bluuebunny/crossref_metadata_2025 huggingface dataset:
Verification and validation of MoodyMarine - A free simulation tool for modelling moored MRE devices
Authors: Palm Johannes , Eskilsson Claes
Published: September 2023

This work presents the verification and validation of the freely available simulation tool MoodyMarine, developed to help meet some of the demands for early stage development of MRE devices. MoodyMarine extends the previously released mooring module MoodyCore (Discontinuous Galerkin Finite Elements) with linear radiation-diffraction bodies, integrated pre-processing workflows and a graphical user interface. It is a C++ implementation of finite element mooring dynamics and Cummins equations for floating bodies with weak nonlinear corrections. A newly developed nonlinear Froude-Krylov implementation is verified in the paper, and MoodyMarine is compared to CFD simulations for two complex structures: a slack-moored floating offshore wind turbine and a self-reacting point-absorber with hybrid mooring.
Novel Hybrid Floating Breakwater- Wave Energy Converter Device: Preliminary Experimental Investigations
Authors: Russo Sara , Lugni Claudio , Contestabile Pasquale , Vicinanza Diego
Published: September 2023

The marine space is increasingly gaining ground as the ideal candidate to drive the energy economic sector as it hosts a huge amount of natural resources to be exploited, such as waves, wind, and solar irradiation. Innovative devices harnessing these marine renewable resources have been thought to be assembled in a new concept of an energy hub for the Mediterranean Sea, recently proposed by the National Research Council of Italy.

The feasibility of this floating energy archipelago is strongly dependent on the creation of a protected sea area with reduced wave heights, where to safely install new types of floating devices for energy harvesting from the sea, like solar islands.

For this purpose, a floating breakwater module has been specifically designed to surround the archipelago with one or more rows. Moreover, investigating the possibility to implement a dual and alternative use of this floating module, as a traditional dissipative system and wave energy converter has resulted in an extremely challenging task. With respect to the existing hybrid floating breakwater-Wave Energy Converters in fact, the novelty of this device is the optimization of both functionalities by varying its draft.

In extremely rough seas, the hybrid module should only serve as a passive breakwater, soaking up incoming waves and safeguarding the equipment installed inside the archipelago. Otherwise, the floating module should operate as a WEC in more frequent mild sea states, assisting the archipelago's energy output. The whole produced energy can be stored and used to supply the development of new productive activities, such as aquaculture, the expensive process of seawater desalination, as well as the production of low environmental impact fuels like methanol or hydrogen.

The model's dual functionality is accomplished by different draft values. This parameter is directly influenced by the volume of water pumped into the module, which raises the floater's displacement. The module is almost completely immersed in the first scenario, which simulates breakwater functioning, increasing the device's stability and the amount of reflected and dissipated waves. On the other hand, when the module exhibits WEC behavior, a lower displacement is necessary, allowing greater device motions, able to better exploit the energy of the waves.

In this study, preliminary results obtained from an experimental campaign carried out on a 1:10 Froude-scaled model are reported. In particular, the dynamic behaviour of the hybrid device is evaluated in terms of response amplitude operators, while the attenuation performances are condensed in the transmission coefficient which indicates the reduction of the wave height inside the archipelago.
Influence of the spatial variation of upstream velocity on a vertical-axis tidal turbine performance
Authors: Flores Mateos Lilia , Frost Carwyn , Baker-Horne Nicholas , Kregting Louise , Mc Cormack Vincent
Published: September 2023

Assessment of the upstream flow available to the tidal energy converters (TEC) is key to evaluate its performance. Simultaneously, TEC technology has been innovating on its concepts and designs to expand the potential sites to harvest energy generated by tidal currents and rivers. The Gkinetic CEFA 12 is an easy-to-deploy device suitable to operate on estuary environments. The design consists of two 1.2 m vertical axis turbines attached to the sides of a buoyant platform, which uses a bluff body to accelerate the incoming flow to the rotors. The device was deployed on a single point mooring enabling passive flow alignment. As part of the Vertical axis tidal turbines in Strangford lough project (VATTS), the upstream flow has been measured using acoustic doppler profilers (ADP) mounted on the TEC during its operation in Strangford lough. Recommendations of IEC-200 were followed when mounting the ADPs relative to Gkinetic. However, the continuous repositioning of the TEC according to the prevailing tidal regime affects the ADPs heading. The implications of the spatial variation of the rotor’s upstream velocity on the resource assessment and device performance are not clear since this situation is not typical.To investigate the spatial variation of the upstream velocity two ADCP deployment locations were made. A seabed (upward facing) ADCP as per the current standards and a device mounted (downward facing) ADCP upstream of the rotor plane. Evaluation of the influence of the following three factors were made: i) the ADPs direction repositioning according to prevailing tidal regime, ii) the proximity of the sensors to the sea-surface, and iii) the proximity of the sensors to the TEC.These three factors will be evaluated using ADP datasets collected at Strangford narrows during the VATTS project. The datasets were obtained at approximately the same location of the TEC operation. They enable the study of the following scenarios 1) incoming flow to the rotors during operation, 2) incoming flow on undisturbed conditions (no turbine operation), and 3) a harmonic analysis prediction of the undisturbed incoming flow, which solely captures the tidal-driven flow.The investigation of these three scenarios will provide a better understanding on the rotor’s upstream flow spatial variation, and the influence of the device’s proximity and near sea surface conditions on the mean flow. These findings would benefit developers of alternative TEC designs that operate near the sea-surface.
Designing Vortex Generators for Tidal Turbine Blades
Authors: Manolesos Marinos , Kaufmann Nicholas , Papadakis George
Published: September 2023

Increasing tidal turbine performance through innovation is crucial if the cost of tidal energy is to become competitive compared to other sources of energy. The present investigation deals with the application of Vortex Generators (VGs) on tidal turbines in view of increasing their performance. The more mature wind energy industry uses passive VGs either as a retrofit or in the blade design process to reduce separation at the inboard part of wind turbine blades. Tidal turbine blades also experience flow separation and here we examine whether passive vane VGs can be used to reduce or suppress that separated flow.

Vortex generators (VGs) in various forms have been used and studied for flow separation control on wings since the 1940s [1]. Their working principle is relatively simple: they generate streamwise vortices that energise the boundary layer on the surface they are attached to, by bringing high momentum fluid closer to the surface [2]. This mechanism has been described by various researchers [3–6], while a number of studies have provided optimization guidelines under a variety of flow conditions [7–13].

In the present investigation, a VG configuration is selected following a thorough wind tunnel campaign. It is found that sizing parameters for the tidal turbine profile are very similar to the wind turbine relevant literature [13,14]. The best performing vane VG configuration had a height of 0.007c, which corresponded to half the local boundary layer height (0.5δ) for operational Reynolds numbers. The results are also used to validate a Reynolds Averaged Navier Stokes (RANS) VG modelling approach using the BAY model [15]. The validated method is used to simulate the flow past a tidal turbine in both model size (1:8) and full scale, see Figure 1. The results show that VGs do suppress flow separation in both cases. However, and importantly, it is revealed that the significance of rotational effects is such that when deciding VG placement locations, only the full size blade should be considered. In the interest of brevity, the performance increase caused by a standard VG configuration is show in Figure 2, where a power coefficient improvement of 1.05% is predicted at λ=3. Figure 3 shows the effect on the normal and tangential forces on the blade. In the final paper and presentation, the results for different VG locations will be included and analysed in detail.
Relevance of Robustness and Uncertainties Analysis in the Optimal Design of Wave Energy Converters
Authors: Giorcelli Filippo , Sirigu Sergej Antonello , Basile Dario
Published: September 2023

The optimisation design of Wave Energy Converters (WEC) to reduce the cost of energy of the technology is a widely investigated topic. In literature classical optimisation strategies have been presented and applied to identify the optimal system parameters of WECs to optimise specific techno-economic metrics. The performance of the optimal identified devices relies on these nominal parameters and it can be strongly affected by construction and modelling uncertainties. In this context, the concept of robustness of the optimal solution plays a relevant role in the identification of a device whose performance is affected as little as possible by uncertainties of various kinds. In the first part of this paper different declinations of robustness concept are derived from other fields of application and described. The identified robustness indexes are then applied to optimal solutions obtained via classical optimisation to evaluate its importance in the design process of WECs.

Strictly related to this kind of methodology is the Sensitivity Analysis (SA) technique, it aims to investigate how the input variation (due to uncertainties or external noise or additional environmental parameters) influences the output results of a defined numerical model and highlight the relative input parameters relevance. Sensitivity Analysis, therefore, can be a valuable tool applicable in the uncertainty set estimation to identify the variables most subject to such uncertainties and their prominence.

The main objective of the work is to underline the importance of introduce the robustness evaluation of WECs during the optimisation process since classical optimisation techniques can lead to solutions that are affected by uncertainties.
Multi wave absorber platform design, modelling and testing
Authors: McLean Niall , Bannon Elva , Holland Matthew , Forehand David , Giles Thomas , Smith Katie , Davey Thomas
Published: September 2023

The subject of this paper is the development of physical and numerical models and a tank test programme to investigate the performance of a multi wave energy absorber platform (MWAP). The platform is inspired by the proposed designs for large scale platforms to be used for floating offshore wind (FOW). The modular design of the physical model enables a variable number of absorbers to be mounted to the platform, with up to 9 absorbers tested simultaneously. The absorbers used are a simplified version of a submerged pressure differential device, with each absorber incorporating a set of mechanical springs to approximate the response of the real internal air spring. Physical model tank tests will be undertaken during 2023, utilizing a range of environmental conditions representative of those at an exposed site on the west coast of Scotland, leased through the ScotWind programme and which has an appropriate water depth and wave resource for large scale wave energy exploitation. Measurements taken during physical model testing will be used to validate numerical models of the MWAP and will allow subsequent investigation of key drivers of annual energy performance, exploring platform configuration options not tested in the wave tank. The motivation for this project, design considerations and balance between tank scale & full-scale design requirements will be given. Discussion will be provided on the implications of the limitations and assumptions made during the physical and numerical modelling work, as well as next steps for utilisation of the tools beyond the scope of this project.
Numerical investigation of the power performance of a wave energy converter comprising a multi-body power take-off
Authors: Elefant Félix , Ferrant Pierre , Babarit Aurélien
Published: September 2023

This article presents a wave energy converter exploiting the pitch of a floating body moored to the seabed. When the floating body tilts under the action of an incoming wave, a movable mass, placed inside the hull, moves relative to the floating body and actuates an electrical generator. Most devices of this type have the drawback that the moving mass sequentially accelerates, slows down, stops and then repeats this sequence in the opposite direction. This generates an irregular instantaneous power output.
The proposed concept consists of (at least) two eccentric bodies having the same mass and revolving atopposite speeds around a vertical axis. In this « counterrotating » solution, the oscillations of the float result in the continuous circular motion of the direct-drive PTO, though the global centre of gravity of the eccentric bodies moves back-and-forth along the symmetry axis of the device. If the eccentric bodies move at constant speed, their global centre of gravity moves in a sinusoidal manner along its pathway.
The present study aims to investigate, through modelling and numerical simulations, the influence of the main parameters, such as the phase and the PTO mass moment, on the performance of a counter-rotating device exposed to waves of various heights and various wavelengths. Optimal phase and mass moment are determined numerically. The resulting output power is close to the theoretical maximum power that can be harvested by the floating body.
A study on tidal rotors under the combined effects of currents and waves using actuator-line CFD simulations
Authors: Zilic de Arcos Federico , McNaughton James , Vogel Christopher , Pinon Grégory
Published: September 2023

Determining loads and power on a tidal rotor under realistic flow conditions is challenging. Methods used by offshore industries for the design and deployment of marine devices rely on simulations of a significant number of cases that combine different environmental and operational conditions. Design studies of tidal rotors rely on engineering models of low to medium computational cost that often omit important hydrodynamic effects such as blockage, multi-rotor interactions, wave diffraction, etc., and have a questionable accuracy under conditions such as high-thrust regimes or highly unsteady flows. Alternatively, high-fidelity CFD simulations can implicitly capture most of the relevant physics, but their computational cost often limits their application in engineering practice.

This study will present a numerical study of a tidal rotor operating near the free surface and affected by combined currents and surface waves. The simulations will be performed with an intermediate fidelity actuator-line model implemented within OpenFOAM. The AL model is embedded within a simulated tank discretised with the finite volume method, that employs a RANS turbulence model with a Volume of Fluid (VoF) approach for the free surface. Relaxation zones, implemented with the Waves2Foam library, are used for the generation and absorption of surface waves and reflections. A preliminary render of the assembled model simulating a test condition can be seen in fig. 1.

The paper manuscript will present the results of an initial validation of the modelling strategy that will compare simulated cases with towing-tank experiments. The validation will be followed by a quantification of the interactions between the rotor and the free surface, as well as an analysis of the transient loads and power fluctuations for different operating conditions.
Development of the Exowave Oscillating Wave Surge Converter
Authors: Krogh Iversen Sarah , Andersen Jacob , Wigant Lars , Frigaard Peter
Published: September 2023

With increasing demand for renewable energy resources, the development of alternative concepts is still ongoing. The wave energy sector is still in vast develop- ment on the way to contribute to the energy production world wide. The present study presents the development of the Exowave wave energy converter made so far. A numerical model has been established supported by wave flume tests performed at Aalborg University during the first phase of the development. Furthermore, a successful open sea demonstration has been performed on 7 meters of water at Blue Accelerator, Belgium, from which the concept has been proven. As part of the ongoing research, verification of the numerical model will be made through experimental testing in the wave tank of Aalborg University, and an open sea demonstration at 14 meters of water depth will be executed off the coast of Hanstholm, Denmark.
Observer-Based Fault Estimation Applied to a Point Absorber Wave Energy Converter
Authors: Papini Guglielmo , Faedo Nicolas , Mattiazzo Giuliana
Published: September 2023

The economic viability of wave energy conversion systems is one of the open points among the research community. To lower the energy cost, the devices in charge of extracting the wave power, called wave energy converters (WEC), are often controlled by means of optimal control (OC) strategies. Such OC systems, which have proven their effectiveness in wave energy applications, often rely on a mathematical model of the device (and, in some cases, on the wave excitation force) to optimize the control action provided to the system. Nevertheless, the marine environment results hostile for general device safe operations, potentially triggering a variety of faults in the WEC system. Such condition (for example, a sensor failure or additional friction inside a gearing) directly affects the system dynamics. If this deviation is not considered by the control algorithm, the energy production performance can degrade considerably, or the control action itself can cause a more serious fault. A possible solution is that of designing an algorithm capable of compensating for eventual faults in the system, while still respecting the initial design performance or, when not possible, preserving the main device functionalities. Such a control strategies belong to the family of Fault Tolerant Control (FTC) techniques, which can be divided into two macro-categories: Passive (PFTC) and active (AFTC) algorithms. While PFTC systems are designed offline and can account only for a predefined set of system faults, AFTC algorithms are more suitable to tackle significant system deviations from the nominal model. For this purpose, such algorithms may require some routine to detect, isolate and eventually estimate the specific fault. This task is accomplished by Fault Detection and Identification (FDI) routines. According to the AFTC algorithm, the FDI module must accomplish different tasks. Furthermore, the FDI module accuracy plays a crucial role in some AFTC strategies, since the poor estimation of a faulty signal can induce the controller to behave incorrectly. This paper presents an FDI algorithm applied to a point-absorber wave energy converter (WEC). The proposed structure consists of an observer-based strategy in charge of detecting, isolating, and tracking effectively faulty signals occurring in numerical simulations. The results demonstrate the proposed observer effectiveness for a predefined set of actuator and sensor faults, both in the case of independent, and simultaneous fault occurrence.
Identification of optimal sites for the deployment of wave energy converters: the importance of a technology-centred approach
Authors: Novo Riccardo , Giorgi Giuseppe , Cervelli Giulia , Faedo Nicolas , Mattiazzo Giuliana
Published: September 2023

Driven by climate issues and geopolitical uncertainties, Europe faces the need to transform its energy supply dramatically and quickly. Various renewable technologies are proposed as a medium- to long-term solution for an environmentally and economically sustainable energy mix: among the available solutions, wave energy converters (WECs) are attracting growing interest due to the large untapped wave energy potential in European seas. In this context, the choice of optimal locations for the use of wave energy is fundamental to limit the technological gap with other fully developed conversion technologies, and to ensure competitive energy costs. In this paper, we compare different possible strategies to identify suitable sites for the installation of WECs, namely the one based on pure analysis of the wave energy resource, and that considering the productivity of the device in different sea states, i.e., its power matrix. Using the performance matrices of notional WECs, particularly an Oscillating Surge Wave Energy Converter (OSWEC) and a Heaving Point Absorber (HPA), we estimate optimal locations on the Italian coasts and highlight the advantages and disadvantages of the two approaches. The analysis shows the importance of a technology-based approach for the spatial planning of future wave power plants and highlights significant differences compared to the approach that can be used for the preliminary identification of sites for wind farms and, especially, for photovoltaic plants. We use the obtained results to introduce the MORE-EST platform, a novel web-based tool for straightforward estimation of wave resources and WECs productivity in European seas. The proposed platform is able to integrate information on wave resource assessment, bathymetry, marine space use and technological features, and represents a tool aimed at researchers, WECs developers, and policy makers.
Degrees of Freedom Effects on a Laboratory Scale WEC Point Absorber
Authors: Beringer Courtney , Bosma Bret , Robertson Bryson
Published: September 2023

The number of rigid bodies and operational degrees of freedom of a wave energy converter (WEC) have significant impacts on power production magnitude and efficiency across wave periods, but this concept is not well studied. Investigating the effect of the number of bodies and degrees of freedom will help WEC developers design devices that most efficiently meet power and cost needs. This paper presents experimental and numerical results for a point absorber WEC across three modes of operation in regular waves. The three modes of operation are ‘one body heave only’, ‘two body heave only’, and ‘two body six degrees of freedom’.
The Laboratory Upgrade Point Absorber (LUPA) was used as the test article. This work builds on the 2021 EWTEC paper [1] by completing fabrication and undergoing wave testing. The LUPA experiment took place in the Large Wave Flume at the O.H. Hinsdale Wave Research Laboratory at Oregon State University in Corvallis, Oregon, USA; the installation and a wave test are shown in Figure 1. LUPA is constructed as a 1:20 scale two body point absorber with a buoyancy driven float, and a spar with a heave plate to act as a reactionary body. The spar is 3.7 meters tall and the float has a 1-meter diameter.
Figure 1. (Left) Mooring line installation. (Right) Wave tests in the Large Wave Flume.
The ‘one body heave only’ mode locks the LUPA spar so only the float is moving, and only in heave (vertical). The ‘two body heave only’ mode allows both the float and spar to move but both bodies are restricted to heaving. The ‘six degrees of freedom’ mode has taut mooring lines connected to the spar and LUPA can translate and rotate in all directions.
A damping optimization of the power take off was performed experimentally and numerically by sweeping damping values across a wide range of regular wave periods. The optimal damping value is used to compare the power generation of the three modes of operation.
The LUPA project is an open-source, lab-scale wave energy converter that acts as a testing platform for students and researchers. The data from this testing along with numerical models and engineering design files will be publicly available here: https://github.com/PMEC-OSU/LUPA. This paper presents how increasing complexity of WECs through the number of bodies and degrees of freedom affects power production. It also provides a baseline case for LUPA which other researchers can compare against when applying their research to the LUPA project.
References
[1] B. Bosma, C. Beringer, M. Leary, and B. Robertson, “Design and modeling of a laboratory scale WEC point absorber,” 14th Eur. Wave Tidal Energy Conf., pp. 1–9, 2021.
Tidal barrage operation optimization using moment-based control
Authors: Skiarski Agustina , Faedo Nicolás , Ringwood John
Published: September 2023

As decarbonization of energy systems becomes an imperative and the deployment of intermittent renewables increases, the operation of electrical grids becomes challenging. In this sense, tidal barrage schemes can supply clean and predictable energy with more flexibility than the more traditional wind and solar plants. However, the high infrastructure costs associated with tidal barrage plants hinders its deployment. An optimal operation is key to maximize energy output and assure the project’s feasibility.

Recently, Ringwood and Faedo [3] introduced a novel approach to tidal barrage control by applying wave energy control techniques, with promising results. The model consists on a two-way tidal barrage scheme, where an analogy is made between latching/declutching algorithms applied in WEC control and holding/sluicing from tidal barrage. The optimization was done using the moment-based framework developed in [1] and [2], which can formulate linear and non-linear problems in a concave quadratic environment, thus allowing the application of efficient numerical solution algorithms. This preliminary study has a number of simplifying assumptions, leaving a pathway to further examine the optimal control problem.

This paper extends the results of the analysis from [3] by adding complexities to the model. Crucially, the basin is modeled such as the area is a polynomial function of the water level, instead of assuming constant surface area. This will affect the operational head of the optimal solution, as the volume of water at the top of the basin will be higher than at the bottom. Another added constraint will be the minimum head that the turbine requires to generate electricity. Furthermore, a cost function is introduced to penalize the energy consumption of the sluice gates, as shown in figures 1.a) and 1.b). This not only increases the accuracy of the model, but in many cases improves the convergence of the algorithm by adding a quadratic term. Figure 2 shows the value of the overall energy yield (as a fraction of the energy output without penalty) and simulation run time (as a fraction of the run time without penalty) with different penalty coefficients.

1.a) Sluice gate area without considering cost function

1.b) Sluice gate area with penalty factor of 3

 

 

2. Energy and run time variations with penalty

 

 

References:[1] N. Faedo, G. Scarciotti, A. Astolfi, and J. V. Ringwood. Energy-maximising control of wave energy converters using a moment-domain representation. Control Engineering Practice, 81:85–96, 2018.

[2] N. Faedo, G. Scarciotti, A. Astolfi, and J. V. Ringwood. Nonlinear energy-maximizing optimal control of wave energy systems: A moment-based approach. IEEE Transactions on Control Systems Technology, 29(6):2533–2547, 2021.[3] J. V. Ringwood and N. Faedo. Tidal barrage operational optimisation using wave energy control techniques. IFAC-PapersOnLine, 55(31):148–153, 2022. 14th IFAC Conference on Control Applications in Marine Systems, Robotics, and Vehicles CAMS 2022.
Techno-economic Optimization of an Offshore Hybrid Power System: Argentine Basin Case Study
Authors: Palmer Sarah , Dillon Trent , Polagye Brian
Published: September 2023

Ocean observation and monitoring relies on data gathered from multiple sources including gliders, cabled observatories, underwater vehicles, and moored buoys. Moored buoys, augmented by resident autonomous underwater vehicles, are potentially well-suited to long-term oceanographic data collection with the resolution and scope of data collection increased by utilizing in-situ power generation. While power needs could be provided by a single generation source (e.g., diesel generator, solar photovoltaics, or wave energy converter) with battery backup, a hybrid power system can potentially smooth seasonal variations that would otherwise require large generation and storage capacities, and be tailored to a locations’ resource availability. By reducing system size through hybridization, we have the potential to reduce overall system cost. To this end, we developed an optimization model that defines the generator and storage capacities of the cost-optimal hybrid power system for a given location and load profile. The model considers generation by wave energy converters, wind turbines, solar photovoltaics, diesel generators, and current turbines with a battery for energy storage. The model uses the defined load profile and location specific time series of resource availability for a time-domain simulation of the power generated and battery state of charge. Based on the power system size, mooring, and mission specific maintenance schedule, the model calculates capital and operating costs for each potential combination of generation and storage capacities. The optimization model searches the 6-dimensional design space to find the lowest cost system that can satisfy the load requirements. In this paper, we focus on a case study of a hybrid power system serving an ocean observation buoy with a resident autonomous underwater vehicle located at the Mid-Atlantic Shelf Break. Diagnostic metrics such as the cost-breakdown and generator capacity factors are evaluated to understand cost drivers and draw comparisons to the costs of single generation systems. Additionally, the model sensitivity to key assumptions such as battery life, maintenance vessel cost, survival loads, and required persistence are discussed.
Intracycle Control Sensitivity of Cross-Flow Turbines
Authors: Athair Ari , Snortland Abigale , Scherl Isabel , Polagye Brian , Williams Owen
Published: September 2023

Intracycle control for cross-flow turbines employs sinusoidal perturbations in rotational speed to affect turbine power output and loads. This technique is explored for one- and two-bladed turbines with experiments that combine performance measurements with in-rotor flow-field measurements using non-intrusive particle image velocimetry. Performance enhancement is demonstrated for a wide range of control parameters but is found to be more sensitive to the sinusoidal phase offset than amplitude. Optimal performance is observed under conditions which maintain constant nominal blade angle of attack and consistently high blade-relative velocities once the static stall angle is exceeded during the power stroke. This maintains high lift and delays vortex separation. Perhaps most significantly, kinematics are also identified which decrease peak turbine loading by 12% while still producing marginally higher power output, highlighting the utility of intracycle control for load mitigation. The range of control parameters that produce these beneficial loading properties is relatively narrow and flow-fields are similar to operation at a constant rotation rate. We hypothesize that reductions in maximum loading are achieved by smoothing the changes in angle of attack and blade relative velocity profiles throughout the cycle.
Floating wind and wave energy technologies: applications, synergies and role in decarbonization in Portugal
Authors: White Craig , Carrelhas Ana , Gato Luís , Portillo Juan , Cândido José
Published: September 2023

Floating offshore wind and wave energy are both promising marine renewable energy technologies that are still at an early stage of development. This paper reviews synergies between the two technologies that can be mutually beneficial and facilitate the path to commercial exploitation. The analysis focuses on three different types of combined wave and wind systems: Co-located arrays, hybrid systems and island systems. The decarbonisation potential of co-located systems is discussed. Existing carbon emissions from marine technologies are compared and how synergies can achieve these reductions are explored. A case study is presented to calculate the impact of multi-purpose platforms on the Portuguese energy system. Portugal was chosen because it has an excellent climate for marine resources, deep waters, positive political support for renewable marine energy and previous success in deploying first technology demonstrators for floating wind and wave energy systems.
A turbines-module adapted to the marine site for tidal farms layout optimization
Authors: Pucci Micol , Zanforlin Stefania , Bellafiore Debora , Frangioni Antonio
Published: September 2023

The ocean energy exploitation is arousing growing interest in the renewable energy sector. In theshort term, horizontal axis tidal turbines are the most promising technology due to the accumulatedknow-how in the field of wind energy. In order to maximize the performance of the devices in acluster, it is essential to optimize the layout. The marine environment offers different conditions thanatmospheric situations, in terms of confinement and turbulence intensity. Moreover, tidal currentsexhibit a highly predictable pattern in speed intensity and direction unlike the wind resource, whichhas a more random behaviour. Nonetheless, most of tidal sites are characterized by the inversionof flow where the two prevailing directions are not perfectly aligned and opposite, hence the anglebetween those directions should be a design variable. In this work we will consider as a case studythe site proposed in [1], where this angle is ±20°.For those sites with a flow inversion of almost 180°, the staggered configuration is preferable toavoid wakes interference as mentioned in [2]. Furthermore, many studies [3] had analysed positiveinteraction between neighbouring devices in a cluster, hence it is important to establish the optimalrelative position accounting for fluid dynamic positive effects, and not only negative aspects suchas wake interactions. For this reason, in this work we present a novel approach to determine thebest configuration of a cluster of few turbines, a ”module”, which will be the optimized ”buildingblock” for the whole farm. The procedure to be followed consist of two phases in which boththe characteristics of the site and those of the turbine are taken into consideration. To place thedevices in an optimal configuration, we first consider the change of flow direction during the tidalcycle for the site of interest, allowing only those configurations which avoid wake interference forboth prevailing flow directions; then, we assess the best layout by exploiting positive interactionsbetween devices in the cluster. The mutual fluid dynamic influence is analysed by means of a 3DBlade Element Momentum model of the turbine [4] implemented in the Open Source SHYFEMcode. A series of simulations is performed to outline the power production trend of the module, andconsequently find the optimal distancing between the machines. CFD simulations are also used toextract the module wake characteristics.
Design, Manufacture and Testing of an Open-Source Benchmark Composite Hydrokinetic Turbine Blade
Authors: González-Montijo Miguel , Murray Robynne , Beach Ryan , Murdy Paul , Neary Vincent , Kim Dongyoung , Wosnik Martin
Published: September 2023

In a trend towards clean energy alternatives, recent years have seen great strides in the marine energy space. This has resulted in a pressing need for the design, development, and validation of novel energy harvesting technologies such as hydrokinetic devices, which capture kinetic energy from waves, tides, and currents. However, these devices span numerous concepts and designs that often lack solid benchmark research that can be freely referenced. This work focuses on the design process of an open-source composite hydrokinetic turbine blade for a three-bladed marine turbine rotor assembly with a diameter of 2.5 m. The proposed blade consists of two structural composite skins that are bonded with an adhesive and filled with a foam core. This study will explore and contrast the efficiency and resolution of low-fidelity rapid design methodologies and comprehensive high-fidelity approaches for the blade design, modeling, and analysis efforts, a key objective in this research. Blade hydrodynamic loads were modeled and applied to finite-element blade models to study deformations and potential failure. Ongoing efforts will result in blade manufacture and structural testing at the National Renewable Energy Laboratory. In future work, multiple blades will be deployed at the Living Bridge site at the University of New Hampshire and will be compared to rigid aluminum blades of the same geometry, developed by Sandia National Laboratories. Ultimately, this research will lay foundational groundwork for researchers and manufacturers, establishing a baseline composite blade design that will serve as a benchmark in the development of future hydrokinetic turbine blades.
Dynamic response of floating offshore renewable energy devices: Sensitivity to mooring rope stiffness
Authors: Smith Katherine , Davey Thomas , Forehand David , Pillai Ajit , Xiao Qing , Tao Longbin
Published: September 2023

The offshore renewable energy sector has seen a rise in floating devices, all of which require mooring and anchoring systems. Synthetic ropes have emerged as a promising technology for cost reduction in this system. However, characterising the behaviour of these materials, which exhibit complex non-linear, visco- elastic and plastic structural properties, presents challenges. Numerical modelling and tank testing are the available tools for developers to overcome these challenges, however, there is a lack of guidelines for test facilities regarding the design of tank-scale mooring systems. The present work focuses on the numerical design of a typical semi-taut mooring system using synthetic materials suitable for future-generation floating offshore wind turbines. A coupled time-domain hydrodynamic model was employed to explore the dynamic sensitivity of the device to changes in mooring rope stiffness. The results demonstrate that changes in line axial stiffness have a greater impact on platform surge and mooring line tension than on heave and pitch responses. These findings establish preliminary margins for target stiffness values, which are valuable for selecting mooring materials for scaled tank test models. Although the case study was floating wind, the results have broader applicability to wider floating marine energy device design.
Hardware-in-the-loop testing framework for active accumulator wave energy converters
Authors: Zeng Chen , Gaspar José , Mendes Mario , Guedes Soares Carlos
Published: September 2023

The hardware-in-the-loop technique is a hybrid co-simulation approach that joins real physical and virtual components. The real components may be the power take-off while the virtual ones the numerical models of sea wave and wave energy converter hydrodynamics. This simulation approach has been published with some regularity, however a review of the state-of-the-art has not been found, in particular in the research field dedicated to wave energy converters. Thus, the objective of this paper is to provide the ongoing results of such review, such as the generic testing framework and taxonomy, and their  articulation on the simulation of a new oil-hydraulic power take-off concept. In this new concept, different power take-off nominal pressures may be regulated according to different sea states, by changing the hydraulic accumulator charging characteristics. Therefore, this active accumulator is intended to allow an increase on the range of possible Power Take-Off damping forces, thus, better wave energy harvesting performance. The paper results are also intended to support novice and advanced researchers to design simulation approaches in a clear and appropriate manner.
Early Design Phase Method for Characterizing and Comparing Wave Energy Converter Archetypes
Authors: Roach Aeron , Meek Moira , Syed-Muhammad Ali Raza , Robertson Bryson , DuPont Bryony
Published: September 2023

The ocean is both a precious resource for coastal communities and a vast source of largely untapped renewable energy that can help combat climate change. This presents a unique opportunity for wave energy converters (WEC) to provide both utility-scale and small-scale electricity for resilient, energy-efficient communities that can better withstand the effects of climate change. Designing a WEC is not straightforward as the ocean supports a wide range of uses and the highly energetic environment can threaten survival. This requires WEC designers to deconflict their use area and select deployment locations that minimize risk. Subsurface WEC designs provide a potential solution for these challenges as their deployment depth can mitigate area-use conflicts with other ocean users. A fully submerged WEC also has increased survivability due to being in a less energetic environment and at a depth that they are less likely to collide with ocean vessels. However, a submerged WEC may also suffer from the less energetic environment as it decreases the amount of electricity the WEC can generate. These tradeoffs make it unclear when subsurface WECs are beneficial to deploy. There is little research to date that offers comprehensive understanding of this field of WECs in regard to their capabilities or constraints. This paper presents a method for characterizing and understanding the functions of WEC archetypes by leveraging functional decomposition to examine high level overlaps between archetypes. Functional decomposition is a well-established engineering design method for breaking down complex systems into constituent parts to track flows of energy, information, and materials. The method enables engineers understand how each component contributes to the overall functionality of the system and enables us to analyze functional performance overlaps between WEC archetypes. We apply this method to submerged WECs and present an analysis of the high level functions. The findings of this case study shed light on the functional uniqueness of submerged WEC archetypes and can be used to guide future development in subsurface WEC technology. Better identifying functional overlaps between WEC archetypes will help researchers and developers generate effective designs that build resilient coastal communities.
Limiting the available pneumatic power in a U-OWC
Authors: Henriques Joao , Gato Luís , Falcão António , Ferreira Diogo
Published: September 2023

A fixed oscillating water column is a hollow structure open to the sea at its submerged part. The water column motion alternately compresses and decompresses the enclosed air above the inner free surface, which drives a self-rectifying air turbine. In 2003, Boccotti proposed the so-called U-OWC having in view the integration into breakwaters. In this configuration, the inner water is connected to the sea by a U-shaped duct whose opening faces upwards rather than sideways or downwards. This allows the OWC length to be extended (and the resonance frequency reduced) without placing the opening too deeply submerged where wave energy is attenuated by distance to the free-surface. An advantage of OWC converters is the capability to control or dissipate the excess energy available to the power take-off system in excessively energetic sea states.  This is in general done by limiting the air turbine torque by controlling a by-pass air valve or a valve in series with the turbine. What is proposed here is to take advantage of the water column configuration to limit the energy absorbed from the waves in the more energetic sea states. This requires the tidal amplitude to be small as occurs in coastal areas like the Mediterranean Sea. The distance of the OWC opening to the mid-sea-level should be chosen such that, in the more energetic sea states, that opening is left uncovered by the troughs of the higher waves. This introduces a limitation to the energy absorbed in the more energetic sea states. This paper reports experiments with a 1:40th-scale U-OWC in a wave flume. The results show that limitations to the capture width ratio occurs in the more energetic wave systems.
The Impact of Uncertainty on the Control of a Multi-Axis Wave Energy Converter
Authors: Hall Carrie , Wu Yueqi , Rizaev Igor , Sheng Wanan , Dorrell Robert , Aggidis George
Published: September 2023

As global energy demands and climate concerns continue to grow, the need for renewable energy is becoming increasingly clear and wave energy conversion (WEC) systems are receiving growing interest. Over the years, many WEC systems have emerged but most of these systems are designed to extract energy from a single direction of motion. In reality, there are six degrees of freedom that a conversion device can potentially harness and a device that can operate on multiple axes, should be able to more effectively and consistently produce power. However, the design and control of the power take off (PTO) system for a multi-axis device is challenging due to the system complexity and nonlinearity. WEC systems often utilize optimal control techniques for PTO operation and leverage a prediction of the upcoming wave force to ensure power optimization.  Prior work has clearly demonstrated that high power production can be achieved when an exact system model is used and the upcoming wave conditions are known, but uncertainty in the underlying model or the wave prediction can degrade performance.  PTO control on a multi-axis WEC must leverage predictions of forces in multiple directions and if model predictive strategies are used, must leverage a simplified model of the WEC dynamics to be able to optimize in real time. The uncertainty in these predictions and the model could severely degrade the WEC’s power output. This work examines the control of a multi-axis WEC system, TALOS, and leverages machine learning to predict wave forces over the upcoming time horizon. TALOS is a point-absorber type WEC with multi-axis PTO system. The PTO uses a heavy ball that is attached to the hull with springs and hydraulic cylinders. When the hull is pushed by the external waves, the relative motion between the ball and hull moves the hydraulic cylinders causing them to pump a fluid through a circuit, thereby driving a hydraulic motor to produce electricity. This design has shown promising results in energy output but is more challenging to control since the PTO can move over six degrees of freedom. This paper seeks to quantify wave prediction uncertainty and its seasonal variation and to examine the impact of the uncertainty of the prediction on a model predictive controller’s ability to optimize the power output of TALOS.