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The wave energy, as a clean and non-pollution renewable energy sources, has become a hot research topic at home and abroad and is likely to become a new industry in the future. In this article, to effectively extract and maximize the energy from ocean waves, a vertical axisymmetric wave energy converter (WEC) was presented according to investigating of the advantages and disadvantages of the current WEC. The linear and quadratic equations in frequency-domain for the reactive controlled single-point converter property under regular waves condition are proposed for an efficient power take-off (PTO). A method of damping coefficients, theoretical added mass and exciting force are calculated with the analytical method which is in use of the series expansion of eigen functions. The loads of optimal reactive and resistive, the amplitudes of corresponding oscillation, and the width ratios of energy capture are determined approximately and discussed in numerical results. [ABSTRACT FROM AUTHOR]

An algorithm has been developed for the resistive control of a nonlinear model of a wave energy converter using least-squares policy iteration, which incorporates function approximation, with tabular and radial basis functions being used as features. With this method, the controller learns the optimal power take-off damping coefficient in each sea state for the maximization of the mean generated power. The performance of the algorithm is assessed against two online reinforcement learning schemes: Q-learning and SARSA. In both regular and irregular waves, least-squares policy iteration outperforms the other strategies, especially when starting from unfavorable conditions for learning. Similar performance is observed for both basis functions, with a smaller number of radial basis functions underfitting the Q-function. The shorter learning time is fundamental for a practical application on a real wave energy converter. Furthermore, this paper shows that least-squares policy iteration is able to maximize the energy absorption of a wave energy converter despite strongly nonlinear effects due to its model-free nature, which removes the influence of modeling errors. Additionally, the floater geometry has been changed during a simulation to show that reinforcement learning control is able to adapt to variations in the system dynamics. [ABSTRACT FROM PUBLISHER]

Wave energy converters (WECs) have received much attention with the increasing environmental concerns. And the direct-drive WECs are more attractive due to the elimination of intermediate mechanical conversion parts. We have proposed a concept of a WEC device, in which a tubular linear generator (TLG) is directly driven by a heaving buoy. We design a high-temperature superconducting TLG (HTS-TLG), a permanent magnet (PM) TLG, and a copper TLG for the WEC. In this paper, we give a brief description on the conceptual structures and the electrical design method of these three types of TLGs, then show the way of determining main machine parameters considering the basic generator performance (weight, efficiency, and the amount of field conductors/PMs). Design results of these TLGs are finally presented with machine performances and costs compared. We found that the HTS-TLG is the most promising one compared to the other counterparts. [ABSTRACT FROM PUBLISHER]

Numerical modelling has become commonplace in the development of offshore structures, however for dynamic systems such as Wave Energy Convertors (WECs) conventional numerical tools may not be able to capture the full range of behaviours required for engineering analysis. This is particularly problematic in extreme seas where the nonlinearities and coupled nature of these systems become important. In this work a fully nonlinear, coupled tool for simulation of WECs is produced and compare with physical measurements. Regular wave interactions with both a fixed and freely-pitching, 1:10 scale model of the Wavestar are reproduced numerically. The numerical model is shown to be capable of predicting the pressure on the float's surface and the fully coupled motion of the device. However, the results indicate that the higher-order free surface behaviour in the vicinity of the device is not being captured correctly. Finally, the numerical model is shown to cope with an extreme regular wave including large amplitude motion, full submersion and high levels of free surface distortion. The results presented suggest that the quality of the numerical reproduction does not decrease with wave steepness; however the execution time of simulations increases significantly with increased float oscillation. [ABSTRACT FROM AUTHOR]

Ocean waves are a more predictable resource with a higher energy density compared to solar and wind. In addition, and specifically for the United States, resource locations with high wave power are close to major load centers being located along coastlines. These features have sparked a surge of attention in the United States on trying to economically harness ocean wave power. The aim of this article is to provide a concise review of the current state of ocean wave energy conversion technologies and industry status in the United States including research and development as well as commercial activities and governmental support, concluding with a discussion of future industry perspectives. Existing facilities, softwares as well as laboratory and open-water test facilities and resources, active research groups and commercial activities have been identified. Over one third of commercially active wave energy developers worldwide are located within the United States, but only a few have reached a high Technology Readiness Level. These findings, together with a relevant practical resource located within the U.S. and the advantageous nature of the resource compared to other renewable resources, indicate that the United States is well positioned to advance the wave energy industry in the near future. [ABSTRACT FROM AUTHOR]

As a result of international agreements on the reduction of CO2 emissions, new technologies using hydrogen are being developed. Hydrogen, despite being the most abundant element in Nature, cannot be found in its pure state. Water is one of the most abundant sources of hydrogen on the planet. The proposal here is to use energy from the sea in order to obtain hydrogen from water. If plants to obtain hydrogen were to be placed in the ocean, the impact of long submarines piping to the coast will be reduced. Further, this will open the way for the development of ships propelled by hydrogen. This paper discusses the feasibility of an offshore installation to obtain hydrogen from the sea, using ocean wave energy. [ABSTRACT FROM AUTHOR]

Sigma Energy has performed its foremost prototype tests of scaled wave energy converter in a real sea environment. The prototype was a point absorber with a cylindrical buoy, a mechanical power take-off system with a counterweight, moored to the seabed as a tension leg platform (TLP) with three equal tendons. In these extensive experiments, numerous device characteristics were measured and analysed. The present paper focuses on the dynamic forces in the mooring lines, and some unexpected and rare data obtained. It is well known that TLP tendons are prone to a brief loss of tension (the slacking) and that, after such events, high snapping forces of short duration can arise. Partly by intention, and partly due to underestimation of the dynamical forces, several such slacking-snapping incidents were recorded during the experiments. In some severe storms, the snapping forces were up to six times higher than the tendon pretension. The paper presents several recordings of dynamic forces and platform motion during these critical events. It analysis them, and gives a typical scenario under which they occur. It gives also some theoretical explanations, and numerical predictions of dynamical tendon forces, with their comparison to the experimental results. • Sea trials of novel wave energy converter. • Dynamic forces in tension leg platform (TLP) mooring lines. • Slacking and snapping of TLP tendons. • Recordings of dynamical forces and platform motion in slacking-snapping incidents. • A typical scenario of critical slacking-snapping events. [ABSTRACT FROM AUTHOR]

The lack of an efficient and reliable power supply is currently one of the bottlenecks restricting the practical application of unmanned ocean detectors. Wave energy is the most widely distributed ocean energy, with the obvious advantages of high energy density and predictability. In this paper, a novel wave energy converter (WEC) for power supply of low-power unmanned ocean detectors is proposed, which is a small-scale counter-rotating self-adaptive point absorber-type WEC. The double-layer counter-rotating absorbers can achieve the torque balance of the whole device. Besides, the self-adaptation of the blade to the water flow can maintain a unidirectional continuous rotation of the single-layer absorber. The WEC has several advantages, including small occupied space, simple exchange process and convenient modular integration. It is expected to meet the power demand of low-power ocean detectors. Through modeling and CFD analysis, it was found that the power and efficiency characteristics of WEC are greatly influenced by the relative flow velocity, the blade angle of the absorber and the interaction between the upper and lower absorbers. A physical prototype of the WEC was made and some related experiments were conducted to verify the feasibility of WEC working principle and the reliability of CFD analysis.

In guiding the progression, development, and operation of wave energy converters (WECs) in a more efficient way, mathematical analysis and understanding of the dynamic process is essential. Mathematical WEC models, obtained either by numerical analysis or physical modelling, form the basis of most (model-based) energy maximising control strategies available in the literature, where experimental design and system identification methodology directly impact the resulting model. This study, using an experimental-based WEC model (which can be used for linear control design), investigates the dynamic behaviour of a WEC by analysing the dominant poles of the system, generated using fully nonlinear computational fluid dynamics (CFD)-based numerical wave tank (NWT) experiments. The aim is to effectively track the dominant dynamics of the WEC, using different force-input amplitude levels in the NWT setup, and perform a comparison with the classical linear boundary-element-methods (BEM) equivalent methodology. Thus, the presented case studies are shown to agree with previously proposed model assessment of linear WEC models, based on a free-decay NWT setup. In addition, the representative WEC models determined as part of this study can be used for WEC controller design, either singly, or using a form of model/controller gain scheduling. • Representative linear wave energy converter models for model-based control design. • Assessment of wave energy device dominant dynamics. • Dominant pole trends for wave energy converters using force-input experiments. • Model identification of wave energy converters from numerical wave tank data. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to analyze the energy production in the Maltese islands, focusing on the employment of renewable energies in order to increase their energy independence. The main renewable source here proposed is wave energy: thanks to a strategic position, Malta will be able to produce electrical energy using an innovative type of Wave Energy Converter (WEC) based on the prototype of a linear generator realized by University of Palermo. The use of this new technology will be able to cut down the electrical energy production from traditional power plants and, consequently, the greenhouse gas emissions (GHG).Wave energy source and off-shore photovoltaic (PV) technology are here proposed. Particularly, the installation of 12 wave farms, for a total installed capacity of 86 MW, will generate about 9.5% of Malta's energy requirement in 2025, while the installation of 9.6 MW of off-shore PV will generate about 0.73%. [ABSTRACT FROM AUTHOR]

This paper presents the design and modelling of generator for wave energy conversion system in Malaysia. This paper aims to identify the most promising topology to be used and to propose initial designs of the generator. Literature review on the previous technologies, power take-offs and linear generator have been completed and from the review, the criteria for the proposed generator designs are acquired. Two designs have been proposed in which one of the designs utilizes alternate slot winding concept. Both of the designs are simulated using Finite Element software, Ansys Maxwell. The preliminary results of flux distribution, air gap flux density, flux linkage and induced back EMF are obtained. From the simulation results, air gap flux density of both designs is within the expected range. It is also found that by implementing alternate slot winding concept, even though the total number of turn is the same, the induced back EMF produces is slightly lower than the full slot winding. [ABSTRACT FROM AUTHOR]

Marine energy sources represent an attractive and inexhaustible reservoir able to contribute to the fulfillment of the world energy demand in accordance with climate/energy regulatory frameworks. Wave energy converter (WEC) integration into the main grid requires both the maximization of the harvested energy and the proper management of the generation variability. The present paper focuses on both these mentioned issues. More specifically, it presents an embedded point pivoted absorber (PPA) and its related control strategy aimed at maximizing the harvested energy. Experimental and numerical investigations have been carried out in a wave/towing tank facility in order to derive the design characteristics of the full-scale model and demonstrate the validity and effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

The energy absorption of the wave energy converters (WEC) characterized by a limited stroke length --like the point absorbers developed at Uppsala University--depends on the sea level variation at the deployment site. In coastal areas characterized by high tidal ranges, the daily energy production of the generators is not optimal. The study presented in this paper quantifies the effects of the changing sea level at theWave Hub test site, located at the south-west coast of England. This area is strongly affected by tides: the tidal height calculated as the difference between the Mean High Water Spring and the Mean LowWater Spring in 2014 was about 6.6 m. The results are obtained from a hydro-mechanic model that analyzes the behaviour of the point absorber at the Wave Hub, taking into account the sea state occurrence scatter diagram and the tidal time series at the site. It turns out that the impact of the tide decreases the energy absorption by 53%. For this reason, the need for a tidal compensation system to be included in the design of the WEC becomes compelling. The economic advantages are evaluated for different scenarios: the economic analysis proposed within the paper allows an educated guess to be made on the profits. The alternative of extending the stroke length of the WEC is investigated, and the gain in energy absorption is estimated. [ABSTRACT FROM AUTHOR]

This work presents the application of reinforcement learning for the optimal resistive control of a point absorber. The model-free Q-learning algorithm is selected in order to maximise energy absorption in each sea state. Step changes are made to the controller damping, observing the associated penalty, for excessive motions, or reward, i.e. gain in associated power. Due to the general periodicity of gravity waves, the absorbed power is averaged over a time horizon lasting several wave periods. The performance of the algorithm is assessed through the numerical simulation of a point absorber subject to motions in heave in both regular and irregular waves. The algorithm is found to converge towards the optimal controller damping in each sea state. Additionally, the model-free approach ensures the algorithm can adapt to changes to the device hydrodynamics over time and is unbiased by modelling errors. [ABSTRACT FROM PUBLISHER]

The Lysekil wave energy converter (WEC), developed by the wave energy research group of Uppsala University, has evolved through a variety of mechanical designs since the first prototype was installed in 2006. The hundreds of engineering decisions made throughout the design processes have been based on a combination of theory, know-how from previous experiments, and educated guesses. One key parameter in the design of the WECs linear generator is the stroke length. A long stroke requires a taller WEC with associated economical and mechanical challenges, but a short stroke limits the power production. The 2-m stroke of the current WECs has been an educated guess for the Swedish wave climate, though the consequences of this choice on energy absorption have not been studied. When the WEC technology is considered for international waters, with larger waves and challenges of energy absorption and survivability, the subject of stroke length becomes even more relevant. This paper studies the impact of generator stroke length on energy absorption for three sites off the coasts of Sweden, Chile and Scotland. 2-m, 4-m, and unlimited stroke are considered. Power matrices for the studied WEC prototype are presented for each of the studied stroke lengths. Presented results quantify the losses incurred by a limited stroke. The results indicate that a 2-m stroke length is likely to be a good choice for Sweden, but 4-m is likely to be necessary in more energetic international waters. [ABSTRACT FROM AUTHOR]

Modeled nearshore wave propagation was investigated downstream of simulated wave energy converters (WECs) to evaluate overall near- and far-field effects of WEC arrays. Model sensitivity to WEC characteristics and WEC array deployment scenarios was evaluated using a modified version of an industry standard wave model, Simulating WAves Nearshore (SWAN), which allows the incorporation of device-specific WEC characteristics to specify obstacle transmission. The sensitivity study illustrated that WEC device type and subsequently its size directly resulted in wave height variations in the lee of the WEC array. Wave heights decreased up to 30% between modeled scenarios with and without WECs for large arrays (100 devices) of relatively sizable devices (26 m in diameter) with peak power generation near to the modeled incident wave height. Other WEC types resulted in less than 15% differences in modeled wave height with and without WECs, with lesser influence for WECs less than 10 m in diameter. Wave directions and periods were largely insensitive to changes in parameters. However, additional model parameterization and analysis are required to fully explore the model sensitivity of peak wave period and mean wave direction to the varying of the parameters. [ABSTRACT FROM AUTHOR]

In this paper, we present a comprehensive numerical simulation of a point wave absorber in deep water. Analyses are performed in both the frequency and time domains. The converter is a two-body floating-point absorber (FPA) with one degree of freedom in the heave direction. Its two parts are connected by a linear mass-spring-damper system. The commercial ANSYS-AQWA software used in this study performs well in considering validations. The velocity potential is obtained by assuming incompressible and irrotational flow. As such, we investigated the effects of wave characteristics on energy conversion and device efficiency, including wave height and wave period, as well as the device diameter, draft, geometry, and damping coefficient. To validate the model, we compared our numerical results with those from similar experiments. Our study results can clearly help to maximize the converter's efficiency when considering specific conditions. [ABSTRACT FROM AUTHOR]

The wave energy converter (WEC) studied and developed at Uppsala University in Sweden is a point absorbing buoy connected to a linear generator (LG) on the seabed. Previous studies have improved the sustainability of the generator, changing its magnets from Nd2Fe14B-magnets to ferrites. In this paper, the magnetic circuit of the linear generator is further studied. Ferrite magnets of two different types (Y30 and Y40) are studied along with different shapes of pole shoes for the system. The finite element method (FEM) simulations in a program called Ace are performed. The results show that a linear generator including both Y30 and Y40 magnets and shortened T-shaped pole shoes can generate a similar magnetic energy in the airgap as a linear generator only containing Y40 magnets and rectangular pole shoes. This shows that the magnetic circuit can be altered, opening up sizes and strengths of magnets for different retailers, and thereby possibly lowering magnet cost and transportation. This work was previously presented as a conference at the European Wave and Tidal Energy Conference (EWTEC) 2017 in Cork, Ireland; this manuscript has been carefully revised and some discussions, on magnet costs for example, have been added to this paper.

Despite the huge potential of ocean waves as an alternative renewable energy resource, very low wave to wire efficiency of wave energy converters (WECs) hampers its commercialization. In this study, a novel streamlined chamber design has been proposed for performance improvement of an oscillating water column (OWC) with a sloping wall. Physical experiments are carried out for the calculation of capture width ratio (CWR) as a measure of hydrodynamic performance for various levels of PTO damping and sea conditions. The results are compared with those of a classical OWC chamber design. It is found that streamlined chamber design has an important bearing on OWC efficiency. As opposed to classical chamber shape, proposed streamlined chamber geometry increases the OWC performance as much as 31% for the incident waves under which the OWC operates efficiently. Further, results show that optimal level of PTO damping that for utmost energy extraction depends on the chamber design. Streamlined chamber geometry even further improves the OWC efficiency even when dominant sloshing water column motion is present in the chamber with a maximum and average value of 54% and 44%, respectively, however, chamber design has no influence on the mechanism that generates sloshing phenomenon in the chamber. • A new novel streamlined OWC chamber geometry is proposed for improved efficiency. • Efficiency of streamlined and a classical OWC experimentally obtained and compared. • A maximum of 31% efficiency improvement is found due to streamlined chamber design. • Optimum level of PTO damping that has to be applied is influenced by chamber design. • Design of chamber geometry has no bearing on the sloshing generating dynamics. [ABSTRACT FROM AUTHOR]

This paper presents a new concept of multi-axis wave energy converter (WEC), which can capture wave energy from multiple directions of motion. It describes the modelling of the multi-axis WEC and presents the results of laboratory experiments on the power capture of the multi-axis WEC in a wave tank subjected to synthesized scaled sea waves. The experiments investigate the influence of parameters such as buoy structure, damping and inertia modification (ballasting) on the hydrodynamic performance. The experimental results indicate that the multi-axis WEC yields very good performance under a variety of wave conditions. It is also demonstrated that, by utilizing more than one direction of motion, the multi-axis WEC proves capable of supplying more power than a single-axis WEC. This work constitutes a preliminary step towards the development of an advanced concept of WEC. [ABSTRACT FROM AUTHOR]

This article reports on a state-dependent model of a hydraulic power takeoff (PTO) for an inverse pendulum wave energy converter. The PTO influences the energy conversion performance by its efficiency and by the damping force exerted, which affects the motion of the body. The sta te-dependent model presented gives a description of the damping force and the internal dynamics of the hydraulic PTO system. Different values of the parameters of the accumulator and the motor torque are analyzed in order to improve the dynamic performance of the converter. The simulation results prove that it is possible to achieve a great enhancement of the power output with the implementation of optimization parameters of the hydraulic PTO and that a possible combination of some of them m ight be beneficial for improved efficiency of the system. [ABSTRACT FROM AUTHOR]

This paper deals with the hydrodynamic parameter computation of a wave energy converter (WEC) that consists of a cylindrical buoy sliding along a partially submerged platform made up of a plate and a column. The computed parameters are especially needed for the development of a simple hydrodynamic time-dependant model, based on the Cummins' formulation. This model is intended for WEC control purposes. A semi-analytical approach is proposed for the computation of the hydrodynamic coefficients and the excitation forces. The boundary value problem is solved by using variable separation and matched eigenfunction expansion methods. Analytical expressions for the velocity potential are then obtained for each subdomain. The hydrodynamic coefficients and the excitation force can then be computed by using these expressions. Numerical results are given for different buoy, column, and plate radii and clearly the bearing surface of the plate has a significant influence on the wave excitation force applied to the submerged platform. [ABSTRACT FROM PUBLISHER]

Wave energy converter (WEC) designs are always discussed in order to find an optimum design to generate power. The power output from wave energy converters may be increase by controlling the oscillation in order to approach an optimum interaction between the WEC and the incident wave. However, in order to control the oscillation of the heave buoy, the wave profile and the device's response must be examined and fully understood. Analysis carried out by study heave buoys response on Malaysian water using MathCAD software. The results shows that the heave buoy give a good heave response with regards of the wave phase. In this particular area, it is estimated that the wave force can produce as much as 4x10 5 kW/m. From the response, the strategies to optimize power output can be proposed in order to maximize the active power to generate an optimum power output. [ABSTRACT FROM AUTHOR]

This study is on the vertical wave-induced velocity through an opening in a fixed, submerged and impervious horizontal disk, that is positioned near the free surface. Piercing this body is a tubular section, having an opening flush with the top surface and extending completely through the body. Experiments are conducted in a wave flume, where monochromatic waves propagate over the submerged surface of a free-standing disk model. Wave elevation is recorded using a capacitive-type wave gauge. The oscillating wave-induced flow through the submerged surface is measured by a particle image velocimetry (PIV) laser. Numerically, the flow within the opening of the submerged surface is modeled by use of the Green function method within the confines of linear potential theory. Both the experimental and numerical results of this phenomenon are compared. The outcome is pertinent to the development of a new wave energy converter. [ABSTRACT FROM AUTHOR]

In order to reduce the cost of electricity produced by wave energy converters (WECs), the benefit of selling electricity as well as the investment costs of the structure has to be considered. This paper presents a methodology for assessing the control strategy for a WEC with respect to both energy output and structural fatigue loads. Different active and passive control strategies are implemented (proportional (P) controller, proportional-integral (PI) controller, proportional-integral-derivative with memory compensation (PID) controller, model predictive control (MPC) and maximum energy controller (MEC)), and load time-series resulting from numerical simulations are used to design structural parts based on fatigue analysis using rain-flow counting, Stress-Number (SN) curves and Miner's rule. The objective of the methodology is to obtain a cost-effective WEC with a more comprehensive analysis of a WEC based on a combination of well known control strategies and standardised fatigue methods. The presented method is then applied to a particular case study, the Wavestar WEC, for a specific location in the North Sea. Results, which are based on numerical simulations, show the importance of balancing the gained power against structural fatigue. Based on a simple cost model, the PI controller is shown as a viable solution. [ABSTRACT FROM AUTHOR]

The development of new wave energy devices (WECs) has continued unabated over the past decades. For large-scale applications, integrating individual WEC into an array system (WEC net) requires considerable expertise and research due to its highly complex and interrelated nature. Often for a WEC net, it contains main structures and multiple sub-structures. The WEC net response is defined as the total responses from all sub-structures, which is highly complex and closely interconnected with each other. This paper aims to develop a fully-coupled numerical modeling tool that can cope with the wave-structure interaction as well as the mechanical interaction among each sub-structure in a WEC net. The fluid field is solved by a Computational Fluid Dynamic (CFD) solver coupled with a Multi-body Dynamic structural solver. The hydrodynamic and power take-off performance of Albatern 12S Squid WEC net is studied and the results are validated against available laboratory testing data, and commercial mooring and hydrodynamics analysis software. It is found that the motion response of the CFD and experimental approach is in close agreement with each other. The interaction force among sub-structures can be well captured, and the results indicate that the mode response of individual float is strongly affected by the mechanical linking-arms as well as the incident wave conditions, which is hard to achieve without such integrated CFD tool. The power take-off (PTO) is modeled using a damping system. The predicted peak output power is found to increase with the decreasing of wave period and an optimal device's damping to reach a maximum power capture exists, which is dependent on the incoming wave period and height. • A numerical modeling tool coupling Computational Fluid Dynamic (CFD) and Multi-body Dynamic (MBD) is developed that can cope with the wave-structure interaction as well as the mechanical interaction among each sub-structure in a WEC net. • The interaction force among sub-structures can be well captured, the dynamic mode response of individual float is studied, which is strongly affected by the mechanical linking-arms as well as the incident wave conditions. • This work serves as a solid foundation for the optimizing of WECs in a design stage. It can also predict the weakest mechanical component, where the peak mechanical force may occur and thus become the most vulnerable part in the system. [ABSTRACT FROM AUTHOR]

Renewable energies are mostly compared using the Levelised Cost of Energy (LCoE). Two major components of LCoE are of interest in this study, the others being still experimental: the Annual Energy Production (AEP) and the Capital Expenditure (CapEx). Since many Wave Energy Converters (WECs), including Wavepiston, are wave direction-dependent, this research investigates the wave direction impact on the relationship between the site-configurations (site characteristics and wave climates), WEC-configurations and power, alongside AEP and CapEx. Wave climate and WEC power are expressed in 3-dimension by adding the wave direction to the common 2-dimensional space of wave height and period. Wavepiston's WEF costs are calculated using the CapEx method. Assessing the relationship between the diverse sources of AEP/CapEx variations, enabled the development of the Cost-AEP Threshold Criterion (CAEPTC) to determine the threshold where an increase in AEP becomes negligible compared to CapEx increase. CAEPTC is perhaps a better alternative to LCoE for enhanced WEC/site-configuration pairing. Based on this Criterion and the limited dataset (a challenge to most wave companies), it was apparent that the best WEC/site-configuration pairs came from configurations with the highest yearly energy production, which is not necessarily the most expensive, and for sites with lower wave energy. • Wave direction-dependent active-surge Wave Energy Converter (WEC) power analysis. • Wavepiston WEC farm Capital Expenditure (CapEx) and Annual Energy Production (AEP). • WEC-configuration, site characteristic, wave climate, CapEx/AEP interrelationship. • Development of the Cost-AEP Threshold Criterion for WEC/site-configuration pairing. • Unidirectional or high-energy wave climates appeal less WEC/site-configuration pair. [ABSTRACT FROM AUTHOR]

Abstract: The application of renewable energies has increased rapidly in the previous decade to solve some problems such as growing energy demand and environmental issues. Wave power as a high potential renewable energy, is more predictable compared to other renewable sources. Although there are many research works about wave energy, however a few of them considered a suitable wave energy converter (WEC) as a power system for remote islands. Wave energy potential for remote islands is discussed in this review by regarding environmental impacts, various types of wave energy converters and applied wave power projects for various islands. The results show that wave energy plays a key role for sustainable development of offshore islands by considering the traditional looks and environmental protection. [Copyright &y& Elsevier]

Abstract: Offshore wind is an important source of renewable energy and is steadier and stronger than onshore wind. Offshore areas not only have strong winds but also contain other potential renewable energy sources, such as ocean waves and tidal currents. Therefore, it is interesting to investigate the possibility to utilise these energy potentials simultaneously, particularly the combination of wind and ocean wave energy due to their natural correlation. For this reason, previous researchers have examined the use of a floating wind turbine (FWT) and a wave energy converter (WEC) on a single platform (Aubault et al., 2011; Peiffer et al., 2011; Soulard and Babarit, 2012). In this paper, a combined concept involving a spar-type FWT and an axi-symmetric two-body WEC is considered and denoted as STC. With respect to operational conditions, a previous study (Muliawan et al., 2013) indicates that the STC not only reduces the total capital cost but also increases the total power production compared to the use of segregated FWT and WEC concepts. As with other floating systems, the STC must be designed to ensure serviceability and survivability during its entire service life. One of the design criteria is the ultimate limit state (ULS), which ensures that the entire STC system will have adequate strength to withstand the load effects imposed by extreme environmental actions. Therefore, in the present study, coupled (wave- and wind-induced response mooring) analysis is performed using SIMO/TDHMILL in the time domain to investigate such responses of the STC system as mooring tension, spar-tower interface bending moment, end stop force, and contact force at the Spar-Torus interface under extreme conditions. Environmental conditions that pertain to the northern North Sea metocean data are selected and include operational, survival and 50-year conditions. Finally, the ULS level responses that are capital cost indicators for both FWT alone and for the STC system are estimated and compared. [Copyright &y& Elsevier]

This paper details a method for strain measurements in the inner framework structure of the single heaving buoy wave energy converter (WEC). This type of the WEC consists of a linear direct drive generator placed on the seafloor and connected to the floating buoy through the connection line. The study focuses on estimation of stress in the inner framework structure of the WEC using strain measurements in the material. Stress in ocean structures is as important as maximum stress. The offshore experiment took place at the Lysekil research site a few kilometers from the Swedish west coast. Stresses had the maximum value when the translator hit an end stop. Interesting observations were made: compressive stress occurred in the framework crossbar at a sea state of 1.32-m waves, but both compressive and tensile stresses occurred at a sea state of 3.2-m waves. A computational procedure employs good results. Error estimation is calculated and represented. This work is a step that may influence future design of wave energy devices in terms of the material aspect, survivability in a hard wave climate, and cost-effective renewable energies. [ABSTRACT FROM PUBLISHER]

This paper investigates power smoothing in a full-scale offshore oscillating water column (OWC) wave energy converter (WEC) by integrating supercapacitors (SCs) with the inertia of a Wells turbine controlled at variable speed. With the simulation package Simulink developed by MathWorks, a model is developed for the WEC system utilizing sea-state data and an SC system is sized to smooth and reduce the grid peak power for a 570-kW (peak) system. Long component lifetime is a requirement for offshore WECs. Hence, a computer-controlled test rig has been built to validate SC lifetimes to manufacturer's specifications and determine application lifetime. Cycle testing is carried out on individual SCs at room temperature and also at rated temperature utilizing a thermal chamber and equipment interconnected by the general purpose interface bus (GPIB) and programmed by the MathWorks developed computing environment Matlab. Application testing is carried out using time-compressed scaled-power profiles from the model to allow a comparison of lifetime degradation. The SCs under standard testing at ambient and rated temperature, and application testing at ambient temperature, have undergone approximately 4 000 000, 700 000, and 500 000 cycles, respectively. The results demonstrate cycle lifetimes in excess of manufacturer specifications. [ABSTRACT FROM PUBLISHER]