Hydrodynamic performance of an oscillating water column integrated into a hybrid monopile foundation

• Published in: Ocean engineering 2024-05, Vol.299, p.117062, Article 117062
• Main Authors: Liu, Zhao, Jin, Yuan, Cao, Linquan, Liu, Guize, Guo, Hao
• Format: Article
• Language: English
• Subjects: Combined concept; Monopile wind turbine; Optimal pneumatic damping; Oscillating water column; wave energy device
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2024.117062

In this study, a combined concept consisting of an annular oscillating water column device (OWCD) and a bottom-standing offshore wind turbine is considered. Such a system has the ability to harness different types of offshore sustainable energy. The offshore wind turbine is supported by a hybrid monopile foundation, in which the foundation is reinforced by a friction wheel located at the soil surface. An analytical approach is constructed to model the air-water interaction within the chamber and evaluate the hydrodynamic efficiency of the system. In addition, a pneumatic model is employed to elucidate the correlation between the air pressure and air movement in the chamber. Concerning the effects of the oscillating air pressure, expression of the velocity potential in the form of an orthogonal series is searched via the variable-separation method. Unknown coefficients in the series are solved via the enforcement of the continuity of the potential and its normal derivatives over the common interfaces that connect neighboring subdomains. The convergence of the solution in relation to the truncated number is examined and its validity is confirmed by comparing the wave power extraction efficiency based on different methods. Subsequently, an in-depth numerical analysis is carried out. It is noted that the maximum wave power extraction efficiency is achieved when the water column in the chamber experiences a piston-mode resonance. When the width of the cross section (denoted by B) and the draft of the OWCD are equal to 1.0 and 1.5 times of the radius of the monopile, respectively, the maximum wave power absorption can exceed 80% of the incident wave energy over a width of 2B. In addition, it is found that the effect of the friction wheel on the performance of the system is apparent in low-frequency region, but not obvious for short incident waves. This is owing to that the energy of short incident waves is highly concentrated near the free surface, leading to a weak action on the friction wheel located at the soil surface. •The hydrodynamic performance of a combined concept is assessed by a meshless method.•Various motion modes of the internal wave field is analyzed, among which the piston mode contributes the most to wave power absorption.•The frequency of the piston-mode resonance can be tuned by adjusting the chamber size.•The friction wheel can improve the wave power absorption in the low-frequency region.