Performance characteristics and parametric analysis of a novel multi-purpose platform combining a moonpool-type floating breakwater and an array of wave energy converters. (15th June 2021) - Cheng, Yong
Graphical abstract: This paper gives a detail analysis on the hydrodynamic performance of a multi-purpose with a moonpool-type floating breakwater and an array of heaving WECs. A time-domain three-dimensional (3D) numerical wave tank (NWT) is developed based on the potential theory with fully nonlinear boundary conditions on wetted body surfaces and free surfaces. A series of parametric studies including comparison with isolated WECs or floating breakwater, WEC diameter, wave nonlinearity, PTO damping, moonpool layout and wave direction are conducted to give guidance for the design and configuration of the multi-purpose platform. The results indicate that internal fluid motion in the moonpools has a positive effect on wave energy conversion of WECs which in turn enhance wave attenuation capacity of the floating breakwater. For an unequal layout of moonpools in a multi-purpose platform, the thinner moonpools are the major contributor to wave energy extraction, especially in short wave region. WECs with larger diameter have larger water-plane area, which leads to smaller natural period and more extracted wave energy. Figure Multi-purpose platform of a moonpool-type floating breakwater and an array heaving WECs. Highlights: Integrating WECs with floating breakwaters can provide a multi-function solution. A 3D nonlinear method is developed to evaluate the mutual relationship. Internal fluid motion has beneficial effects on both energy extraction and wave attenuation. The optimization of moonpool size can broaden the bandwidth for a practical wave farm. The multi-purpose platform performs a better energy extraction in short oblique waves. Abstract: Integration of Wave Energy Converters (WECs) with floating breakwater system provides a multi-function solution to wave energy extraction and offshore infrastructural protection. The contribution of this work is to guide the optimal size and configuration of a multi-purpose platform including a moonpool-type floating breakwater and an array of heaving oscillating-buoy (OB) WECs. The investigation is performed using a developed time-domain numerical wave tank (NWT) based on the three-dimensional (3D) potential flow theory with fully nonlinear boundary conditions on transient wetted body surfaces and free surfaces. The comparison of the hydrodynamic performance among the multi-purpose platform, the isolated array WECs, and the isolated floating breakwater are examined. The internal fluid motion in the moonpools has a positive effect on the wave energy absorption of WECs, which in turn enhances the wave attenuation capacity of the floating breakwater. WECs with larger diameter have a larger water-plane area, which leads to more extracted wave energy. The wave nonlinearity reduces the optimal PTO damping value and has an adverse effect on the wave energy extraction. However, when wave nonlinearity becomes prominent, the wave attenuation capacity is improved with increasing PTO damping. For an unequal layout of moonpools, the thinner moonpools are the major contributor to wave energy extraction, especially in the short wave region. As a result of mass exchange of fluid from the moonpool to the outer domain, the multi-purpose platform indicates favorable performance of wave energy absorption. The novel floating system makes the utilization of wave energy over a wider frequency range.