This thesis presents a new active-passive treatment developed to reduce structural vibrations and their associated radiated sound. It is a contribution to the research of efficient and low cost devices that implement the advantages of active and passive noise control techniques. A theoretical model has been developed to investigate the potential of this new "active-passive distributed absorber". The model integrates new functions that make it extremely stable numerically. Using this model, a genetic algorithm has been used to optimize the shape of the active-passive distributed absorber. Prototypes have been designed and their potential investigated. The device subsequently developed can be described as a skin that can be mechanically and electrically tuned to reduce unwanted vibration and/or sound. It is constructed from the piezoelectric material polyvinylidene fluoride (PVDF) and thin layers of lead. The tested device is designed to weight less than 10% of the main structure and has a resonance frequency around 1000 Hz. Experiments have been conducted on a simply supported steal beam (24"x2"x1/4"). Preliminary results show that the new treatment out-performs active-passive point absorbers and conventional constrained layer damping material. The compact design and its efficiency make it suitable for many applications especially in the transportation industry. This new type of distributed absorber is totally original and represent a potential breakthrough in the field of acoustics and vibration control. / Master of Science

No description available.

No description available.

Os transformadores de potência elétrica produzem um elevado nível de ruído que em alguns casos gera desconforto à comunidade vizinha. O presente trabalho desenvolve um modelo estrutural de elementos nitos que, com carregamento adequado, é capaz de reproduzir o deslocamento, medido durante a operação, de um transformador de potência elétrica. Este modelo estrutural é utilizado para calcular a redução do deslocamento das superfícies deste transformador decorrentes do emprego de absorvedores dinâmicos de vibração. Este modelo estrutural foi desenvolvido para estimar o número de absorvedores dinâmicos, sua massa e sua localização que permitiria reduzir o ruído acústico emitido por este transformador de potência até alcançar níveis de intensidade de som em comformidade com a legislação brasileira. / Electrical power transformers produce a high level of noise, which, in some cases, generate discomfort to the surrounding community. The present work develops a structural model by the Finite Element Method that, with adequate loading conditions, is capable of reproducing the displacement, measured during operation, of the transformer tank. The structural model has been used to compute the displacement reduction of the transformer surfaces by using dynamic vibration absorbers. The structural model was developed to estimate the number of dynamic absorbers, the mass and localization that could reduce the acoustic noise to levels of intensity of sound in accordance to the Brazilian law.

Os transformadores de potência elétrica produzem um elevado nível de ruído que em alguns casos gera desconforto à comunidade vizinha. O presente trabalho desenvolve um modelo estrutural de elementos nitos que, com carregamento adequado, é capaz de reproduzir o deslocamento, medido durante a operação, de um transformador de potência elétrica. Este modelo estrutural é utilizado para calcular a redução do deslocamento das superfícies deste transformador decorrentes do emprego de absorvedores dinâmicos de vibração. Este modelo estrutural foi desenvolvido para estimar o número de absorvedores dinâmicos, sua massa e sua localização que permitiria reduzir o ruído acústico emitido por este transformador de potência até alcançar níveis de intensidade de som em comformidade com a legislação brasileira. / Electrical power transformers produce a high level of noise, which, in some cases, generate discomfort to the surrounding community. The present work develops a structural model by the Finite Element Method that, with adequate loading conditions, is capable of reproducing the displacement, measured during operation, of the transformer tank. The structural model has been used to compute the displacement reduction of the transformer surfaces by using dynamic vibration absorbers. The structural model was developed to estimate the number of dynamic absorbers, the mass and localization that could reduce the acoustic noise to levels of intensity of sound in accordance to the Brazilian law.