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A wind-wave hybrid system consisting of a semi-submersible floating wind turbine and an array of heaving wave energy converters (HWECs) provides a solution for co-located marine renewable energy extraction. The knowledge of the coupled dynamic and power features of the hybrid system is important to the design and operation but is poorly understood. This study proposes a comprehensive numerical model that can tackle the full couplings by bridging the aerodynamic module of OpenFAST and the hydrodynamic simulator WAFDUT through an in-house code based on multi-body dynamics. The coupled dynamic and power generation characteristics of the hybrid system are investigated, with an emphasis on the influence of the HWECs on the wind-induced motion, mooring tension, and wind power generation of the turbine. Results show that the HWECs do not produce negative effects on the wind-induced surge, heave, and pitch motions. The HWECs can slightly reduce the mooring tension and slightly improve wind power generation. The array of HWECs can generate over 500 kW wave power in the waves with periods of 6 s–10 s, which can be a qualified supplement to wind power. The findings offer useful knowledge about the key properties of the hybrid system for practical use. [ABSTRACT FROM AUTHOR]

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]

An abreast pair of floating parabolic breakwaters is proposed as part of a breakwater-WEC (wave energy converter) hybrid system. An objective is providing a basis for tackling the problem of unreasonable shape while applying an isolated parabolic breakwater along a long shore. The other is providing multiple wave amplification chambers for the WECs. Wave attenuation and amplification are investigated using an open-source code HAMS. The effects of gap length and connection manner between the two parts in the pair are analyzed. Results show that for non-zero gap length, the application of a rigid connection slightly improves the wave attenuation by increasing the area of the low wave region on its lee side and greatly improves the wave amplification by increasing the area of the high wave amplification region on the weather side. An increase in the gap length intensifies the separation of low and high wave regions on the lee side by increasing both their areas, whereas it has negligible influence on the wave amplification. The worst wave amplification is obtained for rigidly connected breakwaters with no gap in between. A small gap is therefore recommended to be retained to improve the wave amplification without damaging the wave attenuation. • An abreast pair of parabolic breakwaters is proposed. • Wave attenuation and amplification performances of the breakwaters are evaluated. • Influence of the gap length between the two parts in the pair is analyzed. • Influence of the connection manner between the two parts in the pair is analyzed. • The different roles of the gap length and the connection manner are interpreted. [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 numerical model of a multi-floating-body connected by constraint is established. • The breakwater is designed based on the distribution of wave amplitude. • The wave extraction performance of the WECs of hybrid system is improved. • The optimal layout of the WEC array is close to the upward side of the breakwater. • The vertical force on the breakwater of hybrid system increases. Combining wave energy converters (WECs) with a floating breakwater provides a potential approach to help develop commercial-scale wave power operations. This paper aims to design and optimize a three-dimensional floating breakwater integrated with a WEC array by developing a numerical model of a multi-floating-body coupled system based on potential flow theory with viscous correction in the frequency domain. By analyzing the wave surface elevations around the breakwater, the size of the breakwater was optimized and the optimal installation locations of the WECs were determined. Under the condition of coupled constraints and six degrees-of-freedom motion, the interactions between the WEC array and the breakwater were analyzed. Subsequently, the number of WECs and the distance between the WECs and the breakwater were optimized to maximize the wave energy conversion performance of the hybrid system. Results show that the wave focusing areas appear more frequently near the breakwater. These focusing areas significantly improve WEC power, and thus better wave energy conversion performance can be achieved when the WECs are placed close to the breakwater. The vertical forces on the breakwater significantly increase due to the presence of the WECs, however the horizontal forces are decreased. The findings of this paper provide guidance to design and optimize a hybrid WEC-breakwater system in practical engineering applications. [ABSTRACT FROM AUTHOR]

The effects of gap wave resonance on the performance of a dual-floater hybrid system consisting of an oscillating-buoy type wave energy converter (WEC) and a floating breakwater are important for the design of such a hybrid system. This paper investigates the gap wave resonance by employing a two-dimensional numerical wave flume developed using the Star-CCM + software. The maximum wave elevation in the WEC-breakwater gap and the effects of the gap wave resonance on the performance of the dual-floater hybrid system were studied. The influence of the WEC motion and the geometrical parameters of the hybrid system on the maximum wave elevation were analyzed. The maximum gap wave elevation is essentially controlled by the vertical velocity of the free surface in the WEC-breakwater gap. The gap wave resonance was found to significantly improve the wave energy extraction performance of the hybrid system. This allowed the maximum conversion efficiency to exceed the well-known limit of 0.50 for a symmetric body in single degree-of-freedom motion. The wave resonance frequencies in the WEC-breakwater gap decreased with the increase of the gap width and the WEC draft. Due to the energy extraction of the WEC, the horizontal and vertical forces on the breakwater were reduced by up to 0.79 and 0.59, respectively. • The wave resonance in the WEC-breakwater gap is investigated. • Maximum wave elevations in WEC-breakwater gap and fixed floaters gap are compared. • Narrow gap resonance improves the energy extraction capability of the WEC. • The front wave energy converter reduces the forces on the breakwater. • Effects of hybrid system geometry on the gap wave resonance are analyzed. [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]

• The dual-floater hybrid system and single-floater integrated system are compared. • The hybrid system has better wave attenuation and energy extraction performances. • Narrow gap resonance has a significant impact on energy extraction capability. • The front wave energy converter reduces the forces on the breakwater. • The dual-floater hybrid system with asymmetric WEC is optimized. The high cost of power generation impedes commercial-scale wave power operations. The objective of this work is to provide a cost-sharing solution by combining wave energy extraction and coastal protection. A two-dimensional numerical wave tank was developed using Star-CCM+ Computational Fluid Dynamics software to investigate the hydrodynamic performance of a dual-floater hybrid system consisting of a floating breakwater and an oscillating-buoy type wave energy converter (WEC), and was compared with published experimental results. The differences between the hydrodynamic performance of the hybrid system, a single WEC and a single breakwater were compared. Wave resonance in the WEC-breakwater gap has a significant impact on system performance, with the hybrid system demonstrating both better wave attenuation and wave energy extraction capabilities at low wave frequencies, i.e., wider effective frequency. Forces on the breakwater were generally reduced due to the WEC. Wave resonance in the narrow gap has an adverse effect on the energy efficiency of the hybrid system with an asymmetric WEC, while a beneficial effect with a symmetric WEC. The wave energy conversion efficiency of hybrid system can be improved by increasing the draft and width of the WEC and decreasing the distance between the WEC and the breakwater. The findings of this paper make wave energy economically competitive and commercial-scale wave power operations possible. [ABSTRACT FROM AUTHOR]

Floating Photovoltaic (FPV) systems are emerging as a new type of ocean renewable energy, offering advantages such as avoiding land use and promoting power generation efficiency. Providing significant cost-effectiveness for manufacturing, transportation, and installation, FPV systems with modular floating platforms exhibit the potential to replace the conventional large steel-frame one. However, the performance of such multi-floating body structures under wave conditions remain underexplored. In this paper, based on potential flow theory, the motion characteristics and power performance of the proposed FPV array connected by the articulated system are evaluated. The results indicate that the FPV arrays with shorter floating structures exhibit greater pitch motion, especially when the wave condition matches the pitch resonance. For multi-float cases, the articulated system, optimized with appropriate parameters, demonstrates efficacy as attenuators. Additionally, the proposed FPV array has great potential to serve as an infrastructure for integrating solar and wave energy. For a selected offshore site, potential wave energy output from motion attenuators between FPV floaters is assessed together with solar energy output. Overall, this study serves as a valuable reference for the design and optimization of the multi-modules FPV and advances the research on combined solar and wave energy utilization on floating structures. • Constraint dynamics of a wave and solar hybrid system are modeled. • Key factors in the power performance of the devices are analyzed. • An optimization strategy for the array is proposed. • Power performance is evaluated based on real wave environment in China seas. [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]