Publications
Publications listing
| Category | Category | Keywords | Year | Title | Abstract | Actions |
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Journal Article |
Journal Article | 2025 |
Calibrating hydrodynamic viscous damping in engineering models of floating wind platform utilising simplified CFD models |
Accurately investigating hydrodynamics for floating wind platforms using potential theory poses challenges due to uncertainties in quadratic damping estimation, significantly influenced by drag coefficient selection. Costs associated with wave basin testing for calibration data have prompted a shift towards the use Computational Fluid Dynamics (CFD) to estimate appropriate drag coefficients to calibrate potential theory models. However, CFD simulation of six-degrees-of-freedom floating substructure, with addition of turbine loading across varying metocean conditions, demands substantial computational resources. This study evaluates whether simplified CFD models can fine-tune viscous terms in potential theory models or if a fully complex model is needed. Decay, steady current, and wave condition tests were conducted in the CFD model of a floating wind platform. Calculated drag coefficients from these CFD-based approaches varied by 15–85% of offshore standards. Coefficients obtained were used to calibrate potential theory models of the platform. Without viscous correction, the potential theory model overestimated response amplitude operator values at the platform's natural frequency for surge and pitch degrees of freedom by up to twofold. Applying viscous drag coefficients from CFD methods reduced these differences to within 10–20%. This research guides numerical modellers in choosing dynamic complexity levels and adjusting CFD simulation accuracy within computational resource limits. | More details Read publication | |
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Journal Article |
Journal Article | 2025 |
A techno-economic study on the utilisation of airborne wind energy for reverse osmosis seawater desalination |
Airborne wind energy is an emerging technology that can harness stronger and more consistent winds in higher altitudes using less mechanical and civil infrastructures than conventional wind energy systems. This article outlines a techno-economic study on using this technology for reverse osmosis seawater desalination in which a semi-permeable membrane process is used to remove salts and contaminants from water. To understand the techno-economic feasibility of such a system, this research work studies a 2 MW airborne wind-driven reverse osmosis plant. Different energy recovery devices are also studied to find their impact on improving the desalination plant's techno-economic performance. Results show the techno-economic practicality of an airborne wind-driven reverse osmosis plant with a competitive levelised-cost-of-water compared to similar-sized wind and solar energy-driven seawater desalination systems. | More details Read publication | |
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Journal Article |
Journal Article | 2024 |
Automating the quantification of coastal change using historical aerial photography: A case study along the coastline of county Cork, Ireland |
Coastlines worldwide are coming under increasing pressure due to climate change and human activity. Data on shoreline change are essential for coastal managers and when no long-term monitoring programs are implemented and shoreline change is typically on the order of less than 1 m/yr., as observed in Ireland, aerial photography is the most valuable source of information. A well-established literature exists for automated vegetation extraction from digital images based on the near infrared reflectance, but there is less research available on spectrally limited colour photography. This study develops a methodology for automating vegetation line extraction from a series of historical aerial photography of the Cork coastline in the South-West of Ireland. The approach relies on the Normalised Green–Blue Difference Index (NGBDI), which is versatile enough to discriminate disparate coastal vegetation environments, at different resolutions and in various lighting and seasonal conditions. An iterative optimal threshold process and the use of LiDAR ancillary datasets resulted in an automated vegetation line measurement with uncertainties estimated to be between 0.6 and 1.2 m. Change rates derived from the vegetation lines extracted present uncertainties in the range of ±0.27 m/yr. This robust and repeatable method provides a valuable alternative to time-consuming and subjective manual digitisation. | More details Read publication | |
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Journal Article |
Journal Article | 2024 |
An integrated methodology for significant wave height forecasting based on multi-strategy random weighted grey wolf optimizer with swarm intelligence |
While wave energy is regarded as one of the prominent renewable energy resources to diversify global low-carbon generation capacity, operational reliability is the main impediment to the wide deployment of the related technology. Current experience in wave energy systems demonstrates that operation and maintenance costs are dominant in their cost structure due to unplanned maintenance resulting in energy production loss. Accurate and high performance simulation forecasting tools are required to improve the efficiency and safety of wave converters. This paper proposes a new methodology for significant wave height forecasting. It is based on incorporating swarm decomposition (SWD) and multi-strategy random weighted grey wolf optimizer (MsRwGWO) into a multi-layer perceptron (MLP) forecasting model. This approach takes advantage of the SWD approach to generate more stable, stationary, and regular patterns of the original signal, while the MsRwGWO optimizes the MLP model parameters efficiently. As such, forecasting accuracy has improved. Real wave datasets from three buoys in the North Atlantic Sea are used to test and validate the forecasting performance of the proposed model. Furthermore, the performance is evaluated through a comparison analysis against deep-learning based state-of-the-art forecasting models. The results show that the proposed approach significantly enhances the model's accuracy. | More details Read publication | |
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Journal Article |
Journal Article | 2024 |
An advanced geospatial assessment of the Levelised cost of energy (LCOE) for wave farms in Irish and western UK waters |
With the climate crisis becoming an ever-growing concern, Europe is striving to reduce its energy related greenhouse gas emissions. On the western edge of this continent, wave energy is a logical future clean energy consideration for Ireland and the U.K. to help realise ambitious targets recently being set in policy. Yet to reach commercialisation, there is still much uncertainty surrounding the financial feasibility of wave farms in the region of interest, and where exactly the most feasible locations are likely to be. The Levelised Cost of Energy (LCOE) is the most commonly used metric in determining the financial feasibility of an energy project, and it is very much site dependant when it comes to wave energy, varying considerably from one location to the next. This study uses the geographic approach to address this and estimate the LCOE of wave energy farms in the region, considering different technology types and the geospatially variable inputs at play. The results reveal areas of high project feasibility in the Atlantic Ocean (off the west coast of Ireland), the Celtic Sea and the Inner Seas off the West Coast of Scotland (ISWCS), with LCOE values below 110€/MWh along the coasts of these areas. | More details Read publication | |
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Journal Article |
Journal Article | 2024 |
Inspection of Floating Offshore Wind Turbines Using Multi-Rotor Unmanned Aerial Vehicles: Literature Review and Trends |
Operations and maintenance (O&M) of floating offshore wind turbines (FOWTs) require regular inspection activities to predict, detect, and troubleshoot faults at high altitudes and in harsh environments such as strong winds, waves, and tides. Their costs typically account for more than 30% of the lifetime cost due to high labor costs and long downtime. Different inspection methods, including manual inspection, permanent sensors, climbing robots, remotely operated vehicles (ROVs), and unmanned aerial vehicles (UAVs), can be employed to fulfill O&M missions. The UAVs, as an enabling technology, can deal with time and space constraints easily and complete tasks in a cost-effective and efficient manner, which have been widely used in different industries in recent years. This study provides valuable insights into the existing applications of UAVs in FOWT inspection, highlighting their potential to reduce the inspection cost and thereby reduce the cost of energy production. The article introduces the rationale for applying UAVs to FOWT inspection and examines the current technical status, research gaps, and future directions in this field by conducting a comprehensive literature review over the past 10 years. This paper will also include a review of UAVs’ applications in other infrastructure inspections, such as onshore wind turbines, bridges, power lines, solar power plants, and offshore oil and gas fields, since FOWTs are still in the early stages of development. Finally, the trends of UAV technology and its application in FOWTs inspection are discussed, leading to our future research direction. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2024 |
Modelled Cost Reductions for the X-Rotor Offshore Wind Turbine |
The XROTOR project is developing an innovative turbine (X-Rotor Concept - XRC) that is a Vertical Axis Wind Turbine (VAWT)/Horizontal Axis Wind Turbine (HAWT) hybrid. The objective of this paper is to assess the XRC Levelised Cost of Energy (LCoE), applying different sensitivity analysis to determine a realistic LCoE range. This will then be compared with LCoE estimates for three traditional HAWT drivetrain configurations to evaluate the potential cost savings for the XRC. The paper considers a hypothetical farm of 100x5MW XRCs on generic monopiles, 100km from shore and commissioned in 2030 with a 30-year project. Analysis uses the University of Strathclyde Operation and Maintenance (O&M) model and an LCoE tool developed by University College Cork to calculate results. Sensitivity analysis varies key cost driving elements and uncertain inputs including the O&M strategy, distance from shore and the financial assumptions to determine an optimised LCoE estimated range. Results for the XRC are then compared with estimates derived using the same methodology for the HAWT configurations. Analysis indicates that the novel design may facilitate cost reductions, reducing OPEX by removing heavy components that would require costly heavy lift vessels to maintain. It also removes the failure modes around the gearbox, multi-pole generator and yaw system. The XRC could also reduce the capital cost of drivetrains through a power take-off approach that does not require a gearbox or a multi-pole generation but achieves comparable levels of power conversion. Ultimately the XRC could achieve LCoE cost reductions of 10-19%, compared with the traditional HAWTs. Further savings are considered possible but require additional design and analysis that are outside the scope of this paper. | More details Read publication | |
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Report |
Report | 2024 |
The IEA Wind Task 49 Reference Floating Wind Array Design Basis |
This report provides a general design basis for the development of reference floating wind farm designs. These reference array designs will extend the scope of existing reference floating wind turbine designs to facilitate research on array-level floating wind technology challenges and innovations. The design basis promotes coordination and consistency in developing the reference array designs. International Energy Agency Wind Technology Collaboration Programme (IEA Wind) Task 49 on Integrated Design of Floating Wind Arrays is an international collaboration aiming to advance the development of large-scale floating wind farms by providing open-access resources to the research and development and planning communities. The work of Task 49 focuses on array-level challenges related to the colocation of many floating wind turbines; their layouts, mooring systems, and cabling systems; failure risks; logistical considerations; marine spatial planning needs; and future research needs and innovation directions. Task 49 is a 4-year effort that began in December 2021 and that includes representatives from project developers, technology providers, universities, consultancies, regulatory agencies, and research institutions from 12 countries. Its four work packages (WPs) have the following objectives: • WP1: Curate a set of site conditions representative of the global floating wind pipeline • WP2: Develop reference array designs for typical site conditions and technology types • WP3: Catalogue array-level failure risks, consequences, and mitigation strategies • WP4: Identify critical innovation opportunities and marine spatial planning requirements. This design basis report is the first major output from WP2, and it presents the approach for developing reference floating wind array designs. The contents of this design basis were developed from extensive discussions among WP2 participants, including five working groups focused on different areas during the first phase, and a group of three design teams that identified more specific challenges and approaches during the start of the design phase. Floating wind farm design involves many additional factors relative to individual floating wind turbines or fixed-bottom wind farms. Further, reference designs have different requirements than real projects. Therefore, this design basis contains important information and decisions to give definition to the reference floating wind array design effort. | More details Read publication | |
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Journal Article |
Journal Article | 2024 |
Modelling the installation of next generation floating offshore wind farms |
The offshore wind industry is advancing with larger turbines (10 MW+) into sites in deeper waters (>60 m), necessitating innovative floating substructures. However, Floating Offshore Wind (FOW) must still be proven to be cost-efficient, with special attention paid to developing installation, Operations and Maintenance (O&M) and decommissioning strategies that will ensure FOW is competitive. Simulation is an efficient way to assess the viability of new technologies and the innovative operations required to install and maintain them. This paper presents a novel tool that simulates the installation of fixed/floating offshore wind farms across an hourly time-series of Metocean data, producing a total estimation of costs as part of the total capital expenditure (CAPEX). The paper validates the model by simulating installation of Hywind Scotland, the FOW farm, and comparing results with published data. Given the lack of real-world cost data and experience, this paper then seeks to provide a well-defined case-study for future researchers to develop further in other regions and with different technologies. The tool is applied to a theoretical large commercial 1GW FOW farm commissioned in 2035 at a representative site in the Celtic Sea. This considers a promising location for FOW development outside the existing demonstration/early commercial FOW projects, which are primarily focused on the North Sea. Results indicate a CAPEX (including installation) of €3492/kW, which is in line with industry expectations. Sensitivity analysis applies a learning rate to reduce platform costs, and varies farm capacity, demonstrating the potential economies of scale when increasing farm size. Simulation identifies weather operational limits and cable installation duration as key contributors to installation time and costs. This quantifies where cost-savings can be found and optimisation should focus. Further modelling considers the scale of their impact on results. A final Levelised Cost of Energy assessment estimating an LCoE range of €52.3–64.59/MWh, placing the FOW farm in the context of global economic targets. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2024 |
Design of a 6-DOF Aerial Hybrid Cable-Driven Parallel Manipulator |
This paper presents the design of a 6-degreeof-freedom (DOF) hybrid cable-driven parallel manipulator (HCDPM) with a central elastic rod. HCDPM is integrated with a multi-rotor unmanned aerial vehicle (UAV) for the contact inspection of floating offshore wind turbines (FOWTs) by delivering a sensor. Flexible cables allow the end-effector (EE) to actively adapt to the target’s movements during approach. Once the EE attaches to the target, the central rod detaches from the EE and the cables slacken. This setup enables the sensor to directly detect signals from the FOWTs without being influenced by the UAV’s movements and vibrations, thanks to the unidirectional tension transmission in the cables. Finally, the accuracy of the modeling and the significance of introducing the central rod were validated through co-simulation and workspace calculation. The results indicate that the inclusion of the rod significantly improves the model’s precision, design’s stiffness, and the workspace. | More details Read publication | |
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Journal Article |
Journal Article | 2024 |
Wave basin investigation of floating wind turbine model using underwater particle image velocimetry: investigating hydrodynamic wake structures |
This paper conducts a fundamental study on the hydrodynamic performance of a floating offshore wind turbine (FOWT). This includes investigating the impacts of platform motion, turbine operation, and environmental conditions on hydrodynamic wake development behind the FOWT. Using underwater particle image velocimetry in a wave basin, the fluid flow behaviour behind the floating wind substructure model is compared for different test configurations. The FOWT is examined in three configurations: I. Zero degrees of freedom (fixed), II. Six degrees of freedom (floating), and III. Floating with turbine in operation (full system). The results reveal significant hydrodynamic wake turbulence differences between fixed and floating systems, with 95% and 89% increases in turbulent kinetic energy (TKE) and turbulence intensity (TI), respectively. Turbine loading in configuration III results in additional damping and reduces eddy shedding, resulting in a 26% and 31% decrease in TKE and TI, compared to the floating configuration II. It is found that neglecting turbine operation overestimates substructure drag terms by at least 30%, while fixing the model underestimates drag terms by 54%. This study highlights a trade-off between model accuracy and dynamic complexity when estimating viscous effects on FOWT. It also provides a valuable set of high-fidelity validation data for the development of numerical tools for FOWT analysis. | More details Read publication | |
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Journal Article |
Journal Article | 2024 |
Failure Consequence Cost Analysis of Wave Energy Converters—Component Failures, Site Impacts, and Maintenance Interval Scenarios |
In the early stages of developing wave energy converter (WEC) projects, a quantitative assessment of component failure consequence costs is essential. The WEC types, deployment site features, and accessibility should all be carefully considered. This study introduces an operation and maintenance failure consequence cost (O&M-FC) model, distinct from conventional O&M models. The model is illustrated with case studies at three energetic Atlantic sites, each of which considers two types of generic floating WECs: a 300 kW point absorber (PA) with a hydraulic power-take-off (PTO) and a 1000 kW oscillating water column (OWC) with an air-wells-turbine PTO. This study compares 39 failure modes for PA and 27 for OWC in terms of direct repair costs and indirect lost production costs, examining the impact of location accessibility, capacity factors, and the mean annual energy production. The discussion revolves around the sensitive parameters. Recommendations for failure mitigations are presented, and the impact of planned maintenance (PM) during the operational phase is examined for 20 MW PA and OWC WEC projects. For a given WEC type, the method thoroughly evaluates how the location affects performance metrics. It offers a decision-making tool for determining optimal PM intervals to meet targets such as O&M costs, operating profit, or availability. | More details Read publication | |
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Journal Article |
Journal Article | 2024 |
Towing Analysis and Validation of a Fully Assembled Floating Offshore Wind Turbine Based on an Experimental Study |
The offshore wind sector is moving into deep waters and using floating platforms to harness the higher wind speeds in exposed locations. There are various floating platform types currently in development, but semi-submersibles are considered the most prominent early movers. Such floaters need to be towed to and from wind farm locations for installation, special cases of repair and decommissioning. As with any other offshore activity, metocean limits exist for towing operations which can impact the development of a wind farm. It is important to calculate the motion and loads of the platform before commencing the towing operations and to check whether they exceed the defined limits to enable safe execution. In this paper, two approaches using two different numerical tools to predict the motion of a fully assembled floating wind platform under tow are presented and compared. A potential flow-based method derived from a low forward speed approach and a hybrid approach combining potential flow and Morison equation methods are investigated, and the numerical predictions are compared and validated against experimental results. Both methods demonstrate accurate predictions, depending on the wave condition and towing speed, albeit differing in execution time and the simplicity of the simulation setup. The first method was found to provide good predictions of the motion in low-speed (0.514–1.543 m/s) towing conditions. The second method provides better results for all the towing speeds and wave heights. As the wave height and towing speed increase, deviations from experiments were observed, signifying non-linear phenomena that are difficult to analyse using the mentioned potential-flow-based methods. | More details Read publication | |
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Journal Article |
Journal Article | 2023 |
Development and Application of a GIS for Identifying Areas for Ocean Energy Deployment in Irish and Western UK Waters |
Ireland and the UK possess vast ocean energy resources within their respective maritime areas. However, not all offshore areas are suitable for deployment of ocean energy devices. This article describes the development of a multitude of geospatial data relating to ocean energy site suitability, as well as a Web-GIS tool for hosting and performing analysis on this data. A validation of wave, water depth and seabed character data used in the study revealed good correlation between modelled and in situ data. The data is mapped, and the spatial patterns are discussed with relevance to ORE sector implications. A site selection model, which included much of this data, was developed for this study and the Web-GIS tool. A survey conducted with ocean energy technology developers revealed their desired site criteria. The responses were applied in a case study using the site selection model to uncover potential and optimum areas for deployment of both wave and tidal energy devices. The results reveal extensive areas of the Atlantic Ocean and Celtic Sea appropriate for wave energy deployment and less extensive areas for tidal energy deployment, in the Irish Sea and Inner Seas off the West Coast of Scotland. | More details Read publication | |
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Journal Article |
Journal Article | 2023 |
The Integration of Tools for the Techno-Economic Evaluation of Fixed and Floating Tidal Energy Deployment in the Irish Sea |
Marine renewable energy (MRE) development will be crucial to achieve worldwide energy decarbonization. In Europe, 1 GW and 40 GW of ocean energy are set to be developed by 2030 and 2050, respectively. Support is essential if wave and tidal stream arrays are to become more economically viable than they currently are. Four recently developed open-access software tools are used in this study to investigate the critical and expensive elements of potential demonstration and commercial scale tidal projects. The tools have been designed and built to assist users with array configurations, foundation and mooring (F&M) design, operation and maintenance (O&M) strategies, and techno-economic analysis. Demonstration of their use is performed in this study to model scenarios for 2 MW, 10 MW, 40 MW, and 100 MW tidal energy projects employing typical 500 kW fixed and 2 MW floating turbines at the West Anglesey Tidal Demonstration Zone in the Irish Sea. The following metrics are examined: the power output and wake losses of staggered and line configurations; the design and costs of simple gravity-based foundations, gravity-based anchors and the four-chain catenary mooring system of a single turbine; the mean O&M costs and farm availability over the project life; and the breakdown of levelized cost of energy (LCoE) for all eight scenarios to ultimately reveal minimum values of 173 EUR/MWh and 147 EUR/MWh for fixed and floating tidal energy technologies, respectively. The thorough analysis facilitated within these four tools to forecast realistic situations in a specific location can help users design a tidal energy project for an area with considerable potential for commercial scale projects, and thus assist the ocean energy community in promoting and nurturing the sector in the years and decades ahead. | More details Read publication | |
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Journal Article |
Journal Article | 2023 |
Cost-benefit assessment framework for robotics-driven inspection of floating offshore wind farms |
Operations and maintenance (O&M) of floating offshore wind farms (FOWFs) poses various challenges in terms of greater distances from the shore, harsher weather conditions, and restricted mobility options. Robotic systems have the potential to automate some parts of the O&M leading to continuous feature-rich data acquisition, operational efficiency, along with health and safety improvements. There remains a gap in assessing the techno-economic feasibility of robotics in the FOWF sector. This paper investigates the costs and benefits of incorporating robotics into the O&M of a FOWF. A bottom-up cost model is used to estimate the costs for a proposed multi-robot platform (MRP). The MRP houses unmanned aerial vehicle (UAV) and remotely operated vehicle (ROV) to conduct the inspection of specific FOWF components. Emphasis is laid on the most conducive O&M activities for robotization and the associated technical and cost aspects. The simulation is conducted in Windfarm Operations and Maintenance cost-Benefit Analysis Tool (WOMBAT), where the metrics of incurred operational expenditure (OPEX) and the inspection time are calculated and compared with those of a baseline case consisting of crew transfer vessels, rope-access technicians, and divers. Results show that the MRP can reduce the inspection time incurred, but this reduction has dependency on the efficacy of the robotic system and the associated parameterization e.g., cost elements and the inspection rates. Conversely, the increased MRP day rate results in a higher annualized OPEX. Residual risk is calculated to assess the net benefit of incorporating the MRP. Furthermore, sensitivity analysis is conducted to find the key parameters influencing the OPEX and the inspection time variation. A key output of this work is a robust and realistic framework which can be used for the cost-benefit assessment of future MRP systems for specific FOWF activities. | More details Read publication | |
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Journal Article |
Journal Article | 2023 |
Hydrodynamic Processes Controlling Sand Bank Mobility and Long-Term Base Stability: A Case Study of Arklow Bank |
Offshore sand banks are an important resource for coastal protection, marine aggregates, and benthic habitats and are the site of many offshore wind farms. Consequently, a comprehensive understanding of the baseline processes controlling sand bank morphodynamics is imperative. This knowledge will aid the development of a long-term robust marine spatial plan and help address the environmental instability arising from anthropogenic activities. This study uses a validated, dynamically coupled, two-dimensional hydrodynamic and sediment transport model to investigate the hydrodynamic processes controlling the highly mobile upper layer of Arklow Bank, while maintaining overall long-term bank base stability. The results reveal a flood and ebb tidal current dominance on the west and east side of the bank, respectively, ultimately generating a large anticlockwise residual current eddy encompassing the entire bank. This residual current flow distributes sediment along the full length of the sand bank. The positioning of multiple off-bank anticlockwise residual current eddies on the edge of this cell is shown to influence east–west fluctuations of the upper slopes of the sand bank and act as a control on long-term stability. These off-bank eddies facilitate this type of movement when the outer flows of adjacent eddies, located on both sides of the bank, flow in a general uniform direction. Whereas they inhibit this east–west movement when the outer flows of adjacent eddies, on either side of the bank, flow in converging directions towards the bank itself. These residual eddies also facilitate sediment transport in and out of the local sediment transport system. Within Arklow Bank’s morphological cell, eight morphodynamically and hydrodynamically unique bank sections or ‘sub-cells’ are identified, whereby a complex morphodynamic–hydrodynamic feedback loop is present. The local east–west fluctuation of the upper slopes of the bank is driven by migratory on-bank stationary and transient clockwise residual eddies and the development of ‘narrow’ residual current cross-flow zones. Together, these processes drive upper slope mobility but maintain long-term bank base stability. This novel understanding of sand bank morphodynamics is applicable to bedforms in tidally dominated continental shelf seas outside the Irish Sea. | More details Read publication | |
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Journal Article |
Journal Article | 2023 |
Morphological Modelling to Investigate the Role of External Sediment Sources and Wind and Wave-Induced Flow on Sand Bank Sustainability: An Arklow Bank Case Study |
Offshore anthropogenic activities such as the installation of Offshore Renewable Energy (ORE) developments and sediment extraction for marine aggregates have been shown to disrupt current flow, wave propagation, and sediment transport pathways, leading to potential environmental instability. Due to the complexity of the interconnected sediment transport pathways in the south-western Irish Sea combined with an increase in planned anthropogenic activities, the assessment of this risk is imperative for the development of a robust marine spatial plan. Subsequently, this study uses two-dimensional morphological modelling to build upon previous studies to assess the dependency of Arklow Bank’s local sediment transport regime on external sediment sources. Additionally, scenario modelling is used to identify vulnerable areas of this offshore linear sand bank to wind and wave-forcing and to examine the nature of this impact. A sediment budget is estimated for Arklow Bank, whereby seven source and nine sink pathways are identified. New evidence to support the exchange of sediment between offshore sand banks and offshore independent sand wave fields is also provided. The areas of the bank most vulnerable to changes in external sediment sources and the addition of wind- and wave-induced flow are analogous. These high vulnerability zones (HVZs) align with regions of residual cross-flow under pure current conditions. The restriction of sediment sources off the southern extent of Arklow Bank impacts erosion and accretion patterns in the mid- and northern sections of the bank after just one lunar month of simulation. Where tidal current is the primary driver of sand bank morphodynamics, wind- and wave-induced flow is shown to temporarily alter sediment distribution patterns. Wind and wave-induced flow can both accelerate and decelerate the east-west fluctuation of the upper slopes of the bank, yet the nature of this impact is inconsistent due to the misalignment of the directionality of these two forces. The methods and new knowledge derived from this study are directly applicable to tidally-dominated environments outside the Irish Sea. | More details Read publication | |
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Journal Article |
Journal Article | 2023 |
Scenario Analysis of Cost-Effectiveness of Maintenance Strategies for Fixed Tidal Stream Turbines in the Atlantic Ocean |
This paper has developed an operation and maintenance (O&M) model for projected 20 MW tidal stream farm case studies at two sites in the northeast Atlantic in France and at EMEC’s Fall of Warness site in the UK. The annual energy production, number of incidents, and downtimes of the farms for corrective and planned (preventive) maintenance strategies are estimated using Monte Carlo simulations that vary weather windows, repair vessel availabilities, and mean annual failure rates modelled by Weibull distributions. The trade-offs between the mean annual failure rates, time availability, O&M costs, and energy income minus the variable O&M costs were analysed. For all scenarios, a 5-year planned maintenance strategy could considerably decrease the mean annual failure rates by 37% at both sites and increase the net energy income. Based on a detailed sensitivity analysis, the study has suggested a simple decision-making method that examines how the variation in the mean annual failure rate and changes in spare-part costs would reduce the effectiveness of a preventive maintenance strategy. This work provides insights into the most important parameters that affect the O&M cost of tidal stream turbines and their effect on tidal energy management. The output of the study will contribute to decision-making concerning maintenance strategies. | More details Read publication | |
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Journal Article |
Journal Article | 2023 |
A review of geographic information system (GIS) and techno economic (TE) software tools for renewable energy and methodology to develop a coupled GIS-TE software tool for marine renewable energy (MRE) |
Accurate and up-to-date Geographic Information System (GIS) and Techno Economic (TE) tools are pertinent to helping to develop the renewable energy sector. This paper reviews the state of the art in existing GIS and TE tools for renewable energy and proposes a methodology to develop a coupled GIS-TE software tool that is geared specifically to Marine Renewable Energy (MRE) applications and bespoke to Irish and Western UK waters. Methods for approaching GIS and TE analysis within existing tools for renewable energy are presented and compared. Many existing tools of this nature have some interesting functionalities, but most are unsuitable for MRE; are limited by a lack of information on both the technology and the site; and focus solely either on GIS or TE aspects of analysis. Additionally, almost all of those with a TE focus are not open access. The proposed tool aims to incorporate increased resolution and site relevance of resource data; the most up-to-date geospatial data for site selection; and will provide site specific TE indicators and recommendations for contemporary MRE devices. The result will be the development of an open-access GIS-TE software tool for MRE. | More details Read publication | |
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Journal Article |
Journal Article | 2023 |
Geospatial dimensions of the renewable energy transition — The importance of prioritisation |
The renewable energy transition is a priority for many researchers, policy makers, and political leaders because it is projected to stop the dependence of economic growth on increasing fossil fuel use and thus curtail climate change. This study examines how expert judgments affect development decisions to enable the renewable energy transition. Geospatial Multi-Criteria Decision Analyses (MCDA) are frequently used to select offshore wind energy (OWE) sites, however, they are often weak and/or often rely on limited judgement. The Analytical Hierarchy Process is used here with 25 diverse experts to assess the variability in priorities for OWE siting criteria. A geospatial MCDA is implemented using experts' individual priorities, aggregated weights and Monte Carlo simulations. Case study results reveal large variations in expert opinions and bias strongly affecting MCDAs weighted by single decision-makers. A group-decision approach is proposed to strengthen consent for OWE, underpinning the renewable energy transition. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2023 |
Weight Reduction Methodologies for Wave Energy Devices: A Structural Analysis Approach |
The floating Backward Bent Duct (BDD) Buoy oscillating water column model generates electricity through the fluctuation in wave height. Wave energy conversion devices are often faced with a particularly high levelized cost of energy (LCOE) whencompared to other renewable energy devices, and various investigations into bridging this gap have been carried out in recent history. Previous studies on the BBDBuoy have suggested that a significant reduction in required construction material is possible as a result of reduced differential pressures acting across the hull walls in operational conditions. Various structural analysis campaigns have been conducted on sections of the hull to assess this theory. A Finite Element Analysis (FEA) was performedon a full-scale model of the BBDBuoy under extremedesign wave loadings in based on wave dataat EMEC’s Billia Croo test facility in Orkney, Scotland using Robot Structural Analysis software. A maximum pressure of 145kPa was calculated for an 18.7 m peak wave height at Billia Croo. The BBDBuoy was modelled for both static and dynamic load conditions under various constraint layouts. A modal analysis was conducted on the model which estimates the natural frequency of the BBDBuoy to be approximately 6.67Hz. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2023 |
Life Cycle Assessment of a wave energy device – LiftWEC |
Evaluatingthe overall advantages of a new configuration of wave energy technologies goes beyond techno-economic performance and reliability. As the marine renewable energy sector expands, it is important toensure that the technologies prove to be environmentally friendly alternatives. A cradle-to-grave life cycle assessment was conducted on a novel energy converter (LiftWEC) to evaluate its potential cumulative impacts. The global warming potential was characterized, indicating that the configuration could be a potential low-carbon alternative compared with many wave energy devices and conventional forms of energy production. The carbon and energy payback time were also analysed to estimate the time requiredto offset the carbon emission and demanded energy. This assessment highlighted the impact of the characteristic energy mixprofileand energy production potential of the deployment regionon the results obtained. The study also analysed alternative scenarios of materials, deployment locations, and end-of-life strategies to identify potential improvement opportunities to reduce the environmental impacts. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2023 |
Compilation of Development Metrics Applicable to Wave Energy Converters (WECs): Current Status and Proposed Next Steps |
The compilation summarised in this paper and its discussion aim to provide a practical reference source concerning metrics for WEC development, which is currently unavailable in the published literature in terms of broadness and condensed presentation. Such compilation includes multiple formulations from the wave energy sector and other relatable industries (e.g. wind energy) that are typically diluted among specialist literature, standards, guidelines and recommendations, scientific papers, and project reports. The paper is concluded with a reflection of any salient gaps that are not addressed by current metrics, in a context of accelerating the development of WEC technologies. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2023 |
Wild Atlantic Wind Farms, Are They Cost-Effective? |
Ireland has ambitious targets to deliver 7GW of offshore wind capacity by 2030. Although to date, only the 25MW Arklow Bank wind project is installed; there are significant offshore wind resources that could potentially power the entirety of Ireland’s electricity needs and export to mainland Europe. Initially development will focus on delivering fixed OW farms on the East Coast in the Irish Sea. However, the substantial resources in the Celtic Sea (South Coast) and Atlantic Ocean (West Coast) could be exploited by FLOW.Wind farms moving into deeper waters are often further from shore, in harsher conditions. Sites in the Atlantic Ocean will have particularly dynamic metocean conditions. A year-round accessibility of only 26% has been calculated at a representative location off the West Coast c.71km from shore, assuming a 6hour window where the Significant Wave Height (Hs) is <= 2m. [1] Standard accessibility challenges will be exacerbated with the new problems of deploying a nascent FLOW technology with no convergence on logistical best practices/standards. Therefore, developers must consider whether the substantial potential resource of Atlantic Ocean sites can outweight the difficulties they will encounter when deploying and operating FLOW farms. The purpose of this paper is to determine with Atlantic FLOW can be cost-effective.The paper models the installation and Operation and Maintenance (O&M) of a theoretical 1GW FLOW farm off the West Coast of Ireland. It applies a suite of logistics and financial models designed to simulate activities across an hourly timeseries of metocean data. Outputs include estimates of costs, broken down for each life-cycle stage, and energy production. These will be used to calculate a final Levelised Cost of Energy (LCoE) estimate for the case-study, which will be validated against FLOW farm cost estimates in the literature. A series of sensitivity studies test the case-study assumptions and the impact of potential improvements to operational weather restrictions, reliability and reductions in CAPEX. Analysis identifies the key bottlenecks to achieving high production and low costs. Finally, the paper presents a worst, medium and best-case LCoE estimate to determine whether and/or under what conditions (e.g. reliability, accessibility, O&M strategy) the potential of the wild Atlantic winds can be harnessed.The paper concludes that the best-case LCoE at the Atlantic Ocean is an average of €81.58/MWh for a deployment of 2030-2035. Taking industry targets of €53-76/MWh as a baseline for achieving cost-effectiveness, the paper finds that this site is not competitive with the current assumptions and the nascent state of the Irish Offshore Wind industry. However, there are a number of potential areas for improvement that could provide further LCoE reductions and enable exploitation of the Atlantic Ocean wind resources. These include, increasing site accessibility and improving availability from 91%-95% and applying further CAPEX and OPEX cost reductions in line with cost-reduction pathway methodologies in the current literature. Further work is needed to determine how these could be achieved at this site. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2023 |
Adapting Optimal Preventive Maintenance Strategies for Floating Offshore Wind in Atlantic Areas by Integrating O&M Modelling and FMECA |
Ireland is among the countries best suited for the floating offshore wind (FLOW) boom. The Irish government's goal is to produce 80% of its power from renewable sources achieving 7 GW of offshore wind capacity by 2030. This will be aided by the significant effort that has already been made in developing FLOW projects in Atlantic and Celtic Sea areas. However, there are issues that must be resolved before floating turbines can be widely deployed particularly in areas like the Atlantic. One of these challenges is the harsh environment, which limits the accessibility of the vessels needed for Operation and Maintenance (O&M), especially in the winter. This paper has conducted an O&M cost criticality assessment of a 1 GW scale floating offshore wind (FLOW) project in two case studies off the West and South coasts of Ireland. The consequences of failures, and therefore the criticality of each component, are calculated in an integrated O&M-Failure Mode, Effects and Criticality (FMECA) model. In the model the mean time between failure, the type of vessel and their costs, technician and spare part costs, weather window and farm availability are determining factors of the criticality scores of components in each location. The ability to analyze the impact of different Planned Maintenance (PM) strategies on the failure rate of components is a particular functionality offered in this O&M model. A PM strategy that directly affects O&M expenses can help the project by improving farm availability, maintaining a low rate of unexpected failure and lowering O&M costs as a way to balance costs and availability. Several PM intervals are looked at for the two Projected FLOW locations.The importance of minor failure mode of components like the ‘Electric component, ‘Generator leak’, ‘Pitch hydraulic minor’, ‘Floating structure’, and ‘Tower’ is emphasized in both places, but especially on the West coast. For the FLOW system at both locations, the component criticality ratings are ranked relative to one another. The total lifecycle O&M cost, including the cost of energy losses, of a 15MW FLOW turbine over 25-year lifetime is found €55.8 m in the West and €29.4 m in the South. At subsystem level, ‘Structural subsystem’ typically accounts for 31% of the cost-criticality, followed by auxiliary subsystem with 29%, pitch hydraulic with 18%, generator with 13%, and gearbox with 9%. Implementing a semi-annual PM for turbines, a PM every two years for substructure, and a thorough PM every 10 years may, in the best scenario, boost the availability of the FLOW farm in the West from 80.0% to 95% in the best case. This resulted from a drop in remedial interventions from 5.5 to 1.2 per turbine per year in the West and from 6.8 to 2.8 in the South. Due to the lack of experience with operating FLOW turbines in the sea, the input data for modeling the O&M strategies of a large-scale FLOW farm are somewhat uncertain. These uncertainties can be reduced when more exact facts become available. The study did show that scenario studies can, at this point of development, disclose some potential PM solutions that, if correctly implemented, might result in a large reduction in O&M expenses because of the reduction in unexpected incidents and the rise in farm availability. This area of research may benefit from increased component life expectancy after PM in the model, which lowers unexpected model intervention. The model illustrates a method to balance the costs and benefits of a PM strategy. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2023 |
Data-driven assessment of the Survivability and Maintainability of Offshore Renewable Energy devices in Ireland’s harsh maritime climate |
Unobstructed across the vast expanse of the North Atlantic Ocean, the Irish maritime area encompasses some of the world’s most energy-intensive waves. However, high winds and associated large waves present a substantial engineering challenge to ensure the survivability of offshore renewable energy devices during extreme weather events. Finding adequate weather windows for installation, operation, and maintenance activities is another obstacle when deploying these devices. This paper presents the results of a large-scale analysis of wave and wind data around the coasts of Ireland and Wales. Extreme Value Analysis calculates the expected wave heights and wind speeds for extreme events (1-year, 10-year, 50-year and 100-year return periods). Weather windows are also calculated based on a matrix of wave heights, wind speeds and minimum durations required. A custom-developed GIS (Geographic Information System) tool visualises the results. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2023 |
A study of the towing characteristics of a semi-submersible floating offshore wind platform |
A robust pipeline of floating wind energy has emerged with a general trend of projects becoming larger, further from shore, and placed in increasingly energetic seas. The installation process for these farms involves the pre-assembly of components onshore or in sheltered waters before towing the platform to the operational location using tugs. It can be expected that such marine operations will be repeated in reverse at the time of decommissioning. The cost and safety of these operations will be influenced by the tugs used, towing speed, the local metocean conditions, the platform/turbine characteristics and other factors. This paper investigates the hydrodynamic characteristics of a large semi-submersible floating offshore wind turbine (FOWT) under tow. The motions of the FOWT are analysed using a numerical tool and validated using a towing test. A framework is proposed for the assessment of FOWT towing operations. Various limiting factors have been identified and the hydrodynamic performance of the system has been evaluated using the framework. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2023 |
Variability of Kinetic Response Estimates of Froude Scaled DeepCwind Semisubmersible Platforms Subjected to Wave Loading |
Froude scaling for Floating Offshore Wind Turbine (FOWT) platforms is typical for understanding and interpreting their behavior and subsequent designs for testing in wave basins. Despite its popularity, the variability and uncertainty of the kinetic responses of such floating structures as a function of scaling require more attention. This work addresses the question of consistency of Froude scaling by comparing the hydrodynamic responses of a range of DeepCwind semisubmersible FOWT scaled models (full model, 1/2, 1/4, 1/9, 1/16, 1/25, 1/36, 1/49, and 1/50). The comparison was made both in the mooring-line tension and bending moment of structural members, which are directly related to their safety limit states. Hydrodynamic forces due to diffraction, radiation, and viscosity along with hydrostatic forces and mooring boundaries are modeled by ansys-Aqwa, which were subsequently converted to bending moment estimates. The variability of kinetic responses like mooring-line tensions and bending moment estimates was investigated for each scaled model, along with the identification of regions of inconsistencies. In the context of offshore renewable energy development through technological readiness levels, the study is especially pertinent for understanding how force variabilities and uncertainties are related to these kinetic responses of semisubmersible platforms. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2022 |
An experimental investigation into the most prominent sources of uncertainty in wave tank testing of floating offshore wind turbines |
There is an urgent need to replace carbon-based energy sources with renewable energy sources, and floating offshore wind is seen as a critical component in the drive towards energy diversification. Floating offshore wind facilitates accessing a far vaster wind resource that exists in deeper waters, further offshore. Floating offshore wind platforms must undergo wave tank testing in the early stages of development to assess model responses to different wave and wind conditions. Wave tank testing, while highly beneficial, is liable to have errors arising throughout the testing campaign. Errors can arise during wave tank setup, testing, and analysis of results. One such error is the error in the inertia and centre of gravity (CoG) of the platform. In this research, testing was completed using two very different floating offshore wind concepts. A sensitivity analysis was completed by varying the model inertia and centre of gravity. It was found that the effects of each variation were magnified at resonance, and the magnitude of platform response was affected to a greater extent than the period of resonance response. Of all the variations to the model properties conducted, the inertia about the y-axis and location of the centre of gravity along the x-axis affected pitch response to the greatest extent. | More details Read publication | |
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Journal Article |
Journal Article | 2022 |
Subsea superconductors: The future of offshore renewable energy transmission? |
The European Union has set the ambitious target of becoming climate-neutral by 2050 and reducing greenhouse gas emissions by at least 55% before 2030, compared to 1990. Greater energy generation can be achieved by increased reliance on renewable energy, but the transmission of this energy to match supply with demand is a likely bottleneck in maximising renewable energy use. In this paper, we examine medium-voltage DC superconductors as a potential solution for low-loss, high-power transmission of offshore renewables. We look at what has been achieved to date in onshore superconducting cable deployment and what needs to be done for such superconductors to be deployed subsea, with the goals of exporting electricity from offshore wind farms and acting as grid interconnectors. The offshore oil and gas industry represents state of the art in terms of subsea pipe design. This paper explores how the experience of the offshore oil and gas industry can be applied to subsea superconductor cable design and identifies aspects of superconductor design likely to present a challenge to subsea deployment. The key areas identified as requiring research are the development of flexible pipes suitable for cryogenic usage that can withstand the dynamic loading encountered in the marine environment; robust and low-maintenance insulation systems suitable for subsea deployment; and cooling systems to enable pipelines greater than 100 km in length. Although the primary focus of this research is on superconductor cables, the information is also applicable to other subsea conduits requiring cryogenic cooling such as ‘green’ hydrogen. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2022 |
Looking for a simplified approach for the propagation of systematic uncertainty in the motion response of a floater |
This new research considers the 3 main motions of the moored floater (surge, heave and pitch) in head waves and it explores ways to estimate the systematic uncertainties on the RAOs, and 2 other metrics for these signals. Based on linear hydrostatics and the linear potential flow theory, simple relations can be found that bind the main characteristics of a floater. These relations are transformed using linear algebra to express how uncertainty bias on the main characteristics of the tested system can be propagated to the motion responses of the floater. Thanks to this approach, variations of the mooring stiffness, position of the centre of mass, radia of gyration can be represented through simple formulations that allow to very effectively assess their impact of the motion RAOs and other metrics. This approach is verified by comparing simulation and test results of the semisubmersible of the MARINET2 floating wind round robin campaign to approximations deduced from these theoretical relations. | More details Read publication | |
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Journal Article |
Journal Article | 2022 |
An investigation of the applicability of SPIV for the analysis of the dynamics of floating offshore wind platforms |
There is a need for new numerical tools to capture the physics of floating wind platforms more accurately to refine engineering designs and reduce costs. The conventional measurements apparatus in tank tests, including wave probs, velocity and current profiler, as well as doppler sensors, are unable to give a full 3D picture of velocity, pressure, and turbulence. In tank testing, the use of the underwater stereoscopic PIV method to fully characterise the 3D flow field around floating platforms can provide a rich source of validation data and overcome some of the limitations associated with more classical measurement techniques. This optical technique can be used to accurately measure the random and chaotic structure of turbulent flows around the floater. Moreover, the main characteristics of turbulence of the flow around the floater, such as rotationality, diffusivity, irregularity, as well as dissipation, can be extracted and studied. The underwater S-PIV method has been widely used for marine and offshore applications, including studies on ship and propeller wakes and tidal stream turbines; however, to date, this technology has not seen widespread use for the hydrodynamic study of floating offshore wind turbines. Therefore, in the current study, the key considerations for using S-PIV for this purpose are discussed; meanwhile, the related studies in the field of quantitative flow measurements are reviewed. | More details Read publication | |
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Journal Article |
Journal Article | 2022 |
Analysis of Floating Offshore Wind Platform Hydrodynamics Using Underwater SPIV: A Review |
There is a need for new numerical tools to capture the physics of floating offshore wind turbines (FOWTs) more accurately to refine engineering designs and reduce costs. The conventional measurement apparatuses in tank tests, including wave probes, velocity and current profilers, and Doppler sensors, are unable to provide a full 3D picture of velocity, pressure, turbulence, and vorticity profile. In tank tests, use of the underwater stereoscopic particle image velocimetry (SPIV) method to fully characterise the 3D flow field around floating wind platforms can overcome some of the limitations associated with classical measurement techniques and provide a rich source of validation data to advance high-fidelity numerical tools. The underwater SPIV method has been widely used for marine and offshore applications, including ship and propeller wakes, wave dynamics, and tidal stream turbines; however, to date, this technology has not seen widespread use for the hydrodynamic study of FOWTs. This paper provides a critical review of the suitability of underwater SPIV for analysing the hydrodynamics of FOWTs, reviews the challenges of using the method for FOWT tank test applications, and discusses the contributions the method can make to mitigating current research gaps in FOWT tank tests. | More details Read publication | |
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Journal Article |
Journal Article | 2022 |
Applications of robotics in floating offshore wind farm operations and maintenance: Literature review and trends |
Marine operations required to transfer technicians and equipment represent a significant proportion of the total cost of offshore wind. The profile of sites being considered for floating offshore wind farms (FOWFs), e.g., further from the shore and in harsher environments, indicates that these costs need to be assessed by taking into account the maintenance requirements and restricted weather windows. There is an immediate need to investigate the potential use of robotic systems in the wind farm's operations and maintenance (O&M) activities, to reduce the need for costly manned visits. The use of robotic systems can be critical, not only to replace repetitive activities and bring down the levelised cost of energy but also to reduce the health and safety risks by supporting human operators in performing the desired inspections. This paper provides a review of the state of the art in the applications of robotics for O&M of FOWFs. Emerging technology trends and associated challenges and opportunities are highlighted, followed by an outline of the agenda for future research in this domain. | More details Read publication | |
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Journal Article |
Journal Article | 2022 |
Development and Dynamics of Sediment Waves in a Complex Morphological and Tidal Dominant System: Southern Irish Sea |
With the recent push for a transition towards a climate-resilient economy, the demand on marine resources is accelerating. For many economic exploits, a comprehensive understanding of environmental parameters underpinning seabed morphodynamics in tidally-dominated shelf seas, and the relationship between local and regional scale sediment transport regimes as an entire system, is imperative. In this paper, high-resolution, time-lapse bathymetry datasets, hydrodynamic numerical modelling outputs and various theoretical parameters are used to describe the morphological characteristics of sediment waves and their spatio-temporal evolution in a hydrodynamically and morphodynamically complex region of the Irish Sea. Analysis reveals sediment waves in a range of sizes (height = 0.1 to 25.7 m, and wavelength = 17 to 983 m), occurring in water depths of 8.2 to 83 mLAT, and migrating at a rate of 1.1 to 79 m/yr. Combined with numerical modelling outputs, a strong divergence of sediment transport pathways from the previously understood predominantly southward flow in the south Irish Sea is revealed, both at offshore sand banks and independent sediment wave assemblages. This evidence supports the presence of a semi-closed circulatory hydrodynamic and sediment transport system at Arklow Bank (an open-shelf linear sand bank). Contrastingly, the Lucifer–Blackwater Bank complex and associated sediment waves are heavily influenced by the interaction between a dominant southward flow and a residual headland eddy, which also exerts a strong influence on the adjacent banner bank. Furthermore, a new sediment transfer system is defined for offshore independent sediment wave assemblages, whereby each sediment wave field is supported by circulatory residual current cells originating from offshore sand banks. These new data and results improve knowledge of seabed morphodynamics in tidally-dominated shelf seas, which has direct implications for offshore renewable developments and long-term marine spatial planning. | More details Read publication | |
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Journal Article |
Journal Article | 2022 |
Far-Wake Meandering of a Wind Turbine Model with Imposed Motions: An Experimental S-PIV Analysis |
Intra-array wake meandering increases fatigue loading in downstream turbines and decreases farm total power output. In the case of floating offshore wind turbines (FOWTs), the motions of the floating substructure could have a non-neglectable contribution to wake meandering dynamics. This research experientially analyses the influence of imposed motions on the far-wake meandering of a FOWT. The study considers a 1:500 scaled porous disc representation of the 2 MW FLOATGEN system (BW Ideol) located off the coast of Le Croisic, France. A representative marine neutral atmospheric boundary layer is generated in a wind tunnel whilst monochromic and multi-frequency content three degrees of freedom (surge, heave, pitch) motion is imposed on the model tower. The stereoscopic particle image velocimetry (S-PIV) is then utilised to measure velocity vectors at a cross-section located at 8.125 D downstream of the model. No significant effect on the far-wake recovery in the velocity, turbulence and turbulent kinetic energy distribution is observed. However, the frequency characteristics of the imposed motions were observed in the far-wake meandering spectral content and streamwise characteristics of far-wake, such as normalised available power. While the frequency spectrum of the vertical oscillations showed more sensitivity to the three degrees of freedom (3DoF) imposed motion in all frequency ranges, the lateral oscillation was sensitive for the reduced frequency above 0.15. The monochromic motions with a reduced frequency of less than 0.15 also did not influence the far-wake centre distribution in both lateral and vertical directions. Regardless of reduced frequency, imposed motions show a strong effect on average power, in which the harmonic signature can distinguish in far-wake memory. This study provides an investigation, which its result could be beneficial to developing and examining wake models for offshore wind turbines, with a particular focus on the influence of FOWTs motions. | More details Read publication | |
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Conference Paper / Proceedings |
Conference Paper / Proceedings | 2022 |
Combined current and wind simulation for floating offshore wind turbines |
This paper describes the validation of a novel method to simulate current loading on a floating offshore wind turbine model. A dynamic winch actuator is used to emulate the drag force of current on the platform of the model with a Software in the Loop application. Current loads are combined with wave- and wind loads. The results of experiments with physical current are validated against the results of experiments with simulated current. A method to simulate wave-current interactions is also described. The results show that the winch actuator can reliably emulate current induced drag forces in comparison with physical current under various combinations of environmental loads. Experimental repeatability of the response of the platform is shown to be superior when using simulated- rather than physical current. | More details Read publication | |
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Journal Article |
Journal Article | 2022 |
Offshore wind speed short-term forecasting based on a hybrid method: Swarm decomposition and meta-extreme learning machine |
As the share of global offshore wind energy in the electricity generation portfolio is rapidly increasing, the grid integration of large-scale offshore wind farms is becoming of interest. Due to the intermittency of wind, the stability of power systems is challenging. Therefore, accurate and fast offshore short-term wind speed forecasting tools play important role in maintaining reliability and safe operation of the power system. This paper proposes a novel hybrid offshore wind forecasting model based on swarm decomposition (SWD) and meta-extreme learning machine (Meta-ELM). This approach combines the advantages of SWD which has proven efficiency for non-stationary signals, with Meta-ELM which provides faster calculation with a lower computational burden. In order to enhance accuracy and stability, the signal is decomposed by implementing a swarm-prey hunting algorithm in SWD. To validate the model, a comparison against four conventional and state-of-the-art hybrid models is performed. The implemented models are tested on two real wind datasets. The results demonstrate that the proposed model outperforms the counterparts for all performance metrics considered. The proposed hybrid approach can also improve the performance of the Meta-ELM model as a well-known and robust method. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
Uncertainty in Wave Basin Testing of a Fixed Oscillating Water Column Wave Energy Converter |
This research presents a methodology for carrying out uncertainty analysis on measurements made during wave basin testing of an oscillating water column wave energy converter. Values are determined for type A and type B uncertainty for each parameter of interest, and uncertainty is propagated using the Monte Carlo method to obtain an overall expanded uncertainty with a 95% confidence level associated with the capture width ratio of the device. An investigation into the impact of reflections on the experimental results reveals the importance of identifying the incident and combined wave field at each measurement location used to determine device performance, in order to avoid misleading results. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
Floating offshore wind turbines: Installation, operation, maintenance and decommissioning challenges and opportunities |
The global floating offshore wind energy industry is rapidly maturing with several technologies having been installed at pilot and demonstration scales. As the industry progresses to full array-scale deployments, the optimization of marine activities related to installation, operation \\& maintenance and decommissioning presents a significant opportunity for cost reduction. This paper reviews the various marine operations challenges towards the commercialisation of floating wind in the context of spar-type, semi-submersible and Tension Leg Platform (TLP) technologies. Knowledge gaps and research trends are identified along with a review of innovations at various stages of development which are intended to widen weather windows, reduce installation costs and improve the health and safety of floating wind related marine operations. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
Round Robin Laboratory Testing of a Scaled 10 MW Floating Horizontal Axis Wind Turbine |
This paper documents the round robin testing campaign carried out on a floating wind turbine as part of the EU H2020 MaRINET2 project. A 1/60th scale model of a 10 MW floating platform was tested in wave basins in four different locations around Europe. The tests carried out in each facility included decay tests, tests in regular and irregular waves with and without wind thrust, and tests to characterise the mooring system as well as the model itself. For the tests in wind, only the thrust of the turbine was considered and it was fixed to pre-selected levels. Hence, this work focuses on the hydrodynamic responses of a semi-submersible floating foundation. It was found that the global surge stiffness was comparable across facilities, except in one case where different azimuth angles were used for the mooring lines. Heave and pitch had the same stiffness coefficient and periods for all basins. Response Amplitude Operators (RAOs) were used to compare the responses in waves from all facilities. The shape of the motion RAOs were globally similar for all basins except around some particular frequencies. As the results were non-linear around the resonance and cancellation frequencies, the differences between facilities were magnified at these frequencies. Surge motions were significantly impacted by reflections leading to large differences in these RAOs between all basins. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
Standardising Marine Renewable Energy Testing: Gap Analysis and Recommendations for Development of Standards |
Marine renewable energy (MRE) is still an emerging technology. As such, there is still a lack of mature standards and guidance for the development and testing of these devices. The sector covers a wide range of disciplines, so there is a need for more comprehensive guidance to cover these. This paper builds on a study undertaken in the MaRINET2 project to summarise recommendations and guidance for testing MRE devices and components, by reviewing the recently published guidance. Perceived gaps in the guidance are then discussed, expanding on the previous study. Results from an industry survey are also used to help quantify and validate these gaps. The main themes identified can be summarised as: the development progression from concept to commercialisation, including more complex environmental conditions in testing, accurately modelling and quantifying the power generated, including grid integration, plus modelling and testing of novel moorings and foundation solutions. A pathway to a standardised approach to MRE testing is presented, building on recommendations learnt from the MaRINET2 round-robin testing, showing how these recommendations are being incorporated into the guidance and ultimately feeding into the development of international standards for the marine renewable energy sector. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
Round Robin Testing: Exploring Experimental Uncertainties through a Multifacility Comparison of a Hinged Raft Wave Energy Converter |
The EU H2020 MaRINET2 project has a goal to improve the quality, robustness and accuracy of physical modelling and associated testing practices for the offshore renewable energy sector. To support this aim, a round robin scale physical modelling test programme was conducted to deploy a common wave energy converter at four wave basins operated by MaRINET2 partners. Test campaigns were conducted at each facility to a common specification and test matrix, providing the unique opportunity for intercomparison between facilities and working practices. A nonproprietary hinged raft, with a nominal scale of 1:25, was tested under a set of 12 irregular sea states. This allowed for an assessment of power output, hinge angles, mooring loads, and six-degree-of-freedom motions. The key outcome to be concluded from the results is that the facilities performed consistently, with the majority of variation linked to differences in sea state calibration. A variation of 5–10% in mean power was typical and was consistent with the variability observed in the measured significant wave heights. The tank depth (which varied from 2–5 m) showed remarkably little influence on the results, although it is noted that these tests used an aerial mooring system with the geometry unaffected by the tank depth. Similar good agreement was seen in the heave, surge, pitch and hinge angle responses. In order to maintain and improve the consistency across laboratories, we make recommendations on characterising and calibrating the tank environment and stress the importance of the device–facility physical interface (the aerial mooring in this case). | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
Levelized Cost of Energy Assessment for Offshore Wind Farms—An Examination of Different Methodologies, Input Variables, and Uncertainty |
Levelized cost of energy (LCoE) is the most common metric used in renewable energy assessments. However, this can be a very complex calculation with numerous methodologies depending on the perspective taken. Inputs including costs, energy production are generally forecasts and predictions based on publicly available information; therefore, they are key areas of uncertainty. Elements of the calculation are site or region specific such as the tax rate or inclusion of grid connection costs. The business case and financial assumptions applied will be very project specific, e.g., the discount rate applied. These numerous variables and uncertainties must be fully understood in order to effectively apply the metric or review and compare LCoEs. Therefore, this paper provides a comprehensive set of LCoE methodologies that provide a reference basis for researchers. A case study demonstrates the application of these methods and the variation in results illustrates the importance of correctly selecting the discount rate and cash flow based on the perspective and motivation of the user. Sensitivity studies further investigates the potential impact of key variables and areas of uncertainty on results. Analysis indicates that the energy production and discount rate applied will have the most significant impact on LCoE, followed by Capital Expenditure (CAPEX) costs. While the key areas of uncertainties cannot necessarily be solved, this paper promotes consistency in the application and understanding of the metric, which can help overcome its limitations. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
Special Section on Risk and Uncertainties in Offshore Wind and Wave Energy Systems |
This special section of the ASCE-ASME Journal of Risk and Uncertainty in Engineering Systems: Part B comprises seven papers related to recent advances and emerging approaches on the risk and uncertainties that are associated with the fast-changing sector of offshore renewable energy. A concerted effort was made to achieve broad geographic representation, with thematic and methodological diversity, variety in industrial needs. The papers present developments in both fundamental research and engineering applications and are expected to be a snapshot in time around the risks and uncertainties of this topic. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
Comparison of Response Amplitude Operator Curve Generation Methods for Scaled Floating Renewable Energy Platforms in Ocean Wave Basin |
Response amplitude operator (RAO) curves are commonly employed to assess the dynamic behavior of floating offshore structures in the frequency domain. There are multiple methods used to obtain RAOs for numerical models, scaled physical models, and full-scale tests. While for numerical modeling many studies detail the precise methods used, the literature around experimental RAO curves often do not detail them or leave methodological information incomplete. There exists inadequate experimental evidence in assessing the differences in results obtained by following different RAO generation methods from scaled physical testing. This paper addresses this gap by comparing two most popular RAO generation methods: the energy spectra (ES) and the cross spectral auto spectra (CSAS) method. These are experimentally compared on scaled semisubmersible and spar-buoy platforms in an ocean wave basin. Differences of heave and pitch RAOs generated by different methods are investigated. A method for reasonably collating multiple tests to create a representative RAO is also presented. RAO amplitudes vary significantly and how they decay off beyond certain frequencies is dependent on the method adopted to create them. This variation can be a source of significant uncertainty for floating structures for further analysis, design, control, or repair. Some RAOs (e.g., pitch) are sensitive to scaling and should be considered when converting scaled tests to full-scale equivalent. Detailing methods of RAO generation and comparing approaches of developing them can be important for crucial decisions from scaled physical testing of floating structures at design/development stages. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
Field Observations of a Multilevel Beach Cusp System and Their Swash Zone Dynamics |
This paper presents the observed morphological evolution of a multilevel beach cusp system in Long Strand, Co. Cork, Ireland. The surveys were carried out with an Unmanned Aerial Vehicle (UAV) system between March and September 2019. From this site, three levels of beach cusps on the beachface (i.e., lower beach level, mid beach level and upper beach level), and critical cusp parameters are reported, including cusp spacing, cusp elevation, cusp depth, and cusp amplitude. Thus far, such an extensive dataset has not previously been reported in the literature from a single site. The evolution of the different cusp parameters is then linked with the hydrodynamics in the study area, and new prediction theories are proposed for the different cusp parameters. The Lower beach level cusps (1 < z < 2.5 m Irish Transverse Mercator (ITM)) changed with every tide and appeared when surf-similarity parameter-ξ0 < 1.55. These cusps had a mean cusp spacing of λmean = 11.09 m, which are closely linked with the predictions of the self-organisation theory (p < 0.05). In contrast, the Mid beach level cusps (2.5 < z < 3.5 m ITM) are less dynamic compared to the Lower beach level cusps and can persist between spring tidal cycles. They had a mean cusp spacing of λmean = 18.17 m. The Upper beach level cusps (approximately z = 6 m ITM) are above astronomical tide levels and have a mean cusp spacing of λmean = 40.26 m. They did not change significantly over the survey period due to a lack of major storm events. These findings give a better understanding of the evolution of different cusp parameters for a multilevel beach cusp system and can be used to formulate a global theory regarding their change over time. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
The Irish Sea bed load parting zone: Is it a mid-sea hydrodynamic phenomenon or a geological theoretical concept? |
On tidally-dominated shelf seas, hydrodynamic flow exerts shear stress on the seabed, inducing sediment transport and seabed evolution. Net sediment transport pathways and associated bed load partings zones (the ‘head’ of sediment transport pathways) are important elements of this sediment dispersal process. A robust comprehension of these dynamics on a local and regional scale are crucial for a range of offshore activities, including the rapidly growing offshore renewable energy industry. Previous studies infer a bedload parting zone (BLP) in the central Irish Sea, yet this predominantly bedform-derived BLP remains to be fully supported by underlying hydrodynamics. This study reviews how sediment transport pathways in the Irish Sea are defined to date, investigates whether a hydrodynamic regime capable of supporting this inferred BLP exists, and if proven, aims to elucidate its origin. Tidal asymmetry indicators, derived from the phase and amplitude relationships of numerically modelled M₂ and M₄ tidal constituents, reveal the existence of a symmetrical tidal zone in the proximity of the inferred BLP. New numerically modelled residual tidal current and bed shear stress vectors reinforce the presence of this distinct tidal character change and further reveal strong opposing tidal flows extending from this region, thus supporting the presence of a tidal flow capable of producing divergent bedload patterns. Analysis of tidal propagation through the Irish Sea Basin concludes that the origin of the BLP is mainly attributed to the intersection of the north and south tidal fronts at an inclined angle due to Coriolis Forcing and coastline interactions. Minor factors impacting the shape and location of the BLP are the change in tidal character at (a) abrupt bathymetry changes, (b) headlands and intricate coastline topography, and (c) large-scale constrictions. Further investigation into localised morphodynamics is needed. These findings are highly valuable to efficient marine spatial planning, underpinning a movement towards a climate resilient economy. The integrated approach used in this body of work can be applied to tidally-dominated continental shelves beyond the Irish Sea. | More details Read publication | |
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Journal Article |
Journal Article | 2021 |
A new seabed mobility index for the Irish Sea: Modelling seabed shear stress and classifying sediment mobilisation to help predict erosion, deposition, and sediment distribution |
Response amplitude operator (RAO) curves are commonly employed to assess the dynamic behavior of floating offshore structures in the frequency domain. There are multiple methods used to obtain RAOs for numerical models, scaled physical models, and full-scale tests. While for numerical modeling many studies detail the precise methods used, the literature around experimental RAO curves often do not detail them or leave methodological information incomplete. There exists inadequate experimental evidence in assessing the differences in results obtained by following different RAO generation methods from scaled physical testing. This paper addresses this gap by comparing two most popular RAO generation methods: the energy spectra (ES) and the cross spectral auto spectra (CSAS) method. These are experimentally compared on scaled semisubmersible and spar-buoy platforms in an ocean wave basin. Differences of heave and pitch RAOs generated by different methods are investigated. A method for reasonably collating multiple tests to create a representative RAO is also presented. RAO amplitudes vary significantly and how they decay off beyond certain frequencies is dependent on the method adopted to create them. This variation can be a source of significant uncertainty for floating structures for further analysis, design, control, or repair. Some RAOs (e.g., pitch) are sensitive to scaling and should be considered when converting scaled tests to full-scale equivalent. Detailing methods of RAO generation and comparing approaches of developing them can be important for crucial decisions from scaled physical testing of floating structures at design/development stages. | More details Read publication |