Proceedings of the European Wave and Tidal Energy Conference
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European Wave and Tidal Energy Conference
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Tidal energy resource characterization and assessment in Turnagain Arm of Cook Inlet: from pilot to commercial scales
There have been significant efforts worldwide in the development of tidal stream energy as a potential renewable energy source to mitigate the climate crisis. Cook Inlet in the State in Alaska, USA, is one of the top energetic tidal sites in the world, with great potential for tidal energy exploitation. Cook Inlet consists of several strong tidal current hotspots in the USA, including East and West Forelands, Turnagain Arm and Knik Arm. Currently, most of the tidal stream resource assessment studies have focused on the Foreland areas, where the strongest tidal currents are present in Cook Inlet. However, the tidal energy resource in Turnagain Arm in the upper Cook Inlet has never been characterized in detail. Micro-grid scale tidal energy development could play an important role in helping remote communities in Alaska to meet the power needs. In this study, we developed a high-resolution three-dimensional tidal hydrodynamic model using the Finite Volume Community Ocean Model to simulate the tidal currents and characterize tidal energy resource in Turnagain Arm. The model was validated with field data for water levels and tidal currents. Model performance was evaluated using error statistics, including root-mean-square-error, scatter index, bias, and linear correlation coefficient. Model configuration, validation, and resource characterization follow closely the International Electrotechnical Commission Technical Specification for tidal energy assessment and characterization. Specifically, a set of tidal energy variables, including tidal power density, probability of velocity exceedance, and annual energy production were used to characterize the energy potential. Extractable energy was assessed using a tidal energy conversion module in the numerical model based on various specific tidal turbine technologies and different array layouts, with turbine farm sizes ranging from pilot scale to commercial scale in Turnagain Arm. Extractable power per turbine was calculated and analyzed to identify the optimal siting location for turbine farm. Finally, far-field effects of tidal energy extraction on tidal circulation and its implication for sediment erosion near the tidal turbine farms are analyzed by comparison of flow fields with and without tidal turbine farms. This study demonstrates that Turnagain Arm has a great potential for tidal energy harvesting at both pilot and commercial scales, which could be integrated into the nearby power grid system to supplement the power demand of the Railbelt of Alaska region, which covers about 75% of the population of Alaska.
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Hydrokinetic Energy Potential in Southern Patagonia: Le Maire Strait site
In this work, the hydrokinetic energy potential of a new part of the Argentinian coastline is assessed. This site is on the surrounding coast of Isla de los Estados, off the eastern tip of the main island of Tierra del Fuego Province. Located at the southernmost part of Argentina, this site is composed of multiple high energetic locations, subdivided into: Le Maire Strait, exposed coastline East of the Isla de los Estados, and fiords inside this island. Here, only Le Maire Strait is analyzed due to its larger size and relevance: it extends for 30 km between the main island of Tierra del Fuego and the west coast of Isla de los Estados with an average depth of 100 m and plays a crucial role for navigation onto the Drake Passage and Antarctica. This first approach replicates former assessments in the region by means of a numerical 2D (depth-averaged) hydrodynamical model made in Delft3D-FLOW. Results were obtained by a nested modelling strategy that accurately propagates astronomical tidal dynamics from open seas onto the shores without disproportionately increasing computational costs. Since the region presents a strong astronomical tidal dominance, even though it might not be the case for this site, no meteorological tide nor waves were included at this stage. Previous works in the region have shown that Patagonian Estuaries have significant tidal energy potential, which, even though is not top rated worldwide, is still of importance and could be harnessed mostly by small to medium devices, and with some areas for larger turbines. On this site, however, mean current velocities higher than 1 m/s are found in large areas (around 30.000 Ha), with over 200 Ha above 1.5 m/s and high-power density (>1.5 kW/m2). Even though no mean current velocities above 2 m/s were found, Le Maire Strait is probably the site with the largest amounts of available power in Argentina for this kind of renewable energy and might be an ideal site once the technology has matured. Finally, a comparison with Alderney Race (France), which is one of the best sites in the world for hydrokinetic energy is made to bring a wider perspective of the hydrokinetic power available on this site.
Optimising Tidal Lagoon Design and Operation for Energy Generation
This study aims to design and optimise tidal lagoon schemes in Wales, focusing on three case studies: North Wales Tidal Lagoon, Cardiff Tidal Lagoon, and Newport Tidal Lagoon. By integrating genetic algorithms with traditional 0-D methodologies, the research optimises design parameters and turbine selection while exploring flexible operational schemes to significantly enhance energy output and economic performance. Additionally, it examines the long-term performance of these systems under climate change scenarios for the years 2085, 2135, and 2185, providing insights into future resilience and adaptability. The modelling outcomes will also inform evaluations of supply chain dynamics and economic feasibility. This study highlights the potential of tidal lagoon developments in enhancing energy generation, storage, and economic benefits, contributing to a sustainable and resilient energy future for the UK and beyond.
Remote Sensing Applications in Tidal Current Hotspot Mapping
The Mearim River region, located in the state of Maranhão, Brazil, offers geographic and climatic conditions favorable for the exploration of marine renewable energies, such as wind, solar, and tidal power. This region has an extensive coastline, significant solar irradiation, constant winds, and a large tidal range.One of the primary advantages of this area is its proximity to urban centers and electrical infrastructure, including high-voltage transmission lines and substations. This proximity allows for direct connection of power generation to Brazil’s National Interconnected System (SIN).The main objective of this study is to identify hotspots (areas with the highest energy potential within the studied zone) for electricity generation using tidal currents.The proposed methodology combines satellite imagery with the open-source hydrodynamic modeling tool Delft-3D. To achieve this objective, the study was divided into two phases.The first phase involved three campaigns of in situ measurements, each lasting 25 hours and conducted across different tidal cycles and locations. This approach provided greater data variability, including current speed, depth, temperature, salinity, turbidity, and other parameters. Using these data, along with tide tables and regional mapping, hydrodynamic models of the site were generated by Delft-3D.The second phase consisted of acquiring satellite images and processing them. Finally, a correlation is established between the measured real-world data, the generated model, and the satellite images, enabling the identification of hotspots for harnessing tidal currents.Preliminary results show that this is a more economical alternative route, in addition to reducing the time and number of measurement campaigns, and therefore increasing costs, and, at the same time, resulting in detailed information that allows an analysis of the selected areas in a short period of time.
Prediction of tidal currents in the Inner Sound of the Pentland Firth using RTide
The design and operation of tidal stream energy farms will require the accurate prediction of tidal currents from field data. In the present paper we compare the performance of a physics based flow model, the traditional harmonic analysis method, and a newly developed code RTide. RTide is based on the Response Method proposed by Munk and Cartwright in the 1960s and uses machine learning to overcome the key disadvantages of their original approach. We use field data from the Meygen site in the Inner Sound of the Pentland Firth. We find RTide predictions based solely on the field data outperform both the flow model predictions and the currents predicted by harmonic analysis. Interestingly, feeding the physics-based flow model into RTide as an additional input does not outperform the predictions based on the field data alone. However, RTide can still be used as a correction tool to physics-based flow models.
The role of patenting in emerging renewable energy technologies: the case of wave energy technology development
Understanding the role of intellectual property (IP) in the development of emerging renewable energy technologies is critical, especially as nations transition to low-carbon energy systems. This study investigates the function and effectiveness of patents in the wave energy sector, focusing on their value as innovation indicators and their potential limitations due to the long development timelines of wave energy technologies and patent registration, and the risk of patent expiration. Alternative IP strategies, such as licensing and trade secrets, are considered in light of these challenges. The study explores how wave energy developers engage with patents and manage IP, examining the approaches of companies across the spectrum of open and closed innovation models. Companies are classified based on their IP strategies, including whether they prioritise patenting or rely on publication to disseminate knowledge. This raises the question of the intrinsic value of patents: do they drive innovation or create barriers, and how they compare to other dissemination methods such as academic publishing? The study looks at wave energy technology intellectual property protection from the perspective that the risk of copying diminishes depending on whether the technology being developed is the device itself, the Power Take-off (PTO) mechanism or the controller. Wave energy technology patenting is also contrasted with global trends in wind and solar energy, which have seen significant patent activity. Data for this analysis is drawn from European Patent Office (EPO) reports, International Renewable Energy Agency (IRENA) studies, stakeholder interviews, and recent academic literature on the subject. These sources highlight the global state of patenting in wave energy and how patent reports can provide insights into overcoming technical barriers. By identifying technological advancements documented in patents, this study evaluates how such information can inform both innovation strategies and policy frameworks. A central question addressed is whether patents encourage innovation in wave energy or inhibit progress due to their restrictive nature. Patent studies reveal that wave energy technologies are making strides in overcoming challenges such as efficiency, durability, and scalability. These findings suggest that patent information could be better utilised for technology assessment and strategic development. By integrating insights from patent reports into policy and innovation strategies, stakeholders can accelerate the development of wave energy technologies. This study contributes to the broader discourse on the role of patents in renewable energy innovation. It emphasises the need for tailored IP strategies that balance protection and knowledge dissemination while accounting for the unique challenges faced by emerging technologies such as wave energy. The findings have implications for policymakers, developers, and investors aiming to advance the wave energy sector in Ireland and globally.
Supply chain, economic, social, legal and political aspects of ocean energy
Large Eddy Simulation of an Energetic Tidal Strait with Device-Scale Turbulence
Tidal channels suitable for tidal power devel- opments exhibit complex, turbulent flow, at high Reynolds numbers with dynamic features over a wide range of scales that can persist for several hours. Modelling such flow plays a key part in characterising the conditions that tidal turbines will experience in situ. However, simulations of these channels are extremely challenging, and many numerical models compromise on either fidelity or size to keep computational complexity down to a manageable scale. New numerical techniques are required to overcome these restrictions, and provide the tidal energy industry with valuable insights into the marine environment. This paper presents a non-hydrostatic, high-fidelity com- putational fluid dynamics model of the Grand Passage in the Bay of Fundy, Canada, using the coastal and tur- bine modelling software CoastED. The model employs a Discontinuous Galerkin finite element formulation of the Navier-Stokes momentum equation, coupled with a Vreman subgrid eddy viscosity model, a variant of Large Eddy Simulation adapted for anisotropic grids. This, along with the use of a novel unstructured grid scheme, allows flow features from centimetres to kilometres to be captured over several M2 tidal cycles. By comparing virtual Acoustic Doppler Current Profiler (ADCP) results data with measurements from real ADCPs in the Grand Passage, we show that the model is effective in recreating aspects of the tidal currents often missed in hydrostatic simulations. We also examine some of larger modelled tidal flow features, and contrast them with evi- dence from satellite data.
Parametric Design and Evaluation of Floating Tidal Turbines under Real World Wave Scenarios
The design and evaluation of floating horizontal-axis tidal turbines involves a vast design space, especially in the early conceptual stages. Both the turbine and the floating platform must be carefully considered, as the rotor's performance is directly influenced by the dynamic motion of the platform, which responds to the environmental conditions at the deployment site. This study investigates the relationship between platform design features and turbine performance under wave conditions informed by real world data. An automated workflow has been developed to assess performance metrics for parametric platform designs. This workflow begins with generating hull geometries based on specified design parameters. Using the boundary element method, the radiation and diffraction problems are solved, and the added mass and inertia matrix is obtained for each hull. The Added mass and inertia matrices are converted to WAMIT format for coupled aero-hydro-elastic model analysis within OpenFAST. Rotor performance is evaluated using blade element momentum theory, with the addition of a Beddoes-Leishman correction model for unsteady flows, capturing the effects of platform motion. The workflow is validated against experimental data for the rotor, and computational simulation for the combined platform and rotor. By analysing platform-turbine combinations across real world environmental scenarios, sensitivity to design changes such as the beam of the float, and the tension in the mooring system can be evaluated. Key metrics include blade loads, the presence of flow separation, turbine thrust, and overall power output. Response amplitude operators (RAOs) (Figure 1) quantify the excitation of platform motion by wave direction and frequency, and its subsequent impact on turbine dynamics. By selecting platform-turbine combinations, a parameter space of limiting operating conditions will defined. This workflow offers a cost-effective tool for exploring design impacts on system performance early in the development process, complementing higher-fidelity models that are typically constrained by computational expense and time.
Towards parametrized modeling of the current vertical structure during extreme events: application to Alderney Race.
This study aims to improve the parameterized modeling of velocity vertical profiles in coastal environments under strong tidal currents. The primary study site is the Alderney Race in Normandy, France, a macro-tidal, semi-diurnal site characterized by powerful sheared currents reaching up to 5 m/s. As part of the FloWatt project, led by HydroQuest, this site will host a pilot farm of seven tidal turbines. Ultimately, this study may simplify the representation of hydrodynamic processes at tidal energy converter deployment sites, predict vertical current shear during extreme events, and support turbine load assessments. The analytical laws traditionally used to evaluate the current rely on logarithmic or power-law formulations and are based on zero-equation turbulence closure models or partial similarity theory. These models predict velocity profiles in the bottom boundary layer well for collinear waves and currents. However, research indicates that wave-current interaction (WCI) alters the velocity profile across the entire water column. During extreme events, where waves significantly affect mean velocities, deviations from the logarithmic law are observed in the upper layers (Bennis et al., 2022). Additionally, the parameters of these analytical laws are subject to high variability, depending on factors such as bathymetry, tidal phase, and ambient turbulence, often diverging from recommended literature values (Sentchev et al., 2020). An improved logarithmic law was tested to address these difficulties, as Yang (2006) proposed. The data for this study originate from a combination of in-situ measurements and numerical modeling. In 2018, towed and mounted ADCPs were deployed in the Alderney Race as part of the Hyd2M project and HF radars were installed along the coast (Bailly du Bois et al., 2020). For the numerical part, the Coastal and Regional Ocean COmmunity model (CROCO) was coupled with the spectral wave model WAVEWATCH-III to incorporate WCI. Simulations were performed for a calm sea period (July 2018) and a winter storm period (January 2018). These simulations revealed spatial variations in model accuracy and current vertical shear, partly linked to bottom parameterization. Nevertheless, the models demonstrated good agreement near the future tidal farm. Observations and models also revealed deviations from the logarithmic law, prompting the implementation of an improved log law (Yang, 2006), which appeared to reduce discrepancies between the idealized profiles and observed/modeled data. Further work is required to correlate the newly introduced law's parameters with waves, wind, and tides. To this end, additional numerical experiments were conducted, including scenarios with artificially amplified wave energy or reduced wind and wave conditions. These experiments confirmed that the vertical velocity profiles were significantly altered, highlighting the sensitivity of the flow dynamics to changes in external forcing.
Novel Approach for a Tidal Energy Resource Assessment within Long Island Sound Using a Spatial Multi-Criteria Decision Analysis Process
The marine environment is a vast energy resource with the potential for supporting the world’s growing energy demand. Increasing the number of marine energy (ME) projects diversifies renewable energy portfolios, supporting decarbonization and energy security. Most of the energy potential along the U.S. coastline is in the <5 MW range, especially for tidal energy. On the opposite end of the spectrum, the UK Marine Energy Council has a target of 1 GW from tidal energy by 2035. However, the lack of robust and coherent site information, globally, leads to ignored resources, misdirected technology development, and perception of high project risk for stakeholders. To address this gap, a TEAMER (Testing & Expertise for Marine Energy) funded study was conducted to assess the pre-feasibility of tidal energy in Long Island Sound, an area bordered by the Connecticut and New York coastlines with representative characteristics to many U.S. tidal energy sites. The work used a novel spatial data analysis approach and development of a geodatabase to identify the area’s tidal energy resource potential. The geodatabase, at the foundation of the methodology, integrates numerical model based probability distributions of tidal currents as well as relevant geospatial data including, but not limited to, natural resources, bathymetry, oceanographic conditions, existing infrastructure, and socioeconomic data layers throughout the region of interest. Potential tidal energy siting limitations and opportunities were examined through a spatial multi-criteria decision analysis process. This involved the identification of key data layers and weighting factors to identify the areas most suited for tidal energy devices. The primary data layer was the available tidal resource, which directly influences the potential energy output. Power matrices for multiple generalized tidal turbines were included to calculate estimated power and mean annual energy production using international standards. Other data layers incorporated into the decision analysis library included binary exclusion zones such as marine protected areas and shipping lanes, ‘cost’ factors such as distance to transmission connection points or cable landing areas, and ‘benefit’ factors such as population density. Existing renewable energy infrastructure was also considered, as it impacts the ease of integration and distribution of the generated power. Areas of stakeholder concern, including environmental and socio-economic factors, were considered to ensure sustainable ME development. This novel methodology provided detailed insights into potentially suitable areas for tidal energy extraction. Despite the current limitations of tidal turbine technologies, our novel geodatabase and spatial analysis toolkit identified previously overlooked tidal energy sites along Connecticut's coastline. This approach assumes that future technologies will be optimized for lower energy environments, highlighting the potential for advancement in tidal energy. The findings demonstrate the efficacy of using automated geospatial processing and spatial analysis tools in ME resource assessments. The application of quantitative marine spatial planning techniques enables more effective planning of tidal energy infrastructure and improved technology development. Future plans include applying the method to other coastal regions worldwide and including considerations for other ME conversion technologies such as wave energy.
Tidal Energy, Long Island Sound, Geodatabase, Spatial Analysis, Geographical Information System (GIS)
Quantifying the regional blockage effects of tidal arrays within multi-scale channel network models
Past studies on global blockage have shown that some level of array-induced flow diversion away from the exploited channel is inevitable. The magnitude of this diversion is a function of the total resistance introduced by the turbine array, as well as the physical characteristics of the domain, i.e., channel cross-sectional area, seabed roughness, mixing losses. Furthermore, islands and headlands establish what could be considered a network of sub-channels among which the overall volumetric flux is distributed based on the equilibrium of retarding forces each experiences. Blockage effects must therefore be a function of not just the overall resistance exerted by the exploited channel, but also of the resistance properties of any alternative flow paths. The limited availability of spatial parameter data like bathymetry and bed friction makes resource assessment results sensitive to assumptions and approximations made within numerical models. Insufficient knowledge about the domain of interest may therefore lead to erroneous estimates of energy yield, with the propagation of uncertainty also becoming more difficult to follow, increasing project risk and deterring investment. A multi-scale nested channel network approach is developed to quantify the sensitivity of tidal array performance to the spatial parameters describing the region. 1D gradually varied flow models are interlinked in parallel and series to create a larger model representing the complex domains often considered for tidal stream development. Array scale core and bypass flow is modelled by a set of parallel channels, nested within another set of parallel channels representing the sub-channels created by islands, which is then nested within another channel representing the overall region. The model can therefore capture the interactions between tidal arrays and the regional scale dynamics that are overlooked by existing analytical and 1D models of comparable computational cost. Although the model cannot reproduce phenomena that higher order models would (e.g., wake interactions, mixing), its low computational cost allows for its use in non-deterministic analysis, whilst still capturing the hydrodynamics most relevant to array and global scale blockage. The model is used to investigate the impact of tidal arrays on a number of scales – the performance differences between fully spanning arrays and partial arrays that allow for flow bypass; the impact of turbine-induced resistance on funnelling flow through adjacent channels or away from the domain altogether; the changes in energy flux from the standard ambient baseline.
A multi-scale analytical model for the performance of a tidal stream array in a tidal channel
Assessing the tidal resource is central to the feasibility analysis of any development of tidal stream turbines. This is true for the CoTide project which seeks to optimise the design of tidal stream turbines by building an integrated design tool considering hydrodynamics, structural effects, fatigue, environmental impact, etc. However, there is no closed-form analytical solution for the tidal resource assessment. Motivated by this, this paper proposes a multi-scale framework for tidal resource assessment for the Co-Tide project. The key element of this framework is to model the system, i.e. an array of turbines (arranged in a row) partially occupying a tidal channel, at different scales (channel-scale, array-scale, turbine-scale), and then coupling them together through the net resistance of the turbine array solved by a drag model that might be derived from laboratory experiments or numerical simulations. The channel-scale flow dynamics is described by the Garrett & Cummins (2005) model [1] whereas based on the scale separation model of Nishino & Willden (2012) [2] the array-scale and turbine-scale flows are modelled separately by the Garrett & Cummins (2007) model [3] and then coupled together. Using characteristics representative of a tidal site (including tidal flow characteristics, channel geometry and turbine geometry) as inputs, we have employed the framework to predict the velocity in the channel, velocity through the array and the power generated by the array over time. Only two principal tidal constituents are considered here as increasing the number of tidal constituents significantly increases the computational cost. The model can be adapted for other tidal energy projects and has flexibility to incorporate more detailed sub-models in future.
Tidal energy, resource assessment, physical model
Barnacle Probes: Effect of motion on turbulence measurements
Reliable turbulence measurements are essential for deploying underwater tidal energy due to the effect of unsteady flow on turbine performance and lifespan. This paper investigates the application of motion-correction techniques to a novel turbulence sensor, the Barnacle, for more accurate turbulent flow estimation. Instrument deployment was conducted in Strangford Narrows during October and November 2024 from a floating flow-facing offshore barge, with multiple Barnacles validated against a Nortek Vector ADV. Preliminary validation of the smaller Barnacle probe indicated good streamwise-normalised median velocity agreement of within 20% in all three directions for a long-term 12-hour deployment. Motion-corrected median TKE and median streamwise TI were also within 12% of the Vector-derived values and agreed with previously published data from the deployment location. While Vector data were used to correct for acceleration-induced contamination due to limitations of the inertial measurement unit of the Barnacles, this will be rectified in future work to further improve motion correction.
Blade root force measurements on vertical axis tidal turbine
In 2019, Hydroquest tested its first 1MW-rated full-scale tidal turbine at Paimpol-Bréhat site. The success of this deployment has enabled the company to launch the development of the next generation of turbines through the FloWatt and Verti-Lab projects. In these projects, the validation of the industrial development tools are based on comparisons of experimental, numerical and in-situ data at both small and large scales. In this context, a 1:20 scale tidal turbine model, similar to the geometry of the demonstrator designed for deployment in the Alderney Race, is tested under representative conditions in the wave and current circulating tank of Ifremer. The experimental set-up specifically developed for this project enables synchronised measurements of performance (from the rotor torque), blade forces and flow characteristics (from 2D PIV measurement) to be carried out. The paper aims to describe in-depth the effects of fluid-structure inter- actions between the hydrodynamic loads and the blades of the turbine. To this end, we will first detail the experimental setup based on the use of a full quadrirotor twin vertical axis tidal turbine model and a single rotor de- vice. Then, we will study the angular distribution of the blade forces and the flow characteristics close to the blade for several configurations in order to analyse the effect of the different parts of the model, the central structure and the gravity base, on the rotor dynamic behaviour. The comparison be- tween the quadrirotor and the single rotor cases will help to understand the angular repartition of the blade lift and drag forces. In this way, the dynamic stall, which is typical of vertical axis tidal turbines, can be characterised from both the rotor mechanical behaviour and the dynamic of the flow around the blades. The trials are carried out in January 2025 and the data will be fully anal- ysed in February in order to be able to send the paper before end of March.
Improved Hydrodynamics Modeling for Marine Turbines in OpenFAST
OpenFAST is an open-source turbine simulation tool developed by the National Renewable Energy Laboratory (NREL). OpenFAST was originally developed for land-based wind turbines and later expanded to model fixed-bottom and floating wind turbines as well. It is a widely used tool within the wind energy industry and research community for turbine simulation, design, and loads analysis. Over the past few years, NREL researchers have been adding features and capabilities to OpenFAST to enable modeling of fixed and floating marine turbines. This development has focused on capturing additional physics relevant to operation in water and enabling the simulation of more diverse turbine geometries. Capabilities previously introduced for marine turbines include the inclusion of buoyant, added mass, and fluid inertia loads on the rotor, calculation of accelerations from the incoming current field, superposition of wave and current velocities, and a cavitation check to warn users if cavitation is occurring on a blade. OpenFAST development is also ongoing to enable modeling of multi-rotor systems, with multiple rotors attached to a single support structure. Additional work to further adapt OpenFAST for marine turbines was recently funded by the U.S. Department of Energy. Development for marine turbines is focused on capturing additional physics relevant to operation in water and enabling the simulation of more diverse support structure geometries. The work includes adding a flow confinement model for the rotor, a new dynamic stall model, rotor flow impacts from generalized support structures, cross-flow turbine controls, lifting loads on faired towers, and Keulegan-Carpenter (KC) number dependent platform drag forces. The final two additions are currently in development and will be discussed in more detail. Marine turbines can often take advantage of unidirectional or bidirectional inflow, with faired towers for reduced drag loads. These faired members physically introduce lift when there is some offset from the anticipated current direction, which could lead to important unexpected system loads. Lift force calculations on faired towers will be performed in the AeroDyn module following the same functions used for blade element lift forces. A separate input file option will allow users to define lift vs. angle of attack curves for the faired towers. This implementation will consider modification of the tower dam and tower shadow models, if necessary. Marine turbine support structures are subject to significant viscous drag loads with the inherent presence of current. Accurately capturing these loads is critical for mooring system and structural design. Drag coefficients in oscillatory flow are strongly dependent on KC number. Often, offshore wind support structure drag coefficients are changed depending on depth and sea state, accounting for changes in the KC number. The addition of current to wave and structure velocities further complicates the changes in drag between load cases. An option will be added to the HydroDyn module to have actively adjust drag coefficients as a function of the local instantaneous KC number.
On the role of wave energy in the renewable energy mix complementarity: A comparative study between Italy and Ireland
Achieving a fully renewable energy future necessitates the integration of marine renewable energy sources, such as wave and tidal energy, into the current energy mix. These underutilized resources offer significant potential to enhance the reliability of renewable energy systems by complementing other climate-dependent sources, such as wind and solar energy, across various temporal scales. The inclusion of wave and tidal energy in the energy portfolio improves power output stability, reduces periods of energy generation shortfall, and lessens the dependency on energy storage solutions. This study employs innovative complementarity metrics—including total variation, variance, and standard deviation—to evaluate the interactions among wave, tidal, wind, and solar resources. A comparative analysis between the Mediterranean Sea conditions surrounding the Italian peninsula and the Atlantic Ocean conditions of Ireland reveals significant differences in the potential of wave and tidal energy. The complementarity analysis further underscores the advantages of diversifying the renewable energy mix, demonstrating that the inclusion of wave and tidal resources yields higher complementarity metrics and enhances the overall performance of the energy system in both regions.
Co-location, hybridization and synergies in the Blue Economy
Influence of Restoring Force Absence and Unidirectional Power Flow on the Power Absorption Performance of WavePiston
The WavePiston wave energy converter (WEC) is a novel device which consists of multiple energy collectors coupled on a string. Each collector includes a sail designed to harness the surge excitation of incident waves and a hydraulic power take-off (PTO). This recently developed WEC possesses a variety of distinctive features. First, since the sails are constrained to move horizontally and are assumed not to deform in this study, and because there is no external spring mechanism on the energy collectors, no restoring force acts on the WEC. This distinguishes the WavePiston from conventional wave energy converters that function as resonators and possess inherent self-centering capabilities. Second, in its current version, the PTO is passive, and is only capable of absorbing power, meaning that power transmission from the PTO to the energy collector is not feasible. Considering (i) the lack of resonating capabilities of the WavePiston baseline configuration, and (ii) the inherent passivity of its PTO, this study aims to evaluate how these properties impact the device power absorption performance. To achieve this, four different WEC configurations are assessed: Two of them introducing an external spring mechanism—one featuring a passive PTO and the other a non-passive PTO—and two configurations without the spring mechanism, featuring passive and non-passive PTOs, correspondingly. The external spring mechanism may operate as a complement to the PTO control action, in addition to ensuring self-centering capabilities. For each scenario, the optimal direct transcription-based spectral controller is evaluated. In cases where non-passive PTO is assumed, both positive and negative power transmission is allowed on the control side (reactive control); however, with passive PTO, only positive power transfer (passive control) is permitted. In all cases, position and force constraints are considered, and the spectral optimal solution is evaluated in terms of the energy absorption across varying sea states. For the sake of simplicity, this work focuses on a device consisting of a single energy collector. Finally, an analysis is conducted by comparing the results for the baseline WavePiston configuration, with no inherent restoring force and a passive PTO, with the other three proposed scenarios. The discussion highlights the implications for power absorption performance arising from the limitation of passive PTO operation, and the unique design characteristics of the WavePiston that differentiate it from conventional resonator WECs. Furthermore, the findings identify critical factors that could influence key design aspects of the WavePiston WEC, posing a control co-design challenge to address. This study also provides a foundation on the control side for future research on how reliability and power absorption performance may collectively impact the levelized cost of energy (LCOE), marking an initial step toward this essential analysis.
Grid/off-grid integration, power take-off and control
Power optimisation of a heaving buoy in a wave-enhancing contraction
Power optimisation of a heaving-buoy wave-energy device will be considered for a device placed in a wave-amplitude enhancing (V-shaped) contraction. The device has a nonlinear wave-to-wire model consisting of three components: (i) hydrodynamics, (ii) buoy motion and (iii) power generation. It is ideally placed in a breakwater or in an array of contractions moored at sea. The model will be partitioned and analysed in (ii-iii) a buoy-generator sub-model/set-up and (i-ii) a hydrodynamic wave and buoy sub-model. The (ii-iii) buoy-generator model will either be driven by a specified hydrodynamic force or via a driven hanging system, the latter also designed and built for model validation in the dry laboratory wave tank. Advances of the buoy-generator sub-model (ii-iii) are: (a) extension to an $N$-induction-coil model, enhancing power output relative to a single coil of similar length; (b) nonlinear simulations of the ordinary differential equations of the buoy-generator model; (c) adaption of a Shockley power-using load showing that it is similar to a Butler-Volmer battery model; and, (d) experimental validation of the dry model hanging from a driven moving point in its dry setting. Advances for the wave-buoy sub-model (i-ii) are in progress and will include: the numerical potential-flow model with reduced/optimized vertical resolution, coupled to buoy motion, and an efficient numerical strategy to couple nonlinear wave hydrodynamics of this wave model and buoy motion, using a novel inequality-constraint technique, formulated here.
Power optimisation of generator, laboratory data, wave model, inequality-constraint formulation
The Development of China’s National Marine Test Sites and Field Testing Technology
the Open Sea Test Sites, which is called National Marine Test Site in China, plays an irreplaceable role in promoting the development and utilization of marine renewable energy. It provides R&D entities with complete, open, and shared test conditions, enhances the maturity of marine energy converters through field testing and evaluation, reduces R&D costs, and facilitates the development of green, safe, and pollution-free marine renewable energy. China has initiated the construction and operation of national marine test sites. In accordance with the layout of "North, East, South, shallow seas + deep seas", the Ministry of Natural Resources is systematically advancing the construction of national marine test sites. Currently, four national marine test site areas have been planned, namely Weihai, Zhoushan, Zhuhai and Shenhai. This paper introduces the functional positioning and construction progress of the four test sites in Weihai, Zhoushan, Zhuhai and Shenhai, and analyzes the core functions of each site area. On this basis, combined with the field testing requirements of tidal current and wave energy converters in China, the field testing and evaluation methods that have been carried out field testing work for tidal current and wave energy converters are introduced. The field testing systems developed for power characteristics and power quality characteristics are presented. Using the established field testing methods and the developed field testing systems, the field testing work were conducted on tidal current energy converters and wave energy converters. This paper aiming to provide references for technical exchanges and cooperation among international peers.
Operations, maintenance and decommissioning
A spectral-domain wave-to-wire model for wave energy converters with a geared rotary generator
Numerical modelling plays a pivotal role in the design and optimization of wave energy converters. Spectral-domain (SD) modelling has recently received significant research interest as a newly emerging numerical tool. SD modelling is commonly characterized as an extension of frequency-domain (FD) modelling but can incorporate nonlinearities. Thereby, it combines high computational efficiency and adequate accuracy. Previous studies have demonstrated the applicability of SD modelling to a variety of nonlinear hydrostatic/hydrodynamic effects, including viscous drag force, nonlinear hydrostatic force, nonlinear mooring force, etc. However, there also exist influential nonlinear effects in the power generation phase in wave energy conversion. For instance, previous studies have demonstrated that the current limit of the electrical generator could impact the PTO force and the dynamics of the whole system. Therefore, it is necessary to further develop the SD modelling to cover the entire wave-to-wire process in WECs. In this paper, a SD model is derived to simulate the wave-to-wire process of a point absorber WEC. A mechanical PTO system coupled with a rotary permanent-magnet generator is considered for the WEC. Representative nonlinear effects of the wave-to-wire process are incorporated, including viscous drag force, nonlinear PTO force, and the current limit of the generator. A nonlinear time-domain (TD) wave-to-wire model is established correspondingly to serve as the accuracy reference because it is inherently associated with higher modelling fidelity. The dynamic response and the power performance of the proposed SD model are verified against those of the nonlinear TD wave-to-wire model. Additionally, the computational efficiency of the proposed SD model and the TD model is identified and compared.
A simplified approach to optimize wave attenuation for floating energy islands: the role of flat plates
Recent advancements in offshore energy technologies have positioned floating offshore energy islands as cost-effective solutions for large-scale marine energy production [1]. The Mediterranean Sea, abundant in natural resources such as waves, wind, and solar irradiation, has been identified as an ideal location for the innovative Floating Energy Archipelago, a concept recently proposed by the National Research Council of Italy. A key challenge in realizing this vision lies in creating a sheltered marine area with reduced wave heights, enabling the safe deployment of floating renewable energy systems, such as solar islands [2]. To address this challenge, the hydrodynamic performances of a box-type floating breakwater augmented with flat plates are evaluated in this study. The flat plates, arranged symmetrically and asymmetrically, are designed to improve wave attenuation, with their effectiveness assessed through key performance metrics such as transmission, reflection, and dissipation coefficients [3]. Additionally, the dynamic response of the structure under various sea states is analyzed, offering critical insights into its feasibility for integration with a Power Take-Off system. This dual analysis is crucial: wave attenuation performance determines the capability of the breakwater in protecting the energy archipelago, while global wave-induced motion inform future PTO system design and implementation. This study develops a simplified numerical model based on Morison-type equations to provide an efficient decision-support framework for early-stage design and optimization [4] . To account for viscous effects, the drag coefficient is determined through both experimental testing and high-fidelity Computational Fluid Dynamics simulations. This coefficient is subsequently incorporated into the simplified model to ensure an accurate representation of fluid-structure interactions, with a particular focus on assessing the impact of the flat plates. Preliminary results indicate that the integration of flat plates significantly improves the hydrodynamic performance of the box-type floating breakwater, reducing wave transmission and contributing to the creation of a sheltered area, while enhancing stability under various conditions. The ability to adapt the configuration of the flat plates - whether in terms of symmety and geometry - offers further flexibility to optimize performance based on site-specific requirements. This research highlights the ability of flat plates to enhance wave attenuation in marine infrastructure while supporting the development of hybrid systems with energy generation capabilities. The findings contribute to scalable and cost-effective solutions for the Floating Energy Archipelago, reinforcing its role as a key driver of blue energy transition.
A Study on Optimal Layouts of Multiple Point-Absorber Wave Energy Converters Using Metaheuristic Algorithms
The design of ocean wave energy structures depends heavily on the geometry and layout of the structures. Particularly, when multiple structures are installed near the coast, their optimal placement based on incident wave conditions becomes a critical design factor for maximizing energy extraction. Thus, the optimization of the layout of multiple ocean wave energy structures involves determining the most efficient arrangement that maximizes energy production while considering interactions between the structures. However, as the number of design variables increases, the time and computational effort required for optimization also grows significantly. To address this, optimization algorithms can be employed to derive efficient and accurate optimal design variable values within a shorter timeframe. Specifically, metaheuristic algorithms are advantageous as they can avoid local maxima and achieve global maxima with fewer computations. In this study, the optimal layout of multiple point-absorber wave energy converters (WECs) installed in front of a vertical sea wall was determined using metaheuristic algorithms to maximize wave power generation efficiency. All WECs were assumed to have the same size and shape, and the design variables included the position of each WEC (x,y), the distance from the vertical wall, and the spacing between WECs. For the hydrodynamic analysis of the WECs, the commercial hydrodynamics program Ansys AQWA was utilized. A metaheuristic algorithm implemented in Python was integrated with the AQWA computational process to establish an optimization framework. The optimization was performed using metaheuristic algorithms such as Differential Evolution, Particle Swarm Optimization (PSO), and Advanced PSO, which were tested and validated in previous studies (Jeong and Koo, 2023). Finally, the optimal positions of the WECs for maximum power generation efficiency were calculated, and the resulting values and trends in power production were analyzed.
Enhancing the performance of a BBDB using sloshing tanks
This work investigates the potential of improving the performance of a Backward Bent Duct Buoy (BBDB) wave energy converter by integrating sloshing tanks into its structure. A frequency-domain model is developed to couple the hydrodynamic response of the BBDB with additional pitch moments generated by sloshing, which are computed using Smoothed Particle Hydrodynamics (SPH) simulations with \textit{DualSPHysics}. The influence of four tank geometries is assessed, focusing on how their dynamic behaviour interacts with the BBDB’s peak energy absorption frequency. Results show that the linearised model is valid for small pitch angles, and a particle spacing of dp=0.004m provides sufficient resolution for accurate simulation of the sloshing response. When the sloshing resonance matches the BBDB’s response period, energy capture is significantly enhanced achieving a maximum 40% increase in Capture Width Ratio. However, this improvement is frequency-dependent and not guaranteed for all configurations. Larger pitch amplitudes did not always translate into better performance.
A Review of Wave Energy Converters for Stabilisation and Power Output Optimisation of Floating Offshore Wind Platforms
Hybrid wind-wave systems, which integrate floating offshore wind turbines with wave energy converters, have emerged as a promising solution for enhancing the stability and energy efficiency of offshore renewable platforms. This review explores recent advances in the use of wave energy converters and control strategies aimed at improving platform motion suppression, structural load mitigation, and power production within hybrid wind-wave systems. Particular emphasis is placed on the dynamic coupling between wind and wave subsystems, with a focus on co-optimised control approaches that leverage the power take-off of wave energy converters to support traditional wind turbine control mechanisms. The review includes an overview of classical wind turbine control, passive damping techniques such as tuned mass dampers, and recent methodologies that combine conventional wind turbine controllers with power take-off control systems. Additionally, a comparative summary of typical hybrid wind-wave systems topologies and control architectures is presented.
Numerical investigation of a novel hybrid wind-wave system and its variable pneumatic chamber volume control
This work presents a numerical investigation of a novel control system for a new hybrid wave-wind energy floating platform. It comprises the design of a control system for controlling the variable pneumatic chamber volumes coupled with the hydrodynamics of the floating platform to maximise wave power production. The numerical model is developed in the object-oriented non-casual language Modelica, for which a new module for the control system was integrated into an existing package developed at IST/ULisboa. A sensitivity analysis of the main control parameters in terms of techno-economic parameters is performed and analysed. Results show that the envelope of control parameters’ values for increasing conversion efficiencies and power production is narrow, and an increase of about 30% was achieved with the best case compared with the base case. Moreover, it was observed that the variable volume of the pneumatic chambers shows significant variations on a part of the operational periods typical of the west of Portugal.
pneumatic chamber variable volume control
Experimental investigation of a novel wave energy floating platform for hybrid wind-wave applications: The OctaPlat
The work presents the process of model design and testing and the experimental results for the OctaPlat, a new wave energy floating platform, conceived at IST/ULisboa. A physical model was designed on the basis of the Octaplat concept, which comprises five oscillating water columns (OWCs). The physical model design considered only three of the five OWCs due to infrastructure constraints and was made of acrylic material on a scale of 1:100th scale. The experimental campaign comprised free decay tests and tests under both regular and irregular wave conditions. Different power take-off systems for OWCs (impulse air turbines) were approximated through small orifices. Parameters such as RAO, dimensionless pressure, and the capture width ratio (CWR) were determined and analysed to understand the model performance under different conditions. Under regular waves, the results showed that the coupled hydrodynamic interaction between pitch and surge motions mainly affects the chambers located at the outer edges of the platform. Furthermore, the RAOs of the OWCs seem to be influenced by the natural coupled heave frequency, the natural frequencies of OWC1 and OWC3, and possibly the submultiple of the coupled heave natural frequency (k=1.5). Results also show that the different orifice plates considerably affect the CWR and the peaks' frequencies of its maximum values. Under irregular waves considering full-scale values, for a 2.5 m significant wave height, the peak pneumatic power reached 1.6 MW at 0.077 Hz with an equivalent rotor air turbine diameter of 6.3 m (that is, 30 mm orifice diameter) and 1.9 MW at 0.083 Hz with an equivalent rotor air turbine diameter of approximately 4 m (i.e., 20 mm orifice diameter). For a significant wave height of 3.4 m, the 30 mm orifice produced 3.6 MW at 0.077 Hz, while the 20 mm orifice reached 3.8 MW at 0.091 Hz. These results confirm the platform's feasibility for megawatt-scale wave energy conversion, supporting a key claim of this technology. The experimental results were compared with the numerical ones in terms of CWR. Good agreement was found between both, with a coefficient of determination (R^2) of about 0.94, and the relative difference between them was always less than 20%, except for a few peak deviations.
Evaluating the Dynamic Response and Power Performance of a Floating Hybrid Wind-Wave Energy System
Hybrid wind-wave systems combine a floating offshore wind turbine (FOWT) with wave energy converter (WEC) units, boosting overall power production and reducing operating expenses, thereby decreasing the Levelised Cost of Energy. Amongst the various WEC concepts to advance to the stage of full-scale prototype development, the Oscillating Water Column (OWC) stands out as one of the most promising. The primary objective of this study is to support the development of a floating, hybrid OWC – wind energy module, intended for deployment in the Fiji Islands. The research integrates the University of Maine’s VolturnUS-S Semi-Submersible FOWT with three cylindrical OWCs embedded within its platform. Experimental investigations evaluated the power performance of the OWCs and the dynamic response of the combined system under various regular wave conditions. Different OWC orifice plate configurations were also tested to assess the impact of power take-off (PTO) damping on platform stability and power generation efficiency. Results indicate that incorporating OWC WEC units significantly improves platform stability compared to the stand-alone VolturnUS-S platform. Additionally, a spatial variation in power generation was observed across the three OWCs, with the aft chamber producing more power than the port and starboard chambers. These findings highlight the substantial development potential of the combined OWC – wind concept, due to its increased power output and improved platform stability. The outcomes of this study are expected to inform the design, construction, and operation of practical hybrid wind – wave energy systems.
Hydrodynamic Response and Energy Conversion Characteristics of the Net-Cage-Integrated Self-Sustaining Pendulum Wave Energy Converter
As the importance of marine energy development increases, deep-sea aquaculture net cages, critical for improving energy efficiency and modernizing fisheries, face challenges such as high power supply costs, maintenance difficulties, and environmental impact. This paper proposes a Two-wing Pendulum Wave Energy Converter (TPWEC) suitable for offshore deep-sea regions. The device captures wave energy through a pendulum wing system, converting it into electricity to support deep-sea aquaculture, while efficiently utilizing marine resources. A three-dimensional numerical wave tank is developed based on viscous flow theory, and convergence analysis is performed using the k-ε turbulence model. The hydrodynamic and energy conversion characteristics of the TPWEC under various sea conditions are analyzed. The results show that the shape of the pendulum wings significantly impacts energy capture. Within a reasonable range, increasing the wing width enhances the wave moment and captured energy, but the rate of increase becomes slower as the width grows. Regarding the PTO damping constant, the system's average power output increases with linear damping up to an optimal point, then decreases. The optimal damping constants vary between 2.5 and 7.5 N·m·s/rad depending on the wave period. Additionally, the spacing between the TPWEC and the aquaculture float structure significantly affects its hydrodynamic response. The motion response is largest when the spacing ratio (D/a) is 1.5. The energy capture efficiency is also influenced by the number and relative positioning of the devices. Maximum energy capture is achieved when six devices are placed symmetrically on both sides of the net cage. Simulation results from Comsol software further confirm the energy output characteristics of the TPWEC. This study concludes that the TPWEC offers high energy efficiency and environmental adaptability, providing a viable solution for integrating renewable energy generation with deep-sea aquaculture systems.
Modelling and control of wave energy converters with nonlinearities: An LPV and robust control approach
This work presents a linear parameter-varying (LPV) framework for the modelling and control of a wave energy converter (WEC) system, explicitly addressing the nonlinear hydrodynamic effects that are critical for accurate representation of the dynamics of the system. Among these effects, viscous drag, for example, is a significant contributor to the nonlinear behaviour of WECs, particularly under realistic operational conditions. By incorporating this nonlinear behaviour directly into the LPV definition, the proposed framework provides a systematic approach to bridge the gap between traditional control-oriented models, which often oversimplify these phenomena, and the complex nonlinear dynamics of practical systems. The methodology begins with the definition of a quasi-LPV system to represents the nonlinear dynamics of the WEC. The nonlinear contributions, including those stemming from viscous drag, are embedded into the parameter-varying structure, enhancing the ability of the model to capture the true behaviour of the system. A realistic wave excitation input, modelled using the JONSWAP spectrum, is employed to validate the LPV model. This validation demonstrates the capacity of the LPV model to represent key nonlinearities, while retaining sufficient simplicity to facilitate analysis and control design. To further advance the framework, the nonlinear system is reformulated in a Linear Fractional Transformation (LFT) form. This transformation enables a robust control design that leverages the flexibility of the LFT representation to incorporate structured uncertainties. The control strategy is designed to address both parametric uncertainties, such as variations in system parameters due to environmental changes, and non-parametric uncertainties, which may arise from unmodelled dynamics or sensor dynamics. The proposed robust control loop operates as a reference-tracking energy-maximising framework. The reference signal, representing an optimal velocity trajectory, is generated externally and provides a target for the control system to follow. Weighted transfer functions are used within the control design to ensure both performance optimisation and robustness to uncertainties. This approach highlights one of the key strengths of the methodology: its ability to guarantee an acceptable level of performance even in the presence of significant uncertainty, thereby enhancing the reliability of WEC operation under varying ocean conditions. Simulation results validate the proposed approach, showcasing its ability to maximise energy extraction while effectively managing the nonlinearities and uncertainties inherent to WEC systems. The incorporation of viscous drag into the LPV model proves crucial in capturing the complex dynamics of the system, ensuring that the control strategy is well-tuned to the actual behaviour of the device. Furthermore, the robust control design demonstrates strong performance across a range of scenarios, highlighting its potential for real-world implementation. This work provides a comprehensive framework for integrating nonlinear hydrodynamic effects into WEC models and emphasises the critical role of robust control in achieving reliable and efficient operation. By addressing key challenges in modelling and control, the presented methodology contributes to advancing the practical deployment of wave energy systems, establishing the way for more effective utilisation of renewable ocean energy resources.
Numerical analysis of design variations in a longline aquaculture system under wave and current loads
This paper presents a numerical study on the behavior of a longline system with lantern nets subjected to wave and current loads. The system consists of a main longline secured at both ends by chains connected to anchor points, along with buoys and lantern nets suspended from the longline. The system is modeled using OrcaFlex, employing a lumped-mass approach for line objects. Hydrodynamic loads are incorporated through an extended form of the Morison equation, with drag and inertia coefficients sourced from the literature. The study examines the system's response under various environmental conditions, including different wave heights, periods, current speeds, and headings. Regular waves are analyzed in combination with currents. The operating depth of the lanterns is explored as a potential adjustable parameter that could be optimized for both productivity and survivability. This study investigates how variations in depth affect system performance, as lowering the lanterns may help reduce wave-induced loads and motions. To accommodate different lantern depths, five design variations are proposed and evaluated. Anchor loads and lantern motions are analyzed and compared, using the baseline model as a reference. All design variations were evaluated based on multiple performance criteria. DV1 and DV2 reduced horizontal lantern motion and mean inclination due to deeper lantern placement, with DV2 also decreasing anchor loads by using longer buoy lines. DV3, which incorporated fewer surface buoys and a submerged longline, achieved a significant reduction in anchor tension, up to 40% compared to the baseline, while also minimizing lantern motion and maintaining compatibility with existing infrastructure. DV4, which used ballasted lanterns, effectively reduced mean inclination by up to 74%, but increased anchor loads due to the added weight. DV5 performed similarly to DV4, notably reducing mean inclination and increasing anchor loads, but also introduced operational complexity due to its double longline configuration.
Station-keeping, moorings and foundations