Opening the air‐chamber of an oscillating water column spar buoy wave energy converter to avoid parametric resonance

Abstract

The oscillating-water-column (OWC) spar-buoy is a type of wave energy converter that may exhibit undesirable large roll and pitch amplitudes caused by a dynamic instability induced by parametric resonance. The occurrence of this phenomenon not only reduces the power extraction but significantly increases the structural loads on the buoy, the turbine rotor and on the mooring system. The paper compares the parametric resonance behaviour of two configurations of an OWC spar-buoy using experimental data obtained in a wave flume at a scale of 1:100. The configurations investigated were: (1) closed and ( 2) fully open-air chamber. The experimental tests covered a wide range of regular and irregular waves, as well as in free decay experiments. Results showed that opening the air chamber reduces the coupling between the buoy and the OWC within, thus shifting the damped natural heave frequency of the system in comparison with the closed chamber configuration. This effect changes parametric resonance characteristics of the two configurations due to the coupling between roll/pitch and heave modes. Moreover, for specific wave frequencies, the occurrence of parametric resonance observed when the chamber is closed do not occur while the air chamber is fully open. These results suggest the possibility of controlling a pressure relief valve installed on top of the device to reduce parametric resonance whenever this dynamic instability is detected.

Modelling of Parametric Resonance for Heaving Buoys with Position-Varying Waterplane Area

“…The passive control methods consider the inclusion of strakes/fins [36], utilising the mooring system [37] or modifying the initial design of the geometry and mass distribution [38]. The active control methods utilise systems, such as the power-take off [39], variable inertia mechanisms [40] or a pressure relief valve, in an oscillating water column [41,42]. A real-time detection system for the onset of parametric resonance in WECs has also been developed to give early warning to such active control systems [43].…”

Parametric excitation suppression in a floating cylinder via dynamic vibration absorbers: a comparative analysis

“…The use of fins was also investigated by Gomes et al [23] to suppress parametric pitch and roll in the OWC spar buoy, which was previously observed to be prone to parametric resonance [24,25]. Also considering the OWC spar buoy, Davidson et al [26,27] investigated the use of a pressure relief valve in the OWC chamber to decouple the motion of the spar and internal water column, analogous to the notch filter used in [20].…”

“…We then substitute a new variable x a3 = xa3 + l 0 into Eqs. (25)-(27), where x a3 marks the relative displacement of the absorber's mass starting from the buoy CoM, obtaining(M + m a3 ) ẍ3 − m a3 x a3 ẍ5 sin(x 5 ) −2m a3 ẋ5 sin(x 5 ) ẋa3 − m a3 x a3 ẋ2 5 cos(x 5 ) +m a3 cos(x 5 ) ẍa3 = F 3 (x 3 , x 5 , ẋ3 , ẋ5 , ẍ3 , ẍ5 ; t) (m a3 x 2 a3 ẍ5 − m a3 x a3 ẍ3 sin(x 5 ) + 2m a3 x a3 ẋ5 ẋa3 − m a3 gx a3 sin (x 5 ) = F 5 (x 3 , x 5 , ẋ3 , ẋ5 , ẍ3 , ẍ5 ; t) (30)m a3 ẍa3 + m a3 ẍ3 cos(x 5 ) − m a3 ẋ2 5 x a3 + k 1 − 2k 2 l 0 + 3k 3 l 2 0 x a3 + (k 2 − 3k 3 l 0 )x +m a3 g cos(x 5 ) + b a ẋa3 = 0.…”

A Computationally Efficient Analytical Modelling Approach for Parametric Oscillations in Floating Bodies

“…Parametric resonance in floating bodies has become an increasingly important area of study due to its relevance in offshore engineering [1][2][3][4][5][6][7], wave energy conversion [8][9][10][11][12][13][14], and naval architecture [15][16][17][18][19][20][21]. Understanding the dynamics of floating structures and the interaction with waves is crucial for the development of efficient and reliable marine systems.…”