bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Development of Open-Ended Math Questions on Grade V Students of Elementary School
Authors: Surya Yenni Fitra , Zulfah  , Astuti  , Marta Rusdial , Wijaya Tommy Tanu 
Published: September 2020

Abstract
The purpose of this research is to produce valid, practical and effective open-ended based mathematical questions in measuring the high-level thinking ability of grade V students of elementary schools. The study was conducted at 002 and 008 Public Elementary Schools in Bangkinang. The research was a Design Research, which is another term of development research according to Plomp and Nieveen. The development model used is the Plomp model consisting of three stages; preliminary research, prototyping phase, and assessment phase. Based on the results of the development, there were obtained 8 questions for cube and cuboid material and 8 questions for statistic material. Some characteristics of valid mathematical questions based on open-ended are (1) the questions developed have several possible answers or have various ways of answering, (2) the resulting questions can measure higher-order thinking abilities; analysing, evaluating, and creating (3) the material asked is in accordance with the level of the school, which is grade V of elementary school related to cube and cuboid, and statistics materials, (4) the questions are related to the students’ daily life. The characteristics of practical open-ended mathematical questions are that can be used by teachers as an evaluation tool. This question will also be easily obtained because it will be posted in a blog owned by researchers and fellow students.
Analysis of secondary school mathematics teachers’ pedagogical content knowledge and intended teaching in curriculum reformation
Authors: Hidayat A S E , Setyawan F 
Published: September 2020

Abstract
This study was conducted in response to the curriculum reform in Indonesia which have encouraged a different approach to teach the mathematics content employing innovative methodology or model in teaching and learning. This study aimed to understand the secondary school mathematics teachers’ Pedagogical Content Knowledge (PCK) towards curriculum reformation. Every participant was interviewed in relation to the domain of PCK, and some intended teaching practice in K-13. The result shows that each teacher has a unique approach to teaching system of linear equations of three variables (SLETV) in curriculum reform. Though the content structures are different, the patterns for teaching two variables to three variables of SLETV are similar. Some intended teaching may still not be implemented regarding students’ and classroom teaching/practices condition which in the end makes the teachers return to the old paradigm of teaching. Hence, although the government has provided good efforts in suggesting some innovative teaching practices to increase the achievement of students, those ideas may still not be executed in the classroom practice.
Modal analysis of a wind turbine tower by digital image correlation
Authors: Curt Jordan , Capaldo Matteo , Hild François , Roux Stéphane 
Published: September 2020

Abstract
Operational Modal Analysis is a method widely used in the wind industry to characterize structures and perform structural health monitoring or numerical model calibration. To reach this goal, optical techniques are becoming appealing because of their non-intrusiveness and their full-field feature in contrast to sensor-based methods. An innovative method is proposed herein for modal measurement with a single camera via Digital Image Correlation. The first resonance frequency of the tower is well captured from images of a shut down turbine.
Determination of wind farm life consumption in complex terrain using ten-minute SCADA measurements
Authors: Natarajan Anand , Bergami Leonardo 
Published: September 2020

Abstract
Measured ten-minute mean turbine performance characteristics are used to characterize the turbulence within wind farms. A neural network is trained to reproduce turbulence at each mean wind speed, given the ten-minute mean power production, blade pitch angle and rotor speed. The predicted turbulence from the neural network is verified using simulated wind turbulence that is input to aeroelastic simulations. The neural network is further trained to predict loads time series, given SCADA input time series. The load predictions are validated using an instrumented turbine. Based on the verified ability to predict wind turbulence and loads, the methodology is extended to reproduce loads on the blade and tower of wind turbines within wind farms in complex terrain. The input to the neural network is reduced to only the ten-minute mean measurements from the wind turbines, which are converted to 10-minute time series using Principal Component Analysis (PCA). The output of the neural network is the load time series, which are processed to damage equivalent loads. The standard deviation of measured power is used as a proxy for loads, to validate the predicted damage equivalent loads. The methodology is shown to provide a useful indication of relative fatigue life consumption within the wind farm, even when only mean SCADA measurements are available.
Wind Farm Energy Production Optimization Via Wake Steering
Authors: Lima L A M , Blatt A K , Machuca M N 
Published: September 2020

Abstract
The wake steering technique consists in misaligning turbines with respect to the incoming wind with the goal of displacing their wake region and reducing the wake wind speed deficit, thus increasing the power production of other turbines downwind. In this paper, an algorithm is proposed to estimate the amount of production gain a wind farm could achieve by employing this technique. Details about data treatment are provided and an analytical wake model that can represent the wakes displacement is described. A minimization algorithm to calibrate the wake model parameters based on SCADA data is presented, and the complete math needed to solve this problem is developed. Similarly, to find the optimal yaw angle values that maximize the wind farm production, a maximization problem is described along with the full development of the equations behind it. Insights on an efficient computational implementation to solve these problems are shown, based on matrix representation of the described variables. A case study is presented for a small wind farm owned by Voltalia, consisting of five turbines. Results point to an AEP gain in the order of 1%, a relevant value over the course of a project’s lifetime.
Natural frequency estimation by using torsional response, and applications for wind turbine drivetrain fault diagnosis
Authors: Moghadam Farid K. , Nejad Amir R. 
Published: September 2020

Abstract
A method based on torsional vibration measurements for a system-level condition monitoring of the drivetrain system is developed in this paper. The latter is tested by using a 10MW wind turbine drivetrain simulation model, and experimentally validated by the drivetrain operational data obtained from a 1.75MW turbine. The method relies on the estimation of the drivetrain torsional natural frequencies by using the torsional responses residual function and subsequent monitoring of the variations in the eigenfrequencies and normal modes. In other words, an abnormal deviation from the reference values of these dynamic parameters can be translated into a meaningful interpretation on the propagation of a specific fault in the driveline. Local sensitivity analysis is employed to establish a relationship between different types of drivetrain faults and the system dynamic properties.
Modelling, Parametrization and Observer Design of a 20 MW Reference Wind Turbine for Control Purposes
Authors: Chamoli Suryans , Gambier Adrian 
Published: September 2020

Abstract
In the present contribution, the model development of a wind turbine with focus on an advanced control system design is reported. The aim is to produce a model that captures essential dynamics over the simplest cases but maintaining an acceptable level of complexity. The problem of parameter reduction from high-resolution models, as used in the simulation of reference turbines, to models with low number of parameters, as normally used for control purposes, is also studied. The obtained parametric model is validated by developing an observer, which can be used for state-space control as well as effective wind speed estimation. As numerical example, a 20 MW reference wind turbine is used. Very large wind turbines are very flexible and nonlinear, therefore very simple rigid models do not lead to satisfactory results. The proposed observer is adjusted during operation in order to overcome this problem.
Toward flow control: An assessment of the curled wake model in the FLORIS framework
Authors: Bay Christopher J , King Jennifer , Martìnez-Tossas Luis A , Mudafort Rafael , Hulsman Paul , Kühn Martin , Fleming Paul 
Published: September 2020

Abstract
In this work, a new controls-oriented wake model is modified and compared to an analytical Gaussian wake model, high-fidelity simulation data, and experimental wind tunnel campaign. This model, called the curled wake model, captures a wake phenomenon that occurs behind yawed turbines, modeled as a collection of vortices shed from the rotor plane. Through turbine simulations, these vortices are shown to have a significant impact on the prediction of the wake steering’s performance. Overall, the results support the concept of secondary steering, or a yawed turbine’s ability to deflect the wake of a downstream turbine, and suggest that future turbine wake studies and yaw optimizations should include the curled wake phenomenon.
A Structured Wind Turbine Controller Evaluation Process Embedded into the V-Model for System Development
Authors: Requate Niklas , Wiens Marcus , Meyer Tobias 
Published: September 2020

Abstract
Controller design is always accompanied by an evaluation of control performance. However, for wind turbines, there is only a diffuse consensus on what a good controller constitutes, and no clear method to evaluate overall controller performance. Most evaluations, which can be found in wind turbine control literature, follow similar approaches. However, details, such as the models used, the scope of simulation or the result evaluation metric, can change the validity of results greatly. We sort these different evaluation approaches and align them with the V-Model for system design. This yields a structured process which defines requirements within three major domains: Stable automated operation, energy production and structural loads and limits. By following our proposed process, an impartial control evaluation scheme can be setup. Doing so, the complexity of evaluation and validation is handled in a systematic way. We give a clear indication which requirements need to be specified and show which difficulties arise when setting up an evaluating method. Furthermore, the influence of different evaluation parameters on the resulting controller quality measures is shown by evaluating results in slightly different ways. Thereby, the importance of the careful selection of quality measures is emphasized considering the high complexity of the task.
A Comparison of Multi-Objective Optimisation of Two Wind Turbine Controller Designs
Authors: Yu W. , Engels W. P. , Stock-Williams C.F.W. 
Published: September 2020

Abstract
This paper presents a comparison between two pitch controllers for a 10MW wind turbine, a baseline using PI and a state-space model, where each controller’s parameters have been chosen using Bayesian optimization. Four objectives are simultaneously examined: energy output; pitch action; blade load; and tower load. First, it is shown that, for both controllers, using parameters selected from the obtained Pareto fronts achieves higher energy production with less energy consumption of pitch activities and with less load in blade and tower, compared with settings chosen by an expert. Second, in this robust comparison of the capabilities of both controllers, the increased degrees of freedom and reduced simplification in the more advanced controller are seen to have greater potential to improve each of the objectives.
Fault Detection of the Mooring system in Floating Offshore Wind Turbines based on the Wave-excited Linear Model
Authors: Liu Yichao , Fontanella Alessandro , Wu Ping , Ferrari Riccardo M.G. , van Wingerden Jan-Willem 
Published: September 2020

AbstractFloating Offshore Wind Turbines (FOWTs) are more prone to suffer from faults and failures than bottom-fixed counterparts due to the severe wind and wave loads typical of deep water sites. In particular, mooring line faults may lead to unacceptably high operation and maintenance costs due to the limited accessibility of FOWTs. Detecting the mooring line faults is therefore critical, but the application of Fault Detection (FD) techniques has not been investigated yet. In this paper, an FD scheme based on a wave-excited linear model is developed to detect in a reliable way critical mooring line faults occurring at the fairlead and anchor ends. To reach the goal, a linear model of the FOWT is obtained by approximating the wave radiation and incident wave forces. Based on this model, an observer is built to predict the rigid rotor and platform dynamics. The FD scheme is thus implemented by comparing the Mahalanobis Distance of the observer prediction error against a probabilistic detection threshold. Numerical simulations in some selected fault scenarios show that the wave-excited linear model can predict the FOWT dynamics with good accuracy. Based on this, the FD scheme capabilities are demonstrated, showing that it is able to effectively detect two critical mooring line faults.
Repetitive Individual Pitch Control for Load Alleviation at Variable Rotor Speed
Authors: Kallen T , Zierath J , Dickler S , Konrad T , Jassmann U , Abel D 
Published: September 2020

Abstract
In recent years, wind turbines have been growing in size and became more lightweight and thus more flexible. Spatial variation in the wind speed results in asymmetrical blade loads, which include a periodic component increasing with growing wind turbine size. Asymmetrical blade loads can be reduced by individual blade pitch control in general and repetitive control can reduce especially the periodical parts of the loads. We investigate, how a repetitive control based individual blade pitch controller as extension to an existing collective pitch controller can reduce periodical loads resulting from unsteady non-uniform wind conditions under consideration of variable rotor speeds. As plant, we use a simulation model of a 3 MW wind turbine, developed by W2E Wind to Energy GmbH, and control it with a model predictive collective pitch controller. This controller is extended with the proposed repetitive individual pitch control scheme. This study shows, that the presented repetitive controller reduces especially the tower yaw moments by up to 65% and higher harmonics of the blade root moments by up to 30% at the cost of increased pitch activity. Hence, for the use of this controller one has to balance the load reduction of blades and tower with increased loads of the pitch actuators.
Modelling and assessing the near-wake representation and turbulence behaviour of control-oriented wake models
Authors: Hulsman Paul , Martínez-Tossas Luis A. , Hamilton Nicholas , Kühn Martin 
Published: September 2020

Abstract
Due to the interaction between the wake of an upstream turbine on a downstream turbine, power losses and increased fatigue loads occur. By yawing the upstream turbine with regard to the wind direction, one can potentially reduce the power losses of the downstream turbine and reduce the fatigue loads. The evolution of the wake depends on the pressure gradient within the near-wake region and the turbulent kinetic energy and must be incorporated in existing wake steering algorithms to provide an accurate estimation of the wake flow. This paper will show a first approach to implement a near-wake model and a turbulence model in the curled wake model within the controls-oriented framework FLORIS. The near-wake model is based on an analytical expression of the velocity profile to model the pressure gradient. Furthermore, two turbulence models are incorporated within the curled wake model based on a Gaussian-distribution and a mixing length formulation. The adapted curled wake model is then assessed with the measurement data acquired in the wind tunnel at ForWind – University of Oldenburg. The evaluation of the models show good agreement for the velocity deficit and representation of the near-wake region. Furthermore, the turbulent kinetic energy behaved as expected in comparison to other work, showing a ring of high turbulent kinetic energy at non-yawed condition which is deflected to a curled shape at large yaw angles with the turbulence model based on a mixing length formulation.
Experimental Study on Inflow Estimation Using Pressure Sensor Mounted on Spinner of Horizontal Axis Wind Turbine
Authors: Harada Honoka , Kamada Yasunari , Maeda Takao , Tsumura Kosuke 
Published: September 2020

Abstract
The spinner anemometer can measure the wind velocity in front of rotor by ultrasonic wind sensors mounted on the spinner. To estimate the undisturbed wind speed in far upstream, the detail calibration is required. This study proposes the wind speed measurement by pressure sensors mounted on the spinner as a new technology. The inflow wind speed and the inflow angle are estimated with the pressure sensors mounted on a spinner. The performance of wind speed measurement is evaluated by wind tunnel measurements with a model HAWT. The measured wind speed by stagnation and static pressures show good agreements between reference wind tunnel speed and accuracy of measured wind speed was assessed.
Sub-Regional Variability in Wind Turbine Blade Leading-Edge Erosion Potential
Authors: Letson F , Barthelmie R J , Pryor S C 
Published: September 2020

Abstract
Leading Edge Erosion (LEE) of wind turbine blades leads to significant degradation of aerodynamic performance. Previous research has suggested kinetic energy transferred to the rotating blades from hydrometeor impacts are an important source of LEE. The Southern Great Plains (SGP) of the United States has substantial wind energy development and experiences a high frequency of heavy rain and hail that contribute to atypically high LEE potential. The current study quantifies the degree to which the drivers of LEE exhibit sub-regional variability across a 500,000 km2 area of the SGP. The analysis uses five years of data from nine RADAR stations to characterize the precipitation climate and wind speeds from ERA5. The results illustrate strong spatial gradients in all three atmospheric drivers of LEE: (i) Frequency of power producing wind speeds. (ii) Occurrence of intense precipitation. (iii) Occurrence of hail and maximum hail size. For example, annual precipitation varies by a factor of 10 across Texas and the prevalence of hail events ranges from hundreds of 5-minute events per year to nearly zero. Northwestern Texas has high wind turbine installed capacity and high joint probability of hail and/or heavy precipitation and power-producing wind speeds.
Inclusion of rotor moments in scaled wave tank test of a floating wind turbine using SiL hybrid method
Authors: Pires O. , Azcona J. , Vittori F. , Bayati I. , Gueydon S. , Fontanella A. , Liu Y. , de Ridder E.J. , Belloli M. , van Wingerden J.W. 
Published: September 2020

Abstract
The hybrid testing method developed by CENER for floating wind turbine scaled tests combining wind and waves (SIL) has been upgraded in order to introduce not only the wind turbine rotor thrust, but also the out-of-plane rotor moments (aerodynamic and gyroscopic). The former ducted-fan has been substituted by a multi-propellers actuator system. The new system has been completely developed, calibrated and used on a test campaign carried out at MARIN’s Concept Basin. It was installed on a 1/50 scaled model of the DeepCwind 5MW semisubmersible turbine built by MARIN within the EU MARINET2/Call No.3 under ACTFLOW project framework. The control strategy of the floating turbine was developed by POLIMI and TUDELFT and integrated into the SIL numerical model. The experiment has proved a good behaviour of the enhanced SiL method. It has revealed that the relative importance of gyroscopic moments is low in comparison with the aerodynamic rotor moments in the considered cases. The results also show how rotor moments are particularly important in the floating turbine dynamics in cases with large rotor load imbalances such as situations where one blade fails to pitch.
ANDroMeDA - A Novel Flying Wind Measurement System
Authors: Molter Christian , Cheng Po Wen 
Published: September 2020

Abstract
A noval multirotor aircraft was developed at the University of Stuttgart, designed especially for wind speed measurements. Currently the aircraft is equipped with a combined Prandtl / triple hot wire probe but in general the design is modular. The measurement performance of the overall system is validated and compared to conventional measurement techniques. Methods of validation are a free flight in calm air, wind tunnel tests and a hovering flight next to a met mast. It could be shown that the measurements show a good agreement between 4 m/s and 13 m/s. The maximum wind speed that can be measured could be determined to 25 m/s by extrapolation of the flight envelope but has to be confirmed in the future.
Longitudinal coherence and short-term wind speed prediction based on a nacelle-mounted Doppler lidar
Authors: Debnath M. , Brugger P. , Simley E. , Doubrawa P. , Hamilton N. , Scholbrock A. , Jager D. , Murphy M. , Roadman J. , Lundquist J. K. , Fleming P. , Porté-Agel F. , Moriarty P. 
Published: September 2020

Abstract
The spatial structure of turbulence in atmospheric boundary layer flows is highly relevant to wind energy. In particular, wind turbine control strategies based on inflow preview measurements require knowledge of the longitudinal evolution of turbulent flow as it approaches the rotor. These upstream measurements are usually obtained with nacelle-mounted wind lidars. In contrast to traditional in situ anemometry, lidars collect measurements within a probe volume which varies in size depending on the technology of the commercial system being used. Here, we address two issues related to the use of wind lidar to measure the incoming flow to a wind turbine: (i) whether existing longitudinal coherence models can be used to predict flow at the rotor, based on measurements performed at a distance away from the rotor; and (ii) what effect probe-volume averaging has on the inflow predictions. These two questions are critical to the design and implementation of robust wind turbine control strategies. To address these questions, we perform field measurements and large-eddy simulations to determine which incoming flow structures can be readily predicted with existing coherence models, and which require additional corrections to account for lidar volumetric averaging effects. Results reveal that the wind turbine induction zone has a negligible impact on the longitudinal coherence and first-order turbulence quantities, such as the standard deviation of velocity fluctuations. However, the phase of the signal, from which advection time periods of the turbulent structures are derived, is affected by the rotor blockage effect.