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Analytical Modelling (analytical + modelling)

Distribution by Scientific Domains
Engineering75%

Selected Abstracts

Analytical Modelling of the Radiative Properties of Metallic Foams: Contribution of X-Ray Tomography

ADVANCED ENGINEERING MATERIALS, Issue 4 2008
M. Loretz
Two metallic foams exhibiting a similar porosity but different cell sizes have been characterized using X-ray tomography. The images have been processed and analysed to retrieve the morphological properties required for the calculation of the radiative properties such as the extinction coefficient. The multiple possibilities of using the X-ray tomography method rather than conventional optical methods like SEM have been quantified. The extinction coefficient has then been determined from two approaches. First, the resulting morphological properties have been used as the input data of the conventional independent scattering theory. A special emphasis is put on the determination of morphological properties and their influence on the results. In the second approach, an original method is also proposed in order to determine the extinction coefficient of highly porous open cell metal foams, from the tomographic images and without any calculation or hypothesis. Results show a good agreement with the extinction coefficient obtained from experimental measurements. Our novel method enables to reduce uncertainties considerably. [source]

Analytical modelling of users' behaviour and performance metrics in key distribution schemes

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 1 2010
Massimo Tornatore
Access control for group communications must ensure that only legitimate users can access the authorised data streams. This could be done by distributing an encrypting key to each member of the group to be secured. To achieve a high level of security, the group key should be changed every time a user joins or leaves the group, so that a former group member has no access to current communications and a new member has no access to previous communications. Since group memberships could be very dynamic, the group key should be changed frequently. So far, different schemes for efficient key distribution have been proposed to limit the key-distribution overhead. In previous works, the performance comparison among these different schemes have been based on simulative experiments, where users join and leave secure groups according to a basic statistical model of users' behaviour. In this paper, we propose a new statistical model to account for the behaviour of users and compare it to the modelling approach so far adopted in the literature. Our new model is able to to lead the system to a steady state (allowing a superior statistical confidence of the results), as opposed to current models in which the system is permanently in a transient and diverging state. We also provide analytical formulations of the main performance metrics usually adopted to evaluate key distribution systems, such as rekey overheads and storage overheads. Then, we validate our simulative outcomes with results obtained by analytical formulations. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Analytical modelling of the current distribution in resistive loaded thin-wire antennas excited by a transient electric field

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2006
2Article first published online: 28 FEB 200, F. Sagnard
Abstract The analytical modelling of the excitation of a Wu and King loaded dipole by an oblique transient electric-plane wavefront has been revisited and extended in order to analyze in detail the physical phenomena involved in the time and space domains. The role of several components of the current induced along a dipole as a function of different parameters is discussed. The modelling developed herein allows us to consider a V-dipole. This study will allow us to consider, in a future work, the case of an assembly of dipoles in the space domain for representing more complex antenna geometries. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 730,736, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21459 [source]

Überwachung und Analyse der Lebensdauer von Tunnelbauwerken

BETON- UND STAHLBETONBAU, Issue 1 2007
Konrad Bergmeister Prof. Dipl.-Ing.
Im Tunnelbau bildet die Überwachung der signifikanten Einwirkungs- und Strukturparameter während der Bauphase und des Betriebs die Basis für die Bewertung des Zustands und der Sicherheit des Bauwerks. Die erfassten Daten stellen des Weiteren die Grundlage zur nummerischen und mechanischen Modellbildung dar, um eine effiziente Entscheidungsfindung und Maßnahmenplanung zu gewährleisten. Die Überwachung beinhaltet die Erfassung und Bewertung der geologischen Gegebenheiten, der induzierten Auswirkungen während des Vortriebs und die kontinuierliche Kontrolle für den weiteren Betrieb und Unterhalt des Bauwerks. Methoden der Bauwerksüberwachung und Diagnose stellen aufgrund der quantitativ erfassten Systemparameter ein wesentliches Element für die Zuverlässigkeitsanalyse dar. Die geeignete Wahl von Kontroll- und Messinstrumenten ist jedoch nur einen Teilaspekt der Bauwerksüberwachung. Die Auswertung und Interpretation der erhobenen Daten, die Gegenüberstellung mit den normativen Anforderungen und Grenzwerten, die Anpassung der analytischen Modellannahmen aufgrund des Vergleichs von gemessenen und berechneten Daten zeigen die Komplexität dieses Aufgabengebietes. Monitoring and Analysis of Durability of Tunnels Monitoring continuously the decisive parameters, during both the construction and the operation phase, provides the quantitative basis for safety and condition assessment, analytical modelling and decision making. This includes evaluating the conditions and induced effects during excavation and construction, and continues during operation in terms of maintenance decision making and reliability assessment. The utilisation of monitoring devices and measurement elements is however only the start of monitoring field performance. Interpretation of the acquired data is equally important, namely the validation of compliance with normative specifications and the comparison of measured and calculated data in order to evaluate analytical model assumptions. [source]