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The oscillating‐water‐column (OWC) spar‐buoy is a type of wave energy converter that may exhibit undesirable large roll and pitch amplitudes caused by a dynamic instability induced by parametric resonance. The occurrence of this phenomenon not only reduces the power extraction but significantly increases the structural loads on the buoy, the turbine rotor and on the mooring system. The paper compares the parametric resonance behaviour of two configurations of an OWC spar‐buoy using experimental data obtained in a wave flume at a scale of 1:100. The configurations investigated were: (1) closed and (2) fully open‐air chamber. The experimental tests covered a wide range of regular and irregular waves, as well as in free decay experiments. Results showed that opening the air chamber reduces the coupling between the buoy and the OWC within, thus shifting the damped natural heave frequency of the system in comparison with the closed chamber configuration. This effect changes parametric resonance characteristics of the two configurations due to the coupling between roll/pitch and heave modes. Moreover, for specific wave frequencies, the occurrence of parametric resonance observed when the chamber is closed do not occur while the air chamber is fully open. These results suggest the possibility of controlling a pressure relief valve installed on top of the device to reduce parametric resonance whenever this dynamic instability is detected.

One method of measuring precipitation and wind over the ocean is through analysis of the underwater ambient acoustics. In this study, the ambient ocean noises recorded by a passive aquatic listener (PAL) in the Mediterranean are used to compare the effectiveness of the machine learning techniques for measuring the wind speed and precipitation rate with the empirical methods from previous works. The data were collected over the timeframe of June 2011 to May 2012 and included two storms that caused severe coastal flooding in Genoa, Italy. A spar buoy at the surface above the PAL provided high-quality in situ measurements to act as the reference data for model training and validation. The results using the machine learning models show correlation coefficients of 0.95 between the acoustic data and wind speed and a reduction in unexplained variance by over a third from previous methods. For precipitation, CatBoost and random forest models are used to measure the total precipitation for 12 events using leave-one-event-out cross-validation, demonstrating mean errors of 28% and 34% and median errors of 18% and 17%, respectively. The ability to measure wind and precipitation by applying machine learning on data from underwater acoustic recorders shows potential to help improve in situ measurements over oceans globally.

Feasibility study of a long-lived autonomous sea observatory on the basis of a stabilized spar buoy is presented. The buoy design is developed to sustain harsh weather and hydrodynamic conditions of near-shore of the North-Eastern Black Sea with expected life-time over 10 years. It has the following dimensions: diameter of 2.4 m, length of 45 m, prestressed concrete bearing structure length of 33 m, floating draft of 30 m, 12 m steel mast, dry weight of about 120 tonnes. The buoy is equipped with mooring anchors and three submerged floatages for its stabilization and minimization of an observational noise during measurements. To perform design testing, elaborate technical requirements and adopt particular technological and logistical solutions numerical simulations are conducted. The strength and durability of the buoy are assessed primarily through a random response analysis of its stress-strain state under irregular wind-wave conditions with requirements of actual standards and codes also taken into consideration. Characteristics of near-shore environment, in particular, mean and extreme wind-wave conditions, are specified for a site of the Field Research Facility of the Southern Branch of the P.P. Shirshov Institute of Oceanology of Russian Academy of Sciences (the Gelendzhik Bay, Russia) using historical data and theoretical models of wind-wave growth in the near-shore. Low-cost concrete buoys of the proposed design can be used both as autonomous sea stations and as units of networks for marine studies and sea environment monitoring. Dynamical characteristics of the buoy ensure high-precision measurements and its applications in telecommunication, maritime safety, etc.

Oshore wind turbines have the potential to capture the high-quality wind resource. However the signicant wind and wave excitations may result in excessive vibrations and decreased reliability. To reduce vibrations, passive structural control devices, such as the tuned mass damper (TMD), have been used. To further enhance the vibration suppression capability, inerter-based absorbers (IBAs) have been studied using the structure-based approach, i.e. proposing specic stiness-damping-inertance elements layouts for investigation. Such an approach has a critical limitation of being only able to cover specic IBA layouts, leaving numerous benecial congurations not identied. This paper adopts the newly introduced structure-immittance approach, which is able to cover all network lay out possibilities with a predetermined number of elements. Linear monopile and spar-buoy turbine models are rst established for optimisation. Results show that the performance improvements can be up to 6.5% and 7.3% with 4 and 6 elements, respectively, compared to the TMD. Moreover, a complete set of benecial IBA layouts with explicit element types and numbers have been obtained, which is essential for next step real-life applications. In order to verify the eectiveness of the identied absorbers with OpenFAST, an approach has been established to integrate any IBA transfer functions. It has been shown that the performance benets preserve under both the Fatigue Limit State (FLS) and the Ultimate Limit State (ULS). Furthermore, results show that the mass component of the optimum IBAs can be reduced by up to 25.1% (7486kg) to achieve the same performance as the TMD.

The performance of an array of floating Oscillating Water Column (OWC) devices, known as spar-buoy OWC, is analysed for a configuration with inter-body mooring connections. This configuration has the potential of being a more economically viable solution due to drastic reductions in the amount of mooring cables, when compared to independently moored configurations. Numerical simulations for an array of independently moored devices and for an unmoored array are presented and compared. The frequency-domain model considered throughout this paper uses linear hydrodynamic and hydrostatic forces; real fluid viscous effects are accounted for by using a linear approximation, while the mooring connections are linearised using perturbation theory. For regular waves, by including an inter-body mooring system, the average heave response amplitude of the array’s three buoys decreases by approximately 6 . 8 % at the peak frequency, while the average capture width of the three buoys remains approximately the same. The influence of the wave incidence angle on the array performance is evaluated. A stochastic analysis is conducted to assess the behaviour of the array with mooring connections. A comparative analysis between the performance of an array with inter-body mooring connections and an isolated device suggests a positive park effect for a realistic wave climate.

Conventional tide gauges are usually housed along the coast. Satellite altimetry works well in the open ocean but poorly near the coast due to issues such as signal contamination by land returns. T...

This paper presents a new frequency domain modeling approach for floating offshore wind turbines with coupled wind turbine, floating platform, and mooring system sub-models. The sub-models are generated using the validated numerical tools FAST and WAMIT to obtain the frequency domain aerodynamic and hydrodynamic characteristics, respectively, for any given design candidate. The turbulent wind and irregular wave loads are incorporated in the frequency domain model using wind and wave power spectral density functions, the JONSWAP and Kaimal spectra, respectively. To validate the proposed 6 DOF frequency domain framework across standard operational environmental conditions, predicted system responses of a 5 MW NREL offshore wind turbine with three classes of reference platforms including the OC3-Hywind, the MIT/NREL TLP, and the OC4-DeepCwind semisubmersible were compared to the outputs of 6 DOF and 22 DOF FAST time domain simulations. The comparison over an aggregate of eleven environmental conditions focused on differences in predicted platform rigid body motions and structural considerations including platform surge, roll, and pitch, and rotor thrust, total blade root and tower base bending moments/fatigue loads, fairlead and anchor tensions/fatigue loads. In terms of platform motions, the worst match of frequency and time domain model predictions was seen for the OC4-DeepCwind semisubmersible with errors of 13.2% in peak displacement values. The frequency domain model predictions of rotor thrust, blade root and tower base bending moments demonstrated the largest error in the case of the OC3-Hywind spar buoy with the peak loads differing by up to 12.8%. Errors in the predictions of maximum fairlead and anchor tensions were less than 11.5% with maximum error occurring for the MIT/NREL TLP. In terms of fatigue load comparison, the blade root and tower base fatigue load predictions showed less than 9.8% errors for all the reference platforms. Comparison of the fairlead and anchor fatigue loads showed that errors were less than 13.8% with the largest error seen for the OC3-Hywind spar buoy platform. Overall, the frequency domain model provides reliable means for assessing platforms dynamics at the conceptual stage of the design process.

The main topics of this paper is the investigation of motion characteristics of the spar-buoy with ring fin motion stabilizer, which is developed to use as a platform for wind observation with a doppler lidar in shallow sea, some mooring conditions to apply it for deep sea. Four different mooring conditions are applied the spar-buoy and it motion in a designed sever wave condition are measured in the towing tank of Osaka Prefecture University. The results show that the amplitude of pitching in deep sea is smaller than the results in shallow sea, even if the wave condition in deep sea are severer than that in shallow sea. From further investigation about the effects of four different mooring conditions on motion characteristics, it has that the center of pitching at four mooring conditions are almost same but the amplitude of pitching is smaller by changing the mooring point and the intermediate sinker position.

The purpose of this study is to propose an optimal design method of the spar-buoy with ring-fin motion stabilizer for shallow sea and its mooring system, in order to avoid the occurrence of snap load. The mechanism of occurrence of snap load is investigated by model tests, and design parameters for avoiding the occurrence of snap load are investigated. From the observation of model’s motion, it has been realized that the snap load is caused by the tension of mooring line to stop the buoy’s horizontal motion, which relaxes the mooring line. Moreover, it has been confirmed that the horizontal motion is caused by the horizontal forces acting on the center pipe and float of the buoy, which relates to the acceleration component of wave excitation forces. In this paper, the effects of changing of design of the buoy (: diameter of center pipe and float, size of stabilizer, density of the buoy, length of mooring line) on avoiding or reducing snap load are investigated by using a numerical simulation (OrcaFlexver.11.0b), and the wear amounts are also estimated by using an empirical method (Takeuchi et al., 2019). From the results, it is confirmed that changing the buoy’s motion mode by shortening mooring line is effective to avoiding the occurrence of snap load, and to reduce the wear amount of the mooring line.

The FLoating Instrument Platform (FLIP), a seagoing vessel managed by the Scripps Institution of Oceanography, in La Jolla, California, offers an unorthodox vantage point on the sea. In its horizontal conformation, FLIP travels like an ordinary oceangoing craft. But by “flipping” 90 degrees into a vertical position once it arrives at its destination—with all the furniture and instrumentation inside swiveling correspondingly—it becomes an enormous spar buoy, more or less stationary in the wave field. With most of the platform’s 108-meter length below the surface, scientists can work in a stable environment, which helps them study sea surface phenomena such as waves against a largely unwavering baseline. This article offers an anthropologically informed media studies account of work on FLIP, as the author reports on working ethnographically alongside wave scientists in this Escheresque environment, a setting that often sees scientists shifting between aspirations to steady objectivism and moments of fleeting but motivating wonder. Placing FLIP in a longer history of physical oceanography, the author also argues that what wave scientists take ocean waves to be has been strongly imprinted by the techniques and technologies—mathematics, photography, spectral analysis, wave tanks—through which waves have been studied and come to be known. Wave science also inherits knowledge from mid-twentieth-century ocean observation projects in the Pacific Ocean that were conditioned by Cold War American maritime expansion. The paper suggests that the technological mediations, orientations, and re-orientations offered to scientists at sea on FLIP may serve as allegories for apprehending American oceanography’s oscillating visions of the relationship of science to society, of present research to future implications, and of objectivity to politics — visions that come into focus as scientists (and their anthropological interlocutors) switch, alternate, and flip their paradigm scripts, their frames of epistemic reference.

The hydromechanics analysis of floating offshore wind turbines is a fundamental and time consuming part of the design process, traditionally analysed with methods of computational fluid dynamics. In this work, an alternative computational framework is suggested, able to significantly accelerate the design process with minimal accuracy loss. Through the use of a state-of-the-art potential-flow code, a surrogate model is developed with the aim to approximate the Response Amplitude Operators of any arbitrary floating offshore wind turbine of the spar buoy type. The results, measured in terms of accuracy and computational effort, demonstrate that this approach is able to approximate the potential-flow solver with very high accuracy at a fraction of the computational cost.

In the present work, a spar-buoy scaled model was designed and built through a “Lab-on-Sea” unit, equipped with an energy harvesting system. Such a system is based on deformable bands, which are loyal to the unit, to convert wave motion energy into electricity by means of piezo patch transducers. In a preliminary stage, the scaled model, suitable for tests in a controlled ripples-type wave motion channel, was tested in order to verify the “fixed-point” assumption in pitch and roll motions and, consequently, to optimize energy harvesting. A special type of structure was designed, numerically simulated, and experimentally verified. The proposed solution represents an advantageous compromise between the lightness of the used materials and the amount of recoverable energy. The energy, which was obtained from the piezo patch transducers during the simulations in the laboratory, was found to be enough to self-sustain the feasible on-board sensors and the remote data transmission system.

With increasing deployment of offshore wind farms further from shore and in deeper waters, the efficient and effective planning of operation and maintenance (O&M) activities has received considerable attention from wind energy developers and operators in recent years. The O&M planning of offshore wind farms is a complicated task, as it depends on many factors such as asset degradation rates, availability of resources required to perform maintenance tasks (e.g., transport vessels, service crew, spare parts, and special tools) as well as the uncertainties associated with weather and climate variability. A brief review of the literature shows that a lot of research has been conducted on optimizing the O&M schedules for fixed-bottom offshore wind turbines; however, the literature for O&M planning of floating wind farms is too limited. This paper presents a stochastic Petri network (SPN) model for O&M planning of floating offshore wind turbines (FOWTs) and their support structure components, including floating platform, moorings and anchoring system. The proposed model incorporates all interrelationships between different factors influencing O&M planning of FOWTs, including deterioration and renewal process of components within the system. Relevant data such as failure rate, mean-time-to-failure (MTTF), degradation rate, etc. are collected from the literature as well as wind energy industry databases, and then the model is tested on an NREL 5 MW reference wind turbine system mounted on an OC3-Hywind spar buoy floating platform. The results indicate that our proposed model can significantly contribute to the reduction of O&M costs in the floating offshore wind sector.

The spar buoy platform for offshore wind turbines is the most utilized type and the OC3 Hywind system design is largely used in research. This system is usually moored with three catenary cables with 120° between each other. Adding clump weights to the mooring lines has an influence on the platform response and on the mooring line tension. However, the optimal choice for their position and weight is still an open issue, especially considering the multitude of sea states the platform can be exposed to. In this study, therefore, an analysis on the influence of two such variables on the platform response and on the mooring line tension is presented. FAST by the National Renewable Energy Laboratory (NREL) is used to perform time domain simulations and Response Amplitude Operators are adopted as the main indicators of the clump weights effects. Results show that the clump weight mass is not as influential as the position, which turns out to be optimal, especially for the Surge degree of freedom, when closest to the platform.

An Inner-shelf SPAR buoy (I-SPAR) for measuring atmospheric fluxes was developed for use in 7–20 m water depth as part of the ONR Coastal Land Air Sea Interaction (CLASI) effort. The design requirements are: 1) measurements obtained above the wave boundary layer (>4 m above sea level), 2) lightweight (< 100 kg), 3) dynamically stable, 4) modular for small boat transportation and deployment, and 5) able to acquire data for two months. The designed I-SPAR buoy has a 9 and 11 m length based on water depth and weighs 92 kg. The I-SPAR has an in-line configuration to reduce asymmetric wind drag. Atmospheric fluxes are estimated using a standard eddy-covariance, moving-platform technique that requires a fast-sampling sonic anemometer and inertial motion unit (IMU) to remove buoy motions and provide measurements in a geographic coordinate frame. The technique is modified by using a data-fused, Kalman filter IMU output. The I-SPAR is built with lightweight, high-strength carbon fiber tubes that are interconnected. The I-SPAR will follow low-frequency swell, where high-frequency wind waves are filtered out with a bottom damping plate. It is also designed for a maximum static tilt of 25° and a dynamic roll of 5.6° when exposed to a 15 m/s wind using vertical fins. A collocated solar-powered battery float will provide continuous power at a 50% duty cycle and includes an iridium modem for transmitting bulk statistics, including fluxes as well as providing a safety watch circle. http://archive.org/details/isparbuoydesigno1094566607 Lieutenant Commander, United States Navy Approved for public release. distribution is unlimited

The present paper deals with the Life-Cycle Cost (LCC) of an offshore renewable energy farm that is currently a topic of interest for operators and investors. The LCC analysis refers to the Cost Breakdown Structure (CBS) considering all the phases of life span, and it has been carried out for floating offshore wind farms (FOWFs) and hybrid wind-wave farms (HWWFs). For HWWFs, this paper proposes a hybrid wind-wave energy system (HWWES), which provides the coupling of wave energy converter (WEC) with Tension Leg Platform (TLP) or Spar Buoy platform (SB). The LCC analysis has been carried out considering: (i) FOWF consisting of TLP floating platforms; (ii) FOWF consisting of a SB floating platforms; (iii) HWWF realized with the conceived hybrid system coupling the WEC with the TLP platform; (iv) HWWF realized with the conceived hybrid system coupling the WEC with SB platform. In addition to the LCC evaluation, the Levelized Cost of Energy (LCOE) analysis has also been carried out. The site chosen for the study is off the port of Brindisi, southern Italy. This work’s interest lies in having performed a LCC analysis for FOWF and HWWF in the Mediterranean that is an area of growing interest for offshore renewable energy, and obtained results have allowed making assessments on costs for offshore energy farms.

Low power data acquisition systems that are either supplemented or completely powered by renewable energy can be very useful for oceanographic purposes. The spar-buoy Oscillating-Water-Column (OWC) concept, typically studied for large scale energy production, can be re-designed to meet the power requirements of oceanographic applications, which results in a much smaller device working outside resonance conditions under typical sea states, and therefore with a smaller energy conversion efficiency. Preliminary experimental results are presented for a 1:10 th scale model of a spar-buoy OWC, undertaken in a wave channel. A calibrated orifice plate was used to model the flow characteristic of an impulse turbine, which will be used in the full-scale system. The experimental set-up is presented. Measurements of the relative buoy-OWC motion, air chamber pressure, and power absorption are examined, for regular and irregular wave conditions. The results show the presence of non-linear effects, caused by viscous flow and turbine damping. For an energy period of 8 s, the device presents a capture width ratio of about 0.03, which makes it adequate for the supply of oceanographic sensors in North Atlantic wave climates.

An active control method, to suppress the onset of pitch/roll parametric resonance on an oscillating water column (OWC) spar buoy, is proposed in this paper, which utilises a pressure relief valve at the top of the OWC air chamber. The paper examines the hypothesis that by opening the relief valve, to reduce the air chamber pressure difference and to decouple the dynamics of the spar buoy and the OWC within, the natural pitch/roll frequencies of the system will be shifted, allowing parametric resonance to be cancelled when its onset is detected. The paper reports on experiments, performed to test the stated hypothesis, with a small-scale model OWC spar buoy in a wave flume. Two configurations are considered and tested in a range of monochromatic waves (1) fully closed air chamber; (2) fully open chamber. The results partially confirm the hypothesis, demonstrating that the occurrence of parametric resonance observed for certain wave frequencies when the chamber is closed does not occur when the chamber is open. However, the change in the natural pitch/roll frequencies between the two configurations is very small, and parametric resonance occurs in both confurations for waves with twice this frequency.

Representative models of the nonlinear behavior of floating platforms are essential for their successful design, especially in the emerging field of wave energy conversion where nonlinear dynamics can have substantially detrimental effects on the converter efficiency. The spar buoy, commonly used for deep-water drilling, oil and natural gas extraction and storage, as well as offshore wind and wave energy generation, is known to be prone to experience parametric resonance. In the vast majority of cases, parametric resonance is studied by means of simplified analytical models, considering only two degrees of freedom (DoFs) of archetypical geometries, while neglecting collateral complexity of ancillary systems. On the contrary, this paper implements a representative 7-DoF nonlinear hydrodynamic model of the full complexity of a realistic spar buoy wave energy converter, which is used to verify the likelihood of parametric instability, quantify the severity of the parametrically excited response and evaluate its consequences on power conversion efficiency. It is found that the numerical model agrees with expected conditions for parametric instability from simplified analytical models. The model is then used as a design tool to determine the best ballast configuration, limiting detrimental effects of parametric resonance while maximizing power conversion efficiency.

Wave energy devices are designed, and controlled, to be extremely responsive to incoming wave excitation, hence, maximising power absorption. Due to the consequent large motion excursions, highly nonlinear behaviour is likely to occur, especially in relation to variations in wetted surface. Moreover, nonlinearities may induce parametric instability, or activate internal mechanisms for exchanging energy between different degrees of freedom (DoFs), usually affecting the overall efficiency of the device. Consequently, single-DoF linear models may produce overly optimistic power production predictions, and neglect important dynamics of the system. One highly nonlinear phenomenon, potentially detrimental to power absorption for several wave energy converters, is parametric roll/pitch; due to parametric excitation, part of the energy flow is internally diverted, from the axis where the power take-off is installed, to a secondary axis, generating parasitic motion. This paper proposes a computationally efficient multi-DoF nonlinear model, which can effectively describe nonlinear behaviour, such as parametric pitch and roll, and their impact on motion prediction, power production assessment, and optimal control parameters.

Simulations are conducted in time domain to investigate the transient response of a SPAR-type floating offshore wind turbine in scenarios with fractured mooring lines. Towards this end, a coupled aero-hydro-elastic numerical model is developed. The methodology includes a blade-element-momentum model for aerodynamics, a nonlinear model for hydrodynamics, a nonlinear restoring model of SPAR buoy, and a fully nonlinear dynamic algorithm for intact and fractured mooring cables. The OC3 Hywind SPAR-type FOWT is chosen as an example to study the dynamic response after one of its mooring lines is suddenly broken. The motions of platform, the tensions in the mooring lines and the power generation performance are documented in different cases, including different fractured cables and different shutdown strategies. An interesting finding is that in terms of drift distance, it might be more dangerous to shut down the turbine in certain scenarios. Furthermore, the potential impacts of mooring failure on adjacent FOWTs are discussed for two designs of the wind farm.

Quantitative reliability, availability, and maintainability (RAM) assessments are of fundamental importance at the early design stages, as well as planning and operation of marine renewable energy systems. This paper presents an RAM framework adaptable to different offshore renewable technologies, conceived to provide support in the choice of the device components and subsequent planning of the O&M strategies. A case study, characterizing a pilot farm of oscillating water column (OWC) wave energy converters (WECs), is illustrated together with the method used to obtain reliable estimate of its key performance indicators (KPIs). Based on a fixed feed-in-tariff for the project, economic figures are estimated, showing a direct relationship with the availability of the farm and the cost of maintenance interventions. Consequently, the probability distributions of the most relevant output variables are presented, and the mutual correlations between them investigated using principal components analysis (PCA) with the aim of discovering the relationships influencing the performance of the offshore farm. In this way, the contributions of the individual factors on the profitability of the project are quantified, and generic guidelines to support the decision-making process are derived. It is shown how this type of analysis provides important insights not only to ocean energy farm operators after the deployment of the devices, but also to device developers at the early design stage of wave energy concepts.

We examine the structure of turbulent airflow over ocean waves. Based on an analysis of wind and wave observations derived from a moored and floating Air–Sea Interaction Spar buoy during the Shoaling Waves Experiment field campaign, we show that the cospectra of momentum flux for wind–sea conditions follow established universal scaling laws. Under swell-dominant conditions, the wave boundary layer is extended and the universal cospectral scaling breaks down, as demonstrated previously. On the other hand, the use of peak wave frequency to reproduce the universal cospectra successfully explains the structure of the turbulent flow field. We quantify the wave-coherent component of the airflow and this clarifies how ocean waves affect momentum transfer through the wave boundary layer. In fact, the estimated wave-induced stresses for swell-dominant conditions explain the anomalous cospectral shapes observed near the peak wave frequency.

Direct measurements of marine dimethylsulfide (DMS) fluxes are sparse, particularly in the Southern Ocean. The Surface Ocean Aerosol Production (SOAP) voyage in February–March 2012 examined the distribution and flux of DMS in a biologically active frontal system in the southwest Pacific Ocean. Three distinct phytoplankton blooms were studied with oceanic DMS concentrations as high as 25 nmol L−1. Measurements of DMS fluxes were made using two independent methods: the eddy covariance (EC) technique using atmospheric pressure chemical ionization–mass spectrometry (API-CIMS) and the gradient flux (GF) technique from an autonomous catamaran platform. Catamaran flux measurements are relatively unaffected by airflow distortion and are made close to the water surface, where gas gradients are largest. Flux measurements were complemented by near-surface hydrographic measurements to elucidate physical factors influencing DMS emission. Individual DMS fluxes derived by EC showed significant scatter and, at times, consistent departures from the Coupled Ocean–Atmosphere Response Experiment gas transfer algorithm (COAREG). A direct comparison between the two flux methods was carried out to separate instrumental effects from environmental effects and showed good agreement with a regression slope of 0.96 (r2= 0.89). A period of abnormal downward atmospheric heat flux enhanced near-surface ocean stratification and reduced turbulent exchange, during which GF and EC transfer velocities showed good agreement but modelled COAREG values were significantly higher. The transfer velocity derived from near-surface ocean turbulence measurements on a spar buoy compared well with the COAREG model in general but showed less variation. This first direct comparison between EC and GF fluxes of DMS provides confidence in compilation of flux estimates from both techniques, as well as in the stable periods when the observations are not well predicted by the COAREG model.

This paper presents the development of a Computational Fluid Dynamics (CFD) model for a free heaving Oscillating Water Column (OWC) spar buoy with non-linear Power Take Off (PTO). Firstly, a freely heaving barge was applied to a 2D Numerical Wave Tank (NWT), used to validate a 1 Degree Of Freedom (DOF) modelling methodology. Multiple sets of regular waves were used to assess the heave response compared to previous experimental and numerical studies. In parallel, the NWT was extended to 3D where analyses of incident waves have been conducted to ensure accurate waves are portrayed. A PTO boundary condition was created to replicate a non-linear impulse turbine, typically simulated by an orifice plate in scaled models. The PTO boundary was compared and validated using experimental data. Finally, a comprehensive system comprising of the 3D NWT, 1DOF set-up and non-linear PTO allowed the development of a heave-only OWC spar buoy model with a non-linear PTO. Experiments completed by UCC MaREI centre in LIR-NOTF ocean wave basin under FP7 MARINET project is detailed and used to validate the comprehensive model. A range of regular waves were applied and responses of heave and chamber pressures were compared to experimental data, which showed excellent correlation.