Since their invention in the early 1900s, Tuned Vibration Absorbers (TVAs) have shown to be effective in suppressing vibrations of machines and structures. A vibration absorber is a vibratory subsystem attached to a primary system. It normally consists of a mass, a spring, and a damper. Mounted to the primary system, a TVA counteracts the motions of the primary system, "absorbing" the primary structure's vibrations. A conventional passive TVA, however, is only effective when it is tuned properly, hence, the name "tuned" vibration absorber. In many practical applications, inevitable off-tuning (or mistuning) of a TVA occurs because of the system's operating conditions or parameter changes over time. For example, the mass in a building floor could change by moving furnishings, people gathering, etc., which can "off-tune" TVAs. When TVAs are off-tuned, their effectiveness is sharply reduced. Moreover, the off-tuned TVAs can excessively amplify the vibration levels of the primary structures; therefore, not only rendering the TVA useless but also possibly causing damage to the structures. Off-tuning is one of the major problems of conventional passive TVAs. This study proposes a novel semiactive TVA, which strives to combine the best features of passive and active TVA systems. The semiactive TVA in this study includes a Magneto-Rheological (MR) damper that is used as a controllable damping element, for providing the real-time adjustability that is needed for improving the TVA performance. This study is conducted in two phases. The first phase provides a numerical investigation on a two-degree-of-freedom (2-DOF) numerical model in which the primary structure is coupled with a TVA. The numerical investigation considers four semiactive control methods for the MR TVAs, in addition to an equivalent passive TVA. These numerical models are optimally tuned using numerical optimization techniques to compare each TVA system. These tuned systems then serve as the basis for numerical parametric studies for further evaluation of their dynamic performance. The parametric study covers the effects of damping, as well as system parameter variations (off-tuning). The results indicates that semiactive TVAs are more effective in reducing the maximum vibrations of the primary structure and are more robust when subjected to off-tuning. Additionally, the numerical study identifies the "On-off Displacement-Based Groundhook control (on-off DBG)" as the most suitable control method for the semiactive TVA among control methods considered in this study. For the second phase of this study, an experimental study is performed on a test setup, which represents a 2-DOF structure model coupled with an MR TVA. Using this setup, a series of tests are conducted in the same manner as the numerical study to evaluate the performance of the semiactive TVA. The primary purposes of the experiment are to further evaluate the most promising semiactive control methods and to serve as a "proof-of-concept" of the effectiveness of this MR TVA for floor vibration applications. The results indicate that the semiactive TVA with displacement-based groundhook control outperforms the equivalent passive TVA in reducing the maximum vibrations of the primary structure. This confirms the numerical result that identifies on-off DBG control method as the "best" control method for the MR TVA among four semiactive control schemes considered. The experimental robustness study is also conducted, focusing on the dynamic performance of both the passive and the semiactive TVAs when the mass of the primary system changes (mass off-tuning). The mass of the primary system varied from -23 % to +23 % of its nominal value by adding and removing external masses. The experimental results show that the semiactive TVA is more robust to changes in the primary mass than the passive TVA. These results justify the benefits of the use of semiactive MR TVAs in structures, such as building floor systems. The off-tuning analysis further suggests that, in practice, semiactive TVAs should be tuned slightly less than their optimum in order to compensate for any added masses to the structure. Additionally, the lessons learned from the experimental study have paved the way for implementing the semiactive MR TVA on a test floor, which is currently in progress under a separate study. / Ph. D.

Cette recherche porte sur le phénomène des vibrations éoliennes de structures cylindriques, une instabilité aérodynamique qui affecte généralement les corps non-profilés. Le détachement tourbillonnaire causé par l'interaction fluide-structure peut amener une structure en résonance si la fréquence d'émission tourbillonnaire correspond à une de ses fréquences naturelles. Il est possible d'estimer les vitesses critiques de ce détachement en appliquant la relation de Strouhal qui utilise la fréquence naturelle de la structure, la vitesse d'écoulement et le nombre de Strouhal propre à la géométrie extérieure. Les expérimentations antérieures ont démontré que différents types de détachement tourbillonnaire se produisaient lors de cette instabilité, les dit 2P et 2S par exemple. Chaque type de détachement est associé à une différente courbe ou"branche" d'amplitude de vibration en fonction de la vitesse. Il a également été observé que ces deux courbes d'amplitude peuvent être présentes pour une même plage de vitesse, causant ainsi un hystétéris au phénomène. En utilisant un montage expérimental à très faible amortissement mécanique, ces branches d'amplitude ont été observées et étudiées pour extraire les caractéristiques des comportements instationnaire et permanent. L'ajout d'un nouveau système de visualisation haute vitesse a permis d'observer les types de détachement tourbillonnaire associés à ces branches. Les données obtenues étaient cohérentes avec la littérature et présentaient certains éléments de nouveauté. Une modélisation semi-empirique basée sur les travaux de Scanlan et les données expérimentales ont permis de déterminer les paramètres aérodynamiques nécessaires à sa formulation. Une solution numérique a été mise au point et le développement d'un code numérique a permis de reproduire les comportements vibratoires observés expérimentalement. Afin de recréer certains comportements, tels que la composante hystérétique du phénomène, l'utilisation de générateurs de nombres aléatoires s'est avérée indispensable.

Ce projet de recherche dans le domaine du génie parasismique concerne la vulnérabilité des bâtiments contenant de la maçonnerie non armée (MNA). Ce matériau de construction a longtemps été utilisé dans la construction d'écoles, d'hôpitaux et d'autres bâtiments jugés comme prioritaires au niveau de la sécurité du public selon le code national du bâtiment canadien (CNBC). Suite, entre autres, au séisme du Saguenay en 1988 une inquiétude s’est présentée au niveau des dangers associés à la présence de MNA pour les occupants de ces bâtiments publics supposés sécuritaires. Cette recherche s’intégre donc à l’initiative du Réseau canadien pour la recherche parasismique (RCRP) visant à l’établissement de procédures pour l’inspection et la réhabilitation de bâtiments jugés prioritaires, construits avant l’implantation de la conception parasismique. Les objectifs de cette recherche comprennent la documentation de la présence de MNA dans un échantillon de bâtiments dans la région de Sherbrooke, l’évaluation des propriétés dynamiques de ces bâtiments et l’utilisation de ces propriétés pour la modélisation de bâtiments existants sur un logiciel commercial de calcul structural. Les efforts de recherche portent sur la détermination des propriétés dynamiques pour des écoles de la commission scolaire de la Région-de-Sherbrooke (CSRS). L’échantillon de bâtiments est principalement de type charpente de béton avec murs de remplissage (BMR) suite à l’analyse statistique des types de charpentes présentes dans le parc immobilier de la CSRS. L’instrumentation des bâtiments à l’aide de capteurs de vitesse a permis de mesurer les vibrations ambiantes des bâtiments sélectionnés. L'analyse des données obtenues à l’aide de techniques d'analyse numérique telles que la décomposition dans le domaine fréquentiel (FDD) a permis d'obtenir l’amortissement, la période fondamentale et les déformées modales pour onze bâtiments comportant des murs de remplissage en maçonnerie non armée. Enfin, les résultats obtenus ont été comparés à des études similaires dans les régions du Centre-du-Québec et de Montréal.

No description available.

A consequence of high speed rail transportation is the generation of elevated ground borne vibrations. This thesis presents several original contributions towards the prediction of these vibrations. Firstly, a new three dimensional finite element model capable of vibration prediction was developed. Its main feature was its ability to model complex track geometries while doing so through a fully coupled vehicle-tracksoil system. Model output was compared to experimental results obtained during this thesis and also to independent data sets. It was shown to predict velocity time histories, vibration frequency spectrums and international vibration descriptors with high accuracy. An appraisal of the suitability of a finite difference time domain modelling approach for railway vibration prediction was also undertaken. This resulted in the development of a new ‘higher order’ perfectly matched layers absorbing boundary condition. This condition was found to offer higher performance in comparison to current alternative absorbing boundary conditions. Field work was then undertaken on high speed lines with varying embankment conditions in Belgium and England. Vibration data was recorded up to 100m from each track and geophysical investigations were performed to determine the underlying soil properties. The results were used for numerical model validation and also to provide new insights into the effect of various embankment conditions on vibration propagation. It was found that embankments generate higher frequency excitation in comparison to nonembankment cases and that cuttings generate higher vibration levels than noncuttings. Once validated the finite element model was used to provide new insights into the effect of train speed, embankment constituent materials and railway track type on vibration levels. It was found that the shape and magnitude of ground vibration increased rapidly as the train’s speed approached the Rayleigh wave speed of the underlying soil. It was also found that ballast, slab and metal tracks produced similar levels of vibration and that stiffer embankments reduced vibration levels at distances near and far from the track. Two vibration mitigation techniques were also explored through numerical simulation. Firstly, an analysis was undertaken to determine the ability of a new modified ballast material to actively isolate vibration within the track structure. Secondly, wave barrier geometries were investigated to optimise their performance whilst minimising cost. It was found that barrier depth was the most influential parameter, whereas width had little effect. Additionally, geometry optimisation was found to result in a 95% cost saving in comparison to a base case. Using a vast array of results generated using the previously developed finite element model, a new empirical prediction model was also developed, capable of quickly assessing vibration levels across large sections of track. Unlike currently available empirical models, it was able to account for soil properties in its calculation and could predict a variety of international vibration metrics. It was shown to offer increased prediction performance in comparison to an alternative empirical model.

No description available.

Les matériaux viscoélastiques sont utilisés dans tous les domaines de l'ingénierie et des systèmes mécaniques, de l'électroménager, spatial, l'automobile, l'aéronautique ou le génie civil (ponts...) grâce à leur capacité d’amortir les chocs ou de filtrer les vibrations. Ce travail constitue une contribution à l’étude du comportement dynamique non linéaire des composants viscoélastiques notamment les élastomères. Dans ce mémoire, on introduit, d’abord, les propriétés mécaniques des élastomères, pour les aspects viscoélasticité et friction. Un rappel des différents phénomènes physiques et une liste non-exhaustive des modèles existants dans la littérature sont présentés. Ensuite, on propose des techniques expérimentales afin de décrire le comportement dynamique sous sollicitations uniaxiales d’un élastomère. Une description des bancs d’essais, des chaines d’analyse vibratoire, des méthodes de traitement des données des essais et d’analyse des mesures expérimentales est détaillée dans ce manuscrit. Une nouvelle approche du modèle de Maxwell généralisé a été proposée pour décrire le comportement dynamique du composant viscoélastique. Ce modèle permet une description précise et une bonne connaissance du comportement dynamique des composants viscoélastiques en fonction de l’amplitude, de la précharge et de la fréquence. La dissipation d'énergie identifiée sous forme d'amortissement peut être issue de l'amortissement intrinsèque des matériaux polymère comme de la friction aux interfaces dans le cas de composants caoutchoucs non adhérisés sur les pièces, dans ce travail, un nouveau modèle visco-tribologique a été développé en couplant les propriétés rhéologiques linéaires du modèle de Maxwell généralisé et le modèle de frottement de Dahl pour la description du comportement de frottement hystérétique des liaisons viscoélastiques non adhérisées. / Viscoelastic materials are used in all areas of engineering and mechanical systems, appliances, aerospace, automotive, aerospace and civil engineering (bridges...) through their ability to absorb shock and vibration filtering. This work is a contribution to the study of nonlinear dynamic behavior of viscoelastic components particularly elastomers. In this dissertation, we introduced the mechanical properties of elastomers, for both viscoelasticity and friction aspects. A review of the different physical phenomena and a non-exhaustive list of existing models in the literature are presented. Then, we propose experimental techniques to describe the dynamic behavior under uniaxial stress of an elastomer. A description of test benches, vibration analysis chains, methods of processing data and analysis of experimental measurements is detailed in this manuscript. A new approach of generalized Maxwell model was proposed to describe the dynamic behavior of viscoelastic component. This model allows an accurate description and a good knowledge of the dynamic behavior of viscoelastic components depending on amplitude, frequency and preload. Energy dissipation identified as damping can be from intrinsic damping of the polymer as friction at the interfaces in case of not bonded rubber component to mechanical part, a new viscoelastic model tribological was developed by combining the rheological properties of linear generalized Maxwell model and the Dahl friction model for describing the behavior of viscoelastic hysteretic friction of not bonded connections.

Os modos vibracionais localizados dos pares H-H-, D-D- e H-D- em KCl, KBr, KI, RbCl e NaCl foram estudados para diversas configurações. As frequências dos modos infravermelho ativos determinados experimentalmente mostram boa concordância com o modelo de dois osciladores harmônicos acoplados. A largura de linha para os diferentes modos nos cristais examinados é discutida. A dependência com a temperatura da largura de linha para os modos transversais T1 e T2 no sistema KCl+ H- H-, indica que o alargamento das mesmas é devida ao \"mecanismo de decomposição\", no qual dois fônons são criados. Estes fônons são devidos ao decaimento do modo localizado em fase num fônon acústico da rede e num fônon localizado fora de fase. Propriedades gerais, como a lei de Ivey e diversas outras particularidades dos halogenetos alcalinos estudados são apresentadas / The localized vibrational modes of H-H-, D-D- and H-D- in KCl, KBr, KI, RbCl and NaCl were studied for different pair configurations. The measured frequencies of the infrared active modes were found to be in good agreement with a model of two coupled harmonic oscillators. The line width for different modes in the salts studied is discussed. The temperature dependence for the transversal modes T1 and T2 of the line width for the H- H- pairs in KCl indicates that the broadening of these lines is due to the \"decomposition mechanism\", that generates two phonons. The generated phonons due to the decay of the localized phonon that corresponds to the out of phase vibration of the H- H- pair. The general properties, as the Ivey law and several particulars of the properties in the alkali-halides studied are presented

Since the identification, in the UK, of the need for further information on the dynamic loading of grandstands in the early 1990s, a number of research projects have investigated the issues relating to dynamic loading of structures due to groups of people participating in synchronised activities. These studies have, to date, largely focused on producing load models to accurately represent the dynamic crowd load and the human-structure interaction. However, whilst the vibrational response of grandstand structures is becoming better understood, the question arises as to what level of dynamic response is acceptable to the users. Currently there is very little experimental data available regarding human perception of vibrations in such crowd loading situations. As a result those producing design standards and design guides have very little information on which to base serviceability requirements. To address this, tests have been carried out at the University of Bath using a section of grandstand, whose dynamic properties could be varied, with the aim of developing acceptability criteria. Groups of participants were subjected to a range of vibrations induced by selected members of the group jumping in synchrony. Both those seated and jumping during the tests were asked to rate their perception and emotion of each vibration as well as the acceptability of the vibration in a real grandstand situation. These ratings were then used to statistically model perception and emotion to find the key vibration characteristics influencing the human response of both the seated and jumping participants prior to developing acceptability curves for each group. It was found that those seated are more sensitive to vibrations than those jumping to create them. The response of the jumpers is relatively simple and can be fairly accurately modelled using just a single variable namely the square of vertical RMS displacement. The seated response is much more complex but can be relatively accurately represented using logarithm of vertical RMS acceleration. The proposed acceptability criteria and load model generally tie in well with previously published guidelines provided that the serviceability criteria are in the same format as the original research upon which they were based (i.e. peak accelerations).

This thesis examines the quantification of uncertainty in real-world engineering systems using the multilevel Monte Carlo method. It is often infeasible to use the traditional Monte Carlo method to investigate the impact of uncertainty because computationally it can be prohibitively expensive for complex systems. Therefore, the newer multilevel method is investigated and the cost of this method is analysed in the finite element framework. The Monte Carlo and multilevel Monte Carlo methods are compared for two prototypical examples: structural vibrations and buoyancy driven flows through porous media. In the first example, the impact of random mass density is quantified for structural vibration problems in several dimensions using the multilevel Monte Carlo method. Comparable eigenvalues and energy density approximations are found for the traditional Monte Carlo method and the multilevel Monte Carlo method, but for certain problems the expectation and variance of the quantities of interest can be computed over 100 times faster using the multilevel Monte Carlo method. It is also tractable to use the multilevel method for three dimensional structures, where the traditional Monte Carlo method is often prohibitively expensive. In the second example, the impact of uncertainty in buoyancy driven flows through porous media is quantified using the multilevel Monte Carlo method. Again, comparable results are obtained from the two methods for diffusion dominated flows and the multilevel method is orders of magnitude cheaper. The finite element models for this investigation are formulated carefully to ensure that spurious numerical artefacts are not added to the solution and are compared to an analytical model describing the long term sequestration of CO2 in the presence of a background flow. Additional cost reductions are achieved by solving the individual independent samples in parallel using the new podS library. This library schedules the Monte Carlo and multilevel Monte Carlo methods in parallel across different computer architectures for the two examples considered in this thesis. Nearly linear cost reductions are obtained as the number of processes is increased.