bluuebunny/crossref_metadata_2025_split huggingface dataset:
Lidar error in complex terrain - case study based on two measurement campaigns
Authors: Bischoff Oliver , Hofsäß Martin , Clement Dominic , Schmitt Carolin , Cheng Po Wen 
Published: June 2024

Abstract
Nowadays, lidar devices are increasingly being used to determine wind potential. The decision to use a lidar device or a meteorological measuring mast depends, among other things, on the topology of the terrain. In flat terrain lidar profilers are sufficiently accurate compared to previously used measuring masts. Due to their measuring principle, however, there are differences in measuring accuracy depending on the terrain. This deviation compared to a measurement with a measuring mast or with anemometers attached to it is referred to as lidar error. However, there are still uncertainties regarding the measurement accuracy of lidar profilers, especially in complex terrain.
Among other things, the size of the lidar error in relation to terrain complexity or terrain type is unclear. The lidar error can also differ for different lidar devices with different measuring principles. In order to investigate this in more detail, various lidar devices are compared in this work with regard to their measurement uncertainty in complex terrain. For this purpose, measurement data from two measurement campaigns lasting several months were analyzed. In both measurement campaigns, the lidar devices are compared with data from a measuring mast.
There are clear differences between the lidar devices. These are type-dependent, wind speed-dependent and also wind direction-dependent. The latter is due in particular to different terrain topographies from the different cardinal directions. These differences are analyzed with the help of suitable statistical parameters and then evaluated in the context of current scientific research.
Digitalization of Large-Scale Testing Facilities for the Wind Industry: DIGIT-BENCH Digital Twin
Authors: Baş Elif Ecem , Abbiati Giuseppe , Gonçalves Gomes Cláudio Ângelo , Jassmann Uwe , Larsen Peter Gorm 
Published: June 2024

Abstract
Testing of large wind turbine components plays a central role in delivering reliable yet cost-effective technology. However, these experiments are often lengthy and costly. Fatigue testing of a wind turbine blade might take up to 12-14 months, whereas highly accelerated lifetime testing of a nacelle demands 6-8 months. The exchange of simulation models and data between OEMs and test facilities is recognized as a critical factor in the planning of an experimental campaign. In fact, OEMs are typically very protective of their industrial secrets, and sharing such sensitive information may constitute a threat. It follows that the use of simulation models to enable more effective experimentation is not pursued efficiently.
Digital twins are emerging as a key enabling technology to improve the operation & maintenance of test benches for the wind industry. A digital twin combines physical systems and their digital models into a cyber-physical system to provide functionalities that cannot be attained by either physical or digital assets independently. The seamless integration of the test bench with digital models offered by a digital twin is expected to enhance the interaction between OEM and test bench operators.
This proceeding illustrates the status of the development of the DIGIT-BENCH digital twin developed by R&D Test Systems (R&D) and Aarhus University to serve large-scale test facilities for the wind industry. The digital twin utilizes FMI-based co-simulation to enable the coupling of physical/digital components in an industrial-secret-friendly environment. The digital twin concept is demonstrated on a 2-degrees-of-freedom test bench installed at Aarhus University.
Constrained synthetic wind fields from high-resolution 3D WindScanner measurements
Authors: Meyer Paul Julian , Giyanani Ashim , Gottschall Julia 
Published: June 2024

Abstract
The limited spatial and temporal resolution of wind measurements within the inflow of a wind turbine requires statistical modeling of synthetic wind fields, integrating actual measurements or derived statistics along with selected turbulence models. The short-range WindScanner technology enhances atmospheric wind measurements with high resolution in both spatial and temporal dimensions. This contribution utilizes 3D turbulent inflow measurements from three synchronized WindScanner to generate synthetic turbulent wind fields. Both, mean wind field parameters and turbulent time series are analyzed, and different input configurations for the constrained wind field generation are evaluated.
Our findings indicate the presence of periods characterized by dominant horizontal shear and veer events, with wind speed and direction differences up to 1.53 ms−1 or 8.45° across the rotor span. Additionally, the study reveals that the optimal measurement configuration for constrained turbulence modeling varies depending on the specific evaluated location and velocity component being analyzed. Another observation is that excessive constraints, placed too closely, may lead to overfitting, thereby diminishing the representativeness of the synthetic field for the lateral velocity component.
Validation of the stochastic inversion algorithm for acoustic travel-time tomography: a large eddy simulation study
Authors: Maric Emina , Hamilton Nicholas , Quon Eliot , Lee Bumseok , Thedin Regis 
Published: June 2024

Abstract
Acoustic tomography (AT) is explored as a remote sensing technique to obtain instantaneous snapshots of temperature and velocity fluctuations for wind energy applications. This study integrates Large Eddy Simulation (LES) with the Stochastic Inversion (SI) method to validate the algorithm’s capacity for accurate reconstruction of atmospheric fluctuations. The initial findings demonstrate the efficacy of the method in accurately capturing the predominant flow structures. Normalized L2 error evaluations further inform the algorithm’s precision, with errors accentuated in less sampled peripheral regions. The results underscore the method’s promise as a non-intrusive observational tool, with ongoing development poised to improve its precision and reliability.
Study of implicit CFD modeling of riblets on wind turbine airfoil in transitional flow
Authors: Vimalakanthan Kisorthman , Bakhmet Iana 
Published: June 2024

Abstract
The study introduces a novel hybrid boundary condition, derived from existing literature, crafted for predicting the impact of riblets on airfoils in transitional flow. In contrast to models tailored for fully turbulent flow, the hybrid approach successfully captures the operational dynamics of riblets, as demonstrated through meticulous testing. The boundary condition integrates slip length and a modified specific dissipation rate (ω) boundary to encompass the entire riblet regime. Adjusting the model to match measured drag behavior enables predictions of riblet effects at higher Reynolds numbers pertinent to wind turbine blades. Validation reveals the model’s proficiency in capturing the order of magnitude in drag reduction and aligns the change in drag in the correct direction for diverse riblet heights, yet highlights discrepancies in replicating absolute drag reduction values, particularly at smaller angles of attack. This underscores the imperative for further refinement and tuning, necessitating additional experimental data at higher Reynolds numbers and across various angles of attack to ensure the model’s robust applicability across a broader spectrum of conditions.
Development of a machine learning model for wind turbine fatigue and ultimate loads based on static loads
Authors: Barlas T , Göçmen T , Riva R 
Published: June 2024

Abstract
A machine learning model is trained on HAWC2 time-domain aeroelastic load simulations in order to provide a load surrogate model from static rotor loads input to lifetime wind turbine design loads, to be utilized in fast design loads evaluation for design optimization. The simulations are performed on the IEA-3.4-130-RWT with a range of design variations for tip-speed-ratio, pitch-ramp settings, and blade length scaling. The surrogate model is shown to provide accurate predictions of lifetime blade and turbine ultimate and fatigue loads for design variations within the training design space.
Prediction of the friction torque of scaled blade bearings in a test rig using machine learning
Authors: Hohmann M , Blechschmidt E , Hallerberg S , Menck O 
Published: June 2024

Abstract
Blade bearing friction torque is a required parameter for the design of a pitch actuator, and deviations from a bearing’s initial torque can be utilized for condition monitoring of the bearing. The torque of large-scale bearings can, however, be difficult to predict due to quality fluctuations in the production of these large-scale components. Therefore, this paper employs machine learning approaches to predict the torque of a given set of bearings in a controlled test environment based on measurement data from that same set of bearings. Possible applications of the model include use for condition monitoring by checking for deviations from the bearing’s initial behavior.
Influence of wakes interaction and upstream turbulence on three tidal turbines behaviour
Authors: Dufour M-A , Pinon G , Rivoalen E , Germain G 
Published: June 2024

Abstract
The current study presents numerical results on three tidal turbine models (two in front, one downstream) interacting in a turbulent upstream flow. The numerical results come from a lifting-line (LL) embedded in a Lagrangian vortex particle (VP) solver: Dorothy LL-VP. The objective is to assess the extent to which this numerical tool is suited to reproduce accurately wakes interaction as well as fluctuating loads perceived by the downstream turbine. To this aim, the numerical set-up reproduces an experimental campaign led at IFREMER’s wave and current flume tank. The downstream turbine is placed at different positions to change the wakes interaction. Two upstream turbulence intensities (TI) experimentally tested are reproduced numerically using the synthetic eddy method (SEM). Favourable comparisons are obtained between numerical and experimental wakes, including velocity profiles. Preliminary results suggest that the downstream turbine performance decrease is numerically well captured. More investigations are needed on the loads fluctuations with longer computation time, and adding an angular velocity controller as well as hub modelling to Dorothy LL-VP.
Lattice Boltzmann simulation for wake interactions of aligned wind turbines using actuator line model with turbine control
Authors: Watanabe Seiya , Hu Changhong 
Published: June 2024

Abstract
A wind turbine wake causes a decrease in wind speed and an increase in turbulence intensity. The wind turbine wake interaction is essential for predicting the power output of a wind farm consisting of many wind turbines. This research proposes a CFD method able to reproduce wake interactions and power outputs of multiple wind turbines with high speed and accuracy. Large eddy simulations with the lattice Boltzmann method are used for fluid calculations, specifically for large-scale CFD simulations. The wind turbines are represented using an actuator line model. Optimal power generation efficiency is achieved by controlling the rotor speed and blade pitch angle. Large-scale simulations of eight aligned wind turbines are conducted using 1.75 billion grid points and 40 GPUs. We compare two cases with and without control to investigate the effect of turbine control on wake and power output. Both the instantaneous and mean streamwise velocities confirm that the turbine control reduces the wake velocity deficit of the downwind wind turbine. High-speed inflow of wind to the downstream turbines augments their power output. With implementation of turbine control, the power outputs of the downstream turbines agree well with the observation data obtained in an earlier study. The results demonstrate the importance of controlling the rotational speed and pitch angle for actuator line simulations.
Impact of 3D segment profiling on friction losses of plain bearings in wind turbines main bearings
Authors: Jakobs T , Jacobs G , Euler J , Rolink A , Röder J 
Published: June 2024

Abstract
Wind power is a crucial technology in transitioning to a carbon-free energy future. To increase the economic competitiveness, the levelized cost of electricity of wind power needs to be further reduced. A critical factor contributing to maintenance expenses is the failure of main rolling bearings. Replacing these rolling bearings in the case of damages is a costly procedure as it necessitates dismantling the wind turbine drivetrain. Unlike conventional rolling bearings, segmented plain bearings allow for the up-tower replacement of individual faulty segments, significantly reducing downtime and maintenance costs. The FlexPad plain bearing concept specifically addresses the need for an easy-to-maintain main bearing for wind turbines. While the current FlexPad design guideline focuses on global geometrical parameters disregarding a detailed segment profile optimization, literature suggests that a 3D-profile on the segments can enhance bearing performance by reducing frictional losses. However, the investigations conducted in literature were limited to stationary thrust bearings. The FlexPad bearing's inherent flexibility and conical shape preclude direct application of the findings in literature. Therefore, a coupled elastohydrodynamic-multi-body simulation model was developed to account for the bearing's flexibility while investigating different 3D-profiles. This study quantifies the impact 3D-profiles on friction power, solid contact, and maximum hydrodynamic pressure, demonstrating the advantages. The best 3D-profiles achieve a decrease in friction power of 18.3% with an increase of the maximum hydrodynamic pressure of just 4.9%.
On the influence of rotor nacelle assembly modelling on the computed eigenfrequencies of offshore wind turbines
Authors: Reinhardt T , Sastre Jurado C , Weijtjens W , Devriendt C 
Published: June 2024

Abstract
Motivated by the mismatch of measured and computed eigenfrequencies for the second tower mode of offshore wind turbines as well as previous studies examining the influence of including flexible blades in structural models, the need to extend the current integrated model to include flexible blades became apparent. A basic modelling approach which takes the blades as beam elements was implemented in an in-house finite element model of offshore wind turbines and benchmarked for the NREL 5 MW reference turbine with OpenFast. Moreover, the modelling approach was benchmarked with measurements that were obtained during the installation of a Belgian offshore wind turbine. The inclusion of flexible blades is shown to have a significant influence on the second tower mode and is able to reduce the mismatch between measurements and computations. Furthermore, the capability of the inclusion of flexible blades to model the effects of additional parameters is presented. Overall, the need to extend the rotor nacelle modelling in structural models of offshore wind turbines beyond a lumped mass approach is demonstrated.
Comparative analysis of rolling contact fatigue life in a wind turbine pitch bearing with different modeling approaches
Authors: Rezaei Ashkan , Schleich Florian , Menck Oliver , Grassmann Matthis , Bartschat Arne , Nejad Amir R. 
Published: June 2024

Abstract
The load calculation for wind turbines usually does not take pitch bearings into account, and the pitch-bearing internal load distribution is calculated in a decoupled process. In the current study, a coupled wind turbine load simulation considering the pitch bearings is proposed. Internal pitch-bearing load distribution and roller contact fatigue life are compared to a decoupled approach using a high-fidelity finite-element model. Internal pitch-bearing load distribution can be an essential variable in almost all major pitch-bearing failures. Furthermore, rolling contact fatigue is one of the major types of pitch-bearing failure that can represent the bearing service life. The results show that the flexibility of the surroundings has an effect on the contact forces. As a result, the finite element model-based life calculation of the NREL 5 MW turbine predicts a longer rolling contact fatigue life for the bearing than the multi-body system-based one. For the IWT7.5, sample load cases indicate that this behavior is different, leading to the conclusion that the life of the bearing is significantly affected by the stiffness of the bearing and its surrounding components.
Leveraging Vision Transformers for Detecting Porosity in Wind Energy Composites
Authors: Khan AW , Balzani C 
Published: June 2024

Abstract
The structural robustness and operational efficiency of wind turbine rotor blades are crucial for the overall effectiveness of wind energy systems, often constructed with fiber-reinforced polymers (FRPs) and adhesives. However, porosity within these materials poses a significant threat, weakening structural strength and effectiveness. Air pockets lead to stress concentration points, reducing load-carrying capacity and elevating the risk of blade failure, especially under dynamic wind loads. Manual detection of these air pockets is laborious, necessitating automated inspection techniques. Advanced imaging technologies, such as computed tomography (CT) scanning and deep learning, hold promise for identifying and quantifying porosity in FRPs and adhesives, reducing labor while enhancing accuracy. The study introduces a transformer-based model for porosity detection, departing from convolution-based methods, emphasizing the incorporation of global context throughout the network. Leveraging Vision Transformer (ViT) framework advances, the model is applied to porosity segmentation in wind energy blades, showing promising results with limited datasets. The prospect of using larger datasets suggests potential for a versatile solution in segmenting porosity or voids in various wind energy blade composites, including adhesives.
Numerical simulation of stabilisation of floating wind with submerged hydrofoil
Authors: Wang Junxian , Yang Liang , Xing Jingru , Yang Jianhui 
Published: June 2024

Abstract
This research focuses on the optimal design and method of attaching a submerged hydrofoil to an offshore platform to enhance stabilisation. The flapping hydrofoil, exhibiting a hybrid motion combining heave and pitch, is engineered to convert incoming wave energy. It generates a distinctive wake that effectively counteracts incoming waves, thereby reducing wave impact. In this study, a NACA0030-type hydrofoil was strategically positioned between two columns of the platform model. Comprehensive analyses were conducted to evaluate the free-floating platform’s response to regular waves, with a focus on the attached hydrofoil. The results indicate that the hydrofoil significantly reduces the surge motion and drifting speed of the platform, affirming its effectiveness in enhancing stabilisation.
A Hybrid Testing Framework for Wind Turbine Mechanical Components
Authors: Nordtorp F. , Baş E. E. , Gomes C. , Abbiati G. 
Published: June 2024

Abstract
As wind turbines continue to increase in size, hybrid testing is emerging as a key-enabling solution for experimental assessment of their large mechanical components. Hybrid testing is conducted using a hybrid model which combines physically tested and numerically simulated components. In this work, the Kane method is proposed to formulate the equation of motion for the hybrid model of a wind turbine rotor system where one single blade is physically tested. The Kane method allows for formulating the equation of motion of multi-body-dynamic models efficiently and, therefore, it is widely used in state-of-art simulation software. The hybrid model of the rotor is successfully implemented on a single-degree-of-freedom test bench with a cantilever steel beam serving as the physical substructure. The performance of the implemented hybrid model is assessed through a comparison with a pure numerical simulation of the same system. The main finding of the study emphasizes the efficiency of incorporating physically measured restoring force as model parameters while formulating the equation of motion of a hybrid model.
Enhancing CFD-based design of wind turbine blades
Authors: Aa Madsen M H , Zahle F , Sørensen N N , Bottasso C L 
Published: June 2024

Abstract
CFD-based shape design is a state-of-the-art approach in wind energy that can lead to novel shape features. High computation costs have, however, until now hindered a widespread use of the approach. To address this issue, this work investigates two ways to enhance a CFD-based design framework, using a shape study of wind turbine blade tips as a test case. First, a quantification of the speed-up factor (× 3.6) achieved through so-called tailored meshes is presented. Then, a comparison of mesh adaptation strategies is given, further speeding up the procedure (× 2.3). The combined speed-up factor reaches above 8, showing that CFD-based shape design procedures may indeed be accelerated using tailored meshes and a correct mesh adaptation strategy.
Modelling of Wind Turbines as Porous Disks for Wind Farm Flow Studies
Authors: Catania M. , Pomaranzi G. , Fontanella A. , Zasso A. 
Published: June 2024

Abstract
This study explores the use of porous disks as a modeling approach for wind turbines in both wind tunnel experiments and computational fluid dynamics (CFD) simulations. Experimental testing is conducted on a 0.2m diameter disk made of wired mesh, measuring its wake for several yaw angles. The experiment is recreated in a CFD environment based on the porous-medium approach. The CFD model is validated against part of the measurements and it is used to further investigate the disk wake. Results indicate the porous disk wake resembles that of a wind turbine, especially at a downstream distance of four diameters, and the CFD model effectively captures the disk behavior. Discrepancies between experiment and CFD appear further downstream mainly due to the wake recovery process being only partially captured by the CFD model. When the disk has a yaw angle the wake is displaced laterally, but less than in a widely-accepted deflection model, and this could be due to the lack of wake curling.
A stably-stratified atmospheric inflow assimilated to measured mean profiles interacting with a wind park
Authors: Wrba Linus , Bührend Lukas , Englberger Antonia , Dörnbrack Andreas , Wildmann Norman 
Published: June 2024

AbstractIn this paper, a simulation chain is presented. This method comprises the precursor large-eddy simulation (LES) of a stably-stratified atmospheric boundary layer (ABL), the assimilation of the simulated mean velocities to measured wind profiles, and finally a simulation of the generated turbulent ABL flow passing through two wind turbines in a row. The high-resolved precursor simulation with a horizontal grid spacing of 3 m accounts for the characteristic turbulence of the stably-stratified ABL. Using an assimilation technique, the horizontal velocities are adapted accurately to the measured mean wind profiles for the WiValdi wind farm site at Krummendeich. The wakes of two wind turbines in a row with the assimilated inflow is successfully computed. With the simulation chain presented, it is possible to generate realistic atmospheric inflows for wind-turbine simulations with manageable computational effort.