Analisa o comportamento tribológico do pneumático. Discute o coeficiente de atrito do pneu, a influência do pavimento e os avanços na modelagem. Apresenta uma metodologia para estimativa do desgaste de pneus pelo método dos elementos finitos. Usa o conceito de trabalho de abrasão. Considera nas condições de contorno do modelo de pneu o efeito do camber e do ângulo de deriva. Investiga a interação vibracional entre o pneu e a suspensão como causa de desgaste irregular. Utiliza modelagem de ônibus rodoviário por multicorpos com eixo flexível. Emprega técnica tempo-freqüência para análise do acoplamento modal entre pneu e suspensão. Propõe novos modelos para estudo do desgaste em pneus analisando-se um modelo completo de veículo pelo método dos elementos finitos. Sugere análises de sensibilidade considerando os parâmetros de regulagem da suspensão e condições operacionais dos componentes. Propõe análises estocásticas da especificação do pneu para otimização do sistema pneu-suspensão. / The tire tribological behavior is analyzed. The friction coefficient of rubbers is presented, and its inherent modeling difficulties regarding the operational condition dependence during measurements are discussed. The influence of the pavement roughness and the advances in friction modeling are presented. A predictive methodology to evaluate the tread wear using finite element method and the concept of frictional energy was used. Camber, lateral forces and slip angles are taken into account as boundary conditions for the tire simulations in steady state. The vibrational interaction between tire and suspension concerning irregular wear on front axle truck tires was investigated. A multibody bus model with flexible front axle was used for modal analysis purposes. A time-frequency methodology was applied to identify modal vibrations of the tire and suspension assemblage. A new simulation model for the tire wear was proposed intending to analyze the whole vehicle with under the finite element method. Sensitivity analysis of the vehicle suspension setup and operational conditions of components was suggested. Stochastic analysis of tire specification is recommended to optimize the tire-suspension system.

[pt] Neste trabalho um modelo dinâmico para um rotor vertical em balanço, considerando o fenômeno de contato com a sua guarda, é analisado. A conjunto é modelado como um sistema eixo-rotor-estator com contato. A análise do contato é particularmente complexa pela não linearidade nas equações de movimento. O impacto com o estator é levado em conta através do modelo de contato tipo Kelvin-Vôigt, e, as equações de movimento, do rotor, são deduzidas através da formulação Lagrangeana; estas equações podem capturar os fenômenos devido à vibração lateral, como: precessão direta, precessão retrograda, rolamento e escorregamento. Pela existência de diferentes parâmetros combinados e devido à não linearidade da equação de movimento, a resposta dinâmica não é simples de ser obtida apriori. Portanto, métodos numéricos são empregados para a solução, especificamente emprega-se o método de Runge-Kutta Fehlberg de passo variável. Os resultados da simulação mostram que para certas condições, o rotor pode mudar de orbita devido aos impactos com o estator, podendo chegar a realizar precessão retrograda. Este tipo de fenômeno é considerado como o mais violento e perigoso nas maquinas rotativas. Com o fim de estudar a dinâmica lateral do sistema, um rotor vertical em balanço com guarda anular é investigado. A passagem dela através de sua velocidade critica, quando conduzida por um motor elétrico, é analisada (e também quando o sistema opera em velocidades constantes). Além disso, neste trabalho, os resultados experimentais obtidos da bancada de experimentação são usados para estudar o fenômeno da precessão. / [en] In this work a dynamic model for the overhung rotor, considering the contact phenomenon between the rotor and the stator is analyzed. It is modeled as a shaft-rotor- stator system with contact. The analysis of contact is particularly complex, due to the high nonlinearity of motion equations. Impact with the stator is accounted by a consistent contact model, as Kelvin-Vôigt model, and, rotor`s motion equation is encountered employing Lagrangean`s method; this equations are capable of capturing the phenomenon due to lateral vibration, as: forward whirl, backward whirl, rolling or sliding along the stator. Due to the combined parameters and the effect of nonlinearity in motion equations, the dynamical response is not simple or easily predictable. Numerical simulation is the preferred method of analysis, exactly is used the Runge-Kutta Fehlberg method with variable step. Simulation results show that under certain conditions, a rotor changes its orbit due the impacts with the stator and after that, it executes backward whirl motion. It is a kind of phenomenon, which is considered as the most violent and dangerous in rotating machines. To this end, the analysis of a vertical overhung shaft-disc system with annular guard is investigated. The passing through its critical speed is analyzed when driven by an electric motor (also when the system operates under a constant rotational velocity). In addition, in this work the results obtained with an experimental test rig are used to investigate the whirl phenomenon.

[pt] Identificação paramétrica de sistemas mecânicos é uma das principais aplicações das técnicas de identificação de sistemas na Engenharia Mecânica, especificamente para a identificação de parâmetros modais de estruturas flexíveis. Um dos principais problemas na identificação é a presença de ruido nas medições. Este trabalho apresenta uma análise na presença de ruído de alguns dos métodos no domínio do tempo aplicáveis na identificação de parâmetros modais de sistemas mecânicos lineares invariantes no tempo com múltiplas entradas e múltiplas saídas (MIMO), usando como base o modelo em espaço de estados tipicamente usado em Dinâmica e Vibrações. Os algoritmos de subespaço envolvidos neste estudo destacam-se pela utilização da decomposição em valores singulares (SVD) dos dados, obtendo subespaços ortogonais dos modos associados ao sistema e dos modos associados ao ruído. Outros complicadores no processo de identificação que serão explorados neste trabalho são: flexibilidde e baixo amortecimento. Comparam-se as técnicas usando o modelo no espaço de estado da estrutura Mini- mast desenvolvida pela NASA Langley Research Center e simulações são feitas variando o nível de ruído nos dados, o amortecimento e a flexibilidade da estrutura. O problema de identificação de parâmetros estruturais (matrizes de massa, rigidez e amortecimento) também é estudado, as características e limitações dos algoritmos utilizados são analisados. Como exemplo de aplicação prática, um experimento foi realizado para identificar os parâmetros modais e estruturais de um rotor flexível e os resultados são discutidos. / [en] Parametric identification of mechanical systems is one of the main applications of the system identification techniques in Mechanical Engineering, specifically for the identification of modal parameters of flexible structures. One of the main problems in the identification is the presence of noise in the measurements. This work presents an analysis in the presence of noise of some of the time domain methods applicable in modal parameters identification of linear time-invariant mechanical systems with multiple inputs and multiple outputs (MIMO), using as base the state-space model typically used in Dynamics and Vibrations. The subspace algorithms involved in this study are distinguished for the use of the singular values decomposition (SVD) of the data, obtaining ortogonal subspaces of the modes associates to the system and of the modes associates to the noise. Other complicators in the identification process that will be explored in this work are: flexibility and low damping. The techniques are compared using the state-space model of the Mini-mast structure developed for NASA Langley Research Center and simulations are made varying the level of noise in the data, the damping and the flexibility of the structure. The problem of identification of structural parameters (mass, stiffness and damping matrices) also is studied, the characteristics and limitations of the used algorithm is analyzed. As example of practical application, an experiment was made to identify the modal parameters of a flexible rotor and the results are discussed.

One of the common research goals in disciplines such as computer graphics and robotics is to understand the subtleties of human motion and develop tools for recreating natural and meaningful motion. Physical simulation of virtual human characters is a promising approach since it provides a testbed for developing and testing control strategies required to execute various human behaviors. Designing generic control algorithms for simulating a wide range of human activities, which can robustly adapt to varying physical environments, has remained a primary challenge. This dissertation introduces methods for generic and robust control of virtual characters in an interactive physical environment. Our approach is to use the information of the physical contacts between the character and her environment in the control design. We leverage high-level knowledge of the kinematics goals and the interaction with the surroundings to develop active control strategies that robustly adapt to variations in the physical scene. For synthesizing intentional motion requiring long-term planning, we exploit properties of the physical model for creating efficient and robust controllers in an interactive framework. The control design leverages the reference motion capture data and the contact information with the environment for interactive long-term planning. Finally, we propose a compact soft contact model for handling contacts for rigid body virtual characters. This model aims at improving the robustness of existing control methods without adding any complexity to the control design and opens up possibilities for new control algorithms to synthesize agile human motion.

Die vorliegende Arbeit liefert eine ausführliche systematische Untersuchung der Gestellschwingungen von Rollen- und Bogen-Offsetdruckmaschinen. Sie dient dazu, die modalen Eigenschaften (Eigenfrequenzen, Eigenformen) zu identifizieren und die erzwungenen Schwingungen zu simulieren. An drei Rollen-Offsetdruckmaschinen wurden experimentelle und theoretische Modalanalysen durchgeführt. Es wurden die Einflüsse des Baugrundes, der Aufstellung und der Schraubenverbindung auf die modalen Eigenschaften analysiert. Weiterhin wurde die Standsicherheit bei seismischer Erregung überprüft. Für alle vier untersuchten Offsetdruckmaschinen wurden FE-Modelle unter Berücksichtigung ihrer Besonderheiten gebildet und mittels der Messergebnisse abgesichert. Bei Bogen-Offsetdruckmaschinen wurden erzwungene Schwingungen bei vier verschiedenen Erregungen und bei ungleichmäßiger Aufstellung simuliert. Aus den vorliegenden Resultaten können Schlussfolgerungen für die Weiterentwicklung von Druckmaschinen gezogen werden. / This work provides a detailed systematical research about the frame vibrations of web-offset-printing machines and sheetfed-offset-printing machines. It serves to identify the modal properties (natural frequencies and mode shapes) and to simulate the forced vibrations. The experimental and theoretical modal analysis have been realised at three web-offset-printing machines. The influences of the base, installation and screw connection on the modal properties have been analysed, furthermore the stand security under seismic excitation has been verified. The FE-models of all four investigated offset-printing machines have been built under consideration of their characteristics and have been updated with measurement results. Forced vibrations of sheetfed-offset-printing machines have been simulated on four different excitations and for uneven installation. The results of this work can be used for the further development of printing-machines.

This research study presents a new vibration-based non-destructive global structural damage identification and condition monitoring technique that can be used for detection, localization and quantification of damage. A two-stage damage identification process that combines non-model based and model-based damage identification approaches is proposed to overcome the main difficulties associated with the solution of structural damage identification problems. In the first stage, performance assessment of various response parameters obtained from the time-domain, frequency-domain and spectral-domain analysis is conducted using a non model-based damage detection and localization approach. In addition, vibration response parameters that are sensitive to local and global damage and that possess strong physical relationships with key structural dynamic properties are identified. Moreover, in order to overcome the difficulties associated with damage identification in the presence of structural nonlinearity and response nonstationarity, a wavelet transform based damage-sensitive parameter is presented for detection and localization of damage in the space domain. The level of sensitivity and effectiveness of these parameters for detection and localization of damage are demonstrated using various numerical experimental data determined from one-dimensional and two-dimensional plate-like structures.

[pt] Esta dissertação tem como principal objetivo estudar aplicações da expansão ou decomposição de Karhunen-Loève em dinâmica de estruturas. Esta técnica consiste, basicamente, na obtenção de uma decomposição linear da resposta dinâmica de um sistema qualquer, representado por um campo vetorial estocástico, tendo a importante propriedade de ser ótima, no sentido que dado um certo número de modos, nenhuma outra decomposição linear pode melhor representar esta resposta. Esta capacidade de compressão de informação faz desta decomposição uma poderosa ferramenta para a construção de modelos reduzidos para sistemas mecânicos em geral. Em particular, este trabalho aborda problemas em dinâmica estrutural, onde sua aplicação ainda é bem recente. Inicialmente, são apresentadas as principais hipóteses necessárias à aplicação da expansão de Karhunen-Loève, bem como duas técnicas existentes para sua implementação, com domínios distintos de utilização.É dada especial atenção à relação entre os modos empíricos fornecidos pela expansão e os modos de vibração intrínsecos a sistemas vibratórios lineares, tanto discretos quanto contínuos, exemplificados por uma treliça bidimensional e uma placa retangular. Na mesma linha, são discutidas as vantagens e desvantagens de se usar esta expansão como ferramenta alternativa à análise modal clássica. Como aplicação a sistemas não-lineares, é apresentado o estudo de um sistema de vibroimpacto definido por uma viga em balanço cujo deslocamento transversal é limitado por dois batentes elásticos. Os modos empíricos obtidos através da expansão de Karhunen-Loève são, então, usados na formulação de um modelo de ordem reduzida, através do método de Galerkin, e o desempenho deste novo modelo investigado. / [en] This dissertation has the main objetive of studying applications of the Karhunen-Loève expansion or decomposition in structural dynamics. This technique consists basically in obtaining a linear decomposition of the dynamic response of a general system represented by a stochastic vector field. It has the important property of optimality, meaning that for a given number of modes, no other linear decomposition is able of better representing this response. This information compression capability characterizes this decomposition as powerful tool for the construction of reduced-order models of mechanical systems in general. Particularly, this work deals with structural dyamics problems where its application is still quite new. Initially, the main hypothesis necessary to the application of the Karhunen-Loève expansion are presented, as well as two existing techniques for its implementation that have different domains of use. Special attention is payed to the relation between empirical eigenmodes provided by the expansion and mode shapes intrinsic to linear vibrating systems, both discrete and continuous, exemplified by a bidimensional truss and a rectangular plate. Furthermore, the advantages and disadvantages of using this expansion as an alternative tool for classical modal analysis are discussed. As a nonlinear application, the study of a vibroimpact system consisting of a cantilever beam whose transversal displacement is constrained by two elastic barriers is presented. The empirical eigenmodes provided by the Karhunen-Loève expansion are then used to formulate a reduced-order model through Galerkin projection and the performance of this new model is investigated.

Dans le cadre de la discrétion acoustique des navires militaires, cette thèse contribue à la modélisation de structures amorties par des matériaux viscoélastiques, sous forme de couches contraintes. Afin de pouvoir optimiser et dimensionner la structure et le matériau amortissant, il est souhaitable de disposer d'un outil numérique prédictif et efficace. Dans un premier temps, une stratégie de caractérisation et de modélisation du comportement de matériaux viscoélastiques est proposée. Elle inclue une méthode de recalage de résultats de mesures par DMA basée sur le respect des relations de Kramers-Kronig, permettant ainsi de construire des courbes maîtresses du matériau en accord avec le principe de causalité. Dans un deuxième temps, un code de calcul par éléments finis est développé, puis des essais de vibration sur structures sandwich sont réalisés afin de valider la modélisation par éléments finis de structures munies de matériaux viscoélastiques. Dans le cas d'une fine couche viscoélastique insérée dans une structure maillée par des éléments volumiques, deux éléments d'interface sont développés : ils permettent de tester simplement plusieurs configurations. Enfin, dans un troisième temps, deux catégories de méthodes de réduction adaptées au calcul de la réponse fréquentielle de structures fortement amorties par des matériaux viscoélastiques sont étudiées : les méthodes de projection sur bases modales et la méthode de reconstruction par approximants de Padé. Dans le cadre d'études paramétriques pour l'optimisation des performances acoustiques des traitements viscoélastiques contraints, les avantages des méthodes développées sont mis avant à travers deux cas d'application. / In the context of acoustic discretion of naval ships, this thesis contributes to the modelling of viscoelastically damped structures by means of thin constrained layers. In order to optimize and design the structure and the damping material, a predictive and efficient numerical tool is desirable. Firstly, a characterization and modelling strategy of the behaviour of viscoelastic materials is proposed. A shifting procedure of DMA measurements based on the fulfillment of the Kramers-Kronig relations is developed in order to build master curves of the material which are consistent with the causality principle. Secondly, a finite element code is developed, and vibration experiments are realized in order to validate the finite element modelling of structures with viscoelastic materials. In the case of thin constrained viscoelastic layers applied to a structure meshed using brick elements, two interface finite elements are developed, which facilitate parametric studies. Finally, two families of reduction methods adapted to the calculation of the frequency response of structures highly damped by viscoelastic materials are studied: modal projection methods and Padé approximants reconstruction method. The advantages of the proposed methods, in the frame of parametric studies for the optimization of the acoustic performances of constrained viscoelastic layers, are highlighted through two applications.

La plupart des problèmes d'ingénierie des deux derniers siècles ont été résolus grâce à des modèles structuraux pour poutres, plaques et coques. Les théories classiques, tels que Euler-Bernoulli, Navier et de Saint-Venant pour les poutres, et Kirchhoff-Love et Mindlin-Reissner pour plaques et coques, ont permis de réduire le problème générique 3-D, dans le problème unidimensionnel pour les poutres et deux dimensionnelle pour les coques et les plaques. Théories raffinés d'ordre supérieur ont été proposées au cours du temps, comme les modèles classiques ne consentez pas à d'obtenir une complète domaine des contraintes et des déformations. La Carrera Unified Formulation (UF) a été proposé au cours de la dernière décennie, et permet de développer un grand nombre de théories structurelles avec un nombre variable d'inconnues principales au moyen d'une notation compacte et se référant à des nuclei fondamentales. Cette formulation unifiée permet de dériver carrément des modèles structurels d'ordre supérieur, pour les poutres, plaques et coques. Dans ce cadre, cette thèse vise à étendre la formulation pour l'analyse des structures fonctionnellement gradués (FGM), en introduisant aussi le problème thermo-mécanique, dans le cas des poutres fonctionnellement gradués. Suite à la formulation unifiée, les variables génériques déplacements sont écrits en termes de fonctions de base, qui multiplie les inconnues. Dans la deuxième partie de la thèse, de nouvelles fonctions de bases pour la modélisation des coques, qui représentent une approximation trigonométrique des variables déplacements, sont pris en compte / Most of the engineering problems of the last two centuries have been solved thanks to structural models for both beams, and for plates and shells. Classical theories, such as Euler-Bernoulli, Navier and De Saint-Venant for beams, and Kirchhoff-Love and Mindlin- Reissner for plates and shells, permitted to reduce the generic 3-D problem, in onedimensional one for beams and two-dimensional for shells and plates. Refined higher order theories have been proposed in the course of time, as the classical models do not consent to obtain a complete stress/strain field. Carrera Unified Formulation (UF) has been proposed during the last decade, and allows to develop a large number of structural theories with a variable number of main unknowns by means of a compact notation and referring to few fundamental nuclei. This Unified Formulation allows to derive straightforwardly higher-order structural models, for beams, plates and shells. In this framework, this thesis aims to extend the formulation for the analysis of Functionally Graded structures, introducing also the thermo-mechanical problem, in the case of functionally graded beams. Following the Unified Formulation, the generic displacements variables are written in terms of a base functions, which multiplies the unknowns. In the second part of the thesis, new bases functions for shells modelling, accounting for trigonometric approximation of the displacements variables, are considered.

L’hydrogène liquide est un ergol utilisé en complément de l’oxygène liquide pour la propulsion de nombreux lanceurs en particulier ceux de la famille Ariane. Cependant, sa dangerosité interdit la réalisation d’essais, en particulier vibratoires, sur des réservoirs remplis. Cette thèse explore une piste d’étude permettant de réaliser ces essais vibratoires sur le réservoir rempli d’un matériau de substitution : un ensemble de billes pré-contraintes. L’objectif est d’obtenir un comportement modal similaire en termes de modes et de fréquences propres à celui du réservoir rempli d’hydrogène liquide pour l’étude des premiers modes. Pour répondre à cet objectif, cette étude est développée en deux parties. Dans la première partie, une approche analytique basée sur une méthode par équivalences fréquentielles est détaillée. Après avoir présenté les grandes lignes de la méthodologie utilisée et l’ensemble des modèles développés, la méthodologie est appliquée au cas étudié expérimentalement de manière à mettre en évidence l’influence des différents paramètres et de proposer une première méthode pour choisir un jeu de billes adapté. La seconde partie, traite principalement des aspects expérimentaux et numériques. Après avoir détaillé la caractérisation des billes utilisées, le montage expérimental conçu et réalisé pour effectuer des essais vibratoires sur un réservoir rempli de billes pré-contraintes est présenté. Les différents résultats obtenus avec ce montage sont étudiés au regard de l’approche analytique, mais aussi de modèles numériques utilisant des éléments-discrets et des éléments-finis. / Liquid hydrogen is a propellant alternatively used with liquid oxygen for the propulsion of many launchers, especially those of the Ariane family. However, its dangerousness prohibits vibration tests on filled tank. The aim of this PHD is to explore the possibility to carry out such vibration tests by filling these tanks with a substitute material : a set of pre-stressed balls. As further argued and developed in the report, the objective is to obtain a modal behavior similar in term of mode shapes and natural frequencies to those of the tank filled with liquid hydrogen for the first modes. In the first part, an analytical approach based on a method using frequency equivalences is detailed. After presenting the outlines of the methodology used and all the models developed, the methodology is applied to the experimentally studied case in order to highlight the influence of the different parameters as well as then to propose a first method to choose a set of well adapted balls. The second part deals mainly with experimental and numerical aspects. Firstly, the balls used in the thesis are characterized. Then, the experimental set-up designed and realized to carry out vibration tests on a tank filled with pre-stressed balls is presented. The different results obtained are compared with both analytical results and numerical based on discrete-elements and finite-elements results.