bluuebunny/crossref_metadata_2025_split huggingface dataset:
Language competition modeling and language policy evaluation
Authors: Templin Torsten 
Published: March 2020

Abstract
In this paper, we present a framework for the analysis of effects of language policies on the competition between
languages. At the core of this framework is a language competition model that takes into account four pivotal factors for the
evolution of the linguistic composition of a society: intergenerational language transmission, formal language education, adult
language learning and migration. In contrast to the majority of models available in the literature, our model operates with
parameters that can be estimated from empirical socio-linguistic data. It allows the reconstruction of past and simulate future
dynamics. Language policies can be modeled as changes in model parameters. Therefore, projections derived from the model can be
utilized to compare the effects of different policy options. We use Basque and Spanish within the Basque Autonomous Community in
Spain to illustrate the application of the model.
Wind turbine power curve upgrades: methods for the assessment and test cases study
Authors: Castellani Francesco , Astolfi Davide , Terzi Ludovico 
Published: March 2020

Abstract
The research about wind turbine control and blade design optimization has flourished in the latest years and has provided the opportunity of diffusely updating the technology of operating wind turbines. Due to multivariate dependence of wind turbine power on ambient conditions and working parameters, it is complex to estimate the actual impact of power optimization strategies. This problem therefore calls for devoted operation data mining and statistical techniques, which are explored in the present work. In particular, two test cases of multi-MW wind turbines power upgrades are discussed: the former is a combined aerodynamic and control optimization, the latter is the optimization of the yaw control. The assessment of the upgrades impact is performed through the comparison between the post-upgrade measured production and a model estimate of the pre-upgrade production in the same conditions. The wind turbines nearby to the target upgraded ones are employed as references for the operation conditions and their working parameters are employed for a principal component regression of the power of the target wind turbine. The proposed method is general and, for the selected test cases, it arises that the aerodynamic and control optimization improves the Annual Energy Production of the order of the 3%, while the yaw control optimization provides a 1% AEP improvement.
Turbine Wake Deflection Measurement in a Wind Tunnel with a Lidar WindScanner
Authors: Hulsman Paul , Wosnik Martin , Petrović Vlaho , Hölling Michael , Kühn Martin 
Published: March 2020

Abstract
Wind turbines are typically closely spaced in wind farms, and thus operate in the wake of upstream turbines and experience power losses. Currently, one of the techniques to reduce the wake interaction between turbines within a wind farm is to yaw the upstream turbine with regards to the incident wind direction. The objective is to deflect the wake, which can potentially increase the overall power output and the annual energy production of the wind farm. Experimental data can aid the process to thoroughly analyse the wake deflection under different inflow conditions, which is necessary to apply a yaw-based wind farm control model. The aim of the present research is to investigate the possibility and accuracy of the experimental setup to measure the wake characteristics with a high spatial and temporal resolution through the use of a short-range Lidar WindScanner, within the wind tunnel of ForWind-Oldenburg. This technique provides the opportunity to analyse the flow structures at different operational and inflow conditions in a relative fast manner without disturbing the flow. Experiments were conducted using a model wind turbine in a large cross-section wind tunnel. The short-range Lidar WindScanner is used as the primary instrument to map the wind turbine wake at different downstream locations. The flow structures of the wake were measured from 1 D up to 10 D downstream of the turbine rotor. A stable flow within the wind tunnel segment is measured, which is crucial for the analyses of the evolution of the wake. In addition, a high detailed spatial resolution of the wake profile is observed, showing the symmetric and asymmetric behaviour of the wake, for unyawed and yawed conditions, respectively. Furthermore, the calculation of the thrust coefficient from the velocity data show expected behaviour, giving further credibility to the measurement technique.
Wind turbine control: open-source software for control education, standardization and compilation
Authors: Mulders S P , Zaaijer M B , Bos R , van Wingerden J W 
Published: March 2020

Abstract
Standardized, easy to use, and preferably open-source research software is an important aspect in supporting and solidifying the wind turbine community. To this end, three contributions in the form of open-source software projects are presented in this paper. First, a community-driven wind turbine baseline controller, the Delft Research Controller (DRC), is presented. The DRC is applicable to high-fidelity simulation software that uses the DISCON controller interface. The controller distinguishes itself by the variety of available control and estimation implementations, its ease of use, and the universal applicability to wind turbine models. Secondly, in the wake of the DRC, the SimulinkDRC graphical controller design and compilation environment has been developed. Users having access to Simulink can benefit from the convenient way of controller development the tool provides. Finally, the FASTTool has been developed for educational purposes, by focusing on the graphical aspect of wind turbine (controller) design. The tool simplifies interaction with the advanced FAST simulation software, by comprehensive visualizations and analysis tools. This paper demonstrates and describes the functionality of all three software projects.
Optimizing the Use of LIDAR in Wind Farms: Minimizing Life-Cycle Cost Impact of Yaw Error
Authors: Bakhshi Roozbeh , Sandborn Peter 
Published: March 2020

Abstract
Yaw error lowers the efficiency and reliability of wind turbines resulting in higher maintenance costs. LIDAR devices can correct the yaw error; however, they are expensive, which creates a trade-off between their costs and benefits. In this study, a stochastic discrete-event simulation model is developed that models the operation of a wind farm. We optimize the net present value (NPV) changes associated with using LIDAR devices in a wind farm to determine the optimum number of LIDAR devices and their associated turbine stay time as a function of number of turbines in the wind farm for specific turbine sizes.
Aerodynamic performance prediction of SG6043 airfoil for a horizontal-axis small wind turbine
Authors: Shin Pyungho , Kim Keonhoon 
Published: March 2020

Abstract
In order to design a small wind turbine, the performance of SG604x airfoil and previously existing 15 airfoils was reviewed at a Reynolds number of 300,000, which suggests the maximum lift-to-drag ratio of the airfoils, corresponding lift coefficient, and the maximum lift coefficient for both free and fixed transition. The SG6043 airfoil provides enhanced lift-to-drag ratio performance as compared with previously existing airfoils at a Reynolds number of 300,000. Only a SG6043 airfoil for small wind turbine performance prediction is applied along the length of the blades. This is why a blade constructed using airfoils of different performance may not exhibit the expected performance. A code based on BEMT(Blade Element/Momentum Theory) was used for performance predictions of small horizontal axis wind turbine. As important input parameter of BEMT, distributions of chord and twist was derived by the optimization method using genetic algorithm. The power performance prediction of airfoil data of SG6043 using BEMT is presented over a wide range of wind speeds. The results of BEMT using SG6043 show that the rated wind speed can be reduced to 10 m/s for a rotor radius of 7.25m and a rating of 32kW. The reduced rated wind speed would increases the annual capacity factor as compared the existing airfoils.
A graduate level course on economic metrics and innovative finance mechanisms for wind
Authors: Miller L , Carriveau R 
Published: March 2020

Abstract
A graduate level course on economic metrics and innovative finance mechanisms for has been developed. Topics include non-traditional financing structures for project development and the application of economic metrics to investment decision making. The development of this course was motivated by recent surveys and through consultation with wind energy professionals. Recent surveys have indicated that highly qualified persons entering renewable energy fields are lacking knowledge of the technical, economic, and policy-connected aspects of their work. Synthesis of these discussions, which have guided the development of course content, highlighted that an understanding of market policy and project economics would greatly enhance the efficacy of energy technical professionals. The purpose of this course is to develop holistically equipped wind energy professionals who can intelligently engage with business and finance professionals in their field. Both live instruction and online versions of this course intend to provide this knowledge through application-based lectures and case studies to set graduates of this course apart from their peers. Course delivery, topics, learning outcomes, and evaluation methods are provided.
Surface roughness for offshore wind energy
Authors: Golbazi Maryam , Archer Cristina L. 
Published: March 2020

AbstractThe Northeastern coast of the U.S. is expected to increase its offshore wind capacity from 30 MW today to 86 GW by 2050. Measurements of wind speeds are available near sea level, but not at hub height, thus extrapolation is often required using the surface roughness,z0. The focus of this study is to estimate the surface roughness length off the Northeastern coast of the U.S. using field measurements from Nantucket Sound, MA, with three methods: 1) analytical, dependent on friction velocity and atmospheric stability, 2) the Charnock relationship between zo and friction velocity, and 3) a statistical method, based on wind speed observations at three heights. The main results of this paper are: a comparison of the three methods, a comprehensive error analysis of each method, a regionalz0value of 10–3m, and a new mathematical interpretation of surface roughness.
Large eddy simulations of offshore wind turbine wakes for two floating platform types
Authors: Johlas H M , Martínez-Tossas L A , Lackner M A , Schmidt D P , Churchfield M J 
Published: March 2020

Abstract
The growing prospect for large farms of floating offshore wind turbines requires a better understanding of wake effects for floating turbines. In this work, large eddy simulations with an actuator line model are used to study the wake of the NREL 5 MW reference turbine mounted on the OC3-UMaine spar and OC4-DeepCwind semi-submersible platforms. The simulations are carried out in the Simulator fOr Wind Farm Applications (SOWFA) coupled with OpenFAST for the platform and turbine motion. The wake location, deficit, and turbulence levels are compared for the two floating platforms and equivalent fixed-turbine cases. The effects of neutral versus stable atmospheric conditions are also compared. Most notably, floating-turbine wakes are deflected upwards compared to fixed-turbine wakes, because of mean platform pitch. The spar wake deflects upwards more than the semi-submersible, while the stable atmosphere increases this vertical deflection compared to the neutral. The time-varying rotor motions do not significantly affect the mid-to-far wake, though the stable atmosphere shows larger fixed-floating differences in horizontal wake fluctuations.
Comparison of dynamic response and levelized cost of energy on three platform concepts of floating offshore wind turbine systems
Authors: Kikuchi Yuka , Ishihara Takeshi 
Published: March 2020

Abstract
Spar, semisubmersible and barge platforms are modelled based on the full-scale demonstration projects in Japan for a generic 5 MW turbine. Three platforms are evaluated with the structural and stability parameters. The characteristic of floater motions and mooring forces are clarified by performing the dynamic analysis. The dynamic responses are validated with the water tank tests. The levelized cost of energy is assessed by using the engineering cost model.
Influence of the Mass and Line Stiffiness on the Dynamic Line Tension of a Floating Offshore Wind Turbine Stabilized by a Suspended Counterweight
Authors: Ward J C , Goupee A J , Viselli A M , Dagher H J 
Published: March 2020

Abstract
As the offshore wind industry moves towards deeper waters, developers are adapting classical floating platform designs to optimize performance and cost. One such concept is a multi-body system consisting of a counterweight suspended from a buoyant hull using flexible cables. If the suspension lines remain in tension, the system may be assumed to behave as a rigid body. However, if a suspension line loses tension, relative motion between the bodies will occur which may destabilize the system. In this work, the hanging-mass floating offshore wind turbine is idealized as a forced spring pendulum. A parametric study is conducted by varying the line stiffness and counterweight mass to determine their effect on the dynamic line tension and global response of the system.
A computational model of wind turbine blade erosion induced by raindrop impact
Authors: Hu W , Wang X , Chen W , Wang Y , Liu Z , Tan J , Pryor S C , Barthelmie R J 
Published: March 2020

Abstract
This research focuses on developing a computational model for analysing wind turbine blade erosion induced by raindrop impact. A stochastic rain texture model is used to simulated realistic rain events determined by a rain intensity and a rain duration. A new smoothed particle hydrodynamic approach is implemented to study the influence of the raindrop size, impact speed, impact angle, and raindrop shape on the impact stress. In addition, a stress interpolation method is proposed to accurately and efficiently calculate the impact stress under a random rain event. The fatigue damage of the top coating material is evaluated under a rain event based on the rainflow cycle counting method and the Miner’s rule.
Wind Farm Simulation and Layout Optimization in Complex Terrain
Authors: Allen Jeffery , King Ryan , Barter Garrett 
Published: March 2020

Abstract
This work reports on incorporating complex terrain into wind farm simulations for the purpose of layout optimization. Adding complex terrain boundary conditions to NREL’s medium fidelity Reynolds averaged Navier-Stokes flow model, WindSE, produces significant separation, flow curvature, and speedup effects that would otherwise be difficult to capture with lower-fidelity models or a flat-terrain assumption. These flow features, in turn, can significantly impact the optimal turbine array layout. We demonstrate the addition of complex terrain improves agreement with SCADA data by 34.8% in mean average error. Additionally, we discuss modifications to the code that enable gradient-based layout optimization using terrainaware adjoints with arbitrary topography. Through several optimization case studies, we show that the layout optimization process takes advantage of speedup effects on terrain high points, and leverages flow curvature effects that modify wake trajectories. This yields substantial power improvements over gridded layouts, and hints at future research directions in simulation and optimization for wake trajectories in complex terrain.
Investigation of the near-wake behaviour of a utility-scale wind turbine
Authors: Abraham Aliza , Dasari Teja , Hong Jiarong 
Published: March 2020

Abstract
Super-large-scale particle image velocimetry and flow visualization with natural snowfall is used to collect and analyse multiple datasets in the near wake of a 2.5 MW wind turbine. Each dataset captures the full vertical span of the wake from a different perspective. Together, these datasets compose a three-dimensional picture of the near-wake flow, including the effect of the tower and nacelle and the variation of instantaneous wake expansion in response to changes in turbine operation. A region of high-speed flow is observed directly behind the nacelle, and a region of low-speed flow appears behind the tower. Additionally, the nacelle produces a region of enhanced turbulence in its wake while the tower reduces turbulence near the ground as it breaks up turbulent structures in the boundary layer. Analysis of the instantaneous wake behavior reveals variations in wake expansion – and even periods of wake contraction – occurring in response to changes in angle of attack and blade pitch gradient. This behaviour is found to depend on the region of operation of the turbine. These findings can be incorporated into wake models and advanced control algorithms for wind farm optimization and can be used to validate wind turbine wake simulations.
Comparison of Rotor Wake Identification and Characterization Methods for the Analysis of Wake Dynamics and Evolution
Authors: Quon E. W. , Doubrawa P. , Debnath M. 
Published: March 2020

Abstract
Optimal wind power plant design requires understanding of wind turbine wake physics and validation of engineering wake models under wake-controlled operating conditions. In this work, we have developed and investigated several different wake identification and characterization methods for analyzing wake evolution and dynamics. The accuracy and robustness of these methods, based on Gaussian function fitting and adaptive contour identification, have been assessed by application to a large-eddy simulation data set. A new contour-based method based on downstream momentum deficit has been considered. Uncertainties arising from wake-identification errors result in characterizations of the wake expansion, recovery, and meandering motion that differ by 19% of the rotor area, 4% of the freestream, and 15% rotor diameter, respectively.
ExaWind: A multifidelity modeling and simulation environment for wind energy
Authors: Sprague M A , Ananthan S , Vijayakumar G , Robinson M 
Published: March 2020

Abstract
We introduce the open-source ExaWind modeling and simulation environment for wind energy. The primary physics codes of ExaWind are Nalu-Wind and OpenFAST. Nalu-Wind is a wind-focused computational fluid dynamics (CFD) code that is coupled to the whole-turbine simulation code OpenFAST. The ExaWind environment was created under U.S. Department of Energy funding to achieve the highest-fidelity simulations of wind turbines and wind farms to date, with the goal of enabling disruptive changes to turbine and plant design and operation. Innovation will be gleaned through better understanding of the complex flow dynamics in wind farms, including wake evolution and the impact of wakes on downstream turbines and turbulent flow from complex terrain. High-fidelity predictive simulations employ hybrid turbulence models, geometry/boundary-layer-resolving CFD meshes, atmospheric turbulence, nonlinear structural dynamics, and fluid-structure interaction. While there is an emphasis on very high-fidelity simulations (e.g., blade resolved with full fluid-structure coupling), the ExaWind environment supports lower-fidelity modeling capabilities including actuator-line and -disk methods. Important in the development of ExaWind codes is that the codes scale well on today’s largest petascale supercomputers and on the next-generation platforms that will enable exascale computing.
Wake meandering in a model wind turbine array in a high Reynolds number turbulent boundary layer
Authors: Turner V John J. , Wosnik Martin 
Published: March 2020

Abstract
Wake meandering is the dynamic shift observed in the spatial location of a wind turbine wake as it evolves downstream, considered to be caused primarily by the interaction of large flow structures in the atmospheric boundary layer with the turbulent wake. Experiments were conducted in a large boundary layer wind tunnel to investigate meandering in the wakes of both individual model wind turbines and in a wind turbine array with a large number of model turbines (19 rows x 5 columns = 95 model turbines). Unlike bluff body vortex shedding, the meandering phenomenon for a turbine wake is not characterized by a well-pronounced peak in the frequency domain, but rather by a broad spread over a low-frequencies range. For individual turbine models, both rotating three-bladed models and non-rotating porous disks, frequencies and peak energies observed in the velocity spectrum in the wake return to those of the incoming high Reynolds number turbulent boundary layer. Wake meandering also presents itself in the large wind turbine array. Here, frequencies and peak energies observed in the velocity spectrum in the wake do not return to those of the incoming turbulent boundary layer. Instead, a lower dominant frequency corresponding to the wind velocity at hub height and array spacing is observed within the array, indicating forcing of the meandering by the array itself (a type of resonance). Higher peak energies are observed in the array due to large flow structures representative of the turbine spacing.
Large-eddy simulations of idealized atmospheric boundary layers using Nalu-Wind
Authors: Kaul C M , Ananthan S , Churchfield M J , Mirocha J D , Berg L K , Rai R 
Published: March 2020

Abstract
Accurate prediction of wind-plant performance relies, in part, on properly characterizing the turbulent atmospheric boundary layer (ABL) flow in which wind turbines operate. Large-eddy simulation (LES) is a powerful tool for simulating ABLs because it resolves the largest, most energetic scales of three-dimensional turbulent motions. Yet LES predictions are well known to depend on modeling choices such as grid resolution, numerical discretization schemes, and closures for unresolved scales of turbulence. Here, we evaluate how these choices influence predictions of ABL winds using Nalu-Wind, a wind-specific fork of the open-source, generalized, unstructured, massively parallel flow solver NaluCFD/Nalu.
Short-term wind forecasting using statistical models with a fully observable wind flow
Authors: Perr-Sauer J. , Tripp C. , Optis M. , King J. 
Published: March 2020

Abstract
The utility of model output data from the Weather Research and Forecasting mesoscale model is explored for very short-term forecasting (5-30 minutes horizon) of wind speed to be used in large scale simulations of an autonomous electric power grid. Using this synthetic data for the development and evaluation of short-term forecasting algorithms offer many unique advantages over observational data, such as the ability to observe the full wind flow field in the surrounding region. Several short-term forecasting algorithms are implemented and evaluated using the synthetic data at several different time horizons and for three different geographic locations. Comparison is made with observational data from one location. We find that short-term forecasts of the synthetic data considering wind flow from the surrounding region perform 26% better than persistence in terms of root mean square error at the 5-minute time horizon. This improvement is comparable to studies of observational data in the literature. These results provide motivation to use synthetic data for short term forecasting in grid simulations, and open the door to future algorithmic improvements.