1,720,973 research outputs found
Model-based prognostics for energy-constrained mobile systems operating in stochastic environments
Full text linkDue to development of novel and more efficient energy storage systems we bear witness to the dawn of a new era of mobile systems. They have become sophisticated in terms of hardware components and software applications which have made it possible to develop integrated solutions for a large number of imaginable applications ranging from electric vehicles all the way to fully autonomous systems operating in a wide variety of ecosystems, e.g., service, surveillance or bio-inspired robots. Generally it is expected that a mobile system exhibits a sufficient degree of autonomy in the sense of energy availability such that it at least accomplishes the mission objectives for which it is intended. Nevertheless, such autonomy, is influenced to a large extent by the remaining energy that can be retrieved from its energy storage system and by the environment conditions in which the system operates. Assessing the reliability of a mission requires using systems internal and external situational awareness to determine if the available energy at least meets the energy needs demanded by the future operation of the mobile system in order to determine its remaining useful life (RUL). Having this information as soon as possible may allow the decision maker to apply a contingency plan to intervene and reconfigure the mission execution strategy in order to improve the probability of success, in those situations in which the system becomes incapable of achieving the original mission objectives.
Numerous studies have been published for assessing mission reliability and estimating the RUL of mobile systems. However, they deal with structured environment conditions and thus with relatively deterministic loads. Moreover, these approaches neglect the inherent uncertainty which stems from multiple sources such as the lack of knowledge about the true energy available in the mobile system, the noise introduced by sensors or the randomness of the operation environment, just to mention a few. The approach presented in this work is built around the belief that the RUL estimation is formulated as an uncertainty propagation problem. Accordingly, to estimate the RUL multiple sources of uncertainty involved in its estimation are first characterized and then propagated with the aim of computing their combined effect, expressed in terms of a probability density function. The approach developed here achieves this estimation in a Monte-Carlo fashion in which several RUL realizations are simulated in order to accurately estimate its entire probability distribution. The aim of this work is therefore devoted to develop a solution capable of estimating the RUL with application to energy-constrained mobile systems operating in stochastic environments
Experimentelle und numerische Identifikation eines homogenisierten Materialmodells für Blechpakete elektrischer Maschinen
Full text linkElectric motors are part of various industrial machines. The main issue of this thesis is the consideration of large industrial electric motors. To reduce material costs and weight, the motor frames become smaller and light weighted. An electric motor consists of a stator and a rotor which both contain lamination stacks. As the motor frame is reduced the mechanical behavior of the lamination stack becomes more relevant for the behavior of the motors, through the behavior of the stack is relatively unknown. The lamination stacks are an assembly of metal sheets, which have a coreplate varnish to provide mutual electrical insulation. The main task of the stacks is to increase the motors efficiency. They consist of stacked and packaged sheets containing windings of copper wire or cages of copper or aluminium. The mechanical behavior of the stack depends on both the material of the components and the contact interactions within the stack.
The aim of this thesis is to identify the contact behavior between the sheets as their stiffness behavior has a major influence on the behavior of the whole lamination stack. The geometry and the material of the contact partners as well as the surface roughness are relevant for the contact behavior. To identify this behavior experiments for the normal and the tangential direction are performed. Creeping processes in normal direction occur caused by the varnish of the sheets. The experimentally determined contact behavior is simulated with different models. For the normal direction the elastic Bush-Gibson-Thomas model and the plastic Bowden-Tabor model are combined. The creeping process is simulated with Rust’s model for the creep rate. A modified Olofsson model simulates the behavior in tangential direction. The modification refers to the model for normal contact which the Olofsson model is based on. A FE-calculation considering a resolution of the contact zones is possible but numerically very expensive. Therefore a two scale approach is chosen which is based on the use of a representative volume element. With the aid of this representative volume element numerical experiments are performed and via homogenization techniques based on these experiments an effective phenomenological constitutive law is derived. Due to the nonlinearity of the contact stiffness the constitutive material model is also nonlinear.
One of the material model’s application is for example the simulation of the packaging process of the lamination stack without necessarily simulating the single sheets. A further benefit of the model is that dynamical calculation like modal analysis are possible. Therefor the model has to be linearized at the working point. Thereby, the working point is a result of the packaging process and the relaxation. In this thesis calculations for both the packaging process and the modal analysis are presented.Elektromotoren sind Bestandteil vieler Maschinen, wobei in dieser Arbeit der Fokus auf großen Industriemaschinen liegt. Um weniger Material zu verbrauchen, wird das Gehäuse dieser Motoren zunehmend reduziert. Ein Bauteil des Stators und des Rotors eines Elektromotors ist das Blechpaket. Die Hauptaufgabe des Blechpakets besteht darin, den Wirkungsgrad des Motors zu erhöhen. Blechpakete bestehen aus gestapelten und paketierten Blechen, in welche eine Kupferdrahtwicklung oder ein Kupfer- oder Aluminiumkäfig eingebracht ist. Die Bleche sind zur elektrischen Isolation mit einer Lackschicht versehen. Es wird deutlich, dass sich das Paketverhalten aus dem Materialverhalten der einzelnen Bauteile sowie den Kontakten zwischen den Bauteilen ergibt. Auf Grund der Reduktion des Gehäuses steigt der Einfluss des mechanischen Paketverhaltens auf das Verhalten des gesamten Motors und sollte daher bekannt sein.
In dieser Arbeit werden die Kontakte zwischen den Blechen untersucht, da deren Steifigkeitsverhalten starken Einfluss auf das Verhalten des gesamten Pakets hat. Das Kontaktverhalten wird sowohl von den Kontaktpartnern als auch von der Oberflächenrauheit bestimmt. In Experimenten wird das Kontaktverhalten in normaler und in tangentialer Richtung bestimmt. Dabei wird auch ein Kriechen in Normalrichtung ermittelt, dass vor allem von der Lackschicht auf den Blechen herrührt. Das identifizierte Kontaktverhalten kann mit einer Kombination verschiedener Modelle simuliert werden. In dieser Arbeit werden für den Normalkontakt das elastische Bush-Gibson-Thomas-Modell und das plastische Bowden-Tabor-Modell mit einem Modell von Rust für die Kriechgeschwindigkeit kombiniert. Für den Tangentialkontakt wird das Modell von Olofsson mit dem für den Normalkontakt zugrunde liegenden Gesetz leicht modifiziert. Mit diesen Kontaktmodellen ist es möglich, das mechanische Verhalten eines Blechpakets mittels einer Modellierung der einzelnen Bleche und der Kontaktebenen mit der FE-Methode zu berechnen. Dieses Vorgehen ist auf Grund der vielen Kontaktzonen numerisch sehr aufwendig, so dass zur Vereinfachung ein Ersatzmaterialmodell für den gesamten Stapel identifiziert wird. Dazu wird ein für den Blechstapel repräsentatives Volumenelement ausgewählt und es werden unter Nutzung der Methode der Homogenisierung numerische Experimente durchgeführt. Hierbei werden unterschiedliche Deformationszustände an das repräsentative Volumenelement angelegt und die entsprechenden Spannungszustände berechnet. Auf Basis der so ermittelten Spannung-Dehnung-Zusammenhänge wird ein Materialmodell identifiziert, welches das Verhalten des gesamten Pakets wiedergibt. Wegen der Nichtlinearität der Kontaktsteifigkeiten ist auch dieses Ersatzmaterialmodell nicht linear.
Das Materialmodell kann beispielsweise dazu verwendet werden den Paketiervorgang des Blechstapels abzubilden, ohne die Bleche explizit modellieren zu müssen. Für dynamische Berechnungen, wie die Modalanalyse, ist ein lineares System erforderlich. Dazu kann im Arbeitspunkt eine Linearisierung des Ersatzmodells erfolgen. Der Arbeitspunkt ergibt sich aus dem Paketierdruck, der nach der Relaxation verbleibt. Sowohl für den Paketiervorgang als auch für die Modalanalyse werden Beispielrechnungen gezeigt
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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