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Wave energy is a promising source of sustainable clean energy, yet its inherent intermittency and irregularity pose challenges for stable grid integration. Accurate forecasting of wave energy power is crucial for reliable grid management. This paper introduces a novel approach that utilizes a Bidirectional Gated Recurrent Unit (BiGRU) network to fit the power matrix, effectively modeling the relationship between wave characteristics and energy output. Leveraging this fitted power matrix, the wave energy converter (WEC) output power is predicted using a model that incorporates a Convolutional Neural Network (CNN), a Bidirectional Long Short-Term Memory (BiLSTM) network, and deformable efficient local attention (DELA), thereby improving the accuracy and robustness of wave energy power prediction. The proposed method employs BiGRU to transform wave parameters into power outputs for various devices, which are subsequently processed by the CNN-BiLSTM-DELA model to forecast future generation. The results indicate that the CNN-BiLSTM-DELA model outperforms BiLSTM, CNN, BP, LSTM, CNN-BiLSTM, and GRU models, achieving the lowest mean squared error (0.0396 W) and mean absolute percentage error (3.7361%), alongside the highest R 2 (98.69%), underscoring its exceptional forecasting accuracy. By enhancing power forecasting, the method facilitates effective power generation dispatch, thereby mitigating the adverse effects of randomness on the power grid. [ABSTRACT FROM AUTHOR]

A series of quantitative analyses were performed to identify the wave properties and potential, by means of records collected from an offshore buoy in North-West Ireland. Based on the data collected, a series of quantitative analyses was conducted to determine the dominant wind directions and wave properties on an annual basis. In addition, the wave power is computed based on relevant wave heights and periods, and the Pierson-Moskowitz spectral model was used to generate the maximum wave energy spectra for each year. The results show that waves with wave powers of around 100 kW/m were mostly approaching eastward at a rather narrow frequency. In order to compare the relative capture width and the power absorption capacity of three floating structures, the Wave Dragon, Board Net Breakwater, and Cylindrical Floating Breakwater are analyzed. Also outlined is the impact of the transmission coefficient on the effectiveness of wave energy converters (WEC) throughout the energy harvesting process. This was accomplished by fusing information from three distinct field investigations and experimental research with four different wave transmission coefficient models. The results show that as the wave steepness increases, the transmission coefficient decreases and the hydrodynamic performance of wave energy converters increases. Also, it is found that the hydrodynamic efficiency of wave energy converters is higher in summer than in winter, and the Wave Dragon is the most efficient wave energy converter in regard to relative capture width and power absorption. [ABSTRACT FROM AUTHOR]

Introduction. This paper presents the novel design and analysis of a hybrid renewable energy system that combines a wave energy converter (WEC) with a floating photovoltaic (FPV) system for offshore installation, with a specific focus on Oran as a case study. The purpose of integrating these two technologies is to harness both wave and solar energy, thereby maximizing energy output and enhancing the reliability of renewable energy sources in offshore environments. The goal of this study is to develop a hybrid system that leverages the complementary nature of WEC and FPV technologies to maximize energy output and improve reliability. By integrating these technologies, the system aims to overcome the limitations of standalone energy systems. The methodology includes selecting suitable WEC and FPV technologies, optimizing their configurations, and analyzing their combined performance under various environmental conditions. To assess the energy production potential, structural stability, and economic feasibility of the hybrid system, computational simulations and data analysis are employed. This comprehensive approach ensures rigorous testing and optimization for real-world applications. The results demonstrate substantial improvements in energy yield and system resilience compared to standalone WEC or FPV systems. The hybrid system shows enhanced performance, particularly in consistent energy output and structural robustness. These findings indicate that combining WEC and FPV technologies can lead to more reliable and efficient offshore renewable energy solutions. The practical values are significant, providing insights into efficient and sustainable offshore renewable energy solutions. By focusing on Oran, it offers a localized perspective that can be adapted to similar coastal areas globally, contributing to the advancement of renewable energy technologies. The hybrid system’s enhanced reliability and efficiency support the broader goal of sustainable energy development in marine environments, highlighting its potential for widespread application and impact. [ABSTRACT FROM AUTHOR]

Wave energy holds significant promise as a renewable energy source due to the consistent and predictable nature of ocean waves. However, optimizing wave energy devices is essential for achieving competitive viability in the energy market. This paper presents the application of a nonlinear model predictive controller (MPC) to enhance the energy extraction of a heaving point absorber. The wave energy converter (WEC) model accounts for the nonlinear dynamics and static Froude–Krylov forces, which are essential in accurately representing the system's behavior. The nonlinear MPC is tested under irregular wave conditions within the power production region, where constraints on displacement and the power take-off (PTO) force are enforced to ensure the WEC's safety while maximizing energy absorption. A comparison is made with a linear MPC, which uses a linear approximation of the Froude–Krylov forces. The study comprehensively compares power performance and computational costs between the linear and nonlinear MPC approaches. Both MPC variants determine the optimal PTO force to maximize energy absorption, utilizing (1) a linear WEC model (LMPC) for state predictions and (2) a nonlinear model (NLMPC) incorporating exact Froude–Krylov forces. Additionally, the study analyzes four controller configurations, varying the MPC prediction horizon and re-optimization time. The results indicate that, in general, the NLMPC achieves higher energy absorption than the LMPC. The nonlinear model also better adheres to system constraints, with the linear model showing some displacement violations. This paper further discusses the computational load and power generation implications of adjusting the prediction horizon and re-optimization time parameters in the NLMPC. [ABSTRACT FROM AUTHOR]

Hydrodynamic tools reveal information as to the behaviour of a device in the presence of waves but provide little information on how to improve or optimise the device. With no recent work on the transfer of power (energy flux) from a wave field through the body surface of a wave energy converter (WEC), we introduce the energy flux method to map the flow of power. The method is used to develop an open-source tool to visualise the energy flux density on a WEC body surface. This energy flux surface can also be used to compute the total power capture by integrating over the surface. We apply the tool to three WEC classes: a heaving cylinder, a twin-hulled hinged barge, and pitching surge devices. Using the flux surfaces, we investigate power efficiency in terms of power absorbed to power radiated. We visualise the hydrodynamic consequence of sub-optimal damping. Then, for two pitching surge devices with similar resonant peaks, we reveal why one device has a reduced power performance in a wave spectrum compared to the other. The results show the effectiveness of the energy flux method to predict power capture compared to motion-based methods and highlight the importance of assessing the flux of energy in WECs subjected to different damping strategies. Importantly, the tool can be adopted for a wide range of applications, from geometry optimisation and hydrodynamic efficiency assessment to structural design. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Shanghai Jiaotong University (Science) is the property of Springer Nature 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.)

Offshore wind power is a kind of important clean renewable energy and has attracted increasing attention due to the rapid consumption of non-renewable energy. To reduce the high cost of energy, a possible try is to utilize the combination of wind and wave energy considering their natural correlation. A combined concept consisting of a semi-submersible wind turbine and four torus-shaped wave energy converters was proposed and numerically studied under normal operating conditions. However, the dynamic behavior of the integrated system under extreme sea conditions has not been studied yet. In the present work, extreme responses of the integrated system under two different survival modes are evaluated. Fully coupled time-domain simulations with consideration of interactions between the semi-submersible wind turbine and the torus-shaped wave energy converters are performed to investigate dynamic responses of the integrated system, including mooring tensions, tower bending moments, end stop forces, and contact forces at the Column-Torus interface. It is found that the addition of four tori will reduce the mean motions of the yaw, pitch and surge. When the tori are locked at the still water line, the whole integrated system is more suitable for the survival modes. [ABSTRACT FROM AUTHOR]

Nowadays, numerous governments have instituted diverse regulatory frameworks aimed at fostering the assimilation of sustainable energy sources characterized by reduced environmental footprints. Solar, wind, geothermal, and ocean energies were subject to extensive scrutiny, owing to their ecological merits. However, these sources exhibit pronounced temporal fluctuations. Notably, ocean dynamics offer vast energy reservoirs, with oceanic waves containing significant amounts of energy. In the Central American Pacific context, the exploration of wave energy resources is currently underway. Accurate numerical wave models are required for applied studies such as those focused on the estimation of exploitable wave power; and even more so in Central American region of the Pacific Ocean where existing numerical models simulations have so far relied on coarse resolution and limited validation field data. This work presents a high-resolution unstructured wave hindcast over the Central American Pacific region, implemented using the third-generation spectral wave model WAVEWATCH III over the period between 1979 and 2021. The results of the significant wave height have been bias-corrected on the basis of satellite information spanning 2005 to 2015, and further validation was performed using wave buoy and acoustic Doppler current profiler (ADCP) records located in the nearshore region of the Central America Pacific coast. After correction and validation of the wave hindcast, we employed the dataset for the evaluation and assessment of wave energy and its possible exploitation using different wave energy converters (WECs). This evaluation addressed the need to diverse the energy portfolio within the exclusive economic zones of Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Colombia, and Ecuador in a sustainable manner. Moreover, a comprehensive analysis was carried out on the advantages of harnessing wave energy, juxtaposed with the imperative of regulatory frameworks and the current dearth of economic and environmental guidelines requisite for development within the region. [ABSTRACT FROM AUTHOR]

This research proposes a new adaptive binned Kernel Density Estimation (KDE) method to fit significant wave height data in order to more accurately calculate the sea state parameter distribution tails. The brief details of the proposed new methodology are to utilize the fast Fourier transform to perform the convolution of the data with the kernel to find the kernel density estimates on the bin nodes. The Crámer-von Mises test statistic for the proposed adaptive KDE distribution is calculated to be 0.0926 based on a measured wave data set. The Crámer-von Mises test statistic value for the fitted 3-parameter Weibull distribution based on the identical measured data set is 251.2463, indicating a much poorer fit to the empirical distribution function. The advantages of using a more reliable and accurate contour line derived using the proposed new method for long term reliability analysis of wave energy converters have been finally substantiated. [ABSTRACT FROM AUTHOR]

In recent times, the point absorber Wave Energy Converter (WEC) has gained popularity due to its practicality. Investigating the parameters of the Hydraulic Power Take-Off (HPTO) in the WEC, including hose diameter and check valve variations, is crucial. This study analyzes optimization using the Sequential Quadratic Programming (SQP) method in MATLAB/SimScape, leading to a more comprehensive understanding of the interactions among HPTO components, such as hydraulic cylinders, check valves, hoses, accumulators, motors, and generators. Key system performance indicators, including pressure drop, flow rate, and power output, were assessed in both single and two-point absorber HPTO configurations. The optimization process yielded a maximum hydraulic power output of 7.33 kW, a mechanical power output of 6.41 kW, and an electrical power output of 5.4 kW using a 2-inch hose diameter. Additionally, utilizing a two-point absorber model enhanced power generation capacity by 47.4%, reaching 9.45 kW. The findings highlight the significant pressure drop at the check valve, with the 2-inch hose model experiencing a drop of 31.874 bar. These results demonstrate that optimizing HPTO parameters can significantly improve the efficiency of converting wave energy into electricity, providing valuable design recommendations for WEC technology. [ABSTRACT FROM AUTHOR]

Introduction. This paper presents the novel design and analysis of a hybrid renewable energy system that combines a wave energy converter (WEC) with a floating photovoltaic (FPV) system for offshore installation, with a specific focus on Oran as a case study. The purpose of integrating these two technologies is to harness both wave and solar energy, thereby maximizing energy output and enhancing the reliability of renewable energy sources in offshore environments. The goal of this study is to develop a hybrid system that leverages the complementary nature of WEC and FPV technologies to maximize energy output and improve reliability. By integrating these technologies, the system aims to overcome the limitations of standalone energy systems. The methodology includes selecting suitable WEC and FPV technologies, optimizing their configurations, and analyzing their combined performance under various environmental conditions. To assess the energy production potential, structural stability, and economic feasibility of the hybrid system, computational simulations and data analysis are employed. This comprehensive approach ensures rigorous testing and optimization for real-world applications. The results demonstrate substantial improvements in energy yield and system resilience compared to standalone WEC or FPV systems. The hybrid system shows enhanced performance, particularly in consistent energy output and structural robustness. These findings indicate that combining WEC and FPV technologies can lead to more reliable and efficient offshore renewable energy solutions. The practical values are significant, providing insights into efficient and sustainable offshore renewable energy solutions. By focusing on Oran, it offers a localized perspective that can be adapted to similar coastal areas globally, contributing to the advancement of renewable energy technologies. The hybrid system’s enhanced reliability and efficiency support the broader goal of sustainable energy development in marine environments, highlighting its potential for widespread application and impact. References 23, tables 4, figures 17.

In recent times, the point absorber Wave Energy Converter (WEC) has gained popularity due to its practicality. Investigating the parameters of the Hydraulic Power Take-Off (HPTO) in the WEC, including hose diameter and check valve variations, is crucial. This study analyzes optimization using the Sequential Quadratic Programming (SQP) method in MATLAB/SimScape, leading to a more comprehensive understanding of the interactions among HPTO components, such as hydraulic cylinders, check valves, hoses, accumulators, motors, and generators. Key system performance indicators, including pressure drop, flow rate, and power output, were assessed in both single and two-point absorber HPTO configurations. The optimization process yielded a maximum hydraulic power output of 7.33 kW, a mechanical power output of 6.41 kW, and an electrical power output of 5.4 kW using a 2-inch hose diameter. Additionally, utilizing a two-point absorber model enhanced power generation capacity by 47.4%, reaching 9.45 kW. The findings highlight the significant pressure drop at the check valve, with the 2-inch hose model experiencing a drop of 31.874 bar. These results demonstrate that optimizing HPTO parameters can significantly improve the efficiency of converting wave energy into electricity, providing valuable design recommendations for WEC technology.

Ocean waves represent a substantial renewable energy source, prompting this study's exploration of harnessing this potential via multi-point floating absorbers equipped with hydraulic Power Take-Off (PTO) systems. The study's primary motivation is to comprehensively model a Wave Energy Converter (WEC), including the hydraulic PTO system's control mechanism and protection system. To optimize the WEC design, we first investigate the hydrodynamic parameters of the floating absorber, employing potential flow theories and assessing the effects of varying the diameter-to-draft ratio. Our research involves analyzing Response Amplitude Operators (RAOs) and hydrodynamic forces for different ratios to identify the most effective design, followed by using computed wave forces as inputs for PTO simulations in MATLAB/SimScape to determine the unit parameters. The analysis of RAOs and wave-exciting forces reveals that diameter-to-draft ratios between 0.67 and 1.0 yield the best WEC performance, offering promising recommendations. In the final step, we compare the performance of single and multi-point absorber system simulations, assessing factors such as pressure drop, flow rate, and power output at the hydraulic motor. This comparison concludes that multi-point absorbers generate a more stable power output than their single-absorber counterparts.

A dual-pontoon WEC-breakwater system is proposed to optimise space utilisation and reduce construction costs by integrating wave energy converters (WECs) with breakwaters. Previous parametric studies on the dimensions and layout of WECs have primarily used potential flow theories, often neglecting the viscous effects in wave–pontoon interactions. In this research, I employ a fully nonlinear viscous model, OpenFOAM®, to address these limitations. I examine multiple parameters, including the gap width between the pontoons, the draft, and the structure breadth, to assess their impact on the functional performance of this hybrid system. Furthermore, I discuss the accurate hydrodynamic performance of waves interacting with multiple floating structures and explore how various parameters influence the dual-pontoon WEC-breakwater integrated system's functionality. I discuss a novel analysis of the effective frequency bandwidth, considering both wave energy conversion efficiency and wave attenuation efficiency, to reflect the overall performance of the integrated system. This paper investigates wave–structure interactions and suggests optimisation strategies for the WEC-breakwater integrated system. [ABSTRACT FROM AUTHOR]

The objective of this project is to develop a numerical approach that simulates the behavior of sloshing water with linear free surface waves on a sloping beach inside a 2D rectangular tank. The current computational approach represents the first stage in the development of a precise modeling framework for wave energy converters (WEC). The 2D tank model was generated using the ANSYS FLUENT program, with the Navier–Stokes equations being discretized on a regular structured grid employing the finite volume method (FVM). The validity of the model has been shown for linear sloshing conditions. Moreover, an examination is conducted to analyze the impact of tank flexibility on the phenomenon of liquid sloshing. The simulation was conducted under seven different wave steepness conditions. The primary objective of this study was to investigate the phenomenon of fluid–structure interaction in the context of movable plates. The investigation of the flow domain encompasses a crucial study on the output power of the plate WEC, specifically focusing on scenarios where plate heights remain constant and the motion of fluid streamlines around the plate is considered. The primary objective of this study is to investigate the relationship between drag force and wave steepness. This observation illustrates a positive correlation between wave steepness and drag force. The revolutionary structure of the ocean buildings may provide a novel and exact method for estimating the wave strength. The usefulness of WEC lies in its capacity to interact with water waves and harness renewable energy from the ocean. This study introduces a novel computational fluid dynamics (CFD) methodology that effectively captures the dynamic interaction between a solid object and a two-phase flow. The examination of the impact of wave steepness on the dynamics of a movable thin plate in intermediate water is a fresh and noteworthy subject of inquiry. This study has substantial importance as a valuable resource for the development of practical systems and possesses direct relevance in the design of WEC for the purpose of harnessing oceanic energy. [ABSTRACT FROM AUTHOR]

Wave energy converters (WECs), particularly oscillating water column (OWC) systems, offer a range of economic and ecological benefits that make them an attractive and promising renewable energy source. To improve energy extraction in medium wave power regions, such as the Mediterranean beaches, the concept of an OWC device with an optimized oscillation chamber according to a sequential process is considered. In this regard, experimental tests, using sequential optimization procedure, are performed in this paper on an onshore OWC device focusing on its overall hydraulic effectiveness. Major emphasis is given to analyze the effects of the underwater front-wall vertical and angular positions, the oscillating chamber geometry, wave conditions and the power take-off (PTO) shape on hydrodynamic performances. The variation of the front-wall was studied according to two criteria: vertical type and angular type where the range of variation is between the angles 0° and 35° with a step of 5°. The chamber volume varying is ensured by inserting a pair of air-guide plates between the roof and the fluid free-surface. The obtained results revealed that changing the chamber front-wall direction affects the OWC oscillation energetic characteristics and the aerodynamic behavior of the turbine driving flow. Water elevation ratio "η/h", absorbed power, hydraulic efficiency, inlet air velocity upstream of the turbine and turbine rotating speed showed a gradual growth with increasing the wall opening angle up to FWA = 20°. The dimensionless turbine coefficients exhibited also an improvement in their behavior with this angle value. The air-guide plates addition leads to a raise of inlet air velocity, turbine speed and device efficiency by 5.5%, 12.3% and 7.5%, respectively. The developed process can greatly help to enhance the performance of real-size OWCs. [ABSTRACT FROM AUTHOR]

This study numerically analyzes a submerged horizontal plate (SHP) device subjected to both regular and irregular waves. This device can be used either as a breakwater or a wave energy converter (WEC). The WaveMIMO methodology was applied for the numerical generation and wave propagation of the sea state of the Rio Grande coast in southern Brazil. The finite volume method was employed to solve conservation equations for mass, momentum, and volume fraction transport. The volume of fluid model was employed to handle the water-air mixture. The SHP length (Lp) effects were carried out in five cases. Results indicate that relying solely on regular waves in numerical studies is insufficient for accurately determining the real hydrodynamic behavior. The efficiency of the SHP as a breakwater and WEC varied depending on the wave approach. Specifically, the SHP demonstrates its highest breakwater efficiency in reducing wave height at 2.5Lp for regular waves and 3Lp for irregular waves. As a WEC, it achieves its highest axial velocity at 3Lp for regular waves and 2Lp for irregular waves. Since the literature lacks studies on SHP devices under the incidence of realistic irregular waves, this study significantly contributes to the state of the art. [ABSTRACT FROM AUTHOR]

We developed a synergistic ocean renewable system where an array of Wave Energy Converters (WEC) with adaptive resonance was collocated with a Floating Offshore Wind Turbine (FOWT) such that the WECs, capturing wave energy through the resonance adapting to varying irregular waves, consequently reduced FOWFT loads and turbine motions. Combining Surface-Riding WECs (SR-WEC) individually designed to feasibly relocate their natural frequency at the peak of the wave excitation spectrum for each sea state, and to obtain the highest capture width ratio at one of the frequent sea states for annual average power in a tens of kilowatts scale with a 15 MW FOWT based on a semi-submersible, Bayesian Optimization is implemented to determine the arrangement of WECs that minimize the annual representation of FOWT's wave excitation spectra. The time-domain simulation of the system in the optimized arrangement is performed, including two sets of interactions: one set is the wind turbine dynamics, mooring lines, and floating body dynamics for FOWT, and the other set is the nonlinear power-take-off dynamics, linear mooring, and individual WECs' floating body dynamics. Those two sets of interactions are further coupled through the hydrodynamics of diffraction and radiation. For sea states comprising Annual Energy Production, we investigate the capture width ratio of WECs, wave excitation on FOWT, and nacelle acceleration of the turbine compared to their single unit operations. We find that the optimally arranged SR-WECs reduce the wave excitation spectral area of FOWT by up to 60% and lower the turbine's peak nacelle acceleration by nearly 44% in highly occurring sea states, while multiple WECs often produce more than the single operation, achieving adaptive resonance with a larger wave excitation spectra for those sea states. The synergistic system improves the total Annual Energy Production (AEP) by 1440 MWh, and we address which costs of Levelized Cost Of Energy (LCOE) can be reduced by the collocation. [ABSTRACT FROM AUTHOR]

In the early stages of developing wave energy converter (WEC) projects, a quantitative assessment of component failure consequence costs is essential. The WEC types, deployment site features, and accessibility should all be carefully considered. This study introduces an operation and maintenance failure consequence cost (O&M-FC) model, distinct from conventional O&M models. The model is illustrated with case studies at three energetic Atlantic sites, each of which considers two types of generic floating WECs: a 300 kW point absorber (PA) with a hydraulic power-take-off (PTO) and a 1000 kW oscillating water column (OWC) with an air-wells-turbine PTO. This study compares 39 failure modes for PA and 27 for OWC in terms of direct repair costs and indirect lost production costs, examining the impact of location accessibility, capacity factors, and the mean annual energy production. The discussion revolves around the sensitive parameters. Recommendations for failure mitigations are presented, and the impact of planned maintenance (PM) during the operational phase is examined for 20 MW PA and OWC WEC projects. For a given WEC type, the method thoroughly evaluates how the location affects performance metrics. It offers a decision-making tool for determining optimal PM intervals to meet targets such as O&M costs, operating profit, or availability. [ABSTRACT FROM AUTHOR]

A multi-chamber oscillating water column wave energy converter (OWC-WEC) integrated to a breakwater is investigated. The hydrodynamic characteristics of the device are analyzed using an analytical model based on the linear potential flow theory. A pneumatic model is employed to investigate the relationship between the air mass flux in the chamber and the turbine characteristics. The effects of chamber width, wall draft and wall thickness on the hydrodynamic performance of a dual-chamber OWC-WEC are investigated. The results demonstrate that the device, with a smaller front wall draft and a wider rear chamber exhibits a broader effective frequency bandwidth. The device with a chamber-width-ratio of 1:3 performs better in terms of power absorption. Additionally, results from the analysis of a triple-chamber OWC-WEC demonstrate that reducing the front chamber width and increasing the rearward chamber width can improve the total performance of the device. Increasing the number of chambers from 1 to 2 or 3 can widen the effective frequency bandwidth. [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.)

Hydraulic power take-off (PTO) is increasingly favored as energy regulation and transmission system in wave energy converters (WEC), significantly smoothing the inherent randomness and fluctuation of wave energy. This paper designed a novel hydraulic PTO system composition of a double-acting hydraulic cylinder pump and accumulators. The dynamic process sub-division principle in an operating period of the hydraulic cylinder pump and accumulator and the mathematical model for explaining the fluctuations of pressure and flow rate in the hydraulic pump and accumulator circuit by means of the sub-division principle are put forward. The MATLAB/Simulink simulation model used to analyze pressure fluctuation in the hydraulic PTO system is established based on the mathematical model. The numerical results and MATLAB simulation results are mutually verified about the fine analysis of the accumulator smoothing fluctuation in the hydraulic PTO system. The results show that the pressure fluctuation amplitude of a hydraulic circuit is negatively correlated with the accumulator pre-charge pressure and the accumulator volume, and is positively correlated with the operating period of a hydraulic pump. The energy transfer efficiency of the hydraulic PTO system with accumulator fine compensation can be above 90%. The theory and model in this paper will serve as a valuable reference for designing fluctuation compensation parameters in hydraulic systems. [ABSTRACT FROM AUTHOR]

Existing studies within the literature that focus on designing parametric energy-maximizing controllers for Wave Energy Converter (WEC) systems predominantly rely on the impedance-matching (IM) principle, originally developed for linear time-invariant systems. Alternatively, iterative optimization routines are commonly employed for nonlinear WECs. However, these approaches often face a trade-off between effectiveness in maximizing energy extraction and computational efficiency. To address this limitation, this study proposes a computationally efficient controller tuning method for analogous synthesis in the case of nonlinear WECs. The proposed approach combines a statistical linearization technique known as spectral-domain modeling with the IM principle, to synthesize a Proportional–Integrative (PI) controller for a nonlinear WEC. Furthermore, a comparison is performed with two other synthesis methods: one based on a standard (i.e. linear) frequency-domain representation of the WEC that incorporates the IM principle, and the other employing a gradient-free optimization routine applied to the nonlinear time-domain model of the WEC for PI parameter tuning through exhaustive numerical search. A discussion on the effectiveness of each tuning method in maximizing energy absorption is provided, including an appraisal of their associated computational time requirements. Numerical analyses demonstrate that the proposed method, which integrates spectral-domain modeling and IM, can achieve (almost) optimal PI controller design for a nonlinear WEC. Furthermore, this study addresses the inaccuracies inherent in the frequency-domain approach and significantly reduces the computational time compared to the exhaustive search procedure. The findings of this research represent a significant advancement towards the development of simple, effective, and efficient IM-based techniques for synthesis of controllers in nonlinear WEC systems [ABSTRACT FROM AUTHOR]

The impact of wave-induced forces on the integrity of stationary oscillating water column (OWC) devices is essential for ensuring their structural safety. In our study, we built a three-dimensional numerical model of an OWC device using the computational fluid dynamics (CFDs) software OpenFOAM-v1912. Subsequently, the hydrodynamic performance of the numerical model is comprehensively validated. Finally, the hydrodynamic performance data are analyzed in detail to obtain meaningful conclusions. Results indicate that the horizontal wave force applied to the OWC device is approximately 6.6 to 7.9 times greater than the vertical wave force, whereas the lateral wave force is relatively small. Both the horizontal and vertical wave forces decrease as the relative water depth increases under a constant wave period and height. In addition, the highest dynamic water pressure is observed at the interface between the water surface and device, both within and outside the front wall of the gas chamber. The dynamic water pressure at different locations on the front chamber increases and subsequently decreases as the wave frequency increases. [ABSTRACT FROM AUTHOR]

Wave energy converters (WECs) have significant potential to meet the increasing energy demands and using an oscillating water column (OWC) is one of the most reliable ways to implement them. The OWC has a simple structure and excellent durability. However, control of the power take-off (PTO) system is difficult due to variability in the input wave energy. In particular, the design and control of the PTO system are complex, as the average-to-peak ratio of the output generation is large. Owing to the nature of the OWC, if the energy above the rating cannot be controlled, the power generated is inevitably reduced due to the decrease in operating time. We propose a method to reduce the angular speed of the turbine by dividing the section according to the input energy and correspondingly changing the torque coefficient, thereby increasing the operating time of the OWC. The control methods for the PTO system of OWC are verified through a 30 kW full-scale experimental device to be installed in a real sea area. The full-scale experimental device consists of an inverter that simulates the mechanical torque of an OWC based on the aerodynamic simulation of an impulse turbine, an induction motor, a permanent magnet synchronous generator, an AC/DC converter, and a battery for the energy storage system. The performance of conventional control methods and the proposed method are compared based on the results of numerical simulations and experiments. We show that the fluctuation in the turbine angular velocity in the proposed method is significantly reduced compared with that in the conventional control methods under regular and irregular wave conditions. [ABSTRACT FROM AUTHOR]

This study focused on optimizing the power generation of a heaving point-absorber wave energy converter (HPA-WEC) by integrating submerged breakwaters. An optimization analysis was conducted based on a framework developed in the authors' previous work, aiming to maximize the capture width ratio (CWR) by inducing Bragg resonance. Numerical simulations were conducted using a two-dimensional frequency domain boundary element method (FD-BEM) under irregular wave conditions. Advanced particle swarm optimization (PSO) was used for the optimization, with design variables that included the power take-off (PTO) damping coefficient, spring constant, and position and shape of the submerged breakwaters. The results showed that the CWR almost doubled when two breakwaters were used compared with the case without breakwaters. The CWR significantly increased, even with only one breakwater installed behind the WEC. A coastal stability analysis showed that installing two breakwaters provided the best performance, reducing the transmitted wave energy by approximately 25%. Furthermore, the CWR reached its maximum when the distance between the breakwater endpoints equaled the wavelength of the peak wave frequency, indicating the occurrence of Bragg resonance. This study underscores the potential of submerged breakwaters in enhancing power generation and coastal stability in the design of HPA-WECs. [ABSTRACT FROM AUTHOR]

Additive manufacturing has established itself to be advantageous beyond small-scale prototyping, now supporting full-scale production of components for a variety of applications. Despite its integration across industries, marine renewable energy technology is one largely untapped application with potential to bolster clean energy production on the global scale. Wave energy converters (WEC) are one specific facet within this realm that could benefit from AM. As such, wire arc additive manufacturing (WAAM) has been identified as a practical method to produce larger scale marine energy components by leveraging cost-effective and readily available A36 steel feedstock material. The flexibility associated with WAAM can benefit production of WEC by producing more complex structural geometries that are challenging to produce traditionally. Additionally, for large components where fine details are less critical, the high deposition rate of WAAM in comparison to traditional wrought techniques could reduce build times by an order of magnitude. In this context of building and supporting WEC, which experience harsh marine environments, an understanding of performance under large loads and corrosive environments must be understood. Hence, WAAM and wrought A36 steel tensile samples were manufactured, and mechanical properties compared under both dry and corroded conditions. The unique microstructure created via the WAAM process was found to directly correlate to the increased ultimate tensile and yield strength compared to the wrought condition. Static corrosion testing in a simulated saltwater environment in parallel with electrochemical testing highlighted an outperformance of corroded WAAM A36 steel than wrought, despite having a slighter higher corrosion rate. Ultimately, this study shows how marine energy systems may benefit from additive manufacturing components and provides a foundation for future applications of WAAM A36 steel. [ABSTRACT FROM AUTHOR]

Composable life under the extensive global warming of the Earth encourages the progress of renewable energy devices and the adoption of new technologies, such as artificial intelligence. Regarding enormous potential of wave energy and its consistency, wave energy converter (WEC) plays vital role in uniform energy harvesting field. In this paper, the significant environmental changes in the ocean prompt us to propose an intelligent feedback control system to mitigate the impact of disturbances and variable wind effects on the efficacy of WECs. Deep reinforcement learning (DRL), as a powerful machine intelligence technique, is capable of identifying WECs as black-box models. Therefore, based on the DRL model, the disturbance and unmeasured state variables are simultaneously estimated in the extended state observer section. Leakage in identification data and real-time application requirements of limited number of layers in the deep neural networks are compensated by implementation of immersion and invariance-based extended state observer which improves coping with the unwanted exogenous noises as well. In the overall intelligent control system, the estimated parameters are inputted into the DRL as the actor-critic networks. The initial actor network is responsible for predicting the control action, while the subsequent critic network determines the decision criterion for evaluating the accuracy of the actor's estimated amount. Next, the output value of the critic stage is backpropagated through the layers to update the network weights. The simulation test results in MATLAB indicate the convergence of unmeasured parameters/states to the corresponding true values and the significance of newly designed intelligent DRL method. [ABSTRACT FROM AUTHOR]

Nowadays, numerous governments have instituted diverse regulatory frameworks aimed at fostering the assimilation of sustainable energy sources characterized by reduced environmental footprints. Solar, wind, geothermal, and ocean energies were subject to extensive scrutiny, owing to their ecological merits. However, these sources exhibit pronounced temporal fluctuations. Notably, ocean dynamics offer vast energy reservoirs, with oceanic waves containing significant amounts of energy. In the Central American Pacific context, the exploration of wave energy resources is currently underway. Accurate numerical wave models are required for applied studies such as those focused on the estimation of exploitable wave power; and even more so in Central American region of the Pacific Ocean where existing numerical models simulations have so far relied on coarse resolution and limited validation field data. This work presents a high-resolution unstructured wave hindcast over the Central American Pacific region, implemented using the third-generation spectral wave model WAVEWATCH III over the period between 1979 and 2021. The results of the significant wave height have been bias-corrected on the basis of satellite information spanning 2005 to 2015, and further validation was performed using wave buoy and acoustic Doppler current profiler (ADCP) records located in the nearshore region of the Central America Pacific coast. After correction and validation of the wave hindcast, we employed the dataset for the evaluation and assessment of wave energy and its possible exploitation using different wave energy converters (WECs). This evaluation addressed the need to diverse the energy portfolio within the exclusive economic zones of Guatemala, El Salvador, Honduras, Nicaragua, Costa Rica, Panama, Colombia, and Ecuador in a sustainable manner. Moreover, a comprehensive analysis was carried out on the advantages of harnessing wave energy, juxtaposed with the imperative of regulatory frameworks and the current dearth of economic and environmental guidelines requisite for development within the region.

An oscillating buoy (OB) could function simultaneously as a wave energy converter and a breakwater. In this work, a numerical study is conducted to assess the ability of the buoy to perform both aforementioned tasks by quantitatively and qualitatively assessing its hydrodynamic performance. The computational fluid dynamics solver used for the numerical study is ANSYS Fluent, which uses Reynolds-averaged Navier-Stokes equations and Volume of Fluid method for the design and simulation of the numerical model, which consists of a rectangular OB that floats on the surface of a numerical wave tank. First, a total of six independent studies, namely the time, meshing, damping, overset geometry, flow viscosity, and spatial studies, were conducted for validation purposes. Second, calculation and analysis of the heave and transmission coefficients and vorticity magnitude were conducted to assess the hydrodynamic performance. Results of independent studies show cases with a high degree of accuracy to the experimental model, whereas results for hydrodynamic performance show a generally increasing heave movement of OB and transmission coefficient across the range of wave periods studied. Meanwhile, the vorticity magnitude flow fields show at least two vortices for all wave periods studied, except for the shortest two wave periods.

Free-floating and submerged wave energy converters (SWECs) are regarded as promising technologies for renewable energy production. These converters rely on a heave-motion buoy to capture the kinetic energy of ocean waves and convert it into electrical energy through power conversion systems. To better understand the impact of various factors on power generation and efficiency, the effects of different buoy shapes (rectangular, circular cylinder, and trapezoidal fin), submergence depths (0, 0.1, and 0.2 m), wave heights (0.04, 0.06, and 0.1 m), and spring stiffness (50 and 100 N/m) were investigated. A 2D numerical wave tank with a buoy was simulated, and the results were validated against experimental data. Information on vorticity, vertical displacement, power absorption, and efficiency are provided. The findings indicate that the buoy shape and wave height significantly affect power absorption and efficiency. Additionally, this study reveals that increasing submergence leads to higher power absorption and lower conversion efficiency. [ABSTRACT FROM AUTHOR]

Introduction: The study presents an integrated system comprising a central platform and four wave-energy converters, with a focus on investigating their coupled motions induced by ocean waves. The interaction between the buoys and the central platform is achieved through the implementation of spring components. The power take-off system is simulated by incorporating damping coefficients and stiffness into these spring components, enabling a detailed analysis of the energy conversion of such system. Methods: Numerical simulations based on the continuity equation and the Reynolds-Averaged Navier-Stokes (RANS) equations, coupled with the realizable k -- e turbulence model, are conducted. The two-phase flow model employs the Volume of Fluid (VOF) method to accurately capture free surface elevations. Additionally, frequency-domain predictions, based on the linearized velocity potential flow theory, are provided for a single central platform and buoy for comparative purposes. Results: Detailed results regarding the effects of wave frequency and the damping coefficient of the power take-off system are presented. Discussion: The results reveal that while both the platform's motion and the relative motions between buoys and the platform are suppressed, the absolute motion of buoys varies depending on their respective locations within the system and ocean waves. This variation is deeply influenced by the interaction between incident, reflected and diffracted waves within the system. [ABSTRACT FROM AUTHOR]

Although there are constant improvements in wave energy converter (WEC) technology, it is crucial to investigate site-specific sea conditions for optimal power absorption and efficiency. This study compares the efficiency of a floating buoy-type WEC device, with three differently shaped floats: a semi-sphere, a cylinder considered suitable for a location near Ensenada, on the Baja California peninsula, and a novel, rounded, semi-rectangular float. A statistical analysis of the wave climate of the last 42 years was performed to define the conditions to which the device is subjected. The WEC location was chosen for shallow waters, using a computational model that solves the modified mild slope equation. The hydrodynamic response of the three float designs was then analyzed in the frequency and time domains, using the software ANSYS AQWA 19.2, to assess the dynamics of the floating body, the forces exerted, and the power absorbed, as well as the suitability of the proposed power take-off (PTO) system. The findings show that the proposed float design absorbs the most energy, with an annual power of 135.11 MW, and that the PTO mechanism is appropriate. [ABSTRACT FROM AUTHOR]

With the acceleration of the global warming process, the clean energy crisis is becoming serious; conventional energy is unlikely to solve the current crisis, so people pay attention to new energy. As wave energy is widely distributed, renewable, and clean, hundreds of wave energy converters emerge. In order to understand the research progress of wave energy converters better, this paper divides wave energy converters into overtopping type, oscillating water column type, and oscillating body type according to the working principle and divides the oscillating body type into oscillating float type and oscillating pendulum type by different ways of energy capture. Based on the classification, various types of engineering cases, physical tests and digital simulation, and other academic research results are summarized, especially the generation power and energy conversion efficiency of various devices, and some shortcomings and suggestions are put forward, hoping to provide help for readers to study wave energy generation converters. [ABSTRACT FROM AUTHOR]

A Surface-Riding Wave Energy Converter (SR-WEC) featuring a sliding magnet inside a pitching cylindrical hull is investigated as an easily deployable small power device to support small-scale marine operations. This study extends the earlier development of the system by authors to enhance power performance through the application of end spring and latching control. The inclusion of springs at the tube's end enhances the magnet release and travel speeds as well as the average power output compared to systems without them. Further improvement of power output can also be achieved by employing optimal latching control. We introduced constant-angle and variable-angle unlatching strategies to determine optimal parameters in combination with passive and reactive power take-off (PTO) controls to assess their effectiveness. The optimized latching control and end spring can increase 60–80% more power output compared with the case without them under certain PTO damping. Additionally, we discussed the effects of limiting peak powers and associated energy leaks with latching. [ABSTRACT FROM AUTHOR]

Recently, most wave energy research has targeted sea areas with high power density under extreme wave conditions for deployment. This trend often leads to higher energy costs for wave power plants. However, many marine areas with low power density, characterized by wavelet conditions and less destructive forces than extreme wave conditions, remain underexplored. Therefore, this study aimed to propose a wave-activated body model for sea regions with wavelet conditions. The wave-activated body design process encompassed site selection, parameter determination, geometry design, comparison and performance evaluation using the ANSYS® AQWA model. The results indicated that the proposed device achieved the desired heave motion, with an amplitude range of 1.2 to –2.5 m, validating its potential for deployment in marine regions with wavelet conditions. Notably, while the proposed design is optimized for wavelet conditions, it was found to have potential limitations in extreme wave environments. This observation emphasizes the challenge of formulating a generalized design suitable for both conditions. Consequently, it is pivotal for wave-activated body designs to be customized based on the specific ocean conditions they target, underscoring the need for specialized designs of wave energy converters that consider the unique wave characteristics of their deployment sites. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid marine renewable energy-harvesting system to increase energy production, reduce levelized costs of energy and promote renewable marine energy. Firstly, various marine renewable energy resources and state-of-art technologies for energy exploitation and storage were reviewed. The site selection criteria for each energy-harvesting approach were identified, and a scoring matrix for site selection was proposed to screen suitable locations for the hybrid system. The Triton Knoll wind farm was used to demonstrate the effectiveness of the scoring matrix. An integrated energy system was designed, and FE modeling was performed to assess the effects of additional energy devices on the structural stability of the main wind turbine structure. It has been proven that the additional energy structures have a negligible influence on foundation/structure deflection (<1%) and increased system natural frequency by 6%; thus, they have a minimum influence on the original wind system but increased energy yield. [ABSTRACT FROM AUTHOR]

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