1,720,956 research outputs found
Systematische Betrachtung von Technologien für den Umschlag von Paketen im Pulk und deren Simulation mit der Diskrete-Elemente-Methode
No full textIndustrielle Anbieter von Technologien für den Umschlag von Paketen im Pulk nutzen häufig die
Diskrete-Elemente-Methode (kurz: „DEM“), um die Funktionsweise von Entladelösungen und den
damit verbundenen Durchsatz zu analysieren. Zusätzlich zur Analyse des Materialflusses der Pakete,
kann eine Anlage virtuell in Betrieb genommen werden, indem die Steuerung der Fördertechnik
emuliert wird. Für die Emulation ist die Echtzeitfähigkeit der Modelle relevant, die mit zahlreichen,
heute verfügbaren Physik-Engines und einem vergleichsweise hohen Zeitschritt erreicht werden
kann. Diese sogenannte »Non-smooth DEM« steht im Verdacht, den Materialfluss von Paketen
im Pulk nicht so genau abzubilden wie die sogenannte »Smooth DEM«, bei der der Zeitschritt im
Vergleich kleiner ist. Für die Untersuchung von dieser These wurde ein Pulkaufgabeversuchsstand
für den Umschlag von 100 Stückgütern (hauptsächlich DHL Packsets XS und S) entworfen,
gebaut und in Betrieb genommen, um die Versuchsergebnisse anhand von den eingeführten
Validierungskriterien Massenstrom, Pulkausprägung und Stoßbelastung mit der DEM-Simulation
zu vergleichen. Für die »Smooth DEM«-Simulation von diesem Pulkaufgabeversuch wurde nicht
die sogenannte »Multi-Sphere«-Approximation verwendet, weil die Modellierung der Oberfläche
eines Paketes nur mit vielen Primär-Partikeln möglich ist, was zu hohen CPU-Rechenzeiten führt,
die für die Anwendung in der industriellen Praxis ungeeignet sind. Außerdem hängen die für die
Paketaufgabe im Pulk relevantesten Stückgut-Eigenschaften Reibung (Kalibrierung mit dem
Schiefe-Ebene-Versuch) und – je nach verwendeter DEM-Software – auch das Rücksprungverhalten
(Kalibrierung mit dem Fallversuch) von der Anzahl und Größe der Partikel im Kontakt ab,
was die Kalibrierung von einheitlichen Haftreibungs- und Restitutionskoeffizienten erschwert.
Stattdessen wurde die sogenannte »Superquadric«-Formapproximation verwendet, mit der wesentlich
kürzere CPU-Rechenzeiten möglich sind, weil jedes Paket nur mit jeweils einem Partikel
modelliert wird, dessen Form mit der sogenannten »Blockiness« eingestellt wird. Dieser Parameter
wurde bei der Kalibrierung der Parameter des DEM-Kontaktmodells schwerpunktmäßig
untersucht, um den besten Kompromiss aus Formapproximation und CPU-Rechenzeit zu finden.
Durch die Gegenüberstellung der »Smooth DEM«- und »Non-smooth DEM«-Simulation des
Pulkaufgabeversuches mit den Versuchsergebnissen wurde die These verifiziert, dass die »Smooth
DEM« den Massenstrom von Paketen im Pulk genauer vorhersagen kann als die »Non-smooth
DEM«. Auch der durch die Pulkaufgabe auf eine mit Datenlogger ausgerüstete Sensorbox aus
Plexiglas® wirkende Stoß konnte durch die Kalibrierung der Elastizitätsmoduln von Partikeln
und Kontaktflächen innerhalb der Standardabweichung des realen Stoßes mit der »Smooth DEM«
simuliert werden, weil dieser ein sogenannter »soft particle approach« zugrunde liegt. Diese
Erkenntnisse wurden mit dem »Blockiness«-Wert der »Superquadrics« von n = 5 erreicht, was
die Kalibrierung der Parameter des DEM-Kontaktmodells ergeben hat. Mit dieser vergleichsweise
niedrigen »Blockiness« konnte der 30 Sekunden lang dauernde Pulkaufgabeversuch in ungefähr
fünf Stunden simuliert werden, während das vergleichsweise ungenauere Simulationsergebnis
der »Non-smooth DEM« in Echtzeit entsteht. Diese Arbeit ist für Anwender von Bedeutung, die
den Umschlag von Paketen im Pulk nicht nur schnell, sondern auch genau simulieren möchten.Industrial suppliers of technologies for parcel handling in bulk mode often use the discrete element
method (in short: ”DEM”) to analyse the operation and throughput of unloading equipment.
In addition to analysing the material flow of the parcels, a system can be virtually commissioned
by emulating the controls of the conveyor equipment. For emulation, the real-time capability of
the models is relevant, which can be achieved with several physics engines available today and
a comparably high time step. In comparison to the so-called ”Smooth DEM”, which has smaller
time steps, the so-called ”Non-smooth DEM” is considered to represent the material flow of
parcels in bulk mode less accurately. For the investigation of this hypothesis, a bulk handling test
plant for the handling of 100 loads (mainly DHL Packsets ”XS” and ”S”) was designed, built and
operated to compare the experimantal results with DEM simulation based on the validation
criteria of mass flow, bulk profile and impact load. For the Smooth DEM simulation of this bulk
handling test, the so-called ”multi-sphere approximation” was not used, because modeling the
parcel surface is only possible with many particles, which lead to high CPU computing times
unsuitable for industrial application. In addition, the most relevant parcel properties for bulk
feeding, being friction (calibration with the inclined plane test) and – depending on the used
DEM software – also rebound (calibration with the free fall test) rely on the number and size of
particles in contact, impeding calibration of uniform static friction and restitution coefficients.
Instead, the so-called ”superquadric approximation” was used, allowing significantly shorter CPU
computing times because each parcel is modeled with only one particle at a time, whose shape is
set with the so-called ”blockiness”. This parameter was analyzed in detail during the calibration
of the parameters of the DEM contact model in order to find the best compromise between shape
approximation and CPU computing time.
The hypothesis that the Smooth DEM can predict the mass flow of parcels in bulk mode more
accurately than the Non-smooth DEM was verified by comparing Smooth DEM and Non-smooth
DEM simulation of the bulk handling test with the experimental results. The shock resulting
on a sensor box made of Plexiglas® and equipped with a data logger could be simulated by
calibrating the elastic moduli of particles and contact surfaces within the standard deviation
of the experimental impact with the Smooth DEM being based on a soft particle approach.
These observations were made with the superquadrics’ blockiness value of n = 5, which was
the result of calibrating the parameters of the DEM contact model. With this relatively low
blockiness, the 30-second bulk handling test could be simulated in about five hours, while the
less accurate simulation result of the Non-smooth DEM is produced in real time. This work is
valuable for users who want to simulate the handling of parcels in bulk mode not only quickly
but also accurately
Application of Discrete Element Method for Damage Rate Reduction of Parcel Bulk Handling Units
Full text linkDie bis zum Jahr 2021 prognostizierte Entwicklung der KEP-Sendungsvolumina auf über 4 Mrd. Sendungen [1] – getrieben durch die im Zeitalter des E-Commerce wachsende Konsumbereitschaft – stellt die Paketdienstleister vor die Herausforderung, den Umschlag von großen Paketmengen in kurzer Zeit zu realisieren. Die Optimierung der Durchlaufzeiten von Wechselbrücken ist daher eine immer wichtiger werdende Aufgabe des Dock & Yard Managements. Um eine beschädigungsarme Paketentladung zu realisieren, werden erste Ergebnisse von Validierungsuntersuchungen für Simulationen auf Basis der Diskrete Elemente Methode (DEM) für den Umschlag von Paketen im Pulk vorgestellt. Das Ziel ist die dem Feldeinsatz vorgelagerte Bewertung von Entladetechnologien hinsichtlich der Einhaltung von Grenzwerten für die Paketbelastung.For the development of CEP shipment volumes of more than 4 billion shipments until 2021 are forecasted [1]. This is based on the increasing willingness to consume in the era of e-commerce and forces CEP services to realize the handling of large numbers of parcels in short time periods. Therefore, optimizing the unloading of swap bodies becomes an increasingly urgent task of the dock & yard management. To realize a gentle unloading process, a method for the validation of the Discrete Element Method (DEM) for the parcel unloading in bulk mode is presented. The goal of this research is the evaluation of unloading technologies – with respect to parcel stress limits – prior to the onsite operation
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
- …
