bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Underwater Berlin Research Turbine: A Wind Turbine Model for Wake Investigations in a Water Towing Tank
Authors: Krumbein S. , Jentzsch M. , Saverin J. , Nayeri C. N. , Paschereit C. O. 
Published: June 2024

Abstract
The design of a three-bladed horizontal axis research wind turbine for wake investigations is described. The turbine has a rotor diameter of 1.3 m and will be operated in a large water towing tank at a submergence depth of 2.5 m, yielding 3.3 % blockage. The test rig is configured to allow for underwater-stereo-particle-image-velocimetry measurements of the near and the far wake at chordwise Reynolds numbers approaching 700 000. The low-Reynolds number airfoil SG6040 is selected to constitute the rotor blades. Cavitation-free operation is assured by assigning a rated angle of attack of 1°. The blades are designed to maintain a constant circulation along the blade span and to minimize tip deflections. The blade pitch angles are adjustable. Various blade designs, with and without passive flow control devices, can be tested by replacing individual blade sections. This eliminates the need for multiple sets of blades. Sensors for acquiring the turbine’s thrust, torque, rotational speed, the azimuthal positions of the blades, and the imposed blade root bending moments are incorporated into the design. The wind turbine simulation suite QBlade is utilized to simulate the turbine characteristics. A model of the entire test rig is derived, representing its structural properties. Results from the analytical verification of the structural model are provided. QBlade is utilized to analyze the test rig design by imposing design loads and calculating the modal properties.
Extracting Atmospheric Stability Information from Dual-Doppler Radar Scans in the AWAKEN Campaign
Authors: Nadolsky J S , Schroeder J L , Hirth B D 
Published: June 2024

Abstract
Dual-Doppler (DD) derived wind direction (β) fields are used in a novel approach to assess atmospheric stability by way of power spectral density (PSD) and bulk statistical analyses. Data on atmospheric stability, thermodynamic profiles, and wind behavior, as acquired during the AWAKEN campaign, are examined for a measurement time period featuring two stability transitions to analyze differences in flow structure as a function of stability regime. Analysis of the β fields yielded promising results when compared to stability regime and can be applied to other cases.
Deviation of drive torque and rotational speed of a wind turbine drivetrain between test bench and wind turbine simulations
Authors: Krause A , Jacobs G , Röder J , Zweiffel M. , Roth J 
Published: June 2024

Abstract
Wind turbines are a major contributor to a clean and independent energy mix in the future and therefore need to have as little downtime as possible. Downtime can be minimised by increasing the robustness of the wind turbine. The drivetrain is one of the major contributors of downtime in wind turbines. One way of increasing the robustness of wind turbine drivetrains is extensive drivetrain testing and loop-back optimization of the design and control. On the drivetrain test bench torque and other wind loads are applied. To ensure that the drivetrain reaction to the loads is the same as of the erected wind turbine the accuracy of the application of the loads needs to be sufficient. Only if the reaction loads of the drivetrain are similar to the rotor loads of the erected wind turbine a robustness increase can be achieved via the loop-back optimization after the tests. This paper therefore quantifies the deviations occurring in torque and rotational speed of the hub between the erected wind turbine and the test bench for a specific wind turbine. To do so the results of a test bench simulation are compared to results of an aerodynamic simulation of the wind turbine. For the investigated wind turbine drivetrain, the deviation in drive torque increases slightly with higher windspeeds. The torque values are maximum 2 % higher at the wind turbine compared to the rated torque. The rotational speed values are represented very well regarding the time series as well as the occurring frequencies. The speed values deviate maximum 0.5 % compared to the rated speed. The deviations are a result of differences in an underestimation of the drivetrain efficiency in the aerodynamic simulation and the inertia of the drivetrain on the test bench and wind turbine. Since the deviations are small the abstraction losses at the test bench regarding torque and speed are acceptable.
Error analysis of low-fidelity models for wake steering based on field measurements
Authors: Letizia Stefano , Doubrawa Paula , Martinez-Tossas Luis A. , Maric Emina 
Published: June 2024

Abstract
The observations collected by two scanning lidars deployed on the roof of a 2.8-MW turbine undergoing a series of imposed yaw offsets are analyzed. The wake lateral displacement detected by the rear-facing lidar correlates well with the yaw offset sensed by the forward-facing lidar. We find that the high-frequency part of the yaw offset signal is connected to wake meandering, whereas the low frequency component is a good predictor for wake displacement due to yaw misalignment. Conditionally averaged wake velocity data for different yaw offsets are used as benchmarks for the validation of a linearized Reynolds-averaged Navier-Stokes and an empirical wake model. A mean error as low as 2% and a good prediction of the wake trajectory are achieved, provided that the wake recovery rate matches the observations.
Comparison of line-of-sight wind speed measurements from an X-band radar and a long-range scanning lidar
Authors: Hung Lin-Ya , Gottschall Julia , Lilén Vöhringer A. , Hirth Brian D. , Schroeder John 
Published: June 2024

AbstractAs a still novel wind measurement technology, a dual-Doppler X-band wind radar system has been a substantial element of the full-scale onshore campaignAWAKEN(The American WAKE experimeNt). In order to select suitable further applications in the future and, particularly, the most optimal use cases in the wind industry for this technology, a line-of-sight wind speed verification campaign using a co-located scanning lidar as reference was set up as part of theAWAKENcampaign. The wind radar scanned in azimuth sector or plan position indicator (PPI) mode, with multiple elevations (volumetric PPI scan), while the scanning lidar remained fixed in a specific position during the verification campaign. Considering the individual spatial and temporal resolutions of the two systems, the closest points from the radar scanned volumes were compared with measurements from the scanning lidar after threshold-based and statistical data quality control. For a linear regression with 30-minute resolution data collected at 2 km range, a coefficient of determination ofR2= 0.99 was found. Radar mean values, binned according to reference wind speed, do lie in part within the reference uncertainty but not consistently for the investigated range of line-of-sight wind speeds. Part of the reference uncertainty is hereby also associated with the procedure of comparison but kept as low as possible by optimizing the verification setup and procedure.
Redefining Digital Twins – A Wind Energy Operations and Maintenance Perspective
Authors: Tuton Eamonn , Ma Xinhui , Dethlefs Nina 
Published: June 2024

Abstract
Digital Twin (DT) technology has seen an explosion in popularity, with wind energy no exception. This is particularly true for Operations & Maintenance (O&M) applications. However, this expanded use has been accompanied by loose, conflicting, definitions that threaten to reduce the term to a buzzword and prevent the technology from meeting its full potential. A number of attempts have been made to better define and classify DTs, however, these either oversimplify the term or tighten criteria, leading to the exclusion of many DT applications. A new definition framework dubbed the Digital Twin Family Tree is therefore proposed. This widens “Digital Twin” to a general umbrella term for the technology, accompanied by specific definitions. DT Tags are also used to provide individualised characteristics for implementations. A sector-specific definition was devised for component and system monitoring and predictions in wind energy O&M dubbed a CS-DT and suitable DT Tags created. The proposed framework was used to review existing research in literature, demonstrating the potential for increased understanding, explainability, and accessibility of DTs for expert and non-expert stakeholders.
Data-driven met-ocean model for offshore wind energy applications
Authors: Yousefi Kianoosh , Hora Gurpreet S. , Yang Hongshuo , Giometto Marco 
Published: June 2024

Abstract
In recent years, the global transition towards green energy, driven by environmental concerns and increasing electricity demands, has remarkably reshaped the energy landscape. The transformative potential of marine wind energy is particularly critical in securing a sustainable energy future. To achieve this objective, it is essential to have an accurate understanding of wind dynamics and their interactions with ocean waves for the proper design and operation of offshore wind turbines (OWTs). The accuracy of met-ocean models depends critically on their ability to correctly capture sea-surface drag over the multiscale ocean surface—a quantity typically not directly resolved in numerical models and challenging to acquire using either field or laboratory measurements. Although skin friction drag contributes considerably to the total wind stress, especially at moderate wind speeds, it is notoriously challenging to predict using physics-based approaches. The current work introduces a novel approach based on a convolutional neural network (CNN) model to predict the spatial distributions of skin friction drag over wind-generated surface waves using wave profiles, local wave slopes, local wave phases, and the scaled wind speed. The CNN model is trained using a set of high-resolution laboratory measurements of air-side velocity fields and their respective surface viscous stresses obtained over a range of wind-wave conditions. The results demonstrate the capability of our model to accurately estimate both the instantaneous and area-aggregate viscous stresses for unseen wind-wave regimes. The proposed CNN-based wall-layer model offers a viable pathway for estimating the local and averaged skin friction drag in met-ocean simulations.
Challenges in simulating the wind over a coastal complex-shaped site: Madeira Island
Authors: Coimbra I L , Palma J M L M 
Published: June 2024

Abstract
The wind behaviour on Madeira Island is shaped by the intricate coastline and mountainous terrain, features that are not easily represented in numerical models. Thus, this study addressed some challenges and possible solutions in setting up a meso-to-microscale model chain, with the WRF (1-km mesh) and VENTOS®/M (50-m mesh in the high-resolution area) models, in Madeira’s coastal and complex terrain. Wind measurements from four meteorological towers (located in the eastern peninsula–T0978/E–and on the SE–T0521/SE, S–T0522/S, and N–T0960/N–coasts) served as references to assess the simulations. First, due to WRF’s landmask position, land areas were misclassified as sea (and vice versa). This issue was addressed by altering the domain position to better allocate the landmask on the east peninsula, resulting in improved near-surface wind simulations at T0978/E (reducing RMSE and bias by 19% and 67%). Secondly, WRF’s default interpolation of the SST variable did not account for missing and masked data. As such, a different SST interpolation method was employed, leading to improved near-surface wind simulations at T0960/N (reducing RMSE and bias by 11% and 84%) and T0522/S (10% and 16% reduction) masts, but higher errors at T0978/E (7% and 45% increase). The negative influence arose from an incorrect speedup with the new interpolation method. Thirdly, the impact of SST_SKIN, which influences the temperature distribution at the skin level, was evaluated in WRF. Activating SST_SKIN led to a slight improvement in the near-surface wind simulation only at T0521/SE (2% and 6% RMSE and bias reduction), probably due to the dominant smaller-scale nature of the atmospheric circulation in the area, which contrasts with the circulation at the other towers, dominated by the trade winds (N and E masts) and the Island’s wake (S mast). When using the WRF outputs as boundary conditions, these effects on the microscale runs were less pronounced than on the mesoscale results. Nonetheless, the RMSE and bias of the near-surface wind simulation in VENTOS®/M were reduced by 6% and 9% at T0978/E.
Wake Modelling Based on the Stokes Stream Function and the Toroidal-Poloidal Decomposition
Authors: Warncke Norbert G.W. , Lokken Thomas S. , Leo Ilaria 
Published: June 2024

Abstract
The Stokes stream function and its generalisation, the Toroidal-Poloidal decomposition, are well-suited for the derivation of axisymmetric engineering wake models, as they are solenoidal and fulfil conservation of mass of an incompressible fluid by construction. The presented model consists of a time-independent contribution based on Laguerre basis functions with a simple parametrisation that is well-suited for the diffusion-dominated far wake. A time-dependent part can be added based on a poloidal component that can model either helical or toroidal vortex structures, and its parametrisation can be closed towards the total thrust force on the rotor. Despite requiring an external solver, the presented model shows potential as a drop-in replacement for the Ainslie wake model that is widely used in the Wind Energy industry as part of the Dynamic Wake Meandering model.
Uncertainty Quantification Analysis in the Blade Element Momentum Method
Authors: Cao G. , Fei Z. , Vogel C.R. 
Published: June 2024

Abstract
The blade element momentum (BEM) method is a widely used non-linear model for the efficient performance evaluation and design of wind turbines. The aim of this paper is to quantify the uncertainty related to BEM model inputs and sub-models, and investigate how these propagate through the model. Uncertainties related to viscous dissipation in the wake, aerofoil force coefficients, and tip-loss models are considered. Global sensitivity to these parameters is analysed using non-intrusive polynomial chaos expansion, which provides a structured method for uncertainty propagation and sensitivity quantification. Sobol indices are employed to rank the relative importance of each factor to the overall uncertainty in the system. By analysing the NREL 5 MW and DTU 10 MW reference wind turbines, we observe that the different rotors may exhibit different levels of sensitivity to input parameters. The effect of viscous mixing in the turbine wake is found to have a significant impact on predicted rotor performance. Uncertainty in tip-loss model coefficients is also found to generally be important, particularly when evaluating spanwise variations in rotor loads. Uncertainty quantification has the potential to improve understanding of BEM modelling, and provide guidance on the importance of sub-model improvements.
Design and optimization of a modular Electro-Thermal Ice Protection System for a Horizontal Axis Wind Turbine
Authors: Gallia Mariachiara , Caccia Francesco , Guardone Alberto 
Published: June 2024

Abstract
In this work, an Electro-Thermal Ice Protection System (IPS) design was refined and optimized on the NREL 5 MW reference wind turbine. These improvements involved optimization of the distribution of heat flux in both the stream-wise and span-wise directions to minimize power consumption and avoid run-back ice formation. The design conditions focus on a 3-hour rime ice accretion event. The chosen optimization algorithm is a derivative-free method called Mesh Adaptive Direct Search. his optimization effort results in a 55% reduction in power consumption necessary to maintain a completely clean blade surface. The power and energy losses associated with this new optimized design are compared with those from various ice shapes and with the clean blade conditions established in the initial design phase from previous work. The new optimized design allows to keep the blade clean from ice with much larger energy saving. Indeed, only initially, during the first two hours of ice accretion, the energy losses due to this IPS design are higher than without IPS. Beyond this short initial period, substantial energy savings are achieved, especially considering that after the accretion event, the blade remains ice-free, and there are no more power losses.
Static response of wind turbine blades: Comparison of low- and high-fidelity numerical models
Authors: Antunes A M , Verelst D R , Riva R , Kim T , Haselbach P U , Zahle F , Berring P 
Published: June 2024

Abstract
As wind turbine blades become longer and more flexible, the structural models employed in current aeroelastic simulation tools, usually based on beam formulations, are challenged. Effects previously considered negligible in the response of these beam-like structures might now become significant to obtain accurate predictions of their behaviour. To assess this, a test matrix covering key geometric and material characteristics of wind turbine blades is defined and three test cases are analysed as an initial stage of this study. For each case, the static deflection of the beam model from the aeroelastic tool HAWC2 is compared against higher-fidelity shell/solid finite element models. Three structures are studied: an isotropic box beam, a composite box beam and a 12.6 m wind turbine blade from DTU. A good match is observed for the box beam test cases, which study the effects of out-of-plane and distortion warping and bend-twist coupling. Important aspects of high-fidelity models (such as end effects) are highlighted. The study of the DTU 12.6 m blade shows a significant difference (15%) in the torsion natural frequencies of the beam model, though a good agreement in twist angle under torsional loading. More pronounced differences in twist angle are observed when a load distribution based on the steady state response is applied, likely resulting from challenges in modelling complex structural features and three-dimensional effects.
Impact of low-frequency fluctuations on loads of a fixed-bottom offshore reference wind turbine
Authors: Syed Abdul Haseeb , Hannesdóttir Ásta , Mann Jakob 
Published: June 2024

Abstract
Marine atmospheric turbulence is predominantly characterized by large-scale structures associated with low-frequency wind turbulence. However, conventional turbulence models for assessing wind turbine loads often fall short of adequately integrating these low-frequency wind fluctuations. In this study, we used a model for low-frequency wind fluctuations to generate wind fields representative of offshore wind conditions in the North Sea. The IEA 15 MW reference wind turbine was subjected to three distinct incoming wind fields: high-frequency (3D) turbulence, low-frequency (2D) turbulence combined with high-frequency (3D) turbulence, and 3D turbulence scaled by target or measured standard deviation of wind components. We found that increased damage equivalent loads by incorporating the low-frequency wind fields are only significant for the tower base fore-aft and blade root fore-aft moments. The impact of low-frequency wind turbulence on the damage equivalent loads was more pronounced for below-rated wind speeds. The scaled 3D turbulence yielded the highest lifetime damage equivalent loads, i.e., in the range of 8-18% more than the unscaled 3D turbulence and combined 2D +3D turbulence. This method leads to an overestimation of loads and, hence, more expensive turbines. Incorporating 2D+3D turbulence in wind fields resulted in a 3.8% increase in lifetime damage equivalent loads for the tower base fore-aft and blade root flapwise moments compared to unscaled 3D turbulence. These findings underscore the importance of considering low-frequency wind fluctuations in the turbine design process, especially for a more accurate estimation of loads.
Aeroelastic code comparison using the IEA 22MW reference turbine
Authors: Collier W , Ors D , Barlas T , Zahle F , Bortolotti P , Marten D , Jensen C S L , Branlard E , Zalkind D , Lønbæk K 
Published: June 2024

Abstract
Reference wind turbine designs and the associated aeroelastic models are widely used in both research and industry. Reference models representing future concepts are of particular interest. Current state of the art aeroelastic tools are relied upon to design the next generation of large wind turbines. However, modelling assumptions may be invalidated by upcoming very large turbines, and different aeroelastic tools may give inconsistent results. A 22MW turbine model has been defined as part of International Energy Agency (IEA) Wind Task 55 on Reference Wind Turbines and Farms to represent future turbines to be deployed in the 2030s. In this study, an aeroelastic model of this turbine has been created in four tools; Bladed, HAWC2, OpenFAST, and QBlade. Code comparisons are presented for steady state operation, linear stability analysis, and time domain power production simulations in steady and turbulent wind. Generally, the codes show a good agreement, but with some differences present in the linear stability analysis, periodic azimuthal variation, and time domain simulations. The models are a good basis for further study with the IEA 22MW turbine, and further code comparison exercises.
Section force calculation in flexible substructures modelled by wind turbine design tool Bladed
Authors: Nim Erik , Roadnight John , Moharram Hassan , Collier William , Jensen Chr. Sigurd L. 
Published: June 2024

Abstract
Aeroelastic simulation tools are widely used to predict the coupled response for onshore, offshore and floating wind turbines. A key output of the analysis is the section forces in the flexible substructures, such as blades, towers, and floating foundations. Individual substructures are typically modelled as a single linear flexible body, which is a part of a multibody system used for modelling the complete wind turbine. However, in some floating foundation concepts, in particular those with pre-tensioned cables, geometric non-linearities in the substructure can have a significant effect. With the conventional method for calculating section forces, such non-linearities are not captured accurately. In this paper, a new equilibrium-based method for calculation of section forces is presented, as part of the wind turbine design tool Bladed. This method relies on equilibrium between the section forces and the applied loads. The section forces are determined in terms of Lagrange multipliers, which represent the internal constraint forces in the structural elements. This method is valid even when significant geometric non-linearities are present, with reduced order models, and for statically indeterminate substructures. A case study is presented demonstrating the self-consistency of the new method for the OC4 semi-submersible floating platform, modified to include pre-tensioned cables. A verification against ANSYS is also presented for some elementary cases.