bluuebunny/crossref_metadata_2025_split huggingface dataset:
Biomimetic individual pitch control for load alleviation
Authors: Coquelet M , Bricteux L , Lejeune M , Chatelain P 
Published: September 2020

Abstract
Individual pitch control has shown great capability of alleviating the oscillating loads experienced by wind turbine blades due to wind shear, atmospheric turbulence, yaw misalignement or wake impingement. This work presents a bio-inspired structure for individual pitch control where neural oscillators produce basic rhythmic patterns of the pitch angles, while a deep neural network modulates them according to the environmental conditions. This mimics, respectively, the central patterns generators present in the spinal chord of animals and their cortex. The mimicry further applies to the neural network as it is trained with reinforcement learning, a method inspired by the trial and error way of animal learning. Large eddy simulations of the reference NREL 5MW wind turbine using this biomimetic controller show that the neural network learns how to reduce fatigue loads by producing smooth pitching commands.
Rejecting wake-rotor overlapping load disturbances: An extension to active power control of wind farms
Authors: Vali M , Petrović V , Steinfeld G , Kühn M 
Published: September 2020

Abstract
This paper studies an extension to the active power control of wind farms for further structural load alleviation of waked wind turbines. We demonstrate that the structural fatigue loading of a downstream turbine, which its rotor overlaps with wakes of its upwind turbine, can be significantly alleviated, while the wind farm power production follows a power reference signal. A load variations model is proposed, based on the multi-rotor concept, to sense the variations of the wind velocity and the associated loading across the rotor area of a single wind turbine. Then, an individual rotor control is proposed to reject the rotor-wake overlapping load disturbances about an operating condition, commanded with the closed-loop APC at the wind farm level. The applicability and key features of the controller are discussed with a wind farm example consisting of 2×2 turbines. A large-eddy simulation model is employed for resolving the turbulent flow, the wake structures and its interaction with an atmospheric boundary layer. The effectiveness of the proposed load disturbance rejection is evaluated using the damage equivalent load of the tower base fore-aft bending and torsional moments of the individual wind turbines.
Wake redirection for active power control: a realistic case study
Authors: Kretschmer Matthias , Raach Steffen , Taubmann Julian , Ruck Nico , Cheng Po Wen 
Published: September 2020

Abstract
This paper presents a realistic case study of how wake redirection can be used to provide ancillary grid service. Wake redirection is a wind farm control approach in which the wake of a wind turbine is redirected by imposing a yaw misalignment to minimise the flow interactions with downwind wind turbines. The increase in power is controlled in our approach to meet a requested power increase. The methodology is implemented in FAST.Farm, a mid-fidelity wind farm simulation tool. In a case study with 12 wind turbines the applicability of the methodology is analysed. Hereby, provision of active power control was achieved in some cases. Structural loads were investigated at tower base, blade root and drivetrain of the turbines, indicating that the concept tends to increase the fatigue damage compared to a baseline case where all turbines are operated with zero yaw misalignment.
Experimental Analysis of a Scaled-Down Vestas Four-Rotor Wind Turbine
Authors: Filsoof Oliver Tierdad , Yde Anders , Bøttcher Peter , Zhang Xuping 
Published: September 2020

Abstract
In this work, a 1/30 scaled-down Vestas four-rotor demonstrator wind turbine is established as an experimental setup. The experimental setup is used to analyze how the structural natural frequencies are affected by the rotor speed for a multi-rotor wind turbine. To have comparable dynamic behavior between the Vestas turbine and the experimental setup, Froude scaling is used. For standstill tests, a metal brushing technique is employed to excite the setup, and when rotating an automated impulse mechanism provide impulses to the rotor blades. Modal testing experiments are conducted, and testing results show that standstill frequencies between the Vestas turbine and experimental setup coincided. The experiment demonstrates that by using the automated impulse mechanism from 40 rpm to 110 rpm, edgewise whirling modes are excited and proportional to the rotor speed. The setup experiences large vibrations if the rotor speed continues increasing beyond 110 rpm using the impulse mechanism. Switching to the metal brushing technique achieves better results, and makes it possible to see that both the flapwise and edgewise whirling modes are proportional to the rotor speed.
Reference Design and Simulation Framework of a Multi-Megawatt Airborne Wind Energy System
Authors: Eijkelhof Dylan , Rapp Sebastian , Fasel Urban , Gaunaa Mac , Schmehl Roland 
Published: September 2020

Abstract
In this paper, we present the design and computational model of a representative multi-megawatt airborne wind energy (AWE) system, together with a simulation framework that accounts for the flight dynamics of the fixed-wing aircraft and the sagging of the tether, combining this with flight control and optimisation strategies to derive the power curve of the system. The computational model is based on a point mass approximation of the aircraft, a discretisation of the tether by five elastic segments and a rotational degree of freedom of the winch. The aircraft has a wing surface area of 150 m2 and is operated in pumping cycles, alternating between crosswind flight manoeuvres during reel out of the tether, and rapid decent towards the ground station during reel in. To maximise the net cycle power, we keep the design parameters of the aircraft constant, while tuning the operational and controller parameters for different wind speeds and given contraints. We find that the presented design can generate a net cycle power of up to 3.8 megawatts.
Flight Anomaly Detection for Airborne Wind Energy Systems
Authors: Salma Volkan , Schmehl Roland 
Published: September 2020

Abstract
Airborne wind energy (AWE) systems use tethered flying devices to harvest wind energy beyond the height range accessible to tower-based turbines. AWE systems can produce the electric energy with a lower cost by operating in high altitudes where the wind regime is more stable and stronger. For the commercialization of AWE, system reliability and safety have become crucially important. To reach required availability and safety levels, we adapted an fault detection, isolation and recovery (FDIR) architecture from space industry. This work focuses on, “flight anomaly detection” layer of the FDIR. Tests verifies that proposed architecture is capable of detecting flight anomalies without generating false alarms.
An hybrid approach for the comparison of VAWT and HAWT performances for floating offshore wind turbines
Authors: Matoug C , Augier B , Paillard B , Maurice G , Sicot C , Barre S 
Published: September 2020

Abstract
This article describes the experimental comparison of the DTU 10MW HAWT with the WindQuest 10MW VAWT scaled models when both fitted on the Nautilus-10 semi-submersible. For the campaign in Ifremer Wind&Wave tank, different rotor representations are tested from inertia only to hybrid testing with propellers and a Software in the Loop. The hybrid testing uses a tabulated approach for thrust computation and is discussed in this article. The different thrust reproduction methods are compared to OpenFAST simulations calibrated during the Lifes50+ project and used as reference points. When quantifying the scale model’s fidelity to Open Fast, cross-correlation was increased up to 14% with the use of the SiL. Thanks to the validation of hydrodynamic simulations based on experimental responses of the floater, it is shown that the VAWT rotor can be upscaled to 13MW for the same platform.
Characterizing turbine inflow during a stability transition using dual-Doppler radar measurements
Authors: Hirth Brian D. , Schroeder John L. 
Published: September 2020

Abstract
Measurements from two specialized Doppler radars are used to construct a dual-Doppler synthesis of the boundary layer wind flow during an unstable-to-stable transition. Three rotor sweep concepts are inserted into the flow to evaluate turbine inflow variability across the rotor sweeps. One-second turbine inflow forecasts are constructed using an advanced advection correction technique at each rotor grid point allowing for detailed statistical analysis of shear, veer, and turbulence intensity across the three rotor sweeps.
OC6 Phase I: Investigating the underprediction of low-frequency hydrodynamic loads and responses of a floating wind turbine
Authors: Robertson A N , Gueydon S , Bachynski E , Wang L , Jonkman J , Alarcón D , Amet E , Beardsell A , Bonnet P , Boudet B , Brun C , Chen Z , Féron M , Forbush D , Galinos C , Galvan J , Gilbert P , Gómez J , Harnois V , Haudin F , Hu Z , Dreff J Le , Leimeister M , Lemmer F , Li H , Mckinnon G , Mendikoa I , Moghtadaei A , Netzband S , Oh S , Pegalajar-Jurado A , Nguyen M Q , Ruehl K , Schünemann P , Shi W , Shin H , Si Y , Surmont F , Trubat P , Qwist J , Wohlfahrt-Laymann S 
Published: September 2020

Abstract
Phase I of the OC6 project is focused on examining why offshore wind design tools underpredict the response (loads/motion) of the OC5-DeepCwind semisubmersible at its surge and pitch natural frequencies. Previous investigations showed that the underprediction was primarily related to nonlinear hydrodynamic loading, so two new validation campaigns were performed to separately examine the different hydrodynamic load components. In this paper, we validate a variety of tools against this new test data, focusing on the ability to accurately model the low-frequency loads on a semisubmersible floater when held fixed under wave excitation and when forced to oscillate in the surge direction. However, it is observed that models providing better load predictions in these two scenarios do not necessarily produce a more accurate motion response in a moored configuration.
Long-range Doppler lidar measurements of wind turbine wakes and their interaction with turbulent atmospheric boundary-layer flow at Perdigao 2017
Authors: Wildmann Norman , Gerz Thomas , Lundquist Julie K. 
Published: September 2020

Abstract
As part of the Perdigão 2017 campaign, vertical RHI (range-height indicator) scans with long-range pulsed Doppler wind lidars were performed aligned with the main wind direction and a wind turbine (WT) located on a mountain ridge. The measurements are used to not only retrieve flow velocities, but also their variance and - by using the turbulent broadening of the Doppler spectrum - also turbulent kinetic energy (TKE) dissipation rate. The study shows that turbulence in the WT wake is dependent on the turbulence of the inflow, but also on atmospheric stability. In stable atmospheric conditions, wakes could be analyzed up to five rotor diameters downstream (D) and showed the maximum turbulence in the wake at 2-3 D, whereas in unstable conditions, the maximum was found at 2 D and the wake could not be detected further than 3 D. A clear dependency of wake turbulence enhancement on inflow turbulence intensity is found, which levels out to no further enhancement at turbulence intensities of 30%.
Experimental test of variable loads on a vertical-axis wind turbine
Authors: Brandetti L , Tavernier D De , Leblanc B , Ferreira C 
Published: September 2020

Abstract
The paper presents an experimental study of applying variable loads on a vertical-axis wind turbine (VAWT). The experiment is conducted in an open-jet wind tunnel on a two-bladed Darrieus VAWT equipped with active individual blade pitch control. Variable loads are achieved by dynamically changing the pitch angle of the individual blades and by keeping the wind speed of the tunnel constant. The blade loads are measured using strain gages and the flow velocity is measured upwind and downwind of the rotor using a hotwire. Dynamic inflow phenomena are clearly visible both in the turbine loads and in the velocity field. A time delay based upon the flow convection in the wake is identified. It results that the induction of the turbine can be controlled by changing the pitch of the blades. The experimental database allows to validate a new dynamic inflow model for VAWT and will be made publicly available for research purposes.
Wind tunnel testing of a wind turbine in complex terrain
Authors: Nanos Emmanouil M , Yilmazlar Kutay , Zanotti Alex , Croce Alessandro , Bottasso Carlo L 
Published: September 2020

AbstractThe paper describes the development of a scaled model of complex terrain, suitable for terrain-wind turbine interaction wind tunnel studies, taking into account flow similarity criteria. The size and the geometry of the experimental model of the complex terrain were refined using results of CFD simulations in order to achieve the best possible flow similarity and avoid edge effects arising from the finite (relative to the rotor size) terrain geometry. Moreover, Particle Image Velocimetry was used to survey the flow field on a longitudinal plane along the terrain center line. Flow measurements with and without a wind turbine model enabled to quantitatively evaluate the speed up produced by the terrain in the region of the wind turbine and the effect of the terrain on the wake characteristics of the wind turbine model.
Bayesian based estimation of turbulent flow fields from lidar observations in a conventionally neutral atmospheric boundary layer
Authors: Bauweraerts Pieter , Meyers Johan 
Published: September 2020

Abstract
In this paper, we consider the reconstruction of 3D turbulent flow fields from a time series of lidar data in a conventionally neutral atmospheric boundary layer (CNBL). For the reconstruction we use the maximum a posteriori estimate of the flow field. This corresponds to an optimization problem, with a cost function that has two contributions; a first term originating from the prior belief on the probability of having a certain turbulent flow field without any observations. Flow field fluctuations are assumed normally distributed and thus statistically fully determined by the mean and two-point covariance of the velocity field. The second term, is related to the likelyhood of the observations, influenced by model and measurement uncertainties. The two-point covariance is computed and found to be significantly altered by the Coriolis force, breaking up longer streamwise velocity streaks and veering spanwise structures by ∼ 45° with respect to the mean flow direction. For the reconstruction, we consider two different scanning modes, a plan position indicator (PPI) mode and a trajectory which is based on a Lissajous curve. For the PPI scanning mode we find that the mean squared error of the reconstructed velocity field is around 10% of the background variance in the scanning plane, and quickly increases outside this region. The Lissajous curve on the other hand attains an average error of 40% over the scanning region, which spans almost the whole BL height.
High-Torque Oscillating Wind Energy Generator
Authors: Garzozi A , Dunaevich L , Greenblatt D 
Published: September 2020

Abstract
This research investigates a novel concept in small-scale wind-energy generation. Instead of rotating turbine blades, the present concept produces reciprocating motion that is achieved by alternately activating boundary layer control (slot blowing) on opposite sides of a circular cylinder. This is commonly called the Coandă-effect, and here we deploy it periodically on a spring-stabilized vertical cylinder, to produce reciprocating motion. This
Co
andă-based
Re
ciprocating (CoRe) system converts wind energy to mechanical work. Compared to wind turbines and windmills, the CoRe system generates higher torque and is therefore well suited to directly driving positive displacement pumps for drip-irrigation or reverse osmosis water desalination. This new approach necessitates the investment of energy in order to extract energy from the wind and therefore a major challenge is to maximize the output/input ratio in order to render the concept viable. Previous preliminary wind tunnel tests conducted on the CoRe system produced gross and net power coefficients of 10% and 3% respectively. However, the blowing slot design has a decisive impact on output power. On the basis of data presented in the literature and our computational analysis, the CoRe system produces significantly greater torque than all types of wind turbines with net power coefficients over 10%.
Small Wind Power (SWP) as a Renewable Energy Source in Morocco
Authors: Tenghiri Lhoussaine , Zair Rachid , Koubida Sallem , Bentamy Anas 
Published: September 2020

Abstract
This paper has two main objectives: (1) to identify the causes behind the low penetration of SWP in Morocco, and (2) to study the design of a horizontal axis wind turbine for domestic applications in the Moroccan context by following the design requirements of the international standard of small wind turbines IEC 61400-2. The three most relevant barriers in Morocco are found to be in this order: a) the regulatory barrier, b) the technical barrier and, c) the financial and market barriers. Further, a proposed design of a 11 kW SWT power that would be the most in demand helps in identifying clearly the technical barrier. Within the list of components of this typical design, locally manufactured components are limited to the rotor, the main shaft, the nacelle cover and frame as well as the tower and the foundation. The total cost associated to these components is very low compared to the other imported components in the wind turbine assembly. The constraint of designing a 11kW SWT’s economic viability can therefore only be fully satisfied if all components are locally produced.
Probabilistic Design Space Mapping: Application to Airfoil Design for HAWT
Authors: Mazza P. , Pereira R. , De Oliveira G. 
Published: September 2020

Abstract
This work presents an airfoil probabilistic design methodology for wind energy applications, using an analytical approach to estimate the angle-of-attack fluctuations produced by non-uniformities in the incoming wind field. The contemplated wind speed perturbations include wind shear, yaw misalignment and atmospheric turbulence, and several combinations of the perturbation sources are considered. A probabilistic design space mapping is carried out to evaluate which wind conditions occur more often in practice and how likely each specific combination of perturbation sources is to occur, for both an onshore and offshore scenario. The proposed probabilistic method and specifically the level of angle-of-attack fluctuations is verified by employing the aero-elastic simulation tool FAST for each case. Finally, the probabilistic approach is used to design airfoils sections employing the genetic multi-objective airfoil optimization tool Optiflow, where the probability of angle of attack fluctuations for a given scenario is used to prescribe the operational angle of attack range over which the airfoil performance is relevant. Results of the airfoil optimization for a 24% thick section are presented, illustrating the trends in foil geometry and aerodynamic performance for three different possible optimization objective functions.
Wind farm layout optimization with special attention on noise radiation
Authors: Cao Jiufa , Zhu Weijun , Shen Wenzhong , Sun Zhenye 
Published: September 2020

Abstract
This work presents a new wind farm layout design methodology that calculates the noise radiation using an advanced sound propagation model. Firstly, the wake velocity in wind farm is calculated via an improved engineering wake model. Then, the aero-acoustic noise source of wind turbine is obtained using the BPM method. To simulate the noise level at far field, the basis of propagation model is built on the parabolic wave equation (PE) method. The cost of energy for wind farm is assessed via an engineering model. Finally, based on the genetic algorithm (GA) optimization method, and taking the noise radiation level into account, a new wind farm layout design methodology is developed to solve a trade-off between cost and noise for wind farm.
Combined wind turbine design and wind farm layout optimisation under wind resource uncertainty
Authors: Swamy S Krishna , Szklarz S , Fonseca R M , Bulder B H 
Published: September 2020

Abstract
Applications of the wind farm layout optimisation problem focus on optimally positioning a certain number of turbines within a wind farm so that annual energy production (AEP) is maximised. This study addresses an earlier stage in the wind farm development process. Instead of optimising the individual positions of a certain number of turbines of a selected model, the control variables in the optimisation are rotor diameter of a wind turbine of fixed nominal power, number of turbines in a wind farm of fixed area and orientation angle of turbines in the farm. In addition to AEP, this study considers capital and operational expenses of a wind farm to calculate the levelized cost of energy (LCoE), which is the objective function. Given the stage of development addressed, it is also essential that uncertainty is considered; here the focus is on the impact of wind resource uncertainty. The optimisation is performed with a recently developed state-of-the-art stochastic gradient based method (StoSAG) which has shown in different domains to be computationally efficient and accurate when dealing with optimisation problems under uncertainty. Our results show non-trivial optimal designs with LCoE reductions of ∼0.5% compared to the most optimal solution from a sensitivity analysis.
Global sensitivity analysis of model uncertainty in aeroelastic wind turbine models
Authors: Kumar P. , Sanderse B. , Boorsma K. , Caboni M. 
Published: September 2020

Abstract
A framework is presented for performing global sensitivity analysis of model parameters associated with the Blade Element Momentum (BEM) models. Sobol indices based on adaptive sparse polynomial expansions are used as a measure of global sensitivities. The sensitivity analysis workflow is developed using the uncertainty quantification toolbox UQLab that is integrated with TNO’s Aero-Module aeroelastic code. Uncertainties in chord, twist, and lift- and drag-coefficients have been parametrized through the use of NURBS curves. Sensitivity studies are performed on the NM80 wind turbine model from the DanAero project, for a case with 19 uncertainties in both model and geometry. The combination of parametrization and sparse adaptive polynomial chaos yields a new efficient framework for global sensitivity analysis of aeroelastic wind turbine models, paving the way to effective model calibration.
Wind farm layout optimization with load constraints using surrogate modelling
Authors: Riva Riccardo , Liew Jaime , Friis-Møller Mikkel , Dimitrov Nikolay , Barlas Emre , Réthoré Pierre-Elouan , Beržonskis Arvydas 
Published: September 2020

Abstract
Minimizing the cost of energy of a wind farm is a difficult task, which involves reducing the wake effects while satisfying several constraints. Due to its multidisciplinary nature, this problem is usually solved through numerical optimisers. TOPFARM is one of these tools, and in this paper, we have added to it a constraint on the fatigue loads. The efficiency of the implementation is guaranteed by an extensive use of gradients and load surrogate models. The paper is concluded by showing some case studies.