bluuebunny/crossref_metadata_2025 huggingface dataset:
Unraveling nucleation pathway in methane clathrate formation
Authors: Li Liwen , Zhong Jie , Yan Youguo , Zhang Jun , Xu Jiafang , Francisco Joseph S. , Zeng Xiao Cheng
Published: September 2020

Significance

Understanding the clathrate formation mechanism has important implications on natural gas exploitation, storage, and transportation. A key toward clathrate formation is the hydrate nucleation, which involves complex interplay between water and guest molecules at nanoscale and multiple kinetic stages. Herein, by tracing the kinetic evolution of multiple ternary water-ring aggregations based on trajectories of large-scale molecular dynamics simulations, we identified a generic nucleation pathway to clathrate formation. This observed nucleation pathway is driven by numerous compression/shedding processes among the methane hydration layers, and it can explain the widely accepted “blob” model of clathrate nucleation. The molecular insight into the nucleation pathway allows us to quantitatively assess the nucleation timescales as well as the critical nucleus sizes in the clathrate formation.
Astroglial FMRP deficiency cell-autonomously up-regulates miR-128 and disrupts developmental astroglial mGluR5 signaling
Authors: Men Yuqin , Ye Liang , Risgaard Ryan D. , Promes Vanessa , Zhao Xinyu , Paukert Martin , Yang Yongjie
Published: September 2020

Significance

How the loss of FMRP affects nonneuronal glial development especially underlying mechanisms remains essentially unexplored. By employing astroglial
Fmr1
conditional knockout (cKO) mice and human FMRP-deficient astroglia, in the current study, we showed that the loss of astroglial FMRP cell-autonomously up-regulates brain enriched miR-128-3p in mouse and human FMRP-deficient astroglia, which selectively disrupts developmental astroglial (but not neuronal) mGluR5 signaling. Subsequent transcriptome and proteome profiling from in vivo isolated FMRP-deficient astroglia further indicates that FMRP commonly and preferentially regulates protein expression through posttranscriptional (but not transcriptional) mechanisms (such as miR) in astroglia. Overall, our study defines an FMRP-dependent cell-autonomous miR pathway that alters developmental astroglial mGluR5 signaling, which unveils astroglia-specific molecular mechanisms involved in FXS pathogenesis.
Teaching communication strategies in China
Authors: Xia Danni
Published: September 2020

Since English is now used as a Lingua Franca (ELF), it is important to explore how English learners may be trained to employ multiple Communication Strategies (CSs) to achieve mutual understanding, particularly in ELF contexts. This study explores which CSs were taught in recent years in China and how the teaching content is presented in domestic textbooks from an ELF perspective. Ten college English textbooks that were published in the past five years (2014–2019) were selected and evaluated based on an adapted framework of CSs. The findings revealed a notable inclination toward certain types of macro-strategies and were not systematically mapped out. Moreover, an initial effort in manifesting “cultural diversity” was observed but failed to construct intercultural contexts. Knowledge explanation as well as student-oriented exercises were found to be conducive in consolidating learners’ acquisition of forms. However, the function and context of the target CSs were neglected. Furthermore, an absence of sociocultural pragmatic concern resulted in a discrepancy between explicit knowledge explanation and context-based practice. Accordingly, this study suggests implications for both textbook writers and instructors in practice.
Translator training outdoors
Authors: Torres-Hostench Olga
Published: September 2020

Before the COVID-19 pandemic, there was no real need to integrate outdoor education into translation studies, as it was easy to balance indoor and outdoor time before and after translation classes. However, the lockdown has deeply affected not only learning but also the mental and physical health of teachers and students, and outdoor education may contribute to recovery afterwards. The proposals in this paper focus on the benefits that being outdoors has for physical health, knowledge, social relations, mental health and attitude to learning. Moreover, being outdoors allows for social distancing. The activities presented in this paper are related to specialized translation, sight translation, simultaneous interpreting, consecutive interpreting, role-play interpreting, translation theory, song translation, theatre translation, machine translation post-editing, translators’ employability, translation project management and, last but not least, intermodal transcreation.
Europeanisation from below: Still time for another Europe? Introduction to the special issue of the European Journal of Cultural and Political Sociology
Authors: della Porta Donatella
Published: September 2020

The focus of this special issue is on social movements’ alternative visions and practices of ‘another Europe’. As trust in the European Union (EU) is dramatically falling amongst its citizens, research on alternative visions of Europe ‘from below’ appears all the more relevant in order to understand the potential for changes in EU politics, policies, and polity. The general question we want to address refers therefore to the ways in which the financial crisis and related political turmoil have affected the position of progressive social movements towards the Europeanisation process. In addressing the development of alternative visions of Europe, this special issue looks at anti-austerity protests, and related mobilisations in the period of 2011–2016. The various contributions assess the effects of the financial crisis on the multilevel governance of European countries and, therefore, on the ways in which social movements formulate claims, frames, and justifications about European institutions. This editorial introduces the main approaches to the Europeanisation of social movements, discusses how they might apply in times of crisis, and then presents the articles included in the special issue.
HOTS problem on function and probability: Does it impact to students’ mathematical literacy in Universitas Terbuka?
Authors: Prastiti T D , Tresnaningsih S , Mairing J P , Azkarahman A R
Published: September 2020

Mathematical literacy is one of the essential skills for students both during their learning and other daily activities. This study aimed to describe the effectiveness of worksheet consisting of higher order thinking skills (HOTS)-based mathematics problems on function and probability to improve the students’ mathematical literacy in Universitas Terbuka (UT) Surabaya. This research was an experimental research, involving six study groups of UT Surabaya students who took mathematics course as the research subjects. The research subjects were then selected using clustered random sampling technique, and two study groups (Tuban and Jombang) were chosen as the research sample. The instruments used in this study were pre-and post-test of mathematical literacy, HOTS-based worksheet, and tutorial kit. The data were analyzed using Wilcoxon non-parametric test as the research data were not normally distributed. The effectiveness of HOTS-based worksheet was measured by using normalized gain measurement with the medium category was set at 0.3. The results showed a significant positive effect (normalized gain value > 0.3) of the mathematics HOTS-based worksheet. It can be concluded that the application of mathematics HOTS problems were effective to improve mathematical literacy of UT Surabaya students.
Representation skills students reviewed from the prior knowledge through realistic mathematics education in a linear material program
Authors: Laelasari  , Darhim  , Prabawanto S
Published: September 2020

The ability of mathematical representation in mathematics can be seen from the process of mathematical representation in various dimensions, one of which is the students’ initial knowledge of students. This study aims to examine differences in the achievement of mathematical representation between students who get lectures with realistic mathematics education and those who get lectures with conventional reviews in (a) overall; (b) prior knowledge based on high, medium, or low level. Through realistic mathematics education and describe the process of error in students’ mathematical representation of students for each indicator. This type of research is a Mixed Method research, and the research design is Concurrent Embedded. Whereas the comparative test of the control and experimental groups with the average difference test. Research subjects consisted of 32 people in semester IV. The results showed differences in mathematical representation ability between students who received lectures with Realistic mathematics education, and those who received lectures with conventional review as a whole, based on students’ initial abilities for the upper, middle and lower groups. Most students still have difficulty determining the example used and many errors using inequality marks, difficulty drawing graphics, determining the area of resolution.
Study in statistics: motivation, independence, and learning achievement
Authors: Irawan Edi
Published: September 2020

Statistics are very important for students to master, but many experience difficulties. This study aims to determine the effectiveness of a combination of blended learning and problem based learning in improving student motivation, independence, and statistical learning achievement. This research is a quasi-experimental study conducted on IAIN Ponorogo students. The instruments used for data collection were achievement tests, learning independence tests, and learning motivation questionnaires. The data collected was analyzed using MANOVA and continued with the Bonferroni Test. The result of the MANOVA test has obtained a significance of 0.000 so that it can be concluded that the combination of blended learning and problem-based learning was more effective in increasing student motivation, independence, and statistical learning achievement than blended learning and problem based learning methods. Specifically, the combination method is more effective in increasing student learning motivation than blended learning and problem-based learning. In the aspect of increasing student learning independence, the combination method has the same effectiveness as problem-based learning. Both are more effective in increasing the independence of student learning than blended learning. Whereas in the aspect of learning achievement, the combination method is more effective in increasing student statistical learning achievement than blended learning and problem-based learning.
Measurement of mathematics problems solving ability using problem based mathematics question
Authors: Zulfah  , Astuti  , Surya Y F , Marta R , Wijaya T T
Published: September 2020

The purpose of this study is to produce the valid, practical, and effective problem-based questions to measure the mathematical problem-solving abilities of eighth-grade students of junior high school. The materials used as the basis of development are system of linear equation in two variables and the Pythagorean theorem. The development model used is the Plomp model consisting of three stages; preliminary research, prototyping phase, and Assessment phase. Based on the results of these stages, 16 problem-based questions were obtained which are valid to the criteria of content, constructs and determined language, practically used by the teacher, and effective for measuring students’ mathematical problem solving abilities because they can direct students to identify problems, plan solutions, implement solutions, and need to carry out evaluations as indicators of problem-solving abilities.
Improvement of mathematics learning activity through lesson study
Authors: Tanujaya Benidiktus , Mumu Jeinne
Published: September 2020

The purpose of this lesson study was to improve learning activities of Mathematics instruction. Learning activities to be improved is the theory of probability. There are three phases on this lesson study, PLAN, DO and SEE. In PLAN cycle, the researcher organizes chapter design and lesson plan. In the Do cycle, the lesson plan was implemented in instruction using Think-Pair-Share model. Students are thinking individually before they were paired in groups. The teaching process is organized in two sequence classes. In the first lesson, the learning process was quite conducive, but it still needed some improvement. In cycle SEE, based on the observation of the first lesson, teachers are suggested to use more concrete-case examples to build students’ understanding of concepts for the next lesson. The teachers should ask more questions and pay attention to students who are less active during the class. The last recommendation is that students should analyse assignment independently before posing criticisms and providing suggestions to others. The second lesson shows that students are more active compared to the first lessons. Students have more relaxed learning atmosphere. They are more assertive and involved in whole class activities. The students are more confident to ask questions, give objections, and make some corrections.
Analysis of students’ metacognition in solving mathematics problems
Authors: Imaya I A , Budiyono  , Nurhasanah F
Published: September 2020

Metacognition is a thought about the awareness of thinking itself to plan, organize strategy information, monitor strategies, debugging strategies and assess the results of their abilities. Student activities in the use of their awareness can be used to solve problems. Mathematical problems solving is an important thing in the process of learning mathematics so that complex ways of thinking are needed. This study aims to analyze the level of metacognition of students in Boyolali district in solving problems based on differences in mathematical scores and gender. This study is a qualitative study using written test data and interviews with students and mathematics teachers. The results showed that the level of metacognition of male students who had high mathematical scores was at the level of aware use, the subjects are aware of what they are doing and can be used to solve problems, but the subject cannot solve it well and cannot correct his mistakes. The level of metacognition of female students who have high, medium and low math scores are at the level of tracit use. The student cannot understand the problem at hand and does not know the concept used.
Mathematical Literacy on Rectangles And Triangles Based on The Characteristics of Students’ Way of Thinking
Authors: Nurnugroho B A , Arfinanti Nurul , Kartika Ika
Published: September 2020

This study aimed to describe students mathematical literacy on rectangles and triangles based on the characteristics of a students’ way of thinking by Anthony Gregorc. The different ways of thinking produce different ways of learning and ways of thinking. This study is a descriptive qualitative study. The object of this study is seven grades students at MTs Plus Az Zahro Gandrumangu Cilacap. The Instrument to collect data such as test, questionnaire, interview, observation, and documentation. The validity of the data result checked by data triangulation. To analyze the data collected, we use Miles and Huberman‘s’ model. The results of this study show that each student has different ways of thinking. All the characteristics of students’ way of thinking can be said to achieve almost the same literacy abilities. The difference in the characteristics way of thinking is apparent in writing the information obtained from the problem and writing in its solution. Different ways of thinking students require teachers in the learning process to apply a variety of learning models. Varied learning allows students to be able to learn according to their way of thinking so they can achieve better learning outcomes.
Gender differences on students’ self-regulated learning in mathematics
Authors: Rohman F M A , Riyadi  , Indriati D
Published: September 2020

Self-regulated learning (SRL) is a process carried out by students on their awareness in formulating goals, determining strategies, motivating and monitoring themselves in learning and evaluating the results of their learning. This study aims to describe the SRL of junior high school students in learning mathematics from gender differences. The method used in this research is quantitative descriptive. The study was conducted at SMPN 1 Pecangaan. The sample used was 73 8th-grade students, consisting of 35 male students and 38 female students. The data were retrieved by using a questionnaire with Likert scale. The results of this study indicated that there were differences in SRL between male and female students in learning mathematics based on independent t-test (0.001< 0.05). Female students were superior in each indicator of all aspects of SRL, namely metacognition, motivation, and active involvement in learning activities. It can be concluded that female students have better SRL in learning mathematics compared to male students.
Neuroscience study: Gender and mathematical creative thinking skills in vocational high school students
Authors: Adiastuty N , Waluya S B , Rochmad  , Aminah N
Published: September 2020

The main idea in this article is looking at the creative thinking patterns in mathematics learning viewed from gender on vocational high school students. Creative thinking skills are cognitive processes, and cognitive processes are inseparable from how the brain processes work. To see the ability to think creatively, we have to see how the process of creative thinking happens. This is a neuroscience study in mathematics with a quasi-experimental design. We tried to describe the relationship among neuroscience, mathematics creative thinking skills, and gender. We involved 30 male students (automotive major) and 30 female students (accounting major) from the 12th-grade of Islamic Center Vocational High School of Cirebon, West Java, Indonesia. Statistics test used was independent sample t-test to see about mean differences of males and female group. There are three indicators about mathematical creative thinking used are fluency, flexibility and novelty. Finally, we found that male students and female students have their own structure of the brain. Female student has a higher ability of mathematical creative thinking skills than male students in Islamic Centre Cirebon, West Java, Indonesia.
Batak Toba culture on mathematics learning process at Medan high school
Authors: Surya E , Purba C , Syahputra E , Haris D , Mukhtar  , Sinaga B
Published: September 2020

The studi aims to determine the validity, practicality, and effectiveness of teaching materials, and find out the improvement of students’ mathematical problem-solving abilities by using teaching materials that are developed. This type of research is the development using the Dick and Carey development model. This research was conducted at Markus Medan High School, trial I was conducted in class X-IPA while trial II was in class X-IPS. Mathematics learning uses Guided Discovery Learning Model. The results showed that the developed Batak Toba culture based teaching materials could meet valid, practical and effective criteria. Based on expert opinion, the response of students and teachers also states teaching materials can be used easily. Teaching materials meet the completeness of student learning outcomes in a classic way. As for the ability to solve mathematics problem-solving students have increased by 3, 33%. In the first experiment of 83.33% of students who completed, while in the second experiment amounted to 86.66% of students who completed. The conclusion of the research development of teaching materials based on Batak Toba culture fulfills valid, practical and effective criteria. Teaching materials can improve students’ mathematical problem-solving
A system dynamic of the harvesting strategies to sustain the population of squid using logistic growth model
Authors: Lola Muhamad Safiih , Wan Alwi Wan Saliha , Ramlee Mohd Afiq , Zulkifli Fatin Alina , Noor Che Noorlia , Ibrahim Yahya , Abdullah Mohd Tajuddin
Published: September 2020

Loligo Duvauceli, is known as squid in the local name. Squid is a species of high value and a good source of protein besides fish. In this paper, a logistic growth model with constant and periodic harvesting are used to find the optimum sustainable population of Loligo Duvauceli in order to preserve the resource. The data used for this study was obtained from Department of Fisheries. The aims of this study are to estimate to determine the stability of the equilibrium point. Then, the effect of the constant and the periodic harvesting on the population of squids analysed. Finally, to compare the results obtained between the two strategies. The best harvesting selected squids is periodic harvesting.
Project based learning to improve student learning activeness
Authors: Rohmah S N , Waluya S B , Rochmad  , Wardono
Published: September 2020

This paper presents the results of a study of the Project Based Learning model to improve student learning activeness. As for the background of writing this paper because to face the challenges of the 21st Century skills needed to apply knowledge including communication, collaborative, critical thinking and creativity (4 C). Communication and collaborative skills in learning aim to make students more active. Project based learning involves the performance of students directly in making a project, the lecturer acts as a facilitator and supervision that monitors student activities in designing activities, arranging schedules, implementing projects, solving problems and making decisions with the final product that will be reported and presented by students as an evaluation activity from the results of project-based learning. Project-based learning can increase student activity in learning.
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

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

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

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

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

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

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

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

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

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

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

Floating 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

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

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

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

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

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

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

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.
Numerical study and LiDAR based validation of the wind field in urban sites
Authors: von der Grün M , Zamre P , Chen Y , Lutz T , Voß U , Krämer E
Published: September 2020

Within the project “Windy Cities” the economic use of small wind turbines in urban areas is investigated in Tübingen, Germany. This test-site contains complex terrain, forested areas and various types of buildings making the local wind field more turbulent and complex. To avoid damages and reduced life times of small wind turbines caused by high turbulence a detailed prediction of the wind field is essential in the present study. This is done using CFD.

The scope of this study is the validation of the setup including terrain and vegetation. For this, on-site planar wind field LiDAR data are utilized to define the inflow boundary condition for highly resolved Detached Eddy Simulations (DES) using ANSYS Fluent. The required preprocessing steps of the LiDAR data are explained in detail and their assumptions, which are made to interpolate the data onto the numerical inflow plane. Since the inflow region is covered by forested zones a forest model is introduced with a local tree height adaption based on Laser scan data. LiDAR data, which are measured further downstream, are used to validate the forest model. Simulations with and without the considered forest are compared to investigate the influence of the forested region.
Optimizing a wind farm layout considering access roads
Authors: Roscher B , Mortimer P , Schelenz R , Jacobs G , Baseer A
Published: September 2020

Considering building a wind farm, a quarter of the initial investment cost is accounted for planning, construction, and project preparation. Some of those expenses can be reduced within the project concept phase. The wind farm layout is one of the common aspects being optimized.

Commonly, wind turbines are placed such that wake losses are minimal. However, this might lead to long access roads. The cost of a gravel road is estimated to be 75 €/m. In this paper, an optimization problem considering access roads is developed.

Two methods are investigated to determine the influence of the access roads on a wind farm layout optimization. A case study with seven wind turbines is set up. The layout is optimized such that the LCOE is minimal. One method examines a wind farm with nearby existing roads. This method results in a reduction of road costs by 9 000€ while the AEP suffers a loss of 0.134 %. The second method neglects existing roads and develops a new access road network. Comparing an optimized wind farm layout without considering the access roads to an optimization that included the access leads to 22 000 € fewer road investment costs and a loss of AEP of 0.238 %. Those changes seem marginal but indicate a possible gain for large scale wind farms.