bluuebunny/crossref_metadata_2025 huggingface dataset:
A Ka-band linearizer TW accelerating structure for the Compact Light XLS project
Authors: Behtouei M. , Faillace L. , Ferrario M. , Spataro B. , Variola A.
Published: September 2020

In the framework of the Compact Light XLS project, we have designed a higher harmonic RF accelerating structure in order to linearize the longitudinal space phase. The design of this compact Traveling Wave (TW) accelerating structure operating on the third harmonic with respect to the linac frequency (11.994 GHz) with a (100-125) MV/m accelerating gradient is presented, together with numerical electromagnetic simulations were carried out by using the numerical codes High Frequency Structure Simulator (HFSS) and CST Particle Studio.
Challenges and tolerances for a compact and hybrid ultrafast X-ray pulse source based on RF and THz technologies
Authors: Vinatier T , Assmann R W , Dorda U , Lemery F , Marchetti B
Published: September 2020

We present an in-depth tolerance study and investigation of the main challenges towards the realization of a hybrid compact ultrafast (fs to sub-fs) X-ray pulse source based on the combination of a conventional S-band gun as electron source and a THz-driven dielectric-loaded waveguide as post-acceleration and compression structure. This study allows us determining which bunch properties are the most affected, and in which proportion, for variations of the parameters of all the beamline elements compared to their nominal values. This leads to a definition of tolerances for the misalignments of the elements and the jitter of their parameters, which are compared to the state-of-the-art in terms of alignment precision and stability of operation parameters. The most challenging aspects towards the realization of the proposed source, including THz generation and manufacturing of the dielectric-loaded waveguide, are finally summarized and discussed.
Optimization of the arc compressor performance in the MariX free electron laser
Authors: Conti M Rossetti , Bacci A , Rossi A R , Perillo V , Serafini L
Published: September 2020

The MariX FEL is a compact GeV-class X-ray source exploiting a two-pass two-way acceleration in a Super-Conducting linac operated in continuous wave mode. A key component of this peculiar machine layout is the Bubble Arc Compressor (BAC), a 300 m long beamline consisting of 14 “Double Bend Achromat” cells and a bidirectional quadrupole focusing channel, which allows the beam to make a U-turn while it is being compressed to greatly increase its brightness and peak current.

In this paper we present the performance of the BAC of MariX and the solutions we adopted to solve the main issues that the beam dynamics encounters in a line of this kind. We show the beam dynamics in the BAC matching line which is designed to operate on beams propagating in both directions, considering the anti-symmetric quadrupole focusing behavior. We study the Coherent Synchrotron Radiation (CSR) emission in the BAC showing a scheme that preserves the low emittance granting also a linear compression in presence of strong CSR effects. Lastly, we present a strategy to correct the residual dispersion-based beam tilt that is introduced by the CSR kick and would otherwise spoil the FEL emission. Further, the projected emittance is minimized cancelling the dispersive contributions.
High intensity laser hybrid guiding for electron acceleration
Authors: Kim Artem , Maynard Gilles , Cros Brigitte
Published: September 2020

Controlled guiding of laser pulses at relativistic intensities in plasmas over distances exceeding the diffraction length is a crucial requirement of a Laser Plasma Accelerator Stage (LPAS) for achieving high quality electron beams. A hybrid guiding scheme is proposed using a dielectric capillary tube, inside which a plasma channel is generated. A high intensity laser (I = 4.3x1018 W/cm2) focused at the entrance of this structure can be efficiently guided by the combined refraction of this channel and reflection at capillary walls. The efficiency of this guiding scheme as a LPAS has been investigated through numerical simulations of a 10 pC electrons beam injected at 150 MeV and accelerated up to 1.9 GeV inside a plasma channel of density 1.5x1017e.cm−3 and of 15 cm length.
Diagnostics for Electron Pulse Trains at SwissFEL Obtained by Energy Modulation in a Laser-Driven Dielectric Structure
Authors: Hermann Benedikt , Bettoni Simona , Egenolf Thilo , Feurer Thomas , Frei Franziska , Niedermayer Uwe , Prat Eduard , Ischebeck Rasmus
Published: September 2020

Electron pulse trains with sub-femtosecond spike length offer novel possibilities to ultra-fast pump-probe experiments in free-electron lasers. The pulse train can be generated by an energy modulation which is converted to temporal bunching in a magnetic chicane. The source of the energy modulation is typically a resonant interaction with a co-propagating laser in a wiggler magnet. Alternatively, the modulation can be obtained by a dielectric laser accelerator (DLA). The implementation of the DLA modulation scheme at SwissFEL would be enabled by using the experimental chamber installed in the framework of the Accelerator-on-a-Chip International Program (ACHIP) and a magnetic chicane placed afterwards. In this contribution, we will focus on electron beam diagnostics for the DLA-modulated and compressed electron bunch train. Our simulation results predict that measuring the energy spread of the modulated beam and coherent diffraction radiation emitted from a foil with a hole provides a precise tool to characterize and optimize the laser-electron modulation. An absolute measurement of the longitudinal phase-space with a temporal rms-resolution of 350 as is possible with the planned X-band transverse deflecting cavity in Athos.
Numerical modelling of chromatic effects on axicon-focused beams used to generate HOFI plasma channels
Authors: Ross A J , Alejo A , von Boetticher A , Cowley J , Holloway J , Jonnerby J , Picksley A , Walczak R , Hooker S M
Published: September 2020

Hydrodynamic optical-field-ionised (HOFI) plasma channels promise a route towards high repetition-rate, metre-scale stages for future laser plasma accelerators. These channels are formed by hydrodynamic expansion of a plasma column produced by optical field ionisation at the focus of a laser, typically from an axicon lens. Since the laser pulses used to generate the initial plasma column are of sub-picosecond duration, chromatic effects in the axicon lens could be important. In this paper we assess these effects using a numerical propagation code. The code is validated using analytical formulae and experimental data. For the parameter range investigated, dispersive effects are found to be of minor importance, reducing the peak on-axis intensity in the focal region by approximately 10%.
Summary of WG6: Theory and simulations
Authors: Silva T , Massimo F , Vieira J
Published: September 2020

The presentations of working group 6 (theory and simulations) of the fourth edition of the European Advanced Accelerator Workshop presented new ideas for experimental schemes, analytical models, and updates on well-known Particle in Cell codes. New schemes for improving electron beam quality, positron acceleration, ion acceleration, and radiation generation were proposed. Recently developed features of several Particle in Cell codes were also reported.
Single Domain Multiple Decompositions for Particle-in-Cell simulations
Authors: Derouillat J. , Beck A.
Published: September 2020

As a multi-purpose Particle-In-Cell (PIC) code, SMILEI gathers many different features in a single software. Combining some of them is challenging. In particular, spectral solvers and patch based load balancing have a priori non compatible requirements. This paper introduces the Single Domain Multiple Decompositions (SDMD) method in order to address this issue. To do so, different domain decompositions are used for fields and particles operations. This approach allows to keep small domains for particles, necessary for a good load balancing, while having large domains for the fields. It proves beneficial in mitigating synchronization costs and gives the opportunity to introduce more paralellism in the PIC algorithm on top of providing structures compatible with spectral solvers.
Advances in plasma-based beam dump modelling
Authors: Bonatto A , Nunes R P , Jakobsson O , Williamson B , Liang L , Xia G
Published: September 2020

This work presents a short review on the advances of plasma beam dump modelling since they have been first proposed. Analytical models have been derived to estimate the beam energy loss for both passive and active beam dump schemes. For the passive case in particular, tailored plasma density profiles can improve beam-energy extraction by mitigating particle re-acceleration. A semi-analytical model, consisting of the dynamics of test-particles experiencing the previously derived analytical wakefields, is under development to investigate deceleration beyond the saturation point, in the linear to the quasi-linear regime.
Toward the modeling of chains of plasma accelerator stages with WarpX
Authors: Vay J.-L. , Almgren A. , Amorim L. D. , Bell J. , Ge L. , Gott K. , Grote D. P. , Hogan M. , Huebl A. , Jambunathan R. , Lehe R. , Myers A. , Ng C. , Park J. , Rowan M. , Shapoval O. , Thévenet M. , Zhang W. , Zhao Y. , Zoni E.
Published: September 2020

The Particle-In-Cell code WarpX is being developed by a team of the U.S. DOE Exascale Computing Project to enable the modeling of chains of tens of plasma accelerators on exascale supercomputers, for future collider designs. The code is combining the latest algorithmic advances (e.g., boosted frame, pseudo-spectral Maxwell solvers) with mesh refinement and runs on the latest CPU and GPU architectures. An example of the application to the modeling of up to three successive muti-GeV stages is presented. The latest implementation on GPU architectures is also reported.
Critical thinking ability through experiential learning in the calculus class
Authors: Abdullah A A , Shanti W N , Sholihah D A
Published: September 2020

This quasi-experimental study aims to develop students’ mathematical thinking skills in calculus classes. The learning model used is experiential learning, where students develop mathematical concepts from their own experience, data obtained from Student Worksheets, observations of student activity sheets in discussions to solve problems, and draw conclusions through critical thinking processes. The results of the study show that students’ critical thinking skills that can be developed in this learning model are: interpretation, analysis, evaluation, and making conclusions. With an average score of students in the pretest and posttest is 59.55 and 73.18. Changes in pretest and posttest scores were statistically significant (p<0.05) following completion of the experiential learning program. An increase in the average value of critical thinking skills along with the increasing number of students who are categorized as very critical and critical in the hierarchy of critical thinking abilities category.
Students’ mathematical critical thinking reviewed from self-regulated learning
Authors: Susanti V D , Krisdiana I , Adamura F
Published: September 2020

Critical thinking is the ability to think logically, reflectively, and productively which is applied to produce a good decision. Therefore, it is necessary for mathematics learning. This study aims to analyze the students’ mathematical critical thinking in solving numerical analysis problems in terms of self-regulated learning (SRL). The subjects of this study were the seventh semester students of mathematics education at Universitas PGRI Madiun, selected using purposive sampling technique. The instrument in this study was a test for mathematical thinking analysis and a self-regulated learning questionnaire for subject selection. The results suggest that students with high and intermediate SRL are both having a good ability to make generalizations, identify and justify concepts, while students with low SRL only have a good ability to make generalizations, but performed low on the ability to identify and justify the concepts of analysing algorithm.
The ethnomathematics in making woven bamboo handicrafts of osing community in Banyuwangi, Gintangan village as geometry teaching material
Authors: Yudianto E , Susanto S , Sunardi S , Sugiarti T , Fajar F A
Published: September 2020

Ethnomathematics refers to the application of mathematics in cultural life. This research was intended to describe the ethnomathematics in making woven bamboo handicrafts in Gintangan village, Banyuwangi. The things obtained in this research were the changes in of geometric teaching material, covering Test Problem Package with Ethnomatematics as the topic. The type of this research was qualitative research with ethnographic approach. The data collection methods used were observation and interview. The subjects of this research consisted of 2 persons; they were foremen who made the woven bamboo handicrafts, kukusan, ereg, tenong and nyiru. Ethnomathematics emerged when the woven craftsmen carried out the activities to measure, calculate and design. When the process of measuring the thickness of the bamboo whittles came, the measurement concept was meters (m). During the process of calculating the drying time of bamboo and the amount of bamboo whittles, comparative concept of value appeared. During the design process, the concept of quadrilateral and number sequences emerged. The result of this research was geometry teaching material in the form of test package. The question of test package was pointed for the students of class VIII at middle school. The question of Test Package covered 4 C5 and 1 C6 questions
Interactive learning media based on MySQL technology in mathematics
Authors: Aliyah H , Kusmayadi T A , Fitriana L
Published: September 2020

Interactive learning media is one of the factors supporting success in the learning process. This study aims to develop interactive learning media based on MySQL technology and to determine the feasibility of media developed for 8th-grade students on straight line equation material. This system works by using a web application. The population in this study were all 8B grade students at MTs Negeri 7 Kediri odd semester 2019/2020. The model used in this study is the ADDIE model which includes Analysis, Design, Development, Implementation, and Evaluation. The first step is analyzing students ‘difficulties, the second step is designing an appropriate learning program, the third step is developing learning media, the fourth step is implementing learning media for students, and the last step is evaluating students’ abilities by giving tests. The results showed that the interactive learning media had fulfilled the validity, practicality, and effectiveness aspects so that the media was appropriate to be used.
Direct identification of Borobudur temple artefacts for learning flat shapes concepts
Authors: Anista R , Marsigit M
Published: September 2020

Understanding concepts is important in learning mathematics, one of them is learning geometry. The concept of geometry is closely related to daily life, so that introducing directly the object of geometry is expected to facilitate the understanding of geometry concepts for students. This research is a descriptive qualitative research. The purpose of this study was to determine student understanding in studying geometry by directly identifying Borobudur temple artefacts. The subjects of this study were 3 students of class VIII SMP. The instrument in this study was the researcher herself as the main instrument guided by a concept understanding test and interview guidelines based on valid and reliable tests. Data were collected through the provision of pre-test and post-test about understanding the concept of a flat figure which includes 7 indicators and accompanied by interviews as supporting data. The results showed that directly identifying the Borobudur temple artefacts can be used as an alternative to studying the concept of flat wake. The weakness of this study is that the three subjects have not been able to answer the problem in indicator 7, which is about developing sufficient requirements or necessary requirements from the concept of a flat figure. This can be a material or material that can be used as future research.
Students’ mathematical proficiency in solving calculus problems after Maple implementation
Authors: Hamid H , Angkotasan N , Jalal A , Muhtadi D , Sukirwan
Published: September 2020

This research aimed to analyze and explore the capability of mathematical proficiency second semester math education students of Faculty of Teacher Training and Education (FKIP) Khairun University academic year 2017/2018. In this study mathematical problems are presented in Calculus, and given the opportunity for students to understand the problems provided both from the theoretical aspects related to indicators of mathematical proficiency namely conceptual understanding, procedural fluency, strategic competence, adaptive reasoning, and productive disposition, which further uses Interactive Maple Tutor, Maple Assistant, and Show Solution commands. Students in this study can take some steps themselves, and ask Maple to take the next step. Research data were collected and analysed with a descriptive-qualitative approach of student work for each indicator of mathematical proficiency with research subject in total 128 students. The results showed that the ability of the mathematical proficiency of students of mathematics education in the medium category.
The challenge-based learning to students’ spatial mathematical ability
Authors: Susilawati Wati , Suryadi Didi
Published: September 2020

The low ability of students thinking in geometry requires a new perspective in creating a more challenging and better mathematics learning process. This study aims to improve mathematical spatial ability through challenge-based learning using the Quasi-Experiment Method and Non-equivalent Pretest-Posttest Control Group Design. The instruments used PAM test and spatial thinking ability test. Analysis of quantitative data used t-test, Mann–Whitney U test, and Adjusted Rank Transform, two-way ANOVA. The study conducted at a university in Bandung, Indonesia. It involved 62 prospective Madrasah Ibtidaiyah teacher candidates as samples, which categorized into two classes, 32 class B as an experimental class and 30 class A as a control class. The findings show: There is a higher increase in mathematical spatial abilities of students who obtain challenge-based learning than students who obtain expository learning based on the overall student sample and students’ initial mathematical knowledge. There was an interaction effect between type aspects (challenge-based learning and expository learning) and initial mathematical knowledge on students’ mathematical spatial abilities. Challenge-based learning can facilitate the process of conflict, discovery, social interaction, and the reflective process of students. The material is easy to understand and exciting to learn. Thus, spatial ability is better than expository learning.
Augmented Reality for Integer Learning: Investigating its potential on students’ critical thinking
Authors: Suryanti S , Arifani Y , Sutaji D
Published: September 2020

Research on critical thinking has been carried out by researchers. Critical thinking is one of the four skills students must have before the 21st century. In recent years Augmented Reality (AR) technology has provided opportunities by making learning more interesting, that able to visualizing mathematical objects in the real world. This research was conducted in a remote area of Bawean Island after the mathematics teachers participated in Augmented Reality-based mathematics learning media development program. The sample of the study was 95 students of 7th grade junior high school from five schools on Bawean Island. Investigation of the potential use of Augmented Reality technology to critical thinking skills, carried out by providing students with pretest and posttest critical thinking skills. Also, student responses were considered in this study. The results of our analysis, the ability of student’s critical thinking skills after the use of AR-based media is better than before the use of AR-based media, and students give a very good response to the use of AR-based media in this integer learning.
Analysis of the government district RMTDP using FMD and dematel method
Authors: Suhaedi D , Ishfahani A A , Harahap E H , Fajar M Y , Rohaeni O
Published: September 2020

Indonesia is one of the developing countries. Development is carried out in national, provincial, and district areas. Generally, development is done through a plan. Development planning consists of several strategic issues. These strategic issues describe the state of an area, specifically the area of a district. The purpose of this study is to analyze nine strategic issues of the Regional Medium-Term Development Plan (RMTDP) of the Government District in 2016-2021. Each strategic issue includes seven criterion values. Data from each strategic issue is collected using a questionnaire created by the institution. Data on these strategic issues are formulated in the form of a mathematical model, namely multiple criteria decision making (MCDM). Analysis of the MCDM data is performed using the Fuzzy Maximizing Deviation (FMD) and DEMATEL methods. The results of data analysis show that issues that should receive priority attention are still limited to basic environmental facilities and infrastructure, and the most dominant criteria for these nine issues are the tasks and responsibilities of the regional government.
Understanding primary school children’s learning on addition of fractions
Authors: Abbas Nor’Arifahwati Haji , Shahrill Masitah , Indra Prahmana Rully Charitas
Published: September 2020

Fractions are universally known to be difficult to learn. Learning basic fractions may not be sustainable if one is to apply it to more advanced mathematical content knowledge as it is interlinked with other mathematics topics. In the effort to understand how children grasp the learning of fractions additions, a study was carried out with a random sampling of Years 4, 5 and 6 children in Brunei Darussalam. The research participants consisted of 33 children who are currently studying at government and private primary schools in Brunei. A pen-and-paper self-designed test was used as an instrument in collecting the data. The quantitative data was analysed by using a descriptive analysis method. The overall reliability of the self-designed tests indicated that the items have relatively high internal consistency with a Cronbach alpha of .859. The findings revealed that the children’s understanding is stronger on questions with answers regarding proper fractions rather than improper fractions. This could be further explored through future studies employing a qualitative approach.
Mathematics module based on problem-based learning to improve students’ metacognition
Authors: Barokah I , Budiyono  , Saputro D R S
Published: September 2020

Low student metacognition can be improved during the teaching and learning process. This study aims to obtain a mathematics module based on problem-based learning valid, practical, and effective. This research is development research. The development model used refers to the development model according to Budiyono. There are 3 stages in this research, namely preliminary study, product development, and product efficacy test. The population in this study was 8th-grade students of junior high school in Surakarta, Indonesia. Schools selection using a stratified cluster random sampling technique. The sample for preliminary field testing is 29 students. The sample for main field testing is 87 students. The instruments used in this study were module assessment sheets, student and teacher response questionnaires, metacognitive knowledge questionnaires, and metacognitive regulation tests. The results of this study are a mathematics module based on problem-based learning are valid based on expert judgment with very good categories, practical based on the assessment of teachers and students with very agreeable categories and effective because of increasing student metacognition after learning using mathematics module based on problem-based learning.
Google form in engineering mathematics: Innovation in assignment method
Authors: Iswanti  , Astuti S , Suryono  , Sayekti I , Krishna B
Published: September 2020

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

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

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

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

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

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

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

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

Wind 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

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

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

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

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

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

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

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

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

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.