bluuebunny/crossref_metadata_2025_split huggingface dataset:
Development of a novel method for the correction of the nacelle wind speed in stall-controlled wind turbines
Authors: Vivas Larisa , Papi Francesco , Papatsiros Vasilis , Maudhuit Olivier , Bianchini Alessandro 
Published: June 2024

Abstract
Accurate estimation of the oncoming wind is key to ensure an accurate control of any wind turbine. The wind speed is commonly measured with an anemometer located on the nacelle; hence, the measurement is influenced by the rotor and the nacelle itself and needs to be corrected so as not to incur inaccurate energy yield assessments. This study introduces an innovative method for correcting the nacelle wind speed in stall-controlled wind turbines. The development of the method has benefitted from the unique possibility of exploiting two datasets containing 10-minute averaged wind data from two identical EUNICE EW16 wind turbines and a meteorological mast located at the same site. The innovative method is systematically compared with the Nacelle Transfer Function outlined in the IEC 61400-12-2, serving as a benchmark for evaluation. The high accuracy and simplicity of the proposed method make it particularly suitable for the optimization of wind turbine performance in industrial applications. Moreover, an accurate estimation of the incoming wind speed can enable innovative control techniques, such as those based on Tip-Speed-Ratio (TSR) tracking. This is addressed in the study through simulations by comparing a TSR-Tracking strategy with the most common k-ω2 strategy. The study demonstrated that the TSR-Tracking strategy could be adopted in stall-controlled wind turbines if an accurate estimation of the free-stream wind speed is available.
Evaluation of LES-based time-decoupled model-predictive control in different wind farm layouts
Authors: Janssens Nick , Meyers Johan 
Published: June 2024

Abstract
Very recently, Janssens and Meyers (Wind Energy Sci., vol. 9, 65–95, 2024) proposed a time-decoupled model-predictive control (TD-MPC) framework for wind farm power optimization using a control model based on coarse-grid large-eddy simulation (LES). In a receding-horizon fashion, by computing the controls for the next time window based on a prediction of the flow (so ahead of time), they achieved (almost) real-time computational speed. The current paper further explores the potential of this approach in the context of dynamic yaw control, under the assumption of exact state knowledge. To that end, the LES-based, TD-MPC framework is validated on a reference wind farm for three different wind directions, for which we observe gains ranging from 4 (for staggered configurations) to 42% (for aligned configurations w.r.t. the wind direction). The LES-based controller always outperforms a Betz optimal controller and a static (wake model based) yaw controller at near real-time speed. An analysis of the yaw angles reveals that the framework is very effective in steering the wakes away from downstream turbines in upstream and downstream regions, synchronized to the turbulent inflow. By comparing the performance of the LES-based controllers (based on the actuator disc turbine model) against a reference simulation that uses a more accurate actuator sector model, we illustrate the robustness of the approach in the presence of the additional model error.
Active control of yaw drift of single-point moored wind turbines
Authors: Dos Santos C R , Stenbro R , Stieng L E , Hanseen-Bauer Ø W , Wendt F , Psichogios N , Aardal A B 
Published: June 2024

Abstract
Single-point moored floating wind turbines can benefit from the self-alignment of the structure with the prevailing wind direction. However, to be successful, the effects of yaw-drift must be mitigated using effective control strategies during power production. In this work, we investigate sources contributing to yaw drift and propose active control solutions to the problem. The analyses utilize the IEA 15 MW wind turbine mounted on a single-point moored floating foundation. Aero-hydro-servo-elastic simulations using the software 3DFloat are performed under various conditions of wind, waves and current. The results indicate that yaw drift can be actively controlled using nacelle-yaw actuation techniques and individual pitch control of the blades. These approaches effectively align the rotor with the wind direction, increasing the robustness of single-point wind turbines by ensuring increased power production, and maintaining the structural life.
A control-oriented load surrogate model based on sector-averaged inflow quantities: capturing damage for unwaked, waked, wake-steering and curtailed wind turbines
Authors: Guilloré A , Campagnolo F , Bottasso C L 
Published: June 2024

Abstract
This paper presents a novel approach to constructing a load surrogate model. The surrogate estimates the damage equivalent loads (DELs) of a wind turbine of a given type regardless of its position within a wind farm, and under various farm control actions. The model relies solely on local inflow quantities (sector-averaged wind speeds and turbulence intensities) and local control parameters (rotor speed, pitch angle, and yaw misalignment). Despite its highly simplified representation of the complex behavior of the turbulent wind field, wake effects, and controller dynamics, these quantities prove sufficient to characterize DELs. The paper demonstrates the training of this load model within a simulation environment. Validation results using a different wind farm configuration indicate that the surrogate can accurately predict fatigue loads for both unwaked and waked turbines, encompassing scenarios of wake steering and induction control.
Impact of wake steering on loads of downstream wind turbines at an above-rated condition
Authors: Thedin R , Kreeft J , Barter G , Jonkman J , Shaler K 
Published: June 2024

Abstract
Wake steering strategies often seek to gain power at the expense of increased fatigue loads. Here, we investigate the feasibility of applying wake steering at an above-rated condition. In such a condition, the farm is operating at rated power, and thus, increased power output is not the goal. Instead, wake steering is considered in the context of load reduction. We perform a sweep of wind directions and yaw misalignment angles, ranging from negative to positive values. This approach allows us to obtain trends and identify asymmetries in turbine response for symmetric scenarios. We use a wind farm consisting of five aligned IEA Wind 15-MW reference wind turbines, and analyze trends related to the blade-root, low-speed shaft, and tower-base moments, both in terms of standard deviation and damage equivalent loads. We show that for any given fixed wind direction, the turbines can be yawed such that the fatigue loads are reduced. Reductions of up to 5% (depending on the component) in terms of standard deviation and damage equivalent loads can be achieved by negatively yawing the turbine. A negative yaw misalignment has shown to be the direction of larger improvements. Such results contrast those found for below-rated conditions, where a positive yaw misalignment is typically preferred. However, since load reduction is not uniform across all component loads, more study and consideration is required before operational recommendations can be made.
Uncertainty quantification of wind turbine fatigue lifetime predictions through binning
Authors: Sadeghi N. , Noppe N. , Morato P. G. , Weijtjens W. , Devriendt C. 
Published: June 2024

Abstract
Aging wind energy assets demand the development of methods able to effectively support informed decision-making. These needs have inspired the use of data-driven methodologies, which offer valuable insights to wind turbine owners and/or operators. Many approaches can be found in the literature for extrapolating fatigue damage measurements to estimate the lifetime of wind turbines. In some cases, resampling approaches are proposed to compute the confidence levels associated with the generated projections, yet a standardized framework has not been adopted. Most reported studies identify the relationship between short-term damage and long-term Environmental and Operational Conditions (EOCs) by mainly rendering mean lifetime predictions and their associated confidence levels, whereas additional predicted lifetime statistical information is usually overlooked. In this work, we showcase the importance of properly accounting for the variability in lifetime predictions, describe how to summarize binned damages using statistical estimators and investigate bootstrapping variants for computing the confidence levels in the generated damage estimators.
Data-driven forecasting of FOWT dynamics and load time series using lidar inflow measurements
Authors: Gräfe Moritz , Pettas Vasilis , Cheng Po Wen 
Published: June 2024

Abstract
This study focuses on forecasting the fairlead tension and floater dynamics time series of floating offshore wind turbines (FOWTs) using a data-driven approach that incorporates onboard sensor measurements and lidar inflow data. Sensors on FOWTs can provide data on turbine dynamics, such as rotational and translational movements, and load metrics like mooring line loads. However, these sensors are limited to current state measurements and do not provide future signal projections. In this research, we investigate a data-driven forecasting methodology using a simulated dataset. This dataset encompasses FOWT responses to diverse environmental conditions and the associated lidar measurements. Utilizing a Long Short-Term Memory (LSTM) sequence-to-sequence model, this study forecasts the time series of fairlead tension, surge, and pitch for forecasting horizons of 20, 40, and 60 seconds, considering lidar ranges from 100m to 500m. The performance of these forecasting models is benchmarked against a simple persistence model. The results indicate that incorporating lidar inflow measurements significantly improves the forecasts of fairlead tensions and platform motions. The enhancement for pitch motion forecasts is observed across all forecasting horizons. For fairlead tension and surge motion, the enhancement is observed for the longer horizons of 40s and 60s. These findings underscore the value of lidar data in accurate forecasting and emphasize the need to account for the interplay between lidar range, wind speed, and forecasting horizon to achieve optimal forecast accuracy.
Boosting field data using synthetic SCADA datasets for wind turbine condition monitoring
Authors: Milani Ali Eftekhari , Zappalá Donatella , Castellani Francesco , Watson Simon 
Published: June 2024

Abstract
State-of-the-art Deep Learning (DL) methods based on Supervisory Control and Data Acquisition (SCADA) system data for the detection and prognosis of wind turbine faults require large amounts of failure data for successful training and generalisation, which are generally not available. This limitation prevents benefiting from the superior performance of these methods, especially in SCADA-based failure prognosis. Data augmentation approaches have been proposed in the literature for generating failure data instances within a SCADA sequence to reduce the imbalance between healthy and faulty state data points, which is relevant to fault detection tasks. However, the successful implementation of DL-based failure prognosis methods requires the availability of multiple run-to-failure SCADA sequences. This paper proposes a data-driven method for generating synthetic run-to-failure SCADA sequences with custom operational and environmental conditions and progression of degradation. An Artificial Neural Network (ANN) is trained with signals that represent these factors to reconstruct the SCADA signals. Then, it is used to generate synthetic SCADA datasets based on data available from a wind turbine that experienced a gearbox failure. Synthetic data sets generated are evaluated on the basis of the similarity of their signal distributions, the temporal dynamics within each signal, and the temporal dynamics among different SCADA signals with those in similar field datasets. The results show that the generated synthetic datasets are consistent with their field counterparts, with a comparatively lower diversity in their dynamic behaviour in time.
Optimal tuning of individual pitch control using economic goal-oriented objectives
Authors: Aktan H D , Bottasso C L 
Published: June 2024

Abstract
Individual pitch control (IPC) is a method developed to cope with fatigue loads, which works by actively changing the pitch angles of each blade based on feedback. While beneficial for fatigue damage, the use of IPC leads to some reduction in yield and an increase in pitch activity, which can influence operation and maintenance (O&M) costs. Tuning of the IPC parameters plays a significant role, as different settings could result in different trade-offs among lifetime, yield, and O&M costs. In this paper, an optimal parameter tuning method for IPC for existing turbines is proposed. The effects of IPC on competing objectives, i.e. energy production, pitch system wear, and fatigue life are utilized to maximize the long-term profit based on given constraints. The proposed approach is demonstrated in a simplified scenario, where the tower is the only critical component that requires damage reduction to achieve a target lifetime. The performance of the proposed approach is compared to a standard tuning that targets load reductions in terms of d- and q-axis components. Results indicate that the proposed optimal tuning approach provides IPC gains that meet the desired lifetime of the component, and that improve profit compared to the standard approach.
Erosion-safe operation using double deep Q-learning
Authors: Visbech Jens , Göçmen Tuhfe , Réthoré Pierre-Elouan , Hasager Charlotte Bay 
Published: June 2024

Abstract
Leading edge erosion on wind turbine blades can reduce aerodynamic efficiency and cause increased maintenance costs, potentially impacting the overall economic viability. Erosion-safe operation is the concept of reducing the blade tip speed during periods of heavy rain, thereby significantly reducing the erosion development and progression. This study explores the application of reinforcement learning, namely using a double deep Q-network, to implement erosion-safe operation. The proposed methodology involves learning a policy for tip speed control that maximizes revenue over a specific period of time. We demonstrate the concept based on 5 years of simulation of the DTU 10MW reference turbine and mesoscale weather simulation from Horns Rev. The trained model was found to increase the cumulative revenue by 1.6 % compared to not using erosion-safe operation. The model was able to effectively adapt to varying weather conditions and stochastic damage progression. Based on 10,000 random simulations, the trained model outperforms two baseline models in more than 98 % of the simulations.
Analysis and evaluation of two reference LiDAR-assisted control designs for wind turbines
Authors: Steinmann Perez Cedric D. , Lio Alan W.H. , Meng Fanzhong 
Published: June 2024

Abstract
LiDAR-assisted wind turbine control holds promise in reducing structural loads and enhancing rotor speed regulation. However, a research gap exists in the practicality and limitations of commercially available fixed-beam LiDARs for large turbines and evaluating commonly employed LiDAR-assisted feedforward approaches. This study addresses these gaps by examining the implications of utilizing fixed-beam LiDARs in two wind turbine sizes and two reference LiDAR-assisted control strategies. A comprehensive evaluation considers coherence variations, uncertainties related to inaccurate pitch angle mapping with the upcoming wind speed, and their combined impact on load reduction. Numerical simulations reveal that an excessively low cut-off frequency in the low-pass filter can compromise preview time compensation. This is problematic in larger turbines, where coherence with limited LiDAR beams is inferior compared to smaller wind turbines, which deteriorates the effectiveness of the LiDAR-assisted control. Among the reference LiDAR-assisted control methods, the evaluation indicates the Schlipf approach has greater load reduction independence, while Bossanyi’s approach, which uses measurement of current blade pitch, yields positive results with fine-tuned baseline controllers. However, allowing baseline controller-induced frequencies to propagate into the controller may increase system excitation at certain frequencies due to the use of the actual pitch angle for feedforward pitch rate calculation.
Controller design for the X-Rotor offshore wind turbine concept
Authors: Recalde-Camacho L , Leithead W , Morgan L , Kazemi Amiri A 
Published: June 2024

Abstract
This paper explores the design of a full envelope speed controller to operate the X-Rotor Offshore Wind Turbine. The X-Rotor is a heavily modified V-rotor vertical axis wind turbine, in which the primary rotor has conventional blades angled both up and down from the ends of a relatively short and stiff cross-arm. The upper half employs full span blade pitching for speed regulation and the lower half is aimed at reducing overturning moments on the main bearing and provides power take-off through compact secondary horizontal axis turbines mounted at the tip of the lower blades. The operational strategy is somewhat similar to that of a variable speed pitch regulated horizontal axis wind turbine, however it differs in the following aspects: the way aerodynamic torque is balanced across the operating envelope, the adjustment of equilibrium operating points at below rated operation, the relationship of aerodynamic torque on the primary rotor to pitch angle, and the operation of the secondary rotors to increase energy capture. These aspects increase the complexity of the control strategy but also ease the controller requirements. The developed controller is tested on a turbine model with sufficient complexity to model the essential dynamic properties of the turbine concept.
Analysis of Power-Maximizing Region 2 Controllers for Wind and Marine Turbines
Authors: Stockhouse David , Zalkind Daniel , Ross Hannah , Pao Lucy 
Published: June 2024

Abstract
Wind and marine energy are rapidly growing and complementary technologies that share some techniques for simplified modeling and control, particularly in below-rated flow speeds. A turbine operator has several choices of controller for maximizing power in Region 2. The simple and ubiquitous KΩ2 control law is often effective but limited in its flexibility. Alternative controllers use reference tracking to split the control objectives into a low-bandwidth optimal tip-speed ratio tracking loop to maximize steady-state power and a higher-bandwidth proportional-integral control loop to reject inflow turbulence. Several options exist for identifying the slowly varying optimal set point during operation, based on estimating the inflow velocity or filtering the power or torque signals. This study compares the trade-offs between performance and other design priorities for a few choices of reference-tracking controller in the literature for reference wind and marine turbines. Analysis is performed in the frequency domain using the linearization of each controller, and the impact of turbulent disturbances on the closed-loop system is described. The controllers are simulated in OpenFAST to analyze their performance with higher-order nonlinear turbine dynamics.
Impact of floating turbine motion on nacelle lidar turbulence measurements
Authors: Peña Alfredo , Angelou Nikolas , Mann Jakob 
Published: June 2024

Abstract
We determine the impact of floating turbine motion on turbulence measurements from a four-beam lidar by emulating its scanning configuration and retrievals within atmospheric turbulence boxes. Since the elevation angle of the lidar beams is small and the two bottom lidar beams point closely to the horizontal plane, we also evaluate the turbulence estimation abilities of a two-beam lidar. For the two-beam nacelle lidar, the variance of the individual beams is close to the target u-variance and closer than that we compute by reconstructing the u-velocity component with the two lidar beams radial velocities. By using floating turbine motion measurements from Hywind, we show that the floating turbine motion impacts turbulence estimations of the nacelle lidar. Roll does not have a clear impact on nacelle-lidar turbulence, whereas both the beam and the u-reconstructed variances increase with pitch amplitude.
An evaluation of different measurement strategies to measure wind turbine near wake flow with small multicopter UAS
Authors: Wildmann N , Kistner J 
Published: June 2024

Abstract
Wind turbine wake flow, especially in the near wake, that is up to one rotor diameter D downstream, is subject to interaction between tip vortices and ambient turbulence. These interactions are important to understand wake decay, but most difficult to measure with common instrumentation. Small uncrewed aerial systems (UAS) can help to measure at such locations where no masts can be installed. We contrast two measurement strategies, the hover flight with multiple UAS and cross-section flights with single UAS. We show that both strategies have advantages; the cross-section flights provide a full picture of the width and wind speed deficit across the rotor diameter whereas multi-UAS hover flights can provide more reliable turbulence intensity and turbulent flux measurements at specific locations. With both strategies, tip vortices can be detected and qualified to characterize the state of wake decay at different positions. A fit to the vortex models Lamb-Oseen and Burnham-Hallock allows to estimate circulation and core radius of the vortices. For best characterization of the wake, we recommend to combine the hover and cross-section flight strategies in future.
Experimental study on the joint load-bearing behaviour of segmented concrete towers under combined loading
Authors: Fürll F , Klein F , Götze M , Betz T , Marx S 
Published: June 2024

Abstract
Hybrid towers have become increasingly established for tall wind turbines. The concrete part of these towers consists of several stacked circular ring segments. To reduce the amount of fabrication and erection effort, the joints between the segments are usually designed as dry ground joints. This paper presents experimental investigations aimed at determining the torsional load-bearing capacity of such dry ground concrete joints subjected to combined loading of prestressing, bending and torsion. Based on previous investigations, a test set-up consisting of three circular ring segments was developed. The torsional load-bearing capacity was determined by monitoring the tangential joint displacements in detail. The test results demonstrate that an increasing bending load leads to a uniform decrease in the torsional load-bearing capacity. The comparison with the current calculation model shows significant differences and confirms the weaknesses of the model regarding its inadequate interaction with the bending load. In contrast, numerical simulations agree well with the test results.