bluuebunny/crossref_metadata_2025_split huggingface dataset:
Critical Feature and Seawater Testing of Cross-Flow Rotor Components Fabricated with Additive Manufacturing
Authors: McVey James , Zaengle John , Cavagnaro Robert , Fenn Michelle , Lommers Brittnee , Rumple Chris 
Published: September 2023

Cross-flow tidal turbines are an attractive option for powering remote or off-grid applications because of their simplicity as compared to axial-flow turbines. For instance, when oriented vertically, they harvest power from any current direction with a single degree of freedom and no yaw mechanism. Additive manufacturing (AM) offers an opportunity to print parts out of a wide variety of materials that can result in components that are lighter, stronger and/or less expensive to produce than with traditional manufacturing techniques. When coupled with cross-flow turbine rotors, which require critical features (blade-strut, strut-shaft connections) to be both structurally stiff and hydrodynamically shaped, which can be challenging for typical fabrication processes, AM offers the ability to do both well. This paper describes work on the feasibility of using advanced AM techniques to fabricate small cross-flow turbine rotors for applications at sea and near remote coastal communities.
AM materials were categorized into 3 classes – plastics, metals, and ceramics – and reviewed for suitability based on a set of engineering requirements and criteria related to turbine characteristics, material properties, and AM process capabilities. Two plastics and two metals were selected to undergo further testing: Essentium CF25, CarbonX Ult 9085, Titanium Ti-6Al-4V, and Inconel 718. Testing is conducted in three phases: the first is a long-term, 5-month submersion test in the seawater tanks at PNNL-Sequim to study corrosion, water uptake, and biofouling potential; in the second, materials are tensile tested on a load frame to find their failure parameters to compare to material standards; the third test is a fatigue test consisting of cyclically loading test parts with a known force on the order of that exerted on rotor blades in a 1.5 m/s current flow. These tests are designed to discern the suitability of AM materials since their properties from 3D printing processes are known to vary from published parameters. The test samples undergoing submersion testing will be tension tested and compared to control samples not subjected to extended seawater immersion. For fatigue life testing, a small rotor is expected to complete 100 million cycles over the course of a year-long lifespan, but for the case herein is restricted to 1 million for a preliminary performance evaluation. The first 10k cycles are run on an MTS 312.21 load frame at a rate of 0.2 Hz, with the remaining on a custom-built cyclic-deflection test rig at 0.8 Hz.
Experimental Investigation into the Air Compressibility Scaling Effect on OWC Performance and Wave Height
Authors: Cohen Nadav , Flocard Francois , Turner Ian L. , Sergiienko Nataliia , Cazzolato Ben 
Published: September 2023

Wave energy converter arrays have the potential to provide coastal protection in addition to generating power from incoming waves. As part of a wider experimental study to investigate dual-use applications, this paper presents the results of wave flume testing conducted to analyse the performance characteristics of a single, generic Oscillating Water Column (OWC) device, in preparation for the next phase of study that will focus on multi-device arrays. The specific focus of this flume testing was to characterise parameters such as Response Amplitude Operator (RAO), Capture Width Ratio (CWR) and Phase Response, as well as the device’s effect on the local wave field.
A potential limitation when using scaled experimental results for OWCs are the differing scaling factors that should be applied to the device’s submerged volume (λ³) and air volume (λ²) which, together with the Power Take Off (PTO) damping, can greatly affect the air-spring stiffness experienced within the OWC.
A subset of 34 tests (out of a total 134) were conducted under monochromatic wave conditions with wave heights of 20 mm or 40 mm and wave periods ranging from 1.2 s to 2.2 s. In these tests the PTO damping was varied by adjusting the orifice diameter, while the air volume was varied via an adjustable auxiliary air chamber. Results show that for the smaller orifice diameters (i.e., higher damping) tested, air-spring stiffness played a significant role and counterintuitively increased with increased air volume.
Effects of the single OWC device on the wave field within the flume were also investigated. Results revealed that while there is a marked difference when comparing the OWC to an identically-shaped blockage, there was no significant measurable difference in the wave height change observed for all the damping and air volume parameter settings that were modelled, despite a general trend when comparing to the empty flume.
Maximizing the surge amplitude of a floater through an adaptable mooring tightening technique
Authors: Asiikkis Andreas , Grigoriadis Dimokratis , Vakis Antonis 
Published: September 2023

Abstract
A technique to optimize the response of Wave Energy Converters (WECs) by maximizing the amplitude of motion along the surge direction is presented. This is achieved by utilizing an adaptable mooring tightening technique for a floater moored with tension legs (tendons). To gain a deeper understanding of the effect of sea states and mooring cable lengths on the surge response of the system, a series of numerical simulations were conducted for various wave conditions while varying the length of the mooring cables. WEC-Sim [1] was used to solve the multi-body dynamics of a rectangular cuboid floater by solving the equations of motion using a time-domain formulation. The dynamics of the mooring cables were simulated using the MoorDyn model with a lumped-mass formulation [2]. To validate the accuracy of the numerical methods, a series of experimental tests were performed in a small-scale wave tank. It was observed that tightening the mooring cables by decreasing their length amplifies the surge motion of the floater while the mooring forces in the heave direction rise due to the increased tension in the cables. Stretching the cables further was found to (i) decrease the surge amplitude and (ii) drastically increase the mooring forces, threatening the integrity of the cables. Therefore, there is an optimum value of the length of the cables that maximizes the surge amplitude of the floater while ensuring that the cables will not break. The impact of other mooring cable parameters such as diameter and material properties were also evaluated. More specifically, increasing the stiffness by increasing the diameter or the tensile modulus of elasticity was found to reduce the floater’s surge amplitude. For the geometry used in this study, the optimum length, diameter and properties of the cables are provided for several sea states. The current results lay the foundations for the design of new types of WECs that harness the surge motion of a floater rather than the heave which is the most common approach for floating WECs.
References
[1]: Kelley Ruehl, David Ogden, Yi-Hsiang Yu, Adam Keester, Nathan Tom, Dominic Forbush, Jorge Leon, Jeff Grasberger, and Salman Husain. (2022, September), WEC-Sim (Version v5.0.1), DOI: 10.5281/zenodo.7121186.
[2]: Hall, M., & Goupee, A. (2015). Validation of a lumped-mass mooring line model with DeepCwind semisubmersible model test data. Ocean Engineering, 104, 590–603. https://doi.org/10.1016/j.oceaneng.2015.05.035
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.
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.
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.
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.