Analysis Of Wave Energy Converter Research Articles

A new method for analysis of marine sustainable energy systems

This paper proposes to utilise a new adaptive kernel density estimation (KDE) methodology based on linear diffusion processes for predicting the probability distribution tails of sea-state parameters. A key conclusion was reached that the proposed new methodology can lead to more accurate prediction results than traditional methods based on fittings to a measured significant wave height data set at National Data Buoy Center station 46014. This proposed methodology was subsequently utilised for deriving an accurate 50-year environmental contour line that was used in the dynamic analysis of a two-body point absorber wave energy converter. After systematically analysing the calculation results, another key conclusion was drawn that it is advantageous to use a more reliable contour line derived using the proposed new methodology for long-term dynamic analysis of wave energy converters. In summary, the proposed new adaptive KDE methodology is recommended to be utilised and to be refined continuously in future research work in the field of long-term reliability analysis of marine sustainable energy systems.

Multibody Analysis of Wave Energy Converters and a Floating Platform in the Time Domain

Generally, new and renewable energy systems generate electricity by installing and operating multiple modules simultaneously. In the Republic of Korea, recent studies and developments have focused on asymmetric wave energy converters (hereafter referred to as rotors) suitable for marine environments off the western coast of Jeju. These rotors are arranged on a large floating truss-structure platform and designed to harness electricity from the rotors’ pitch motion. However, when multiple rotors operate on a platform, their behavior diverges from that of a single module due to hydrodynamic interactions between them. Moreover, because the rotors are connected to the floating platform, their motion is influenced by the platform’s dynamics. In this study, a time-domain multibody motion equation was established to analyze changes in the behavioral characteristics of the rotors, both with and without a floating platform. The hydrostatic and hydrodynamic coefficients were derived in the frequency domain using WAMIT, a commercial code based on linear potential flow theory for three-dimensional diffraction/radiation analyses. The motion equation was then applied under regular and irregular wave conditions using OrcaFlex version 11.3, a marine systems design and analysis program. The resulting behaviors were compared to elucidate the influence of the platform and hydrodynamic interactions on the rotors’ performance.

Balancing power production and coastal protection: A bi-objective analysis of Wave Energy Converters

Wave Energy Converters (WECs) have the potential to serve dual purposes, generating power and protecting coastlines. Although traditionally the focus has been on maximizing power generation for cost-effectiveness, growing impacts of climate change have made coastal protection increasingly imperative. However, power production and coastal protection have been addressed separately, missing potential synergies. This paper addresses this gap by conducting a bi-objective analysis to investigate the interactions between power extraction and wave attenuation for a single Oscillating Surge Wave Converter (OSWC) and WEC farms of three and five units.A linear Power Take-Off (PTO) system, with passive and reactive control strategies, is examined. By varying the PTO parameters, we assess their influence on both power production and wave field attenuation. Results demonstrate a significant impact of the PTO choice on wave attenuation, with a similar trend observed for power production. This finding highlights the potential for a trade-off, where maximizing wave attenuation may come at the cost of moderate energy output. Furthermore, the interactions observed within the WEC farms enhance this trend.The study emphasizes the importance of a holistic approach to WEC technology development, promoting sustainable and resilient harnessing of wave energy resources, considering both power generation and coastal protection.

An adaptive binned kernel density estimation method for analysis of wave energy converters

ABSTRACT 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.

Constructal Design Applied to Geometric Shapes Analysis of Wave Energy Converters

This paper deals with numerical simulation and the geometrical analysis of an ocean Wave Energy Converter (WEC), which has as the operating principle the Oscillating Water Column (OWC). The goal was to evaluate the geometric shape influence of the OWC chamber in the hydropneumatic power available. Therefore, four geometric shapes were analyzed: i) Rectangle (RT), ii) Trapezium (TP), iii) Inverted Trapezium (TI) and iv) Double Trapezium (DT). For this, the OWC device was subject to a JONSWAP wave spectrum with peak period (TS) equal to 7.5 s and peak wave height (HS) equal to 1.5 m. To do so, Constructal Design was employed varying the Degree Of Freedom (DOF) H1/L (ratio between the height and length of the OWC chamber entrance). The problem constraints were the entrance area and the total area of the OWC chamber that were kept constant. For the numerical solution a Computational Fluid Dynamics (CFD) code, based on the Finite Volume Method (FVM),de0 was used. The multiphase Volume of Fluid (VOF) model was applied to tackle with the water-air interaction. The results indicated that when the Rectangle (RT) geometrical shape was employed an improvement of nearly 99% was achieved.

Introducing non-rigid body structural dynamics to WEC-Sim

This paper describes the development of a structural dynamics add-on to WEC-Sim, an open-source code dedicated to the dynamic analysis of Wave Energy Converters (WECs). When calculating the dynamic response of a body, WEC-Sim by default uses a rigid body dynamics approach. Such an approach ignores the potential effects of structural deformation on the WEC, which can in turn affect e.g. the distributed loads across the WEC and / or the individual (point) load sources that depend on the dynamic response of the WEC. Following a similar approach to tools used in the offshore wind industry, a structural dynamic add-on was developed using Code_Aster as the Finite Element (FE) solver to enable coupled hydro-elastic, time-domain analysis. The add-on was developed and tested using an example Oscillating Wave Surge Converter (OWSC) WEC model, currently being developed as part of the H2020 MegaRoller project. In the examples studied, the inclusion of structural dynamics is shown to affect the estimated peak Power Take-Off (PTO) loads, with variations in PTO force of over 10% being observed when structural dynamics are considered in the analysis.

Experimental analysis of wave energy converters concentrically attached on a floating offshore platform

This paper presents an initial experimental study of wave energy converters concentrically arranged and attached on a floating offshore platform model. The 1:27 scale model, has been designed, built and tested, in two main situations, without and with twelve cone shape wave energy converters. To simulate the power take-off system in each wave energy converter, rotational friction dampers have been installed on the joints of the floaters arms to the platform deck. The experimental results show that the interaction between buoys and platform have a positive effect on the platform heave and pitch motions. However, the reduction in heave and pitch motions of the platform, after installing the wave energy converter array, depends on the damping of the equivalent power take-off system. Thus, the effect of dampers in the motion of buoys is presented to allow an initial understanding of the required damping range of the power take-off system and related control strategies.

Validation of a CFD-based numerical wave tank model for the power production assessment of the wavestar ocean wave energy converter

CFD-based numerical wave tank (CNWT) models, are a useful tool for the analysis of wave energy converters (WECs). During the development of a CNWT, model validation is vital, to prove the accuracy of the numerical solution. This paper presents an extensive validation study of a CNWT model for the 1:5 scale Wavestar point-absorber device. The previous studies reported by Ransley et al. [1] and Windt et al. [2] are extended in this paper, by including cases in which the power-take off (PTO) system is included in the model. In this study, the PTO is represented as a linear spring-damper system, providing a good approximation to the full PTO dynamics. The spring stiffness and damping coefficients in the numerical PTO model are determined through a linear least squares fit of the experimental PTO position, velocity and force data. The numerical results for free surface elevation, PTO data (position, velocity, force), generated power and pressure on the WEC hull are shown to compare well with the experimental measurements.

Wave Energy Potential Assessment and Feasibility Analysis of Wave Energy Converters. Case Study: Spanish Coast

Lopez-Gutierrez, J.S.; Esteban, M.D., and Negro, V., 2018. Wave Energy Potential Assessment and Feasibility Analysis of Wave Energy Converters. Case Study: Spanish Coast. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp.1291–1295. Coconut Creek (Florida), ISSN 0749-0208.Wave energy is one of the marine renewable energy types, essential to achieve a sustainable development. Coastal countries need to know the wave energy potential along their coasts, so its contribution to the future electricity market is estimated. Spain has noticeable variations in its average wave climate, so it is essential to analyse numerous locations. For research purposes, wave energy potential is estimated based on data from the 15 Spanish State Port buoys currently in operation in deep waters. Because these buoys were set up at different times, with some moored around 2005, the sample between 2005 and 2015 is studied with the purpose of comparing results. REDEXT buoys, arranged from highest to lowest wave energy potential, are: Villano-Sisargas (56.84 kW/m), Cabo Silleiro (53.50 kW/m), Estaca de Bares (53.36 kW/m), Cabo de Penas (39.66 kW/m), Bilbao-Vizcaya (39.09 kW/m), Gran Canaria (23.71 kW/m), Mahon (16.21 kW/m), Cabo de Begur (13.95 kW/m), Golfo de Cadiz (12.70 kW/m), Dragonera (10.16 kW/m), Cabo de Gata (8.43 kW/m), Cabo de Palos (8.17 kW/m), Tenerife Sur (6.93 kW/m), Tarragona (6.14 kW/m) and Valencia (5.42 kW/m). Some buoys were moored in the 1990s allowing an analysis to be made of how the average wave climate has changed over the last years. Furthermore, a study is undertaken analysing the feasibility of different wave energy converters, specifically Pelamis 750 kW, Oyster 300 kW, Aquabuoy 250 kW, and SSG 20,000 kW, in the 15 buoy locations. Energy production and the capacity factor of all devices for the 15 locations are calculated, obtaining as a result that the most suitable device for all the locations studied is Oyster, and the least suitable is SSG. All the results are shown in different comparative tables and figures, with a summary of the most emphasizing information in each buoy.

Screening of Available Tools for Dynamic Mooring Analysis of Wave Energy Converters

The focus on alternative energy sources has increased significantly throughout the last few decades, leading to a considerable development in the wave energy sector. In spite of this, the sector cannot yet be considered commercialized, and many challenges still exist, in which mooring of floating wave energy converters is included. Different methods for assessment and design of mooring systems have been described by now, covering simple quasi-static analysis and more advanced and sophisticated dynamic analysis. Design standards for mooring systems already exist, and new ones are being developed specifically forwave energy converter moorings, which results in other requirements to the chosen tools, since these often have been aimed at other offshore sectors. The present analysis assesses a number of relevant commercial software packages for full dynamic mooring analysis in order to highlight the advantages and drawbacks. The focus of the assessment is to ensure that the software packages are capable of fulfilling the requirements of modeling, as defined in design standards and thereby ensuring that the analysis can be used to get a certified mooring system. Based on the initial assessment, the two software packages DeepC and OrcaFlex are found to best suit the requirements. They are therefore used in a case study in order to evaluate motion and mooring load response, and the results are compared in order to provide guidelines for which software package to choose. In the present study, the OrcaFlex code was found to satisfy all requirements.

Hydrodynamic Response Analysis and Wave Energy Absorption of Wave Energy Converters in Regular Waves

AbstractThe hydrodynamic response and the energy capture analysis of wave energy converters (WECs) with three degrees of freedom are conducted using a frequency domain approach. Considering the coupled hydrodynamic coefficients between surge and pitch, motion responses in surge, heave, and pitch are solved for the WECs. The power take-off (PTO) damping is taken as a linear function of the velocity. The power absorption and the absorption efficiency in surge, heave, and pitch are analyzed and compared. The effects of the geometry, diameter, draft, center of gravity position, and PTO damping on the hydrodynamic response, the power absorption, and the absorption efficiency of WECs are investigated. A cylinder, a halfsphere cylinder, and a cone cylinder are examined. From the total power absorption and the efficiency, the cone is the optimum geometry. For the cylinder, the power absorption in heave increases obviously with the increase of the diameter or the draft in a certain range. For the cone, the effect of diameter and draft on the power absorption in heave is relatively small. The cone has a better ability to absorb power in surge and pitch with an intermediate draft and diameter, and the power absorption peak in pitch decreases as Zg increases. The center of gravity position has no effect on the hydrodynamic response and the power absorption in heave. For a cylinder, the optimal PTO damping in heave is higher than that in pitch and surge. The optimum frequency in heave is lower than that in pitch and surge.

Structural Design and Hydrodynamics Analysis of Wave Energy Converter for Falculty of Engineering, Rmu

Due to the continuous fluctuation of the prices of oil and the environmental impact on the economy, a renewable energy becomes debatable issue. The generation of electricity by harnessing the power of sea wave has been the most prominent research into renewable energy for over decades. Various researches have used various power take off mechanisms systems for converting wave power into electrical power such as the pelamis, oscillating water column, Archimedes wave swing etc. In this research, linear generator power take of method is used to convert the motion of wave at its interaction with the devices into electricity since this method offers a great power output at a minimum wave energy power than other methods. Feasibility studies to ascertain the exact location for mooring of the components were conducted using google search. The analysis of a hybrid quantitative and qualitative method is applied. In this aspect, statistical analysis of sea wave data and the consumption of electrical gadget of the faculty engineering of Regional Maritime University were analysed in order to design a suitable wave energy converter. Hydrodynamic analysis of wave energy converter was determined in order to establish the velocity of sea wave, for due to the incident wave, the energy from sea wave and the electrical power generated by the generator as a result of sea wave energy.

Linear parametric hydrodynamic models for ocean wave energy converters identified from numerical wave tank experiments

Mathematical modelling of wave energy devices has many uses, including power production assessment, simulation of device motion and as a basis for model-based control design. Apart from computationally heavy approaches, such as those based on computational fluid dynamics (CFD) and smooth particle hydrodynamics (SPH), the vast majority of models employed in the simulation and analysis of wave energy converters (WECs) are based on boundary-element methods (BEMs). While BEM models have been shown to be useful, they have the inherent limitation that they are linearised around the still water level, with validity only on the immediate vicinity of this equilibrium point. In this paper, we develop a new modelling methodology, which combines the fidelity of CFD models with the computational attractiveness of BEM-type models. This flexible methodology can give representative linear models, or be extended into the nonlinear domain, as desired.

Control application and performance analysis of wave energy converters

A set of fifteen thermophilic fungi were isolated from various lignocellulosic and soil samples, among which Thermomyces lanuginosus VAPS24 showed highest xylanase activity. Xylanase production was optimized using various hybrid statistical tools and validated by batch fermentation using a 5 L bioreactor. Highest values of 130.98 U mL−1 and 115.37 U mL-1 xylanase production of was recorded in shake flask and fermenter, respectively. The xylanase from T. lanuginosus VAPS24 was purified by acetone precipitation followed by ultrafiltration, which resulted in five-fold (5.92) purification. Metal ions such as Hg2+, Fe2+, Cu2+ and reagents such as PEG-2000 and EDTA were inhibitory, whereas Zn2+, Na+, K+ and β-mercaptoethanol behaved as activators for xylanase activity. Thermostability of xylanase at 80 °C for 60 min, was enhanced by 1.52, 1.43 and 1.26 folds through the supplementation of polyols such as sorbitol, mannitol and glycerol, respectively. The agar-agar entrapment of xylanase increased its residual activity to 69.87%, as compared to 42.7% with free enzyme at 80 °C after 60 min. Our study provides a novel method of enhancing thermostability of xylanase from Thermomyces lanuginosus VAPS24, by addition of polyols or agar-agar entrapment, thereby facilitating various industrial applications.

Dynamic analysis of wave energy converter by incorporating the effect of hydraulic transmission lines

A heaving-buoy wave energy converter equipped with hydraulic power take-off is studied in this paper. This wave energy converter system is divided into five subsystems: a heaving buoy, hydraulic pump, pipelines, non-return check valves and a hydraulic motor combined with an electric generator. A dynamic model was developed by considering the interactions between the subsystems in a state space form. The transient pressures caused by starting/stopping the buoy or closing/opening the check valves were predicted numerically using the established model. The simulation results show that transmission line dynamics play a dominant role in the studied wave energy converter system. The length of the pipeline will not only affect the amplitude of the transient pressures but also affect the converted power. The variation of the time-averaged converted electric power with the pipeline length is estimated using the simulation method for the buoy exposed to one irregular sea state. Finally, it is suggested how reduced power efficiency due to the pipelines may be ameliorated.

Theoretical Analysis of Wave Energy Converter

Floating devices, such as a cavity resonance device take advantage of both the water motion and the wave induced motions of the floating body itself. The wave energy converter is known commercially as the WAGB(Wave Activated Generator Buoy) and is used in some commercially available buoys to power navigation aids such as lights and horns. This wave energy converter consists of a circular floatation body which contains a vertical center pipe that has free communication with the sea. A theoretical analysis of this power generated by a pneumatic type wave energy converter is performed and the results obtained from the analysis are used for a real wave energy converter for buoy. This paper presents the analysis results and the design method for the WEC(Wave Energy Converter), and the associate results are application to the commercially available WEC for buoy. Maximum performance of WEC occurs at resonance with driving waves. The analysis of WEC is performed with LabVIEW program, and the design method of WEC for buoy is suggested in this paper.

Including moorings in the assessment of a generic offshore wave energy converter: A frequency domain approach

A method to include the influence of mooring cables in the frequency domain analysis of wave energy converters is presented. In brief the method consists of: (i) A non-linear time domain solution of the mooring line in isolation and at an appropriate equilibrium condition. This is done by enforcing a sinusoidal displacement at the mooring attachment point in each translational degree of freedom. This is repeated at a number of frequencies. (ii) The amplitude and phase of the resulting force is recorded, allowing the equivalent linear resistive and reactive contribution of the mooring line to be estimated separately. Using results at a number of frequencies, frequency dependent impedance properties of the mooring cable can be estimated. (iii) Considering the attachment point and orientation of the mooring cables in a suitable equilibrium condition of the device, the contribution of each mooring cable is resolved to the global co-ordinates of the device and added to the frequency domain equation of motion. The method here is applied to a generic wave energy device based on a truncated vertical cylinder of 100 tonne displacement. The results for the unmoored device are compared to the same device with moorings of varying configuration. The results indicate that moorings may have a significant impact on the performance of devices of this scale, both beneficial and detrimental. The introduction of mooring terms can upset device symmetry and introduce significant cross coupling in the overall mechanical impedance of the device. Arrangements where this can benefit as well as detriment performance are studied.

Design and analysis of wave energy converter for a buoy

This paper introduces the design method for the practical use of a wave energy converter (WEC), and the associated results are application to the commercially available WEC for buoys. Peak performance of WEC occurs at resonance with driving waves. This type of resonance occurs when one of the parameters in an oscillator varies periodically. The water column in a WEC oscillates under the effect of gravity and the compression of an air chamber. The analysis of WEC is developed by assuming independence of the buoy heaving motion and the motion of the water column within the center cylinder. Results of analysis are then compared with simulation data, and applied to designing a WEC for buoys. Also, the effect of the various parameters such as cylinder length, period, mass and wave height is analyzed for the optimum design of a WEC. Finally, the research results are applied to a wave simulator with operating LabView, and some ideas are presented to the design method of WEC for buoy with simulation experiment.