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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Applications of Sure Independence Screening Analysis for Supersaturated Designs

Nicely, Lindsey 25 April 2012 (has links)
Experimental design has applications in many fields, from medicine to manufacturing. Incorporating statistics into both the planning and analysis stages of the experiment will ensure that appropriate data are collected to allow for meaningful analysis and interpretation of the results. If the number of factors of interest is very large, or if the experimental runs are very expensive, then a supersaturated design (SSD) can be used for factor screening. These designs have n runs and k > n - 1 factors, so there are not enough degrees of freedom to allow estimation of all of the main effects. This paper will first review some of the current techniques for the construction and analysis of SSDs, as well as the analysis challenges inherent to SSDs. Analysis techniques of Sure Independence Screening (SIS) and Iterative Sure Independence Screening (ISIS) are discussed, and their applications for SSDs are explored using simulation, in combination with the Smoothly Clipped Absolute Deviation (SCAD) approach for down-selecting and estimating the effects.
2

Optimisation de la qualité vibro-acoustique des structures d'automobiles pour les basses fréquences

Bourmich, Sophie 21 September 2012 (has links)
Les modèles d'éléments finis des automobiles donnent des grandes tailles de problèmes matriciels, ce qui demeure coûteux en ressources numériques pour une procédure d'optimisation. La multiplicité des phénomènes couplés du problème d'interaction de l'air de l'habitacle et de la superstructure rend plus sensible, à des variations mineures des paramètres, une optimisation directe du véhicule. Pour réduire les temps de calculs et l'espace mémoire liés à la simulation numérique en éléments finis, une méthode de double synthèse modale est appliquée sur la structure et le fluide. Ceci permet de diminuer le nombre de degrés de liberté de frontière. Egalement, un algorithme a été développé pour minimiser le nombre d'évaluations de fonction au cours des itérations d'optimisation. L'approche modale permet également de décomposer le problème d'optimisation de la réponse vibro-acoustique par des sous-problèmes couplés d'optimisation de critères modaux. Ces critères modaux explicitent les couplages fréquentiels par des termes d'amplification et les couplages spatiaux par des paramètres effectifs modaux. Ils favorisent ainsi le développement d'une stratégie d'optimisation robuste par le contrôle modal des effets prépondérants sur la qualité vibro-acoustique des véhicules. / Finite element models and the complexity of vehicle passenger compartments make it harder the optimization, mainly because of expensive computing resources and multiple coupled phenomena of fluid-structure problems. Strategies to improve time and memory performance consist in the use of reduction methods, and combined with efficient optimization techniques, vibro-acoustic solutions of better quality can be performed. The complexity of the system is taken into account thanks to a hierarchical optimization process. Both reduction method and gradient-based optimization algorithm are investigated. Based on modal synthesis, special criteria help to determine critical vibration propagation paths. A modified SQP (Sequential Quadratic Programming) algorithm is also developed in order to provide a faster convergence speed. Such process is to be applied on an academic example and hollow parts and panels of a whole passenger compartments. It allows to find relevant and non obvious solutions by minimizing noise and vibration transfer functions in a relatively wide range of frequencies.

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