A potentially powerful influence on the dynamic characteristics of a journal bearing is the thermal deformation of the bearing surface and the journal. Although a few reported research projects consider this effect, most of the journal bearing codes currently utilized in the turbomachinery industry ignore this influence. A study of the thermohydrodynamic behavior including thermoelastic deformation of a two axial groove journal bearing is presented in this thesis. The finite element method has been used to solve the governing differential equations. Quadrilateral nine noded isoparametric elements are used in the finite element model of both the fluid film and the bearing liner. The analytical predictions are compared with the steady load data obtained from two identical 101 mm dia, 57 nm long bearings, one fabricated from steel and the other from bronze. The comparisons are made for several loading values and for operational speeds of 1000 and 5000 RPM (16.66 Hz and 83.33 Hz). Analytical results are also presented for an operating speed of 10000 RPM (166.66 Hz). / Master of Science

Magnetic bearings support turbomachinery by regulating their forces exerted in relation to the displacement of the machine supported. The regulating control system must be tuned for stable and safe operation of the rotor. The ultimate goal of this study is to determine the effects of changing controller gains on the behavior of the rotor during operation in its normal speed range with a known unbalance load. We also endeavor to confirm the model of the rotor supported the magnetic bearings, as an additional goal. We first investigate the modelling of rotors supported by magnetic bearings, including the model of the control system. We present a finite element model of a magnetic bearing supported rotor, and perform experiments to determine the characteristics of the control system which governs the magnetic forces on the rotor. The experimental control system characteristics confirm the expected characteristics from theory. With this knowledge, we perform simulations and experiments under the same forcing conditions to determine the accuracy of the model in predicting the experimental behavior of an unbalanced rotor. The model exhibits satisfactory ability in predicting the experimental behavior of the rotor under this loading. Our next step is to determine the effects of variation of proportional and integral controller gains on the behavior of the rotor. Both simulations and experiments show that an increase in the proportional controller gain results in an increase in the rotor’s first critical speed. An increase in the integral gain results in a small decrease in the location of the peak response speed in the speed range tested, while leaving the peak amplitude insignificantly changed. Again, simulations and experiments predict this result. We reach the following three conclusions from this study. First, the finite element model of the rotor/bearing system is a viable model for predicting the behavior of the experimental system. Second, tuning of the proportional gain shows a significant effect on the behavior of the rotor during unbalance loading across its speed range, due to considerable change in bearing stiffness caused by the tuning of this gain. Last, tuning of the integral gain has a small effect on the behavior of the rotor due to the change in bearing damping, too small to be considered significant. / Master of Science

This thesis presents a generic passive non-contact based acoustic health monitoring approach using ultrasonic acoustic emissions (UAE) to facilitate classification of bearing health via neural networks. This generic approach is applied to classifying the operating condition of conventional ball bearings. The acoustic emission signals used in this study are in the ultrasonic range (20-120 kHz), which is significantly higher than the majority of the research in this area thus far. A direct benefit of working in this frequency range is the inherent directionality of the microphones capable of measurement in this range, which becomes particularly useful when operating in environments with low signal-to-noise ratios. Using the UAE power spectrum signature, it is possible to pose the health monitoring problem as a multi-class classification problem, and make use of a multi-layer artificial neural network (ANN) to classify the UAE signature. One major problem limiting the usefulness of ANN's for failure classification is the need for large quantities of training data. Artificial training data, based on statistical properties of a significantly smaller experimental data set is created using the combination of a normal distribution and a coordinate transformation. The artificial training data provides a sufficient sized data set to train the neural network, as well as overcome the curse of dimensionality. The combination of the artificial training methods and ultrasonic frequency range being used results in an approach generic enough to suggest that this particular method is applicable to a variety of systems and components where persistent UAE exist. / Master of Science

This thesis describes the test rig and results from a project expanding the field of rotor health monitoring by using Active Magnetic Bearings (AMBs) as actuators for applying a variety of known force inputs to a spinning. Similar to modal analysis and other nondestructive evaluation (NDE) techniques which apply input signals to static structures in order to monitor responses; this approach allows for the measurement of both input and output response in a rotating system for evaluation. However, unlike these techniques, the new procedure allows for multiple forms of force input signals to be applied to a rotating structure. This technique is used on a rotating shaft supported in conventional bearings with an AMB actuator added to the system. This paper presents the results from this project including shaft rub and notch. An EDM notch was also tested to attempt a breathing scenario similar to breathing cracks. / Master of Science

Vibrações são intrínsecas às máquinas rotativas e, embora não possam ser completamente eliminadas, devem ser controladas de modo a se evitar fadiga e até mesmo falha da máquina. Neste contexto, devido à sua capacidade de alterar as características dinâmicas destas máquinas, os mancais ativos são uma solução efetiva a fim de se reduzir vibrações em rotores, permitindo não só maior ciclo de vida, mas também aumento de confiabilidade e desempenho. Frequentemente, o projeto do sistema de controle destes mancais baseia-se em um modelo matemático da planta, o qual pode ser de difícil obtenção e, devido à adoção de hipóteses simplificadoras (inerentes ao processo de modelagem), pode ser impreciso. Com base nestes conceitos, propõe-se a utilização de uma técnica de controle do tipo proporcional-derivativa baseada em medições de resposta em frequência (livre de modelos matemáticos) aplicada ao controle de vibrações em sistemas rotativos, contornando dificuldades de modelagem. Esta técnica é testada experimentalmente em uma bancada de testes cujos elementos de atuação são os eletromagnetos de um mancal ativo, e um algoritmo para a identificação automática das FRFs do sistema (algoritmo de autoidentificação) é desenvolvido e implementado, permitindo, de forma autônoma, o cálculo dos ganhos ótimos do controlador PD visando atenuação de vibrações. Com base nos resultados obtidos, tem-se que este trabalho é um estudo preliminar que pode viabilizar o desenvolvimento de um mancal ativo inteligente, o qual, a partir de medições do deslocamento do eixo, seria capaz de obter a resposta em frequência do sistema e determinar, de forma automática, os ganhos ótimos do controlador, possibilitando o controle autônomo de vibrações em sistemas rotativos, a partir de um algoritmo de autoidentificação e de uma metodologia de controle livre de modelos. / Vibrations are intrinsic to rotating machinery and, although they cannot be completely eliminated, it is important to control this kind of motion with the objective of avoiding fatigue and even failure of the machine. In this context, due to their capacity of changing the dynamic characteristics of these machines, active bearings are an effective solution to reduce vibration in rotors, allowing not only longer lifecycle, but also higher performance. Frequently, the design of the control system of these bearings is based on a mathematical model of the plant, whose obtainment can be hard and, due to the adoption of simplifying hypotheses (inherent to the modeling process), it may be imprecise. Keeping in mind these concepts, this dissertation proposes the use of a proportional-derivative control technique based on frequency response measurements (free of mathematical models) applied to the vibration control of rotating systems, overcoming modeling difficulties. This technique is experimentally tested in a test rig whose actuation elements are the electromagnets of an active bearing, and an algorithm for automatic identification of the system\'s FRFs (self-identification algorithm) is developed and implemented, allowing, in an autonomous way, the calculation of the optimum gains of the PD controller aiming at controlling vibrations. Based on the obtained results, this work consists in a preliminary study that may enable the development of a smart active bearing, which, from measurements of the shaft\'s displacement, would be capable of obtaining the frequency response of the system and determine, automatically, the optimum gains of the controller, making it possible the autonomous vibration control in rotating systems, from a self-identification algorithm and a model-free control methodology.

Die vorliegende Arbeit verfolgte die Zielstellung der Substitution des etablierten Weißmetalls als Laufschicht von hydrodynamischen Mehrflächengleitlagern durch neuartige Kunststoffschichten. Dazu wurden vergleichende Bauteilversuche an Mehrflächengleitlagern mit verschiedenen Laufschichten und Bohrungsformen vorgenommen. Eine Zinnbasislegierung als Laufflächenbeschichtung diente dabei als Referenzwerkstoff. Zur Durchführung des Versuchsprogrammes kam ein vorhandener, messtechnisch neu konditionierter Turbinenlagerprüfstand zum Einsatz. Die Versuchsreihen haben durchweg positive Beurteilungen der Lagerkennwerte im untersuchten Betriebsbereich der neuen Lagervarianten ergeben. Die neuartigen Laufschichtvarianten erfüllten die hohen tribologischen und thermischen Anforderungen. Einzelne Abweichungen der ermittelten Kennwerte wurden zahlenmäßig dokumentiert und können mit bereits verfügbaren physikalischen Modellen beschrieben werden. Die Ergebnisse erwiesen sich als unabhängig von der Lagerbauform aber abhängig von der gewählten Schichtvariante. Die Untersuchungen zum Betriebsverhalten unter hydrodynamischer Dauerbelastung sowie im Mischreibungsgebiet und im Notlaufbetrieb führten zu teilweise unterschiedlichen Ergebnissen. Im Mischreibungsgebiet wiesen die untersuchten Lager kaum Unterschiede im Betriebsverhalten auf. Im Dauerversuch zeigten die Lager mit Weißmetall, Gleitlack und Keramikschicht hervorragende Eigenschaften. Die Variante Klüberplast besaß eine ungenügende Bindefestigkeit und führte zu plastischen Verformungen der Schicht infolge der hydrodynamischen Drücke. Im Notlaufbetrieb übertrafen die untersuchten Kunststoffvarianten die Standzeiten des Referenzwerkstoffs Weißmetall. / The aim of this study was to identify and test an alternative liner material instead of common liner materials such as white alloy for multi-lobe radial bearings. For this purpose comparative tests with different radial bearings were carried out. The white alloy material was taken as a reference. In preparation for these test series, the measurement system of the turbine bearing test rig was upgraded. Experiments showed beneficial performances of the bearings with a plastic liner by evaluating the static and dynamic properties of different bearing geometries and liner thicknesses under a wide range of operating conditions. The new bearings fulfilled the high tribological and thermal requirements. Observed deviations of the determined parameters were documented in number and can be described with available physical models. The results were independent of the bearing type and depending on the selected liner material variant. The studies on operating performance in continuous operation in the mixed friction area and in dry running operation led to partially different results. The mixed friction tests showed little difference in the examined stock performance. The bearings with white alloy, ceramic layer and bonded coating showed excellent fatigue properties of long-term experiment. On Klüberplast insufficient bonding strength and plastic deformation of the layer due to the hydrodynamic pressure was found. In the dry running operation the investigated polymers exceeded the lifetime of the referencematerial white alloy.

Vibrações são intrínsecas às máquinas rotativas e, embora não possam ser completamente eliminadas, devem ser controladas de modo a se evitar fadiga e até mesmo falha da máquina. Neste contexto, devido à sua capacidade de alterar as características dinâmicas destas máquinas, os mancais ativos são uma solução efetiva a fim de se reduzir vibrações em rotores, permitindo não só maior ciclo de vida, mas também aumento de confiabilidade e desempenho. Frequentemente, o projeto do sistema de controle destes mancais baseia-se em um modelo matemático da planta, o qual pode ser de difícil obtenção e, devido à adoção de hipóteses simplificadoras (inerentes ao processo de modelagem), pode ser impreciso. Com base nestes conceitos, propõe-se a utilização de uma técnica de controle do tipo proporcional-derivativa baseada em medições de resposta em frequência (livre de modelos matemáticos) aplicada ao controle de vibrações em sistemas rotativos, contornando dificuldades de modelagem. Esta técnica é testada experimentalmente em uma bancada de testes cujos elementos de atuação são os eletromagnetos de um mancal ativo, e um algoritmo para a identificação automática das FRFs do sistema (algoritmo de autoidentificação) é desenvolvido e implementado, permitindo, de forma autônoma, o cálculo dos ganhos ótimos do controlador PD visando atenuação de vibrações. Com base nos resultados obtidos, tem-se que este trabalho é um estudo preliminar que pode viabilizar o desenvolvimento de um mancal ativo inteligente, o qual, a partir de medições do deslocamento do eixo, seria capaz de obter a resposta em frequência do sistema e determinar, de forma automática, os ganhos ótimos do controlador, possibilitando o controle autônomo de vibrações em sistemas rotativos, a partir de um algoritmo de autoidentificação e de uma metodologia de controle livre de modelos. / Vibrations are intrinsic to rotating machinery and, although they cannot be completely eliminated, it is important to control this kind of motion with the objective of avoiding fatigue and even failure of the machine. In this context, due to their capacity of changing the dynamic characteristics of these machines, active bearings are an effective solution to reduce vibration in rotors, allowing not only longer lifecycle, but also higher performance. Frequently, the design of the control system of these bearings is based on a mathematical model of the plant, whose obtainment can be hard and, due to the adoption of simplifying hypotheses (inherent to the modeling process), it may be imprecise. Keeping in mind these concepts, this dissertation proposes the use of a proportional-derivative control technique based on frequency response measurements (free of mathematical models) applied to the vibration control of rotating systems, overcoming modeling difficulties. This technique is experimentally tested in a test rig whose actuation elements are the electromagnets of an active bearing, and an algorithm for automatic identification of the system\'s FRFs (self-identification algorithm) is developed and implemented, allowing, in an autonomous way, the calculation of the optimum gains of the PD controller aiming at controlling vibrations. Based on the obtained results, this work consists in a preliminary study that may enable the development of a smart active bearing, which, from measurements of the shaft\'s displacement, would be capable of obtaining the frequency response of the system and determine, automatically, the optimum gains of the controller, making it possible the autonomous vibration control in rotating systems, from a self-identification algorithm and a model-free control methodology.

Aero-engine assemblies are complex structures typically involving two or three nested rotors mounted within a flexible casing via squeeze-film damper (SFD) bearings. The deployment of SFDs into such structures is highly cost-effective but requires careful calculation since they can be highly nonlinear in their performance, particularly if they are unsupported (i.e. without a retainer spring). The direct study of whole-engine models with nonlinear bearings has been severely limited by the fact that current nonlinear computational techniques are not well-suited for complex large-order systems. The main contributions of this thesis are: • A procedure for unbalance response computation, suitable for generic whole-engine models with nonlinear bearings, which significantly extends the capability of current finite element packages. This comprises two novel nonlinear computational techniques: an implicit time domain integator referred to as the Impulsive Receptance Method (IRM) that enables rapid computation in the time domain; a whole-engine Receptance Harmonic Balance Method (RHBM) for rapid calculation of the periodic response in the frequency domain. Both methods use modal data calculated from a one-off analysis of the linear part of the engine at zero speed.• First-ever analyses on real twin-spool and three-spool engines. These studies illustrate the practical use of these solvers, provide an insight into the nonlinear dynamics of whole-engines and correlate with a limited amount of industrial experimental data. Both IRM and RHBM are directly formulated in terms of the relative response at the terminals of the nonlinear bearings. This makes them practically immune to the number of modes that need to be included, which runs into several hundreds for a typical engine. The two solvers are extensively tested on two/three-shaft engine models (with 5-6 SFDs) provided by a leading engine manufacturer using an SFD model that is used in industry. The tests show the IRM to be many times faster than an established robust conventional implicit integrator while achieving a similar level of accuracy. It is also shown to be more reliable than another popular implicit algorithm. The RHBM enables, for the first time, the frequency domain computation of the nonlinear response of whole-engine models. Its use is illustrated for both Single-Frequency Unbalance (SFU) excitation (unbalance confined to only one shaft) and Multi-Frequency Unbalance (MFU) excitation (unbalance located on two or more shafts, rotating at different speeds). Excellent correlation is demonstrated between RHBM and IRM.The parametric studies compare and contrast the frequency spectra for SFU and MFU cases. They also reveal the varying degree of lift at the unsupported SFDs. The sensitivity of the response to end-sealing and bearing housing alignment is also illustrated. It is demonstrated that the use of suitably preloaded vertically oriented “bump-springs” at the SFDs of heavy rotors produces a significant improvement in journal lift. It is also shown that the consideration of a slight amount of distributed damping in the structure significantly affects the predicted casing vibration levels, bringing them closer to measured levels, while having little effect on the SFD orbits.

[pt] A Dissertação aqui apresentada descreve um acidente em um rotor de máquina de grande porte (compressor de ar) de uma fábrica de fertilizante cujas conseqüências foram perdas financeiras de alta monta tanto para a empresa quanto para o Estado, pela importância econômica onde a fábrica é situada. O objetivo da Dissertação foi simular matematicamente o acidente ocorrido e esclarecer o mesmo. Para se chegar ao diagnóstico do problema se modelou o rotor e o discretizou pelo Método de Elementos Finitos. As técnicas de investigação do problema e a sua seqüência de investigação podem ser tomadas como base em investigação de eventuais acidentes envolvendo rotores futuramente. O capítulo relativo a Análise Modal será extraído como base de apostila para curso envolvendo pessoal da área de Manutenção Mecânica. / [en] A problem related with an air compressor gave birth to the MSc Thesis. Problems related with rotative machines are usual in the industrial field. Difficulties come from the data gathering in order to analyze, and propose a theory of failure in order to explain and avoid the recurrence of such problem. Modelling a rotor with a Timoshenko beam element and the discretization by finite element method permit the dynamical analysis and the modal analysis of the rotor considering its interaction with the radial and thrust bearings (assuming stiffness and rigidity). The work is divided in seven chapters: chapter one introduces the work and gives the overview of it; chapter two describes the industrial problem; chapter three is a brief explanation of bearing types and the fundamental principle of lubrication; chapter four introduces vibration theory and modal analysis; chapter five introduces the finite element method; chapter six is the simulation of the problem, using tailor-made MATLABr programs to reconstruct the problem and to compare the test field results with the here mentioned formulation; chapter seven discusses the results and proposes future works. Appendix shows the kinetic theory and the beam deformation model used in the program and the Laval simple rotor as a limited description of the dynamic of a rotor with distributed mass, rigidity and stiffness. The aim of this work is to help understand and avoid the recurrence of the failure described and to easy the understanding of modal analysis for new engineers and technicians which will deal with rotor dynamics.

As machine topologies and technologies mature, the fundamental function of the device is honed. Direct drive machines have the potential to launch the renewable energy sector into a new era of large scale, reliable, offshore power generation. With advancements in new technologies, such as superconductivity, the reduction of generator mass due to incorporation of machine and device structures, the continued advancements in component and system reliability; direct drive generators have the ability to outsize geared wind systems and simplify submerged linear and rotary power generation. The research held within this thesis will focus on improving direct drive power take off systems for offshore renewable energy power generation by splitting the area into four parts. The first part will discuss the various methods of energy extraction within the offshore and marine environment. The future of the sector will be discussed, and a forecast of technological advancement and existing reliability issues will be provided based on current data. The second part will focus on drive trains and direct drive generators, assessing the current topologies and suggesting alternatives that may thrive in a variety of large and small offshore renewable machines. The third part investigates the application of novel linear bearings in direct drive systems for offshore and submerged operation. A brief study of the loads found in wave applications will be presented and the testing of several polymer bearing materials will be outlined. The final part will discuss the potential benefits of flooding the airgap of a direct drive generator with sea water for marine applications. Results will be presented from two linear test rigs and the marinisation of devices will conclude the report.