The lack of methods for rigorous dynamic analysis of foundations and structures for vibrating machines has resulted in below optimum performance and in some cases reduction of life of machines, structures and foundations. The costs and complexities of these machines make it necessary to conduct proper geotechnical site investigations. and dynamic analyses to obtain the response of the soil, foundation and structure as a system to excitation. In order to highlight the use of dynamic analyses, the response of the foundations and structures were compared to the "rule of thumb" which is based on mass ratio. Furthermore sensitivity analyses were carried out comprising the following variables: • Shear modulus of soil, G • Poisson's ratio of soil,Y • Type of structure (ie raft, table top and multi-storey) • Stiffness of structure • Stiffness of foundation The fundamentals of structural dynamics have not been dealt with in this dissertation. The dynamic analyses were carried out using a finite element analysis program called Strand 7. The results were typical of a finite element analysis, giving stresses, strains, deflections, amplitudes, frequencies and velocities of vibration. The traditional "elastic halfspace model" is deficient as it does not account for soil comprising various layers. The theory has been based on an isolated circular footing. Most foundations are located in soils with layered mediums, are rectangular and in some cases are affected by the interaction of foundations in close proximity. Furthermore there is a need to account for the non-linear effects and properties of soil. It is therefore becoming more attractive to adopt mathematical models of soils using finite elements, where the visco-elastoplastic properties of soils can be realized and modeled. Furthermore the finite element method overcomes limitations such as layering and shapes or foot-prints of foundations. The "rule of thumb" or mass ratio method of design procedure is as follows:- • firstly the requirements of stresses and serviceability must be satisfied. This is usual in a statically loaded system. the ratio of the machine mass to that of the foundation together with the structure should be greater than 3 in the case of a revolving machine and 5 in the case of a reciprocating machine. • in order to obtain uniform settlement of the foundation the distance of the combined centre of gravity of the machine and foundation from the centre of area in contact with the soil is limited to 5% of the corresponding dimension of the foundation. It is evident that the mass ratio lacks accuracy in that there are several parameters that are required to describe the satisfactory performance of a system such as amplitude, frequency and velocity of vibration. The finite element method allows for calibration of the model to account for the real behaviour of the system. Calibration is generally conducted using sensitive transducers called accelerometers. The accelerometers produce power spectral density (PSD) graphs from which deflections and stresses can be back calculated. The deflections and stresses are compared with calculated deflections and stresses. Descriptions of the methods of analysis followed by presentation of results, discussions and interpretations have been included. To motivate the use of dynamic analyses case histories have been presented and discussed. Finally the dissertation concludes with findings of the study together with recommendations for the way forward in terms of research. / Thesis (M.Sc.)-University of Natal, Durban, 2002.

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Orientador: Milton Dias Junior / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-05T03:45:19Z (GMT). No. of bitstreams: 1 Ubinha_JoseAlexandre_M.pdf: 7391942 bytes, checksum: dfd22a1db4bc7dfb566c5fc59bfd5f58 (MD5) Previous issue date: 2005 / Resumo: A identificação de um modelo preciso de fundação flexível e dos parâmetros de desbalanceamento (amplitude e fase) de um sistema girante, através das medições de vibração da máquina, tem sido alvo de constantes pesquisas e desenvolvimento ao longo das últimas décadas. A utilização de programas computacionais, cujos recursos de processamento e visualização de dados são periodicamente atualizados, proporcionou um grande avanço na área de análise de vibrações em máquinas rotativas. Neste contexto, o presente trabalho tem como objetivo a implementação e aplicação de um método híbrido numérico - experimental de determinação dos parâmetros de desbalanceamento e de fundação, que utiliza a resposta ao desbalanço medida durante a partida ou parada da máquina e um modelo numérico preciso do sistema girante. O trabalho apresenta o desenvolvimento teórico da metodologia estudada e discute os aspectos computacionais da implementação numérica do mesmo. O desempenho do procedimento de identificação é verificado numericamente através da simulação de diversos sistemas rotativos e a influência dos diversos fatores que interferem na precisão dos resultados é discutida criteriosamente. Na maioria dos casos, a metodologia apresentou resultados muito bons e verificou-se que a experiência do analista na utilização do método é importante para a obtenção de resultados confiáveis / Abstract: The identification of an accurate model of a flexible foundation and unbalance parameters (amplitude and phase) for a rotating system, through the measurement of the vibration amplitude of the machine, has been subject of frequent researches and development along the last decades. The use of computational software, in which processing resources and data visualization are periodically updated, provided a great progress in the area of vibration analysis in rotating machines. In this context, the present work aims the implementation and application of a hybrid numerical and experimental identification method for the unbalance parameters and the foundation model, through the measurement of the unbalance response during start-up or run-down of the machine and an accurate numerical model of the rotating system This work presents the theoretical development of the this methodology and discusses the computational aspects of the numerical implementation. The performance of the identification procedure is numerically verified through the simulation of several rotating systems and the intluence of many conditions that can affect the accuracy of the method is discussed in detail. In the major part of the cases, the methodology presented very good results and it was observed that the analyst experience in the utilization of method is very important for the achievement of reliable results / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica

Orientadores: Euclides de Mesquita Neto, Edson Antonio Capello Sousa / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica / Made available in DSpace on 2018-08-09T04:23:51Z (GMT). No. of bitstreams: 1 Thomazo_LuizHenrique_M.pdf: 1773463 bytes, checksum: e38435e9b18935ddc2edc19b8b2efac4 (MD5) Previous issue date: 2004 / Resumo: Este trabalho apresenta uma metodologia para a realização de análises dinâmicas estacionárias e transientes em domínios visco-elásticos limitados ou ilimitados, utilizando-se o Método dos Elementos de Contorno. São utilizados como estados auxiliares soluções não-singulares de problemas do semi-espaço e do espaço completo de meios visco-elásticos. Os estados visco-elásticos auxiliares são sintetizados numericamente, tanto no domínio da freqüência, como no domínio do tempo. Os mencionados estados auxiliares são constituídos das soluções em tensão e deslocamento resultantes de cargas espacialmente constantes, aplicadas sob segmentos lineares tanto na superfície de semi-espaços, como no interior de espaços completos. Inicialmente os estados auxiliares são sintetizados numericamente no domínio da freqüência, dando origem à análise de problemas estacionários. Na seqüência estados auxiliares transientes são obtidos a partir da aplicação da transformada de Fourier rápida (FFT) sobre os estados estacionários mencionados. Os estados auxiliares são utilizados para a síntese de uma versão não singular Indireta do MEC (MEC-I) tanto no domínio da freqüência quanto no domínio do tempo. No trabalho ainda é formulada e implementada a inclusão de um corpo rígido interagindo com o meio discretizado pelo MEC-I. O comportamento visco-elástico do contínuo é introduzido pelo princípio da correspondência e são analisados os modelos de histerése constante e de Kelvin-Voigt / Abstract: The main purpose of the present work is to further develop a methodology to perform stationary and transient dynamic analysis of viscoelastic continua by the Boundary Element Method. Numerically synthetized stationary and transient, half-space and full-space auxiliary states are employed to render a non-singular implementation of the indirect version of the Boundary Element Method, IBEM. The auxiliary states used in this word are displacement and traction components stemming from the solution two stress bounary value problems. A constant traction distribution applied at a linear segment over the viscoelastic half-space surface and at the interior of the viscoelastic full-space describe the solutions applied to formulate the BEM. The IBEM is formulated and implemented to render the dynamic solution of bounded and unbounded domains. The interaction of the IBEM mesh with a massless rigid body is also formulated in the context of this work. Viscoelastic effects are included by means of the correspondence principle. The influence of the constant hysteresis and the Kelvin-Voigt damping models are studied. / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestre em Engenharia Mecânica