bluuebunny/crossref_metadata_2025 huggingface dataset:
Towards increased social acceptability of marine renewable energy
Authors: Dunphy Niall P. , Lennon Breffní , Smith A. Luke , Uyarra María C. , Gonçalves Janete , Soulard Thomas , Zubiate Laura
Published: September 2023

The development and deployment of novel technologies, including those associated with marine renewable energy, are vital for the ongoing decarbonisation of our energy system. However, technology on its own is not sufficient to realise the energy transition away from fossil fuels. Non-technical barriers – such as regulatory, economic, environmental or social aspects – can be a substantial impediment to widespread adoption of renewable energy technologies. One such impediment, is public opposition to specific deployments of renewable energy and/or indeed to the use of particular technologies. Within the SafeWAVE project, we are cognisant of the importance of good community relations and the need to develop two-way communication with stakeholders to facilitate the successful scaling up of ocean energy device deployments. Accordingly we have worked to co-develop and demonstrate a framework for education and public engagement (EPE), specifically aimed at ocean literacy for communities in France, Ireland, Portugal and Spain. This EPE framework aims to go beyond social acceptance, which is often equated to acquiescence to a fait accompli, and is designed to contribute to the development of projects which exhibit inherent social acceptability.

This paper presents the work within SafeWAVE project to develop the EPE framework with input from the communities. The first part of the paper reports on critical review of selected EPE programmes associated with marine energy test sites and infrastructure deployments, with methods adopted in each case analysed, key challenges faced identified, and best practices documented.  Next a framework for public education and engagement is presented, which builds on this review and draws from literature across multiple disciplines – including sociology, psychology, political science, education.  Finally, leveraging this developed knowledge the collaborative process of deriving tailored EPE programmes on ocean literacy around marine renewables for the four focal communities is outlined and described. These programmes are intended to reach out to, and engage with, local communities, interested stakeholders and the wider public on issues surrounding the deployment of ocean energy devices, including but not limited to: effects on local communities, implications for marine life, potential impacts for water users, etc.

The paper concludes by discussing the experience of developing the bespoke programmes, outlining emergent feedback from trialling of key elements of the programmes, discussing experiences and proffering guidance based on lessons learned.
Assessing the effect of onshore and offshore Wave Energy Converters on seafloor integrity combining image-based and acoustic methods
Authors: Muxika Iñigo , Vinagre Pedro , Le Bourhis Enored , Villarín Enric , Tanguy Florian , Niclot Clèment , Bald Juan
Published: September 2023

The European Atlantic Ocean offers great opportunities for the development of projects for renewable energy extraction, and the Marine Renewable Energy sector is developing different technologies for energy converters, including Wave Energy Converters. Besides, the European Commission is adopting measures and politics to increase the installed capacity of ocean energy. However, there are still uncertainties on the potential environmental effects of wave energy converters, which led regulators and stakeholders to perceive their operation as a risky activity.
To overcome the non-technological barriers that could hinder the development of marine renewable energies, and improve the knowledge on the impacts on the seafloor integrity (among others), SafeWAVE project set an Environmental Research Demonstration Strategy based on the collection, processing, modelling, analysis and sharing of environmental data collected in Aguçadoura (Portugal), Armintza (Spain) and Le Croisic (France) representing different types of technology, locations and project scales.
Video recordings were carried out, using Remotely Operated Vehicles, to identify the environmental impacts of the moorings on the seafloor morphology. That information was completed by side scan sonar campaigns using an Autonomous Underwater Vehicle.
The video recordings were useful also to assess the attraction effect of the moorings to epibenthic invertebrates and fishes, whereas the side scan sonar provided quantitative information on the area affected by physical alteration (<1% of the total area occupied by the devices at Armintza and Le Croisic).
Understanding the force motion trade off of rigid and hinged floating platforms for marine renewables.
Authors: Arredondo-Galeana Abel , Dai Saishuai , Chen Yongqiang , Zhang Xiantao , Brennan Feargal
Published: September 2023

In this work, we compare the motion and structural response of a rigid and hinged floating structure subject to regular waves. We do this to understand better whether what is the best option for floating marine renewable installations. The hinged structure has two hinges and three pontoons, whilst the rigid structure is made by replacing the hinges with rigid steel bars. We instrument the pontoons with motion detection spheres and with strain gauges to measure vertical point loads. We find that the motion response of the platforms is similar between hinged and rigid at low and high frequencies. However, at intermediate frequency waves, single and triple sagging occur for rigid and hinged structures, respectively. We find significant load alleviation for the hinged structure in the range of frequencies where sagging behaviour occurs. These insights reveal that hinged design can contribute to long term survivability by reducing loads in the structure, whilst identification of motion patterns and natural frequencies are necessary to select operating modes for marine renewable generators mounted on the platforms.
Turbine fatigue load prediction from field measurements of waves and turbulence
Authors: Mullings Hannah , Stallard Tim , Draycott Samuel
Published: September 2023

The interest in this work is understanding the conditions which contribute to the cyclic loading experienced by a tidal turbine. Tidal turbines are placed in locations with high flow speeds in order to extract maximum kinetic energy. These flow speeds combined with other environmental factors can lead to a complex operating conditions. When assessing turbine loading across a site, most models use ambient flow conditions, with very few codes including the impact of waves with currents. Previous studies have analysed the influence of wave conditions from measurements on the loading, through a consideration of the turbine not operating. Although tidal conditions are bi-directional, wave conditions do vary with direction and this combination will be investigated in this study.

Full-scale site data was gathered at Le Raz Blanchard, a potential tidal site as part of the Interreg funded TIGER project. The focus in this study is on data gathered which provides both wave and current conditions over a period of 45 days. Loading on the turbine components is assessed through an efficient blade element momentum theory method, which is combined with a synthetic turbulence model to provide a time-varying onset flow. This work determines the impact of the measured waves, and the way in which they are analysed on the turbulence characteristics in the onset flow, specifically the interaction of waves with current and influence on the loading experienced on the turbine.
A probabilistic framework for fatigue damage of lift based wave energy converters
Authors: Arredondo-Galeana Abel , Lamont-Kane Paul , Shi Weichao , Folley Matt , Brennan Feargal
Published: September 2023

Wave cycloidal rotors are lift based wave energy devices that have shown great potential to harness the energy of the waves through the use of submerged hydrofoils. Although the lift force of the foils can be controlled passively or actively to maximise power extraction, the foils of the rotor are subject to variable loading which can expose these components to premature mechanical failure. Therefore, it is important to develop novel fatigue analysis tools that help predicting the lifetime of this type of lift based devices. In this paper, we test the hypothesis that when cyclorotor operates at constant rotational velocity in irregular waves, the fatigue damage of the hydrofoil stress hot spot can be computed through a probabilistic approach. We compare our results to the fatigue damage computed with well established deterministic methods. We find that for both narrow and broad band stress energy spectra, the probabilistic method works well at high probability sea states, when the range of stresses does not exceed the inflection point of a double slope SN curve. This is a promising outlook since it confirms that the fatigue damage of these versatile lift based wave devices can be treated in a similar fashion to the fatigue damage of conventional offshore structures.
Hybrid wind-wave systems: The case of the VolturnUS-S semi-submersible platform
Authors: Hengstmann Maximilian , Portillo Juan Carlos Chong , Gato Luís Manuel de Carvalho
Published: September 2023

Wind-wave hybrid floating systems are subject to active research and development in academia and industry. Industrialization of hybrid wind-wave energy systems will benefit from modular designs, allowing floating platforms to be used with or without wave energy converters (WECs). This work explores the design process to use oscillating water column (OWC) WECs as modular add-on features to existing semi-submersible floating platform designs. As the base case design, the IEA 15 MW offshore reference wind turbine with the VolturnUS-S floating platform designed by the University of Maine was used. A design approach was proposed, which involved various tools, such as OpenFAST developed by NREL, and the OWC Modelica tool developed at IST/ULisboa. Aero-hydro-servo-elastic simulations were performed to analyze the influence of the wind turbine energy generation design modifications and damage equivalent loads (DELs). The hybrid platform was modeled in the OWC Modelica tool to assess the wave energy conversion and the interaction between OWCs and the floating platform. The investigated hybrid design did not significantly increase DELs of the wind turbine in aero-hydro-servo-elastic simulations. The hybrid system does not decrease the LCOEcompared to a standalone floating wind turbine. The main cost driver was identified to be the material of the OWCs' ducts. Furthermore, the coupling forces between OWCs and the floating platform were found to be in the same order of magnitude as the wave excitation and radiation forces. The  possibilities of including these forces in OpenFAST and the challenges for this are discussed.
Informing development of a socioeconomic data collection toolkit for marine energy: a literature review
Authors: Rose Deborah , Freeman Mikaela , Kaplan Marley
Published: September 2023

Marine energy projects have the potential to create significant benefits by stimulating economic growth, improving local infrastructure and services, and providing energy security and resilience. Collecting social and economic data is necessary to anticipate potential benefits or adverse impacts, and to develop and appropriately site marine energy projects that suitably address community needs, incorporate and align with community values, and satisfy consenting requirements. Despite the importance of this information, consistent methodology for social and economic data collection to inform marine energy development is lacking. We review the literature from marine energy, other renewable energy industries, and relevant coastal sectors to identify common metrics, methods, and applicable tools for collecting data on social and economic effects. From this, we synthesize our findings and identify lessons learned that will form the foundations of a methods toolkit and template for data collection. This literature review and the eventual development of the toolkit will enable marine energy projects to identify, avoid, and mitigate potential negative effects at the forefront. By sharing findings from the literature and the lessons learned in the process of creating the toolkit, we hope to continue to advance the marine energy industry in a way that promotes energy equity, ensures environmental justice, and centers community values and needs.
Techno-economic analysis of marine hybrid clusters in two potential Latin American markets
Authors: Gorr-Pozzi Emiliano , Olmedo-González Jorge , Selman-Caro Diego , García-Nava Héctor , García-Vega Fabiola , Odériz-Martinez Itxaso , González-Huerta Rosa de Guadalupe , Zertuche-González José Antonio , Silva Rodolfo
Published: September 2023

Contemporary communities require innovative solutions to cope with projected increases in demand for natural resources. Diversification and modernization of the energy matrix through the affordable and efficient harnessing of marine renewable energies (MRE) are possible means to mitigate the vulnerability of coastal communities and climate change. While the offshore wind sector has reached sufficient maturity to compete in the energy market, other MRE, such as wave energy, are still in the development phase, which limits their financing and commercial deployment. This study aims to evaluate the techno-economic feasibility of maritime hybrid clusters (MHC) powered by wave energy converters (WEC) and offshore wind turbines (OWT) to electrify households and the marine aquaculture sector, where electricity surpluses can be stored in lithium-ion batteries or for green hydrogen production. Different scenarios for WaveDragon (WD) and Pelamis (PEL) WEC farms were studied in two coastal communities, Coquimbo (Chile) and Ensenada (Mexico). The mean annual wave power availability at Coquimbo is high (26.05 kW/m) and of Ensenada, moderate (13.8 kW/m). The wave energy shows less inter- and intra-annual variability in Coquimbo than in Ensenada. The hybridization between WECs and OWT covers the total electricity consumption, where the PEL-OWT system is the cost-effective option in Ensenada and WD-OWT in Coquimbo. Ensenada demonstrated a higher electricity surplus than Coquimbo, profitable result of storing it to sale in the electricity market or for hydrogen production. For both selected WECs, the seaweed aquaculture integration in a blue economy framework generates higher returns than households, higher in Coquimbo than Ensenada.
Development of an Unmanned Mobile Current Turbine Platform
Authors: Dhanak Manhar , Beaujean Pierre-Philippe , Frankenfield John , Hall Adam , Henderson Edward , McKinney Adriana , Pimentel Hugo , Tran Thanh Toan
Published: September 2023

A prototype low-flow (~0.5 m/s) marine current turbine for deployment from a small unmanned mobile floating platform has been developed at Florida Atlantic University for autonomously seeking and harnessing tidal/coastal currents.  The support platform is an unmanned surface vehicle (USV) in the form of a catamaran with two electric outboard motors and with capabilities for autonomous navigation. An undershot water wheel (USWW), aided by a custom flow concentrator, has been selected as the basic design for the marine current turbine, which is mounted on the stern of the USV.  The concept of operation is that the unmanned surface vehicle would navigate to a designated marine current resource, autonomously anchor at the location, align itself in the current, and deploy the USWW turbine using a custom cable-lift deployment mechanism. As the USWW harnesses the local current, an onboard power-take-off (PTO) device converts the harnessed mechanical energy to electricity which is stored in onboard batteries.  The selected PTO utilizes a spur drivetrain/gearbox coupled with a NuVinci Ball-continuously variable transmission (CVT). It is estimated that the small prototype turbine system will produce over 12W power for currents over 0.5 m/s.  The automated anchoring system consists of an electric winch, a Rocna anchor, anchor chain/rode and a line locking mechanism designed to aid in taking tension off the winch. Preparations have been made to test and demonstrate the application of the platform in harnessing tidal currents in the Intracoastal Waterway in South Florida and coastal currents at locations off Fort Lauderdale, Florida. The preparations include obtaining the necessary environmental permits for conducting in-water testing; developing required mitigation measures in protecting local wildlife and their habitats; and identifying potential in-water test sites and surveying them for their suitability in terms of current resource, bottom type, water depth and local boat traffic. Application of the marine current turbine platform to serve as an unmanned mobile floating recharge station for small aerial drones will be demonstrated. For this purpose, the USV includes a flight deck for landing and takeoff of small aerial drones whose batteries would be recharged via a wireless direct-contact recharging pad powered by the onboard batteries.  Modeling in support of turbine design and parametric studies in support of optimization of the performance of the system will be discussed.  Scaling of the prototype system in terms of size and capacity will be discussed.
On data-based control-oriented modelling applications in wave energy systems
Authors: Pasta Edoardo , Paduano Bruno , Mattiazzo Giuliana , Faedo Nicolás , Ringwood John V.
Published: September 2023

The development of effective energy-maximising control strategies has a crucial role in the empowerment of wave energy technology, and in its improvement towards economic viability. Within the state-of-the-art, most of the strategies adopted to maximise the absorbed energy exploit a model of the wave energy converter (WEC) to be controlled, i.e. they are model-based. These models attempt to replicate the WEC dynamics with a sufficient degree of fidelity, trying, at the same time, to minimise their associated computational burden. However, due to the presence of the hydrodynamic effects , which inherently characterise wave energy systems, simultaneously achieving high-fidelity and computational efficiency is not trivial. Oversimplification of the problem through, for example, linearity assumptions, could lead to non-representative models and/or large uncertainty levels. To overcome these issues, in the last decade, several approaches based on data have been proposed in the wave energy field. These approaches, falling under the umbrella of system identification techniques, exploit data coming from experimental tests or high fidelity simulations, and build control -oriented models with a pre-defined level of complexity. In this paper, we analyse the different strategies that have been adopted in the literature to build data-based control-oriented models for WECs, highlighting the characteristics of each approach, together with their opportunities and inherent drawbacks. An analysis of eventual “partial” data-based modelling of WEC subsystems (e.g. moorings, PTO, or hydrodynamics only) is also reported. Moreover, considerations on the choice of inputs and outputs depending on the WEC type are reported, in  an attempt to highlight the different issues that characterise the system identification problem depending on the WEC technology. Finally, conclusions are drawn regarding the capabilities that this type of approach has in (at least partially) solving the modelling issues that affect WEC control system design, and the pitfalls that pure adoption of these strategies has when applied on larger scales, or in the operational stage.
Fatigue-life prediction methods of a dynamic power cable for a floating testing platform – a numerical approach
Authors: Benites-Munoz Daniela , Ricci Pierpaolo , Touzon Imanol , Salcedo Fernando , Raymond Rupert , Nunes Diogo
Published: September 2023

Floating testing platforms and marine energy devices use Dynamic Power Cables (DPC) to connect to the testing centres or the national grids. These power cables are, therefore, an inherent component in the reliable operation of the floating structure, and their integrity throughout the design life of the device should be ensured from the early stages of the project. Fatigue failure is one of the most common factors affecting the cable's performance due to the cyclic loads caused by waves and currents. However, accurately estimating the fatigue life of DPC has proved challenging due to their material and geometric nonlinearities. In addition to fatigue failure, the cable design life is also characterised by its ability to withstand extreme conditions on-site.

This paper addresses the design, analysis and specification of a dynamic power cable that will be deployed at the Biscay Marine Energy Platform (BiMEP) for the connection of the HarshLab 2.0, a floating testing platform for materials, subsystems and components developed and operated by Tecnalia. BiMEP is exposed to severe waves that induce large motions on the HarshLab buoy, and different numerical models for the analysis of the hydrodynamic response are reviewed and calibrated against model tests.

To address a comprehensive study of the power cable at the design stage, this paper focuses on reviewing different fatigue-life prediction methods employed for a DPC, considering the damage in the steel armour and the conductor cores. It also covers the cable's response when the system operates under extreme sea conditions and the potential implications of sensitive variables such as loss of buoyancy and marine growth. To perform the fatigue-life study, long-term cyclic loading in each cable component was compared with its resistance to fatigue damage. In this case, the damage for each variable was derived from stress- and strain-based curves for the high-strength steel (armour) and the copper (core conductor) depending on the selected approach.

The design iterative process using the studies performed in this paper led to the definition of a Lazy Wave design with a high-level optimisation of some components, e.g. the ballast and buoyancy modules and the bend stiffener. In general, the behaviour across the cable length is similar between the different fatigue-life approaches, with the most significant expected fatigue damage found in localised hot spots near the bend stiffener and the belly (sag-bend region) of the cable, before the buoyancy modules. It is found that, despite a significant difference across the magnitude of fatigue life estimated in sensitive areas, the final design complies with all design criteria and reaches a satisfactory fatigue life.
Beta-version Testing and Demonstration of the Design Load Case Generator
Authors: Neary Vincent , Ahn Seongho , Michelen Carlos , Ahn Seongho , Coe Ryan , Penrose Graham , Bruggemann Mark , Spinneken Johannes
Published: September 2023

International standards for the design, type-classification and certification of marine energy systems, including wave and current energy converters, are essential for the commercialization of these technologies, but their compliance requires significant effort and resources by project developers; e.g., finding the appropriate met-ocean datasets, processing and analysing this data to estimate the design load conditions, design type-class and load response. Herein we present efforts to address these challenges by developing, beta-testing and demonstrating a web-based tool, the “Design Load Case (DLC) Generator.” This tool integrates a host of data search, processing and statistical tools to streamline the analysis of design load conditions and to determine the design load requirements as in the International Electrotechnical Commission (IEC) 62600-2 design standard. It is demonstrated for a test DLC analysis case for the Reference Model 3 (RM3) point absorber at the PacWave South test site. This test case highlights some of the challenges determining design load requirements and the benefits of facilitating a complex workflow within a single web-based platform that leverages a diverse set of data processing and statistical tools. The DLC Generator facilitates and streamlines DLC analyses for significant time and cost savings on a variety of tasks in a complex workflow, including site data search and retrieval, data quality control, extreme value statistical analyses, and archiving of dynamic load response model inputs and outputs.
Solution verification of WECs: comparison of methods to estimate numerical uncertainties in the OES wave energy modelling task
Authors: Eskilsson Claes , Shiri Alex Abolfazl , Katsidoniotaki Eirini
Published: September 2023

High-fidelity models become more and more used in the wave energy sector. They offer a fully nonlinear simulation tool that in theory should encompass all linear and nonlinear forces acting on a wave energy converter (WEC). Studies using high-fidelity models are usually focusing on validation of the model. However, a validated model does not necessarily give reliable solutions. Solution verification is the methodology to estimate the numerical uncertainties related to a simulation. In this work we test four different approaches: the classical grid convergence index (GCI); a least-square version (LS-GCI); a simplified version of the least-square method (SLS-GCI); and the ITTC recommended practice. The LS-GCI requires four or more solutions whereas the other three methods only need three solutions. We apply these methods to four different high-fidelity models for the case of a heaving sphere. We evaluate the numerical uncertainties for two parameters in the time-domain and two parameters in the frequency domain. It was found that the GCI and ITTC were hard to use on the frequency domain parameters as they require monotonic convergence which sometimes does not happen due to the differences in the solutions being very small. The SLS-GCI performed almost as well as the SL-GCI method and will be further investigated.
Analysis of the viability of a radial Double Decker Turbine for application in Oscillating Water Column devices
Authors: Vega-Valladares Aitor , Pereiras Bruno
Published: September 2023

Oscillating Water Column (OWC) devices are the most widespread among the different systems developed to harness the wave energy available on our coasts. Air turbines, normally used as Power Take Off (PTO) in these devices, are their most controversial part. Unidirectional turbines were first used with rectifying valves to take advantage of both characteristic operating stages of the OWC: exhalation and inhalation. The use of valves was quickly discarded and bidirectional turbines, which rotate in the same direction regardless whence the flow comes, were adopted as the most common solution despite reaching lower efficiencies than unidirectional ones. The Twin Turbine Configuration (TTC), based on the use of two unidirectional turbines, emerged then as a promising system, its main drawback being the duplicity of the equipment. The Double Decker Turbine (DDT) concept has been recently introduced to overcome these limitations since it combines in a single design the two typical solutions: self‐rectifying behaviour and the use of unidirectional turbines. In this work, the performance of a radial DDT, composed of an InFlow Radial (IFR) turbine and an OutFlow Radial (OFR) turbine, is assessed. A CFD model is used to design and optimize an IFR turbine to be mounted in combination with an OFR turbine taken from the literature. Finally, a non‐steady analysis is carried out assuming sinusoidal flow conditions. Results demonstrate that this radial version of the DDT could compete with its axial version and with other alternatives.
High-fidelity modelling of a six-turbine tidal array in the Shetlands
Authors: Ouro Pablo , Stansby Peter , Macleod Alasdair , Stallard Tim , Mullings Hannah
Published: September 2023

Micro-siting tidal stream turbines in a confined seabed area requires a extensive understanding of the flow dynamics over the water column at turbine deployment locations so that operating conditions are assessed, wake effects can be estimated to infer the energy yield [1], or bathymetry effects can be quantified. Tidal currents have the advantage of being highly predictable and mostly bidirectional but the uneven bathymetry found at most of sites introduces a high variability to the flow conditions within relatively short distances. Considering future tidal turbine arrays will comprise dozens of devices, deploying ADCPs at each turbine position would be very expensive or very time consuming, outlining the need for accurate modelling tools to be used as digital twins in micro-siting. Shallow-water models are widely adopted in preliminary design of tidal arrays but fail to capture the three dimensional nature of the flow and predict deflected wakes whose streamwise length is also over-predicted [2]. Thus, eddy-resolving method are required to fully capture the turbulence from the free-stream flow, induced by turbines and from bathymetry. \\

This study provides a real-project application of the state-of-the-art large-eddy simulation (LES) code DOFAS (Digital Offshore Farms Simulator) [3] to the six 100kW-turbine array deployed by NOVA Innovation Ltd. in the Shetlands, UK [4]. The bathymetry data has been obtained from EMODnet database with the velocity profiles set at the inlet condition of both ebb and flood tides imported from Macleod et al. (2019) [4]. The deployment site is characterised by steep slopes with a maximum depth of 45 m at the cross-section where turbines are located. The bathymetry has a downwards slope when the flow goes in the ebb tide direction whilst upstream during flood tide. The tidal rose indicated a slight deviation of about 20$^{\circ}$ between ebb and flood directions. The turbines have a diameter ($D$) of 9 m attached to a 10 m long hub whose diameter is 1 m. Three array configurations have been studied: (i) single row of three turbines, (ii) two rows of turbines spaced 8$D$, and (iii) two rows of turbines spaced 12$D$. The computational domain extends over 600 m by 300 m in the horizontal plane yielding 540 million cells, requiring 32,500 CPU hours to compute 30 min of physical time.\\

Results show that bathymetry effects at this site play a larger role when designing the location of the secondary row of turbines compared to wake effects from upstream turbines. During the ebb tide, the increase in water depth reduces the wake recovery far downstream so that the array with 12$D$ row spacing has a lower performance than the 8$D$ one with approx. 30\% decrease in energy yield. Conversely, the uphill shape of the bathymetry during the flood enables a fast wake recovery so that the downstream row experiences almost no energy yield loss due to wakes.
Experimental Investigation on Performance of Counter-rotating Impulse Turbine with Middle Vanes for Wave Energy Conversion
Authors: Suto Koichiro , Takao Manabu , Ogawa Toi , Okuhara Shinya , Kumar Navneet , Alam Ashraful , Kinoue Yoichi
Published: September 2023

In an oscillating water column (OWC) based wave energy device, a water column that oscillates due to the sea wave motion generates a bi-directional airflow in an air chamber, and finally, air turbine driven by the bi-directional airflow converts the pneumatic energy into the mechanical energy. A counter-rotating impulse turbine for bi-directional airflow has been proposed by M. E. McCormick of the United States Naval Academy in 1978. In previous studies by using CFD analysis, the authors investigated the effect of the turbine geometry on the performance of the counter-rotating impulse turbine for bi-directional airflow, and it was clarified that the efficiency of the turbine is higher than that of an impulse turbine with a single rotor for bi-directional airflow in a range of high flow coefficient.On the other hand, this impulse turbine has a disadvantage that the efficiency in a range of low flow coefficient is remarkably low due to the deterioration of the flow between the two rotors. In a previous study, the authros proposed to installed middle vanes between the two rotors in order to overcome the above drawback. And the effect of the middle vanes the turbine performance was investigated by CFD analysis. As a result, it was found that the middle vanes installed to the turbine rectify the flow between the rotors in a range of low flow coefficient and it drastically increases the efficiency.In this study, the middle vanes was actually installed in the counter-rotating impulse turbine for bi-directional airflow, and its performance was elucidated by wind tunnel tests which has the turbine with a inner diameter of 240 mm and a centrifugal fan. It was found from the experiment result that the turbine performance at low flow coefficient is improved and the peak efficiency increases by 1.14 times, by means of the installation of middle vanes to the turbine.
Instabilities in tidal turbine wakes
Authors: Smyth Amanda , Nishino Takafumi , Young Anna
Published: September 2023

We report on the observation of vortex instabilities in the wake of a tidal turbine undergoing harmonic unsteady axial inflow (e.g. due to surface waves). The work was carried out using unsteady RANS (URANS) modelling using the open-source CFD software OpenFOAM, using the `pimpleDyMFoam' solver. The PIMPLE algorithm used in the URANS solver is a combination of the PISO (Pressure Implicit with Splitting of Operator) and SIMPLE (Semi-Implicit Method for Pressure-Linked Equations) algorithms. URANS simulations usually have a limitation on the time step set by the Courant number (C = u (delta t)/(delta x), where delta x is the minimum cell length and u the local velocity. In the PISO algorithm, C<1 is usually required. However, the PIMPLE algorithm allows stable transient simulations at C>>1 by applying under-relaxation to each time-step until a convergence criterion is met, before allowing the time-step to complete with no applied relaxation factors. The turbulence model used was komega-SST, which has been used extensively in tidal turbine modelling.

As with a wind turbine, the response of a tidal turbine to unsteady flow is heavily influenced by the behaviour of the helical wake that returns in close proximity to the turbine blades  times per revolution ( – number of blades). Unsteady inflow causes the blades to shed vorticity into the wake, which in turn leads to a spatial variation in wake vortex strength, such that the vorticity of adjacent returning wake segments can differ, and thus there is a spatially varying velocity deficit in the wake. This spatial variation in velocity deficit triggers instability in the blade tip vortices, the emergence of which we demonstrate is governed by the non-dimensional group  relating the blade passing frequency to the gust frequency. If the ratio between these two frequencies is an integer, the wake is stable. If not, the tip vortices exhibit various forms of instability. If the wake is unstable, adjacent wake segments will eventually coalesce as they move downstream, such that the wake consists of larger regions of vorticity with lower spatial frequency, compared to the wake immediately behind the turbine. There is also some indication that these unstable, coalesced wakes persist further downstream, compared with stable wakes. This has implications for wind and tidal farm design, where interaction of a row of turbines with the wakes of upstream turbines is an important consideration.
Development and validation of the in-house hydrodynamics code and the DNV software for TALOS wave energy converter
Authors: Sheng Wanan , Michailides Constantine , Loukogeorgaki Eva , Aggidis George
Published: September 2023

The Lancaster in-house code is a time-domain analysis code, developed especially for the TALOS wave energy converter, a novel wave energy conversion technology. The TALOS wave energy converter is a point absorber-like wave energy converter, but with a unique power take-off (PTO) system. The whole PTO system is fully enclosed within the structure, hence no moving parts are exposed to the harsh marine environments.

The PTO of the TALOS WEC consists of a mass ball within the structure, with a number of springs and dampers (for instance, direct drives or hydraulic systems) connecting between the mass ball and the structure. Such an arrangement of the PTOs would make the PTO essentially non-linear, regardless whether the actual PTO dampers are linear or nonlinear as well as the linear springs. Therefore, a time domain analysis must be established for the TALOS WEC. Towards the goal, an in-house time-domain model has been developed at Lancaster University, and now it is to be validated via the delicated numerical models built using well-established commercial software (and in the future via experimental data). Within this framework, the present paper presents an effort for validation using the DNV SESAM commercial hydrodynamic and structural analysis software.  

To build a numerical model for TALOS WEC, the Lancaster in-house time domain code is based on the hybrid frequency-time domain approach. That is, the basic hydrodynamic parameters are analysed using the panel methods (WAMIT, HAMS, NEMOH), and then the relevant parameters are transformed for the Cummins’ time-domain equation, such as the added mass at infinite frequency, and the memory effect (the convolution terms). This work is an extension of the comparison between the in-house code and the DNV SESAM software, and the comparisons would include the relevant hydrodynamic analyses, the time-domain analyses with and without the TALOS PTO system, with the aims towards developing the validated tools of both the in-house code and the commercial software.
Enabling the Ocean Internet of Things with Renewable Marine Energy
Authors: Topper Mathew , Jarnoux Nicolas , Costello Ronan , Murtagh Cian , Giorgi Simone , Kennedy Ben
Published: September 2023

Marine renewable energy can play an integral role in reducing the cost and complexity of collecting data from the oceans, and enhancing its exploitation. The processing and transmission of data at sea may be modelled as an `internet of things' (IoT) application. The `thing' is any offshore device which can collect and process data in-situ, while the `internet' represents the medium for transmitting data. IoT is differentiated from other internet based communication paradigms by the constraints on the system. These constraints are typically limited energy budgets and computing power, intermittent and low-bandwidth connectivity, and limited physical access. While land based IoT applications are already well served by a wide selection of hardware and software components, the needs of offshore IoT applications are not well served. Utilizing marine energy can advance the adoption of IoT at sea by providing in-situ energy generation, whilst also benefitting from the same technology. The Sustainable Energy Authority of Ireland funded `BlueBox' project aims to overcome barriers to entry for applying IoT technologies to offshore sensing by developing Ocean IoT (OIoT) hardware and software solutions. Features of the BlueBox system include modular offshore focussed hardware, no-code configuration and control of peripherals (such as sensors and actuators), duplex transmission of data using multiple media, serverless cloud server architecture and an edge computing framework. This paper presents an overview of BlueBox, tank tests for system validation of a prototype wave-energy powered ocean-observing platform, and a discussion of future applications of the technology.
ANTIFOULING AND ANTICORROSIVE PREVENTION WITH CERAMIC COATINGS ON OFFSHORE STRUCTURES FOR RENEWABLE ENERGY
Authors: Sanz Sánchez David Salvador , García Sergio , Trueba Ruiz Alfredo , Boullosa-Falces David , Adolfo Esteban Gustavo
Published: September 2023

In the past, ships, port facilities and offshore platforms dedicated to the exploitation of fossil resources were the only man-made structures that were exposed to seawater, currently the exposed structures are extended to all those used in the field of renewable ocean energy sources, such as waves, tidal flows or oceans streaming and offshore wind energy. Therefore, this study highlights the need for offshore structures to consider the choice of ceramic coatings in the field of surface treatment and marine corrosion control without neglecting another of the main problems that affects structures in contact with seawater, which is the phenomenon known as biofouling. Corrosion is a major problem in offshore environments due to extreme operating conditions and the presence of aggressive corrosive elements. The corrosion resistance can represent the difference between trouble-free long-term operation and costly downtime. On the other hand, biofouling, which is defined as the undesirable phenomenon of adherence and accumulation of biotic deposits on an artificial surface that is submerged or in contact with sea water, can cause variations in the weight distribution of a floating structure, affecting its stability. In addition, biofouling leads to corrosion in the same way that corrosion leads to biofouling, so both factors are studied in parallel.

This study evaluated differences in the total of seawater biofouling attached on coated paints and ceramic coatings in carbon steel for offshore structures. All three different ceramic coatings were made of incorporating active ceramic particles against biofouling as titanium, cobalt and manganese. In this study, the ASTM-D3623 test method, for the protection of submerged marine structures, was used. This method covered the procedure for testing antifouling coatings exposed for a period of two year at an immersion site with a high biological activity in shallow marine environments.

The results of the investigation showed that the cobalt-based coating had the best antifouling properties at the end of the experimentation, although there was no significant difference in the biofouling attached during the two years of exposure, but great differences were shown with respect to the antifouling paints. Biofouling adhesion resistance was greatest when a coating thickness of 217 μm was used and when the substrate surface roughness (Ra) was 0.245 µm. The results indicated up to more 30% total area covered by biofouling in paint coatings than ceramic coatings. On the other hand, the results showed a progressive degradation of the antifouling paint coatings, which meant an exponential increase of biofouling adhered to the samples, but not in ceramic coatings during the two years experiments.
HydroChrono: An Open-Source Hydrodynamics Package for Project Chrono
Authors: Ogden David , Quinton Zuriah , De Lataillade Tristan , Pallud Maxime
Published: September 2023

In this paper we present the development and verification of HydroChrono, a hydrodynamics package for the Project Chrono physics engine. This package includes the implementation of hydrodynamics equations, the added mass for multibody systems, the development of I/O functions as well as a Python API, and comparison against standard reference cases and other existing tools. HydroChrono provides a flexible, fully open-source solution for simulating wave energy converters (WECs), floating offshore wind turbines (FOWTs) platforms, and other hydrodynamic systems.

Here we show, via comparisons with  existing tools for benchmark verification cases, that HydroChrono accurately models hydrodynamic forces - making it a useful tool for the design and optimization of these systems. Additionally, the integration of HydroChrono with Project Chrono offers access to finite element modeling capabilities and high-fidelity modelling – with Chrono’s existing coupling to CFD and SPH codes. This provides numerical modelers with a multifidelity simulation framework for designing and validating these systems.

The development of HydroChrono provides a new, open-source solution for simulating hydrodynamic systems. Its compatibility with other simulation tools enables a more streamlined and efficient design process, advancing the field and providing new opportunities for innovation in this area.
The application of temporal gating in the measurement of response amplitude operators
Authors: Cazzolato Ben , Sergiienko Nataliia , Cohen Nadav , Manasseh Richard , Turner Ian , Flocard Fracois
Published: September 2023

Scale model testing of wave energy converters (WEC) in wave flumes and basins is essential for full scale development. One of the parameters commonly measured is the response amplitude operator (RAO), which represents the response of the WEC to wave excitation.  These are typically measured at discrete frequencies using regular waves.  This approach can be slow, depending on the fidelity and frequency resolution.  An alternative is to use a broadband wave source, however reflections from walls can significantly contaminate the frequency response measurement. In this paper, a rapid method for measuring the RAO is presented using a chirp signal to generate waves in the frequency range of interest to measure the transfer function, and a temporal gating technique (commonly used in experimental acoustics and RF engineering) to remove reflections.  The technique will be demonstrated on numerical data, as well as two scale experiments.
Design Wave analysis of the M4 wave energy converter device
Authors: Lynggard Hansen Christine , Wolgamot Hugh , Taylor Paul , Orszaghova Jana , Kurniawan Adi , Bredmose Henrik
Published: September 2023

We present physical results for a Design Wave analysis of the M4 wave energy converter (WEC), whichis currently being developed for a kW scale deployment in King George Sound, off the coast of Albany, Western Australia. The M4 wave energy converter is a hinged multifloat device utilising relative pitch as the power-producing mode of motion. We have conducted wave basin experiments at the Australian Maritime College in Launceston, TAS Australia, at a scale of 1:15 compared to the ocean trial. We present an experimental analysis of the hinge rotation in a severe sea state identified for the King George Sound location. We identify the most extreme response of the hinge rotation and the wave that causes it – the so-called Design Wave. By averaging the largest structural responses measured in long irregular wave realisations of the extreme sea states, we identify the most likely extreme response.The Design Wave is found to be the average of the surface elevation signals occurring simultaneously with instances of the largest response. The Design Wave thus identified is then produced in the basin and the M4 response measured.
Comparison of physics-based and machine learning methods for phase-resolved prediction of waves measured in the field
Authors: Chen Jialun , Hlophe Thobani , Zhao Wenhua , Milne Ian A. , Gunawan David , Kurniawan Adi , Wolgamot Hugh , Taylor Paul H. , Orszaghova Jana
Published: September 2023

Phase-resolved predictions of surface waves can be used to optimize a wide variety of marine applications. In this paper, we compare predictions obtained using two independent methods for field data, with horizons sufficient to control wave energy converters.
The first method is physics-based prediction. In this method, a set of optimal representative angles, obtained using an optimization algorithm given time histories of a wave buoy motion in 3D, are used for forward propagation based on linear wave theory. The second method is a machine learning method using an Artificial Neural Network (ANN) which requires longer records for training.
Field measurements were obtained from the Southern Ocean of Albany, WA. The field data were collected by an upwave ‘detection’ array of 3 Sofar Spotter wave buoys and a downwave ‘prediction’ point coincident with a Datawell Waverider-4. All buoys were soft-moored, and data were collected over 3 months in 2022. Selected intervals during this period are presented in the paper to compare and contrast the predictions made by the two different methods. We find that some wave fields can be predicted well over more than a period in advance, all that is required for active control of a wave power take-off in a renewable energy application. In contrast, highly spread sea states remain a challenge. The methods are also compared in terms of the complexity and time required for making predictions. Further discussions are made on the applicability of the results to other locations.