bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic optical deformation measurements on wind turbines
Authors: Helming P , Poeck N , v Freyberg A , Sorg M , Fischer A 
Published: June 2022

Abstract
Because of an increase in the size of wind turbines in recent years, efficient structural health monitoring of the turbine’s structure has become critical. Wind turbine towers deform elastically as a result of the loads due to wind and inertial forces acting on the revolving rotor blades. To adequately assess these deformations, an earthbound device is desired that can measure the tower’s movement in two directions from a very large working distance of over 150 m and a single site. For this task, a terrestrial laser scanner in line-scanning mode with horizontal alignment is used to measure the tower cross-section and to determine its axial (in the line of sight) and lateral (transverse to the line of sight) position using a least-squares fit. The method is validated by comparing the data obtained by the laser scanner with continuously measured wind speed data. To test its application, the method is then applied to two separate wind turbines with hub heights of 61.4 m and 128 m and the experimental results are compared with a reference video measurement that records the nacelle movement from below and determines the nacelle movement using point-tracking software. The results are compared for various operating circumstances, such as different wind speeds. The laser-based and the reference measurement have a strong correlation. The measurement uncertainty is determined to be 9.6 mm in the lateral direction and 10.3 mm in the axial direction at a measurement distance of 160 m, respectively. As a result, the proposed approach is identified as an effective tool for the in-process structural health monitoring of wind turbine towers.
Field Study of Turbulence Intensity measurement by Nacelle Mounted Lidar (NML)
Authors: Liang Zhi , Cote Robin , Cariou Jean-Pierre 
Published: June 2022

Abstract
In this paper, Nacelle Mounted LiDAR (NML) was used to study Turbulence Intensity (TI) by dataset from three measurement campaigns, using two approaches: the white box test and the black box test. The white box test was to compare TI LOS using each Line Of Sight, while the black box test was to compare TI Hub using all LOS by relative reconstruction algorithm at wind turbine hub height. The result of white box test showed that the correlation coefficient of TI LOS varied from 0.923 to 0.955 and the slope varied from 0.978 to 1.030. The result of black box test showed that the correlation coefficient of TI Hub is 0.8337∼0.8924 and the slope is 0.904∼0.935. This study provided some promising results to wind energy community, which could be the evidence base for the further investigation for the temporal-spatial turbulence structure in low Atmospheric Boundary Layer.
Evaluation of a Hardware-in-the-loop Test Setup Using Mechanical Measurements with a DFIG Wind Turbine Nacelle
Authors: Neshati Mohsen , Zhang Hongkun , Thomas Philipp , Heller Marcel , Zuga Adam , Wenske Jan 
Published: June 2022

Abstract
The impact of system test benches on the development and validation of wind energy converters is significantly increasing, and that is due to the higher availability as well as the provided powerful actuator and emulation systems. However, the question remains to be answered about how consistent measurements in the laboratory are. Especially in the case where no field measurements are available for prototypes. The challenge in this regard is the unknown accuracy of simulations and the lack of an experimentally calibrated torque measurement in the hardware-in-the-loop (HiL) setup. The presented paper handles this topic and presents an evaluation method to elaborate measurement consistency independent from field tests. A transparent and comprehensive comparison is provided, taking advantage of the deterministic test environment enabled by the HiL system and the dedicated designed torque measurement adapter. Provided results demonstrate consistent measures obtained from the real-time simulation, HiL control system, and the electrical and mechanical measurements, where a low deviation of up to 2 % is partly observed.
Lifetime fatigue response due to wake steering on a pair of utility-scale wind turbines
Authors: Dana Scott , Ivanov Hristo , Doubrawa Paula 
Published: June 2022

Abstract
Quantifying the impacts on turbine loads during wind farm control is an important consideration in assessing power production benefits. Wake steering controls aim to improve total wind farm performance by coordinating the control actions of individual turbines, wherein an upstream turbine is intentionally yawed at an offset angle from the measured wind direction. Consequently, this redirects its wake for improved power production and potentially reduces fatigue loads of the downstream turbines. This paper studies the lifetime fatigue loads associated with wake steering by using utility-scale wind turbine experimental data to conduct an analysis on a pair of wind turbines. This study was part of a large field experiment in which a group of five GE 1.5-MW SLE CWE turbines were selected as targets for conducting wake steering research. A standard loads instrumentation package and data acquisition system were installed on two turbines within the cluster to measure turbine fundamental loads. The time-series databases were used to calculate loads statistics as well as short-term and lifetime damage equivalent loads. Fatigue calculations followed the guidance in Annex H of the International Electrotechnical Commission standard 61400-1, Edition 4. Lifetime fatigue calculation results are presented in this analysis; three methods of assessing lifetime fatigue were used to determine percent difference for blade root moments, main shaft moments, main shaft torque, and tower top torque. For all three fatigue treatments, some components’ lifetime fatigue increases for the controlled turbine; however, the downwind turbine experienced a reduction in lifetime fatigue and combined effect for the turbine pair results in a reduction of fatigue when wake steering controls are applied.
Comparison of dynamic stall on an airfoil undergoing sinusoidal and VAWT-shaped pitch motions
Authors: Brunner C E , Kiefer J , Hultmark M 
Published: June 2022

Abstract
The aerodynamics of vertical axis wind turbines (VAWTs) are inherently unsteady because the blades experience large angle of attack variations throughout a full turbine revolution. At low tip speed ratios, this can lead to a phenomenon known as dynamic stall. To better characterise the unsteady aerodynamics and represent them in models and simulations, data from studies of individual static or pitching airfoils are often applied to VAWT blades. However, these studies often involve sinusoidally pitching airfoils, whereas the pitching motions experienced by VAWTs are more complex. Here, the pressures and forces on an airfoil undergoing VAWT-shaped pitch motions corresponding to various tip speed ratios are compared to those of a sinusoidally pitching airfoil in order to assess whether a sinusoidal motion represents a reasonable approximation of the motions of a VAWT blade. While the lift development induced by the sinusoidal motion yields good agreement with that induced by the VAWT-shaped motion at the higher tip speed ratios, notable discrepancies exist at the lower tip speed ratios, where the VAWT motion itself deviates more from the sinusoid. Comparison with sinusoidal motions at reduced frequencies corresponding to the upstroke or downstroke of the VAWT-shaped motion yield better agreement in terms of the angle of stall onset.
A strongly coupled Eulerian Lagrangian method applied in unsteady 3D external flows around Wind Turbine rotors
Authors: Spyropoulos Nikos , Vlastos Dimitris , Papadakis George , Prospathopoulos John M. , Riziotis Vasilis A. 
Published: June 2022

Abstract
This paper presents a hybrid CFD solver that couples a standard Eulerian approach that solves the compressible Navier-Stokes equations under a cell-centered finite volume discretization, with a Lagrangian one, based on particles representation which carry mass, pressure, dilatation and vorticity. The velocity field is calculated using the Helmholtz’s decomposition theorem. Computational performance is enhanced by employing the Particle Mesh (PM) technique in order to solve the Poisson equations for the scalar potential ϕ and the stream function ψ. Even though validated for 2D flows over airfoils, this specific solver is used for the first time in order reproduce the flow around a wind turbine rotor. The validation simulations concern axial flow over the wind turbine model rotor used in the New MEXICO experimental campaign. Results of the hybrid solver, presented as blade pressure distribution and axial flow velocities are compared against the ones produced by its pure Eulerian counterpart and experimental measurements. PM grids of up to 5 points per chord of the blade section at 75% radius have been used. Comparison with the standard Eulerian solver suggest that the produced blade loads are over-predicted by approximately 7% near the tip and 14% near the root. However, the calculated velocity field is much closer to the experimental measurements as compared to the one produced by the Eulerian approach, which is attributed to the reduced numerical diffusion of the Lagrangian-vorticity formulation.
Sensitivity analysis of geometrical design parameters on the performance of conical plain bearings for use as main bearings in wind turbines
Authors: Rolink Amadeus , Jacobs Georg , Pérez Alex , Bosse Dennis , Jakobs Timm 
Published: June 2022

Abstract
The failure of a wind turbine’s main bearing causes very high repair costs, as the entire drivetrain has to be disassembled with the help of an external crane. Just the costs for a crane for an offshore turbine can sum up to 200.000€ per day [1]. In contrast, segmented hydrodynamic plain bearings offer the advantage that individual bearing segments can be replaced on the tower without the use of an external crane, which offers great potential for savings in repair costs. However, this application requires new, innovative plain bearing concepts for which the current design guidelines are not applicable. This paper presents a simulation-based design approach for a plain bearing concept with conical sliding surfaces. Such a simulation-based approach with a multi-objective optimization is necessary, because due to the geometric complexity the manual, iterative design process is not efficient. In this paper, a bearing geometry optimized in terms of load distribution and friction losses was developed by applying this approach.
Impact of rotor size on aeroelastic uncertainty with lidar-constrained turbulence
Authors: Rinker Jennifer M. 
Published: June 2022

Abstract
Nacelle-mounted lidar measurements offer the opportunity to tailor turbulence to specific conditions, reducing aeroelastic uncertainty in one-to-one wind turbine validation and opening the door for novel lidar-based control methodologies. Despite this, the use of lidar to generate constrained turbulence is not commonplace, partially due to a lack of readily available tools. Kaimal-based constrained turbulence methods—such as the one implemented in the open-source constrained-turbulence generator PyConTurb—can be used to easily generate turbulence constrained to measurements in a matter of minutes. Unfortunately, the limitations of the Kaimal-based methods prevent the direct use of the lidar data as constraints. This paper therefore presents a preprocessing methodology to convert lidar data to PyConTurb-ready constraints. The method is demonstrated by quantifying the aeroelastic uncertainty for the DTU 10 MW and the NREL 5 MW without constraints and comparing it to the corresponding value with lidar constraints. The results show an excellent reduction in the one-to-one aeroelastic uncertainty and an adequate reduction on fatigue loads when lidar-constrained turbulence is used as inflow. The NREL 5 MW is found to have better reduction in uncertainty due to a rotor size that is better suited to the lidar geometry.
Characterization of a Fast Response Probe for Inflow Turbulence Measurements on Wind Turbine Blades
Authors: Sinem Özçakmak Özge , Fischer Andreas , Madsen Helge Aagaard 
Published: June 2022

Abstract
The performance of a wind turbine, its aerodynamic and acoustic predictions, and expected power output are affected by atmospheric turbulence. Previous studies showed that the installation of high-frequency measurement devices on blades is needed in order to analyze the effect of the inflow turbulence on boundary layer transition and on noise emissions. Therefore, the accuracy of a novel 5-hole high-frequency pitot tube designed to measure high-frequency velocity fluctuations is assessed by testing its capability to determine flow angles and velocity components in a well-defined wind tunnel setup. Moreover, the vortex shedding frequency and magnitude for the flow behind a cylinder and wire are analyzed to evaluate its performance for various turbulent flow scenarios. It is seen that the flow angles and the velocity components can accurately be calculated. The peaks observed in the spectra sampled at high frequencies that are relevant for boundary layer analysis demonstrate the characteristics of the flow with high turbulence intensity values. As the probe is validated for inflow turbulence measurements, it will be used on a wind turbine blade to identify the relevant frequencies that are induced by the atmospheric turbulence into the boundary layer and to improve wind turbine noise emission models.
Test of an active flap system on a 4.3 MW wind turbine
Authors: Gomez Gonzalez A. , Enevoldsen P. , Barlas T.K. , Madsen H. Aa. 
Published: June 2022

Abstract
This article describes a field test performed on a 4.3 MW wind turbine with one blade equipped with an active flap system. The results presented focus primarily on the steady state and periodic characterization of the active flap system in different deflection states. The tests were performed between 2020 and 2021 on a test turbine in northern Denmark in close-to-shore conditions. The active flap system is primarily characterized based on the load response of the flapwise bending moment of the blades. Flap actuations are performed both as open-loop on-off swaps (shifting between two different flap positions at fixed time intervals) and as closed-loop 1P activations (cyclic activation of the flap both in phase and counterphase with the blade azimuthal position). For the steady state swap tests, the impact on flapwise bending moment ranges between 3% and 20% depending on the flap actuation level and the wind speed. For the cyclic flap tests, the load impact is based on blade-to-blade fatigue load comparison, showing a potential load reduction of approximately 13%.
Innovative aerodynamic rotor concept for demand-oriented power feed-in of offshore wind turbines
Authors: Ribnitzky Daniel , Berger Frederik , Kühn Martin 
Published: June 2022

Abstract
We introduce an aerodynamic rotor concept for a 15 MW offshore wind turbine which is tailored for an increased power feed-in at low wind speeds. The main objective of the conceptual design is to limit the stationary loads (blade flapwise root bending moment (RBM) and thrust) to the maximum value of the IEA 15 MW offshore reference turbine, while greatly increasing the swept rotor aera. The outer part of the blade (e.g. outer 30% of the rotor) is designed for a higher design tip speed ratio (TSR) and a lower axial induction than the inner part. By operating at the high TSR in light winds, the slender outer part fully contributes to the increased power capture. In stronger winds the TSR is reduced and the torque generation is shifted to the inner section of the rotor. Moreover, the blade is designed in a way that makes the limitation of the flapwise RBM through peak shaving aerodynamically more efficient. With static blade element momentum simulations the characteristics of the rotor are investigated and the economic revenue of the turbine is estimated, considering a wind speed dependent feed-in price. Our results show that the revenue can be increased by 30% compared to the reference turbine with an increase of rotor diameter by 36%.
Influence of soil properties on the shift in natural frequencies of a monopile-supported 5MW offshore wind turbine under scour
Authors: Jawalageri Satish , Jalilvand Soroosh , Malekjafarian Abdollah 
Published: June 2022

Abstract
This paper studies the change in the natural frequencies of the NREL 5MW monopile-supported offshore wind turbine (OWT) due to scour. The natural frequencies are derived from accelerations arising under wind and wave loads, for a range of different soil properties. A model of the wind turbine is developed using OpenFAST and SESAM software which considers aerodynamic and hydrodynamic loading with soil-structure interaction. The superstructure behaviour is modelled using OpenFAST and the foundation behaviour is modelled with SESAM, where soil-structure interaction is incorporated using p-y springs. The influence of soil density and scour hole depth on the obtained natural frequencies are studied. Accelerations are extracted at nine locations along the tower resulting from applied wind and wave loads. The first two system natural frequencies are estimated using frequency domain decomposition (FDD) applied to the acceleration time-histories for each scour depth and soil type. It is shown that the increase in scour depth around the foundation of the OWT leads to a decrease in natural frequencies when compared to the case where there is no scour.
Leading Edge Microspoilers for Load Dumping in Wind Turbine Rotors
Authors: Mertz B , Bortolotti P , Abbas N J , Johnson N , Paquette J , Jordan W 
Published: June 2022

Abstract
As rotor designs have grown in size and flexibility, new design challenges have arisen that could benefit from novel control strategies. Leading edge microspoilers (LEMS) have been shown to effectively reduce forces on airfoils by inducing stall at lower angles of attack. This paper investigates how LEMS can be used to reduce blade loading on large, flexible, downwind rotors during design-limiting design load cases. During shutdown in turbulent flows near cutout speed, LEMS could reduce the tip deflection spikes toward the tower by over 50% and keep flapwise root bending moments below normal operating conditions, thus eliminating these as design-driving load cases. In power producing load cases, deploying LEMS for a short period of time during a load spike can be effective to reduce toward-tower tip deflections without significantly impacting power produced, assuming these load spikes can be identified by a controller. Leveraging this technology could allow for lower specific power machines to be designed.
Repair of Wind Turbine Blades: Costs and Quality
Authors: Mishnaevsky Leon , Bendixen Brian , Mahajan Puneet , Fæster Søren , Johansen Nicolai Frost-Jensen , Paul Daniel , Fraisse Anthony 
Published: June 2022

Abstract
Repair and maintenance operations of wind turbines constitute a significant part of costs of wind energy. In this paper, technologies of structural repair of damaged wind turbine blades are reviewed. Costs of repair, and technological contribution to the costs are discussed. Technologies of repair are compared, including hand layup lamination, vacuum repair with hand layup and infusion, ultraviolet curing and high temperature thermal curing systems. Computational models of repaired blades, and curing as kinetic process are presented. Void formation during repair and curing, and the void influence on the post-repair reliability of blades is discussed.
Analytical determination of the influence of geometric and material design parameters on the stress and strain fields in non-prismatic components of wind turbines
Authors: Migliaccio G 
Published: June 2022

Abstract
Non-prismatic beamlike elements have long been used in engineering applications to optimize the performance of structures such as wind turbines, aircraft, and civil bridges, just to mention some examples. Unfortunately, engineering methods and formulas commonly used to analytically evaluate stresses and strains in prismatic beams do not hold and provide incorrect results for non-prismatic geometries. Large displacements and non-uniform material properties further complicate the analytical prediction. In order to determine the state of stress and strain in non-prismatic beamlike elements and its dependence on important design factors (such as taper parameters), a suitable mapping of the shape of such elements and a variational approach are used. The resulting field equations are exploited to derive application-oriented stress-strain formulas. Examples and comparisons with results of non-linear 3D-FEM analyses confirm the effectiveness of the modelling approach and of the new formulas proposed in this work.
Reduction of gearbox loads of a DFIG wind turbine during grid faults with optimized converter configurations
Authors: Röder J , Jacobs G , Bosse D , Izal J L R 
Published: June 2022

Abstract
Grid faults in wind turbines (WT) with doubly fed induction generator (DFIG) result in dynamic generator torque excitations, which can lead to dynamic load changes within the gearbox. Dynamic load changes in combination with changing rotational speeds can increase the risk of damage in the gearbox. WT gearbox damage occurs mainly on the high speed shaft (HSS) components. The torque excitations have the highest influence on the HSS since it is coupled to the generator. Therefore, an investigation of the correlation between grid faults and gearbox damage is necessary. The torque excitation in DFIG WTs due to grid faults is dependent on the converter and its fault ride through capabilities. The load analysis in this paper is done for a state of the art converter configuration and for one that is optimized in order to stabilize the performance during grid faults. It is shown via simulation with a WT drivetrain model that dynamic load changes of the HSS gear wheel are prevented for symmetrical grid faults with the optimized configuration. The analysis of a HSS bearing shows that the smearing damage risk can be significantly reduced (minus up to 56 percent) by using the optimized configuration. Therefore, the possibility to decrease the gearbox damage risk during grid faults via an optimization of the converter configuration is shown in this paper.
Dynamic inflow and unsteady aerodynamics models for modal and stability analyses in OpenFAST
Authors: Branlard E , Jonkman B , Pirrung G R , Dixon K , Jonkman J 
Published: June 2022

AbstractThis work presents two aerodynamic models that are used to perform modal and stability analyses of wind turbines. Including aerodynamic effects in stability analyses is important to capture aerodynamic inertia, stiffness, and damping. The two models consist of a dynamic inflow model based on Øye’s model and an unsteady aerodynamics model based on a simplified Beddoes-Leishman dynamic stall model. Both models are written in a continuous-time state-space form, which is the form needed to perform linearizations within OpenFAST. In this article, we present the new models, perform some simple verifications against HAWC2 results, and then perform stability analyses. We investigate the contribution of the aerodynamic effects on the turbine modes, particularly the flapwise modes, which are the most affected. Because of the development presented in this work, Campbell diagrams accounting for dynamic stall and dynamic wake effects were generated for the first time using OpenFAST.