Th. doct.-ing.--Besançon, 1981. N°: 120.

Made available in DSpace on 2014-06-11T19:34:59Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-09Bitstream added on 2014-06-13T21:06:53Z : No. of bitstreams: 1 barros_e_dr_guara.pdf: 1499137 bytes, checksum: 5a94296d58a74230125376ce4552f941 (MD5) / Universidade Estadual Paulista (UNESP) / Na presença de não linearidades, a resposta forçada de estruturas exibe diversos fenômenos físicos que não podem ser descritos através de modelos lineares. Estes fenômenos incluem ressonâncias sub-harmônicas, ressonâncias super-harmônicas, jumps , movimentos quasi-periódicos, movimentos de período múltiplo, caos e interações modais. Recentes estudos experimentais indicam que um novo tipo de interação modal pode ocorrer através de mecanismos não ressonantes, decorrente da transferência de energia de modos de alta freqüência e baixa amplitude para modos de baixa freqüência e alta amplitude. Neste trabalho, interações modais não ressonantes são investigadas na resposta planar não linear de vigas cantilever flexíveis sujeitas a excitações externas e paramétricas. As equações diferenciais e as condições de contorno associadas que governam o movimento flexional-flexional não linear de uma viga assumida inextensível, metálica e isotrópica, são apresentadas. O estudo experimental conduzido revelou que a transferência de energia entre modos de alta freqüência para modos de baixa freqüência ocorre via modulação, sendo função do valor da amplitude de excitação e da proximidade entre os valores da freqüência de modulação e da freqüência dos modos ativados. O estudo revelou também que a ativação de modos de baixa freqüência pode ocorrer sob uma variedade de condições de entrada. Em adição, outros fenômenos dinâmicos não lineares classificados como rotas para o movimento caótico são também observados. Em determinadas condições, movimentos quasi-periódicos com amplitudes moduladas caoticamente e moduladas periodicamente são exibidos. Um movimento de resposta de período dois é também observado. / Interesting physical phenomena occur in the forced response of structures in the presence of nonlinearities, which cannot be explained by linear models. These phenomena include subharmonic resonances, superharmonic resonances, jumps, period-multiplying motions, quasiperiodic motions, chaos and modal interactions. Recent studies suggest that another type of modal interaction may occur through nonresonant mechanisms, due to the energy transfer from the low-amplitude highfrequency modes to high-amplitude low-frequency modes. In this work, nonresonant modal interactions in the nonlinear planar motions of flexible cantilever beams subjected to transverse and parametric harmonic excitations are investigated. The governing equations of the nonlinear bending-bending motions and the associated boundary conditions for an isotropic metallic inextensional beam are presented. An experimental study revealed that the transfer of energy from high-frequency to lowfrequency modes occurs via modulation and is found to be function of the excitation amplitude and the closeness of the modulation frequency to the frequencies of the low modes activated. The experimental study also revealed that the energy transfer from high-frequency modes to low-frequency modes occurs for a variety of conditions. In addition, others nonlinear dynamic phenomenas routes to the chaotic motions, are also observed. Under certain conditions, quasiperiodic motion with periodically and chaotically modulated amplitudes are exhibited. Period-doubling motion is also observed.

Many researchers have devoted their work to the development of modal analysis extraction techniques in order to obtain more reliable identification of the modal parameters. Also, as a consequence of all this work, there are some other works devoted to the evaluation and comparison of these methods in order to find which one is the most reliable method with respect to certain characteristics. In this thesis the Rational Fraction Polynomial (RFP) Method, the Prony or Complex Exponential Method (CEM), the Ibrahim Time Domain (ITD) Method, and Hilbert Envelope Method are used to evaluate how the accuracy of the damping ratio is affected with respect to various parameters and conditions. The investigation focuses in the estimation of damping ratio because among the modal parameters, it is the most difficult to model. Each method is evaluated individually in order to understand how the damping ratio estimation is affected with respect to each method when the characteristics of the FRF are changed. Also, they are compared to show that, in general, the Rational Fraction Polynomial Method is a more reliable method than the other methods. To investigate this, a simulated analytical data and an experimental data are processed to estimate the modal parameters, but focusing in the damping ratio. For the simulated analytical data the damping ratio's percent of error were calculated. The highest damping ratio's percent of error of the RFP was 0.0073501%. In the other hand, for the CEM, ITD, and Hilbert Envelope Method their highest damping ratio's percent of error were 83.02%, 99.82%, and 4.077%, respectively. / Master of Science

Spiders weave intricate webs for catching prey, providing shelter and setting mating rituals; arguably the most notable of these creations is the orb web. In this thesis we model the essential vibrations of orb webs by first considering a spider web as a multilinked structure of elastic strings. We then solve the associated eigenvalue problem using a Chebyshev pseudospectral collocation method to discretize the system. This thesis first examines the vibrations of webs with uniform material properties throughout, then investigates the effects of using biologically realistic material parameters for silks within a single web. Understanding how spiders detect and react to the vibrations produced by their webs is of interest for both biological and engineering applications. / Master of Science / Spiders weave intricate webs for catching prey, providing shelter, and setting mating rituals; arguably the most notable of these creations is the orb web. In this thesis we model the essential vibrations of orb webs by first considering a spider web as a multilinked structure of elastic strings. Using numerical methods, we approximate the fundamental frequencies of the web. This thesis first examines the vibrations of webs with uniform material properties throughout, then investigates the effects of biologically realistic parameters of the varying material properties for silks within a single web. Understanding how spiders detect and react to the vibrations produced by their webs is of interest for both biological and engineering applications.

Indoor localization has emerged as a critical technology for enhancing the functionality and efficiency of smart environments. This dissertation focuses on vibro-localization, a novel IOL methodology that determines occupant positions by analyzing floor vibrations caused by footfall patterns. Unlike traditional localization techniques that rely on visual or radio-based sensing, vibro-localization leverages accelerometers fixed to the floor to capture vibro-measurements, offering a cost-effective and privacy-preserving alternative. The primary objective of this research is to address significant limitations in existing vibro-localization approaches, including sensor imperfections, measurement uncertainty, and complex wave dynamics. To this end, we develop comprehensive models that characterize both random and systematic errors introduced by accelerometers, integrating these models into the localization framework to enhance accuracy. Furthermore, we quantify the uncertainty in vibro-measurements and elucidate their contribution to localization errors, providing a robust foundation for error mitigation strategies. A key contribution of this work is the introduction of an information-theoretic Byzantine Sensor Elimination (BSE) algorithm. This algorithm assesses the reliability of vibro-measurement vectors by categorizing sensors into consistent and divergent subsets, thereby minimizing the impact of external uncertainties such as reflections and dispersion. Additionally, we propose multi-sensor vibro-localization techniques that aggregate data from multiple accelerometers, enhancing robustness against individual sensor inaccuracies and environmental variabilities. To accurately model wave propagation, this dissertation advances parametric models that account for dispersion, attenuation, and material inhomogeneities in the floor structure. These models facilitate precise occupant localization even with low-spectral resolution in transfer function estimates. Empirical validation using controlled experimental data demonstrates significant improvements in localization accuracy and precision over baseline methods, highlighting the efficacy of the proposed techniques. The outcomes of this research contribute to the development of economically feasible and ethically sound IOL technologies, broadening their applicability across various domains such as smart homes, healthcare, and energy management. By addressing critical challenges in sensor reliability and wave dynamics, this dissertation paves the way for more accurate, reliable, and scalable indoor localization systems. / Doctor of Philosophy / In our increasingly connected world, knowing the precise location of individuals within indoor spaces—such as homes, offices, and hospitals—has become essential for enhancing convenience, safety, and energy efficiency. Traditional methods for indoor localization often rely on cameras or radio signals, which can be expensive and raise privacy concerns. This dissertation introduces an innovative approach called vibro-localization, which determines the position of occupants by analyzing the subtle vibrations in the floor caused by their footsteps. Vibro-localization utilizes simple and affordable sensors called accelerometers, which are placed on the floor to detect vibrations. When a person walks, their footsteps generate unique vibration patterns that travel through the building structure. By capturing and analyzing these patterns, our system can accurately pinpoint the individual's location without the need for invasive cameras or constant radio signal transmissions. This method not only reduces costs but also preserves the privacy of occupants, as it does not capture visual or personal data. One of the main challenges in vibro-localization is ensuring accuracy despite various sources of error. Sensors can introduce noise and inaccuracies, and factors like the building's materials and layout can affect how vibrations propagate. To overcome these challenges, this research develops sophisticated models that account for sensor imperfections and environmental factors. By understanding and correcting for these variables, the system can deliver precise location data even in complex indoor environments. A significant advancement presented in this work is the development of an algorithm that intelligently selects the most reliable sensor data. This algorithm distinguishes between consistent measurements and those affected by external disturbances, such as echoes or structural inconsistencies, ensuring that only the highest quality data is used for localization. This not only improves accuracy but also makes the system more robust and reliable in real-world settings. Moreover, the dissertation explores the use of multiple sensors working together to enhance localization performance. By combining data from several accelerometers, the system can cross-verify measurements and reduce the impact of individual sensor errors. This multi-sensor approach leads to more stable and accurate location tracking, making the technology suitable for a wide range of applications. To validate the effectiveness of the proposed vibro-localization techniques, extensive experiments were conducted in controlled environments. The results demonstrated significant improvements in both accuracy and reliability compared to existing methods, showcasing the potential of vibro-localization as a practical solution for indoor positioning needs. The implications of this research are far-reaching. In smart homes, vibro-localization can enable automated lighting and climate control based on occupant presence, enhancing energy efficiency and comfort. In healthcare settings, it can assist in monitoring patient movements, ensuring safety and improving care. Additionally, in emergency situations, accurate indoor localization can facilitate quicker and more efficient evacuations. In summary, this dissertation presents a groundbreaking approach to indoor localization that is cost-effective, privacy-preserving, and highly accurate. By leveraging floor vibrations and advanced sensor data processing techniques, vibro-localization offers a viable alternative to traditional methods, with broad applications that can significantly enhance the functionality and safety of indoor environments. This research not only addresses current limitations in indoor localization technology but also paves the way for future innovations in smart building systems and occupant-aware technologies.

Th.--Sci. phys.--Lille 1, 1977. N°: 388.

Ces travaux de recherche s'intéressent de manière générale à la quantification des incertitudes et à la réduction de modèle pour la modélisation numérique des systèmes dynamiques. Dans une première partie, on s'intéresse à la quantification des incertitudes pour les systèmes multicorps. Pour ce type de système, les incertitudes concernent les paramètres du modèle. Ces incertitudes sont liées soit à une variabilité naturelle, soit à un manque de connaissance sur ces paramètres. On s'intéresse en particulier à la modélisation des incertitudes relatives à la distribution de masse des solides rigides. Afin d'être compatible avec le formalisme de la dynamique des systèmes multicorps, cette modélisation est construite directement au niveau des propriétés globales d'inertie des solides rigides. Dans la partie suivante, on s'intéresse à la modélisation et à l'identification en inverse des incertitudes dans les structures déformables pour lesquelles, en plus des incertitudes sur les paramètres, il existe des incertitudes de modèle induites par les erreurs de modélisation (discrétisation, choix de la loi de comportement, ...). Pour prendre en compte ces deux types d'incertitudes, une approche probabiliste mixte paramétrique/non paramétrique est utilisée. L'accent sera mis sur l'identification des hyper-paramètres du modèle stochastique en utilisant des mesures expérimentales. Le troisième partie de ces travaux présente une nouvelle méthodologie d'analyse dynamique des structures à forte densité modale. Celle-ci est basée sur une séparation global/local de l'espace des déplacements admissibles via la résolution de deux problèmes aux valeurs propres séparés, permettant ainsi de construire un modèle réduit des déplacements globaux de petite dimension puis, si cela est nécessaire, de prendre en compte les contributions locales par une approche probabiliste. Enfin, la quatrième partie de ces travaux concerne cette fois-ci l'aléa du chargement appliqué. On s'intéresse en particulier à la génération d'accélérogrammes pour la construction de chargements sismiques. On présente une nouvelle méthodologie de construction et de génération d'accélérogrammes, en grande dimension stochastique, permettant de prendre en compte des propriétés physiques et des spécifications issues de l'ingénierie sismique directement au niveau de la loi de probabilité du processus stochastique modélisant l'accélérogramme.

High cycle fatigue (HCF) failure has been studied extensively over the last two decades. Its impact on jet engines is severe enough that may result in engine losses and even life losses. The main requirement for fatigue life predictions is the stress caused by mechanical vibrations. One of the factors which have major impact on the vibratory stresses of bladed disk assemblies is a phenomenon called &ldquo / mistuning&rdquo / which is defined as the vibration localization caused by the loss of cyclic periodicity which is a consequence of inter&amp / #8208 / blade variations in structural properties. In this thesis, component mode synthesis method (CMSM) is combined with nonlinear forced response analysis in modal domain. Newton&amp / #8208 / Raphson and arc length continuation procedures are implemented for the solution. The component mode synthesis method introduces the capability of imposing mistuning on the modal properties of each blade in the assembly. Forced response analysis in modal domain reduces the problem size via mode truncation. The main advantage of the proposed method is that it is capable of calculating nonlinear forced response for all the degrees&amp / #8208 / of&amp / #8208 / freedom at each blade with less computational effort. This makes it possible to make a stress analysis at resonance conditions. The case studies presented in this thesis emphasize the importance of number of modes retained in the reduced order model for both CMSM and nonlinear forced response analysis. Furthermore, the results of the case studies have shown that both nonlinearity and mistuning can cause shifts in resonance frequencies and changes in resonance amplitudes. Despite the changes in resonance conditions, the shape of the blade motion may not be affected.

A content of this diploma thesis is construction design of torsional vibration rubber damper of four-stroke diesel supercharged engine. It` s realized evaluation of crankshaft from aspect of torsional vibrations and checked mechanical stress of crankshaft without using rubber damper. Consequently basic parameters of rubber damper are specified, then checked mechanical stress of crankshaft and designed own construction design of damper.

La volonté d'améliorer le confort acoustique à bord des bateaux sport est à l'origine de cette étude. Pour trouver des améliorations, des modèles S.E.A. ont été utilisés. Ils sont basés sur des modèles numériques d'ensemble coque-carrosserie.La validation des modèles S.E.A. développés est nécessaire pour trouver des solutions d'optimisation. Une fois que les modèles ont été validés, ils sont considérés comme fiables et pourront être appliqués à de nouveaux bateaux similaires.