This work demonstrates the effectiveness of coextrusion as a method to manufacture negative stiffness inclusions for use in vibrational damping applications. The theory and mechanics of negative stiffness and coextrusion are introduced and the process of creating and extruding a feed rod with negative stiffness architecture explained. Coextrusion is shown to be a viable method to create negative stiffness inclusions / text

This thesis concerns three-dimensional finite element modelling of Biot's equations for elasto-acoustic modelling of wave propagation in layered media including porous elastic materials. The concept of hierarchical (p-version) finite elements are combined with various weak forms of Biot's equations. Computationally efficient methods providing accurate solutions of sound propagation in layered porous media are discussed. The research falls within the areas linear acoustics and numerical acoustics. Important applications of the developed methods may be found within vehicle interior acoustics, e.g. engineering design of damping treatment based on multiple layers of porous materials. / QC 20100618

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A cold extrusion process has been developed to tailor a porous structure from polymeric waste. The use of an extruder to manufacture acoustic materials from recycled waste is a novel idea and the author is not aware of any similar attempts. The extruder conveys and mixes the particulates with a reacting binder. The end result is the continuous production of bound particulates through which a controlled amount of carbon dioxide gas that is evolved during the reaction is used to give the desired acoustic properties. The cold extrusion process is a low energy consuming process that reprocesses the post manufacturing waste into new vibro-acoustic products that can be used to meet the growing public expectations for a quieter environment. The acoustical properties of the developed products are modelled using Pade approximation and Johnson-Champoux-Allard models. Applications for the developed products are widespread and include acoustic underlay, insulation and panels in buildings, noise barriers for motorways and railway tracks, acoustic insulation in commercial appliances and transport vehicles.

Cette thèse porte sur la simulation et la réduction du bruit acoustique d’origine magnétique des alternateurs à griffes ainsi que sur la compréhension des phénomènes mis en jeu dans la génération du bruit. La structure, les différents composants et les particularités du bruit acoustique de l’alternateur à griffes sont détaillés dans la première partie. La problématique ainsi que l’approche générale de cette thèse sont ensuite exposées. Cette approche se base sur la simulation du bruit acoustique d’origine magnétique. Un état de l’art des études sur le bruit acoustique d’origine magnétique des machines électriques est présenté dans la seconde partie. Les modèles électromagnétiques, mécaniques et acoustiques utilisés pour l’étude de ces machines ainsi que les principales solutions de réduction du bruit sont exposés. Les nouvelles approches de modélisation électromagnétique et vibro-acoustique de la machine à griffes sont développées dans la troisième partie. Deux modèles électromagnétiques sont étudiés : un modèle numérique qui repose sur l’utilisation de la méthode des éléments finis et un modèle hybride qui allie le modèle numérique à un modèle analytique. Ce dernier s’appuie sur la décomposition de l’induction magnétique dans l’entrefer en un produit d’une fonction de perméance avec une fonction de force magnétomotrice. Chaque fonction prend en compte les variations axiales dues à la géométrie des griffes. Ce modèle nécessite toutefois l’utilisation d’un modèle numérique afin de prendre en compte la saturation et les forces tangentielles. Un modèle mécanique purement numérique est ensuite construit. Il permet de prendre en compte la géométrie exacte des pièces ainsi que les contacts entre les pièces. Ce modèle mécanique est développé grâce à la corrélation avec des mesures et porte principalement sur trois parties de l’alternateur : le paquet de tôles du stator, le bobinage du stator et l’assemblage stator-paliers. Enfin, les simulations acoustiques avec les modèles numériques sont comparées aux mesures et permettent de retrouver les principaux pics de bruit des alternateurs. Dans la quatrième partie, des études de sensibilités sont menées afin de déterminer les paramètres les plus influents sur le bruit acoustique d’origine magnétique des machines à griffes. Ces études montrent l’influence importante de la géométrie du rotor, du bobinage stator et de la température sur le bruit. Les modifications de la structure ainsi que les imperfections étudiées (i.e. défauts de forme et excentricité) ont une influence moindre. Les caractéristiques des forces magnétiques ainsi que les influences des forces radiales et tangentielles sont ensuite exposées. Finalement, des exemples d’optimisation du rotor sont traités avec les deux modèles électromagnétiques (numérique et hybride). Un prototype est réalisé pour valider expérimentalement les résultats des simulations et un gain de 10 dB est obtenu sur la puissance acoustique. / This thesis aims at simulating and reducing the acoustic noise due to magnetic forces of claw-pole automotive alternators. It also aims at improving the understanding of the noise generation mechanisms. In the first part, the assembly of the claw-pole alternator and its different parts are described. The particularities of the acoustic noise of the alternator are also given. Then, the problem as well as the global approach, based on the vibro-acoustic simulation, are explained. The second part is a review of the studies on the acoustic noise from a magnetic origin of electrical machines. The models used to study these machines as well as the main noise reduction solutions are detailed. In the third part, new electromagnetic and vibro-acoustic models are developed. Two electromagnetic models are considered : a finite element model and a hybrid model which couples the finite element model with an analytical model. This analytical model computes the airgap magnetic flux density as the product of a permeance and a magnetomotive force functions. Each function takes the variations of the claw-pole geometry along the axial direction into account. Saturation and tangential forces are taken into account thanks to the finite element model. Then, a finite element mechanical model is developed. Three unknown parameters of the model are determined thanks to the correlation between the model and experimental data, namely : the equivalent materials of the stator stack and the windings and the contact conditions between the stator and the brackets. Finally, acoustic simulations are compared with measurements. A good correlation is achieved between simulated and measured noise peaks. In the fourth part, sensitivity studies are carried out in order to determine the most influential parameters on the acoustic noise of claw-pole alternators. These studies show the significant influence of the claw-pole geometry, the stator windings and the temperature on the acoustic noise. Structural modifications and studied faults have a smaller influence. Characteristics of the magnetic forces as well as the influences of radial and tangential forces are then detailed. In the end, optimizations with the finite element and the hybrid models are presented. A prototype is built and acoustic measurements show a 10 dB decrease of the sound power level.

Orientador: Jose Roberto de França Arruda / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-06T11:13:15Z (GMT). No. of bitstreams: 1 Padilha_PauloEduardoFranca_M.pdf: 721382 bytes, checksum: 8fae387ba335cdb5b3e7b462935121c1 (MD5) Previous issue date: 2006 / Resumo: Neste trabalho é feita uma comparação de técnicas analíticas e experimentais de Análise de Caminhos de Transferência Vibroacústicos. A Análise de Caminhos de Transferência, ou TPA como é conhecida pela abreviatura em inglês, é uma ferramenta para se avaliar a contribuição de diferentes caminhos de propagação de energia vibroacústica entre uma fonte e um receptor ligados entre si por várias conexões. Uma aplicação típica de TPA é quantificar e determinar a importância relativa desses caminhos numa dada banda de freqüência, verificando-se a contribuição mais significativa para o receptor. Nessa análise, basicamente duas quantidades devem ser obtidas: as forças operacionais em cada caminho de transferência e a Função de Resposta em Freqüência desses caminhos. Essas funções podem ser obtidas tanto experimentalmente quanto analiticamente, considerando-se ou não a impedância mecânica da fonte vibroacústica. As forças operacionais podem ser diretamente obtidas de medições, usando um transdutor de forças, ou indiretamente estimadas a partir de medições auxiliares. Neste trabalho são apresentados dois métodos de obtenção indireta das forças operacionais ¿ o Método da Rigidez Complexa e o Método da Inversão de Matrizes ¿ associados com as duas possíveis configurações para determinação das Funções de Resposta em Freqüência ¿ incluindo e excluindo a impedância da fonte. Essas técnicas são aplicadas a dois modelos: um analítico e um experimental. avaliadas com esse modelo analítico, comentando-se suas vantagens e desvantagens. São avaliados ainda os efeitos do acoplamento entre fonte e receptor e entre os caminhos de transferência. Os experimentos foram realizados numa estrutura concebida como um modelo simplificado de um automóvel. As forças foram obtidas através dessas duas técnicas indiretas e comparadas com as medidas com transdutores de força. Como no modelo analítico, as forças e FRF foram estimadas na presença e na ausência da fonte, e a contribuição de cada caminho calculada através dessas técnicas e configurações. A resposta do receptor, calculada como uma combinação dos diferentes caminhos de transferência, foi comparada à medida nas condições operacionais, de modo a se verificar a exatidão de cada método utilizado. As vantagens e limitações desses métodos e configurações experimentais são então comentadas para uso em aplicações práticas / Abstract: In the present work, analytical and experimental techniques of Vibro-Acoustic Transfer Path Analysis are compared and discussed. Transfer Path Analysis (TPA) is a tool to evaluate the contribution of different vibro-acoustic energy propagation paths between a source and a receiver linked to each other by a number of connections. TPA is typically used to quantify and rank the relative importance of these paths in a given frequency band, determining the most significant one to the receiver. When applying TPA two basic quantities have to be determined: the operational forces at each transfer path and the Frequency Response Functions of these paths. These functions can be obtained either experimentally or analytically, considering or not the mechanical impedance of the source. Operational forces can be directly measured by force transducers or indirectly estimated from auxiliary response measurements. Two methods to obtain the operational forces indirectly ¿ the Complex Stiffness Method and the Matrix Inversion Method ¿ associated with two possible configurations to determine the Frequency Response Functions ¿ including and excluding the source impedance ¿ are presented and discussed in this work. These estimation techniques are applied to two models: an analytical and an experimental model. Analytically, these techniques are applied to a lumped parameter model. The advantages and drawbacks of them are commented and the effect of coupling between source and receiver and among transfer paths is analyzed with this theoretical approach. The experiments are done in a test structure conceived as a simplified model of an automotive vehicle. The forces are obtained via these two techniques and compared to those measured by force transducers. Like in the analytical model, forces and Frequency Response Functions are estimated in the presence and in the absence of the source, and the contribution of each path is calculated based on the combinations of these different estimation methods and setups. The contributions of the different paths at the receiver location are calculated using each estimation method and are compared to those obtained in the operational condition in order to verify the accuracy of these methods. The advantages and limitations of the methods and test setups are then discussed for use in practical applications / Mestrado / Mecanica Computacional / Mestre em Engenharia Mecânica

A cold extrusion process has been developed to tailor a porous structure from polymeric waste. The use of an extruder to manufacture acoustic materials from recycled waste is a novel idea and the author is not aware of any similar attempts. The extruder conveys and mixes the particulates with a reacting binder. The end result is the continuous production of bound particulates through which a controlled amount of carbon dioxide gas that is evolved during the reaction is used to give the desired acoustic properties. The cold extrusion process is a low energy consuming process that reprocesses the post manufacturing waste into new vibro-acoustic products that can be used to meet the growing public expectations for a quieter environment. The acoustical properties of the developed products are modelled using Pade approximation and Johnson-Champoux-Allard models. Applications for the developed products are widespread and include acoustic underlay, insulation and panels in buildings, noise barriers for motorways and railway tracks, acoustic insulation in commercial appliances and transport vehicles.