bluuebunny/crossref_metadata_2025_split huggingface dataset:
Google form in engineering mathematics: Innovation in assignment method
Authors: Iswanti  , Astuti S , Suryono  , Sayekti I , Krishna B 
Published: September 2020

Abstract
This research is a developmental research on the engineering mathematics assignment using google form. There are three activities observed, namely constructing, collecting and evaluating. In constructing activities, there are two criteria, namely individuals and groups. In collecting there are two forms that are observed, namely giving answers directly and indirectly. Indirectly here means by uploading the answers. In this study six types of answer uploads were observed in the form of .ppt, .doc, .xls, .pdf, .jpg and .mp4. In evaluating include two conditions, namely assessment and giving feedback. The results of this study as follows: (i) individual assignments with direct answers, namely the peer assessment, when students assess their friends during presentation session; (ii) individual tasks with indirect answers in the form of routine tasks by uploading.pdf files; (iii) group assignments with indirect answers in three forms: (iii) mini-research assignments by uploading.pdf, image, audio and video files; (iv) group discussions on working out examples by uploading presentation files and (v) project based assignment on the Mathematics application in electrical circuits by uploading .pdf files. On the individual assignment with a direct answer, students are able to see their scores soon after the submission, while for the individual and group assignments with indirect answers, the evaluation can be done within the one-week maximum. This is because the assessment must be done carefully to anticipate plagiarism and providing objective feedback.
Some diagnostics learning problems on basic arithmetic skills of junior high school students
Authors: Hernadi J , Ekayanti A , Jumadi  
Published: September 2020

Abstract
The main obstacle in mathematics learning at junior high school level is the lack of students’ skills in performing basic operations of integers and fractions. This skill should be impeccable on elementary school level, nonetheless a big number of junior high school students experience impediment to follow the learning activities because they did not have enough pre-requisites on basic arithmetic. The similar circumstances are most probably also taken place at senior high school level. This study investigated students’ skills on basic arithmetic and then presents some analyses of diagnostic learning problems. The crucial findings in this research are various facts that might be ignored by teachers over the years, but they were alleged to be roots of the leading causes of the low student skills and understanding in basic operations of numbers. The diagnostic results will be worthwhile to improve the method and approach of mathematics teaching not only at junior high school but also at elementary school. Accordingly, the article offers several approaches to overcome the problems found in the study.
The visualization and classification method of support vector machine in lymphoma cancer
Authors: Kristina B C , Hadi A F , Riski A , Kamsyakawuni A , Anggraeni D 
Published: September 2020

Abstract
In the classical-classification multivariate process, it becomes an interesting topic to be discussed in the research area because of the larger variables with smaller observations. For this we need a method that can handle this problem. One answer is to use machine learning. SVM is a classification method in machine learning that is able to classify these data types. In addition, SVM can also model and classify relationships between variables efficiently and easy interpretation. This paper aims to create a visualization of SVM classifiers, then obtain an accuracy value to have an optimal classification with a misclassification of small numbers. This study aims to find good SVM input parameters by assessing the importance of variables using visual methods. This visualization will distinguish groups of people who contract diffuse lymphoma cancer and follicular lymphoma cancer with data on the genetic expression of lymphoma cancer. The classification using kernel Linear, Gaussian RBF, Polynomial and Sigmoid. The best classification accuracy using linear kernel functions with training data has a classification accuracy of 100% and testing data has a classification accuracy of 94, 73%.
Gender differences in junior high school students’ mathematical connection in geometry
Authors: Sari D N O , Mardiyana  , Pramudya I 
Published: September 2020

Abstract
Gender differences occur in various fields, including education. Male and females should be treated equally in education, but there are many differences between males and females in various ways. This study aims to analyze differences in junior high school students’ mathematical connections by sex. The method used in this study is the subject of qualitative and quantitative research. The research test instrument consisted of 3 questions which included indicators of mathematical connections, namely connections between mathematical topics, connections between mathematics and other fields, and mathematical connections with everyday life. The results of this study showed that of 57 students, 23 male students had an average of 47.41 higher than female students who had an average of 43.15, indicating that men and women had differences in mathematical connection abilities. A common cause is female students who have understood mathematical concepts but have not been able to relate to other things.
Van Hiele’s Theory: Transforming And Gender Perspective of Student’s Geometrical Thinking
Authors: Fitriyani H , Yudianto E , Maf’ulah S , Fiantika F R , Hariastuti R M 
Published: September 2020

Abstract
The purpose of this study was to identify the level of geometrical thinking of junior high school students in Bantul District using the Van Hiele test. The research approach was descriptive qualitative. The research subjects were students in grades VII and VIII in 4 junior high schools in Bantul district. The supporting instruments in this study were tests consisting of 25 multiple choice questions developed by Usiskin. Data were analyzed descriptively and qualitatively through several basic statistics. The results showed that there were 59.15% of students at the visualization level, 8.62% of students at the analysis level, and 1.42% of students at the informal deduction level. While the remaining 30.81% is in the previsualization category. In addition to the above categories, there were several students whose geometric thinking level was in the transition level category. The number of students who meet the criteria for the pre-analysis level and pre informal deduction level was 9.33% and 2.72% respectively. While viewed from a gender perspective. In general, Van Hiele’s geometrical thinking level of male and female respondents did not differ much but male respondents had the potential to increase their geometry thinking level more than female respondents.
Calculus for software engineering: Students’ perception towards flipped classroom
Authors: Ummah S K , Azmi R D , Shofia N 
Published: September 2020

Abstract
The research aimed to analyse the learning readiness and perception of informatics engineering students about calculus. More top-level students taken remedial teaching and the student stated that calculus was dominated by mathematics and lecturers did not relate to software application. The research method which was a case study analysed the learning readiness was further examined by providing an open questionnaire to new students about the calculus learning. The lecture was then carried out as many as 4 meetings. The overall research data was a description of the questionnaire and quiz results. The questionnaire stated that 82% of new students have not yet learned that calculus belongs to the field of mathematics. After lectures using flipped classroom models were implemented, the quiz results show that 38 students reached a score of more than 80. Students also respond positively to the learning using flipped classroom models increased the spirit of learning calculus because all records and exercises were well stored and can be downloaded at any time. Learning using flipped classroom models provided easy learning for new students, practicality in task collection, and effectiveness for communicating with lecturers and group members without being tied to place and time.
A digital twin based on OpenFAST linearizations for real-time load and fatigue estimation of land-based turbines
Authors: Branlard Emmanuel , Jonkman Jason , Dana Scott , Doubrawa Paula 
Published: September 2020

Abstract
Monitoring a wind turbine requires intensive instrumentation, which would be too cost-prohibitive to deploy to an entire wind plant. This work presents a technique that uses readily available measurements to estimate signals that would otherwise require additional instrumentation. This study presents a digital twin concept with a focus on estimating wind speed, thrust, torque, tower-top position, and loads in the tower using supervisory control and data acquisition (SCADA) measurements. The model combines a linear state-space model obtained using OpenFAST linearizations, a wind speed estimator, and a Kalman filter algorithm that integrates measurements with the state model to perform state estimations. The measurements are: top acceleration, generator torque, pitch, and rotational speed. The article extends previous work that derived the linear state-space model using a different method. The new implementation, based on OpenFAST linearization capability, allows for a systematic extension of the method to more states, inputs, outputs, and to the offshore environment. Results from the two methods are compared, and the validation is made with additional measurements using the GE 1.5-MW turbine located at the National Renewable Energy Laboratory test site. Real-time damage equivalent loads of the tower bottom moment are estimated with an average accuracy of approximately 10%. Overall, the results from this proof of concept are encouraging, and further application of the model will be considered.
Efficient tuning of Individual Pitch Control: A Bayesian Optimization Machine Learning approach
Authors: Mulders SP , Pamososuryo AK , van Wingerden JW 
Published: September 2020

Abstract
With the trend of increasing wind turbine rotor diameters, the mitigation of blade fatigue loadings is of special interest to extend the turbine lifetime. Fatigue load reductions can be partly accomplished using individual pitch control (IPC), and is commonly facilitated by the so-called multiblade coordinate (MBC) transformation. This operation transforms and decouples the blade load signals in a non-rotating yaw-axis and tilt-axis. However, in practical scenarios, the resulting transformed system still shows coupling between the axes. To cope with this phenomenon, earlier research has shown that the introduction of an additional MBC tuning variable – the azimuth offset – decouples the multivariable system. However, the introduction of this extra variable complicates the controller design process, and requires expert knowledge and specialized analysis software. To provide an efficient method for the optimization of fixed-structure IPC controllers, based on black box and computationally costly objective functions, this paper considers a Bayesian optimization controller tuning framework. Results show the efficiency of the framework to tune a combined 1P + 2P IPC implementation, without prior knowledge, and based on high-fidelity simulation results using a computationally expensive objective function.
Influence of limiting the projection region on coarse Large Eddy Simulation-Actuator Line Model simulations
Authors: Draper M , López B , Guggeri A , Campagnolo F , Usera G 
Published: September 2020

AbstractWind energy has developed worldwide, becoming a mature technology. Nevertheless, major advances regarding wind turbine aerodynamics and control as well as wind farm control and its integration in the power grid are being foreseen in the near future. To accomplish that, different simulation tools have emerged. The Actuator Line Model (ALM) in the frame of Large Eddy Simulation method has been used to study different related topics, from wake stability to wind turbine interaction and wind farm control, and it is considered the state of the art to simulate with high fidelity the wind flow through wind turbines and wind farms. Despite that, the ALM results, particularly loads and power production, have shown to be dependent on the numerical setup, like the projection function and its smearing parameter. The present paper aims to contribute to the latter by showing the influence of limiting the projection region. It is found that projecting the aerodynamic forces onto a cylinder that confines the rotor disk improves the computed power and loads compared to a Blade Element Momentum code and affects the wake development.
Experimental investigation of wind turbine wake dynamics during yaw variation
Authors: Macrì S , Aubrun S , Leroy A , Girard N 
Published: September 2020

Abstract
This work focuses on the analysis of the wake dynamics during yaw manoeuvres. Farm control is becoming always more crucial and voluntary misalignment is one valuable strategy employed to optimize the overall production. Indeed, the appropriate misalignment of a wind turbine can improve the rate of production and the lifetime of the downstream one, and if properly applied, could also improve the overall farm production. The main objective of this work is to analyze the wake deviation dynamics consequent to an imposed yaw manoeuvre strategy. The analysis is performed through wind tunnel experiments and the wake deviation is captured and measured using Particle Imaging Velocimetry. First, the yaw manoeuvre is reproduced in a homogeneous and isotropic turbulent flow and second, in a more realistic atmospheric boundary layer condition. Results show a different behaviour of the wake according to the imposed yaw manoeuvre.
Characterisation of fatigue damage in a thick adhesive joint based on changes in material damping
Authors: Khoshmanesh Sharif , Watson Simon J , Zarouchas Dimitrios 
Published: September 2020

Abstract
The adhesively-bonded connections in a wind turbine blade, e.g. the spar cap to shear web joins, are key elements for the structural integrity of the blade. These joins can suffer from damage at the bond-line which can propagate through the structure and compromise the operation of the blade. In this paper, we determine the damping properties of a test specimen representative of that joining a spar cap and a shear web during a period of progressive damage. In addition to the experimental damping measurement, an analytical dynamic model based on the visco-elastic properties of the material is developed to relate the damping to the loss factor. The experimental results show that when a crack is initiated in the test specimen, the damping increases by around 5-7%. This value increases with the propagation of transverse cracks in the adhesive and reaches a value of 35% when the adhesive layer experiences crack saturation and the damping reaches 45 % before failure occurs. Although a significant change in the damping is observed, there is no significant change in the natural frequency (<1%) and by association little change in the stiffness of the test specimen.
Scheduled state feedback control of a wind turbine
Authors: Engels W. P. , van der Hoek D. , Yu W. , Reyes Baez R. 
Published: September 2020

Abstract
Many wind turbines are still controlled using gain scheduled, PI(D) controllers. Another option is to use a state feedback controller, such as LQG control. However, for wind turbines that is not straight forward solution, because the system is non-linear and the impact of pitching on the states varies in time. This paper presents a variation on state feedback control. An Extended Kalman Filter is combined with gain scheduling of the state feedback gains depending on aero-dynamic sensitivities, which enables an approximation of non-linear control. This controller structure is intended to be used in more comprehensive controller optimisation studies. The scheduled state feedback controller shows good behaviour and can outperform the original PID controller.
Wake steering strategies for combined power increase and fatigue damage mitigation: an LES study
Authors: López B , Guggeri A , Draper M , Campagnolo F 
Published: September 2020

Abstract
The impact of wake steering control strategy on power production and loads for a cluster of two wind turbines is analysed in this work. The power and loads data base are generated by means of high resolution simulations using an ALM-LES model along with an aeroelastic code for multibody analysis, while the optimal yaw misalignment values are obtained, for different wind directions and performance requirements, using a weighted cost function that accounts for both power production and fatigue damage on main wind turbine components. The sensitivity of the results regarding the inflow conditions, in terms of turbulence intensity, is also analysed. The overall results show that when accounting for both power production and fatigue damage, greater values of optimal yaw misalignment are obtained. This indicates that standard yaw misalignment strategies that accounts only for power production reduce at the same time the loading damage on the wind turbine, compared to greedy configuration.
The Influence of Tether Sag on Airborne Wind Energy Generation
Authors: Trevisi Filippo , Gaunaa Mac , Mcwilliam Michael 
Published: September 2020

Abstract
The aim of this work is to propose engineering models to include the external forces acting on the tether into the power estimation of an Airborne Wind Energy System flying crosswind. The influence of aerodynamic drag, centrifugal force and gravitational force on power production is investigated. These three types of external loading acting on the tether are lumped with the kite and the tether is considered straight. In this way, a set of equations describing the tether shape and its influence on the power production is reduced to just one power equation. The formulation with straight tether and lumped quantities is suitable for preliminary designs and analyses and points out how the tether influence the system. On top of the results concerning the tether modelling, a new analytical model which includes the centrifugal forces into the power estimation for circular paths is presented.
Comparing blade-element theory and vortex computations intended for modelling of yaw aerodynamics of a tethered rotorcraft
Authors: Pfister Jean-Lou , Blondel Frédéric 
Published: September 2020

Abstract
The development of airborne wind energy systems involves many design compromises, which encourages the use of systematic optimization approaches, that rely on simple engineering models for each component. In this paper, we present results concerning rotary-based airborne wind energy devices, that are operating like autogiros tethered to the ground. This configuration results in operating conditions at unusual rotor inclinations with respect to the incoming flow. We therefore focus on the description of the aerodynamics of the rotor, comparing blade-element momentum and free-vortex approaches, so as to determine if simple aerodynamic models are adapted for being used in initial design phases.
Multi-rotor Wind Farm Layout Optimization
Authors: Kirchner-Bossi Nicolas , Porté-Agel Fernando 
Published: September 2020

Abstract
Multi-rotor wind turbines have shown a faster wake recovery than equivalent single-rotor turbines. In this work the potential benefit of a wind farm with multi-rotor turbines is assessed through the optimization of the turbine positions using the CEGA wind farm optimization algorithm, for different power densities. The EPFL analytical wake model is used to compute the power output at each turbine. The wake growth rate in this model depends on the incoming turbulence intensity. However, added turbulence intensities caused by multi-rotors affecting downstream turbines in a wind farm have recently been shown to be different from those by single-rotors. Here, two simple expressions are derived, one for the added turbulence intensity behind a multi-rotor and another for its relationship with the wake growth rate in a downstream turbine. Results on fixed layouts show multi-rotor power output improvements between 6% (3D spacings) and 0.3% (10D spacings). This benefit is bigger under relatively low ambient turbulent levels. The optimization of a full-scale wind farm layout (Horns Rev, 80-turbines) using multi-rotors provides an advantage of 0.66% and 0.79% against the optimized and the baseline single-rotor layouts, respectively. Optimizations of power densities with average inter-turbine distances of 4D and 10D show 2.75% and 0.1% improvements, respectively.
Preliminary design of a hydraulic wind turbine drive train for integrated electricity production and seawater desalination
Authors: Greco F. , de Bruycker D. , Velez-Isaza A. , Diepeveen N.F.B. , Jarquin-Laguna A. 
Published: September 2020

Abstract
The integration of wind energy to desalinate seawater can address the freshwater scarcity issue and alleviate the environmental impact of desalination. This paper presents the use of the Delft Offshore Turbine, an unconventional wind turbine with hydraulic transmission which can be used to directly drive a seawater reverse osmosis desalination process and to produce electricity with a Pelton turbine. A steady-state model is used to identify the potential regions at which it is possible to operate the system and to propose a system settings for maximising water production. The results show that the proposed system provides up to 300 kW of electricity and can desalinate up to 25 m3/h, at rated operating conditions.
Emulating aerodynamic forces and moments for hybrid testing of floating wind turbine models
Authors: Otter A , Murphy J , Desmond C J 
Published: September 2020

Abstract
The use of devices with multiple propellers to simultaneously emulate several aerodynamic loads during hybrid testing of floating wind turbines is the emerging state of the art. In this study a validation methodology and a metric are defined for the standardization of the calibration process for multiple propeller hybrid actuators. A statistical validation between the numerical simulations and experimental results is applied and Power Spectral Density is used to calculate the validation metrics. In this paper, the proposed validation method is applied to a novel design for an actuator, which consists of a custom designed frame with six aerial drone propellers. The actuator is named Multi-Propeller Device (MPD). As a test case for the proposed validation method, the MPD is used in this study to emulate the aerodynamic loads of the NREL 5 MW reference turbine at 1:37 scale. The numerical input is generated with the aero-hydro-elastic solver FAST. The aerodynamic loads and effects investigated are rotor thrust and torque, and gyroscopic moment. The recommended validation metric is the Fraction of Measurements within a user defined Tolerance (FMT), which is 1 for a flawlessly operating device. The MPD performs well at emulating rotor thrust and torque loads, with FMT = 0.97 and 0.98 respectively. However, the MPD underperforms at emulating more complex wind loads, such as gyroscopic moment with FMT = 0.27. The poor results for gyroscopic moment are attributed to the generation of significant amounts of high-frequency vibration when propeller pairs of the MPD are operating intermittently at high rotational speeds.