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by Leung Siu. / Title also in Chinese. / Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 117-118.

La société TRAXENS propose une solution innovante permettant le suivi de l'état d'un conteneur (position, température, chocs, etc.). Ce service est basé sur un capteur sans fil appelé TRAXENS-BOX dont la durée de vie doit être étendue avec un volume de batterie limité. La présence d'une quantité d'énergie vibratoire non négligeable dans l'environnement du conteneur multimodal oriente donc vers la récupération d'énergie vibratoire. L'objectif principal de ce travail de thèse est donc d'identifier une solution permettant de récupérer l'énergie vibratoire dans le contexte particulier du conteneur caractérisé notamment par des vibrations verticales, aléatoires et très basses fréquences.On commence donc par introduire un modèle complet de récupérateur d'énergie vibratoire électromagnétique basé sur un oscillateur à un degré de liberté avant d'étudier son comportement lorsqu'il est soumis à des excitations harmoniques puis aléatoires ; on peut alors en déduire des règles de dimensionnement permettant la conception d'un récupérateur d'énergie vibratoire linéaire hautes performances. Le modèle est ensuite utilisé pour prouver l'intérêt de l'introduction d'une non-linéarité de Duffing dans la raideur du récupérateur, notamment sous les vibrations du transport routier. La partie théorique se termine alors par une comparaison mettant en opposition plusieurs configurations de récupérateur dans le cadre de l'application TRAXENS-BOX ; la solution retenue est l'utilisation d'une raideur non-linéaire HSLD (High Static Low Dynamic).On propose ensuite la conception optimisée puis la fabrication d'un démonstrateur linéaire hautes performances qui nous permet de valider les règles de dimensionnement énoncés dans la partie théorique. Enfin, le démonstrateur est modifié de manière à obtenir un comportement HSLD et prouver la faisabilité de ce concept. / TRAXENS company proposes an innovative solution to enable the monitoring of shipping containers (position, temperature, shocks, etc.). This service is based on a wireless sensor called TRAXENS-BOX whose lifetime must be extended by maintaining a small energy storage volume. In the environment of a shipping container, the presence a non-negligible amount of vibration makes energy harvesting a viable solution. The main objective of this work is to identify the means to scavenge vibration energy in the singular context of shipping container characterized by very low frequency, random and vertical vibration.First, a general electromagnetic vibration energy harvester model based on a single degree of freedom oscillator is introduced before analyzing its behavior when submitted to harmonic and random excitations ; rules to design high performances linear vibration energy harvester are then deduced. Henceforth, the model is used to prove the interest of introducing a Duffing nonlinearity in the harvester stiffness, especially under road induced vibration. The theoretical part ends with performance comparison between several harvester configurations within TRAXENS-BOX context ; the chosen solution is the use of a HSLD (High Static Low Dynamic) stiffness.Then, the design and fabrication of a linear high performances prototype is conducted to validate design rules drawn from the theoretical part. Finally, a HSLD stiffness is added to the prototype to prove the feasibility of this technique.

Orientador: Fernando de Azevedo Silva / Banca: José Elias Tomazini / Banca: Carlos de Andrade Souto / Resumo: Equipamentos aeronáuticos embarcados podem ser submetidos a elevados níveis de vibração durante o vôo. Normas internacionais especificam os níveis de vibração que os componentes de uso civil e militar devem ser capazes de suportar de acordo com o emprego e com o tipo de aeronave ao qual serão integrados. Em alguns equipamentos aeronáuticos considerações de geometria e massa limitam severamente as opções de projeto no sentido de evitar ressonâncias na faixa de freqüência de qualificação do equipamento, o que pode fazer com que componentes eletrônicos internos sofram níveis muito elevados de vibração. O presente trabalho visa à redução das cargas dinâmicas com a introdução de dispositivos do tipo passivo de isolamento de vibração. Para redução e amortecimento de vibrações foram utilizados materiais com baixa rigidez, mas resistência mecânica suficiente para suportar os esforços dinâmicos. Diversas configurações de isoladores fabricadas com vários materiais (poliuretano, silicone, polietileno e uma combinação de polietileno e silicone) foram ensaiadas. A solução adotada foi analisada também por simulações numéricas pelo método dos elementos finitos, obtendo-se respostas em freqüência (acelerações), deslocamentos e tensões. Os deslocamentos e os valores máximos de tensão calculados apresentaram valores inferiores aos máximos admissíveis. Os resultados numéricos e experimentais apresentaram boa correlação entre si. A combinação de polietileno e silicone obteve o melhor desempenho permitindo uma redução de aproximadamente 85% do nível de vibração RMS sobre o equipamento e os componentes eletrônicos. / Abstract: Aeronautical systems can be submitted to high levels of vibration during flight. International standards specify the vibration levels that this kind of systems must withstand according to its function and the aircraft where it will be integrated. For some of these systems, geometry and mass properties are strictly defined by some design issues and therefore cannot be changed in order to achieve better dynamical properties and avoid resonance peaks or high vibrations level in internal electronic components. The main goal of this work is to reduce the dynamic loads acting on sensible electronic equipment using passive vibration isolators. Materials witch provide low suspension resonance frequencies but enough mechanical strength and a medium loss factor are used to build vibration isolators. Some simple vibration isolators devices made by polymers are evaluated by dynamic tests performed with an airborne equipment. The devices tested are made by polyurethane, silica, polyethylene and a combination of the two formers. The dynamical behavior of the configuration with better performance is also analyzed through numerical simulation by finite element method. The numerical results for the dynamic responses are compared with the experimental results and shown good agreement. The combination of silica and polyethylene have show the better performance supporting appropriately the dynamic loads and reducing the RMS vibration level measured in the electronic components in 85%. / Mestre

To visualize vibrations in mechanical systems, e.g., machine tools, their movements are measured by means of suitable sensors. The signals from these sensors are processed and displayed as animated pictures on a computer screen. Accelerometers have been chosen as the most suitable sensors for this purpose. Their main advantages include small size, wide sensitivity range and frequency bandwidth. In addition, accelerometers measure signals with reference to the Earth, so they do not require stable fixtures such as used with cameras or lasers. The visualization methodology involves nine accelerometers attached to a mechanical component, e.g., a dynamometer's platform. Vibration signals were acquired using a data acquisition (DAQ) system which is controlled by a LabVIEW��-based program. These signals are processed to suppress errors and convert acceleration into generalized coordinate that describes motion of the visualized component as a rigid plate's movement in 3-D space. The animation is accomplished by displaying a time series of pictures representing instantaneous position of the plate. The animation program employs homogenous coordinate transformation to draw 3-D 'wireframe' pictures. Since various errors distort the measured signals, the animated movement may be inaccurate. The knowledge of a mathematical model of the system whose vibrations are animated allows detection and suppression of distortions. For this purpose, the signals measured from the actual dynamic system are compared with the signals simulated by the system's model subjected to the same excitation as the actual system. Discrepancies between the actual and simulated signals are detected. They are analyzed to identify possible sources and forms of distorting signals. As the next step, the measured (actual) signals are corrected by removing estimated distortions. A methodology and software package capable of performing all functions necessary to implement the visualization of vibration have been developed in this research using LabVIEW�� programming environment. As compared with commercial software for experimental modal analysis, the most distinctive feature of the developed package is improved accuracy achieved by applying concepts utilized in control theory, such as modeling of multi-input-multi-output (MIMO) systems and on-line system identification for the model development and correction of signals. / Graduation date: 1998

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A State-Switched Absorber (SSA) is a device capable of instantaneously changing its stiffness, thus it can switch between resonance frequencies, increasing its effective bandwidth as compared to classical tuned vibration absorbers for vibration control. This dissertation considers the performance of the SSA for vibration suppression of continuous systems, specifically a beam and a plate. The SSA tuning frequencies and attachment point on the continuous body were optimized using a simulated annealing algorithm. It was found that an optimized SSA outperforms and optimized TVA at controlling vibrations of both a beam and a plate. These performance gains were also observed experimentally employing magneto-rheological elastomers to achieve a stiffness change. This dissertation also considers zero strain switching criteria and the maximum work extraction switching rule used by the SSA. The zero strain switching criteria ensures the system remains stable as no energy is added or released across a switch event. The maximum work extraction switching rule is designed to maximize the power dissipated by the absorber, but also guarantees minimization of the motion of the base to which the absorber is attached.

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