Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 99-101).

Thesis (M.S.)--University of Wisconsin--Madison, 1967. / eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin, 1967. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains xi, 97 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 62-63).

Honeycomb sandwich panels, formed by bonding a core of honeycomb between two thin face sheets, are in wide use in aerospace, automotive and marine applications due to their well-known excellent density-specific properties. There are many technological methods of damping vibrations, including the use of inherently lossy materials such as viscoelastic materials, viscous and friction damping and smart materials such as piezoelectrics. Some have been applied to damping of vibrations, in particular to sandwich panel and honeycomb structures, including viscoelastic inserts in the cell voids. Complete filling of the cell with foam, viscoelastic or particulate fillers have all been demonstrated to improve damping loss in honeycombs. However, the use of an additional damping material inside the core of a sandwich panel increases its mass, which is often deleterious and may also lead to a significant change in dynamic properties. The work presented in this thesis explores the competing demands of vibration damping and minimum additional mass in the case of secondary inserts in honeycomb-like structures. The problem was tackled by initially characterising the main local deformation mechanism of a unit cell within a sandwich panel subjected to vibration. Out-of-plane bending deformation of the honeycomb unit cell was shown to be the predominant mode of deformation for most of the honeycomb cells within a sandwich panel. The out-of-plane bending deformation of the honeycomb cells results in relatively high in-plane deformation of the cells close to the skins of the sandwich panels. It was also highlighted that the magnitude and loading of the honeycomb unit cell are dependent on its location within the honeycomb or sandwich panel and the mode shape of the panel. An optimisation study was carried out on diverse honeycomb unit cell geometries to find locations at which the relative displacement between the honeycomb cell walls of the void is maximal under in-plane loadings. These locations were shown to be dependant of the nature of the loading, i.e. in-plane tension/compression or in-plane shear loading of the honeycomb unit cell and the unit cell geometry. Analytical expressions and finite element analyses were used to investigate the partial filling of the honeycomb unit cell with a damping material, in this case a viscoelastic elastomer, in the target locations identified previously where the relative displacement between the honeycomb cell walls is maximal. Damping inserts in the form of ligaments partially filling the honeycomb cell void have shown to increase the density-specific loss modulus by 26% compared to cells completely filled with damping material for in-plane tension/compression loading. The form of the damping insert itself was then analysed for enhancement of the dissipation provided by the damping material. The shear lap joint (SLJ) damping insert placed in the location where the relative displacement between the honeycomb cell walls of the void is maximal under in-plane loadings was characterised with very significant damping improvements compared to honeycomb cells completely filled with viscoelastic material. A case study of a cantilever honeycomb sandwich panel with embedded SLJ damping inserts demonstrated their efficiency in enhancing the loss factor of the structure for minimum added mass and marginal variation of the first modal frequency of the structure. Partial filling of the cells of the honeycomb core was shown to be the most efficient at increasing damping on a density basis.

This thesis reports on a design and modeling of a micro-machined gyroscope. The proposed sensor is a dual mass type, electro-statically driven to primary mode oscillation and senses, capacitively, the output signal. Full decoupling between drive and sense modes minimizes the mechanical crosstalk and based on this a novel gyroscope is designed and modeled which has separate sensing and driving masses. The dual mass gyroscope is designed such that driving and sensing resonant frequency is 23101 Hz with 0% mismatch (in simulation)with quality factor of 31.6227 and bandwidth of 730.51Hz. The gyroscope when actuated in simulation with 25V ac and 10V dc showed sensing capacitance variation of 126aF for 1 rad/s with base capacitance of 244.16fF. To the design of the gyroscope a new semi automatic tool was formulated for the noise analysis and noise based optimization of the resonant MEMS structures. Design of a sensitive gyroscope needs to take into account the noise shaping induced by damping phenomena at micro scale and is critical for optimization. The analysis was further extended to the design of the gyroscope and estimation shows that there is a trade of between the S/N ratio and the sensitivity and the design could be made much better in-terms of S/N by tuning its resonant frequency to 10⁶Hz. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Experience shows that the noise and sound quality in vehicles are often a recurring criticism. The bodies of modern vehicles consist predominantly of thin sheets of metal. It is hard to prevent the excitation of bending vibrations and the subsequent emission of disturbing noise while driving. The noise spectrum in a car that can be heard by the driver is from ”latent roar” to ”chattering” noise of the body and engine. In automotive vehicles damped materials, especially plastics or materials made from sheet metal and surface damping treatments, are used. Those have high internal energy losses and damp sound oscillatory systems found in the body or interior of cars. A further advantage of such treated components is that they are applied to existing components working over wide temperature and frequency ranges. Many companies provide such ”sound-absorbing compounds”. The requirements for these damping materials are high temperature-resistance, water repellence, fuel and oil-resistance and good adhesion to the base material [17]. The acoustic properties, especially the damping of the plate vibrations through rubber are of interest. the question arises how can the damping coeficient of coated metal sheets can be measured and secondly, by how much the road noise is reduced when built-in sheets are coated with a known damped material. With the Oberst Bar Test Method (named after Dr. H. Oberst) the properties are determined of the internal damping materials that can be used to simulate mechanical constructions to determine damping of larger surfaces. This method describes a laboratory test procedure for measuring the mechanical properties of damped materials. A block diagram of the test system consisting of a damped material bonded to a vibrating cantilever steel bar is shown in figure 2.1. This method is useful for testing materials such as metals, enamels, ceramics, rubbers, plastics, reinforced epoxy matrices and wood. In addition to damping measurement, the test allows for the determination of the Young’s modulus E of the material. E is calculated from the resonance frequency of a given mode and from the physical constants of the bar. By associating the damping factor with the Young’s modulus, a complex quantity is defined which is called the Complex Modulus of Elasticity. Measurements of dynamic mechanical properties are also useful in the research on the molecular structure of materials.

No description available.

Orientador: Paulo José Paupitz Gonçalves / Banca: Marcos Silveira / Banca: Douglas Domingues Bueno / Resumo: O isolamento de vibração é a técnica mais utilizada atualmente para a proteção de mecanismos e estruturas que sofrem excitação, seja ela por choque/impacto, seja ela harmônica. Este trabalho adiciona ao isolador de vibração comum, composto por molas e amortecedores, um elemento conhecido como inerter, que recentemente tem chamado bastante a atenção da comunidade científica, e também, separadamente, adiciona amortecedores não lineares, com o intuito de avaliar a influência destes elementos no isolamento. As curvas de transmissibilidade obtidas, que indicam a performance do isolamento à excitação harmônica, para os isoladores com inerter são comparadas à de um isolador comum composto somente por uma mola, e entre elas, enquanto que as curvas obtidas para os isoladores com amortecedores não lineares são comparadas entre si e à de um isolador comum com amortecimento linear. Os resultados obtidos mostram que a adição do inerter aos isoladores de vibração pode ser muito benéfica para o isolamento em determinadas faixas de frequência, mas em outras não, e tais faixas dependem de como o isolador é construído. Além disso, os isoladores com inerter são benéficos principalmente para sistemas subamortecidos. Os isoladores subamortecidos com inerter apresentaram características de isolamento diferentes uns dos outros, o que os leva a serem aplicados em diferentes situações. Os resultados obtidos para os isoladores com amortecedores não lineares mostraram que tais sistemas também podem mel... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The vibration isolation is currently the most used technique for protecting mechanisms and structures which are under shock/impact or harmonic excitation. This work presents to the common vibration isolator, consisted by springs and dampers, an element known as inerter, which recently has took great attention in the scientific community, and also presents the use of non-linear dampers to analyze the influence of these elements on isolation. The transmissibility curves obtained, which indicate the performance of the isolation for systems under harmonic excitation, for the isolators with the inerter element are compared with the spring-damper isolator frequency response as well the isolators with non-linear damping. The results obtained show that the addition of the inerter element can be beneficial for the isolation performance in a frequency range, but degrades the high frequency isolation, and they depend on how the isolator is built. Besides, the isolators with inerter are beneficial mainly for underdamped systems. The different underdamped systems with inerter presented unique isolation characteristics. The results obtained for the isolators with non-linear dampers presented that such systems can also improve the isolation in certain frequency ranges when compared to an isolator with linear damping. / Mestre

Resumo: Os desastres naturais são um grande interesse em engenharia, pois são fenômenos de caráter dinâmico. O desastre natural estudado neste trabalho é a ocorrência de ações sísmicas sobre estruturas, mais precisamente a ação das vibrações do terremoto em estruturas civis. Amortecedores de massa sintonizados (AMS) ou Absorvedores Dinâmicos são dispositivos para controle passivo de vibrações em máquinas, prédios ou outras estruturas. Com o passar dos anos esses dispositivos foram aprimorados e tornaram-se mais versáteis. Neste contexto, apresentam-se um dispositivo considerando uma dependência cúbica do deslocamento na rigidez do elemento elástico acoplado à massa principal e conectada ao aparelho, ambos em paralelo com um amortecimento viscoso linear. O problema é modelado através de equações diferenciais ordinárias não lineares que serão linearizadas em torno de seu ponto de equilíbrio. Como forma de excitar o AMS, foi utilizada uma excitação sísmica sendo esta uma função espectral real, o espectro Tajimi- Kanai, já que em uma situação real, as propriedades do solo local produzem alteração nas propriedades dinâmicas, causando assim uma instabilidade na estrutura onde foram utilizados parâmetros para encontrar um comportamento caótico no sistema. Como forma de minimizar as vibrações causadas pela excitação sísmica foi desenvolvido um controle hibrido estrutural. A técnica de controle utilizada tem o objetivo de minimizar as vibrações e reduzir o movimento caótico do sistema a um ponto estável. Comprovou-se que a estratégia de controle híbrido adotado demonstra eficiência para este tipo de situação e pode ser utilizada como forma de auxiliar na atenuação de danos provocados às estruturas, evitando prejuízos econômicos, perdas biológicas e materiais