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Existing anchor solutions are limited in their applicability to the floating offshore wind industry, which demands prolonged load endurance in extreme weather conditions and varied seabed soils. This limitation restricts project feasibility and increases costs. In order to address these challenges, the Deeply Embedded Ring Anchor (DERA) is proposed to achieve substantial reductions in anchor costs through efficiency enhancements. Ensuring the long-term safety and reliability of the DERA, especially considering a minimum operational period of 25 years, necessitates a comprehensive understanding of fatigue damage. Induced by repetitive loading below material yield strength, fatigue poses a significant threat to structures exposed to waves and currents. Anchors, vital for station keeping, are susceptible to fatigue damage, particularly in the padeye area. This paper conducts a fatigue analysis, focusing on factors such as the wall thickness of the ring anchor, inner stiffeners, and stiffener thickness, to evaluate the performance of DERA in this context. The results showed that the stiffener significantly affects the elongation of the total life of the anchor. In conclusion, this paper focuses on advancing innovations like DERA, enabling the efficient utilization of offshore wind resources, and addressing safety concerns through meticulous fatigue analysis. [ABSTRACT FROM AUTHOR]

Abstract Existing anchor solutions are limited in their applicability to the floating offshore wind industry, which demands prolonged load endurance in extreme weather conditions and varied seabed soils. This limitation restricts project feasibility and increases costs. In order to address these challenges, the Deeply Embedded Ring Anchor (DERA) is proposed to achieve substantial reductions in anchor costs through efficiency enhancements. Ensuring the long-term safety and reliability of the DERA, especially considering a minimum operational period of 25 years, necessitates a comprehensive understanding of fatigue damage. Induced by repetitive loading below material yield strength, fatigue poses a significant threat to structures exposed to waves and currents. Anchors, vital for station keeping, are susceptible to fatigue damage, particularly in the padeye area. This paper conducts a fatigue analysis, focusing on factors such as the wall thickness of the ring anchor, inner stiffeners, and stiffener thickness, to evaluate the performance of DERA in this context. The results showed that the stiffener significantly affects the elongation of the total life of the anchor. In conclusion, this paper focuses on advancing innovations like DERA, enabling the efficient utilization of offshore wind resources, and addressing safety concerns through meticulous fatigue analysis.

Expanding floating wind into new markets could support emission reduction targets in several national contexts. It furthers the need for adequate assessments to gain a full understanding of the technology's potential in future markets. South Africa is a prime case study as it has seen limited industry and policy developments despite its huge technical potential for floating offshore wind (FOW). This paper assessed the locational potential of floating wind in South Africa through a three-phased approach that evaluated the key technical drivers/barriers of the technology, conducted a Geographic Information System analysis (GIS) using ArcMap 10.8 to exclude unsuitable sites based on a predetermined exclusion criteria (including marine protected zones, underwater cables, major oil and gas deposits, etc.), and estimated the total harvestable capacity in the feasible sites. The study found that 2% (246,105.4 km2) of South Africa's entire Exclusive Economic Zone (EEZ) is suitable for hosting floating wind turbines, with a potential to generate a maximum of 142.61 GW of floating wind power. Although the Western Cape province holds the highest potential (80.52 GW) for floating wind in the country, the Eastern Cape region, with a locational potential of 20.04 GW, is considered most suitable for early-stage developments due to the availability of grid connection points, limited marine traffic, and proximity to appropriate port facilities. Future work can conduct techno-economic assessments to evaluate the technical and economic implications of developing floating wind in distinct sites in the country's EEZ. [ABSTRACT FROM AUTHOR]

The suspended configuration of inter-array power cables between floating offshore wind turbines necessitates using various ancillary equipment, such as buoy elements and bend stiffeners, to maintain the desired cable geometry. The failure analysis is an important step in the design of an inter-array dynamic power cable layout. This study investigates the impact of buoy element failures on the structural integrity and fatigue life of inter-array power cable configurations in offshore environments, focusing on four environmental conditions representative of the North Sea. Utilizing numerical simulations and fatigue analysis in OrcaFlex, static and dynamic analyses are conducted to assess maximum tension, minimum bend radius (MBR), and fatigue life under single and two failure scenarios of buoy elements. The results indicate that single buoy failures significantly increase maximum tension at hang-off points. At the same time, MBR is found to be the smallest at the failure position, aiding in failure point identification. In addition, for the two buoy element failure scenarios, the maximum tension increase poses risks to structural integrity, while MBR and fatigue life have high sensitivity to the applied environmental conditions. [ABSTRACT FROM AUTHOR]

Abstract Expanding floating wind into new markets could support emission reduction targets in several national contexts. It furthers the need for adequate assessments to gain a full understanding of the technology’s potential in future markets. South Africa is a prime case study as it has seen limited industry and policy developments despite its huge technical potential for floating offshore wind (FOW). This paper assessed the locational potential of floating wind in South Africa through a three-phased approach that evaluated the key technical drivers/barriers of the technology, conducted a Geographic Information System analysis (GIS) using ArcMap 10.8 to exclude unsuitable sites based on a predetermined exclusion criteria (including marine protected zones, underwater cables, major oil and gas deposits, etc.), and estimated the total harvestable capacity in the feasible sites. The study found that 2% (246,105.4 km2) of South Africa’s entire Exclusive Economic Zone (EEZ) is suitable for hosting floating wind turbines, with a potential to generate a maximum of 142.61 GW of floating wind power. Although the Western Cape province holds the highest potential (80.52 GW) for floating wind in the country, the Eastern Cape region, with a locational potential of 20.04 GW, is considered most suitable for early-stage developments due to the availability of grid connection points, limited marine traffic, and proximity to appropriate port facilities. Future work can conduct techno-economic assessments to evaluate the technical and economic implications of developing floating wind in distinct sites in the country’s EEZ.

This paper presents a life cycle assessment (LCA) of the International Energy Agency (IEA) 15 MW Reference Wind Turbine (RWT), on floating platforms, deployed in commercial-scale arrays at multiple locations around Scotland in the ScotWind leasing round. Site-specific energy production and vessel operations are provided by a dedicated offshore wind farm operations and maintenance (O&M) model, COMPASS, allowing service operation vessel (SOV) O&M impacts to be assessed with increased confidence. For climate change, the median global warming impact varied from 17.4 to 26.3 gCO2eq/kWh across the four sites within a 95% confidence interval using an uncertainty assessment of both foreground and background data. As is common with other offshore renewable energy systems, materials and manufacture account for 71% to 79% of global warming impact, while O&M comprise between 9% and 16% of the global warming impacts. High-voltage direct current (HVDC) export cables, floating platforms, and composite blades are significant contributors to the environmental impacts of these arrays (by mass and material choice), while the contributions from ballast, vessel transportation emissions, and power-train components are lower. The results suggest that material efficiencies, circularity, and decarbonizing material supply inventories should be a priority for the Scottish floating wind sector, followed by minimizing vessel operations and the decarbonization of vessel propulsion, while avoiding burden shifting to other impact categories. [ABSTRACT FROM AUTHOR]

The suspended configuration of inter-array power cables between floating offshore wind turbines necessitates using various ancillary equipment, such as buoy elements and bend stiffeners, to maintain the desired cable geometry. The failure analysis is an important step in the design of an inter-array dynamic power cable layout. This study investigates the impact of buoy element failures on the structural integrity and fatigue life of inter-array power cable configurations in offshore environments, focusing on four environmental conditions representative of the North Sea. Utilizing numerical simulations and fatigue analysis in OrcaFlex, static and dynamic analyses are conducted to assess maximum tension, minimum bend radius (MBR), and fatigue life under single and two failure scenarios of buoy elements. The results indicate that single buoy failures significantly increase maximum tension at hang-off points. At the same time, MBR is found to be the smallest at the failure position, aiding in failure point identification. In addition, for the two buoy element failure scenarios, the maximum tension increase poses risks to structural integrity, while MBR and fatigue life have high sensitivity to the applied environmental conditions.

Electrical grid layout optimization should consider the placements of turbines and substations and include effects such as wake losses, power losses in cables, availability of different cable types, reliability-based power losses and operational/decommissioning cost besides the initial investment cost. Hence, optimizing the levelized cost of energy is beneficial capturing long-term effects. The main contribution of this review paper is to identify the current works and trends on electrical layout optimization for offshore wind farms as well as to analyze the applicability of the found optimization approaches to commercial-scale floating wind farms which have hardly been investigated so far. Considering multiple subproblems (i.e., micrositing and cabling), simultaneous or nested approaches are advantageous as they avoid sequential optimization of the individual problems. To cope with this combinatorial problem, metaheuristics seems to offer optimal or at least close-to-optimal results while being computationally much less expensive than deterministic methods. It is found that floating wind brings new challenges which have not (or only insufficiently) been considered in present optimization works. This will also be reflected in a higher complexity and thus influence the suitability of applicable optimization techniques. New aspects include the mobility of structures, the configurations and interactions of dynamic cables and station-keeping systems, the increased likelihood of prevailing heterogeneous seabeds introducing priority zones regarding anchor and riser installation, the increased importance of reliability and maintainability due to stricter weather limits, and new floating specific wind farm control methods to reduce power losses. All these facets are crucial to consider when thoroughly optimizing the levelized cost of energy of commercial-scale floating offshore wind farms.

This paper reviews experimental methods for testing floating wind turbines. The techniques covered include early-stage and up-to-date approaches such as a porous disc method and hybrid model testing. First, the challenges induced by Froude and Reynolds similitudes and the importance of the various aerodynamic phenomena are discussed. The experimental methods are evaluated based on their cost, versatility, requirements, and limitations. The work primarily focuses on representing aerodynamic loads via hybrid and physical rotor testing, and a preliminary classification is proposed to facilitate the selection of the approaches. The work does not aim to identify an optimal method, but it provides insights into each method's distinctive features, serving as a roadmap for selecting the most appropriate methodology based on the specific testing goals and level of accuracy. Overall, this study offers a comprehensive resource for testing the coupled hydrodynamic and aerodynamic performance of floating wind turbines. The conclusions offer guidance for selecting an appropriate methodology based on the desired testing outcome. [ABSTRACT FROM AUTHOR]

Experimental results from the Floating Offshore-wind and Controls Advanced Laboratory (FOCAL) experimental program, which tested a performance-matched model of the IEA Wind 15 MW Reference Turbine on a 1:70 scale floating semisubmersible platform, are compared with OpenFAST simulations. Four experimental campaigns were performed, and data from the fourth campaign, which focused on wind and wave testing of the scaled floating wind turbine system, are considered. Simulations of wave-only, wind-only, and wind/wave environments are performed in OpenFAST, and results for key metrics are compared with the experiment. Performance of the real-time Reference OpenSource COntroller (ROSCO) in above-rated wind conditions, including the effects of the floating feedback loop, are investigated. Results show good agreement in mean values for key metrics, and hydrodynamic effects are matched well. Differences in the surge resonant behavior of the platform are identified and discussed. The effect of the controller and floating feedback loop is evident in both the experiment and OpenFAST, showing significant reduction in platform pitch response and tower base bending load near the platform pitch natural frequency. [ABSTRACT FROM AUTHOR]

Electrical grid layout optimization should consider the placements of turbines and substations and include effects such as wake losses, power losses in cables, availability of different cable types, reliability-based power losses and operational/decommissioning cost besides the initial investment cost. Hence, optimizing the levelized cost of energy is beneficial capturing long-term effects. The main contribution of this review paper is to identify the current works and trends on electrical layout optimization for offshore wind farms as well as to analyze the applicability of the found optimization approaches to commercial-scale floating wind farms which have hardly been investigated so far. Considering multiple subproblems (i.e., micrositing and cabling), simultaneous or nested approaches are advantageous as they avoid sequential optimization of the individual problems. To cope with this combinatorial problem, metaheuristics seems to offer optimal or at least close-to-optimal results while being computationally much less expensive than deterministic methods. It is found that floating wind brings new challenges which have not (or only insufficiently) been considered in present optimization works. This will also be reflected in a higher complexity and thus influence the suitability of applicable optimization techniques. New aspects include the mobility of structures, the configurations and interactions of dynamic cables and station-keeping systems, the increased likelihood of prevailing heterogeneous seabeds introducing priority zones regarding anchor and riser installation, the increased importance of reliability and maintainability due to stricter weather limits, and new floating specific wind farm control methods to reduce power losses. All these facets are crucial to consider when thoroughly optimizing the levelized cost of energy of commercial-scale floating offshore wind farms. [ABSTRACT FROM AUTHOR]

Abstract Recently, floating wind has enjoyed much public and governmental attention and is commonly identified as a crucial next step on the route to net zero targets for many countries. However, there is currently a large gap between the scale and readiness‐level of devices in the water and the end‐of‐ the‐decade aspirational targets of many governments. To facilitate the expansion of the industry, a wider acceptance and agreement of the realistic potential of floating wind and the barriers to the sector's development is required, particularly over this crucial 10‐year period, something currently scarce in published literature. In this work, a stakeholder engagement was performed, with subsequent analysis of the results to quantify industry expectations and identify the predominant technical and financial concerns of key stakeholders. The presented results of the work serve to both provide a point of comparison and updated account of industry‐based expert views in the near term, with further scientific analysis investigating distinctions between different stakeholder types. Secondarily, the key concerns of industry were analysed and compared with a literature review of recent research effort within floating wind, providing a high‐level gap analysis. A knowledge of the gaps can inform future areas for academic enquiry, ensuring the future needs of industry and the focus of research is aligned.

Novel wind technologies, in particular airborne wind energy (AWE) and floating offshore wind turbines, have the potential to unlock untapped wind resources and contribute to power system stability in unique ways. So far, the techno-economic potential of both technologies has only been investigated at a small scale, whereas the most significant benefits will likely play out on a system scale. Given the urgency of the energy transition, the possible contribution of these novel technologies should be addressed. Therefore, we investigate the main system-level trade-offs in integrating AWE systems and floating wind turbines into a highly renewable future energy system. To do so, we develop a modelling workflow that integrates wind resource assessment and future cost and performance estimations into a large-scale energy system model, which finds cost-optimal system designs that are operationally feasible with hourly temporal resolution across ten countries in the North Sea region. Acknowledging the uncertainty on AWE systems’ future costs and performance and floating wind turbines, we examine a broad range of cost and technology development scenarios and identify which insights are consistent across different possible futures. We find that onshore AWE outperforms conventional onshore wind regarding system-wide benefits due to higher wind resource availability and distinctive hourly generation profiles, which are sometimes complementary to conventional onshore turbines. The achievable power density per ground surface area is the main limiting factor in large-scale onshore AWE deployment. Offshore AWE, in contrast, provides system benefits similar to those of offshore wind alternatives. Therefore, deployment is primarily driven by cost competitiveness. Floating wind turbines achieve higher performance than conventional wind turbines, so they can cost more and remain competitive. AWE, in particular, might be able to play a significant role in a climate-neutral European energy supply and thus warrants further study.

Offshore wind is poised for huge growth in the coming years, the UK government has set targets of 40 GW of offshore wind, including 1 GW of floating wind, to be installed in the UK by 2030. Many proposed wind development sites are in deeper waters, farther from shore and will therefore need to be developed as floating wind sites. Developing sites in deeper waters provides access to higher, more consistent wind speeds, however this also means increased wave heights and tougher operating conditions. This makes the challenge of site accessibility critical to the goal of lowering the costs of offshore wind. Accessibility is the amount of time that vessels can safely access a given site. The objective of this study was to make a comparison of the accessibility of potential future floating wind sites to existing fixed bottom wind farm sites. Accessibility was calculated by developing Matlab code using established techniques and definitions found in the literature. A case study was then completed using sites in Scottish waters proposed for development as part of the Scotwind leasing plan. The majority of the Scotwind sites will need to be developed as floating wind sites due to the large water depths. This study assesses the accessibility of the Scotwind leasing sites and compares them to a typical fixed bottom site. The study found that accessibility will be a greater challenge for floating farm wind sites compared to fixed bottom sites. Increased access to vessels that can operate in larger wave heights will likely be necessary to operate and maintain floating wind farm sites. [ABSTRACT FROM AUTHOR]

This work evaluates the experimental test results regarding the operational performance of a free-float capable tension leg platform with a 10 MW wind turbine. It covers the platform dynamics in the selected installation area: Ribadeo, Spain. The model and the facility are initially presented, along with the experimental setup and the load cases. The testing campaign includes a software-in-the-loop method to emulate the rotor thrust and the aerodynamic and gyroscopic moments in pitch and yaw. The result sets are structured to start from basic information from system identification cases and continue with responses against regular and irregular waves accompanied by steady and stochastic wind scenarios. The performance in operational and extreme conditions is assessed as well as fault scenarios. The experiments demonstrate auspicious motion dynamics and mooring line behavior when examined against class society rules. [ABSTRACT FROM AUTHOR]

• Detailed Spatial and technological learning inputs improved system-level analysis. • Offshore wind deployment in the North Sea grows to a maximum of 498 GW by 2050. • 222 GW of fixed-bottom and 276 GW of floating wind by 2050 in the North Sea. • Floating wind's role is influenced by cost and capacity to make hydrogen offshore. • Role of emerging offshore renewables remains limited in all scenarios considered. Offshore renewables are expected to play a significant role in achieving the ambitious emission targets set by the North Sea countries. Among other factors, energy technology costs and their cost reduction potential determine their future role in the energy system. While fixed-bottom offshore wind is well-established and competitive in this region, generation costs of other emerging offshore renewable technologies remain high. Hence, it is vital to better understand the future role of offshore renewables in the North Sea energy system and the impact of technological learning on their optimal deployments, which is not well-studied in the current literature. This study implements an improved framework of integrated energy system analysis to overcome the stated knowledge gap. The approach applies detailed spatial constraints and opportunities of energy infrastructure deployment in the North Sea and also technology cost reduction forecasts of offshore renewables. Both of these parameters are often excluded or overlooked in similar analyses, leading to overestimation of benefits and technology deployments in the energy system. Three significant conclusions are derived from this study. First, offshore wind plays a crucial role in the North Sea power sector, where deployment grows to a maximum of 498 GW by 2050 (222 GW of fixed-bottom and 276 GW of floating wind) from 100 GW in 2030, contributing up to 51% of total power generation and declining cumulative system cost of power and hydrogen system by 4.2% (approx. 40 billion EUR in cost savings), when compared with the slow learning and constrained space use case. Second, floating wind deployment is highly influenced by its cost reduction trend and ability to produce hydrogen offshore; emphasizing the importance of investing in floating wind in this decade as the region lacks commercial deployments that would stimulate its cost reduction. Also, the maximum floating wind deployment in the North Sea energy system declined by 70% (162 GW from 276 GW) when offshore hydrogen production was avoided, while fixed-bottom offshore wind deployment remains unchanged. Lastly, the role of other emerging offshore renewables remains limited in all scenarios considered, as they are expensive compared to other technology choices in the system. However, around 8 GW of emerging technologies was observed in Germany and the Netherlands when the deployment potential of fixed-bottom offshore wind became exhausted. [ABSTRACT FROM AUTHOR]

The European North Sea has a vast renewable energy potential and can be a powerhouse for Europe's energy transition. However, currently there is uncertainty about how much offshore wind energy can be integrated, whether offshore grids should be meshed and to what extent offshore hydrogen should play a role. To address these questions, we use the open-source energy system optimization model PyPSA-Eur to model a European carbon-neutral sector-coupled energy system in high spatial and temporal resolution. We let the model endogenously decide how much offshore wind is deployed and which infrastructure is used to integrate the offshore wind. We find that with point-to-point connections like we have today, 310 GW offshore wind can be integrated in the North Sea. However, if we allow meshed networks and hydrogen, we find that this can be raised to 420 GW with cost savings up to 15 bn€/a. Furthermore, we only observe significant amounts of up to 75 GW of floating wind turbines in the North Sea if we have offshore hydrogen production. Generally, the model opts for offshore wind integration through a mix of both electricity and hydrogen infrastructure. However, the bulk of the offshore energy is transported as hydrogen, which is twice as much as the amount transported as electricity. Moreover, we find that the offshore power network is mainly used for offshore wind integration, with only a small portion used for inter-country transmission. • Offshore power grid reduces system cost by 4 bn€/a. • Integration of offshore hydrogen network leads to further cost reduction by 15 bn€/a. • 420 GW offshore wind capacity is deployed in the North Sea, mostly fixed bottom. • Offshore wind in the North Sea can replace missing potential for onshore wind. • Offshore grid mainly for wind integration, less for inter-country transmission. [ABSTRACT FROM AUTHOR]

This paper presents a life cycle assessment (LCA) of the International Energy Agency (IEA) 15 MW Reference Wind Turbine (RWT), on floating platforms, deployed in commercial-scale arrays at multiple locations around Scotland in the ScotWind leasing round. Site-specific energy production and vessel operations are provided by a dedicated offshore wind farm operations and maintenance (O&M) model, COMPASS, allowing service operation vessel (SOV) O&M impacts to be assessed with increased confidence. For climate change, the median global warming impact varied from 17.4 to 26.3 gCO2eq/kWh across the four sites within a 95% confidence interval using an uncertainty assessment of both foreground and background data. As is common with other offshore renewable energy systems, materials and manufacture account for 71% to 79% of global warming impact, while O&M comprise between 9% and 16% of the global warming impacts. High-voltage direct current (HVDC) export cables, floating platforms, and composite blades are significant contributors to the environmental impacts of these arrays (by mass and material choice), while the contributions from ballast, vessel transportation emissions, and power-train components are lower. The results suggest that material efficiencies, circularity, and decarbonizing material supply inventories should be a priority for the Scottish floating wind sector, followed by minimizing vessel operations and the decarbonization of vessel propulsion, while avoiding burden shifting to other impact categories.

This paper reviews experimental methods for testing floating wind turbines. The techniques covered include early-stage and up-to-date approaches such as a porous disc method and hybrid model testing. First, the challenges induced by Froude and Reynolds similitudes and the importance of the various aerodynamic phenomena are discussed. The experimental methods are evaluated based on their cost, versatility, requirements, and limitations. The work primarily focuses on representing aerodynamic loads via hybrid and physical rotor testing, and a preliminary classification is proposed to facilitate the selection of the approaches. The work does not aim to identify an optimal method, but it provides insights into each method’s distinctive features, serving as a roadmap for selecting the most appropriate methodology based on the specific testing goals and level of accuracy. Overall, this study offers a comprehensive resource for testing the coupled hydrodynamic and aerodynamic performance of floating wind turbines. The conclusions offer guidance for selecting an appropriate methodology based on the desired testing outcome.

Recently, floating wind has enjoyed much public and governmental attention and is commonly identified as a crucial next step on the route to net zero targets for many countries. However, there is currently a large gap between the scale and readinesslevel of devices in the water and the end-of-the-decade aspirational targets of many governments. To facilitate the expansion of the industry, a wider acceptance and agreement of the realistic potential of floating wind and the barriers to the sector's development is required, particularly over this crucial 10-year period, something currently scarce in published literature. In this work, a stakeholder engagement was performed, with subsequent analysis of the results to quantify industry expectations and identify the predominant technical and financial concerns of key stakeholders. The presented results of the work serve to both provide a point of comparison and updated account of industry-based expert views in the near term, with further scientific analysis investigating distinctions between different stakeholder types. Secondarily, the key concerns of industry were analysed and compared with a literature review of recent research effort within floating wind, providing a high-level gap analysis. A knowledge of the gaps can inform future areas for academic enquiry, ensuring the future needs of industry and the focus of research is aligned. [ABSTRACT FROM AUTHOR]

Experimental results from the Floating Offshore-wind and Controls Advanced Laboratory (FOCAL) experimental program, which tested a performance-matched model of the IEA Wind 15 MW Reference Turbine on a 1:70 scale floating semisubmersible platform, are compared with OpenFAST simulations. Four experimental campaigns were performed, and data from the fourth campaign, which focused on wind and wave testing of the scaled floating wind turbine system, are considered. Simulations of wave-only, wind-only, and wind/wave environments are performed in OpenFAST, and results for key metrics are compared with the experiment. Performance of the real-time Reference OpenSource COntroller (ROSCO) in above-rated wind conditions, including the effects of the floating feedback loop, are investigated. Results show good agreement in mean values for key metrics, and hydrodynamic effects are matched well. Differences in the surge resonant behavior of the platform are identified and discussed. The effect of the controller and floating feedback loop is evident in both the experiment and OpenFAST, showing significant reduction in platform pitch response and tower base bending load near the platform pitch natural frequency.

This paper reviews the status of floating wind energy expansion, market needs, opportunities, and barriers. Even more expensive than many other generation technologies currently, the floating wind will contribute to the decarbonization of Europe. This document assesses the market strategies available to develop floating wind farms in Europe. The study includes four main phases in addition to the overview of the current state-of-the-art: a technology review, market outlook, opportunities, and commercialization barriers. During its development, the offshore wind has moved from experimentation to a final design (Semisubmersible/barge, Tension Leg Platform, and Spar). [ABSTRACT FROM AUTHOR]

Floating offshore wind is a promising renewable energy source for several Mediterranean Countries. The exploitation of this resource will contribute to reducing carbon dependence and support the clean energy transition towards a climate neutral Europe. This work presents a novel methodology for estimating spatially-resolved Levelised Cost of Energy and offshore wind energy potential to provide optimal design of floating offshore wind farms in the Mediterranean Sea. For the first time, each site is optimised based on electrical grid cable design and wind farm layout optimisation using the Jensen wake model. The largest technical capacity potentials are obtained in Libya, Tunisia, Italy and Greece, accounting for 72.2 % of the total Mediterranean potential with a total installed capacity of 782 GW . The average LCOE is 93.4 €/MWh and the average capacity factor is 31.8 %, while 67.5 % of the technical potential has LCOE below 90 €/MWh which demonstrates that floating offshore wind in the Mediterranean could become soon competitive with other renewable energies. Optimal floating wind farm design parameters show the prevalence of a wind farm array of 10 x 10 wind turbines with a preferred rated power of 15 MW and the HVDC export cable connection. Among the selected floating platforms, Hywind outperforms WindFloat and GICON-SOF in 59.2 % of the suitable areas due to the lower structure material. Policymakers and stakeholders will primarily benefit from this study, which provides them with important information for careful marine spatial planning and the development of floating offshore wind farms in the Mediterranean., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 Published by Elsevier Ltd.)

This work evaluates the experimental test results regarding the operational performance of a free-float capable tension leg platform with a 10 MW wind turbine. It covers the platform dynamics in the selected installation area: Ribadeo, Spain. The model and the facility are initially presented, along with the experimental setup and the load cases. The testing campaign includes a software-in-the-loop method to emulate the rotor thrust and the aerodynamic and gyroscopic moments in pitch and yaw. The result sets are structured to start from basic information from system identification cases and continue with responses against regular and irregular waves accompanied by steady and stochastic wind scenarios. The performance in operational and extreme conditions is assessed as well as fault scenarios. The experiments demonstrate auspicious motion dynamics and mooring line behavior when examined against class society rules.

Offshore wind is poised for huge growth in the coming years, the UK government has set targets of 40 GW of offshore wind, including 1 GW of floating wind, to be installed in the UK by 2030. Many proposed wind development sites are in deeper waters, farther from shore and will therefore need to be developed as floating wind sites. Developing sites in deeper waters provides access to higher, more consistent wind speeds, however this also means increased wave heights and tougher operating conditions. This makes the challenge of site accessibility critical to the goal of lowering the costs of offshore wind. Accessibility is the amount of time that vessels can safely access a given site. The objective of this study was to make a comparison of the accessibility of potential future floating wind sites to existing fixed bottom wind farm sites. Accessibility was calculated by developing Matlab code using established techniques and definitions found in the literature. A case study was then completed using sites in Scottish waters proposed for development as part of the Scotwind leasing plan. The majority of the Scotwind sites will need to be developed as floating wind sites due to the large water depths. This study assesses the accessibility of the Scotwind leasing sites and compares them to a typical fixed bottom site. The study found that accessibility will be a greater challenge for floating farm wind sites compared to fixed bottom sites. Increased access to vessels that can operate in larger wave heights will likely be necessary to operate and maintain floating wind farm sites.

This paper describes an experimental study conducted on a multi-column tension leg platform (TLP) floating offshore wind turbine (FOWT). A prototype model of the TLP FOWT supporting the NREL 5-MW wind turbine with a scale ratio of 1:50 is tested under various wind and wave conditions at the State Key Laboratory of Coastal and Offshore Engineering at Dalian University of Technology, China. This work has particularly focused on the tendon failure and its impact on the dynamic response of the FOWT. Free decay tests, regular wave tests, wind-wave combined tests and tendon failure tests are conducted using different environmental parameters. The results suggest that natural periods, dynamic responses of the platform, and forces in the tendons satisfy the design requirements. The analysis indicates that the impact of tendon failure on the platform surge, heave and pitch responses are found to be insignificant. When one of the tendons is broken, the adjacent tendons experience a significant increase in tensile force; and, the maximum tensile force in the remaining tendon is found to increase by about 130%. The overstepping of the minimum breaking load as recommended by the design standard DNV GL is not reached, and this indicates that the safety of the system is ensured even during the harshest failure condition. • Dynamic responses of a TLP floating offshore wind platform (FOWT) with a failed tendon under wind and wave conditions have been investigated. • Numerical simulations and wave tank experiments of a 1:50 scale model are undertaken under combined wind and wave conditions. • Good agreement in the results between the numerical and physical model tests is achieved. • Several key outcomes observed, including a significant increase of force in the tendon adjacent to the broken tendon, are reported. [ABSTRACT FROM AUTHOR]

This paper reviews the status of floating wind energy expansion, market needs, opportunities, and barriers. Even more expensive than many other generation technologies currently, the floating wind will contribute to the decarbonization of Europe. This document assesses the market strategies available to develop floating wind farms in Europe. The study includes four main phases in addition to the overview of the current state-of-the-art: a technology review, market outlook, opportunities, and commercialization barriers. During its development, the offshore wind has moved from experimentation to a final design (Semisubmersible/barge, Tension Leg Platform, and Spar).

A new validation campaign was conducted at the W2 Harold Alfond Ocean Engineering Laboratory at the University of Maine to investigate the hydrodynamic loading on floating offshore wind substructures, with a focus on the low-frequency contributions that tend to drive extreme and fatigue loading in semisubmersible designs. A component-level approach was taken to examine the hydrodynamic loads on individual parts of the semisubmersible in isolation and then in the presence of other members to assess the change in hydrodynamic loading. A variety of wave conditions were investigated, including bichromatic waves, to provide a direct assessment of difference-frequency wave loading. An assessment of the impact of wave uncertainty on the loading was performed, with the goal of enabling validation with this dataset of numerical models with different levels of fidelity. The dataset is openly available for public use and can be downloaded from the U.S. Department of Energy Data Archive and Portal.

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.

This paper introduces metrics developed for analysing irregular wave test results from 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. While response amplitude operations (RAOs) are a useful tool for assessing device performance in irregular waves, they are not easy to interpret when performing an inter-facility comparison where there are many variables. Metrics that use a single value per test condition rather than an RAO curve are a means of efficiently comparing tests from different basins in a more heuristic manner. In this research, the focus is on using metrics to assess how the platform responds with varying wave height and thrust across different facilities. It is found that the metrics implemented are very useful for extracting global trends across different basins and test conditions.

With the large-scale development in the last decades of fixed offshore wind across Europe and the ever-more present threat of climate change dominating national and global agenda, the exploitation of wind power in deep-water using floating wind turbines is gathering a significant amount of interest. Compared to other types of floating wind platforms, Tension-leg-platforms (TLPs) are less compliant systems resisting dynamic forces through their pre-tensioned tendons. Whilst this reduces the weight of the platform hull, understanding extreme loading cycles in the mooring system becomes an important design issue. Recent research has shown that including sum-frequency second-order and third-order loads is important to capture extreme events such as slack-line events on large and stiff floating systems. This article exposes a review of some of the existing numerical methods available to engineers to calculate second and third-order forces, including both potential (semi-analytical and BEM) and strip-theory approaches (Rainey and FNV). It compares their application in monochromatic waves on a truncated cylinder and a full TLP platform by evaluating forces amplitudes against CFD calculation. The results show that large fully submerged elements of the TLP floater contribute significantly to the third-order forces and are not well represented by existing engineering methods. • Analysis of the distribution of high-order wave loads on a FOWT-TLP floater • High-order strip-theory approaches moderately accurate when applied on complex hull • Semi-analytical solutions appear as useful benchmark in regular waves • Significant contributions to the third-order pitch moment from vertical viscous forces • Demonstration of a porosity wall representation of a complex FOWT hull in CFD [ABSTRACT FROM AUTHOR]

To study the feasibility of deploying a novel type of anchor with variable buoyancy for mooring floating offshore wind turbines, a set of detailed modelling studies was performed in the state of-the-art Marine Simulator at the National Decommissioning Centre. The aim of the multiphysics simulations is to assess fully a proposed craneless deployment method that involves towing the anchor from the harbour to the installation site, pumping liquid ballast to overcome anchor's buoyancy and lowering it to the seabed using only a winch, thereby simplifying the process, and reducing installation costs. As a test case, a novel shape of the floating anchor is considered, to establish the feasibility of its deployment in conjunction with the variable buoyancy technology and installation sequence. The analysis is divided into three sections: characterisation of the anchor buoyancy, positioning the anchor under the stern of the vessel and the controlled descent of the anchor to the seabed, under varying weather and operational conditions (e.g significant wave height, current, winch velocity, liquid ballast mass, ballast pump rate). The analysis allows assessment of the importance of the different factors affecting the proposed deployment scenario of variable buoyancy anchors, such as the winch velocity, the ballast mass and the pump rate. • Feasibility of deploying variable buoyancy anchors for floating wind applications. • Virtual prototyping of anchor deployment scenarios. • Parametric studies of the effect of environmental and operational conditions. • Unveiling complexities of deploying variable buoyancy anchors using simple techniques. • Reducing cost and risk for future offshore deployment of variable buoyancy anchors. [ABSTRACT FROM AUTHOR]

Growing energy demand is causing a significant decrease in the world’s hydrocarbon stock in addition to the pollution of our ecosystem. Based on this observation, the search for alternative sorts of energy to fossil fuels is being increasingly explored and exploited. Wind energy is experiencing a very important development, and it offers a very profitable opportunity for exploitation since the wind is always available and inexhaustible. Several technical solutions exist to exploit wind energy, such as floating vertical axis wind turbines (F-VAWTs), which provide an attractive and cost-effective solution for exploiting higher resources of offshore wind in deep water areas. Recently, the use of the Darrieus vertical axis wind turbine (VAWT) offshore has attracted increased interest because it offers significant advantages over horizontal axis wind turbines (HAWTs). In this context, this article presents a new concept of floating Darrieus-type straight-bladed turbine with three-stage rotors. A double-multiple stream tube (DMST) model is used for aerodynamic simulations to examine several critical parameters, including, solidity turbine, number of blades, rotor radius, aspect ratio, wind velocity, and rotor height. This study also allows to identify a low solidity turbine (σ = 0.3), offering the best aerodynamic performance, while a two-bladed design is recommended. Moreover, the results also indicate the interest of a variable radius rotor, as well as the variation of the height as a function of the wind speed on the aerodynamic efficiency.

The design of reliable station-keeping systems for permanent floating structures such as offshore renewable energy devices is vital to their lifelong integrity. In highly dynamic and/or deep-water applications, including hydrodynamics and structural dynamics in the mooring analysis is paramount for the accurate prediction of the loading on the lines and hence their dimensioning. This article presents a new workflow based on EDF R&D's open-source, finite-element analysis tool Code_Aster , enabling the dynamic analysis of catenary mooring systems, with application to a floating wind turbine concept. The University of Maine DeepCwind-OC4 basin test campaign is used for validation, showing that Code_Aster can satisfactorily predict the fairlead tensions in both regular and irregular waves. In the latter case, all of the three main spectral components of tension observed in the experiments are found numerically. Also, the dynamic line tension is systematically compared with that provided by the classic quasi-static approach, thereby confirming its limitations. Robust dynamic simulation of catenary moorings is shown to be possible using this generalist finite-element software, provided that the inputs be organised consistently with the physics of offshore hydromechanics. [ABSTRACT FROM AUTHOR]

This paper examines the impact on experimental uncertainty of introducing aerodynamic and rotor gyroscopic loading on a model multirotor floating wind energy platform during physical testing. In addition, a methodology and a metric are presented for the assessment of the uncertainty across the full time series for the response of a floating wind energy platform during wave basin testing. It is shown that there is a significant cost incurred in terms of experimental uncertainty through the addition of rotor thrust in the laboratory environment for the considered platform. A slight reduction in experimental uncertainty is observed through the introduction of gyroscopic rotor loading for most platform responses.