Made available in DSpace on 2014-06-11T19:28:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-14Bitstream added on 2014-06-13T18:57:52Z : No. of bitstreams: 1 agostini_ce_me_bauru.pdf: 983936 bytes, checksum: 820b8b8253ca5eab2b12c27892c83928 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho, analisaram-se as freqüencias natuais (axiais, torsionais e de flexão) e as respostas em frequencia de um rotor vertical com um disco rígido na extremidade através da análise modal clássica e complexa. A equação que governa o movimento foi obtida através da formulação Lagrangeana. O modelo considerou os efeitos à flexão, torção e deformação axial do eixo, além dos efeitos giroscópicos e gravitacionais. o método dos elementos finitos foi utilizado para discretização da estrutura em elementos cilíndricos vazados com 12 graus de liberdade. As matrizes de massa, rigidez e giroscópia foram explicitadas de forma consistente. A análise modal tradicional, normalmente aplicada a estrutura estacionárias, não considera uma importante característica das máquinas rotativas que são os modos de precessão direta e retrógrada. Inicialmente, através da análise modal clássica, foram obtidas as frequencias naturais axionais e torsionais no eixo estacionário, já que estas não sofrem influência dos efeitos giroscópicos. Posteriormente a investigação foi executada através da análise modal complexa. Este tipo de ferramenta, que se baseia na utilização de coordenadas direcionais para descrever o comportamento dinâmico do eixo rotativo, permite a decomposição dos modos do sistema em dois submodos, sendo um direto e outro retrógrado. Dessa forma, consegue-se visualizar de maneira clara a órbita e a direção do movimento precessional em torno da linha não deformada do eixo rotativo. Um programa de elementos finitos foi desenvolvido utilizando o software MATLAB e simulações numéricas foram efetuadas de forma a validar o modelo construído. Foram obtidas as frequencias naturais e a resposta forçada em frequencia direcional (dFRF), com o uso da análise modal complexa, para um rotor vertical simples e também para uma coluna de perfuração típica utilizada na construção de poços de petróleo / In this study, natural frequencies were analyzed (axial, torsional and flexural) and frequency response of a vertical rotor with a hard disk at the edge through the classical modal and complex analysis. The equation that rules the movement was obtained through the Lagragian formulation. The model considered the effects of bending, torsion and axial deformation of the shaft, besides the gravitational and gyroscopic effects. The finite element method was used to discretize the structure into hollow cylindrical elements with 12 degrees of freedom. Mass, stiffness and gyroscopic matrices were explained consistently. The classical modal analysis, usually applied to stationary structures, does not consider an important characteristic of rotating machinery which are the method of forward and backward whirl. Initially, through the traditional modal analysis, axial and torsional natural frequencies were obtained in a static shaft, since they do not suffer the influence of gyroscopic effects. Later research was performed by complex modal analysis. This type of tool, based on the use of complex coordinates to describe the dynamic behavior of rotating shaft, allows the decomposition of the system in two submodes, backward and forward. Thus, it is possible to clearly visualize that the orbit and direction of the precessional motion around the line of the precessional motion around the line of the rotating shaft is not deformed. A finite element program was developed using MATLAB, and numerical simulations were performed to validate this model. Natural frequencies and directional frequency forced response (dFRF) were obtained using the complex modal analysis for a simple vertical rotor and also for a typical drill string used in the construction of oil wells

This dissertation forms part of a research project assigned to the University of Pretoria by Eskom (the primary electricity utility in South Africa). The project aims to address, amongst others, the limitations imposed by shaft runout on the usable frequency range of diagnostic data measured by eddy current proximity probes on turbogenerator shafts. This research includes an experimental investigation into the effects of artificially induced faults on a laboratory-scale rotor system, the development and analysis of a mathematical (numerical) model of this rotor system and the development of data processing techniques (including artificial intelligence) to determine the rotor’s condition, faults and diagnostic signal parameters from both the experimental and numerical results. Furthermore, a methodology is to be developed to perform runout compensation in an unsupervised manner. These techniques are then to be implemented for proximity probe vibration data measured on turbogenerators. As part of the research project, this dissertation specifically focuses on the development and rotor dynamic analysis of numerical (finite element) models of the experimental (laboratory-scale) rotor system (using finite element software MSC.Nastran), including gyroscopic effects, a nonlinear force model for the hydrodynamic journal bearing of the rotor system (capable of capturing oil whirl and oil whip instabilities) as well as simulated faults (such as unbalance and rotor-stator rubbing). Since MSC.Nastran does not have a built-in nonlinear hydrodynamic journal bearing model, a custom model of such a bearing was developed and incorporated into the finite element solver, further expanding its already powerful rotor dynamic modelling capabilities. Rotor dynamic analyses performed include the calculation of critical speeds (synchronous complex modes analysis), Campbell diagrams (asynchronous complex modes analysis), steady state frequency response due to unbalance (synchronous frequency response analysis) and nonlinear transient response during rotor run-up. Amongst others, this dissertation explores the seemingly largely unexplored/undocumented capability of finite element software MSC.Nastran to perform rotor dynamic analyses using rotor models constructed with three-dimensional elements. Software (MATLAB code) was also developed to perform post-processing of the simulation results as well as signal processing for investigating the spectral content of transient results. The support structure of the laboratory-scale rotor system was experimentally characterised and an experimental modal analysis was performed on the rotor (excluding its support structure) and its results used to update the finite element rotor models. The transient dynamic response of the experimental rotor system during run-up due to unbalance and rubbing was also analysed in order to validate the developed numerical rotor system models. The numerical results are found to be in good agreement with the experimental results. / Dissertation (MEng)--University of Pretoria, 2015. / Mechanical and Aeronautical Engineering / Unrestricted

[pt] O crescente avanço da tecnologia de equipamentos rotativos tem exigido dos projetistas de máquinas adapta-los às condições de operação mais rigorosas e, consequentemente, projetos mais sofisticados. O aumento da eficiência é frequentemente realizado por operações de minimização de folga entre os elementos rotativos e estacionários e/ou aumento da velocidade de rotação do rotor. A natureza das funções e o custo elevado dos equipamentos rotativos de alta velocidade exigem precisão e segurança no projeto para evitar riscos de operação. Quando o rotor entra em contato com o estator, este pode exibir um comportamento dinâmico fascinante cujo movimento depende de impacto, atrito, e efeitos giroscópicos. Grande parte das preocupações dos engenheiros com relação a vibrações em máquinas rotativas leves e de alta velocidade deve-se aos seus efeitos destrutivos sobre o sistema do estator. Interação devido ao efeito do rubbing entre o conjunto do rotor e sua respectiva carcaça um dos principais causadores de falhas em máquinas rotativas. As forças e tensões desenvolvidas como resultado de pequenas folgas podem resultar em desgaste, perda de desempenho, redução de estabilidade, ruído, calor e vibrações. Obter maior conhecimento sobre este fenômeno torna-se extremamente importante para melhorar a capacidade de proteger o sistema de possíveis danos. O fator chave para almejar este objetivo é continuamente aumentar a habilidade de prever a resposta dinâmica com precisão para então garantir a estabilidade do sistema do rotor. Neste âmbito, o presente trabalho apresenta um estudo teórico, com simulação numérica e validação experimental como objetivo de melhorar nosso conhecimentos sobre o fenômeno. / [en] Increasing demands for high performance, yet reliable operation of rotating machinery continues to increase and have placed stringent requirements on designers and developers to produce efficient, trouble-free rotating machinery. The performance of high-performance turbomachinery can be enhanced by decreasing clearance between rotating parts and housing and/or by increasing the rotor velocity. When a rotor touches upon a boundary, it can exhibit a quite fascinating dynamical behavior and its motion depends on impact, friction, and gyroscopic effects. A large portion of the engineering concern with vibration in high speed rotating machinery results from its destructive effects on the stator system. Rub interactions between a rotor assembly and its corresponding casing structure has been one of the major causes for machine failure. The forces and tensions developed as a result of such clearances can result in wear, loss of performance, reduction of the stability, noise, heat and vibration. Gaining increased knowledge about rnb-related phenomena is important for improving the ability to protect a machine from damage. A key factor in achieving this objective continues to be the ability to accurately predict the dynamic response and stability of a rotor system. This work presents theoretical study, with numerical simulation and experimental validation to improve our knowledge about this phenomena.

No description available.

The turbocharger industry is booming recently, and there is an urgent need for new evaluations of the overall design. As the oil prices continue to rise, along with the new emissions regulations strictly enforced for the in-road as well as the off-road vehicles, the transition to turbocharged engines, and especially for diesel engines, has become irresistible. Higher power, smaller engines, reduced emissions, and overall better efficiency are the main concerns. By means of the recent development in the computational tools, a new era of the product development has emerged. Most diesel engine turbochargers incorporate floating-ring bearings that use the engine's oil for lubrication. The high-speed turbocharger is known to have subsynchronous vibrations at high amplitudes for a wide speed range that could reach 150,000 rpm. The bearing fluid-film whirl instability is the main source of the subsynchronous vibration. The nonlinear reaction forces inside the bearings are usually causing the rotor to whirl in a limit cycle but may become large enough to cause permanent damages. Additionally, the lubrication oil may leak at higher rates through the seals into the engine or the exhaust emissions. This dissertation investigates methods for improving the dynamic stability of the high-speed automotive turbochargers, especially designed for heavy-duty diesel engines that are used for example in heavy machinery, trucks, tractors, etc. The study utilizes the available modern computational tools in rotor-dynamics in addition to the locally developed supportive computer codes. This research is a major part of the turbocharger dynamic analysis supporting the current extensive experimental tests in the Virginia Tech Rotor Dynamics Laboratory for the product development of different high-speed diesel engine turbochargers. The study begins with the method of enhanced-performance hydrodynamic bearings. The aim is to modify the inner surface of the bearing for better dynamic characteristics. The finite-element model of the turbocharger rotor shaft with linearized bearing dynamic coefficients is developed. The system is solved for eigenvalues and eigenvectors in order to evaluate the dynamic stability. The first phase of the study demonstrated that there are two modes of instability that persist during much of the operating speed range, and one of the modes exhibits serious subsynchronous vibration levels at the higher speeds. The first unstable mode builds up at very low speeds forming a conical shape, where both rotor shaft ends whirl forward out-of-phase. The second unstable mode has a cylindrical shape with slight bending, where both rotor ends whirl forward in-phase. The outcome of the study is that the inner surface of the bearing has direct influence on the turbocharger dynamic stability. However, a fixed hydrodynamic bearing may not give total linear stability of the system if it is used without additional damper. The second method is to analytically design flexible damped bearing-supports in order to improve the dynamic characteristics of the rotor-bearing system. The finite-element model of the turbocharger rotor with linearized bearing dynamic coefficients is used to solve for the logarithmic decrements and hence the stability map. The design process attempts to find the optimum dynamic characteristics of the flexible damped bearing-support that would give best dynamic stability of the rotor-bearing system. The method is successful in greatly improving the dynamic stability of the turbocharger and may also lead to a total linear stability throughout the entire speed range when used besides the enhanced-performance hydrodynamic bearings. The study also presents a new method for improving the dynamic stability by inducing the turbocharger rotor unbalance in order to suppress the subsynchronous vibrations. The finite-element model of the turbocharger rotor with floating-ring bearings is numerically solved for the nonlinear time-transient response. The compressor and the turbine unbalance are induced and the dynamic stability is computed. The turbocharger model with linearized floating-ring bearings is also solved for eigenvalues and eigenvectors to predict the modes of instability. The linear analysis demonstrates that the forward whirling mode of the floating-ring at the compressor end becomes also unstable at the higher turbocharger speeds, in addition to the unstable forward conical and cylindrical modes. The numerical predictions are also compared to the former experimental results of a typical turbocharger. The results of the study show that the subsynchronous frequency amplitude of the dominant first mode is reduced when inducing either the compressor or the turbine unbalance at a certain level. In addition to the study of the stability improvement methods, the dissertation investigates the other internal and external effects on the turbocharger rotor-bearing system. The radial aerodynamic forces that may develop inside the centrifugal compressor and the turbine volutes due to pressure variation of the circulating gas are numerically predicted for magnitudes, directions, and locations. The radial aerodynamic forces are numerically simulated as static forces in the turbocharger finite-element model with floating-ring bearings and solved for nonlinear time-transient response. The numerical predictions of the radial aerodynamic forces are computed with correlation to the earlier experimental results of the same turbocharger. The outcomes of the investigation demonstrated a significant influence of the radial aerodynamic loads on the turbocharger dynamic stability and the bearing reaction forces. The numerical predictions are also compared to the former experimental results for validation. The external effect of the engine-induced vibration on the turbocharger dynamic stability is studied. The engine-induced excitations are numerically simulated as time-forcing functions on the rotor-bearings of the turbocharger finite-element model with floating-ring bearings in order to solve for the nonlinear time-transient response. The compressor radial aerodynamic forces are combined to the engine-induced excitations to numerically predict the total nonlinear transient response. The results of the study show that there are considerable amplitudes at the engine-excitation frequency in the subsynchronous region that may also have similar amplitude at the second harmonic. Additionally, the magnitudes of the engine-induced vibration have an effect on the turbocharger dynamic stability. The numerical predictions are compared to the former experimental tests for turbocharger dynamic stability. / Ph. D.

No description available.

Orientador: Luiz de Paula do Nascimento / Banca: Vicente Lopes Junior / Banca: Domingos Alves Rade / Resumo: Este trabalho apresenta uma análise teórica do desempenho de um sistema de controle ativo de vibração de rotores utilizando mancais magnéticos. O esquema de controle ativo proposto utiliza a estratégia de controle ativo feedforward sobreposta ao sistema de controle feedback dos mancais magnéticos. O desempenho desse sistema de controle foi analisado em função da flexibilidade dos rotores considerando o impacto do número e da localização dos atuadores e dos sensores de erro sobre a redução dos níveis de vibração desses rotores, tanto em termos de vibração global quanto em termos de vibração local. O sistema de controle foi aplicado em um modelo teórico de rotor desenvolvido através do método da matriz de impedância. / Abstract: This work presents a theoretical analysis of the performance of a system of active control of rotor vibrations using magnetic bearings. The proposed scheme of active control uses a feedforward active control strategy superimposed on the feedback control system of the magnetic bearings. The performance of this control system was analyzed as a function of the rotor flexibility considering the impact and optimization of the actuators and error sensors placement on the reduction of vibration levels of these rotors, in terms of global vibration as well as in terms of local vibration of the rotor. The control system was applied to a theoretical rotor model developed by the matrix impedance method. / Mestre

Com o intuito de otimizar o projeto de unidades hidrogeradoras e, por conseguinte, aumentar a sua disponibilidade, uma previsão mais precisa do seu comportamento dinâmico é de fundamental importância. Assim, o presente trabalho se propôs a modelar uma unidade hidrogeradora de forma mais completa, considerando os efeitos do empuxo magnético, mancais, perturbações hidráulicas, desbalanceamento e selos labirintos de turbina Francis. A partir do modelo construído, foram realizadas análises modais, temporais e espectrais. Os resultados numéricos são comparados com os dados experimentais de uma unidade hidrogeradora de grande porte. Tanto sinais de tendência temporal, como órbitas, e espectros de frequência dos fenômenos envolvidos são analisados e comparados. Dessa forma, pretende-se obter o modelo menos complexo possível, mas que seja capaz de representar de forma aceitável a dinâmica da unidade hidrogeradora sujeita a diferentes condições de operação. A maior dificuldade encontrada foi na representação das excitações externas ao sistema, principalmente quando a máquina está operando em regime parcial. Constatou-se uma importante influência do selo labirinto na simulação do comportamento dinâmica da turbina Francis operando em carga parcial. Ao final, os aspectos do modelo que podem ser aprimorados são discutidos. / In order to optimize the design of hydro-generating units and therefore increase their availability, a more accurate forecast of their dynamic behavior is of fundamental importance. Thus, the present work has proposed to model a more complete hydrogenerator unit, considering the effects of magnetic pull, guide bearings, hydraulic perturbations, unbalance and Francis turbine labyrinths. From the this model, modal, temporal and spectral analyzes were performed. The numerical results are compared with experimental data of a large hydrogenerator unit. Temporal trend signals, orbits and frequency spectrum of the phenomena involved are analyzed and compared. In this way, it is intended to obtain the less complex model possible, but that is able to represent in an acceptable way the dynamics of the hydrogenerator unit under different operation conditions. The greatest difficulty found was in the representation of external excitations to the system, mainly under partial load. It was observed an important influence of the labyrinth seal in the simulation of the dynamic behavior of the Francis turbine operating in partial load. Finally, aspects of the model that can to be improved are discussed.

Este trabalho propõe uma solução inovadora para o amortecimento de vibrações laterais indesejadas em máquinas rotativas através da conversão de energia cinética em energia elétrica por meio de um dispositivo eletromagnético passivo de colheita de energia, com o mínimo de geração de torque reativo. Para atingir estes objetivos, foram descritas e avaliadas as três principais técnicas de coleta de energia vibratória (piezelétrica, eletrostática e eletromagnética) juntamente com análises qualitativas das equações de eletromagnetismo e pelo Método dos Elementos Finitos. Um protótipo que consiste em um conjunto de ímãs permanentes anexos ao rotor e um conjunto de bobinas no estator demonstrou experimentalmente uma diminuição da amplitude de vibração em até 6,8%, na região de velocidades críticas, com geração não significativa de torque. Estes resultados foram obtidos experimentalmente mantendo-se os enrolamentos independentes entre si. / In this work, it is proposed a novel damping solution for undesired lateral vibrations in rotating machines by converting kinetic energy into electrical energy through a passive electromagnetic energy harvesting device, with minimal generation of reactive torque. In order to achieve these goals, it is described and evaluated the three main vibration energy harvesting techniques (piezoelectric, electrostatic and electromagnetic) along with qualitative analysis of electromagnetic equations and nite element analysis (FEA). Furthermore, a prototype consisting of a set of permanent magnets attached to the rotor and a set of coils attached to the stator showed a decrease in the amplitude of vibration up to 6,8% in the range of critical velocities, with non-signicant torque generation. Such results were obtained experimentally with independent-circuit coils.

Orientador: Luiz de Paula do Nascimento / Banca: Katia Lucchesi Cavalca Dedini / Banca: Gilberto Pechoto de Melo / Resumo: Neste trabalho são otimizadas rotinas computacionais de um método de estimação de rigidez de mancais de máquinas através de um processo de ajuste de modelo, utilizando a análise de sensibilidade. Este método consiste em utilizar a análise de sensibilidade dos autovalores com relação à variação da rigidez dos mancais de um rotor. A eficácia e a robustez do método são analisadas através de simulações teóricas, bem como através de dados experimentais obtidos de um rotor de rotação variável e rigidezes dos mancais ajustáveis. O modelo matemático de ajuste do sistema é desenvolvido pelo método dos elementos finitos e o método de ajuste converge empregando-se um processo iterativo. Este método de ajuste baseia-se na minimização da diferença entre autovalores experimentais e autovalores obtidos com o modelo matemático de ajuste a partir de valores de rigidez dos mancais previamente adotados. A análise é feita com o rotor em diversas velocidades de rotação para verificar a influência do efeito giroscópio, e em diversas condições de valores da rigidez dos mancais para analisar o método quando aplicado em rotores flexíveis e em rotores rígidos. O desempenho do método é analisado com resultados teóricos e experimentais. / Abstract: In this work, computational routines of estimation method of stiffness bearing of machine via a model updating process are optimized, using the sensitivity analysis. This method consists of using the eigenvalue sensitivity analysis, relating to the stiffness bearing variation of a rotor. The efficacy and the robustness of the method are analyzed through the theoretical simulations, as well as, based on the experimental data obtained of a test rotor with variable rotating speeds and adjustable bearing stiffness values. The mathematical model system is developed by the finite element method and the method of adjustment should converge employing an iterative process. The method of adjustment is based on the minimization of the difference between experimental eigenvalues and eigenvalues obtained via mathematical model from previously adopted stiffness bearing values. The analysis is made by using the rotor in different rotating speeds in order to check the influence of the gyroscopic effect, and in several conditions of the stiffness bearing values to analyze the method when applied on flexible and rigid rotors. The performance of the method is analyzed through theoretical and experimental results. / Mestre