sway oscillations perpendicular to the incident wave direction) of a submerged wave energy converter buoy are compared to an extensive experimental dataset. The device is axi-symmetric (resembling a truncated vertical cylinder) and is taut-moored via a single tether. The system is approximately a damped elastic pendulum. Assuming linear hydrodynamics, but retaining nonlinear tether geometry, governing equations are derived in six degrees of freedom. The natural frequencies in surge/sway (the pendulum frequency), heave (the springing motion frequency) and pitch/roll are derived from the linearized equations. When terms of second order in the buoy motions are retained, the sway equation can be written as a Mathieu equation. Careful analysis of 80 regular wave tests reveals a good agreement with the predictions of sub-harmonic (period-doubling) sway instability using the Mathieu equation stability diagram. As wave energy converters operate in real seas, a large number of irregular wave runs is also analysed. The measurements broadly agree with a criterion (derived elsewhere) for determining the presence of the instability in irregular waves, which depends on the level of damping and the amount of parametric excitation at twice the natural frequency.
DA - 2019/01//
PY - 2019
PB - The Royal Society
VL - 475
IS - 2221
SP - 20180459
UR - https://royalsocietypublishing.org/doi/10.1098/rspa.2018.0459
DO - 10.1098/rspa.2018.0459
LA - English
KW - Wave
KW - Modeling
KW - Mooring
KW - Performance
ER -