1,721,045 research outputs found
Minimizing cogging torque in permanent magnet synchronous generators for small wind turbine applications
No full textPermanent magnet synchronous generators have a wide usage among electric machines, especially in small wind turbine systems. However permanent magnet synchronous generators suffer from cogging torque due to the magnetic interaction between the poles of the rotor’s permanent magnets and the steel laminations of the stator’s teeth. The cogging torque drawback is a major problem in this kind of generators that affects its functionality negatively. In the literature many different approaches for reducing the cogging torque are proposed and each different approach achieves different amount of reduction in the cogging torque. In this study 6 different cogging torque reduction techniques are considered and with finite element simulations using the JMAG simulation software, they are compared with each other in terms of percent reduction in the cogging torque. Present simulations show that among the considered different approaches, continuous skewing technique reduces the cogging torque the most with respect to the each other techniques considered. Also using the step skewing of the rotor or stator, changing the slot opening width and having dummy slots techniques can decrease the cogging torque more or less the same amount in magnitude. Present results indicate that changing the radial shoe depth technique has almost no effect in reducing the cogging torque
Prediction algorithm & learner selection for European day-ahead electricity prices
No full textThe prediction of day-ahead electricity prices with higher accuracy is always helpful for the market players of the power exchange. This study was intended in the first place to find out the best time series prediction method for the selected 14 European countries. The test results of four time-series methods show that the next day prices were more in line with the previous day prices in 87% of the selected countries; Later, a classification approach is followed by 33 different features of each country to answer the question of which method would be the best for the other countries, that were not studied in this paper, would be? As a result, the support vector machine algorithm results in 57% accuracy in classifying an unknown European country to determine the best prediction method. Therefore, this paper focuses now on two correlated studies to find out the best time series prediction methods and a classification approach for selected countries
Analysis of Grid Performance with Diversified Distributed Resources and Storage Integration: A Bilevel Approach with Network-Oriented PSO
No full textThe growing deployment of distributed resources significantly affects the distribution grid performance in most countries. The optimal sizing and placement of these resources have become increasingly crucial to mitigating grid issues and reducing costs. Particle Swarm Optimization (PSO) is widely used to address such problems but faces computational inefficiency due to its numerical convergence behavior. This limits its effectiveness, especially for power system problems, because the numerical distance between two nodes in power systems might be different from the actual electrical distance. In this paper, a scalable bilevel optimization problem with two novel algorithms enhances PSO’s computational efficiency. While the resistivity-driven algorithm strategically targets low-resistivity regions and guides PSO toward areas with lower losses, the connectivity-driven algorithm aligns solution spaces with the grid’s physical topology. It prioritizes actual physical neighbors during the search to prevent local optima traps. The tests of the algorithms on the IEEE 33-bus and the 69-bus and Norwegian networks show significant reductions in power losses (up to 74% for PV, wind, and storage) and improved voltage stability (a 21% reduction in mean voltage deviation index) with respect to the results of classical PSO. The proposed network-oriented PSO outperforms classical PSO by achieving a 2.84% reduction in the average fitness value for the IEEE 69-bus case with PV, wind, and storage deployment. The Norwegian case study affirms the effectiveness of the proposed approach in real-world applications through significant improvements in loss reduction and voltage stability
Multi-criteria Decision Model for the Assessment of Offshore Wind Energy Potential of Tunisia
No full textThis paper investigates the potential for the development of offshore wind power plants in Tunisia. The goal of this research is to increase the possibility of using renewable energy available in the country and reduce the dependence on fossil fuels. The data used for the analysis is obtained from remote sensing satellites and weather stations located across the country's coastal regions. A multi-criteria decision model is built to perform geographic and technical analysis of the study area. This research reveals locations suitable for wind turbine installations. The results of this study aid the transition to wind energy with its optimal adaptation in Tunisia. Only 7% of Tunisian offshore territory is found fit for the deployment of fixed-bottom wind farms. Six locations, in particular, were chosen in the Gulf of Tunisia, Gabes, Sousse, Sfax, Bizerte, and Djerba. The GIS-based methodology proposed in this paper can be applied to other offshore wind farm allocation investigations. The environmental impact of proposed wind farms on GHG reduction and employment opportunities are investigated. The suggested wind farms will reduce the GHG emissions and the energy price in Tunisia as well as create new jobs for society
An integrated framework for techno-enviro-economic assessment in nanogrids
No full textThis paper presents an integrated framework designed for capacity planning of grid -connected nanogrid, a small solar and energy storage system that can provide kilowatt -level services to individual buildings. This framework comprehensively evaluates nanogrid cost-effectiveness, sustainability, and reliability, employing a multi -faceted techno-enviro-economic assessment approach. Traditional nanogrid capacity planning often prioritizes peak load requirements, which may lack optimality owing to occasional peak load occurrences. Conversely, optimizing solely for base load requirements might also fall short of effectiveness, compromising reliability and sustainability objectives. The proposed framework employs a threestep, integrated process for nanogrid (NG) capacity planning. Firstly, the Planner module identifies optimal asset sizing considering a two-day lookahead logic. Then, the Operator module serves as a digital twin for the system, conducting hourly calculations over a short-term horizon. Lastly, the Evaluator module evaluates technical, environmental, and economic metrics for each solution, assessing the effectiveness of asset -sizing decisions. A simulated case study has demonstrated the effectiveness of the proposed framework. The technical assessment revealed that a PV size of 24 kW and a storage capacity of 91 kWh led to the most reliable solution, with a probability of local sufficiency of 95 percent. Furthermore, the environmental assessment showcased a renewable fraction of 94% with a PV size of 26 kW and a storage of 85 kWh. Economically, the analysis identified that a PV size of 12 kW and a storage size of 24 kWh led to the minimum total cost. In contrast, a PV size of 26 kW and a storage size of 85 kWh yielded a total operating savings of $4,801.Publisher versio
Postoperative Infusionstherapie kristalloid versus kolloidal auf der kinderkardiochirurgischen Intensivstation
Get PDFDie perioperative Flüssigkeitstherapie mit kristalloiden und kolloidalen Lösungen besitzt insb. bei der Behandlung pädiatrischer Patienten eine hohe klinische Relevanz, wobei die verfügbare Evidenzlage bislang unzureichend ist.
Die vorliegende Arbeit untersucht retrospektiv die klinische Praxis der Infusionstherapie auf der kinderkardiochirurgischen Intensivstation des Universitätsklinikums Bonn. Insgesamt wurden die Daten von 312 Patienten statistisch ausgewertet. Analysiert wurden u.a. die Art der verwendeten Infusionslösungen sowie deren Einfluss auf die Hospitalisierungs- und Beatmungszeit, Drainageverluste (Outcome-Parameter) und weitere klinische Parameter.
Die Haupthypothese, dass die kolloidale Flüssigkeitssubstitution den kristalloiden Lösungen hinsichtlich der Outcome-Parameter überlegen wäre, konnte durch unsere Untersuchungen nicht bestätigt werden. Vielmehr zeigten sich im kolloidalen Kollektiv tendenziell längere Aufenthalts- und Beatmungszeiten sowie höhere Drainageverluste. Hinweise auf einen positiven Therapieeffekt der Kolloide, wie die Reduktion der kumulativen Kristalloidmenge oder des Katecholamin-Bedarfs, ließen sich nicht ableiten. Durch die kolloidale Substitution einer postoperativen Hypalbuminämie war außerdem kein gesicherter Nutzen für den postoperativen Serum Albumin-Anstieg und das Patienten-Outcome zu verzeichnen.
Die Ergebnisse sprechen dafür die kolloidale Flüssigkeitstherapie bei Kindern kritisch zu hinterfragen. Zur Etablierung evidenzbasierter Behandlungsleitlinien sind prospektiv randomisierte Studien erforderlich
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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