bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Life Assessment for Wave Energy Converter Mooring Lines under Realistic Wave Climates
Authors: Martinez Eguzkiñe , Zarketa Ander , Zabala Alaitz , Esnaola Jon Ander , Llavori Iñigo , Penalba Markel
Published: September 2023

Despite the untapped resource stored in ocean waves, none of the suggested wave energy converters (WECs) has yet demonstrated economical viability. This viability lies in two counter-productive aspects: enhancing energy absorption and generation, and reduction of the loads in the critical elements such as mooring lines and dynamic cables. Both objectives are counter-productive in the sense that the former implies enhancing the motion, while the latter requires reducing this motion. Hence, a trade-off between the two objectives must be found.

To that end, the accurate lifetime estimation of the most critical components is crucial, which depends on the fatigue and extreme loads. The latter depends on extreme events, which are highly nonlinear and need to be characterised by fully-viscous fully nonlinear numerical models. In contrast, fatigue effects cause cracks in the material, which appear due to cyclic loading and, thus, computationally more efficient numerical models are required in order to study all the relevant loading conditions within the operating region.

The present study will evaluate different methodologies to assess the impact of fatigue loads in WEC mooring lines, estimating the lifetime of the mooring lines under realistic wave climates. The method follows the following steps:

Mooring line tension is evaluated via hydrodynamic simulations under different realistic resource conditions,

Statistical characteristics of the load cycles are extracted from the time history,

The damage (D) corresponding to each load cycle condition is computed,

The lifetime (L) is estimated by combining realistic resource conditions and the damage corresponding to each condition

In the present study, this approach will be applied to different mooring line configurations (including wire ropes and chains), materials (stud and studless) and dimensions (length and diameter of mooring lines), as shown in Figure 1 for stud and studless chains as a function of the diameter.

The lifetime estimation will be performed in different locations across the European coast, analysing the impact of resource conditions on fatigue lifetime. In addition, the most relevant design parameters will be identified.
Dynamic Simulation of Wave Point Absorbers Connected to a Central Floating Platform
Authors: Saksanian Hallak Thiago , Ferreira Gaspar José , António Pancada Guedes Soares Carlos
Published: September 2023

AmAmong the challenges currently being faced by the wave energy industry, there are the ones related to the mathematical and numerical modelling of Wave Energy Converters. Because various levels of physical complexity are reflected in the dynamics of wave converters, the mathematical modelling of such systems usually comes up with nonlinear dynamic equations to be solved. The nonlinearities, however, may appear in many ways. In this paper, the nonlinear geometric constraints that arise naturally in hinged structures are investigated for floating multi-body systems including wave point absorbers. To achieve that, a method of constraint linearization is proposed and applied to a realistic case study. The method is based on generalized coordinates and generates a robust first-order dynamic matrix to characterize the multi-degrees of freedom hydrodynamic system. The simulation outputs the motion response for all floating bodies, as well as the constraining forces responses, among other parameters. The method requires knowledge of the geometries of the system but rather few assumptions, namely, to perform the linearization of constraints. The method is illustrated with a case study, where three wave point absorbers are concentrically attached to a Floating Offshore Wind Turbine platform with an onboard hydraulic Power-Take Off system.
accuracy of BEMT and CFD on the power and trust prediction of tidal turbines
Authors: Liu Yabin , Gambuzza Stefano , Broglia Riccardo , Young Anna , McCarthy Edward , Viola Ignazio Maria
Published: September 2023

We compute the loads on a model-scale tidal turbine with Blade Element Momentum (BEM) theory and Computational Fluid Dynamics (CFD) simulations, and we compare the results with towing tank tests. CFD simulations are wall-resolved, steady, Reynolds-averaged Navier-Stokes simulations with a k − ω SST turbulence model, where only a 120◦ wedge domain with a single blade is resolved in a non-inertial frame of reference. We undertake a detailed uncertainty analysis to identify the sources of error. BEM uncertainty is computed with a Monte-Carlo approach based on the differences in the predictions of CFD and Xfoil for the sectional lift and drag coefficients,while CFD uncertainty is based on the errors due to the finite number of iterations and spatial resolution.
The maximum error of CFD (8.0%) with respect to the experimental data is about half of that of BEM (15.5%) for the power (CP) and the thrust (CT) coefficients and both errors are within 4.1% for CFD and within 7.2% for BEM around the optimal tip-speed ratio (λ = 6.03). The BEM error is within the uncertainty associated with the imprecise knowledge of the sectional lift and drag coefficients. The sectional forces from CFD and BEM disagree at both the tip and the root, resulting in a substantial BEM underprediction of CP at high λ values (up to 15.5%), yet CT is well predicted (within 2.3%) at every λ. The CFD uncertainty is markedly smaller than the error, which is thus mostly due to a modelling error such as the turbulence model, the neglected effect of the support structure, the free surface, and the imprecise knowledge of the input conditions. Overall these results suggest that CFD provides both a maximum error and uncertainty that are substantially smaller than that of BEM, but both methods suffer from modelling errors that require further investigation.
THE PERFORMANCE OF COUNTER-ROTATING TIDAL TURBINE IN DIFFERENT SEA STATES
Authors: FU Song
Published: September 2023

This paper will report on work being undertaken to evaluate the performance of the counter-rotating tidal turbine in a wave-current coupled operation environment based on Blade Element Momentum Theory (BEMT). The counter-rotating tidal turbine has two rotors rotating in opposite directions on the same axis. It has been proposed on the basis of the theory, which states that a configuration of two rotors having a similar swept area on the same axis has a higher maximum power coefficient than a conventional configuration of a wind turbine with a single rotor. BEMT is a reliable and effective theory for rotor design because it is based on solid physical principles and has a remarkably low computing cost.
Maximizing Wave Energy Converter Power Extraction by Utilizing a Variable Negative Stiffness Magnetic Spring
Authors: Grasberger Jeff T. , Bird Jonathan , Coe Ryan G. , Bacelli Giorgio , Michelén Ströfer Carlos A. , Hagmüller Alex
Published: September 2023

Complex conjugate impedance matching is a key concept for wave energy converter design. Matching the impedance of the power take-off (PTO) system to the complex conjugate of the wave energy converter's (WEC) impedance ensures efficient transfer of energy from the WEC body motion to electrical power. In low frequency waves, impedance matching often requires a negative PTO stiffness. In this paper, an adjustable stiffness magnetic torsion spring will be presented and modeled to understand its potential to improve WEC performance. The spring has the ability to provide a negative stiffness, allowing the PTO impedance to more closely match the complex conjugate of the WEC impedance at low frequencies. The spring also supports an adjustable stiffness value, meaning it can be tuned according to the incoming wave conditions. The spring's tunability may put less stress on the rest of the PTO system in wave conditions outside its normal operation zone without sacrificing electrical power output. The adjustable magnetic spring's effects are modeled and explored in this paper by examining the resultant average annual electrical power and capacity factor. The study suggests that the tunable magnetic spring has the potential to significantly improve capacity factor while maintaining a high average electrical power.
Reliability and Cost Assessment of Critical Components: Electrical generator failure of IDOM wave energy converter
Authors: Fernández Chozas Julia , Johannesson Pär , Cruz Joao , Ruiz-Minguela Pablo , Etxaniz Patxi
Published: September 2023

It is believed that current testing procedures in the wave energy sector are not well-balanced. Most laboratory testing has been focused on functional tests (e.g. of proof of concept and performance assessment for example) disregarding other key performance measures such as reliability and survivability. A new testing procedure that reduces development time and cost, while enabling better understanding of reliability and survivability of critical components at early Technology Readiness Levels (TRLs) has been proposed within the VALID project.

 

In the context of VALID, the work in this paper relates reliability of the critical component to the cost of the whole system, i.e. the wave energy converter. There is usually a trade-off between a very reliable component (low maintenance and high unit cost) against a component with a lower lifetime, lower unit cost and higher maintenance. The loss of revenue of a component failing more time during the project lifetime shall be evaluated against different maintenance strategies and the capital expenditures of the overall system and the component of focus. For that, the LCOE or Levelised Cost of Electricity seems to be the parameter more relevant to capture all these variations. A sensitivity analysis will consider how varying failure rates, component’s cost and maintenance costs affect CAPEX, OPEX and accumulated energy production along project’s lifetime.

 

The assessment will focus on selected critical components representative of three wave energy technologies: CorPower, IDOM and Wavepiston. The three user cases of the VALID project will guide the work, though it is the aim that results will be applicable beyond the VALID project.

Initially, a relative quantification of the impact on the LCOE of increasing the performance and reliability of the critical component will be done. As output data comes from the experimental results, this quantification will be refined.

VALID is a Horizon 2020 research project where fourteen partners around Europe are collaborating into developing a new hybrid testing platform and methodology for critical components. VALID aims at integrating both reliability and testing methods together with relevant data on component failures early in the design and testing process to ensure that the proposed testing procedure is built upon past experience. The focus of the present paper is to statistically relate the realibility of the critical component to the costs of whole system.
Comparing Numerical Models of the TALOS Wave Energy Converter
Authors: Ogden David , Aidan Bharath , Sheng Wanan , Aggidis George
Published: September 2023

In this study, we present the development of a numerical model of the TALOS Wave Energy Converter (WEC) in WEC-Sim and compare it with existing numerical in-house models from Lancaster and results from DNV's Sesam code. The objective of this work is to validate the performance of the TALOS WEC using WEC-Sim and compare the results with those obtained from other numerical models. The TALOS WEC is a promising technology for the generation of clean, renewable energy from ocean waves. The development of a reliable numerical model for the TALOS WEC is crucial for its design and optimization. To achieve this, we have implemented the TALOS WEC in WEC-Sim and compared the results to in-house models from Lancaster and to results from DNV's Sesam code. Our results show good agreement with the results from Lancaster and DNV, demonstrating the accuracy and reliability of the numerical model developed in WEC-Sim. This work advances the field of wave energy conversion by providing a verified numerical model of the TALOS WEC, which can be used for further optimization and design studies.
SEASNAKE: Impact - Marine operations modelling for evidence-based results detailing the impact of using a new fully dynamic cable design for ocean energy devices.
Authors: Kennedy Ben , Giorgi Simone , Senar Adrian , Costello Ronan
Published: September 2023

The SEASNAKE project - an OceanERA-NET project – is aiming for developing fully dynamic cables for ocean energy. Through new design and application of novel coatings the project is designing a dynamic cable that better suits the conditions and user requirements. In order to fully understand the benefits, the Wave Venture TEMPEST™ techno-economic analysis software will be used to simulate the performance of a proposed wave energy farm with a special focus on the contribution of the dynamic cable subsystem. The results obtained from the simulations will not only provide a deep understanding of the reliability and cost-risk areas regarding the use of dynamic cables, but will also allow a comparison with a baseline scenario consisting of a more traditional cabling system. The latter will be key to identify the advantages of the SEASNAKE project and its commercial viability. KPIs (Key Performance Indicators) will include farm availability and power production downtime as a direct result of cable related issues. The reliability, maintainability and survivability of the cabling subsystem will be tested and the KPIs will give clear indication on the performance benefits and ultimately the impact on the LCOE will be of greatest consideration.
Effects of control strategies on the performance of floating WEC point absorbers operating attached to a breakwater by time-domain simulator
Authors: Bonovas Markos , Magkouris Alexandros , Belibassakis Kostas
Published: September 2023

The estimation of the performance of Wave Energy Converter (WEC) arrays of the type of simple floaters operating in nearshore and coastal areas, characterized by variable bottom topography, is important for the estimation of the wave power absorption and determination of the operational characteristics of the system and could significantly contribute to the efficient design and layout of WEC farms. For this purpose, full 3D models based on Boundary Element Method have been developed, supporting the systematic use for optimization studies. Apart from WEC arrays in nearshore and coastal regions a promising possibility is the installation at the exposed side of port breakwaters with significant energy potential. In this work, the analysis of the above system is extended to the prediction of WEC performance in multichromatic incident waves under latching control strategy using a time-domain simulator, showing improvement of performance in particular conditions.
A NEW SEAWATER LOW-HEAD TURBINE FOR THE OBREC
Authors: Contestabile Pasquale , Rubino Luigi , Crispino Gaetano , Mariani Antonio , Unich Andrea , Gisonni Corrado , Vicinanza Diego
Published: September 2023

The OBREC (Overtopping Breakwater for wave Energy Conversion) is based on the overtopping phenomenon [1] where incoming waves run over an overtopping ramp and fall into a reservoir located above the sea level inside a conventional rubble mound breakwater, or into a vertical caisson breakwater. The wave energy is transformed into potential energy, with some contribution of kinetic energy. Then, the flow is driven through a turbine addressing the final transformation into electrical energy. The OBREC prototype is located in the middle of the San Vincenzo breakwater, in Naples harbour (Italy). The key target of the whole pilot project was to demonstrate the high capacity factor of the system (expressed as the ratio of the electrical energy produced to the electrical energy that could have been produced at continuous full power operation), even in a low-energy wave climate. At the study site, in fact, the yearly average wave power was found to be 1.8 kW/m over the last 42 years [2]. However, during last 5 years, a maximum wave height of over 5 m has been registered, confirming the high reliability under severe wave conditions.

Due to the short monitoring period and to the undersize of the previous power take-off (PTO) systems, no definitive power matrix is available for OBREC [3]. The energy conversion efficiency of OBREC has been deeply investigated over the last years through both physical and numerical model tests. Within the ongoing full-scale monitoring activities in real environments, a new set of power take-off was installed. A propeller-type pico-turbine equipment was in 2021, and its final setting was completed in 2022. Performance and reliability of the entire structure were closely monitored under different “stress tests”, i.e. start & stop cycle in marine environment with a high variable combination of flow rate/hydraulic head.

This paper presents the design stage for the new equipment and preliminary results from these tests numerical and field tests.

 

Contestabile, P., Crispino, G., Di Lauro, E., Ferrante, V., Gisonni, C., & Vicinanza, D. (2020). Overtopping breakwater for wave Energy Conversion: Review of state of art, recent advancements and what lies ahead. Renewable Energy, 147, 705-718.

Contestabile, P., Russo, S., Azzellino, A., Cascetta, F., Vicinanza, D. (2022). "Combination of local sea winds/land breezes and nearshore wave energy resource: Case study at MaRELab (Naples, Italy)", Energy Conversion and Management, ISSN 0196-8904, 257, 115356, https://doi.org/10.1016/j.enconman.2022.115356    

Mariani, A., Crispino, G., Contestabile, P., Cascetta, F., Gisonni, C., Vicinanza, D., & Unich, A. (2021). Optimization of Low Head Axial-Flow Turbines for an Overtopping BReakwater for Energy Conversion: A Case Study. Energies, 14(15), 4618.
Analysis of Ocean Energy Integration in Ibero-American Electric Grids
Authors: Lafoz Marcos , Villalba Isabel , Blanco Marcos , Najera Jorge , Navarro Gustavo
Published: September 2023

The development of the marine renewable energy, as referenced in the objectives achievement of many energy roadmaps [1], is conditioned by the possibilities to integrate the marine generation power plants in the electric systems. Offshore wind, floating solar PV, tidal, waves and even saline gradient are the technologies considered. The success of these plans needs to fulfil, among others, the compliance of the electric grid codes, ensuring the stability of electric grids.

The integration of marine renewable energies is still not a problem at the electric grids, since the penetration level is not so high. However, the objectives established in the roadmaps invite to analyse the expected effects of new power plants from the point of view of performance at the electric systems. Actually, some research works have identified an increase in the number of frequency and voltage events in electric systems due to higher penetration of marine energies [2].

The connection of the marine renewable generation is usually taken place in nodes of the electric grids not very favourable in terms of power capacity and voltage drops. Moreover, many of the locations where the marine renewable energies result economically viable are linked to weak areas of the electric grid, meaning that frequency and voltage are more sensible. That is the case of remote isolated areas, as usually coastal areas, or islands. Additionally, some of the technologies considered, such as wave energy, present very oscillatory power profiles which produce an unbalance with the consumption profiles, leading to stability problems.

More and more countries are putting an eye on new sources of energy, integrating them in their energy policies in order to search alternatives to face energy crisis. This is the case of many countries in Centre and South America, that have included in their roadmaps the renewable marine energies [3]. One of the main issues in these countries is the lack of robust electric grids or the condition of weak grids in coastal areas.

This paper presents the result of the analysis of different electric grids in Ibero-American countries. Three different regions have been considered: Mesoamerica, South America and Iberian Peninsula and Macaronesia, and particular areas or countries have been selected from each region as representative of the critical conditions in terms of grid integration. Costa Rica, Peru, Brazil and Argentina, and the Canary Islands in Spain, are the selected case studies. The results presented will summarize: power limits, time response, energy storage and backup generation requirements, power ramps, power oscillation allowed, etc.

This work has been accomplished in the frame of the activities carried out by the groups involved in the thematic network REMAR (Opportunities of Integration of Ocean Energies in Ibero-American Electric Grids), promoted and funded by the Ibero-American Programme of Science and Technology for the Development (CYTED).
Tidal Turbine Benchmarking Project: Stage I - Steady Flow Experiments
Authors: Tucker Harvey S.W. , Chen Xiaosheng , Rowe D. , McNaughton J. , Vogel C.R. , Bhavsar K. , Allsop T. , Gilbert J. , Mullings H. , Stallard T. , Young A. , Benson I. , Willden R.H.J.
Published: September 2023

The tidal turbine benchmarking project, funded by the UK's EPSRC and the Supergen ORE Hub, has conducted a large laboratory scale experiment on a highly instrumented 1.6m diameter tidal rotor. The turbine is instrumented for the measurement of spanwise distributions of flapwise and edgewise bending moments using strain gauges and a fibre Bragg optical system, as well as overall rotor torque and thrust. The turbine was tested in well-defined flow conditions, including grid-generated freestream turbulence, and was towed through the 12.2m wide, 5.4m deep long towing tank at Qinetiq’s Haslar facility. The turbine scale was such that blade Reynolds numbers were Re=3x10^5 and therefore post-critical, whilst turbine blockage was kept low at 3.1.
In order to achieve higher levels of freestream turbulence a 2.4m by 2.4m turbulence grid was towed 5m upstream of the turbine. Measurements to characterise the grid generated turbulence were made at the rotor plane using an Acoustic Doppler Velocimeter and a five-hole pressure probe. An elevated turbulence of 3.1% with homogeneous flow speed across the rotor plane was achieved using the upstream turbulence grid.
The experimental tests are well defined and repeatable, and provide relevant data for validating models intended for use in the design and analysis of full-scale turbines. This paper reports on the first experimental stage of the tidal benchmarking programme, including the design of the rotor and comparisons of the experimental results to blade resolved numerical simulations.
Effects of the spacing between two hydrokinetic turbines on the bedforms by numerical simulations
Authors: Khaled Fatima , Guillou Sylvain , Hadri Farhat , MEAR Yann
Published: September 2023

Accelerating hydrokinetic renewable energy development towards endurance requires investigating interactions between the hydrokinetic turbine and its surrounding physical environment. Interactions between hydrokinetic turbines (HT) and mobile sediment bed are considered as a critical area of assessment, however limited research studies have been published to address this issue. Hill et al. (2015) have shown experimentally that the presence of either single or multiple turbines and the rotation of the blades affect the bed morphology. Musa et al. (2019) have investigated experimentally the local effect of streamwise aligned turbines on the bedload, they found as a result that the geomorphic effects are stronger with increasing shear stress due to the presence of the rotors, inducing an alternating scour-deposition phenomenon. Chen et al. (2017) have investigated the influence of rotor blade tip clearance (distance between blades and seabed) on the scour rate of pile-supported horizontal axis current turbine. The results suggest that the decrease in tip clearance increases the scour depth, hence more sediment transport. Recently, Khaled et al. (2021) have studied the impact of hydrokinetic turbine on erodible sand banks, they showed numerically a significant interaction between the confinement of the turbine and its impact on the near bottom.

 

In the present issue, we study the impact of two interacted turbines on the near bedform morphology. A modelling framework is derived to predict the significant transport induced by the turbines, such as the Euler-Euler (EE) multiphase model for sediment transport and the Blade Element Method (BEM) to model the forces generated by the turbines, using the open source platform OpenFOAM and the library SedFoam (Chauchat et al. 2017). A phase of validation is presented for the combined model (EE and BEM) using experimental results of Hill et al. (2015). The present study consists in considering one sediment class, sand of diameter of 0.25 mm, and two horizontal axis turbines with an axial flow direction corresponding to the riverine case. The approach is configured with four different axial inter-turbines distances. The wake distribution behind the second turbine is altered by the wake of the upstream turbine in all configurations (fig. 2). This interaction promotes the erosion under the turbines and the deposition along the axis of the turbines in the wake due to relation between the dynamics of ripples generation and the wake effects of turbines (fig. 3).
Improved Modelling of Vertical Velocity Profiles at a Tidal Energy Site
Authors: Enders Lilli , Karsten Richard
Published: September 2023

The Minas Passage, one of the Bay of Fundy’s tidal channels, located in Nova Scotia, Canada, presents significant potential for tidal energy development because of its highly energetic flows. As development in the region gains traction, the implementation of floating tidal energy platforms is a topic of growing interest. Tidal energy deployments in Minas Passage have historically been bottom-mounted and stationary, and the transition to arrays of floating turbines requires additional considerations. Particularly, this new application demands characterization of flow over the entire water column, including near the free surface. Complete vertical velocity profiles are essential for the successful deployment of floating tidal turbines, allowing for the estimation of key metrics such as tidal power and shear across turbine blades. Here we explore adaptations to the well-established logarithmic law of the wall with the goal of extending the vertical range over which a fitting regime based in classical turbulence theory can capture the observational records of flow in Minas Passage.

Observational site characterization efforts in Minas Passage have primarily consisted of stationary, bottom mounted Acoustic Doppler Current Profiler (ADCP) deployments. Using historical ADCP records collected in Minas Passage between 2008 and 2021, we fit the vertical profiles of velocity using three methods: logarithmic law of the wall, power law, and an adapted logarithmic law of the wall which includes a “wake function” to improve fits in the upper water column. We find that although the law of the wall results in well-fitted estimations of the vertical velocity profiles near the seabed, observational profiles consistently deviate from the fitted curves in the middle and upper water column, recording significantly faster flow speeds than predicted by the law of the wall. The adapted model, which is rooted in turbulence theory and includes a wake term, is successful in capturing flow in the outer layer of the water column and allows for reverse shear to be captured in the profile. The resulting fits show a sizeable reduction in error throughout the entirety of the water column compared to the law of the wall profiles, and consistently reduce the error in the vertical profile fits when compared to power law fits. In addition to resulting in low error for both individual and averaged vertical profiles of flow, the physical quantities estimated from the adapted model, including drag coefficient, agree well with those computed from the law of the wall, demonstrating the physical usefulness of the adapted model.
On the design of a small scale tidal converter for long time deployment at sea
Authors: Alizzio Damiano , Gurnari Luana , Nardi Vito , Torresi Marco , Coiro Domenico , Filianoti Pasquale Giuseppe Fabio , Camporeale Sergio Mario
Published: September 2023

A scale model of a kite-like converter of tidal energy, the GEMSTAR, is designed to be installed at sea for a long term deployment. The aim of the experiment is to develope a digital twin with fault detection and isolation capabilities. To this aim, a fully-functional 1:10 scale of GEMSTAR is designed, starting from measurements of tidal currents in the site of installation. Several spots were investigated searching for the most suitable current profile. The paper describes the principal issues concerning operational functions and the choice of the physical parameters to monitor during the deployment through several sensors placed on board. A scale model of a kite-like converter of tidal energy, the GEMSTAR, is designed to be installed at sea for a long term deployment. The aim of the experiment is to develope a digital twin with fault detection and isolation capabilities. To this aim, a fully-functional 1:10 scale of GEMSTAR is designed, starting from measurements of tidal currents in the site of installation. Several spots were investigated searching for the most suitable current profile. The paper describes the principal issues concerning operational functions and the choice of the physical parameters to monitor during the deployment through several sensors placed on board.
Test rig for submerged transmissions in wave energy converters as a development tool for dynamic sealing systems
Authors: Jonsson Anthon , Strömstedt Erland
Published: September 2023

A submerged transmission, fitted with a dynamic sealing system, in a wave energy converter (WEC) serves the purpose of transmitting the force, absorbed by a wave activated body, to an encapsulated power take-off (PTO) system, while preventing seawater from entering the capsule. Dry generator operation is generally a prerequisite for attaining long technical service life. Little attention seems to be devoted in publications to the study of dynamic sealing systems in WECs, and to test rigs for experimental verification and/or evaluation of the ability/performance of existing dynamic sealing systems in a controlled laboratory environment. This paper begins by presenting some of our earlier research within the focus area of dynamic sealing systems, incl. design considerations and typical operating conditions. This part also presents the 1st laboratory test rig, used for verifying the sealing ability of the piston rod mechanical lead-through design in the 1st and 2nd full-scale experimental WEC prototype from Uppsala University. In 2021 project DynSSWE (Dynamic Sealing Systems for Wave Energy) was initiated. Drawing from experience, the project includes development of a new test rig, representing a tool for further development of dynamic sealing systems. This paper introduces steps in the design and development process of that new test rig, enabling accelerated long-term test runs with a setup of multiple piston rod specimens. The test specimens’ will be surface treated differently with the aim of improving the prospects of a long maintenance free service life. Since the new test rig is in the design stage, seal testing results are not yet reported. The presented work is funded by the Swedish energy agency with the aim of improving subsystem performance in wave energy devices.
Overview of Resource and Turbine Modelling in the Tidal Stream Industry Energiser project: TIGER
Authors: Mackay Edward , Hardwick Jon , Thies Philipp
Published: September 2023

Tidal energy projects require numerical modelling for the assessment of tidal site conditions and turbine/array performance. The Interreg TIGER project has offered a unique opportunity to implement a wide range of numerical models. This paper provides an overview and comparison of the different numerical models developed by academic partners in the TIGER project. The models cover a variety of spatial and temporal scales. The largest scale models provide long-term climatic studies covering the entire English Channel region, at relatively low resolution, whilst the highest-resolution models provide detailed information about short-term and small-scale turbulent flow and its interaction with tidal turbines. The models are used for various purposes. At one end of the scale, the models have been used to inform the large-scale techno-economic assessment of tidal energy and its impact on the energy mix in the UK and France. At the other end of the scale, the numerical models provide information that feeds into detailed engineering design of tidal turbines at particular sites, and assessment of the energy yield. The models showcase the range of computational tools available to aid the development of the tidal energy industry. This paper will be useful for investors, technology developers and project stakeholders to help identify suitable numerical models to support and develop ongoing and future tidal stream projects.
Combining offshore wind and wave energy to supply a big size desalination plant
Authors: DEL RIO GAMERO BEATRIZ , Schallenberg Rodríguez Julieta , Suarez Arocha Pedro
Published: September 2023

This research analyses the feasibility of supplying a large size desalination energy demand by marine renewables. The case study is Las Palmas III seawater desalination plant, the largest desalination plant in the Canary Islands (Spain), which is located in the northeast of the island of Gran Canaria. Its average daily water production is 62,614 m³/day, consuming a total of 90,669.52 MWh/year. A constant energy production is needed for the optimal plant operation which raises the possibility of using different renewable technologies in order to reduce the energy fluctuations. In this case, the sea and its wind and wave energy resources are key technologies for supplying desalination plants near the coast. For this reason, different configurations have been simulated combining both technologies and analyzing their pairing in hourly terms to achieve a more stable energy production. The proposed methodology contemplates the identification of the hotspot for the technologies location in terms of environmental constraints and resource assessment (both wind and waves). The subsequent selection of the wind turbine and the wave converter and the energy coverage evaluation. Results tried to establish if the combination of offshore wind and wave energy improves the demand coverage in overall terms and in terms of seasonal match.
Design considerations for a hybrid wind-wave platform under energy-maximising control
Authors: Celesti Maria Luisa , Paduano Bruno , Peña-Sanchez Yerai , Pasta Edoardo , Faedo Nicolás , Ringwood John
Published: September 2023

The environmental impact of emissions of fossil fuels and their rising prices, together with countries' commitment to mitigate the effect of the alarming and rapid climate changes, have been a crucial thrust to investigate new solutions to have an energy supply depending on renewable energies. In this scenario, offshore wind-wave hybrid platforms have been recently promoted: sharing facilities, infrastructure, and grid connections, give these systems the potential to increase energy production at a lower cost. However, an efficient realisation of these two combined technologies requires two potentially conflicting control objectives: On the one hand, for the wind turbine, a reduced movement of the platform is required, which essentially translates to enhanced stability of the structure, so that its behaviour resembles standard onshore wind technologies. On the other hand, to maximise the energy produced, wave energy converters (WECs) require optimal control technology, which often leads to large amplitude motion, potentially conflicting with the stability requirement for the wind turbine.

The aim of this study is to investigate the effects of design changes on the dynamics of the hybrid wind-wave platform under energy-maximising control, which can be analysed in terms of the principle of impedance-matching. A semi-submersible platform with an incorporated flap-type WEC will be analysed both from a closed-loop and open-loop perspective, and the control system will be designed to maximise the energy produced by the WEC. Design changes on the wind-wave conversion platform will be in terms of flap dimensions, starting from a nominal geometry based on the so-called Oyster system.  Analyses will be conducted by both increasing and decreasing the flap depth from the nominal case, to investigate the effect of the different geometries on the interactions between the WEC and the platform. A frequency-domain analysis of the overall input/output (velocity) system will be presented, highlighting the situations that can enhance the potential of both devices and exploit their synergies.
Performance evaluation of 30kW class OWC wave power plant integrated with breakwater
Authors: KIM KILWON , Park Sewan , Lim ChangHyuck , Kim Kyong-Hwan , Oh Jeonghwan , Shin Seung-Ho
Published: September 2023

In 2016, Korea started to develop a 30kW class wave power plant connected to a breakwater. After designing, manufacturing and performance testing of each energy conversion device, a demonstration plant was installed in Mukri Port, Jeju Island, Korea in 2021. After passing the completion inspection of the power generation facility, a full-scale grid-connected trial operation began in October 2021. The power plant consists of a sloped Oscillating Water Column, impulse air turbine, permanent magnet synchronous generator, AC-DC converter, energy storage system and integrated control system.

This study introduces the performance evaluation results based on real sea operation data. The performance evaluation of the wave power plant under various wave height and period conditions was performed to evaluate the output power and efficiency of each bin. In addition, performance evaluations were conducted according to wave direction and tidal conditions to examine the effects. The correlation coefficient was derived by analyzing the correlation between wave height, period, wave directions, tide level and output power.
Leveraging Explainable Artificial Intelligence for Real-time Detection of Tidal Blade Damage
Authors: Syed Muslim Jameel , Goggins Jamie , Syed Shahryar Jameel
Published: September 2023

Our current reliance on fossil fuels is the primary contributor to global warming and threatens our survival. Renewable energy is currently considered the leading solution to reduce greenhouse gas emissions. Energy extraction from the ocean tides (tidal turbines) can help fulfill the global renewable energy demand and combat world climate crises. Installations at this scale will have the associated benefit of reducing the levelised cost of tidal energy (LCOE) towards a target of EUR100/MWh, which will make ocean energy a viable option along with other renewable energy sources such as offshore wind. To achieve the target, increased performance and reliability of tidal energy devices are required. Tidal blades are a primary component of tidal turbines, possess a heterogeneous nature and can suffer from complex non-linear damage modes. For example, harsh marine environments can cause impact damage, delamination, matrix crack, fiber breakage or rupture, and others in tidal blades, which could lead to catastrophic failure of the system. Achieving reliable operational health and performance for the tidal blade is thus crucial for tidal energy companies. Fault diagnoses and maintenance operations are challenging in the sea; performance degradation, failure, or breakdown of the entire tidal energy system are more likely if unattended. Therefore, there is the need for real-time and reliable structure health monitoring (SHM) of tidal blades. The existing damage detection techniques have a limitation when dealing with the real-time environment, and do not take into account the along with uncertainty feature, we also addressed the issue of trusthworthiness in system decision employed with explanable artificial intelligence (XAI). This paper presents a real-time damage detection framework, information communication technologies (ICT) based infrastructure for real-time monitoring and proposes a novel model to classify/ detect the damages over blade structure. In addition a XAI based approach is proposed which based on supervised machine learning (ML) and uses an optimized convolutional neural network to classify from the heterogeneous data streams. Testing and evaluation of proposed approach in laboratory and operational settings is the future concern of this study.
Demonstrating real-time hydrodynamic motion response in force control for regular waves in a robotized dry test rig with a point-absorber WEC
Authors: Salar Dana , Hultman Erik
Published: September 2023

A 6-Degrees-Of-Freedom robotized dry test rig has been developed at Uppsala University to test point absorbing WECs (Wave Energy Converters). Using a six joint industrial robot as a buoy movement emulator, the robot's outermost point (joint 6) is connected to the wire from the generator concept WEC PTO (Power Take-Off). The robot's movement in joint 6 thus corresponds to the buoy movement on the sea surface. The test rig can be used for various point absorbing WEC PTO units. In this project, the test rig has been used with a WEC-PTO prototype. The point absorbing WEC-LRTC concept is being developed at Uppsala University. The generator concept is made up of two identical rotating generators. A wire is used as a connection between the generator concept at the seabed and a buoy on the sea surface.

The goal of this article is to demonstrate and evaluate how the test rig interacts with the LRTC-WEC PTO in regular waves. In the presented experiments, a hydrodynamic model with force control method has been used.

The results show a clear difference in the use of the hydrodynamic model with different sizes of the buoy. The test rig with the force control model can be used easily to test different theoretical buoys and different load settings for WEC PTOs. Effective experiments can be performed with real PTO forces instead of simplified simulations.

Future work is to experiment with the position control method and also experiments with irregular waves.
Weight Reduction Methodologies for Wave Energy Devices
Authors: O'Shea Michael , Sharvin Rory
Published: September 2023

The OE Buoy is a wave energy converter based on the Backward Bent Duct Buoy oscillating water column model which generates electricity through the fluctuation in wave height. Wave energy conversion devices are often faced with a particularly high levelized cost of energy (LCOE) when compared to other renewable energy devices, and various investigations into bridging this gap have been carried out in recent history. Previous studies on the OE Buoy have suggested that a significant reduction in required construction material is possible as a result of reduced differential pressures acting across the hull walls in operational conditions. Various structural analysis campaigns have been conducted on sections of the hull to assess this theory.

A Finite Element Analysis (FEA) was performed on a full-scale model of the OE Buoy under maximum design wave loadings in operational conditions at EMEC’s Billia Croo test facility in Orkney, Scotland using Robot Structural Analysis software. A maximum pressure of 145 kPa was calculated for an 18.7 m peak wave height at Billia Croo. The OE Buoy was modelled for both static and dynamic load conditions under various constraint layouts. A modal analysis was conducted on the model which estimates the natural frequency of the OE Buoy to be approximately 6.67 Hz.
Development of a modified BEMT model for the analysis of helical bladed vertical axis tidal turbines
Authors: Fereidoonnezhad Mohammad , Leen Seán , Nash Stephen , Flanagan Tomas , McGarry Patrick
Published: September 2023

Development of a modified BEMT model for the analysis of helical bladed vertical axis tidal turbines

Mohammad Fereidoonnezhad1, Seán Leen1, Stephen Nash1, Tomas Flanagan2, Patrick McGarry1

1 School of Engineering, University of Galway, Galway, Ireland

2 ÉireComposites Teo., Údarás Industrial Estate An Choill Rua, Inverin, Galway, Ireland

E-mail: patrick.mcgarry@universityofgalway.ie  

 

Keywords: Blade element momentum theory, Helical vertical axis tidal turbine, FEA Analysis

Classical blade element momentum theory (BEMT) formulations are not capable of accurately simulating complex blade geometries, such as spiral or helical blade geometries. In this paper, we develop a modified BEMT model to calculate hydrodynamic forces acting on the helical vertical axis tidal turbines. Our framework accounts for curved blade geometries where the leading edge is not orthogonal to the freestream velocity, and chord vectors are not in the azimuthal-radial plane. We validate the model using experimental data for a prototype VAWT. We then perform a parametric analysis of helical bladed VATT designs. Both the helix angle of the blade and the relative orientation of the chord strongly influence the power output of a turbine. Our modified BEMT model also predicts that an increase in blade helix angle results in reduced power fluctuations. Additionally, computed fluctuations in tangential and normal forces acting on blades are shown to reduce significantly with increasing blade helix angle, suggesting a reduction in risk of fatigue failure. We also uncover a complex distribution of normal and tangential forces along the length of a helical blade. Fluctuating hydrodynamic forces computed by our modified BEMT model are input into a finite element (FE) framework to compute the stress state in a fibre reinforced composite blade material for a range of blade azimuthal positions. Analyses reveal that blade deflections are three orders of magnitude lower than the turbine radius, suggesting that sufficient structural stiffness is achieved by the blade design. Results also uncover stress concentrations in the region of strut-blade connection, revealing a higher risk of fracture and fatigue failure at this location.
Analysis of the German tidal energy resource
Authors: Korte Alexander , Windt Christian , Goseberg Nils
Published: September 2023

A transformation of the energy sector towards a low-emission power generation is needed to mitigate global warming and fight the current climate crisis. In recent years, tidal energy technology has matured and shows potential to balance Europe’s future power grid. While reviews of the tidal energy resource exist for a number of European countries, the potential of tidal energy along the German North Sea coast is overlooked so far. This review closes this gap and provides a first analysis of the German tidal energy resource. Germany’s North Sea coast is characterised by comparatively low current velocities and shallow waters. Using available data from the EasyGSH-DB North Sea Model, Germany’s practical tidal energy resource is estimated at 66.6 GWHy−1, under strong restrictions, excluding the most energetic sites in the estuaries of Elbe, Weser, and Ems. Based on the results, future work for a more detailed analysis is suggested.