1,721,017 research outputs found
Numerical simulation of radiative heat transfer in indoor environments on programmable graphics hardware
No full textThe efficient use of energy for heating and cooling of indoor environments requires an accurate prediction and analysis of radiative heat transfer. Therefore it is necessary to use modern computer methods as otherwise the computational costs may become higher than for convective heat transfer, which is known to be a huge computational problem. A key problem in calculations of radiative heat transfer is the problem of mutual visibility arising in the determination of view factors. This is the same challenge that global illumination has to cope with which is one of the fundamental topics in computational graphics. The visibility problem is efficiently solved by modern graphics hardware. Therefore an OpenGL-based algorithm is developed to quickly and accurately calculate view factors for arbitrary, complex geometries. Theoretical and implementation details of the applied methods are given. We demonstrate the advantages of the developed computational method by a virtual test room for a tubular radiator, a heating of a warehouse by ceramic infrared heaters and the heat transfer in a car cabin. (C) 2015 Elsevier Masson SAS. All rights reserved
Fully parallel, OpenGL-based computation of obstructed area-to-area view factors.
No full textWe present a fully parallelized, high-performance, OpenGL-based approach to compute obstructed area-to-area (A2A) view factors for radiative heat transfer. The A2A view factors are computed from the defining surface integral by Gaussian quadrature. The values of the integrand, i.e. the point-to-area view factors, are computed using an OpenGL-based hemicube (HC) method to efficiently solve the obstruction problem by exploiting the hardware-accelerated visibility testing on modern graphics cards. The final steps to maximize hardware usage are rendering the HC and performing the numerical quadrature in parallel such that data transfer times are completely shadowed by computations. To demonstrate the power of our approach we compute the A2A view factor matrices for a warehouse equipped with ceramic infrared heaters and a test cabin conforming to EN 442 containing a section of a panel radiator. To judge the quality of the results we measure the deviation from unity of the area-weighted column sums of the view factor matrix and the error in radiant flux balance. Compared to a previous, ray-tracing-based implementation, we gain three orders of magnitude in speed in the view factor computation. Conservation of radiant flux is also substantially improved
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
Phenomenological Modeling of a Latent Heat Storage and Model Based Design of a Demand Oriented Control of a Heating System
No full textIm Winter wird die Reichweite elektrischer Busse, mit einem elektrisch betriebenen Heizungssystem, nahezu halbiert. Um eine emissionsfreie Beheizung, ohne Beeinträchtigung der Reichweite, zu realisieren, wird im Projekt Heat2Go eine schnellladefähige Latentwärmespeicherheizung entwickelt. Nach dem Prinzip der Gelegenheitsladung erfolgt die elektrische Beladung der Speicherheizung an einer Ladestation, die Wärmeabgabe an den Businnenraum wird über einen hydraulischen Heizungskreislauf realisiert. Das System wird im EDDA-Bus des Fraunhofer IVI demonstriert. Diese Arbeit beschäftigt sich mit dem Entwurf eines Simulationsmodells der Wärmespeicherheizung in MATLAB-Simulink. Das Modell setzt sich aus den Teilmodellen Innenraum, Heizungskreislauf und PCM-Wärmespeicher zusammen. Aufbauend wird für das Modell eine Steuerung entworfen, mit dem Ziel, energieeffizient die Sollinnenraumtemperatur zu gewährleisten. Dafür werden die Sollwerte der Innenraum- und Vorlauftemperatur sowie die Anzahl der notwendigen Speichermodule in Abhängigkeit der Umgebungstemperatur geführt. Die Pumpendrehzahl ist linear an die Anzahl der Speichermodule gekoppelt und wird so gering wie möglich gehalten. Das Modell des PCM-Wärmespeichers wird unter Berücksichtigung der Stoffeigenschaften des PCM und dem konstruktiven Aufbau erstellt und anschließend einer Plausibilitätsprüfung unterzogen. Fortführend erfolgt eine Analyse der Ladezustandsbestimmung. Das Innenraumodell, die Wärmesenke des Heizungskreislaufs, berücksichtigt Wärmeverluste, durch die Zufuhr von Frischluft (Lüftung, Türöffnungen), die konvektiven Wärmeverluste über die Bushülle in Abhängigkeit der Fahrtgeschwindigkeit sowie innere Wärmegewinne durch Passagiere. Anhand von Messdaten wird das Innenraummodell (Wärmedurchgangskoeffizient, Kapazitäten) validiert. Zudem wird der Einfluss verschiedener Faktoren auf den Wärmebedarf des Innenraums untersucht. Die Steuerung wird exemplarisch an einem realen Fahrtzyklus, bei unterschiedlichen Umgebungstemperaturen getestet und positiv beurteilt. Für niedrige Umgebungstemperaturen und großer Entladeleistung der Speichermodule wird die Sollvorlauftemperatur nicht mehr erreicht. Durch die Einführung eines Betriebsmodus mit maximaler Entladeleistung, kann die geforderte Sollinnenraumtemperatur dennoch gewährleistet werden. Um den Nutzungsgrad der Wärmespeicherheizung zu optimieren, wird geprüft, ob durch das Nachladen des Wärmespeichers mit Rekuperationsenergie und aus der Batterie, zwei Speichermodule eingespart werden können. Dabei wird keine wesentliche Reduzierung der Batterielebensdauer festgestellt, somit ist die Einsparung der Speichermodule wirtschaftlich
Empirical analysis of an evaporative cooling device, deduction of optimization, recommendations and discussion about future application
No full textDispelling 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
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