Floating Wind Farm Research Articles

Experimental Analysis of the Wake Meandering of a Floating Wind Turbine under Imposed Surge Motion

With the development of floating wind farms, the understanding of the far wake becomes of utmost importance because it cannot only be based on the experience acquired on fixed offshore turbine as the range of motion of the floater due to met-ocean conditions is in the same order of magnitude compared to the energetic turbulent scales of the atmosphere and to the characteristic scales of the wake. The objective of this wind-tunnel experiment is to analyse the behaviour of the wake center of a floating turbine subject to imposed surge motion. The experiment is carried out in the LHEEA wind tunnel where a 1/500 scale wind turbine model is immersed in a realistic offshore atmospheric-boundary layer. The model is actuated in surge by a linear motor able to reproduced idealised second order surge motion of a floating platform (mainly due to the waves) with a realistic amplitude and range of frequencies. Stereoscopic particle image velocimetry measurements are performed at two planes normal to the free-stream at distances of 4.6 and 8.1 diameters downstream of the turbine. Instantaneous velocity fields acquired at 14.1 Hz are individually analysed by convolution to find the location of the wake center. Results show that the wake center spreading is largely influenced by the downstream distance and only slightly affected by the surge motion. However, when analysing the wake position time series by a power spectral density, the signature of the surge motion becomes very clear for both downstream distances. These findings tell that the far wake (at least up to 8.1 diameters downstream) of a floating wind turbine has a “memory” of the motion in its frequency content. When extrapolating to a floating wind farm, this result suggests that a turbine inside a floating wind farm will be immersed in a flow including a significant dynamic signature in the range of its own motion.

Layout Optimization of a Modular Floating Wind Farm Based on the Full-Field Wake Model

By optimizing the positions of wind turbines in a wind farm, the power loss caused by wake effects can be reduced maximally. A new methodology of layout optimization is proposed utilizing a full-field wake model that integrates the near-field and far-field wake models after modifications, and a random search (RS) algorithm improved with a scale factor for acceleration in high-density layouts. The methodology is applied to a floating wind farm composed of modular platforms, which have a novel configuration and the ability to face toward the wind direction. The applicability and efficiency of the methodology and the improved RS algorithm are validated. The power production of optimized layouts shows a flat crest with an increased number of wind turbines. There is a layout with maximal output power in the wind farm. The real optimal layout should be determined in consideration of both output power and cost. Two sizes of platforms with different number of modules are compared in the application. The wind farm with smaller platforms produces more power. For comparison, a pattern search (PS) algorithm is also implemented in the application. The improved RS algorithm shows outperformance compared with the original RS and the PS algorithm.

Application of Monte Carlo and Fuzzy Analytic Hierarchy Processes for ranking floating wind farm locations

A Monte Carlo simulation procedure is developed to select the optimum location of wind farms by using major decision criteria and applying subjective judgments from decision-makers. The approach combines Monte Carlo simulation with conventional Analytic Hierarchy Process and with the Fuzzy Analytic Hierarchy Process. Monte Carlo simulation is used to determine the confidence level of each alternative determined by the Analytic Hierarchy Process concerning the uncertainty of decision-maker opinions. The proposed method is applied to offshore wind farms located in Spain, and the most appropriate locations for turbine positioning are ranked.

Energy System Design of Offshore Natural Gas Hydrates Mining Platforms Considering Multi-Period Floating Wind Farm Optimization and Production Profile Decay

Energy System Design of Offshore Natural Gas Hydrates Mining Platforms Considering Multi-Period Floating Wind Farm Optimization and Production Profile Decay

A novel multi-criteria decision-making model to evaluate floating wind farm locations

The paper aims to develop a decision tool for planning offshore wind farm locations, combining multi-criteria decision analysis and geographic information systems. This method considers several technological, environmental, social, and economic criteria. The criteria are used as evaluation factors and constraints to rank the identified potential locations through an Analytic Hierarchy Process. During the evaluation of the available areas, a pairwise comparison is used in which a group of experts determines the weights. Sensitivity and consensus analyses evaluate the results robustness. The methodology is developed for a case study in the Atlantic coastal areas of Portugal, Spain, and France. The results show the potential of this tool to support the planners in the designation of regions for floating wind farm development.

Linearized modeling and optimization of shared mooring systems

Shared mooring systems, where adjacent platforms are tethered directly to each other, can reduce anchor quantities and mooring line lengths in a floating array but also introduce new modeling and design challenges. This paper presents and demonstrates a first-order approach to modeling and designing shared mooring systems that simplifies these challenges. We formulate a general, linearized model for the force–displacement response of shared mooring systems, including inter-platform couplings. Using this linearization, we realize significant simplifications to the shared mooring system design problem and propose a corresponding design optimization approach. Finally, we demonstrate the complete approach on a variety of shared-mooring floating wind farm layouts with generic design assumptions and constraints. Some fundamental observations about shared mooring systems can be made from the results. Polygonal array layouts with perpendicular anchor positions appear to maximize shared mooring system efficiency. Also, arrays with greater levels of sharing tend to exhibit larger deviations in offsets between platforms. Overall, the results show how the linearized approach can be applied to efficiently evaluate and systematically optimize preliminary shared mooring system designs.

Application of SADA method on full-scale measurement data for dynamic responses prediction of Hywind floating wind turbines

Floating offshore wind turbines (FOWTs) are promising solutions for offshore renewable energy harvesting, with the successful installation and operation of the world's first commercial floating wind farm, Hywind Scotland, in 2017. However, both academia and industry are still constantly facing challenges in the aspects of cost reduction, monitoring, safety and sustainability improvement for the design and maintenance of FOWTs. The purpose of this paper is to demonstrate an engineering application of a novel Artificial Intelligence knowledge-based method, named SADA, on the full-scale measurement data of an Hywind FOWT. The SADA method was applied to perform numerical optimization and dynamic responses prediction of the FOWTs, based on the full-scale data from one Hywind FOWT in Scotland. The methodology of SADA and the key technology of the application are introduced firstly. Then, the selection of Key Discipline Parameters (KDPs) is introduced, followed with the training of AI-based numerical models with full-scale measurement data, including Floater motions, wind, wave and current data. After that, the numerical model imbedded in SADA is trained to be intelligent for the objective Hywind FOWT under different sea states. The intelligent SADA model is used to do comparisons and predictions. The comparison results show that using SADA method, the AI-trained numerical model can predict the motions of Hywind supporting Floater in higher accuracy. In addition, other physical quantities that cannot be obtained directly in full-scale measurement easily but are of great concern by industry, can also be obtained from a more believable perspective. This AI-based SADA method brings an innovative vision for FOWTs' full-scale measurement technology in the future.

Impact of vessel logistics on floating wind farm availability

This paper presents a study of the impact of the Operations and Maintenance (O&M) vessel logistics over the power availability of an Offshore Wind Farm. In particular, the vessel size and availability are considered. The study is performed with a life-span simulator, based on historical metocean data, walk-to-walk characterization based on a frequency domain hydrodynamic modelling of multibody systems, wind farm fault simulator (based on a catalogue of more than 1800 faults) and an algorithm to reproduce the O&M intelligence (i.e. sea transportation, workability, among others). The frequency domain model is applied on an hourly basis considering the specific significant wave height, peak period, peak enhancement factor, mean heading, directional spreading, and a wave-by-wave strategy is used to find if personnel transfer and workability criteria are met. The WindFloat Atlantic wind farm, located off the coast of Viana do Castello (Portugal), was chosen together with the TRL+ project semi-submersible platform and the 10MW turbine as a reference case. Different vessel logistics options are compared, including full vessel availability and several options of waiting times. The power availability changes among the different cases of study could be compared with the cost changes, optimizing the LCOE (Levelized Cost of Energy) of the wind farm. The presented study is a valuable example of the potential of the proposed O&M simulation model as an optimization tool.

Optimizing the Cost and Reliability of Shared Anchors in an Array of Floating Offshore Wind Turbines

Abstract Commercial floating offshore wind projects are expected to emerge in the U.S. by the end of this decade. Currently, however, high costs for the technology limit its commercial viability, and a lack of data regarding system reliability heightens project risk. This work presents an optimization algorithm to examine the tradeoffs between cost and reliability for a floating offshore wind array that uses shared anchoring. Combining a multivariable genetic algorithm with elements of Bayesian optimization, the optimization algorithm selectively increases anchor strengths to minimize the added costs of failure for a large floating wind farm in the Gulf of Maine under survival load conditions. The algorithm uses an evaluation function that computes the probability of mooring system failure, then calculates the expected maintenance costs of a failure via a Monte Carlo method. A cost sensitivity analysis is also performed to compare results for a range of maintenance cost profiles. The results indicate that virtually all of the farm's anchors are strengthened in the minimum cost solution. Anchor strength is increased between 5 and 35% depending on farm location, with anchor strength nearest the export cable being increased the most. The optimal solutions maintain a failure probability of 1.25%, demonstrating the tradeoff point between cost and reliability. System reliability was found to be particularly sensitive to changes in turbine costs and downtime, suggesting further research into floating offshore wind turbine failure modes in extreme loading conditions could be particularly impactful in reducing project uncertainty.

Incorporating stochastic operation and maintenance models into the techno-economic analysis of floating offshore wind farms

Floating offshore wind is rapidly gaining traction in deep water locations. As with all new technologies, to gain the confidence of developers and investors, the technical and economic feasibility of this technology must be proven and robust cost estimates are necessary. In this paper, the authors present a methodology to calculate the capital and operational indicators of a floating wind farm over its project lifetime. A set of computational models is used to reduce the uncertainties in the estimation of the technical and economical parameters. In particular, the effect of using detailed operation and maintenance models and strategies allows a better estimation of operational cost. The paper highlights the requirements and specific adjustments considered for floating offshore wind technology. The methodology is demonstrated for two case studies inspired by real floating wind installations in the United Kingdom, namely the Hywind and Kincardine projects. The related input data, gathered from publicly available sources, constitute a reference database for future studies in the floating offshore wind sector. Results are presented for the two case studies. These show that availability and energy production are in line with typical values for offshore wind projects, and highlight the substantial contribution of operational expenses to the cost of energy. Results are also compared against previous estimations for floating offshore wind projects, showing satisfactory agreement for the overall project costs but an underestimation of operation and maintenance costs in previous studies. This highlights the importance of using detailed operation and maintenance models to adequately capture operational expenses.

Socio-economic impact of a 200 MW floating wind farm in Gran Canaria

This research analyses the economic impact of a 200 MW offshore floating wind farm in an isolated tourist-led region as the Canary Islands in terms of regional and national gross value added (GVA) and employment. After analysing the value chain of the offshore wind energy industry, the impact of the regional and national economy has been estimated using an input/output model. The main aim is to evaluate this impact in comparison to more industrialized region and to bottom-fixed offshore wind farms. The value chain analysis shows that the floating offshore wind capabilities in Spain are very high. Two different scenarios have been developed to take into account transfers of the value-chain between the regional and the national level. It is concluded that similar level of investment in the Canary Islands and in Mainland-Spain will lead to different impacts in the economy due to their different economic structures. The highly tourism-led Canarian economy, characterised by a marginal industrial sector and overdeveloped services one, will lead to an overall lower GVA and, at the same time, to a higher employment demand. Several indicators have been deployed using the results of this research that show the impact in tourist-led economies and also of floating versus bottom-fixed offshore wind farms. The GVA generated through the whole project is high, reaching 680 million euros at national level, which includes a regional contribution of 365 to 245 million euros, showing the high impact of the project in the national and local economy.

The efficiency and coastal protection provided by a floating wind farm operating in the Romanian nearshore

Overcome by the increasing energy demands nowadays and the limited traditional resources, the foremost objective of the proposed study is to evaluate the efficiency of a floating wind farm operating in the coastal environment of the western Black Sea. Since coastal erosion has become a matter of urgent concern during the last decades and many states in the EU (European Union) consider the issue of coastal protection to be of utmost national importance, this study aims to reveal the positive effects such project might provide to the coastal area of Romania. Due to significant decrease of sediments from the Danube basin to the coast in the north along with the extensive development of tourist resorts, especially in the southern part, the erosion process has become more explicit, posing a severe threat primarily on the population living within an area of tens of kilometres from the coast. To provide a better overview of the principal wave patterns in the targeted area, the ERA5 dataset has been considered for the evaluation of the wave power for the 40-year period (1979–2018) for two reference points located in the proximity of the target area. Four scenarios for the simulations were carried out with a computational structure that combines a circulation model with a wave model. A generic wind farm was defined in the computational domain, taking into consideration steadily increasing distances from the shoreline: 4, 6 and 8 km. Firstly, taking into account the local wave patterns, and three-wave parameters — the significant wave height, the mean wave height and direction, the down-wave effect of the farm was evaluated. Secondly, the influence of the generic farm on the longshore currents was also assessed. The concluding results suggest that if such a project is to be taken into consideration, it would not only provide valuable renewable energy, but it would also guarantee adequate coastal protection by reducing the impact of waves and intensify resilience to terrible weather.

Mooring Analysis of a Dual-Spar Floating Wind Farm With a Shared Line

AbstractWind farms with shared mooring lines have the potential to reduce mooring costs. However, such wind farms may encounter complex system dynamics because adjacent wind turbines are coupled. This paper presents an analysis of the shared mooring system with a focus on the system natural periods. We first apply Irvine’s method to model both the shared line and the two-segment single lines. The response surface method is proposed to replace iterations of the catenary equations of the single lines, and a realistic single line design is presented for OC3 Hywind. Then, system linearization and eigenvalue analysis are performed for the wind farm consisting of two spar floating wind turbines, one shared line, and four single lines. The obtained natural periods and natural modes are verified by numerical free decay tests. Finally, a sensitivity study is carried out to investigate the influence of mooring properties. It is found that the shared line has a significant influence on the natural periods in the surge and sway modes. The natural periods in the surge and sway modes are also most sensitive to the mooring property variations. Two sway eigenmodes are identified, and the lower sway natural period varies between 23 s and 88 s in the sensitivity study. The present analysis method can be used to identify critical natural periods at the preliminary design stage of shared mooring systems.

Dynamic Response of Offshore Wind Turbine on 3×3 Barge Array Floating Platform under Extreme Sea Conditions

Offshore wind farm construction is nowadays state of the art in the wind power generation technology. However, deep water areas with huge amount of wind energy require innovative floating platforms to arrange and install wind turbines in order to harness wind energy and generate electricity. The conventional floating offshore wind turbine system is typically in the state of force imbalance due to the unique sway characteristics caused by the unfixed foundation and the high center of gravity of the platform. Therefore, a floating wind farm for 3×3 barge array platforms with shared mooring system is presented here to increase stability for floating platform. The NREL 5 MW wind turbine and ITI Energy barge reference model is taken as a basis for this work. Furthermore, the unsteady aerodynamic load solution model of the floating wind turbine is established considering the tip loss, hub loss and dynamic stall correction based on the blade element momentum (BEM) theory. The second development of AQWA is realized by FORTRAN programming language, and aerodynamic — hydrodynamic — Mooring coupled dynamics model is established to realize the algorithm solution of the model. Finally, the 6 degrees of freedom (DOF) dynamic response of single barge platform and barge array under extreme sea condition considering the coupling effect of wind and wave were observed and investigated in detail. The research results validate the feasibility of establishing barge array floating wind farm, and provide theoretical basis for further research on new floating wind farm.

INSTALLATION INNOVATION FOR FLOATING OFFSHORE WIND

Floating offshore wind turbines are an emerging technology with notable prototype and demonstration projects being installed in recent years. Future floating wind farms enable the access to significant new wind resources in expanses of water too deep for conventional, bottom-fixed farms. Spar, barge, TLP and semisubmersible types have been deployed as demonstration units. Pre commercial units have been installed off the coasts of Portugal and the East Coast of Scotland. This paper discusses naval architecture requirements for the temporary conditions of construction, ocean transport and installation. The requirements of Marine Warranty Surveyor guidelines for temporary conditions and the Classification Society requirements during the temporary phase are also taken into account. It is expected that major offshore maintenance will be carried out on floating offshore wind turbines by towing them back to more sheltered port locations. This paper is a literature and guideline review with additional information on intact stability during the tow to the offshore location. Thus, marine operations play a pivotal role throughout all phases of a floating wind farm’s life cycle. In particular, uncertainties associated with offshore installation work can extend construction schedules and increase the capital expenditure required for the project. This paper will be of interest to researchers and practitioners in the floating wind sector, considering innovative installation methods as a means to reduce overall project lifecycle cost.

Spatio-Temporal Metocean Measurements for Offshore Wind Power

This paper presents the case for the use of HF radar to provide wave, current and wind measurements and maps during the surveying, resource and impact assessment, construction, maintenance and performance assessment phases of an offshore fixed or floating wind farm or other marine renewable project. The data presented are from the Celtic Sea which is currently the focus of a lot of offshore wind interest. The data are from a dual radar system deployed at the Wave Hub site off the Cornwall coast since 2011, a single radar system in North Devon reactivated in 2017, and data from 2005 when the North Devon radar was operated as a dual radar with a second site in South Wales. The accuracy of the wave and wind data is discussed and examples of the sort of data that could be available are presented.

Assessing intermittency characteristics via cumulant analysis of floating wind turbines wakes

Turbulence intermittency in the wake behind a single floating wind turbine as well as merging wakes due to a pair of floating turbines is investigated using magnitude cumulant analysis and non-analytical cumulant analysis. This low-order statistical approach is used to compute the intermittency for its impact on fatigue loading and power output signals. In the near wake, a 60% increase in the intermittency coefficient compared to the inflow is found. Pitch motion causes a 17% increase in intermittency compared to fixed turbines. The pitch-induced intermittency depletes in the far-wake, and hence, investigating whether a pitch-induced intermittency of one turbine affects a successive one in a wind array setting is recommended. Non-local scale interactions near rotor tips are observed as undulations in the cumulant profiles, referred to as tip-effect fluctuations. The impact of turbulence intensity on intermittency is also examined, and a positive correlation between the two is found in the near-wake. In the far-wake, however, it is found to speed up the pitch-induced intermittency depletion. The wake merging region between two neighboring turbines experiences lower intermittency and damps tip-effect fluctuations. This work provides more reliable intermittency estimation by utilizing lower moment statistics. The findings aid description, turbulent loading quantification, and stochastic modeling for floating wind farm wakes as well as fixed ones for both single and merging wakes.

Dynamic Response of Floating Wind Farm Platform Based on Barge Platform under Common Sea Conditions

Dynamic Response of Floating Wind Farm Platform Based on Barge Platform under Common Sea Conditions

Influence of wakes and atmospheric stability on the floater responses of the Hywind Scotland wind turbines

AbstractAs the worlds first floating wind farm, one of the main technical challenges in the design phase of Hywind Scotland was the uncertainty related to wake interaction effects between the floating wind turbines. In this paper, we address this challenge by presenting an analysis of full‐scale measurements from the Hywind Scotland wind farm. Measurements of the floaters' roll, pitch and yaw motions are presented, both in the form of statistical data and response spectra. The floater responses of a turbine in free wind and a turbine in wake are compared, and the influence of different atmospheric stabilities on the floater motions is investigated. Despite the large distance between the turbines of 9 rotor diameters, wake effects in the measured floater motions are observed at the downstream turbine. Furthermore, both the wake responses and the free wind responses show a clear dependency on atmospheric stability. However, overall motions are small for all wind speeds, showing that the design performs satisfactorily in both free wind and wake conditions.

Motion and Whiplash Effect of a Floating Crane Model und er Wave Load: Experiment

Zhou, J.; Wang, H., and Jiang, Z., 2020. Motion and whiplash effect of a floating crane model under wave load: Experiment. In: Zheng, C.W.; Wang, Q.; Zhan, C., and Yang, S.B. (eds.), Air-Sea Interaction and Coastal Environments of the Maritime and Polar Silk Roads. Journal of Coastal Research, Special Issue No. 99, pp. 346–357. Coconut Creek (Florida), ISSN 0749-0208.The top parts of tall terrestrial buildings are sometimes damaged or even destroyed during strong earthquakes because of the whiplash effect. Similarly, the marine floating high-rise multibody structure with a floating base may experience the whiplash effect even more easily, which means that marked motion of the upper part of the structure will occur accompanying minor motion of the floating base under the action of an external load induced by a wave or seismic load. The whiplash effect would threaten the operation and the survival of these offshore high-rise platform structures.In this paper, a physical experiment involving a floating crane without a mooring system under wave loads was set up. The data and results were analyzed and discussed mainly in terms of the motion and the whiplash effect of the floating crane. The whiplash coefficient is defined to estimate the magnitude of the whiplash effect. Some factors, including wave amplitude, wave length, boom angle and boom length, are investigated to determine how they affect the motion and the whiplash effect of the floating crane. Some suggestions are given to control the whiplash effect, and those are useful for the operation of offshore floating platform structures, such as the oil-drill platform, the floating wind farm, the floating crane and some other high-rise marine floating structures.