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In order to enhance the generation efficiency of wave energy converter (WEC) arrays, an optimization method for three-tether WEC array based on an improved honey badger algorithm is proposed. First, to overcome the shortcomings of the primal honey badger algorithm (HBA), such as slow convergence speed and low convergence accuracy, three improvement strategies are introduced, i.e., good point set initialization, chaos mechanism, and honey badger population mutation. Then, three wave farms including 2-buoy, 10-buoy, and 20-buoy are tested to verify the advancement and effectiveness of the improved honey badger algorithm (IHBA). The simulation results of the 2-buoy array demonstrate that there are multiple groups of optimal solutions in WEC array optimization. Furthermore, IHBA, HBA, genetic algorithm, and particle swarm optimization can find these optimal solutions at different speeds. Nevertheless, with increasing size of the WEC array, three comparative algorithms fall into local optima solutions. On the contrary, IHBA still exhibits a strong optimization ability and can seek global optima solutions. Finally, the q-factor values obtained by IHBA in 10-buoy and 20-buoy arrays reach 1.059 and 0.968, respectively, which are dramatically larger than those of other algorithms.

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In the face of depleting fossil energy and the imperative of sustainable development, there is a compelling drive towards advancing renewable energies. In this context, sustainable and predictable alternatives, like marine energy, gain prominence. Marine energy presents a cleaner option devoid of the adverse effects associated with fossil fuels, playing a crucial role in environmental sustainability by safeguarding coastlines against erosion. This study focuses on Astara Port in the Caspian Sea, exploring the utilization of wave energy converters (WECs). The originality of this study's research lies in exploring WECs' dual role in energy generation and coastal protection. Using MIKE21 software simulations, the impact of number, location, arrangement, and orientation of WECs across various scenarios was investigated, including two WEC number scenarios (11 and 13), three structural placement scenarios (north, front, and south of the port), two structural arrangement scenarios (linear and staggered), two port layout scenarios (original layout and modified layout), and two orientation scenarios for the structures (facing north-east, which is the dominant wave direction, and facing southeast). The results show a remarkable decrease in the significant wave height behind WECs, notably with 13 staggered devices facing dominant waves (from northeast), reducing the significant wave height Hs by 23–25%. This setup also shows the highest wave height reduction, notably 36.26% during a storm event. However, linear WEC setup offers more extensive coastline protection, covering 47.88% of the model boundary during storms. Furthermore, the 11 staggered WECs facing southeast (SE) arrangement had the lowest sediment accumulation at 0.0358 m over one year, showing effective sedimentation mitigation potential. Conversely, the 13 linear WECs facing northeast (NE) had the highest accumulation at 0.1231 m. Finally, the proposed port design redirects high-velocity flow away from the port entrance and removes rotatory flow, reducing sediment accumulation near the harbor entrance. [ABSTRACT FROM AUTHOR]

The coupled dynamic analysis of a hexagon-shaped Frustum Tension-leg platform (FTLP) combined with wave energy converters (WECs) supporting a 5-MW wind turbine is performed to analyse the dynamic responses of the hybrid system. The responses of the FTLP are investigated using the time-domain numerical simulation for the operational sea-states of the wind turbine. The FTLP is integrated with an array of point absorber-type WECs in a circular pattern to analyse the influence of the WECs on the dynamic responses of the floating platform. The aero-servo-hydro-elastic simulation tool FAST and hydrodynamic simulation tool WAMIT is used to study the rigid body motions of the system. The study observes higher rigid body motions in the surge, sway and yaw directions for the hybrid system. Further, the investigation is performed for the forces and moments developed at the base of the wind turbine and the tension developed on mooring cables to understand the integrity and stability of the hybrid platform. [ABSTRACT FROM AUTHOR]

Copyright of DYNA - Ingeniería e Industria is the property of Publicaciones Dyna SL and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the face of depleting fossil energy and the imperative of sustainable development, there is a compelling drive towards advancing renewable energies. In this context, sustainable and predictable alternatives, like marine energy, gain prominence. Marine energy presents a cleaner option devoid of the adverse effects associated with fossil fuels, playing a crucial role in environmental sustainability by safeguarding coastlines against erosion. This study focuses on Astara Port in the Caspian Sea, exploring the utilization of wave energy converters (WECs). The originality of this study’s research lies in exploring WECs’ dual role in energy generation and coastal protection. Using MIKE21 software simulations, the impact of number, location, arrangement, and orientation of WECs across various scenarios was investigated, including two WEC number scenarios (11 and 13), three structural placement scenarios (north, front, and south of the port), two structural arrangement scenarios (linear and staggered), two port layout scenarios (original layout and modified layout), and two orientation scenarios for the structures (facing north-east, which is the dominant wave direction, and facing southeast). The results show a remarkable decrease in the significant wave height behind WECs, notably with 13 staggered devices facing dominant waves (from northeast), reducing the significant wave height Hs by 23–25%. This setup also shows the highest wave height reduction, notably 36.26% during a storm event. However, linear WEC setup offers more extensive coastline protection, covering 47.88% of the model boundary during storms. Furthermore, the 11 staggered WECs facing southeast (SE) arrangement had the lowest sediment accumulation at 0.0358 m over one year, showing effective sedimentation mitigation potential. Conversely, the 13 linear WECs facing northeast (NE) had the highest accumulation at 0.1231 m. Finally, the proposed port design redirects high-velocity flow away from the port entrance and removes rotatory flow, reducing sediment accumulation near the harbor entrance.

The numerical performance of a buoy-type wave energy converter (WEC) under regular wave conditions is described in this paper. The open-source computational fluid dynamics software OpenFOAM® was used to couple a grid for the solid body motion of the WEC, with the grid designed for wave propagation, in order to calculate buoy movement parameters. The buoy has a horizontal, cylindrical structure, with a pivot point for semi-axis rotation. Five buoy-radiuses were analyzed, as this parameter considerably increases the efficiency of the WEC point absorber. To better understand the interaction of the WEC with the waves, the transmission and reflection coefficients were calculated, along with two non-linear parameters: skewness and asymmetry. The results indicate that, with this system, more power can be extracted from shorter waves, T = 4 s, compared to T = 8 s of the same wave height. This implies that a small buoy could be employed at sites with this prevailing wave regime, without a decrease in efficiency and with considerable cost reductions. Finally, this WEC increases the values of wave skewness, which is linked to onshore sediment transport; therefore, if appropriately designed, WEC arrays installed near the coast could also promote onshore sediment transport. [ABSTRACT FROM AUTHOR]

A hybrid system of a spar-type floating offshore wind turbine and a heaving annular wave energy converter (WEC) provides a promising solution for collocated ocean renewable energy exploitation. The performance of the hybrid system depends on the dimensions of the WEC. Here an optimization method is proposed to determine the outer radius and the draft of the WEC under the wave condition in a randomly chosen operational site. First, three candidate models are selected based on three operational conditions of energy harvest: (1) The natural frequency of the system is matched with the peak wave frequency in the target site (referred to as synchronized mode), where the wind turbine and the WEC nearly heave together in a near-resonance condition, (2) The natural frequency of the WEC is matched with the peak wave frequency (ring mode), (3) The maximum wave power is harnessed under the peak wave frequency (target mode). Then the candidate modes are evaluated to obtain an optimum. Results show that the extracted wave power under the above operational conditions has an upper bound that can hardly be surpassed by enlarging the dimensions of the WEC only. The optimal annual wave energy production is achieved in the synchronized mode because of the superior performance of WEC over a wide bandwidth of effective energy conversion. [ABSTRACT FROM AUTHOR]

As waves in China seas are not high, a wave energy converter consisting of a coaxial annular buoy and a cylindrical buoy that extracts wave energy using two generators through the relative heave motion between the buoys and the pitch motion of the cylinder could be a more efficient choice. A dynamic model considering constraints and assuming linear power take-off is established to evaluate the power performance of the device. The influences of two key factors, the diameter of the annular buoy and the power take-off stiffness of the pitching generator, and their couplings on the power performance are analyzed. The power of the pitching generator accounts for a major proportion of the total power. An increase in the annular buoy diameter increases the power of the heaving generator while greatly decreases the power of the pitching generator. An increase in the power take-off stiffness of the pitching generator greatly decreases its power while has little influence on the power of the heaving generator. These two factors also influence the peak period of the total power. Based on the findings and practical limitations, an optimization strategy is proposed. Further, the device is optimized based on a real wave environment in Shandong Province, China. [ABSTRACT FROM AUTHOR]

The fractional open-circuit voltage (FOCV) method is extensively used in low-power energy harvesting (EH) sources to extract maximum power. For fast-varying EH sources, a fast sampling rate is required. This work theoretically analyzes the influence of the sampling time and period on the harvested power of sinusoidal EH sources. In addition, the circuit limitations to achieve a fast sampling rate are presented and circuits to deal with them proposed and implemented. Furthermore, one of the circuits is based on a novel pseudoFOCV method and achieves the fastest sampling rate. Experimental tests are performed with a 2 Hz, 1 to 3 V sinusoidal source having an output resistance of 127 Ω, and the results are shown to agree with theoretical predictions. It is shown that the harvested power increases with the sampling rate when the sampling time is negligible (sampling 15 times faster than the source frequency extracts around 99% of the maximum), and for fixed sampling times, there is an optimum sampling rate where the harvested power is maximum. The first result is generic and valid for methods other than the FOCV. Tests were also performed with a small-scale wave energy converter placed in a linear shaker emulating a sea environment. Harvested power increases by 25% with respect using a commercial FOCV unit with a low sampling rate. [ABSTRACT FROM AUTHOR]

A major challenge to the emergence and establishment of new energy technologies such as ocean wave energy is the insufficient or nonexistent database for estimating resource potential. Despite having an extensive coastline, wave energy sources are yet to be developed in India. Hence, the main objective of this study is to identify the potential sites and assess the technical and economic feasibility of harnessing wave energy along the Indian coast. Three hotspots are identified in three coastal regions (east, south and west) based on optimum hotspot index and depth constrain criterion using 19 years of high-resolution wave hindcast. Results indicate that the theoretical potential of location along the west coast (12 kW/m) is highest as compared to a hotspot near the south (8 kW/m) and east coast (6 kW/m). The technical potential and cost of electricity generation at hotspot locations are estimated and compared using four different wave energy converters (WECs): Wavedragon, Pelamis, Oceantec, and Aquabuoy. Oceantec, among all WECs, generates more power (40–57 GWh) and attain a maximum capacity factor (22–31%) as well as the most cost-effective WEC with the lowest Levelized Cost of Energy (LCOE) ranging from 354 to 505 €/MWh at all hotspots. Economic sensitivity analysis reveals that interest rate and operation and maintenance costs are the most and least sensitive parameters, respectively. Outcomes of the present study will contribute to reducing the barriers to the current knowledge of wave energy resources in India. [ABSTRACT FROM AUTHOR]

• An advanced higher-order boundary element method is employed to examine the functional performance of arbitrarily shaped MCMT OWCs. • Two specific scenarios that an MCMT OWC integrated into a monopile foundation and a barge-type breakwater are investigated. • Dividing the chamber into multiple modules can convert the free-surface movement of sloshing mode into separate piston modes. • The multiple chamber modules can operate in coordination during different wave phases to optimize wave energy utilization. • The peak hydrodynamic efficiency and effective frequency bandwidth of MCMT OWCs significantly exceed those of single-chamber OWCs. The advancement of marine renewable energy technology has led to increased demands on current marine energy devices, particularly in relation to the energy capture capacity of wave energy converters (WECs). Among WECs, oscillating water column (OWC) devices are considered highly promising. This study examines the potential for enhancing the wave energy capture of OWC devices through the utilization of multi-chamber multi-turbine (MCMT) technology. Unlike traditional single-chamber OWCs, MCMT OWCs consist of multiple chamber modules that can operate in coordination during different wave phases to optimize the wave energy utilization. The interplay of water column movements within various chamber modules is closely interconnected. By considering these coupling effects, a reciprocal relationship between the air pressure and air-flow movement in different chamber modules is established, and a numerical model is developed to assess the functional performance of three-dimensional MCMT OWCs of arbitrary geometric shapes using a higher-order boundary element method (HOBEM). The study focuses on representative MCMT OWC designs with annular or rectangular cross-sections. Two specific scenarios are investigated: an annular MCMT OWC integrated into the monopile foundation of an offshore wind turbine, and a rectangular MCMT OWC integrated into a barge-type breakwater. Detailed numerical analyses are conducted, revealing that dividing the chamber into multiple modules can convert sloshing-mode free-surface movement into separate piston-mode movements, thereby enhancing the wave energy capture. By utilizing suitable turbine parameters and chamber dimensions, the peak hydrodynamic efficiency of MCMT OWCs has the potential to exceed unity, surpassing that of single-chamber OWCs by a factor of three. Additionally, employing a low rotational speed for the air turbine in MCMT OWCs can result in a doubled effective frequency bandwidth compared to single-chamber OWCs. This bandwidth can be extended even further with an increase in the rotational speed. This study also suggests that designing chamber modules with identical cross-sectional shapes may not always be the most advantageous approach for maximizing the wave energy capture. [ABSTRACT FROM AUTHOR]

This experiment aims to harvest wave energy from a trench connecting the ocean and a coastal reservoir. This experiment was conducted using the wave conditions of the Port of Hualien, and an NDD (nozzle-diffuser duct) was used to simulate a culvert to extract wave energy. The geometry of the NDD is optimized through the harmony search method. Preliminary results are verified with reported data before further investigation is conducted. The influence of two parameters, reservoir width, and wave height, on the flow velocity in NDD was analyzed. The results show that reservoir width and wave height are among the key factors affecting flow velocity in the NDD. A significant increase in flow velocity was also found in the middle part of the NDD. When scaled up to real sea conditions, it is suitable to install turbines that operate to capture energy from the water flowing through the NDD. Compared to other types of WEC, this model performs better energy flux extraction potential and an NDD associated with a coastal water tank is a highly efficient wave energy collector and worth to be promoted. • The resonant water flow wave energy converter may boost energy capture efficiency by 50% over traditional OWC systems. • Power is cubic to velocity; increasing flow velocity by 3.25 times boosted power density by 34 times, with more gains expected through optimization. • This approach boosts the efficiency of the wave energy conversion system and enhances the stability and reliability of energy output. [ABSTRACT FROM AUTHOR]

ObjectivesAiming at a mooring system design with cost-effectiveness and high performance for wave energy converter (WEC) , the effects of such systems on the capability of power take-off (PTO) system and positioning performance of WEC are investigated.MethodsA two-body floating point absorber is chosen as the sample WEC. The open-source WEC-Sim and MoorDyn codes are used to design two types of mooring system for the WEC: one is a chain mooring system and the other is an integrated chain-rope (i.e., polyester fiber rope) mooring system. By performing time-domain analysis for the WEC with different mooring lines, the responses, such as WEC displacement, power take-off (PTO) and mooring line tension, are obtained respectively.ResultsThe results show that, the effects of mooring systems on the displacement response of the floater are small, but these effects on the response of the spar body is obvious. For the WEC with a linear damper, these effects on the PTO response are negligible. Moreover, the line tensions of the integrated mooring system are lower than the corresponding tensions of the chain mooring system under the operational sea state.ConclusionsThe results of this study have reference value for the improved design of WEC mooring systems.

Ocean energy systems (OESs) convert the kinetic, potential, and thermal energy from oceans and seas to electricity. These systems are broadly classified into tidal, wave, thermal, and current marine systems. If fully utilized, the OESs can supply the planet with the required electricity demand as they are capable of generating approximately 2 TW of energy. The wave energy converter (WEC) systems capture the kinetic and potential energy in the waves using suitable mechanical energy capturers such as turbines and paddles. The energy density in the ocean waves is in the range of tens of kilowatts per square meter, which makes them a very attractive energy source due to the high predictability and low variability when compared with other renewable sources. Because the final objective of any renewable energy source (RES), including the WECs, is to produce electricity, the energy capturer of the WEC systems is coupled with an electrical generator, which is controlled then by power electronic converters to generate the electrical power and inject the output current into the utility AC grid. The power electronic converters used in other RESs such as photovoltaics and wind systems have been progressing significantly in the last decade, which improved the energy harvesting process, which can benefit the WECs. In this context, this paper reviews the main power converter architectures used in the present WEC systems to aid in the development of these systems and provide a useful background for researchers in this area. [ABSTRACT FROM AUTHOR]

This paper presents the Nenuphar concept, an innovative wave energy converter designed to use the kinetic and the potential energy of sea waves, based on the motions of seven modules. First, the main characteristics of the Nenuphar and its work principle are presented. Afterwards, the mathematical formulation of its dynamics is introduced and its validation with a simplified device. A specific MATLAB code was developed to determine the dynamics of hinged, multi-directional bodies. Then, the system's behaviour was analysed under different wave conditions. The system performance was not strongly dependent on the wave characteristics or the device inclination angle. This initial study confirms the Nenuphar as a potential technology to extract energy from waves. [ABSTRACT FROM AUTHOR]

To offer point absorber wave energy converters (WECs) as a bankable product on the marine renewable energy market, multiple WECs will be installed together in an array configuration. The wave energy community (research and industrial) has identified the urgent need for available realistic and reliable data on WEC array tests in order to perform a better WEC array optimization approach and in order to validate recently developed (non-linear) numerical models. The 'WECfarm' project is initiated to cover this scientific gap on necessary experimental data. The 'WECfarm' experimental setup consists of an array of five generic heaving point-absorber WECs. The WECs are equipped with a permanent magnet synchronous motor (PMSM), addressing the need for WEC array tests with an accurate and actively controllable power take-off (PTO). The WEC array control and data acquisition are realized with a Speedgoat Performance real-time target machine, offering the possibility to implement advanced WEC array control strategies in the MATLAB-Simulink environment. The presented article describes the experimental setup, the performed tests and the results of the test campaign using a single, isolated 'WECfarm' WEC in April 2021 at the wave basin of Aalborg University (AAU), Denmark. A Coulomb and viscous friction model is determined to partly compensate for the drivetrain (motor, gearbox, rack and pinion) friction. A system identification (SID) approach is adopted considering the WEC system to be composed of two single input single output (SISO) models, the radiation and the excitation model. Radiation tests yield the intrinsic impedance. Excitation tests yield the excitation frequency response function. Adopting an impedance matching approach, the control parameters for the resistive and reactive controller are determined from the complex conjugate of the intrinsic impedance. Both controllers are tested for a selection of regular wave conditions. The performed experimental test campaign using an isolated 'WECfarm' WEC allows a full evaluation of the WEC design prior to extending the setup to five WECs. Within the 'WECfarm' project, an experimental campaign with a five-WEC array in the Coastal and Ocean Basin (COB) in Ostend, Belgium, is under preparation. [ABSTRACT FROM AUTHOR]

Commercial wave energy exploitation will be realised by placing multiple wave energy converters (WECs) in an array configuration. A point-absorber WEC consists of a floating or submerged body to capture wave energy from different wave directions. This point-absorber WEC acts as an efficient wave absorber that is also an efficient wave generator. Optimising the WEC array layout to obtain constructive interference within the WEC array is theoretically beneficial, whereas for wind farms, it is only important to avoid destructive interference within an array of wind turbines due to wake effects. Moreover, the WEC array layout should be optimised simultaneously with the applied control strategy. This article provides a literature review on the state of the art in physical modelling of point-absorber WEC arrays and the identification of research gaps. To cover the scientific gap of experimental data necessary for the validation of recently developed (nonlinear) numerical models for WEC arrays, Ghent University has introduced the "WECfarm" project. The identified research gaps are translated into design requirements for the "WECfarm" WEC array setup and test matrix. This article presents the design of the "WECfarm" experimental setup, consisting of an array of five generic heaving point-absorber WECs. The WECs are equipped with a permanent magnet synchronous motor (PMSM), addressing the need for WEC array tests with an accurate and actively controllable power take-off (PTO). The WEC array control and data acquisition are realised with a Speedgoat Performance real-time target machine, offering the possibility to implement advanced WEC array control strategies in the MATLAB-Simulink model. Wave basin testing includes long- and short-crested waves and extreme wave conditions, representing real sea conditions. Within the "WECfarm" project, two experimental campaigns were performed at the Aalborg University wave basin: (a) a testing of the first WEC in April 2021 and (b) a testing of a two-WEC array in February 2022. An experimental campaign with a five-WEC array is under preparation at the moment of writing. [ABSTRACT FROM AUTHOR]

Similar to offshore wind turbines, multiple point absorber wave energy converters (WECs) will be installed in an array configuration, to increase the total capacity, and to benefit from the economies of scale. Whereas wind turbines always interact destructively due to wake effects, WECs can interact constructively, since hydrodynamic interactions between the WECs occur through radiation and diffraction of waves, changing the direction of the incoming wave energy. This paper presents the dataset and results of the experimental modelling of a row of two 'WECfarm' heaving point absorber WECs at the wave basin of Aalborg University (AAU). Impedance matching enables maximum power transfer between two oscillatory systems, from the waves to the Power Take-Off (PTO) of the WEC. While literature covers this impedance matching approach for single, isolated WECs, the research discussed in this paper is unique by applying the experimental modelling of the impedance matching approach on a row of two WECs. Radiation system identification tests are executed to determine the intrinsic impedance of the isolated WECs, and the 2 × 2 impedance matrix of the two-WEC array. A causal impedance matching resistive and reactive controller are designed, implemented and tested for a selection of operational sea states. For centralised control, hydrodynamic interactions are taken into account by considering the complete impedance matrix, whereas for decentralised control no hydrodynamic interactions are taken into account by considering only the diagonal of the impedance matrix. The power absorption performance of the isolated WECs, the two-WEC array with decentralised control, and the two-WEC array with centralised control, are compared. Constructive interaction is identified, yielding enhanced power absorption for the array compared to the WECs isolated. Therefore, the layout of the WEC array and the control of the PTO should be optimised simultaneously, to maximise the power absorption of the array as a whole. • Physical modelling of two 'WECfarm' heaving point absorber wave energy converters. • Execution of radiation system identification tests to determine the intrinsic impedance. • Design of a causal impedance matching resistive and reactive controller. • Performance of isolated WECs, decentralised- , and centralised controlled WEC array. • Open access experimental dataset to validate numerical models. [ABSTRACT FROM AUTHOR]

Local atmospheric conditions surrounding an off-shore Oscillating Water Column device — OWC hereinafter —, in particular wind action, may affect OWC performance and efficiency, specially over long harvesting intervals, i.e. yearly energy production. This work proposes an experimental study of a simple off-shore OWC where different ambient conditions are compared. More specifically, it proposes a set of experimental tests in laboratory wave flume, under both calm and external wind conditions, which represent a more realistic situation in full-scale prototypes. The results show that the external wind modifies the ambient conditions by changing the temperature, humidity and pressure values of the air surrounding the OWC device, affecting the density and the thermodynamic balance. This affects negatively the OWC performance, reducing the maximum pneumatic power by up to 15%, which can be extrapolated to a reduction of 3% in the total amount of annual energy produced. • The modification of external conditions can reduce the pneumatic power up to 15%. • The annual energy production can be reduced around 3% by the external wind. • The external air conditions affect the turbine performance during the release phase. • The isentropic efficiency is lower with the external wind. • The turbine performance makes that internal conditions of the OWC does not change. [ABSTRACT FROM AUTHOR]

The oscillating water column (OWC) wave energy converter (WEC) together with a self-rectifying air turbine and generator which convert alternating airflow induced by the water motion into kinetic energy and then into electric energy is a promising device for the advancement of marine renewable energy. As researchers overcome the modeling challenges of OWCs, such as the nonlinearities due to air compressibility and power take-off (PTO) dynamics, we can integrate control algorithms to improve the efficiency of the OWC. Herein, we present a nonlinear model predictive controller (NMPC) that maximizes the generated electro-mechanical power while maintaining the efficiency of a self-rectifying turbine attached to an OWC WEC. To achieve this goal, a good trade-off between maximizing generated power and turbine efficiency is found by adjusting the importance of both objectives in the computation of the control signal. Furthermore, we apply the proposed NMPC to an array of three WECs that takes into account the hydrodynamic interactions between the devices in the computation of optimal generator torque control signal. [ABSTRACT FROM AUTHOR]

The combined offshore wind and wave energy on an integrated platform is an economical solution for the offshore energy industry as they share the infrastructure and ocean space. The study presents the dynamic analysis of the Submerged Tension-Leg Platform (STLP) combined with a heaving-type point absorber wave energy converter (WEC). The feasibility study of the hybrid concept is performed using the aero-servo-hydro-elastic simulation tool FAST. The study analyzes the responses of the combined system to understand the influence of the WECs on the STLP platform for various operating conditions of the wind turbine under regular and irregular waves. Positive synergy is observed between the platform and the WECs, and the study also focuses on the forces and moments developed at the interface of the tower and platform to understand the effect of wind energy on the turbine tower and the importance of motion amplitudes on the performance of the combined platform system. The mean and standard deviation for the translation and rotational motions of combined wind and wave energy converters are determined for different sea states under both regular and irregular waves to analyze the change in responses of the structure. The study observed a reduction in motion amplitudes of the hybrid floating system with the addition of the wave energy converters around the STLP floater to improve the energy efficiency of the hybrid system. The study helps in understanding the best possible arrangement of point absorber-type wave energy converters at the conceptual stage of the design process. [ABSTRACT FROM AUTHOR]

A semisubmersible platform-based (SPB) bottom-hinged flap (BHF) wave energy converter (WEC) concept is presented in this paper, and its platform hydrodynamic response was studied experimentally. Aimed at studying the special WEC-mounted platform response problem, both regular and irregular wave experiments were conducted. The frequency domain results of regular wave experiments are described in the form of response amplitude operators. The time domain results of irregular wave experiments are treated by statistical analysis and fast Fourier transformation. Regular wave experiments and irregular wave experiments show good consistency. The mooring system strongly affects the whole system, which is a considerable factor for WEC design. The influences of BHF mounted on the platform are revealed in both statistic and frequency spectral ways. The results of experiments give a guide for SPB design aiming to support BHF-WEC. [ABSTRACT FROM AUTHOR]

The Oscillating Water Column (OWC) is leading the Wave Energy Converters in terms of efforts and research devoted. However, the efficiency achieved by these devices is still low enough to become a real renewable energy source. The main objective of this paper is to study the influence of the turbine characteristics in the thermodynamic process inside the OWC chamber, which is defined by the polytropic exponent associated with the polytropic process. Wind tunnel tests have been carried out to obtain experimental data under stationary flow, applying a real gas model where moisture plays a fundamental role. The results show the importance of the turbine characteristics and its effects on the thermodynamic compression process, affecting the power output of the OWC device. In conclusion, this study provides a better understanding of the OWC performance to improve its efficiency. [ABSTRACT FROM AUTHOR]

Ocean buoys are the main equipment for obtaining ocean hydrological information. The lack of efficient and reliable power supply is one of the main technical bottlenecks that limit its long-term stable operation. In this paper, the BUOY-41 surface drifting buoy is taken as an application object, and a novel wave energy converter that can be embedded in the buoy is designed. The novel direct-driven triboelectric–electromagnetic hybridized wave energy converter (DTEWEC) mainly includes triboelectric nanogenerator (TENG) unit and electromagnetic generator (EMG) unit. First, the working principles and basic theories of the two generators were explained. Second, the COMSOL software was used to analyze the influence law of DTEWEC's main structural parameters on power generation performance, and the optimal structural parameters were preliminarily determined. Then, the STAR-CCM+ software was used to analyze the hydrodynamic characteristics of BUOY-41, and its motion response was input to the above two units. Finally, the performance characteristics of DTEWEC under optimal wave conditions were obtained. The results show that the maximum power density of TENG unit can reach 7.68 W/m2, and the maximum power of each phase of EMG unit which has three-phase coil group structure is 59.4 mW, 47.2 mW, and 50.2 mW, respectively. The research in this paper shows that the DTEWEC can be used as a sustainable power supply component of the ocean buoy to realize the autonomous power supply, which can effectively increase the endurance time and operational reliability. [ABSTRACT FROM AUTHOR]

Transverse flux permanent magnet linear generator (TF-PMLG) is widely used in direct drive wave energy converter (DD-WEC) because of its high power density. Traditional transverse flux machine (TFM) is designed and built in form of translator-PM. But translator-PM configuration needs a large amount of PM and the cost is high in long stroke application, like DD-WEC. Recently, the stator-PM linear machines have gained more attention for reducing the PM volume and improving the generator performances under low-speed conditions. In this paper, a novel stator-PM TF-PMLG for DD-WEC has been proposed. The fundamental configuration and operation principle of the generator are illustrated. Then, the expressions of the back EMF and the electromagnetic thrust are derived by magnetic circuit analysis. Main dimension parameters, such as PM thickness, central angle of the outer stator shoe and pole pitch are determined and optimized based on finite element analysis (FEA). This topology has advantages of low PM consumption and high power density, and is a suitable candidate for long stroke applications, like DD-WEC, in which a high power per PM volume is usually needed to reduce the amount of permanent magnet and ensure high power density.

Future nearshore wave energy converter (WEC) arrays will influence coastal wave and sediment dynamics, yet there are limited numerical methodologies to quantify their possible impacts. A novel coupled WEC-Wave numerical method was developed to quantify these possible influences on the nearshore coastal wave climate. The power performance of an Oscillating Surge Wave Energy Converter (OSWEC) array was simulated to quantify the wave energy dissipation due to the array. The OSWEC's effect on the local wave climate was quantified by a novel coupling of two numerical models, WEC–Sim and XBeach. WEC–Sim characterizes the power extraction and wave energy transmission across the OSWEC, while XBeach captures the change in wave dynamics due to the WEC and propagates the waves to shore. This novel methodology provides the ability to directly quantify the impact of the effect of a WEC array on the local wave climate. Three case studies were analyzed to quantify the impact of a single WEC on breaking conditions and to quantify the impact of number of WECs and the array spacing on the local nearshore wave climate. Results indicate that when the WEC is placed 1100 m offshore, one WEC will cause a 1% reduction in wave height at the break point ( H s b p ). As the WEC is placed further offshore, the change in H s b p will become even smaller. Although the change in wave height from one WEC is small, WEC arrays magnify the cross–shore extent, area of influence and the magnitude of influence based on the spacing and number of WECs. For arrays with 10 or 15 WECs, the cross–shore extent was on average 200–300 m longer when the WECs were placed one to two WEC widths apart, compared with being spaced three or four widths apart. When the spacing was one WEC width apart (18 m), there was a 30% greater spatial impact on the nearshore region than arrays spaced three or four widths apart. The trend for the average transmission coefficient is within 5% for a 5, 10 or 15 WEC array, with a cumulative average of 78% transmission across all conditions. [ABSTRACT FROM AUTHOR]

The numerical performance of a buoy-type wave energy converter (WEC) under regular wave conditions is described in this paper. The open-source computational fluid dynamics software OpenFOAM® was used to couple a grid for the solid body motion of the WEC, with the grid designed for wave propagation, in order to calculate buoy movement parameters. The buoy has a horizontal, cylindrical structure, with a pivot point for semi-axis rotation. Five buoy-radiuses were analyzed, as this parameter considerably increases the efficiency of the WEC point absorber. To better understand the interaction of the WEC with the waves, the transmission and reflection coefficients were calculated, along with two non-linear parameters: skewness and asymmetry. The results indicate that, with this system, more power can be extracted from shorter waves, T = 4 s, compared to T = 8 s of the same wave height. This implies that a small buoy could be employed at sites with this prevailing wave regime, without a decrease in efficiency and with considerable cost reductions. Finally, this WEC increases the values of wave skewness, which is linked to onshore sediment transport; therefore, if appropriately designed, WEC arrays installed near the coast could also promote onshore sediment transport.

Ocean energy systems (OESs) convert the kinetic, potential, and thermal energy from oceans and seas to electricity. These systems are broadly classified into tidal, wave, thermal, and current marine systems. If fully utilized, the OESs can supply the planet with the required electricity demand as they are capable of generating approximately 2 TW of energy. The wave energy converter (WEC) systems capture the kinetic and potential energy in the waves using suitable mechanical energy capturers such as turbines and paddles. The energy density in the ocean waves is in the range of tens of kilowatts per square meter, which makes them a very attractive energy source due to the high predictability and low variability when compared with other renewable sources. Because the final objective of any renewable energy source (RES), including the WECs, is to produce electricity, the energy capturer of the WEC systems is coupled with an electrical generator, which is controlled then by power electronic converters to generate the electrical power and inject the output current into the utility AC grid. The power electronic converters used in other RESs such as photovoltaics and wind systems have been progressing significantly in the last decade, which improved the energy harvesting process, which can benefit the WECs. In this context, this paper reviews the main power converter architectures used in the present WEC systems to aid in the development of these systems and provide a useful background for researchers in this area.

This paper presents the Nenuphar concept, an innovative wave energy converter designed to use the kinetic and the potential energy of sea waves, based on the motions of seven modules. First, the main characteristics of the Nenuphar and its work principle are presented. Afterwards, the mathematical formulation of its dynamics is introduced and its validation with a simplified device. A specific MATLAB code was developed to determine the dynamics of hinged, multi-directional bodies. Then, the system’s behaviour was analysed under different wave conditions. The system performance was not strongly dependent on the wave characteristics or the device inclination angle. This initial study confirms the Nenuphar as a potential technology to extract energy from waves.

The economic profitability of future wave energy production along the Galician coast is assessed by analyzing the Levelized Cost of Energy (LCoE) under different Capital Expenditure (CapEx) scenarios and two discounts rates (5% and 10%). Wave resources for the near future under the RCP8.5 scenario are downscaled using SWAN, providing up to 75 m spatial resolution in coastal areas. The study's goal is to enhance the cost-effectiveness by selecting the most suitable wave energy converter (WEC) for each location. Fourteen WECs operating at different depths are considered. This analysis reveals that the Atargis device boasts the lowest LCoE for 64.2% of the coastal area, mainly in deep waters, with an LCoE of 77 €/MWh. In addition, the Oyster and Wave Dragon devices exhibit the lowest LCoE for 12.4% and 15.0% of the coastal area, respectively, excelling in shallow waters and near the coast, with values of 50 €/MWh and 97 €/MWh. These findings demonstrate the profitability of wave energy production along the Galician coast, even when considering a more conservative CapEx of 3 M€/MW, resulting in a cost of 140 €/MWh. This conclusion takes into account the evolving electricity prices in Spain, which reached 0.2068 €/kWh in the second half of 2023. • LCoE analysis of the economic profitability of future wave energy production under different CapEx. • Future wave energy resource downscaled using SWAN under RCP8.5 along the Galician coast. • Fourteen different types of wave energy converters were considered operating at different depths. • Atargis, Oyster and Wave Dragon devices displayed along the Galician coast generate the lowest LCoE (€70/MWh). • Future wave energy production prices along the Galician coast are competitive compared to current Spanish electricity prices. [ABSTRACT FROM AUTHOR]

In the present study, the numerical investigation is performed to analyse the hydrodynamic performance of circular and concentric arrangements of cone-cylinder-type heaving point absorber wave energy converter (WEC) around a Frustum Tension-Leg Platform (FTLP) based on potential flow theory. The responses of the single FTLP and the FTLP-WEC hybrid system are analysed for the rated wind speed of a 5 MW wind turbine to observe the influence of the WECs on wind power absorption of wind turbines supported on FTLP. The presence of the FTLP floating wind turbine platform and other WECs affects the hydrodynamic coefficients of the WEC. The influence of the hybrid system on the hydrodynamic coefficients is analysed on determining the ratio of the hydrodynamic coefficients for a single WEC system to those for a hybrid system. Further, the study analyses the instantaneous wave power absorption for the WECs arranged around the FTLP in a circular and concentric pattern. The hydraulic power take-off for the hybrid system with two different control strategies is then discussed to improve the wave power absorption of the WECs. The study observed higher wave power absorption of the WECs with the influence of the PTO system. The mean interaction factor and the capture width ratio of the hybrid system are further studied to understand the influence of array arrangement for the WECs. The hybrid system is noted to have favourable dynamic responses for different environmental factors and contributes positively in increasing power output. [ABSTRACT FROM AUTHOR]

To offer point absorber wave energy converters (WECs) as a bankable product on the marine renewable energy market, multiple WECs will be installed together in an array configuration. The wave energy community (research and industrial) has identified the urgent need for available realistic and reliable data on WEC array tests in order to perform a better WEC array optimization approach and in order to validate recently developed (non-linear) numerical models. The ‘WECfarm’ project is initiated to cover this scientific gap on necessary experimental data. The ‘WECfarm’ experimental setup consists of an array of five generic heaving point-absorber WECs. The WECs are equipped with a permanent magnet synchronous motor (PMSM), addressing the need for WEC array tests with an accurate and actively controllable power take-off (PTO). The WEC array control and data acquisition are realized with a Speedgoat Performance real-time target machine, offering the possibility to implement advanced WEC array control strategies in the MATLAB-Simulink environment. The presented article describes the experimental setup, the performed tests and the results of the test campaign using a single, isolated ‘WECfarm’ WEC in April 2021 at the wave basin of Aalborg University (AAU), Denmark. A Coulomb and viscous friction model is determined to partly compensate for the drivetrain (motor, gearbox, rack and pinion) friction. A system identification (SID) approach is adopted considering the WEC system to be composed of two single input single output (SISO) models, the radiation and the excitation model. Radiation tests yield the intrinsic impedance. Excitation tests yield the excitation frequency response function. Adopting an impedance matching approach, the control parameters for the resistive and reactive controller are determined from the complex conjugate of the intrinsic impedance. Both controllers are tested for a selection of regular wave conditions. The performed experimental test campaign using an isolated ‘WECfarm’ WEC allows a full evaluation of the WEC design prior to extending the setup to five WECs. Within the ‘WECfarm’ project, an experimental campaign with a five-WEC array in the Coastal and Ocean Basin (COB) in Ostend, Belgium, is under preparation.

Commercial wave energy exploitation will be realised by placing multiple wave energy converters (WECs) in an array configuration. A point-absorber WEC consists of a floating or submerged body to capture wave energy from different wave directions. This point-absorber WEC acts as an efficient wave absorber that is also an efficient wave generator. Optimising the WEC array layout to obtain constructive interference within the WEC array is theoretically beneficial, whereas for wind farms, it is only important to avoid destructive interference within an array of wind turbines due to wake effects. Moreover, the WEC array layout should be optimised simultaneously with the applied control strategy. This article provides a literature review on the state of the art in physical modelling of point-absorber WEC arrays and the identification of research gaps. To cover the scientific gap of experimental data necessary for the validation of recently developed (nonlinear) numerical models for WEC arrays, Ghent University has introduced the “WECfarm” project. The identified research gaps are translated into design requirements for the “WECfarm” WEC array setup and test matrix. This article presents the design of the “WECfarm” experimental setup, consisting of an array of five generic heaving point-absorber WECs. The WECs are equipped with a permanent magnet synchronous motor (PMSM), addressing the need for WEC array tests with an accurate and actively controllable power take-off (PTO). The WEC array control and data acquisition are realised with a Speedgoat Performance real-time target machine, offering the possibility to implement advanced WEC array control strategies in the MATLAB-Simulink model. Wave basin testing includes long- and short-crested waves and extreme wave conditions, representing real sea conditions. Within the “WECfarm” project, two experimental campaigns were performed at the Aalborg University wave basin: (a) a testing of the first WEC in April 2021 and (b) a testing of a two-WEC array in February 2022. An experimental campaign with a five-WEC array is under preparation at the moment of writing.

Direct-drive wave energy converter (DD-WEC) simplifies the structure and improves the efficiency of wave energy conversion. Permanent magnet transverse flux linear generator (PMTFLG) combines the merits of transverse flux linear generator (TFLG) and permanent magnet linear generator (PMLG), and is suitable for low-speed high thrust density applications, like DD-WEC. However, it suffers from a significant demerit which is the high cost due to the rare earth permanent magnets (PMs). A stator-PM spiral translator PMTFLG (ST-PMTFLG) is proposed in this article. Armature winding and PMs are arranged in outer stator and inner stator, respectively while the translator is made of spiral steel blocks and nonmagnetic blocks. Similar to the magnetically geared machine, the proposed topology is suitable to be used in low-speed long-stroke application. Results show that ST-PMTFLG has advantages of low PM consumption and high thrust density. The thrust per PM volume of 12/11 ST-PMTFLG is 4.18 MN/m3. [ABSTRACT FROM AUTHOR]

The utilization of the existing breakwater constructions into wave energy conversion has been often adopted to rendering a revenue of the capital cost of investment. The paper has contributed to viable concept of a new integrated design through more effectively capturing wave-overtopping which finally converts into electrical energy. This design is hereafter called Overtopping Breakwater for Energy Conversion (OBREC). The development of an experimental test of the current OBREC has been conducted to obtain a proper ramp shape through evaluating the amounts of the wave-overtopping discharges into the reservoir incorporated with wave-reflection coefficients. To achieve the objective, ramps of several geometries such as linear, convex, concave and cubic shapes have been experimentally investigated at the National Research Institute Malaysia (NAHRIM) laboratory. The experimental study showed that the cubic-ramp shape has resulted in more significant amount of the wave-overtopping discharge into the reservoir associated with the low wave-reflection coefficient than the other ramp shapes. In general, it is merely concluded that this investigation provides very promising concept of the new proposed OBREC design to harness the larger wave energy. [ABSTRACT FROM AUTHOR]

An improved Maximum Power Point Tracking (MPPT) method based on a purely mechanical wave energy converter (WEC) of gyroscope precession is proposed. The method adopts dynamic perturbation step adjustment, which improves the stability of power output and reduces steady-state oscillation. The paper introduces the principle of the device, establishes the mathematical model, and obtains the complete expression of power. The effect of wave frequency, pitch amplitude, power take-off (PTO) damping coefficient, and flywheel rotating speed on power output is analyzed. The output regression equation is established, and the extraction conditions of the maximum power are summarized and predicted. Aiming at the time-varying nature of actual ocean waves, a variable step size modified maximum power point (MPP) tracking control algorithm based on perturbation and observation (P&O) method is proposed. The algorithm has a unique technology to dynamically change the perturbation size, which not only improves the dynamic response but also reduces the oscillation. Besides, the boundary conditions ensure that the algorithm will not deviate from the motion trajectory, and the average filtering method and steady-state judgment can further reduce steady-state oscillation. In various ocean conditions, the proposed method has better output stability compared with other variable step size algorithms. Finally, different wave working conditions are given in the experiment, and the results verify the effectiveness of the proposed MPPT control strategy in experimental equipment. The device will be suitable for distributed power sources in small islands and ports. [ABSTRACT FROM AUTHOR]