bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations from structural testing of full-scale tidal turbine blades
Authors: Finnegan William , Jiang Yadong , Glennon Conor , Flanagan Michael , Goggins Jamie
Published: September 2023

As the world shifts its reliance from fossil fuels to renewable energy, a reliable, predictable and dependable source of energy is vital; tidal energy provides such a solution. In 2021, the cumulative installed capacity of tidal stream energy in Europe, since 2010, reached 30.2 MW, which is roughly three times as much as the rest of the world. The total electricity produced in Europe from tidal energy increased by 8 GWh to a total of 68 GWh to date. The tidal turbine blades convert the energy in the tidal current to useful mechanical energy that can be converted to electricity. Therefore, the reliability of the blades is paramount to the success for the turbine. Structural testing of composite tidal turbine blades is performed to ensure the design and manufacturing processes [4] produce a reliable component that performs for its design life span. In recent years, a number of structural testing programmes have been performed on full-scale tidal turbine blades, as the sector strives for commercial viability.

In this paper, observations during the structural (static, dynamic and fatigue) testing of full-scale tidal turbine blades are presented and discussed. These observations have been made from 5 testing campaigns on full-scale tidal turbine blades at the Large Structures Testing Laboratory in the SFI MaREI centre in the University of Galway. The length of these blades range from 2-8 metres, for devices of 70kW to 2MW. Therefore, primary aim of this paper is to report significant observations from the full-scale structural testing of tidal turbine blades. The experience gained from these structural testing programmes highlighted a number of best practices that could be introduced to the next revision of both the IEC 62600-3:2020 test specification and the DNV-ST-0164 standard, which includes using a combined flapwise-edgewise loading, the use of a multi-actuator load introduction system to ensure a correct load distribution and the duration of the holding time for static testing.

The inclusion of these potential best practices could benefit all of the tidal energy sector by being included in the next version of the relevant testing standards. These activities, along with the successful testing programmes that has allowed the developers to deploy their devices for operational trials, helps de-risk tidal energy technology aiding in lowering the levelised cost of tidal energy.
Measurements of the wake from a floating tidal energy platform
Authors: Guerra Paris Maricarmen , Hay Alex E , Troncoso Benjamin
Published: September 2023

Wake measurements are critical for quantifying the hydrodynamic impacts of turbine presence and tidal energy extraction on the tidal flow. Turbine wakes are typically assessed using numerical models and controlled laboratory experiments, with only a few field studies available for the wakes of full-scale operating tidal turbines.
 
In this investigation we present field observations of the combined wake generated by the four-turbine array mounted onboard Sustainable Marine Energy Canada PLAT-I 4.63. Measurements were conducted downstream of the platform in Grand Passage, a tidal channel in the southwest of the Bay of Fundy in eastern Canada in October 2020. Velocity data were obtained by a suite of mobile Acoustic Doppler Current Profilers (ADCP), both vessel-mounted and free-drifting. Data were collected during ebb and flood tides (and therefore with time-varying inflow velocity), and under different turbine operating conditions. The collected data were organized according to the turbine inflow velocity for ebb and flood tide. For each tide, the wake and undisturbed flow regions to the sides of the wake were identified. Vertical profiles of velocity in the wake were compared to inflow velocity measured by a current-meter onboard PLAT-I and with measurements in the undisturbed flow to the sides of PLAT-I wake.
 
In all measurements the PLAT-I wake manifests as a reduction in flow speed at the depths spanned by the turbine rotors. The reduction is maximum near the platform for both ebb and flood. For flood, velocity profiles vertically mix less than 5 effective diameters downstream of the array, but velocities remain slower compared to the flow outside of the wake. Flow speed increases downstream, recovering approximately about 20 effective diameters from the platform. For ebb, the velocity reduction persists farther downstream compared to flood, there is less vertical mixing, and the wake shape is still present beyond 10 effective diameters downstream of the platform. Increased turbulence is also observed downstream of the platform, which recovers to levels similar to those of the surrounding undisturbed flow about 10 effective diameters downstream of the turbine for both ebb and flood. Comparisons of results between the two measurements approaches, and between the wake of clean and bio-fouled turbines are also explored.
Methodology for developing a prediction model for the remaining fatigue life and residual strength of tidal turbine blades
Authors: Munaweera Thanthirige Tenis Ranjan , Finnegan William , Goggins Jamie
Published: September 2023

As tidal energy nears commercial viability, the reliability and safety of a tidal energy device becomes more prevalent. A key aspect for determining their reliability and safety, along with reducing risk during operational deployment, is the structural integrity of tidal turbine blades. Therefore, a validated model for predicting the structural integrity of tidal turbine blades will aid in de-risking tidal energy technologies. In this study, a three-phase approach was used to formulate a strategy to predict the remaining fatigue life and residual strength of tidal turbine blades, over their operational lifespan.  In Phase 1, the parameters influencing the structural properties of tidal turbine blades were identified based on the literature review, and the expertise in the field. Then, parameters were extensively studied and classified into four main impact groups, which include load conditions, design and manufacturing, degradation, and unexpected situations. Loading conditions on the blade are directly linked to hydrodynamic forces, maintenance, operating conditions, and corrosion effects. At the same time, these scenarios can vary with fluid-structure interactions, climate conditions, local site conditions, and maintenance and inspection schedules of the blades. The design and manufacturing category mainly represents the impact of the properties of composite materials, the geometry of the blade, and manufacturing process parameters. Similar to the other structures, tidal turbine blades are subject to deterioration and unexpected accidents during their service life, which significantly compromises the structural integrity of the blade. In Phase 2, a data management strategy was formulated related to identified four impact categories and investigated the possible methods of analysing the data. In this context, finite element analysis of composite tidal turbine blades was identified as the most appropriate tool to comprehensively examine collected data, prior to comparing the results to the field and laboratory-based test data. Mesh properties of the numerical models, test standards, instrumentation, and equipment used for field and laboratory-based structural testing of tidal turbine blades, as well as the accuracy of data acquisition systems, influence the comparison of these results. Finally, with the information gathered, as well as knowledge and experience in the field, a method for estimating the residual strength and remaining fatigue life of tidal turbines at each stage of their operation was formulated. The model will undergo a series of extensive validation processes using experimental testing datasets and will be used in the future to develop vulnerability curves related to the remaining structural life of the tidal turbine blades.
Control co-design and uncertainty analysis of the LUPA’s PTO using WecOptTool
Authors: Michelen Strofer Carlos , Coe Ryan , Gaebele Daniel , Beringer Courtney , Bosma Bret , Robertson Bryson , Bacelli Giorgio , Devin Michael
Published: September 2023

Control co-design has been shown to significantly improve the performance of wave energy converters (WEC). By considering the control and WEC design concurrently, the space searched by the optimization routine is greatly expanded which results in better performing devices. Recently, an open-source WEC co-design code, WecOptTool, was released to perform control co-design research and facilitate its adoption in the community. In this study, we use WecOptTool to perform control co-optimization and uncertainty analysis of the LUPA device. The Laboratory Upgrade Point Absorber (LUPA) is a new open-source laboratory-scale WEC that provides a platform for testing new concepts, innovating control schemes, and validating numerical models. The LUPA can be adjusted to different configurations, including changing the number of bodies, the degrees of freedom (DOF), the float and spar geometry, and the diameter of the drive sprocket pulley in the power take off (PTO) system, as well as providing different control algorithms and input waves. The drive sprocket diameter influences the torque vs speed of the generator, which allows for more flexibility in operating under different wave conditions or with different control schemes. In this study we optimize the drive sprocket diameter, while considering the optimal control algorithm for each potential design, to identify the optimal diameter for electric power production at the PacWave South WEC test site. This case study demonstrates several new capabilities of WecOptTool including a multi-body multi-DOF system and multi-directional irregular waves. The PTO dynamics are modeled using first principle methods for a parametrized model of the mechanical subcomponents in combination with generator model obtained using a power-invariant Park transform. The case-study will be made available to serve as a design tool along the LUPA hardware. Users can readily use this model to perform their own design optimization prior to testing with the physical LUPA device. Finally, we use the automatic differentiation capability of WecOptTool to perform a sensitivity and uncertainty analysis of the LUPA device.
Wave energy converter power take-off characterization: comparing dynamometer and field data
Authors: Rusch Curtis , Crisp Corey , Hammagren Erik , Prudell Joe , Thomson Jim
Published: September 2023

Through dynamometer testing of a wave energy converter’s (WEC’s) power take-off system (PTO), we characterize friction and establish a relationship between shaft speed and torque. This characterization is conducted through oscillation of the shaft with a velocity-controlled motor, yielding some key differences between lab tests and response of the system in the field. In this work, we develop an understanding of these differences, provide both linear and nonlinear representations of the PTO that can be used in hydrodynamic modeling, and assess how accurately these representations are reflected in data collected in the field. 

 

The WEC used in this testing is the TigerRAY, built by CPower as part of a WEC-UUV (uncrewed underwater vehicle) system funded by the Naval Facilities Engineering Systems Command. The full device is a two-body point absorber with a subsurface heave plate that acts to hydrodynamically stabilize the system and serves as a docking and charging station for the UUV. The system is undergoing its second year of development and testing, which includes both at-sea trials and shore-side dynamometer experiments at the University of Washington Applied Physics Lab. The dynamometer system records torque at the WEC drive shaft, as well as motor shaft speed. Data acquisition on board the WEC simultaneously records key generator information, such as current, voltage, and angular shaft position. 

 

Through comparison of lab and field data, we draw conclusions about the limits of a velocity-controlled dynamometer. Since this control scheme allows near-instantaneous changes in applied torque, it pushes the WEC through electrical system-induced torque spikes more quickly than is possible in the field. Reduction in the control gains of the dynamometer smooths the applied torque curve at the expense of added noise in the velocity profile. We weigh these tradeoffs using data obtained from field testing of the device in a real wave field. Additionally, we identify key characteristics in the dynamometer data and how they impact device performance in the field. Finally, we make recommendations about how to move forward with future dynamometer testing given these lessons learned.
On tidal array layout sensitivity to regional and device model representation
Authors: Jordan Connor , Angeloudis Athanasios , Coles Daniel , Johnson Fraser
Published: September 2023

In-stream tidal devices are ready to be deployed, yet the largest operational commercial array is limited to 6MW. Upcoming government support should see the size of such arrays increase by orders of magnitude, and thus the optimal placement of turbines within tidal arrays is an emerging challenge for successful commercial integration. Hydrodynamic models are required to predict the power produced by an array and the impact on the surrounding environment. The influence of common model inputs to layout optimisation are investigated herein. This is achieved using a shallow water equation based tidal array modelling framework, Thetis, coupled with a low cost analytical wake model (FLORIS) that allows for rapid assessment of the impact of small changes in hydrodynamic results on array micro-siting. The sensitivity of array optimisation at an intermediate development point (43 turbines) is interrogated through both artificial flow field manipulation and the variation of model input pertinent to the optimisation. A small margin exists in which an optimised array layout will perform efficiently for a deviation in flow prediction accuracy. However, incorrect flow predictions by a range sensitive to model inputs had a reduction of almost 8% on array efficiency relative to a control case. The sensitivity of flow field variance by model input changes, on extractable energy and array layout are substantial. Comparing arrays sited on flow fields using different bathymetry resolution leads to a discrepancy on average of over 2% to average array power. Arrays sited for different mesh resolution and friction representation also see average changes up to and exceeding 0.75%. For array developers and the future of this nascent industry, re-calibration of the model at every stage of data collection coupled with early acquisition of bathymetry data is critical not just for accurate power quantification, but also array efficiency. At a regional scale, quantification of the potential tidal resource must consider the consequences of uncertainty in model input data and site constraints that cannot yet be accounted for.
Wave-to-Wire Control of an Oscillating Water Column Wave Energy System Equipped with a Wells Turbine
Authors: Rosati Marco , Said Hafiz Ahsan , Ringwood John Vincent
Published: September 2023

Wave energy is a significant and relatively untapped source of renewable energy [1], which can considerably contribute to decarbonization. The oscillating-water-column (OWC) [2] is one of the most promising wave energy converters (WECs) for harnessing wave power, especially due to its relatively simple operating principle and the fact that all the moving parts are above the water level.

To improve the commercial viability of WECs, the levelised cost of energy should be minimised and, to this end, comprehensive control strategies to maximise electric energy are essential [3]. Due to the important issue of turbine efficiency, the vast majority of OWC control strategies [4] focus on a simplified control objective, namely turbine efficiency maximisation. While maximising turbine efficiency is a primary focus of OWC control strategies, it is important to note that rotational speed control impacts generator performance. Additionally, for Wells turbines [5], rotational speed control also affects the hydrodynamic performance, specifically the wave-to-pneumatic energy conversion process. Therefore, Wells turbine rotational speed should be ideally modulated to improve the overall wave-to-wire (W2W) efficiency of the OWC system [6], rather than just turbine efficiency.

In this paper, a control strategy for maximising W2W efficiency of a fixed OWC WEC equipped with a Wells turbine is proposed. A schematic of the W2W power train of the OWC WEC considered in this paper is depicted in Figure 1. The proposed control strategy comprises of two parts. Firstly, a `complete' setpoint, which considers the entire OWC W2W model (WEC hydrodynamics, Wells turbine, and generator dynamics), is derived. Secondly, a Lyapunov-based nonlinear controller is designed to track the aforementioned setpoint. Preliminary results from the numerical simulation show that, in comparison to the somewhat traditional turbine efficiency maximising control approach, the proposed W2W control strategy leads to a significant improvement in the electric energy production for all the considered sea states.
Grid value of co-located offshore renewable energy
Authors: Jonasson Erik , Temiz Irina
Published: September 2023

The paper investigates the added grid value of co-locating wave energy converters with offshore wind turbine generators and floating photovoltaic solar panels. Grid value is evaluated in terms of power generation variability and electrical infrastructure utilization. Using meteorological reanalysis data for the region of the North Sea, wave, solar and wind energy converters are modelled on an hourly basis to form the power profile of the joint operation. Necessary power ratings of the transmission system are provided both for stand-alone installations and the hybrid parks and is shown to be of higher utilization for the latter case. Suitable locations of hybrid parks are also analyzed and provided in terms of water depth, solar irradiation and favorable wave and wind climate. The joint operation is found to smoothen the power profile on all time scales but influences long term variations most heavily. Added grid value strongly depends on the park configuration as well as metocean conditions. It is shown that by co-locating wave, solar and wind energy converters the utilization of the electrical transmission system is increased compared to stand-alone installations.
Power quality assessment of a wave energy converter using energy storage
Authors: Ullah Md Imran , Temiz Irina , Forslund Johan , Santos Döhler Jessica
Published: September 2023

Wave energy has been an immense area of interest in research and industry in our move towards a sustainable energy production society due to its high energy density and surface area. However, the grid connection of wave energy converters is still one of the major challenges due to the complexity of varying wave resources (amplitude and frequency). Wave energy converters grid integration can lead to several potential challenges, such as voltage fluctuations, harmonics and flicker. Using an energy storage system can help to mitigate few challenges by balancing the grid demand with the wave energy converter power supply. Hence, improving the power quality. This study assesses the power quality of wave energy converters equipped with energy storage against the scenario without any energy storage at different power levels. The power quality in this paper is investigated using total harmonic distortion (THD) of the grid current, dc-link voltage ripple and battery current ripple. The study shows that the addition of a hybrid energy storage system lowers the grid current THD at the point of common coupling (PCC), stabilizes the dc-link voltage ripple and reduces the stress of the battery.
Verification and validation of blade-resolved viscous-flow tidal turbine simulations
Authors: Rentschler Manuel , Gomes Tiago , Vaz Guilherme , Eça Luís , Turnock Stephen
Published: September 2023

Tidal turbines are a renewable energy source on the rise. The exceptional predictability of tidal currents contributes to a high reliability of this technology, which represents a key advantage in the endeavor to become a major contributor to the energy mix. To foster the development and to support the design process of tidal turbines, reliable numerical modeling techniques are required. This paper presents verification and validation work performed within the framework of the Supergen ORE Tidal Turbine Benchmarking Study. Viscous-flow CFD code ReFRESCO is used to conduct blade-resolved simulations of the towing tank experiments. In a first approximation, a steady-state frozen-rotor approach is chosen. A transition model, γ-Reθ, is employed to predict the flow state transition on the turbine blades. In the process, the sensitivity to input turbulence quantities is highlighted. The numerical uncertainty is estimated based on mesh refinements. Finally, a conclusion is drawn to which accuracy the presented numerical models can predict the outcome of the experiments.
Hybrid linear potential flow - machine learning model for enhanced prediction of WEC performance
Authors: Eskilsson Claes , Pashami Sepideh , Holst Anders , Palm Johannes
Published: September 2023

Numerical models based on the linear potential flow equations are of paramount importance in the design of wave energy converters (WECs). Over the years methods such as wave stretching, nonlinear Froude-Krylov and Morrison drag have been developed to overcome the short-comings of the underlying assumptions of small amplitude wave, small motion and inviscous flow. In this work we present a different approach to enhance the performance of the linear method: a hybrid linear potential flow – machine learning (LPF-ML) model. A hierarchy of high-fidelity models – Reynolds-Averaged Navier-Stokes, Euler and fully nonlinear potential flow – is used to create training data for correction factors targeting nonlinear hydrodynamics, pressure drag and skin friction, respectively. Long short-term memory (LSTM) networks are then trained and added to the LPF model. LSTM networks are heavy to train but fast to evaluate so the computational efficiency of the LPF model is kept high. Simple decay tests of generic bodies (sphere, box, etc) are used to validate the LPF-ML model. Finally, the LPF-ML is applied to a model-scale point-absorber WEC to assess the power production.
Marine Renewable Energies and Maritime Spatial Planning: different national proposals for their legal and spatial context
Authors: Menchaca Iratxe , Galparsoro Ibon , Verling Emma , Machado Inês , LeBourhis Enored , Soulard Thomas , Bald Juan
Published: September 2023

In 2022, the European Commission adopted the REPower EU package which proposes to further increase the 2030 target for renewables from 40 % to 45 % and revise the Renewable Energy Directive to accelerate permitting. Moreover, the European Offshore Renewable Energy Strategy estimates to have an installed capacity of at least 60 GW of offshore wind and at least 1 GW of ocean energy by 2030, reaching 300 GW and 40 GW of installed capacity, respectively, by 2050, which would require less than 3% of the European maritime space.

The marine environment is an ecosystem that supports a set of uses and human activities, contributing to economic and social development. Most of the uses and activities require the use of maritime space, either temporarily or permanently, increasing the potential for conflict with existing and traditional marine uses. The European Directive 2014/89/UE establishes a framework for marine spatial planning (MSP) and requires the competent authorities in each Member State to develop national maritime spatial plans, analysing and organizing human activities in marine areas, applying ecosystem-based approach, involving stakeholders, in order to achieve ecological, economic and social objectives. Moreover, this MSP framework not only intends to mitigate possible present and future spatial conflicts but also contemplates the emerging sectors and the most recent technological development in the sea.  

In the context of the EU-funded SAFEWave project (https://www.safewave-project.eu/), the different National Maritime Spatial Plans in Europe and how the Marine Renewable Energies (MRE) have been considered or integrated in different national plans have been analysed (i.e. Spain, France, Ireland, Portugal and United Kingdom). The outcome of this analysis has identified: (i) the approaches to implementation of MSP plans vary by country and sometimes within countries; (ii) differences in the stakeholder or public involvement in MSP (ii) differences in national MRE targets; (ii) different strategies and priorities for raising the issue of MRE within the national MSP; (iii) for which countries MREs are strategics in their national plans; (iv) conflicts with other uses (i.e. Marine Protected Areas), and mechanisms to solve them; (vi) technical, socio-economic and environmental factors considered for MRE polygons identification in national MSP; (vii) the development of national MSP requires a review of the authorization or concession procedures for the allocation or reservation of areas for MREs. 

Ultimately, comparing the integration of national plans for marine renewable energy (MRE) into national marine spatial plans (MSP) can inform and guide management strategies, legislation, and policies to support management actions and efficiently plan future MRE deployments.
Development of a passive blade-pitch mechanism to reduce the loads on a tidal turbine in high-flow conditions
Authors: Summers Thomas , Oterkus Selda , Tabor Gavin , Shek Jonathan , Wray Bevan , Dadd George
Published: September 2023

Maintenance of tidal turbines is expensive, and relies upon suitable weather conditions and vessel availability, which can lead to costly delays. Turbine reliability can be improved by eliminating complexity in the design. The use of fixed-pitch blades, for example, can greatly reduce maintenance costs by avoiding complex active blade-pitch mechanisms which are the main source of failure in wind turbines.

Pitching rotor blades to feather in high-flow conditions is, however, the most effective means of reducing loads on the rotor. Turbines with fixed-pitch blades therefore necessarily have smaller rotor diameters compared to those with active-pitch systems, in order to keep the thrust force, flap-wise bending moment, and power output within allowable limits. In low-flow conditions, power output is proportional to the square of the rotor diameter, so turbines with small diameter rotors capture less energy over their lifetime.

This study seeks to develop a novel passive-pitch mechanism for tidal turbine blades. This mechanism must be reliable, and should act to reduce the loads on the rotor in high-flow conditions so that a larger diameter rotor can be installed, increasing power capture.

An initial design for a passive-pitch mechanism, which is actuated by the hydrodynamic forces developed by the rotor such that the blades pitch-to-feather in high-flow conditions, has been developed. The design is compatible with proven passive reversible rotor blade technology, eliminating the requirement for a maintenance sensitive yaw mechanism.

Since initial concept design, work has been undertaken to build a tool, based on NREL’s OpenFAST blade element momentum code, which models the forces acting on the rotor blades, coupled with the mechanical response of the passive blade-pitch mechanism. This tool has been used to predict the performance of the turbine for a range of operating conditions, allowing the influence of parameters such as blade geometry, rotor diameter and passive-pitch response to be analysed in terms of rotor loading and turbine performance.

Initial analysis suggests that installing blades with a passive-pitch mechanism could reduce the loads on the rotor in high-flow conditions down to just 25% of the loads that would act on an equivalent rotor with fixed-pitch blades. This would allow larger diameter rotors to be installed which could improve annual energy yield by over 40% at a typical site.

Despite these significant potential performance improvements, the challenges of developing a passive blade-pitch mechanism for tidal turbines are not well understood, as tidal developers have all so far implemented fixed or active pitch mechanisms. These challenges will be addressed throughout the remainder of this study, which will involve detailed design followed by physical tank testing.
Origami-adapted clam design for wave energy conversion
Authors: Yang Jingyi , You Zhong , Cheng Shanshan , Wang Xinu , Puzhukkil Krishnendu , Cox Malcolm , Rainey Rod , Chaplin John , Greaves Deborah
Published: September 2023

The Clam wave energy converter (WEC) is a floating device composed of two side plates connected by a hinge that closes and opens under interaction with wave crests and troughs. A linear power take-off (PTO) may be installed between the two side plates to convert the mechanical motions to electricity, or the volume change may be used to pump air between chambers and across an air turbine PTO. The basic concept has been discussed since 1978 and featured as part of the UK Wave Energy research programme [1]. Some simplified clam models have been built since then and preliminary investigations were conducted by Phillips [2] to understand the wave-structure interactions at the COAST laboratory, University of Plymouth. However, the simplified models were not enclosed and hence seawater can be trapped in the device. To further the investigation, we will design the outer shell of the clam model that is enclosed and thus suitable for use in the (adverse) marine environment.  

Since no enclosed flexible polyhedral structure can change its volume without bending or stretching of facets according to the bellows conjecture, the clam model must be strained when it is in motion. A portion of the wave energy will be consumed to deform the outer shell of the clam model and the rest can be captured by the PTO. Therefore, the design of the clam model will aim at minimising the strain on its facets while achieving the largest volumetric change of the device to maximise the power extraction by the PTO.

Inspired by origami, we will construct the enclosed clam-type offshore device by connecting rigid panels and elastic membranes with rotational hinges. We model the rigid panels to rotate about the hinges without facet deformation and allow stretching on elastic membranes. The strain on the elastic material shall be minimised for better structural integrity and minimal energy loss. Satisfying all the design requirements, the best geometric design is obtained through an optimisation process. Based on the optimised geometry, a downscaled prototype will be built using rigid plywood and rubber membranes and tested under dynamic wave-induced loads to prove that the strain incurred is negligible in response to forces.

 

References:

[1] Peatfield, A. M., Duckers, L. J., Lockftt, F. P., Loughridge, B. W., West, M. J., & White, P. R. S. (1984). The SEA-Clam wave energy converter. In Energy Developments: New Forms, Renewables, Conservation (pp. 137-142). Pergamon.

[2] Phillips, J. W. (2017). Mathematical and Physical Modelling of a Floating Clam-type Wave Energy Converter (Doctoral dissertation, University of Plymouth).
Hydro-elastic interaction of polymer materials with regular waves
Authors: Puzhukkil Krishnendu , Wang Xinyu , Yang Jingyi , Borthwick Alistair , Ransley Edward , Chaplin John , Cox Malcolm , Meng Maozhou , Hann Martyn , Rawlinson-Smith Robert , Zheng Siming , Cheng Shanshan , You Zhong , Greaves Deborah
Published: September 2023

The use of flexible materials has the potential to offer a step-change reduction in the cost of wave energy devices by enabling them to absorb more extreme wave loads through their structural responses. Flexible wave energy converters are often manufactured from polymer, fabric, or reinforced polymer components. The elastic modulus, fatigue performance, seawater ageing, and manufacturing process determine the effectiveness of flexible components at replacing their rigid counterparts. During design, it is necessary to assess the hydrodynamic response of the WEC structure to different wave conditions. This work investigates the hydro-elastic response of a submerged polymer membrane, held in a horizontal frame, exposed to regular wave loading. Fast-Fourier Transform analysis enabled assessment of the non-linear response of the membrane exposed to the different wave conditions. The ratio of harmonic to measured wave amplitude ratio gives insight into the excitation mode of the membrane as a function of frequency. It is found that the peak response of the membrane tends to coincide with the fundamental frequency of regular waves. By varying the ratio of membrane length to wavelength an understanding is provided of the hydro-elastic response of the polymer membrane which should be useful in validating software used in the design of flexible WECs.
Impact of lateral turbine spacing on the performance of a multi-rotor tidal energy device
Authors: Smith Rachael , Townley Bryn , Wray Bevan , Mason-Jones Allan
Published: September 2023

In this work, the impact of local blockage on the power production of a tidal array due to multiple turbines positioned in close proximity is studied. A numerical model of the HydroWing tidal energy device, which features multiple turbines on a retrievable wing, is being developed using geometry-resolved computational fluid dynamics (CFD). For this paper, the influence of two turbines at several spacings is considered.

The CFD model is used to perform  quasi-static steady-state  simulations of two turbines in a twin rotor configuration, where a multiple reference frame (MRF) approach is used to simulate rotor rotation. The lateral spacing between the rotors is varied and the resulting impact on the axial loads and  power performance of the two turbines is studied, with the aim of identifying the optimal turbine spacing for the HydroWing device. The results will be used in future design optimisation work to minimize the levelized cost of energy of a large scale array using HydroWing technology at the proposed site for the Morlais tidal energy project.
Comparison of the European Regulatory Framework for the deployment of Offshore Renewable Energy Project
Authors: Moscoloni Claudio , Carà Caterina , Novo Riccardo , Giglio Enrico , Mattiazzo Giuliana
Published: September 2023

The REPower EU Plan has set a minimum of total renewable energy generation capacity of 1,236 GW by 2030. Achieving this target, and emission reductions by 2050, will require the extensive deployment of offshore energy facilities, especially offshore wind (OW) and wave energy converters (WECs). However, an incomplete and sometimes unfavourable regulatory framework still jeopardises the feasibility of both prototypes and large-scale installations. There are, for example, significant differences between the permitting procedures in different Member States and regions. Moreover, following the transposition of the Directive 2014/89/EU “establishing a framework for maritime spatial planning”, important differences pertain to the way environmental and heritage protection is dealt with. An overview of the offshore permitting schemes for offshore wind in ten European counties (Germany, Denmark, Scotland, Sweden, France, Spain, Portugal, Italy, Belgium, and Ireland) is provided, demonstrating a mismatch between the current members’ complex regulations and the future offshore wind targets. Using customised key performance indicators, we describe and assess the extent to which the regulatory frameworks are conducive to installing industrial devices in achieving the country’s 2030 target. Finally, we propose actions to facilitate the installation of OW while ensuring both environmental protection and industry development in the countries under investigation.
Tracking a large vortex at a tidal power site
Authors: Mercier Philippe , Guillou Sylvain S.
Published: September 2023

Tidal turbines are sensitive to the high turbulence of tidal flows. Large and intense vortices are generated at the seabed and cause extreme loads, fatigue damage and degraded power production. Thus, these vortices must be characterised prior to the turbine installation. The flow characteristics can be assessed through ADCP measurements, but these measurements are sparse. The vortex characteristics are strongly affected by the seabed macro-roughness (rocks, faults) that induces spatial variations of the flow characteristics at a local scale. These local variations are difficult to catch through measurements [1]. Numerical simulations, that cover large areas, can fill in the gaps of measurements. Reynolds Averaged Navier Stokes simulations cover wide domains, but do not simulate the turbulent motions. Large Eddy Simulations (LES) do simulate the turbulent motions, but are computationally expensive, which reduces their spatial and temporal coverages.

LES has been validated for the simulation of turbulence at a tidal power site, with a spatial coverage of about 0.5 km² and a temporal coverage of about 30 minutes [2,3]. However, the high turbulence intensity complicates the analysis of turbulent motions. The tracking and characterisation of vortices is complex and time-consuming. New methods to automate this work would be very welcome.

In this work, we use Large Eddy Simulations to simulate the vortices generated at the rocky seabed of the Paimpol-Bréhat tidal turbine test site (France). A tracking method is used to follow the movement of turbulent motions (see Figure 1). This tracking highlights the long durability of turbulent motions. The impact of the most intense motions on fictive turbines is assessed and extreme flow variations are observed. This confirms the interest of the method for an easy detection of the most troublesome vortices and the locations where they are generated. It paves the way for the identification of the locations where turbine installation should be avoided due to potential damaging turbulent motions.

[1] Togneri, M. & Masters, I. Micrositing variability and mean flow scaling for marine turbulence in Ramsey Sound. Journal of Ocean Engineering and Marine Energy, 2016, 2, 35-46

[2] Mercier, P.; Grondeau, M.; Guillou, S.S.; Thiébot, J. & Poizot, E. Numerical study of the turbulent eddies generated by the seabed roughness. Case study at a tidal power site. Applied Ocean Research, 2020, 97

[3] Mercier, P. & Guillou, S.S. The impact of the seabed morphology on turbulence generation in a strong tidal stream. Physics of Fluids, 2021, 33
Enhancing energy system resilience using tidal stream energy
Authors: Coles Danny , Coyne Richard , Miles Jon
Published: September 2023

During autumn 2021, high global gas demand led to a 400% increase in imported wholesale gas prices in the UK. This coincided with (i) an extended period of low wind resource, where wind turbines provided 60% less energy than typical levels for the time of year, (ii) low nuclear power availability and (iii) depleting domestic natural gas reserves. These simultaneous events led to UK wholesale electricity prices more than doubling. The 2022 military and political impact of Russia’s invasion of Ukraine has led to additional increases in imported fuel prices. These types of disruption have the potential to cause damage worth years of sector revenues [1]. In the future, energy resilience challenges must be overcome whilst also achieving net-zero to limit global warming to within 1.5 degrees Celsius above pre-industrial levels, whilst electricity demand at least doubles.

This research investigates the role of tidal stream energy in enhancing energy system resilience during periods when the energy system is highly stressed, such as during autumn 2021 in the UK. The concept of resilience refers to the ability of the system to survive strong and unexpected disruptions and to recover quickly afterward [1]. This research is motivated by the acknowledgement that the commercial viability of marine power relies on the sector being able to explain how it can provide contributions beyond decarbonisation [2].

We build on an energy system modelling case study of the Isle of Wight [3], using the EnerSyM-RC energy system model. Wind data between 2012 – 2020 is analysed to identify and characterise periods of low wind resource. These data form the inputs to the EnerySyM-RC modelling. The model then applies a simple brute force optimisation method to investigate the most suitable mix of solar PV, offshore wind, tidal stream and energy storage that enhances system resilience on the Isle of Wight.

Initial results show that the adoption of tidal stream energy compliments solar and wind generation by reducing reliance on reserve energy (e.g. imported gas) during high-stress periods. Reduced reliance on imported energy is also achieved because of the distinct generation pattern of tidal power (i.e. 4 periods of power generation, each separated by slack tide, every day), which enhances the utilisation of local energy storage.

References

[1] Jasiunas J, et al., 2021, Energy system resilience – A review, Renewable and Sustainable Energy Reviews, 150:111476

[2] Pacific Northwest National Laboratory, 2021, Grid Value Proposition of Marine Energy: A Preliminary Analysis, PNNL -31123, Technical report

[3] Coles DS et al., 2023, Impacts of tidal stream power on energy system security: An Isle of Wight case study, Applied Energy, 334:120686
Effects of non-isotropic blockage on a tidal turbine modeled with the Actuator-Line method
Authors: Mascrier Enzo , Zilic de Arcos Federico , Pinon Grégory
Published: September 2023

Blockage effects are a consequence of the interaction between a body and the surrounding boundaries in a constrained flow. For the case of tidal rotors, global blockage (β) is usually defined bythe ratio between the swept area of the rotor and the cross-sectional area of a channel. Increasingblockage tends to increase the limits of power extraction (Garrett and Cummins, 2007), as well asthrust on a rotor through an attendant increase of through-rotor mass flow. While these observations have been studied and demonstrated for isotropic blockage effects (e.g., Zilic de Arcos et al.2020, Bahaj 2007 , Mikkelsen 2002), questions remain regarding the validity of such assumptionsfor non-isotropic blockage in channels with, e.g., rectangular cross-sections with varying aspectratios.

In this work, we will use CFD simulations to analyze the effect of non-isotropic blockage on atidal rotor. The study aims to explore these effects using an Actuator-Line representation of anaxial-flow rotor, simulated under different blockage ratios (1 %, 5 %, 10%, and 19.7 %), aspectratios (0.25, 0.5, 0.75, and 1), and tip speed ratios (4, 5, 6, and 7). A total of 64 cases will beconsidered. For each simulated case, the power, thrust, and spanwise force distributions will beextracted as functions of time, and used to understand the effect of blockage on the performanceof tidal rotors.

Our preliminary results, in agreement with existing literature, indicate that blockage affectswake development, as seen in Figure , along with power and thrust. These results, for a constantaspect ratio, show power increases up to 26 % for a blockage of 20 %. The bulk of the simulationmatrix, including the different aspect ratios, is currently under production and is expected to beready before the paper submission deadline.

 

ReferencesGarrett, C., Cummins, P. (2007). The efficiency of a turbine in a tidal channel. Journal of fluidmechanics, 588, 243-251.Zilic de Arcos, F., Tampier, G., Vogel, C. R. (2020). Numerical analysis of blockage correctionmethods for tidal turbines. Journal of Ocean Engineering and Marine Energy, 6, 183-197Bahaj, A. S., Molland, A. F., Chaplin, J. R., Batten, W. M. J. (2007). Power and thrust measurements of marine current turbines under various hydrodynamic flow conditions in a cavitationtunnel and a towing tank. Renewable energy, 32(3), 407-426.Mikkelsen, R., Sørensen, J. N. (2002). Modelling of wind turbine blockage. In 15th IEAsymposium on the aerodynamics of wind turbines, FOI Swedish Defence Research Agency.
Performance enhancement of pitching WECs via oscillating water columns technology
Authors: Fontana Marco , Sirigu Sergej Antonello
Published: September 2023

This paper describes the coupling of an oscillating U-shaped water tank, also called a U-tank, with a pitching floating Wave Energy Converter (WEC) to expand the response bandwidth. The performance of these energy converters strongly depends on their frequency response, and their resonance period is generally fixed once the geometric and inertial parameters of the system have been defined. The integration and appropriate control of dynamic inertial systems based on water ballast tanks enable slow tuning of the system's resonance with the incoming wave, maximizing energy extraction. The dynamic coupling of the hull with the water tank is then analyzed, and a passive control system is developed that acts on the air contained in the reservoirs of the U-tank by partitioning the volume within. Air expansion is then controlled by discretely adjusting the available, properly partitioned volume allowing the variation of the frequency response of the sloshing water tank and device. The resolution of the dynamics involves linear models based on the Boundary-Element-Method as far as hull hydrodynamics are concerned; a solution of the Euler equation describes the oscillating tank. Finally, the expansion and compression of the air contained in the reservoirs of the U-tank are assumed to be governed by a generic polytropic transformation law, and such a condition is linearized around the operating condition. The ISWEC device is adopted as a case study, and its energy harvesting working principle is based on the gyroscope technology. The results aim to confirm the ability to perform slow tuning of the device frequency response via regulation of the air volume of the sloshing water tanks.