Floating Wind Farms Research Articles

An analysis of floating wind turbine towing operations using OpenFAST

Abstract The floating wind industry is slowly entering the commercialisation phase and array-scale floating wind farms are imminent. Irrespective of the type of floater used, towing operations represent a crucial marine activity required during installation, major repairs and decommissioning phases. Numerical analysis of towing operations is vital for predicting hydrodynamic motions and towing loads, enabling the identification of metocean limits crucial for achieving optimised safe and efficient execution. This paper presents a unique approach to utilise OpenFAST for the examination of towing operations. Compared to other numerical analysis tools available in the market, OpenFAST stands out as a free, open-source tool specifically designed for wind turbine analysis. The study introduces and evaluates an analytical method using OpenFAST, demonstrating its efficacy in modelling towing dynamics, predicting forces and assessing motion responses of a semi-submersible floating wind turbine in varying wave conditions. The numerical simulations are compared against the results from an experimental campaign. The capability of the method in simulating towing dynamics and the prediction of motion responses are discussed.

Design optimization of floating offshore wind farms using a steady state movement and flow model

Abstract In this study, we demonstrate how to carry out the design optimization of floating offshore wind farms by considering the impacts brought by the movements of the floating wind turbines. A steady state movement and flow model is applied in the modelling process. This model is developed by building a turbine surrogate model for estimating the steady state movement and power production of floating wind turbines and incorporating it in an open-source static wind farm simulator, PyWake. Using this modelling methodology, layout optimization problems of floating offshore wind farms are solved by using algorithms like Random Search to maximize the energy yield while satisfying certain constraints. Case studies are carried out for two wind farms with met-ocean conditions from a real planned site in Scottland to show the potential of layout optimization for floating wind farms.

Improving O&M Simulations by Integrating Vessel Motions for Floating Wind Farms

Improving O&M Simulations by Integrating Vessel Motions for Floating Wind Farms

Optimization of Connection Parameters of Self-Adaptive Modular Floating Wind Farms

Connection parameters are the key factors influencing the responses of modular floating structures; due to the complexity of structural response properties, the assessment and optimization of connection parameters are still vital issues in designing modular floating structures. In the present work, for a novel structural configuration of self-adaptive modular floating wind farms based on existing works from the case of a mobile offshore base, a quantified approach for the assessment of connection parameters is established based on frequency domain numerical analysis taking into account both the economic effects and generalized performance. Based on the quantified assessment, an optimization process is carried out, to obtain a connection parameter combination. From the optimized connection parameters, it can be found that the most appropriate tri-axial stiffness according to present studies is in the magnitude from 1 × 106 to 7 × 107 N/m, and the damping ratio is close to 1.0 for most connection structures. By contrast with feasible uniform connection parameters, the optimization methodology is confirmed to be able to reduce both connection parameters and responses. Then, a time domain approach for the calculation of motions of interconnected modular floating structures taking into account geometry nonlinearity is proposed and obtained in good accordance with the frequency domain results, and the effectiveness of both the frequency domain and time domain is validated.

A review of the harvesting methods for offshore renewable energy – advances and challenges

The present work offers general information about present-day and developments in offshore renewable energy, specially of wind, wave and the solar energy harnessing structures. In the introduction, the authors raise awareness of the despite more untapped potentials that exist in the oceans and the offshore Wind Energy Market that is experiencing a steep rise in the recent past due to technological advancement and the great policies that support this energy source. This mainly focuses on the very huge additionality of offshore wind power and the improvements in floating solar PV systems. Section three outlines an assortment of studies that were done by different writers on the strengths and weaknesses of offshore renewable energy technologies through a meta-analysis of the literature. The method of data extraction revolved around several factors, namely technological admissibility, resource identification, location and environmental and economic factors. The sources used comprised of scholarly articles published within the peer reviewed journals in the period of 2013 to 2024, to ensure that the study offered a comprehensive analysis on the technological advancements. The results and discussion section gives an analysis of the results achieved and demonstrates the developments in Offshore Wind Energy, Wave Energy Conversion, and Floating Solar PV Systems. Thus, offshore wind energy is described as the rapidly evolving segment and particular focus is made on the floating wind farms and their advancements in the aspects of power density and structural stability. Wave energy converters are discussed regarding their applicability to complement hybrid electricity production despite limited data on the devices’ performance. Another key feature is that the FFPV systems are reported to be more efficient and cheaper than the land mounted systems. Thus, the article emphasizes the need to produce the further literature on offshore renewable energy, political support, and cooperation between different sectors. It concludes that an offshore renewable energy has the potential for the future development due to advancement in the technology as well as due to environmental factors.

Wake Mixing Control For Floating Wind Farms: Analysis of the Implementation of the Helix Wake Mixing Strategy on the IEA 15-MW Floating Wind Turbine

Wake Mixing Control For Floating Wind Farms: Analysis of the Implementation of the Helix Wake Mixing Strategy on the IEA 15-MW Floating Wind Turbine

Preliminary Techno-Economic Study of Optimized Floating Offshore Wind Turbine Substructure

Floating offshore wind turbines (FOWTs) are still in the pre-commercial stage and, although different concepts of FOWTs are being developed, cost is a main barrier to commercializing the FOWT system. This article aims to use a shape parameterization technique within a multidisciplinary design analysis and optimization framework to alter the shape of the FOWT platform with the objective of reducing cost. This cost reduction is then implemented in 30 MW and 60 MW floating offshore wind farms (FOWFs) designed based on the static pitch angle constraints (5 degrees, 7 degrees and 10 degrees) used within the optimization framework to estimate the reduction in the levelized cost of energy (LCOE) in comparison to a FOWT platform without any shape alteration–OC3 spar platform design. Key findings in this work show that an optimal shape alteration of the platform design that satisfies the design requirements, objectives and constraints set within the optimization framework contributes to significantly reducing the CAPEX cost and the LCOE in the floating wind farms considered. This is due to the reduction in the required platform mass for hydrostatic stability when the static pitch angle is increased. The FOWF designed with a 10 degree static pitch angle constraint provided the lowest LCOE value, while the FOWF designed with a 5 degree static pitch angle constraint provided the largest LCOE value, barring the FOWT designed with the OC3 dimension, which is considered to have no inclination.

A study on the dynamic characteristics of alternative arrangements of floating wind farms with varying hub heights

Wind farms with multiple hub heights have the potential to effectively mitigate velocity deficits resulting from wake effects and reduce the levelized cost of energy (LCOE). While existing research has predominantly focused on studying wake effects on floating wind farms with identical hub heights, there is a notable absence of research on floating wind farms with multiple hub heights. Therefore, a comprehensive understanding of the impact of vertical arrangements on floating wind farms is essential. In light of this gap, this study examines the characteristics of two distinct arrangements of a semi-submersible floating wind farm with multiple hub heights. The configuration includes two 15 MW semi-submersible floating offshore wind turbines (FOWT) and two 5 MW semi-submersible FOWTs. A novel wind farm modeling tool utilizing dynamic wake meandering (DWM) is employed to investigate the power production performance, wake characteristics, global dynamic responses, and fatigue damage of crucial components of each individual FWT, associated with the two different arrangements. The paper presents a discussion of the advantages and disadvantages of the two arrangements, accompanied by a summary of the key findings. The insights gained from this research can serve as a foundational basis for improving the design and analysis processes of floating wind farms with various arrangements.

Research on the Power Output of Different Floating Wind Farms Considering the Wake Effect

For floating wind turbines, one of the most interesting and challenging issues is that the movement of the rotor is strongly related to its floating platform, which results in corresponding variations in the wake characteristics of the turbine. Because the aerodynamic efficiency of the downstream turbines is affected by the wake characteristics, the power output will consequently vary depending on the different types of floating wind turbines and floating wind farms used. In this study, the rotor movement, wake characteristics, and corresponding wind farm power output are analyzed using a numerical method for three typical floating wind turbines: the semisubmersible type, spar buoy type, and tension leg platform type with a 5 MW configuration. A fixed-bottom monopile wind turbine is adopted as a benchmark. The simulation results show that of the three floating wind turbines, the rotor position and wake center are most dispersed in the case of the spar buoy type, and its wake also has the lowest impact on downstream wind turbines. Additionally, the power output of the corresponding spar buoy type wind farm is also the highest at different wind speeds, followed by the semisubmersible type, tension leg platform type, and then the fixed-bottom type. In particular, at low wind speeds, the wake effects differ significantly among the various types of wind turbines.

The impact mechanisms of intermediate water depth on the coupled dynamic responses of large-capacity floating wind turbines

ABSTRACT The currently planned floating wind farms in China mostly have water depths in the intermediate range. Therefore, investigating the impact mechanisms of intermediate water depths on the coupled dynamic responses of floating wind turbines is of significant importance. In comparison to deep water, mooring systems in intermediate water depths are more prone to experiencing catenary shape loss and stiffness. The contribution of difference-frequency effects increases with decreasing water depth, resulting in a more substantial impact on low-frequency responses. The Full Quadratic Transfer Function (QTF) method accurately captures low-frequency responses. Placing clump weights in the bottom section of the mooring line effectively restricts the displacement range of floating turbines while maintaining average fairlead tensions at levels similar to the other two forms. On this basis, focusing on the most optimal mooring system performance, experiments were conducted to validate the coupled dynamic responses of floating wind turbines in intermediate water depths.

A novel efficient RFEM for reliability analysis and design of multi-line dynamically installed anchor for floating offshore wind turbines

A novel multi-line dynamically installed anchor was previously proposed by the authors to allow for the mooring of multiple floating offshore wind turbine, resulting in a significant reduction in the total number and cost of anchors required for floating wind farms. Considering the spatial variability of soil properties and the uncertainty of environmental loads, the present study performs reliability analysis and design of the multi-line dynamically installed anchor. Firstly, a strategy to repeatedly use fundamental random variables is proposed and validated for reducing the number of random variables used in Karhunen-Loève expansion in the simulation of random field of soil properties when the ratio of the soil domain dimension to the scale of fluctuation is large. Then, the efficiency, accuracy, and robustness of the RFEM (random finite element method) combined with K-MCS (Kriging model and Monte Carlo simulation) based on the proposed strategy are validated through examples of random capacity of foundations. Next, the random capacities and probabilistic VHMT failure envelopes of the multi-line dynamically installed anchor in spatially variable soil are investigated. Finally, the reliability design of multi-line dynamically installed anchors is conducted and compared with that of multi-line pile anchors, in which both the spatial variability of soil and the uncertainty of loads are condidered. The results show that the costs for multi-line dynamically installed anchors are obviously less than those of multi-line pile anchors.

Bearing performance of a novel caisson–plate gravity anchor

To provide a more reliable shared anchor for floating wind farms, a novel caisson–plate gravity anchor (CGA) is proposed. This design merges the benefits of both gravity anchors and suction caissons. Centrifuge model tests adopting only half of each anchor were carried out to study their bearing performance in sand. In addition, particle image velocimetry analyses were performed to monitor anchor movement and soil displacement. As supplementary data, numerical simulations with an advanced hypoplasticity model were also conducted to reveal the anchor capacity mobilisation mechanism. Findings indicate that the novel CGA possesses a significantly higher bearing capacity compared to standalone caisson or plate designs. By adding a plate above the caisson and increasing its weight, the anchor failure modes may shift from forward rotation to translational movement. In addition, this adjustment may transition the brittle failure to a more reliable ductile failure. This augmented capacity of the CGA stems from the expanded soil mobilisation region and increased soil stress level in front of the caisson. The proposed CGA provides a promising solution for shared anchors in floating wind farms.

Dynamic analysis of an improved shared moorings for floating offshore wind farm

Shared mooring lines have demonstrated their effectiveness in reducing the installation costs of floating offshore wind farms by minimizing the requirement for multiple anchors. However, this innovation has also brought complex restoring properties and a greater tendency towards resonance. To tackle this challenge, this research presents a novel approach for shared mooring systems, implemented in a 2 × 2 orthogonal wind farm arrangement featuring 5 MW wind turbines installed on the Barge platform. Through the application of FAST and AQWA, a comparative analysis is conducted juxtaposing the original mooring (OM) and three new mooring models, namely buoy mooring (BM), clump weight mooring (WM) and buoy clump weight mooring (BWM). A comprehensive examination is carried out to assess the impact of on platform and mooring characteristics. The results show that the BM can effectively reduce the platform's surge and sway response, and that the mooring tension and laid length decrease as the net buoyancy increases. The WM increases the response amplitude at the yaw direction. The BWM with link buoys helps to improve the dynamic response of the platform and increases the length of the mooring laid. This analysis provides valuable insights for the design of floating wind farms incorporating shared mooring systems.

Characterization of the offshore wind dynamics for wind energy production in the Gulf of Lion, Western Mediterranean Sea

A ground-based wind lidar system has been deployed on a coastal landmass off Marseille in the Gulf of Lion, western Mediterranean Sea. This location holds significant relevance as it anticipates the imminent deployment of floating wind farms. Over the course of one year, a comprehensive wind dataset was collected by a lidar profiler at altitudes ranging from 60 to 220 m above sea level, aiming to assess the wind resource potential. This study presents an analysis of monthly wind metrics, including key parameters such as wind speed, wind shear exponent, and turbulence intensity. Weibull distributions are provided, along with their scaling and shaping parameters, to elucidate the probability distribution of wind speeds. The focus extends to the diurnal variation of wind metrics and monthly wind speed vertical profiles. Our results indicate that, at an altitude of 140 m above sea level, the one-year average wind speed is 8.3 m/s, with a turbulence intensity (TI) of 13.0 %. The mean wind shear exponent is quantified at 0.077. Notably, the highest wind speeds are consistently observed between 12:00 and 15:00, coinciding with lower values of TI and wind shear exponent, while night-time reveals high levels of both TI and wind shear exponent. Furthermore, an examination of wind direction unveils a bi-modal pattern with a slight variation, specifically wind veer, at each measurement height relative to the 140 m altitude. Additionally, our study explores low-level jets (LLJs), revealing that 80 % of these phenomena occur at altitudes below 140 m, predominantly during the summer period. The mean LLJ core speed, averaged across all measurement heights, is found to be 8.4 m/s.

Integrated floating wind farm layout design and mooring system optimization to increase annual energy production

As we cluster wind turbines in wind farms to gain energy from sites with high wind speeds, wake losses occur within the wind farm. Wake loss is a term used to describe the lower energy production of a downwind turbine that is totally or partially in the wake of an upwind turbine. To decrease wake losses inside the wind farm, the wind farm’s layout is optimized. However, a variety of factors constrain the wind farm layout optimization, such as the size of the lease area relative to the number of turbines to be placed, or the shape of the lease area. Therefore, many wind farms end up with a regular grid layout, such as the Horns Rev 1 wind farm in the North Sea. The ability of a floating offshore wind turbine (FOWT) to change its position based on the wind direction and its mooring system design presents an opportunity to further decrease wake losses in floating wind farms. In this work, we integrate the design of the FOWT mooring systems with the floating wind farm layout design with the goal of increasing the farm’s annual energy production. We use the Horns Rev 1 wind farm as a case study to demonstrate our method. The results show that allowing the FOWT to relocate can decrease wake losses up to 18%. Moreover, the newly developed mooring systems are less stiff and therefore allow larger motion of the FOWT; hence, the material cost of the mooring system decreases by an estimated 17%.

Design of a robotic platform for hybrid wind tunnel experiments of floating wind farms

Wind tunnel experiments incorporating factors like realistic ambient wind conditions, merging of multiple wakes, and active wake controls are needed to understand and improve modeling of floating wind farms. A key technology for this kind of experiments is the robotic system emulating the wind turbine motion. This article addresses the design of a robotic platform with three degrees-of-freedom (surge, pitch, and yaw) specifically tailored for wind tunnel experiments on floating wind farms. This robotic system aims to accurately reproduce the motion spectrum of floating wind turbines of 10-22MW and to simulate rotor-atmospheric wind interactions. The robotic platform has a compact design to be positioned in multiple units inside the wind tunnel and avoid disturbing the wake of the wind turbine on top of it. To achieve these goals, the wind turbine is partially integrated in the robotic platform that employs a parallel kinematic scheme and has all actuators close to the wind tunnel floor.

Influence of platform motion on the energy production of a floating wind farm

This study investigates the dynamics of energy production in floating wind farms. Unlike their bottom-fixed counterparts, floating wind turbines experience large-amplitude, low-frequency movements affecting the rotor response and the wake development. We employed the multi-physics simulator FAST.Farm to study a seven-turbine wind farm, comparing conventional monopile foundations with semi-submersibles. Results show that, under undisturbed wind conditions, floating turbines exhibit a lower power-conversion efficiency due to platform tilt and the use of a thrust clipping controller. Conversely, waked turbines in a floating configuration have a higher power output than with a bottom-fixed foundation. This is attributed to the higher wind speed in their wake which is due to the lower thrust set point of the floating controller, the vertical deflection of the wake and the dynamic conditions at rotor created by motion.

Passive Mooring-based Turbine Repositioning Technique for Wake Steering in Floating Offshore Wind Farms

Power loss due to wake effects from upstream wind turbines is an important factor in the design of floating wind farms. These wake disturbances also increase fatigue loads on downstream units. Economic-driven wind farm layout optimization may culminate in non-standard, irregular configurations of offshore wind farms that deviate from conventional engineering practices. Consequently, wind farm developers are inclined towards a more geometrically coherent layout that are sub-optimal. Floating wind turbines horizontal offsets can be used to overcome wake losses. In this study, a novel method suggesting various mooring orientation methods to passively reposition the wind turbines in the farm to maximize annual energy yield. Preliminary parametric optimization demonstrates the effectiveness of the proposed method for standard floating wind farm designs to reduce wake effects by as much as 30% at rated wind speed compared to a baseline case, while preserving the farm’s overall uniformity.

Floating wind farm design using social and environmental constraints

This work proposes a wind farm design methodology, integrating several design variables from different design aspects into an optimization problem, such as turbine power, number of turbines, cable types, wind farm layout and site location. A mixed integer genetic algorithm is employed to combine discrete and continuous design variables to find the design with minimum Levelized Cost of Energy (LCoE). The wind farm LCoE is calculated using a wind farm model, which combines detailed cost functions for different cost elements and engineering wake models to estimate Annual Energy Production. The design is constrained not only by technical aspects such as total power, farm area, but also by environmental and social constraints. These include the wind farm visibility, which is a popular concern among the people living along the coast of nearby wind farms, and availability, implying the compliance with the designated exclusion zones. To demonstrate the sensitivity of design constraints, two floating wind farms are sited and optimized as a case study, using different visibility constraints. The developed design tool within this study aims to bridge the gap between wind farm developers and local authorities who are responsible for permitting and zoning of development areas.

Assessing the impacts of wakes on floating wind farms with shared anchors

This paper examines wake effects for floating wind farms with shared anchors. Three 20-turbine farms are examined: a grid-formation baseline with no shared anchors, a farm based on 3-line anchors, and a farm based on 6-line anchors, governed by a wind turbine spacing of 8 rotor diameters. The IEA 15 MW reference turbine on the UMaine semisubmersible platform was used with a taut mooring system in deep- water depths representative of U.S. west coast lease areas. A steady-state wake model showed that, when evaluating a sweep of wind headings, the baseline design had the lowest wake losses, with a value of 11.7 %, followed by the 6-line at 12.9% and the 3-line at 13.8%. Dynamic simulations were run in FAST.Farm to analyse the effects of wakes on mean anchor loads for wind headings that showed significant wake losses. The baseline farm showed the largest anchor load reductions due to wake effects (up to 16%), followed by the 3-line farm (up to 8%), and the 6-line farm, which showed relatively consistent load magnitudes on the 6-line anchors across all headings.