bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical sensitivity analysis of strain gauge configurations in the main shaft of wind turbines
Authors: Bacaicoa J , Iriarte X , Aginaga J , Plaza A 
Published: June 2022

Abstract
Wind turbines are reaching their remaining useful life, thus it is important to guarantee the well status of its components. A common way to check the status is to measure the loads on the Low Speed Shaft with strain gauges, but not always are bonded perfectly. In this work a sensitivity analysis of strain gauge configurations is carried out, where the influence of geometric and material parameters, and misplacement and misalignment parameters is analyzed. An analytical model for a single gauge was developed, obtaining a relation between the exerted loads and the strain measured by the strain gauge. By means of Taylor approximations the estimated loads were approached in order to have into account the influence of the uncertainty of parameters. Results shown that the sensitivities with respect to the geometric and material parameters did not depend on the secondary loads while in the sensitivities with respect to the gauge bonding parameters the cross-talk effect was present. In order to obtain realistic numerical results, a horizontal-axis NREL 5-MW wind turbine was simulated in OpenFAST with two wind-speed scenarios. The uncertainty of the estimated loads by the strain gauge configurations was calculated.
Efficient Loads Surrogates for Waked Turbines in an Array
Authors: Shaler Kelsey , Jasa John , Barter Garrett E. 
Published: June 2022

Abstract
Accurately and efficiently predicting wind turbine structural loading is a crucial step in wind farm design. Without considering structural loading, wind farm optimization could negatively impact turbine fatigue and ultimate loads, especially for waked and partially waked turbines, which could result in higher maintenance costs and reduced turbine lifetime. However, predicting turbine loads throughout an array is a costly step, as these quantities require time-accurate results across long time histories, which is often intractable for large array optimization. Therefore, surrogate models that link array spacing to load outputs are often used, but the surrogates are then unique to the inflow conditions and array configurations in the training library. This work develops surrogate models for many wind turbine load outputs based solely on rotor plane velocity measurements, with no required input about array configuration or freestream inflow parameters. Surrogate models were constructed for many turbine quantities of interest (QoI), considering mean, standard deviation, ultimate, and fatigue loads. In general, most QoI statistics were accurately captured, as measured by predicted vs. actual correlation coefficient, confirming the suitability of the approach. Temporal mean values of the QoI required only temporal mean measurements of the rotor plane inflow velocity. However, accurate prediction of temporal standard deviation, ultimate, and fatigue values of QoI also required temporal standard deviations of the rotor plane velocity field. Poor surrogate performance was observed when too many correlated inputs were used, such as multiple velocity components. If the fewest inflow parameters are used to construct the surrogates, the average correlation coefficient value for all output QoI statistics is 0.89. Surrogates for standard deviations and damage equivalent loads (DELs) of turbine QoIs generally had lower accuracy and tower-base and shaft load channels posed the most difficult to capture accurately. The results suggest that these surrogates could be easily paired with analytic wake models, which are frequently used for pre-construction wind farm array optimization, to account for turbine loading in addition to power production. By including the optimal inflow conditions, the surrogate accuracy can improve to an average correlation coefficient value for all output QoI statistics of 0.92. This work has established the ability to build accurate surrogates for mean, standard deviation, ultimate load, and DEL turbine QoI values based on the rotor plane inflow velocity, and identified which inflow conditions lead to greater surrogate accuracy.
Probabilistic surrogates for flow control using combined control strategies
Authors: Debusscher Charles Marie J , Göçmen Tuhfe , Andersen Søren Juhl 
Published: June 2022

Abstract
Wind farm flow control (WFFC) is a promising technology for improving wind farm operation and design. The presented study focuses on the combination of the two most prominent WFFC strategies, yaw-based wake-steering and axial induction control via constant blade pitch, for maximising the wind farm power production with and without a load constraint. The optimisation is performed via data-driven polynomial-based probabilistic surrogate models, calibrated through a range of LES and aeroelastic simulations for a 2-turbine setup. The results indicate the yaw-based wake-steering to be the driving mechanism to increase the wind farm power production, particularly when loads are not considered. However, axial induction is seen beneficial for load alleviation, especially in close spacings. Overall, the analyses highlight the potential of combined WFFC strategies for power optimisation in a safety-critical system and provides a probabilistic approach for data-driven multi-objective farm flow control.
Study of the influence of met-ocean data in fatigue loads calculations of a floating offshore wind turbine
Authors: Lizarraga-Saenz Ion , Artal-García Jesús , Martín-San-Román Raquel , Vittori Felipe , Azcona-Armendáriz José 
Published: June 2022

Abstract
The design of a floating offshore wind turbine (FOWT) requires the computation of loads with time domain simulations that depend heavily on the metocean conditions of the site. Guidelines, such as IEC 61400-3, recommend the use of scatter tables with the combined probability of the significant wave height (Hs) and peak period (Tp) as a function of the mean wind speed. Nevertheless, at early engineering phases it may be difficult to obtain the adequate environmental wind-wave data where both parameters are correlated for the site of interest. The main objective of this work is to assess the influence of neglecting or not the correlation between wind speed and wave data in the resulting fatigue Damage Equivalent Load (DEL) for different FOWT components. The analysis is performed through the comparison of the fatigue loads obtained for correlated and non correlated wind-wave data. Results show that fatigue loads are very similar for both data sets at the rotor loads, and present slight differences, at mooring tensions and tower base. The use of a simpler metocean data, where wave height and period occurrences are given independently of the wind speed, might be a sufficient solution for initial fatigue load estimations.
Power curve measurement of a floating offshore wind turbine with a nacelle-based lidar
Authors: Özinan Umut , Liu Dexing , Adam Raphaël , Choisnet Thomas , Cheng Po Wen 
Published: June 2022

AbstractUnderstanding the power performance of floating offshore wind turbines is essential for the economics of floating wind, which requires reliable wind speed measurements. This work investigates the use of nacelle-based lidar technology for power curve measurement of a floating offshore wind turbine. In a five-month long measurement campaign, a nacelle-based lidar was installed on top of a 2MW floating offshore wind turbine. It was used to reconstruct the wind field including a carrier-to-noise ratio threshold filter, an availability filter and a hard target filter for the one hertz line of sight measurements. The quality of lidar wind speed estimations were compared to nacelle-based sonic anemometer measurements in terms of their linear correlation and root mean squared error of ten minute averages. The correlation of rotor averaged wind speed estimation of lidar and sonic wind speed measurements showed a 0.97 coefficient of determination. Variability of correlation is investigated in terms of nacelle excitations to identify the uncertainty related to the use of nacelle lidars for floating wind applications. Findings show that the quality of correlation decreased with higher nacelle excitations, which are caused by both wind and waves. Consequently, wind speed estimations were used for power curve measurement to investigate the qualification of using a nacelle-based lidar for such an application. Although lidar measurements showed higher scatter, they provided a reasonable wind speed estimate and a similar power curve to sonic measurements.
Shell buckling simulations of suction buckets with stochastic and deterministic imperfection forms
Authors: Böhm Manuela , Schaumann Peter 
Published: June 2022

Abstract
Suction buckets are large shell structures that have become a prominent alternative to pile foundations for bottom-fixed and floating offshore wind turbines. They are embedded by applying negative pressure, which leads to a high risk of structural buckling during the installation. The prediction of the buckling strength of such large shells is subject to uncertainty, since it depends significantly on the initial geometric imperfections resulting from the fabrication process. The aim of this work is to understand and reduce uncertainties in the determination of the buckling pressure. Previous work on suction buckets revealed that the choice of a representative imperfection form and amplitude is very challenging and has not yet been solved in a generalized manner. In this work, a stochastic modeling approach is introduced, which considers more realistic imperfection patterns. This approach is compared to widely established imperfection forms such as buckling mode affine imperfections and analytically described weld depressions. The generated imperfection patterns are applied to geometrically and materially nonlinear finite element models and the buckling pressures are calculated. By quantifying the impact of different imperfection forms and amplitudes, uncertainties can be reduced, and design optimization and cost minimization are enabled.
Modified Constitutive Relation Error for Multi-Physics Wind Turbine Calibration
Authors: Roussel A. , Capaldo M. , Chamoin L. , Argaud J.-P. 
Published: June 2022

Abstract
Asbtract. Despite the availability of massive operation datasets, numerous uncertain parameters linger in offshore wind modeling. We propose an identification procedure based on reliability of information coming from both modeling and measurements. The procedure is constructed from the modified Constitutive Relation Error concept, which considers measurement noise and model uncertainties. This concept is extended to a multi-physics context involving nonlinear fluid-structure interactions. Several constitutive laws are assumed unreliable and relaxed for comparison with data and safe identification.
Multi-Physical Simulation Toolchain for the Prediction of Acoustic Emissions of Direct Drive Wind Turbines
Authors: Cardaun Martin , Mülder Christoph , Decker Thomas , Dilba Boris , Duda Tobias , Schelenz Ralf , Jacobs Georg , Hameyer Kay , Keuchel Sören 
Published: June 2022

Abstract
To address the acoustic behaviour of wind turbines, particularly tonalities, in an early design stage, accurate simulation toolchains have to be developed. In this work a novel simulation approach for the prediction of tonalities of direct drive wind turbines is presented. Comprehensive work is carried out in the fields of electromagnetic force excitation, structural sound transfer and radiation as well as airborne sound propagation. The developed methods are combined to a simulation toolchain to formulate a multi-physical system model of a direct drive wind turbine in order to predict tonal sound behaviour. These methods will be presented and discussed in detail in the course of this work. First, the approach, integrating the electromagnetic airgap forces of the large generator into a multi body simulation model of the mechanical turbine, is explained and validated with test bench measurements. Following, the modeling of the respective mbs is presented which calculates the resulting surface velocities. This model is solved in the time domain to account for the interaction between the external loads that are highly nonlinear and low-frequency and the high-frequency excitation forces of the generator. Subsequently, the methods for calculating the airborne sound emission in the vincinity of the turbine resulting from the surface velocities are discussed.
A surrogate model of offshore wind farm support structures for wind farm design and financial valuation
Authors: McWilliam Michael K. , Friis-Møller Mikkel , Pollini Nicolò , Dykes Katherine , Jensen Morten 
Published: June 2022

Abstract
In the preliminary phases of offshore wind farm development, very little information on project design are available for supporting financial valuation and site design. In this work, we develop a surrogate model for offshore wind support structure mass for input to techno-economic analysis that is based on a small set of input parameters. Using reference turbines and a broad set of met-ocean conditions, a large design spaced is developed from which a sampling of conditions is used to estimate the dimensions and mass of monopile support structures. The results are parameterized using statistical methods to create a functional model of costs relative to high-level site and technical inputs. To preserve the transparency of the model input-output relationships, a statistical surrogate model is used based on quadratic functions of the inputs. Overall, the rated power and rotor diameter of the turbine has the greatest influence on the mass, followed by the specific power. The water depth was the next most important environmental parameter, followed by wave period. The full surrogate model captures 98.5% of the variance of the monopile mass as a function of the above inputs. We present results related to monopile foundations, but the methodology is flexible and can be applied also in the case of other types of support structures.
Wind farm layout and unconstrained hub height optimization using genetic algorithms applied to different power densities
Authors: Kirchner-Bossi Nicolas , Porté-Agel Fernando 
Published: June 2022

Abstract
LES and wind tunnel studies have shown significant benefit when allowing turbines (T) in a wind farm to adopt different heights. This work presents two new genetic algorithms (GA) that perform wind farm layout optimization (WFLO) involving continuous and top-unconstrained Z-coordinate (XYZ-WFLO), applied to different power densities (PD) and using Horns Rev 1 as case study. One provides each turbine the possibility to adopt any height (XYZInd
). The other is a self-adaptive GA allowing turbines to automatically cluster into a fixed number of maximum heights (XYZClus). When considering 80T, compared to the baseline the levelized cost of energy (LCOE) is reduced up to 2.3% (XYZInd
), vs. a 0.88% improvement obtained through XY-WFLO. XYZClus
shows performances close to XYZInd even with just 2 Z-clusters (2%), which can entail a more feasible solution for the industry. The allowance for different heights exerts the main role in the performance improvement, in contrast to merely allowing turbines to increase their height. Results considering different PD yield the optimum XYZ-WFLO performance through 70T (2.5% LCOE decrease), while XY-WFLO provides best results considering 60T (1.5%). This indicates that the most efficient XYZ-WFLO solution also allows for bigger power productions. The benefit of XYZ-WFLO against XY-WFLO increases with PD. The optimized solutions arrange turbines into very few different heights, whose amount is positively related to PD. Finally, it is verified that the solutions attained reproduce the vertically staggered patterns proposed in conceptual studies (LES, wind tunnel).
Stability analysis of vortex-induced vibrations on wind turbines
Authors: Riva Riccardo , Horcas Sergio G. , Sørensen Niels N. , Grinderslev Christian , Pirrung Georg R. 
Published: June 2022

Abstract
A parked wind turbine can be subjected to large yaw angles, which causes vortex shedding. Under some particular inflow conditions, the interaction between the shed vorticity and the blade structure could lead to Vortex-Induced Vibrations (VIV). VIV are an instability where the response grows until it reaches a limit cycle oscillation. In this paper, we will focus on this last part of the response. We will see that the shedding makes the aeroelastic system linear time-periodic, and study its stability with Floquet theory. We will use high-fidelity simulations of different inflow conditions, and quantify the stability of the system using a model-free approach.
Aeroelastic Stability Analysis of a Quad-Rotor Wind Turbine
Authors: Ferede Etana , Stillman Alexander , Gandhi Farhan 
Published: June 2022

Abstract
This paper presents the aeroelastic stability analysis of a quad-rotor wind turbine and identifies modes with low damping that are otherwise not present on a single-rotor wind turbine. The non-linear dynamics of a wind turbine model in SIMPACK, without considering wind shear and tower shadow, is linearized around a steady-state; followed by MBC transformation resulting in LTI model. Standard eigenvalue analysis of LTI model is carried out to capture the natural frequency and damping of a quad-rotor wind turbine as a function of wind speed. Results show that several modes with low damping (besides the low damping modes observed on a single-rotor wind turbines) are identified where the damping ratio is less than 1% over the entire operation range.
High Wind Speed Performance of AeroMINE at Pilot-Scale
Authors: Houchens B C , Marian D V , Pol S , Westergaard C H 
Published: June 2022

Abstract
AeroMINEs consist of a mirrored pair of foils that have no external moving parts. A low-pressure region is created between the foils. The foils are hollow and the low-pressure side skins contain orifices (air-jets) that allow air to flow from the interior of the foil to the exterior flow, driven by the suction between the mirrored pair. This flow is ducted to an internal turbine and generator, producing electricity. A series of pilot-scale field (1-m chord) demonstrations were performed on AeroMINEs. These included both low wind speed tests (<5 m/s) and high wind speed tests (>9 m/s) at the Sandia National Laboratories Scaled Wind Farm Technology site in Lubbock, Texas, USA. Here the performance in high wind speed conditions is studied while varying the air-jet area. An efficiency of 25%, or 42% of Betz limit, was achieved for the maximum air-jet area.
Real-world development challenges of the Clarkson University 3 meter ducted wind turbine
Authors: Visser Kenneth D. 
Published: June 2022

Abstract
The enticing viability of ducted turbines continues to be demonstrated around the world, both numerically and experimentally, however real-world implementation of this technology has historically been a challenge. Promising wind tunnel results for a 2.5 meter rotor ducted turbine model at Clarkson University have led to the construction of a 3 meter prototype test bed, installed on the Clarkson campus. An overview of the development process and the resulting experimental performance measurements on the 3 meter unit is presented. Construction of a prototype for field tests, including component selection, fabrication details of the structure, and selection of downstream electronics is reviewed. Performance results from various system implementations and lessons learned are compared. The turbine demonstrated Cpt efficiencies, based on the duct area, of up to 0.45.
Numerical Study using RANS model to Predict Loading of a Wind Turbine Blade with a Trailing Edge Flap
Authors: Jami R , Samara F , Johnson D A 
Published: June 2022

Abstract
A numerical study was conducted with a 3D steady state Computational Fluid Dynamics (CFD) model using k-ω SST at SATP conditions for air. The mesh geometry is based on a S833 airfoil with a trailing edge flap to predict the lift and moment loads. This airfoil is representative of a wind turbine blade. A set of static CFD simulation cases were conducted with a free stream velocity of 29 m/s at an angle of attack (α) between -4° and 20°. A trailing edge flap is also present on the airfoil which was operated between an angle (αf) of -20° and 20°. The airfoil has a chord of 178 mm with the trailing edge flap covering 20% of the length and chord-based Reynolds number of 350,000. The CFD results were compared against an experimental study performed in a closed-loop wind tunnel at the University of Waterloo. The wind tunnel has a contraction ratio of 9:1 and a cross section of 0.61 m square. The experimental data showed that lift forces increased at a larger angle of attack and larger downward flap angle up until stall. Moment on the blade is relatively constant regardless of the angle of attack, however, increases significantly with upward flap angle. The CFD results showed very similar results in both the lift and moment coefficient, with all angle configurations having over 90% agreeability excluding α near +/- 20°.
Ground effect for ducted wind turbines: A computational study
Authors: Sheshadri Shraddha M. , Dighe Vinit V. 
Published: June 2022

Abstract
Ducted wind turbines (DWTs) can take the advantage of ground effect (GE) when installed close to urban areas. To this aim, a parametric study to investigate the aerodynamic performance of DWTs in relation to three different ground distances are investigated. The flow around a commercial DWT model using a simplified duct actuator disc (AD) model based on Reynolds Averaged Navier-Stokes (RANS) equations is performed. The results indicate that DWTs placed close to the ground will lead to increased mass flow rate the turbine plane, and thereby improving the aerodynamic performance. However, the additional ground force leads to an asymmetric flow-field at the turbine plane, which will ultimately induce unsteady forces on the DWT system. The present analysis will serve as a strong recommendation to address siting issues for DWT manufacturers.
On Theoretical Foundations of Human and Robot Vision
Authors: Wang Yingxu 
Published: June 2022

Abstract
A set of cognitive, neurological, and mathematical theories for human and robot vision has been recognized that encompasses David Hubel’s hypercolumn vision theory (The Nobel Prize in Physiology or Medicine 1981 [1]) and Dennis Gabor’s wavelet filter theory (The Nobel Prize in Physics 1971 [2]). This keynote lecture presents a theoretical framework of the Cognitive Vision Theory (CVT) [3-6] and its neurological and mathematical foundations. A set of Intelligent Mathematics (IM) [7-13] and formal vision theories developed in my laboratory is introduced encompassing Image Frame Algebra (IFA) [3], Visual Semantic Algebra (VSA) [4], and the Spike Frequency Modulation (SFM) theory [5]. IM is created for enabling cognitive robots to gain autonomous vision cognition capability supported by Visual Knowledge Bases (VKBs). Paradigms and case studies of robot vision powered by CVTs and IM will be demonstrated. The basic research on CVTs has led to new perspectives to human and robot vision for developing novel image processing applications in AI, neural networks, image recognitions, sequence learning, computational intelligence, self-driving vehicles, unmanned systems, and robot navigations.