Oscillating Water Column Device Research Articles

Laboratory modelling of nonlinear power take-off damping and its effects on an offshore stationary cylindrical OWC device

The accurate evaluation of the wave energy conversion of oscillating water column (OWC) wave energy converter has consistently plagued scholars. In this paper, an original and well-validated test platform is proposed for exploring the flow characteristic of a nonlinear power take-off (PTO) damping, with which a more accurate and stable measurement of captured energy is obtained in the laboratory modelling. This study utilizes ten orifices to comprehensively investigate the impact of the PTO damping on an offshore stationary cylindrical OWC device. The joint effect of the PTO damping with wave height (Hi) or draft of OWC (Dr) is examined. The damping coefficient Cf = 10350 is found to be the optimal damping coefficient, in terms of both the peak wave energy conversion and the efficient bandwidth. It is revealed that the variations of the PTO damping can regulate the effect of Dr and Hi on wave energy conversion. An appropriate reduction in PTO damping can alleviate the weak energy output caused by the increased Dr and Hi. The effect of increased Hi on wave energy conversion could be judged by the size relation of the maximum and minimum values of internal pressure data.

Study of the Geometry of an Oscillating Water Column Device with Five Chambers Coupled under Regular Waves through the Constructal Design Method

This research conducts a numerical study of a wave energy converter (WEC) device with five coupled hydropneumatic chambers, operating based on the principle of an oscillating water column (OWC). A turbine was not included, only considering the tube without it. The computational domain was defined by a wave channel housing an OWC device subjected to regular incident waves. The central objective was to assess the impact of chamber geometry on maximizing the total hydropneumatic power in energy conversion. The numerical simulations consider the pressure, mass flow rate, and total hydropneumatic power, with the latter being the performance indicator. To determine the geometries to be analyzed, the Constructal Design method was employed in conjunction with the exhaustive search optimization method to maximize the performance indicator. The degrees of freedom defined were the ratios between the height (Hn) and the length (Ln) of the hydropneumatic chambers (Hn/Ln, where n varies from one to five). Based on the results of the mass flow rate and pressure, their influence on power was evaluated. It was observed that the influence of the degrees of freedom on the pressure difference, mass flow rate, and hydrodynamic power was quite similar, displaying an increase for low ratios of Hn/Ln up to a maximum magnitude and followed by a decrease in magnitude. The best performance was achieved for the geometric configuration with Hn/Ln = 0.2613 (Hn = 5.0625 m and Ln = 15.8219 m), representing an improvement of 98.6% compared to the worst case analyzed.

Multiple moonpools within a vessel free to heave and pitch: An experimental study

Moonpools in marine vessels and offshore platforms are vertical openings through the structure used to support underwater operations. Experimental investigations of multiple moonpool resonant responses coupled with vessel heave and pitch motions are presented in this study. For three moonpools at forward, central, and aft locations of a rectangular vessel, the simultaneous location-dependent free surface response amplitudes and oscillation phases are compared for a range of incident wave frequencies in the piston mode range. For the vessel free to heave and pitch, the central moonpool has the highest response amplitude; whereas, a previous study with fixed vessel (Garad et al. 2023) showed that the largest free surface responses are observed in the forward moonpool. Due to coupled hydrodynamic interactions between the moonpool oscillations and the vessel motions, the moonpool resonance frequency is linked with the vessel heave response. Multiple response amplitudes peaks are observed in the forward and aft moonpools due to body motions. The non-dimensional response amplitude increases nonlinearly with decreasing wave steepness close to the resonance frequency. The multiple moonpool oscillations show distinct phase differences from one another and with the outer wave, the individual values depending on the incident wave frequency. Considering the vessel motions, comparison with experiments without moonpools shows that the pitch response is increased due to multiple moonpool oscillations. The hydrodynamic interactions between multiple moonpools and a floating vessel have prospective applications in the case of marine platforms, where the resonant motions can be used for wave energy conversion through oscillating water column devices.

A new numerical modelling framework for fixed oscillating water column wave energy conversion device combining BEM and CFD methods: Validation with experiments

The Oscillating Water Column (OWC) wave energy converter has been shown to have high potential, thus rendering extensive development in recent years. In order to further accelerate its development, highly accurate yet computationally efficient tools are necessary particularly when studying the interaction of multiple OWC devices. This paper proposes a new framework for fixed OWC devices with an orifice, that uses the input from a high fidelity non-linear numerical model to improve the accuracy of a low fidelity linear numerical model keeping computational costs low. This is done by accounting for the non-linearities in the pressure-flow of an orifice in the input to the linear numerical model. Experimental data is used to validate the framework, thus providing an accurate and computationally efficient linear numerical model, that can be used for the preliminary analysis of fixed OWC devices.

Numerical analysis of 3D hydrodynamics and performance of an array of oscillating water column wave energy converters integrated into a vertical breakwater

Performance and hydrodynamics of an array of Oscillating Water Column (OWC) Wave Energy Converter (WEC) integrated into a vertical breakwater is studied. The FLUENT® software, in which the numerical model is based on the Reynolds-Averaged Navier-Stokes equations and the Volume of Fluid method for free surface flow modeling, is used in a 3D numerical wave tank. Three vertical breakwater configurations subject to the action of incident regular waves with periods from 6 to 12 s are studied: normal breakwater, with vertical walls parallel to the direction along the breakwater length; and two novel breakwater geometries, partially and fully convergent breakwaters, whose converging vertical walls are inclined θ in relation to this direction. Different spacing S from 0 to 20 m between the array of OWC devices and two converging wall angles θ, 30 and 45°, are investigated. Firstly, analysis of the influence of S for the normal breakwater shows that the vertical wall concentrates naturally a higher quantity of the incident wave energy inside OWC chamber devices and, consequently, increases their efficiencies. This effect is intensified as the spacing S increases. Secondly, analyses of the partially and fully convergent breakwaters allow concluding that these novel geometries, which direct an amount of incident wave energy into the OWC chamber, increase significantly the efficiency of the array of the OWC devices at the range of the wave periods. The highest performance of OWC device is obtained by the fully convergent breakwater with S = 20 m and θ = 45°, once 10 OWC devices inserted in a breakwater 300 m long have the same efficiency of 20 OWC devices inserted into the normal breakwater.

Wave Energy Conversion through Oscillating Water Columns: A Review

An oscillating water column (OWC) is designed for the extraction and conversion of wave energy into usable electrical power, rather than being a standalone renewable energy source. This review paper presents a comprehensive analysis of the mathematical modeling approaches employed in OWC systems, aiming to provide an in-depth understanding of the underlying principles and challenges associated with this innovative technology. A prominent classification within the realm of wave energy devices comprises OWC systems, which exhibit either fixed or floating configurations. OWC devices constitute a significant proportion of the wave energy converter prototypes currently operational offshore. Within an OWC system, a hollow structure, either permanently fixed or floating, extends below the water’s surface, creating an enclosed chamber where air is captured over the submerged inner free surface. This comprehensive study offers a thorough assessment of OWC technology in conjunction with air turbines. Additionally, the investigation delves into theoretical, computational, and experimental modeling techniques employed for analyzing OWC converters. Moreover, this review scrutinizes theoretical, computational, and experimental modeling methodologies, providing a holistic understanding of OWC converters. Ultimately, this work contributes a thorough assessment of OWC technology’s current state, accentuating its potential for efficient wave energy extraction and suggesting future research avenues.

Hydrodynamic and energy-harvesting performance of an isolated oscillating water column device: An experimental study

Most previous experimental studies on the hydrodynamic and aerodynamic performances of an oscillating water column (OWC) wave energy converter were conducted in a wave flume. In this study, an experimental study on an isolated OWC plant is carried out in a wave tank. The interactions between the OWC system and incident regular and irregular waves are analyzed by measuring the surrounding wave fields using a wave gauge array. The wave distribution patterns and reflection ratios of the OWC model are presented. In addition, the free-surface elevation, air pressure varying amplitude, turbine torque output, and relative capture width ratios and efficiencies in regular and irregular wave scenarios are measured and analyzed. The operating performances of the OWC model are analyzed and compared to the results derived from the flume tests. An overall performance reduction of over 20% can be observed in the wave tank tests. In addition, the representative results of the overall capture width ratio of the OWC model derived from irregular wave tests are corrected from the scaling effects caused by the similarity contradiction.

Pressure Pulsation Analysis of Oscillating Water Column Rotor Eccentricity Based on the Pulsation Tracking Network Method

An oscillating water column (OWC) is typical of axial rotor turbines, which are used to convert ocean wave energy into electrical energy. This device impacts downstream pressure pulsations when its rotor becomes eccentric. This study compared the details of pressure pulsations downstream of eccentric and non-eccentric rotors under three operating conditions: low flow A, high-efficiency flow B, and high flow C. Computational fluid dynamics (CFD) simulations based on the pulsation tracking network (PTN) method were used for the OWC device to compare the experimental results. The results indicate downstream pressure pulsations were mostly dominated by the blade frequency in non-eccentric low-flow cases. In the other eccentric operating conditions, downstream pressure pulsations were mainly dominated by the 2-, 3.6-, 6-, and 7-times rotation frequencies and the 0.5-times blade frequency. The phase change of downstream pressure pulsations in eccentric and non-eccentric conditions is consistent with the flow direction. The phase change is relatively uniform and steady before eccentricity and becomes turbulent after eccentricity, which affects its steadiness. In this study, the OWC device did not significantly change with or without rotor eccentricity at a 1-time blade frequency intensity; however, at a 1-time rotation frequency, the OWC device showed a significant increase in the pressure pulsation amplitude after rotor eccentricity. The study of the dominant frequency, amplitude, and phase of pressure pulsations in OWC devices with eccentric rotors can help prevent excessive pressure pulsations that can lead to incidents.

3D Numerical Modeling and Geometry Optimization of an Oscillating Water Column Device in Sloshing Conditions Using Openfoam and Genetic Algorithms

Among various types of wave energy converters, the oscillating water column (OWC) has attracted significant research attention. In this paper, a 1:10 scale OWC with dimensions of 100×100×160 cm, variable inlet height and draft was numerically studied. Based on the tests conducted, it was found that the wave amplitude in the range of Caspian Sea waves decreased with the increase of wave frequency, to the extent that at the sloshing frequency, the system efficiency dropped significantly. To solve this problem, changes in the geometry of the device were studied, and numerical simulations were performed at the highest frequency using OpenFOAM software. Using Reynolds-averaged Navier-Stokes (RANS) equations, numerical simulations were performed in 3D, two-phase, and turbulent flow conditions. Changing the geometry was initially investigated by adjusting the height of the OWC inlet duct, and then by adding an inlet at the different angles of 0, 20, and 40 degrees. The results showed that by increasing the height of the inlet by 10 cm while keeping the water depth and wave conditions constant, the maximum output power of the system increased by 54%. However, after the optimization of the inlet duct, it was found that the best angle for an inlet duct is 30°, compared to the case without an inlet, which increased the maximum output power by up to 13% and slightly reduced the sloshing by more than 50%.

Characteristics of vortex evolution around a cylindrical oscillating water column device: An experimental study

The utilization of oscillating water column (OWC) converters with existing hydraulic/coastal structures has emerged as a crucial approach for the development of economically viable and environmentally sustainable green power generation devices. Integrating OWC converters into offshore wind turbine (OWT) monopiles is a promising solution in wind power industrialization. This paper presents an experimental investigation of the flow characteristics of an OWT-OWC system under regular wave conditions, focusing on the evolution of vortex structures. Particle image velocimetry (PIV) is employed to measure the flow field surrounding the OWC converter under different wave heights and wave period conditions. Based on the measured velocity field data, the evolution of vortices is examined using the Q-criterion. The results indicate that the wave period significantly affects the flow patterns. Specifically, an increase in wave period enhances the three-dimensional nature of the flow field. The vortices outside the OWC chamber are observed to connect and form a three-dimensional vortex ring, hindering efficient wave energy conversion. Conversely, the variation in wave height exhibits limited impact on the flow field evolution. However, as the wave height increases, the vortex strength and asymmetry experience a significant rise, making it difficult to form a stable three-dimensional vortex ring. Moreover, based on optimal geometric design considerations, it is recommended to increase the lateral angle and height of the sidewall openings to prevent vortex ring formation and minimize obstructions, while ensuring the structural safety of the OWT.

Design an Optimum Air Duct for Oscillating Water Column Wave Energy Device

Oscillating Water Column (OWC) is a technology that harvests wave energy to generate electricity. It works by harnessing the wave-induced pressure oscillation in the opening mouth of OWC. The oscillation of the pressurised air is extracted using a turbine placed at the top of the OWC structure. Although OWC has been studied for many years, designing an optimum air duct for such devices is still an open research area. The air duct plays a crucial role in the energy conversion process, as it is responsible for directing the airflow towards the turbine, and its design can greatly affect the performance and efficiency of the system. The article aims to study how the air duct design impacts the power output form. Moreover, the result will be compared with the conventional air duct design. The OWC performance is analysed using Computational Fluid Dynamic (CFD) software to identify which shape of the air duct has high efficiency. Autodesk Inventor is used to design the OWC devices modified from the basis design. Then these designs are imported into CFD software to simulate and obtain the energy extraction result. The CFD software is chosen to simulate the hydrodynamics problem. In this study, the oval design shows significant improvement in the energy extraction performance compared to the basis design. The oval design managed to produce 9.81, 10.02, and 11.66 J/kg of mechanical energy compared to 9.81, 9.82, and 10.04J/kg as prompted by the basis air duct design at the wave height of 0.2505, 0.75, and 2.25m, respectively. The result shows that the non-edge produces higher air pressure than the sharp edge of the air duct shape. Thus, the oval air duct design is more efficient, and it may increase the performance of the OWC wave energy converter device at a low wave height of 0.75 m.

Experimental and numerical investigation on hydrodynamic performance of a 3D land-fixed OWC wave energy converter

The hydrodynamic performance of a land-fixed oscillating water column (OWC) wave energy device was thoroughly investigated under various wave conditions and geometric parameters through both experimental and numerical studies in a three-dimensional (3D) wave tank. The study involved the measurement and comparison of water surface elevation, air pressure in the OWC chamber, and hydrodynamic efficiency with the results obtained from the 3D Higher-Order Boundary Element Method (HOBEM). The influences of 3D effects, incident wave amplitude, front wall draught, and incident wave angle on the hydrodynamic performance of the OWC device were analyzed. The results demonstrate that, under actual sea conditions, the 3D effects significantly affect the hydrodynamic efficiency of the OWC, making it exceed unity near the resonance frequency. On the other hand, the incident wave angle was found to have minimal effect on the resonant frequency and varied trend of efficiency. However, the hydrodynamic efficiency decreases with increasing incident wave angle. These results highlight the importance of the consideration of the 3D effects and incident wave angles in optimizing the design and performance of fixed OWC wave energy devices.

Numerical investigation on the hydrodynamic performance of a land-based OWC system with multi-chamber modules

Modular design of wave energy converters (WECs) can offer a promising scheme to improve the economic competitiveness of wave energy by reducing the levelized cost of energy. In this study, the hydrodynamic performance of a land-based oscillating water column (OWC) system with multi-chamber modules is evaluated to optimize the layout and design of the system, the OWC structure is extended to five-chamber modules. A two-dimensional wave flume is developed using the high-order boundary element method to simulate the interaction of the incident waves with the OWC device based on the fully non-linear potential flow theory. The proposed numerical model is validated by published experimental data. It is concluded that the two-chamber installation provides superior hydrodynamic performance compared with the single-chamber OWC. The five-chamber OWC system is more suitable for energy capture in low-frequency wave conditions, where the first and last chambers are dominant in energy extraction. From the perspective of energy conversion efficiency and economy, the two- and three-chamber systems are most suitable for targeting low and high frequency waves in the tested conditions, respectively. Additionally, the resonant frequency of the single-chamber module plays a decisive role in the energy capture of the OWC system, and a chamber with a low resonant frequency and a small orifice opening ratio should be selected as the module unit. This paper provides valuable guidance for the modular application of OWCs and the arrangement of multiple chambers.

Aerodynamic performance and noise emission of different geometries of Wells turbines under design and off-design conditions

The path to the World’s energy system decarbonisation requires the contribution of a mix of renewable energy sources. In particular, wave energy and oscillating-water-column (OWC) devices can be significant contributors. However, they are still in an early stage of development, and their levelized cost of energy (LCOE) is still too high to compete in the utility market. The Wells turbine is an attractive solution to reduce the LCOE of OWC devices. Completing the available information in the literature on the performance of different Wells arrangements is a necessary step towards decision-making on which configuration is most cost-efficient given the hydrodynamic characteristics of a particular OWC wave energy converter (WEC). Furthermore, there is a research gap on these devices’ acoustics, which needs to be filled, given the impact noise might have on surrounding ecosystems. This study investigated the aero-acoustics performance of four Wells turbine geometries, including monoplane and biplane turbines with and without guide vanes. Experimental tests of the turbine models were conducted in an open-circuit test rig under design and off-design flow conditions. The research provides accurate aerodynamic data on very high flow rate (pressure) coefficients, essential to turbine-generator control algorithms and OWC WECs wave-to-wire numerical models. A specific noise level definition was inferred by analysing the aerodynamic noise sources in Wells turbines. This allows the prediction of noise emission from geometrically similar turbines of different sizes and rotational speeds from the experimental noise data collected with the tested Wells turbines.

Theoretical approach to the scale effects of an OWC device

This research deals with the dynamic similarity problem for Oscillating Water Column (OWC) devices, for which air is the fluid that is subject to thermodynamic transformations in the inhalation/exhalation phases. Based on the differential problem, both linearized and full-nonlinear, the scale ratios satisfying similarity are calculated, with specific reference to the case where constraints are present on some of these scale ratios. The paper proceeds to identify the numerous processes of a turbulent interface that scales differently between model and prototype. With the aim of bringing to front the influence of the scale effects on featured aspects of the thermodynamic process involved, it is proposed that a non-equilibrium thermodynamics approach can be more comprehensive and representative not only of transformations, but also of scaling. The study reveals that in the case of OWC thermodynamics, non-equilibrium states which would be less evident in scaled model, would become more relevant as the scale is increased towards the size of the prototype, with consequences on performance.

Influence of circuit on power generation performance of wave energy power generation device using oscillating water column technology

In order to study the influence of the load circuit on the system efficiency and power oscillation of the oscillating water column device, a unified modeling model of the oscillating water column device is built for simulation. According to the coupling relationship in various fields of the oscillating water column device, the differential equation of motion of the turbine generator set is established. The power plant components and systems are modeled by Modelica language. Based on this system, the system-level simulation is carried out and the load circuit is optimized. In addition, experimental tests of the traditional load circuit and the modified load circuit are carried out. Results indicate that the modified load circuit can increase the speed of the turbine to better follow the airflow and balance the system damping, thereby improving the system efficiency. Increasing resistance can reduce the fluctuation of output electric power. Different battery, resistance and generator parameters can cause differences in system efficiency. The research results provide a reference to improve the performance of oscillating water column device.

Performance of OWC device under Stokes second-order waves

The present work simulates the flow behavior in the system having oscillating water column (OWC) device for wave energy conversion using numerical modelling. To achieve this, the OWC device is structured inside the 2-dimensional numerical wave tank (NWT). Using the ANSYS Fluent software and the multiphase-based CFD technique, the issue is resolved. Unsteady, transient, and pressure-based solvers are included in this work. In this numerical model, the governing equations are based on Reynolds Averaged Navier-Stokes (RANS) equations with the Shear Stress Transport (SST) model, to capture the turbulence effect and the interface of 2-phases are implicitly captured by using volume of fluid (VOF) method. Using an open-channel wave generator, this study generates nonlinear “second-order Stokes waves”. In addition, the impact of nonlinearity on the “free surface description” at specific locations, the vertex average of total pressure near the air-duct, and the vertex average of y-velocity through the air-duct per unit width of the OWC device are investigated in detail. The outcomes indicate that the OWC device will consistently extract energy over an extended period of time.

Optimization of the chamber of OWC to improve hydrodynamic performance

Nearly 71% of Earth's surface area is occupied by the ocean, which is abundant in energy, with wave energy being one of its essential components. As a result, the investigation of wave energy generation devices is a crucial matter. This paper analyzes the performance of the oscillating water column (OWC) wave energy conversion device under the influence of unidirectional regular waves and optimizes the OWC device accordingly. The impact of different structural dimensions on the first-stage conversion efficiency of the OWC device is determined. Moreover, to evaluate the performance of the OWC device in real sea conditions, the wave climate at Sanmen Gorge is employed as the experimental parameter. The study examines the performance and characteristic response of the OWC device regarding the air chamber width, thickness of the front wall, and draught of the front wall. The findings reveal that the width of the OWC air chamber and the draught of the front wall significantly affect the OWC performance. Decreasing the width of the air chamber results in a stable horizontal plane, eliminating the occurrence of standing wave phenomena. As the draft of the front wall increases, the reflection coefficient of the air chamber gradually increases, and it becomes difficult for the wave to penetrate into the air chamber section. The Latin hypercube design experiment method was used to select experimental points and establish quadratic polynomial response functions. The OWC device was optimized based on multi-island genetic algorithm. The simulation and fault tolerant optimization methods presented in this paper can be widely used to improve system performance.

Analysis of the viability of a radial Double Decker Turbine for application in Oscillating Water Column devices

Oscillating Water Column (OWC) devices are the most widespread among the different systems developed to harness the wave energy available on our coasts. Air turbines, normally used as Power Take Off (PTO) in these devices, are their most controversial part. Unidirectional turbines were first used with rectifying valves to take advantage of both characteristic operating stages of the OWC: exhalation and inhalation. The use of valves was quickly discarded and bidirectional turbines, which rotate in the same direction regardless whence the flow comes, were adopted as the most common solution despite reaching lower efficiencies than unidirectional ones. The Twin Turbine Configuration (TTC), based on the use of two unidirectional turbines, emerged then as a promising system, its main drawback being the duplicity of the equipment. The Double Decker Turbine (DDT) concept has been recently introduced to overcome these limitations since it combines in a single design the two typical solutions: self‐rectifying behaviour and the use of unidirectional turbines. In this work, the performance of a radial DDT, composed of an InFlow Radial (IFR) turbine and an OutFlow Radial (OFR) turbine, is assessed. A CFD model is used to design and optimize an IFR turbine to be mounted in combination with an OFR turbine taken from the literature. Finally, a non‐steady analysis is carried out assuming sinusoidal flow conditions. Results demonstrate that this radial version of the DDT could compete with its axial version and with other alternatives.

Numerical modelling of a box-type and bottom-detached oscillating water column wave energy conversion device: a comparison with experimental data and between BEM and CFD numerical modelling

Utilization of Boundary Element Method (BEM) based on linear potential flow for modelling Oscillating Water Column (OWC) devices has gained popularity in the last two decades. The commercial BEM solver WAMIT has been used widely for modelling OWCs and validated using experimental modelling (Delauré et. al. 2003, Bingham et. al. 2015, Faÿ 2020). The open-source BEM solver NEMOH has however been mostly ineffective in modelling OWCs since the main approach adopted previously modelled the imaginary piston as a thin disk. In this research, the multi-body interaction problem has been adopted in modelling a box-type and bottom-detached OWC device in NEMOH, where the imaginary piston has been modelled to the length of the internal water column (Penalba et.al. 2017) and compared with experimental data. A further comparison is drawn with the numerical method of Computational Fluid Dynamics (CFD) , which has shown to be accurate for modelling OWC devices (Simonetti et. al. 2015), yet requires significantly higher computational resources than BEM. A two-dimensional CFD numerical wave tank, developed generating and absorbing waves with the waves2Foam toolbox (Jacobsen et al., 2012) of the open-source package OpenFOAM, is used for comparative purposes.
 REFERENCES:
 Delauré, Y. & Lewis, A. (2003). “3D hydrodynamic modelling of fixed oscillating water column wave power plant by a boundary element methods.” Ocean Engineering. 30. 309-330. 10.1016/S0029-8018(02)00032-X.
 Bingham, H.B.; Ducasse, D.; Nielsen, K. et al (2015). “Hydrodynamic analysis of oscillating water column wave energy devices.” J. Ocean Eng. Mar. Energy 1, 405–419 (2015). https://doi.org/10.1007/s40722-015-0032-4
 Faÿ F.-X. (2020). “Modelling and Control for the Oscillating Water Column in Wave Energy Conversion.” PhD Thesis, Universidad del País Vasco.
 Jacobsen, N.G., Fuhrman, D.R. & Fredsøe, J., (2012). “A wave generation toolbox for the open-source CFD library : OpenFoam”. International Journal for numerical methods in fluids, 70, pp.1073–1088.
 Simonetti, Irene & Cappietti, Lorenzo & Elsafti, Hisham & Oumeraci, Hocine. (2015). “Numerical Modelling of Fixed Oscillating Water Column Wave Energy Conversion Devices: Toward Geometry Hydraulic Optimization.” 10.1115/OMAE2015-42056.
 Penalba, M., Kelly, T., Ringwood, J. 2017, NEMOH for Modelling Wave Energy Converters: A Comparative Study with WAMIT. 12th European Wave and Tidal Energy Conference , Cork, Ireland. https://www.researchgate.net/publication/319160625.