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Enhancing the survival performance of wave energy converters (WECs) in extreme wave conditions is crucial, and reducing wave loads is a key aspect of this. Placing the device underwater has been recognized as a beneficial strategy, yet the determination of the optimal submerged depth and the effects of varying wave conditions remain ambiguous. To address this, the study numerically analyzes the total forces in both horizontal and vertical directions, along with their harmonic components, across different wave configurations. A computational fluid dynamics method is employed to investigate a triangular-baffle bottom-shaped oscillating floater, which is known for its high energy conversion efficiency. The findings indicate that submerging the device to a depth equivalent to half the actual focused amplitude (1/2Ab) is the most effective strategy in the given sea state, offering superior wave force reduction vertically and robust performance horizontally. The analysis of harmonics reveals the significant contribution of high-order components to the total wave forces. Additionally, the study examines the impact of focused wave amplitudes and peak frequencies, showing that although force reductions are lessened in more extreme conditions, the optimal submerged depth of 1/2Ab still yields near 30% reduction in total vertical force and 22% in total horizontal force. This research provides theoretical insight that can guide the enhancement of WECs' survival capabilities in practical engineering applications. [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]

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]

• 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]

• A WEC-type floating breakwater with a triangular-baffle bottom is put forward. • The new integrated system has simpler geometry and good hydrodynamic performance. • Asymmetric floaters can more effectively extract wave energy and protect coast. • Reasons causing good energy extraction and coastal protect performances are shown. • Cost-sharing of integrated system can make wave energy economically competitive. Combined floating breakwater and wave energy converter systems have the potential to provide a cost-effective solution to offshore power supply and coastal protection. This will make wave energy economically competitive and commercial-scale wave power operations possible. This paper investigates the hydrodynamic features of wave energy converters that meet the dual objectives of wave energy extraction and attenuation for such a combined system. A two-dimensional numerical model was established using Star-CCM+ commercial software based on viscous Computational Fluid Dynamics theory to investigate the hydrodynamic performance of an oscillating buoy Wave Energy Converter (WEC) type floating breakwater under regular waves. The model proposed in this paper was verified with published experimental results. The hydrodynamics of symmetric and asymmetric floaters were investigated to demonstrate their wave attenuation and energy extraction performance, including square bottomed, triangular bottomed (with and without a baffle plate), and the Berkley Wedge. The asymmetric floaters were found to have higher power conversion efficiency and better wave attenuation performance, especially the Berkeley Wedge bottom device and the triangular-baffle bottom device. The triangular-baffle bottom device with a simpler geometry achieved similar wave attenuation and energy extraction performance characteristics to that of the Berkeley Wedge device. The maximum energy conversion efficiency of the triangular-baffle bottom floater reached up to 93%, an impressive WEC device among many designs for wave energy conversion. There may be a great potential for this newly proposed triangular-baffle bottom WEC type of floater to be an ideal coastal structure for both coastal protection and wave energy extraction. [ABSTRACT FROM AUTHOR]

Abstract A new concept of point-absorber wave energy converter (WEC) with a waterproof outer-floater and a built-in power take-off (BI-PTO) mechanism, named Dual-Resonance WEC (DR-WEC), is put forward and investigated by experiments and numerical simulations. The BI-PTO mechanism includes spring, sliding-mass and damping systems, where the spring system is the most complicated and should be designed specially. A 1:10 scale model is designed. The mechanical performance of the BI-PTO system is investigated by a bench test. The results have shown that the design is feasible, and the added inertia effect of the BI-PTO has a negative influence on the power output. The average mechanical efficiency of the BI-PTO is 65.8% with maximum up to 80.0%. The motion and power responses of the DR-WEC are studied by a wave tank experiment and a linear numerical model with corrected mechanical added mass and viscosity. The viscous added mass and damping correction coefficients are obtained by a free decay test. The good agreement between the experimental measurements and numerical simulations has indicated that the present numerical model with corrections is of enough accuracy and the effects of mooring system and other degree of freedoms on the heave motion and power responses can be ignored. Highlights • A new WEC with waterproof outer-floater and built-in PTO mechanism is put forward. • The spring system of the variable-parameter PTO mechanism is designed in detail. • The Dual-Resonance WEC was tested both on a special test bench and in a wave tank. • The mechanical property of the built-in PTO system is acquired. • The numerical model is validated in comparison with the experiment results. [ABSTRACT FROM AUTHOR]