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Integrating point absorber wave energy converters (PAWECs) and an offshore floating wind platform provide a cost-effective way of joint wind and wave energy exploitation. However, the coupled dynamics of the complicated hybrid system and its influence on power performance are not well understood. Here, a frequency-domain-coupled hydrodynamics, considering the constraints and the power output through the relative motion between the PAWECs and the semi-submersible platform, is introduced to optimize the size, power take-off damping, and layout of the PAWECs. Results show that the annual wave power generation of a PAWEC can be improved by 30% using a 90° conical or a hemispherical bottom instead of a flat bottom. Additionally, while letting the PAWECs protrude out the sides of the triangular frame of the platform by a distance of 1.5 times the PAWEC radius, the total power generation can be improved by up to 18.2% without increasing the motion response of the platform. The PAWECs can reduce the resonant heave motion of the platform due to the power take-off damping force. This study provides a reference for the synergistic use of wave and wind energy. [ABSTRACT FROM AUTHOR]

A hybrid system consisting of wave energy converters and breakwaters can be applied for both wave energy conversion and shoreline protection. Besides, the cost of wave energy conversion is believed to be reduced by such a combination. In this paper, a two-dimensional asymmetric wave energy converter-type breakwater with a triangle-baffle bottom that can convert wave energy through its heave motion is proposed and investigated experimentally in regular waves. A supporting system is designed and established to allow the model to move in a single degree of freedom or prescribed combination of multiple-degree-of-freedoms. The effects of the geometric asymmetry, the bottom slope, the width-to-draft ratio, and the multiple-degree-of-freedom motion on the wave energy conversion and attenuation performances are analyzed. The results show that the triangle-baffle wave energy converter-type breakwater has much higher wave energy conversion efficiency than its rectangular counterpart with the same displacement. Increasing the bottom slope and allowing pitch motion can improve efficiency, allowing surge motion will reduce efficiency, and the effect of increasing the width is uncertain due to two conflicting effects. The asymmetry, bottom slope, and width only have a limited influence on the wave attenuation, whereas surge and pitch motions reduce the wave attenuation in short waves, analogizing a wavemaker. [Display omitted] • A novel WEC-type breakwater with a triangle-baffle bottom is experimentally studied. • The effect of the model's geometric properties on its efficiency is analyzed. • The effect of the model's multi-DoF motions on its efficiency and wave attenuation is studied. [ABSTRACT FROM AUTHOR]

Installing an array of wave energy converters (WECs) on an existing breakwater is viable to reduce the high cost and improve the reliability of wave energy applications. The interaction between WECs and floating breakwater under multi-degree-of-freedom motion is crucial but not well investigated, especially the impact of WECs on the mooring system of the breakwater. This article fills this gap by experimentally studying a hybrid system consisting of a rectangle floating breakwater and an array of oscillating body WECs. The interactions between the WEC and the breakwater, the effect of the WEC bottom shape on the hybrid system, and the performance of the hybrid system in waves with different nonlinearities are investigated. Results indicate that the wave amplification effect of the breakwater improves the wave energy conversion performance of the WEC by up to 324.6%. As the WEC absorbs wave energy, the mooring forces of the breakwater in the pitch and surge directions decrease by up to 19.8% and 47.4%, respectively. When the incident wave height increases, the energy extraction performance of the hybrid system improves while the wave attenuation performance decreases. This study provides a reference for the practical application of WEC-breakwater hybrid systems and test data for the validation of numerical methods. • The multiple degrees-of-freedom motion of the hybrid system is considered. • The interactions between the breakwater and WEC are analyzed. • The mooring forces on the breakwater are influenced by the WEC. • The asymmetric shape of the WEC has two contradictory effects on its power. • Good power generation and attenuation hardly coexist due to wave nonlinearity. [ABSTRACT FROM AUTHOR]

Deploying a cylindrical heaving wave energy converter (WEC) in front of a parabolic breakwater forms a basic module for synergetic coast protection and power generation. The interactions in the hybrid system are important to its performance but poorly understood. Here the power amplification effect of the parabolic breakwater on the WEC and the additional wave attenuation effect of the WEC on the parabolic breakwater are investigated based on the potential flow theory of linear regular waves. A parabolic breakwater and five WECs with optimized geometry and generator parameters are employed in comparative numerical studies conducted using an open-source code HAMS. Results show that the parabolic breakwater has similar power amplification effects on different WECs, despite the significant differences in their dimensions and power-take-off damping. The power of a WEC can be increased by more than 120% at its natural period. A WEC can shadow the region behind it and reduce the wave amplitude on the opening wall of the parabolic breakwater. It also slightly reduces the amplitude of the relatively high waves in the protection zone behind the breakwater. A flatter WEC with a larger diameter-to-draft ratio is recommended as it generates more power and has a stronger shadow effect. • A novel breakwater-WEC hybrid system is proposed and optimized. • The system involves a heaving cylindrical WEC in front of a parabolic breakwater. • The overall power generation and wave attenuation performance is investigated. • The interactions between the breakwater and the WEC are analysed. • Recommendations for the WEC geometry are provided. [ABSTRACT FROM AUTHOR]

A hybrid system consisting of a spar-type wind turbine and an annular wave energy converter (WEC) is prospective in joint offshore wind-wave energy exploitation. Its coupled dynamic and power features in vast operating sea states are a valuable reference for design but are poorly understood. This study aims to fill the gap. By combining the wind module of OpenFAST and an in-house code, a numerical tool that can tackle the full aero-servo-hydro-mooring couplings in the hybrid system is developed. Dynamic features, mooring tensions, and energy conversion performance of a Hywind-annular WEC hybrid system are analyzed in a wide range of operating conditions with varying speeds of steady winds and periods of regular waves, emphasizing the effect of the annular WEC on the dynamic and power performance of the Hywind. Results show that the annular WEC improves the wind power generation below the rated wind speed and the stability of the Hywind by reducing its pitch displacement. But it also increases the motion amplitude in the heave direction. The annular WEC has a neglectable influence on the maximum mooring tensions. An evaluation of the annual wind-wave power based on hindcast sea states shows that wave power can effectively supplement wind power. • A rigorous performance analysis of a Hywind-annular WEC hybrid system is performed. • A numerical tool tackling the full aero-servo-hydro-mooring couplings is developed. • The annular WEC can help stabilize the Hywind in surge and pitch. • The annular WEC can improve wind power generation. [ABSTRACT FROM AUTHOR]

Integrating wave energy converters (WECs) on an offshore wind platform provides an economic and robust solution for co-located wind and wave power exploitation. The power performance of the hybrid system depends on the hydrodynamic interactions between the platform and WECs, but most of these effects remain unclear. In this study, through a hybrid system consisting of a semi-submersible platform and heaving point absorber WECs, this matter is addressed based on the higher-order boundary element method and multi-body constrained dynamics. Results show that a new prominent power peak appears while the platform and WECs are in a so-called synchronized mode regardless of the layout of the WECs, wherein the power of a single WEC can be increased by up to 41.4% and the total power by up to 26.7% and the heave motion of the platform increases. Out of the vicinity of the synchronized mode frequency, the WECs have a small impact on the surge motion and pitch motion of the platform, whereas reducing its resonant heave motion at the natural frequency. This work reveals useful insights into the dynamic and power performance of a wind-wave hybrid system, providing detailed configurations and potential guidance for the practical design and application. • Constrained dynamics of a platform and multiple wave energy converters are modeled. • Influences of platform motion on generator damping and power output are analyzed. • Mutual hydrodynamic and dynamic influences in the hybrid system are analyzed. • A new prominent power peak and the corresponding mechanism are revealed. • Power performance is evaluated based on measured wave data in China seas. [ABSTRACT FROM AUTHOR]

A hybrid system integrating a power take-off (PTO) system into a floating breakwater is a promising candidate for both shoreline protection and commercial wave energy extraction. Although geometric asymmetry is important to such PTO-integrated breakwaters, its role in energy conversion efficiency and wave attenuation is poorly understood. In this study, a two-dimensional semi-analytical model dealing with floats with arbitrary bottom shapes is established based on the potential flow theory. To quantify the geometric asymmetry reflected by PTO-integrated breakwaters with different contours, the degree of asymmetry and the absolute asymmetry are newly defined mathematically. A set of symmetric and asymmetric PTO-integrated breakwaters are comparatively studied to demonstrate the effect of linear PTO damping and geometric asymmetry on the transmission coefficient, the reflection coefficient, and the energy conversion efficiency. Results show that no matter the hybrid system is symmetric or asymmetric, a larger PTO damping is beneficial for wave attenuation in longer waves, particularly at the heaving natural period of the device. On the premise that the PTO damping is optimized, an increase in the degree of asymmetry greatly improves the energy conversion efficiency. An increase in the absolute asymmetry slightly improves wave attenuation. • Interactions between waves and a float with arbitrary bottom shapes are modeled. • Installing a power take-off (PTO) on a breakwater improves its wave attenuation. • The degree of asymmetry (DoA) of a float is newly defined mathematically. • DoA greatly influences PTO-integrated breakwater's energy conversion efficiency. • DoA slightly influences PTO-integrated breakwater's wave attenuation. [ABSTRACT FROM AUTHOR]

• Combined floating platform and WECs system can provide a cost-effective solution. • An accurate method is developed to optimize size and layout of WECs on a platform. • Larger WECs capture more wave energy in a limited region and a specific sea state. • Added WECs reduce the maximum horizontal force and pitch moment on the platform. • The synergy between wave and wind energy utilization on floating platform is shown. Combined floating offshore wind platform and Wave Energy Converters (WECs) systems have the potential to provide a cost-effective solution to offshore power supply and platform protection. The objective of this paper is to optimize the size and layout of WECs within the hybrid system under a given sea state with a numerical study. The numerical model was developed based on potential flow theory with viscous correction in frequency domain to investigate the hydrodynamic performance of a hybrid system consisting of a floating platform and multiple heaving WECs. A non-dimensional method was presented to determine a series of variables, including radius, draft, and layout of the cylindrical WEC at a typical wave frequency as the initial design. WECs with larger diameter to draft ratio were found to experience relatively smaller viscous effects, and achieve more wave power, larger effective frequency range and similar wave power per unit weight compared with those with the smaller diameter to draft ratio in the same sea state. The addition of WECs reduced the maximum horizontal force and pitch moment on the platform, whereas the maximum vertical force increased due to the increasing power take-off force, especially at low frequencies. The results presented in this paper provide guidance for the optimized design of WECs and indicate the potential for synergies between wave and wind energy utilization on floating platforms. [ABSTRACT FROM AUTHOR]

A hybrid system consisting of a floating offshore wind turbine and wave energy converters (WECs) is promising for multiple extractions of ocean renewable energy. Optimization of the layout and an evaluation of the performance of the hybrid systems are important before practical use but are not well done due to limited simulation tools. This study fills these gaps by proposing a complete toolkit based on the OpenFAST-AQWA framework together with a code that can deal with the full couplings in the problem. A novel DeepCWind-Wave Stars hybrid system is proposed as a representative to validate and practice the new tool. The key parameters of the WECs are optimized using an easily performed method based on the local wave contour disturbed by the platform. Motions, mooring loads, and power of the hybrid system are evaluated under a wide range of wind and wave conditions to examine the influence of the WECs. Results show that the integration of the WECs brings no harm to the stability of the system. The WECs reduce the fluctuation in the mooring force but slightly increase the average mooring force. The generated wave power is an adequate supplement to wind power, especially at a small wind speed. • A novel DeepCWind-Wave Stars hybrid system is proposed and its layout is optimized. • A FAST to AQWA (F2A) code delivering the full couplings between the two is developed. • The Wave Stars have no harm to the stability of the DeepCWind platform. • The generated wave power is found to be an effective supplement to wind power. [ABSTRACT FROM AUTHOR]