1,720,962 research outputs found
Vääntövärähtelyn ominaistaajuuden havainnointi taajuusmuuttajalla
No full textVibrations generated in the drive train can be a serious problem for the reliability and safety of the system. Usually the problems are related to the lowest torsional mode. Typically, the measurements needed for the torsional analysis require external tools and skilled personnel, which tend to be expensive. The rising reliability and safety requirements in the industry lead to increased usage of variable frequency drives (VFD) for improved control of the machine. The usage of the VFD to identify the mechanical characteristics would provide reliability to the non-existing and also to the existing vibration analysis.
In this master's thesis the identifiability of the lowest torsional frequency resonance with VFD is studied by simulations and experimental measurements. The studied signals are stator current, rotational speed and electromagnetic torque. Pseudo random binary sequence (PRBS) is used as the excitation signal for the identification. Welch's modified peridograms are used for spectral analysis of the signals. The reference resonance frequency was identified with the encoder feedback. The closed-loop experiments, where the motor was controlled with speed feedback from either encoder or estimator, show positive results for the rotational speed signal. When using the estimator the errors of the identified resonance frequencies of the tested cases were < 5 %.Voimansiirtolinjalla tapahtuva värähtely voi aiheuttaa vakavia ongelmia järjestelmän luotettavuudelle ja turvallisuudelle. Useimmiten ongelmat liittyvät vääntövärähtelyn alimpaan muotoon. Vääntöanalyysiin tarvittavat mittaukset vaativat yleensä ulkoisia mittalaitteita sekä ammattitaitoista henkilökuntaa, mistä johtuen tämä on kallista. Teollisuuden kasvavat luotettavuus- ja turvallisuusvaatimukset johtavat sähkökäyttöjen yleistymiseen, mikä mahdollistaa tarkemman säädön koneille. Sähkökäyttöjen hyödyntäminen mekaniikan identifiointiin toisi luotettavuutta värähtelyanalyysiin. Näin ollen kriittisiä nopeuksia pystyttäisiin varmemmin välttämään.
Tässä diplomityössä tutkitaan vääntövärähtelyn alimman resonanssin havaittavuutta taajuusmuuttajalla simulaatioiden ja käytännön mittauksien avulla. Tutkittavat signaalit ovat moottorin staattorivirta, pyörimisnopeus sekä vääntömomentti. Herätesignaalina identifioinnissa käytetään PRBS (pseudo random binary sequence) signaalia. Tutkittavia signaaleja analysoidaan taajuustasossa käyttäen Welchin menetelmää. Vertailuresonanssi identifioitiin takaisinkytketystä systeemistä käyttämällä mitattua nopeutta. Suljetun systeemin mittauksien perusteella, missä nopeuden takaisinkytkentä oli joko anturilta tai estimaattorilta, resonanssi oli selvästi havaittavissa pyörimisnopeudesta. Testatuissa tapauksissa, pyörimisnopeudesta identifioitujen resonanssien virhe oli alle 5 % anturittomassa tapauksessa
Framework for automated optimization of FEM design of permanent magnet motor bearing unit
Full text linkOptimizing a motor usually requires many stages from building the model and setting the conditions to very time consuming finite element analysis of the electromagnetic behaviors. Usually FEA needs to be ran several times to the most optimized results.
The first goal of this work is to realize communication between MATLAB (MathWorks) and JMAG-Designer (JSOL Corporation) which is a major requirement for the second goal of this work. The second goal of this work is to present a framework to automatically optimize a desired motor’s parameters. Calculations and recursion are performed using MATLAB. The optimization is done using differential evolution. Electromagnetic analysis is performed using 3rd party program, which is JMAG Designer in this case study.
The framework is tested on a magnetic levitation realized a permanent magnet linear synchronous machine. The objective is to minimize thrust and normal force ripples. The parameters to optimize are motor’s end tooth’s dimensions. After running the script, the simulations show that the thrust and normal force ripples are reduced ~52-80 %
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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