No description available.

Subsynchronous vibrations such as those caused by rotor instability represent one of the most harrowing scenarios of rotor vibration. They are related to a great diversity of destabilizing forces and some of them are not well understood yet. Therefore, special attention must be paid to this type of vibration. Active Magnetic Bearings (AMBs) monitor the position of the shaft and change the dynamics of the system accordingly to keep the rotor in a desired position, offering the possibility of being used as dampers for vibration control. In the present work, a single-disk and a three-disk rotor were built to evaluate the effectiveness of an Active Magnetic Damper (AMD) in damping subsynchronous vibrations. An AMD was used to inject a signal simulating a subsynchronous vibration in the rotor, as another AMD was used to perform active control. Two locations of the AMD were considered for each rotor. For the single-disk rotor, experimental data was taken with the AMD located at three-quarters of the rotor-span and with the AMD located at midspan. For the three-disk rotor, experimental data was taken with the AMD located at a quarter-span and with the AMD at two-thirds of the rotor span. An undamped critical speed and a forced response analysis were performed on the rotors in order to predict the dynamic characteristics of the rotors with and without the AMD. It was demonstrated that an AMD is effective in damping subsynchronous vibrations. The addition of an AMD introduces damping and stiffness to the rotor-bearing system resulting in a change in the synchronous response and a consequent increase of the amplitude of vibrations at synchronous frequencies. This effect must be carefully considered when designing a system with an AMD. / Master of Science

O Motor Assíncrono Tubular para Aplicação na Extração de Óleo do Subsolo MATÆOS foi desenvolvido na Escola Politécnica da Universidade de São Paulo (EPUSP) com a função de acionar diretamente uma bomba de sucção, instalada no fundo de um poço de petróleo em terra. Dando continuidade aos trabalhos realizados na EPUSP envolvendo sistemas de levitação magnética, foi desenvolvido um mancal magnético ativo (AMB - Active Magnetic Bearing), aplicado ao protótipo do motor em substituição ao mancal mecânico tradicional existente. O projeto abrange a construção de um protótipo de mancal magnético composto das partes mecânicas, elétricas e de software necessárias ao funcionamento do sistema. O projeto do eletroímã foi realizado por meio do método dos elementos finitos (MEF), para análise da densidade de fluxo e da relação entre a força radial e a corrente elétrica nas bobinas. O controle da levitação do mancal é realizado por meio de controlador digital com placas conversoras AD/DA e algoritmo de controle implementado em hardware FPGA. Utilizando o modelo do sistema, os controladores são sintonizados para atender aos requisitos de estabilidade e rejeição de perturbações, que desviem o entreferro do seu valor nominal. Na configuração do AMB, ao invés do sistema tradicional com oito pólos, um conceito diferente é adotado. Neste, uma máquina primitiva bearingless é excitada com corrente contínua e usada como mancal magnético. Os resultados experimentais obtidos com o protótipo em funcionamento mostram que o sistema em malha fechada é estável e apresenta uma resposta transitória satisfatória. / A tubular linear induction motor applied to onshore oil exploitation, named MATÆOS (which is in the Portuguese acronym for Tubular Asynchronous Motor for Onshore Oil Exploitation) was built at Escola Politécnica da Universidade de São Paulo (EPUSP). Its purpose is to directly drive the sucker-rod pump installed in the down hole of the oil well. In continuing the research accomplished at EPUSP concerning magnetic levitation systems, an Active Magnetic Bearing (AMB) was developed and applied to the prototype of the motor in substitution to the existing traditional bearing. The design includes the construction of the magnetic bearing prototype composed of mechanical, electric and software components required to the operation of the system. The electromagnet design was accomplished using the Finite Element Method (FEM) in the analysis of both the flux density and the relationship between the radial force and the suspension winding current. The magnetic bearing levitation control is executed by a digital controller using an AD/DA converter and a control algorithm implemented in FPGA hardware. Using the system model, the controllers are tuned to provide both stability and rejection of disturbances that tend to move the air gap from its nominal value. Instead of the usual eight-pole AMB, a different concept is adopted where a DC-excited primitive bearingless machine is used as a magnetic bearing. The experimental results obtained with the prototype in operation show that the closed-loop system is stable and exhibits a satisfactory transient response.

The problem addressed in this thesis is the delevitation modelling of an active magnetic bearing (AMB) supported rotor. A system model needs to be developed that models the highly non-linear interaction of the rotor with the backup bearings (BBs) during a delevitation event. The model should accurately predict forward and backward whirl as well as the system forces experienced. To this end, the severity of rotor delevitation events should be characterised. The contributions of the research include a more comprehensive model of a cross-coupled flexible rotor-AMB-BB system, a method to obtain repeatable experimental results, two methods for quantifying the severity of a rotor-drop (RDQ and Vval) and the simulation of forward whirl. A simulation model (BBSim) was developed to predict the behaviour of a rotor in rolling element BBs in an AMB system during a rotor delevitation event. The model was validated using a novel rotor delevitation severity quantification method (Vval) to compare experimental and simulated results. In this study the force impulse values as the rotor impacts the BBs are seen as critical to monitor, as an indication of rotor drop severity. The novel quantification method was verified by comparing the impulse values of delevitation events to the values obtained for the same delevitation events using the novel quantification method. The simulation model (BBSim) was developed by integrating and cross coupling various simpler models to obtain a model that could accurately predict the behaviour of a rotor during a delevitation event. A plethora of simulation results were generated for various initial conditions. The simulation results were used to perform a parametric study, from which the effects that certain design parameters have on the severity of rotor delevitation events are determined. The novel quantification method results presented in this research compared well to the impulse values. Since most AMB systems that have BBs do not have force measurement capabilities, the development of the novel quantification method enables the quantification of rotor drop severity solely based on position data. The simulation model BBSim was found to accurately predict the behaviour of a rotor during a delevitation event. The parametric study completed using BBSim revealed that the severity of rotor delevitation events is less sensitive to the bearing stiffness than the bearing damping. The parametric study also found that the severity of a delevitation event is slightly sensitive to the angle of delevitation. The friction factor between the rotor and the inner-race of the rolling element bearings moderately influences the severity of the rotor delevitation event. The inertia of the rolling element bearing’s inner-race and balls influences the behaviour in a complex manner, where the inertia should be kept as low as possible for actively braked rotors, and should be higher for free running rotors. The unbalance of the rotor plays a major role in the severity of rotor delevitation events. A rotor with a high unbalance usually tends to go into forward whirl, whereas low unbalance could promote the development of backward whirl if the inertia of the inner-race and the friction factor between the inner-race and the rotor are excessively large. Some of the recommended future work to be done on BBSim Include investigations into load sharing, various failure modes of AMBs, the effect that rotor circularity has on the stability of AMB control and an investigation into forward whirl. Envisaged improvements that can be made to BBSim are the inclusion of an axial rotor AMB and BB model, cross-coupled with the existing BBSim model. Other improvements could be the inclusion of thermal modelling and the ability to simulate other types of BBs. Future experimental work could include a comparison of simulated and experimental results of larger systems and using the developed quantification methods to refine the defined threshold values for the safe operation of AMB systems. / PhD, North-West University, Potchefstroom Campus, 2014 / Appendix C is attached seperately because of the size of the pdf (920 MB). If it is too large to download, please loan the hardcopy with the CD from the Loan desk in the Ferdinand Postma Library.

The problem addressed in this thesis is the delevitation modelling of an active magnetic bearing (AMB) supported rotor. A system model needs to be developed that models the highly non-linear interaction of the rotor with the backup bearings (BBs) during a delevitation event. The model should accurately predict forward and backward whirl as well as the system forces experienced. To this end, the severity of rotor delevitation events should be characterised. The contributions of the research include a more comprehensive model of a cross-coupled flexible rotor-AMB-BB system, a method to obtain repeatable experimental results, two methods for quantifying the severity of a rotor-drop (RDQ and Vval) and the simulation of forward whirl. A simulation model (BBSim) was developed to predict the behaviour of a rotor in rolling element BBs in an AMB system during a rotor delevitation event. The model was validated using a novel rotor delevitation severity quantification method (Vval) to compare experimental and simulated results. In this study the force impulse values as the rotor impacts the BBs are seen as critical to monitor, as an indication of rotor drop severity. The novel quantification method was verified by comparing the impulse values of delevitation events to the values obtained for the same delevitation events using the novel quantification method. The simulation model (BBSim) was developed by integrating and cross coupling various simpler models to obtain a model that could accurately predict the behaviour of a rotor during a delevitation event. A plethora of simulation results were generated for various initial conditions. The simulation results were used to perform a parametric study, from which the effects that certain design parameters have on the severity of rotor delevitation events are determined. The novel quantification method results presented in this research compared well to the impulse values. Since most AMB systems that have BBs do not have force measurement capabilities, the development of the novel quantification method enables the quantification of rotor drop severity solely based on position data. The simulation model BBSim was found to accurately predict the behaviour of a rotor during a delevitation event. The parametric study completed using BBSim revealed that the severity of rotor delevitation events is less sensitive to the bearing stiffness than the bearing damping. The parametric study also found that the severity of a delevitation event is slightly sensitive to the angle of delevitation. The friction factor between the rotor and the inner-race of the rolling element bearings moderately influences the severity of the rotor delevitation event. The inertia of the rolling element bearing’s inner-race and balls influences the behaviour in a complex manner, where the inertia should be kept as low as possible for actively braked rotors, and should be higher for free running rotors. The unbalance of the rotor plays a major role in the severity of rotor delevitation events. A rotor with a high unbalance usually tends to go into forward whirl, whereas low unbalance could promote the development of backward whirl if the inertia of the inner-race and the friction factor between the inner-race and the rotor are excessively large. Some of the recommended future work to be done on BBSim Include investigations into load sharing, various failure modes of AMBs, the effect that rotor circularity has on the stability of AMB control and an investigation into forward whirl. Envisaged improvements that can be made to BBSim are the inclusion of an axial rotor AMB and BB model, cross-coupled with the existing BBSim model. Other improvements could be the inclusion of thermal modelling and the ability to simulate other types of BBs. Future experimental work could include a comparison of simulated and experimental results of larger systems and using the developed quantification methods to refine the defined threshold values for the safe operation of AMB systems. / PhD, North-West University, Potchefstroom Campus, 2014 / Appendix C is attached seperately because of the size of the pdf (920 MB). If it is too large to download, please loan the hardcopy with the CD from the Loan desk in the Ferdinand Postma Library.

Made available in DSpace on 2014-06-11T19:27:14Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-03-03Bitstream added on 2014-06-13T18:31:08Z : No. of bitstreams: 1 goncalvesjr_r_me_ilha.pdf: 1793490 bytes, checksum: 31bd12dfbef20fead2490b33aa2d1148 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / 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. / 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.

O Motor Assíncrono Tubular para Aplicação na Extração de Óleo do Subsolo MATÆOS foi desenvolvido na Escola Politécnica da Universidade de São Paulo (EPUSP) com a função de acionar diretamente uma bomba de sucção, instalada no fundo de um poço de petróleo em terra. Dando continuidade aos trabalhos realizados na EPUSP envolvendo sistemas de levitação magnética, foi desenvolvido um mancal magnético ativo (AMB - Active Magnetic Bearing), aplicado ao protótipo do motor em substituição ao mancal mecânico tradicional existente. O projeto abrange a construção de um protótipo de mancal magnético composto das partes mecânicas, elétricas e de software necessárias ao funcionamento do sistema. O projeto do eletroímã foi realizado por meio do método dos elementos finitos (MEF), para análise da densidade de fluxo e da relação entre a força radial e a corrente elétrica nas bobinas. O controle da levitação do mancal é realizado por meio de controlador digital com placas conversoras AD/DA e algoritmo de controle implementado em hardware FPGA. Utilizando o modelo do sistema, os controladores são sintonizados para atender aos requisitos de estabilidade e rejeição de perturbações, que desviem o entreferro do seu valor nominal. Na configuração do AMB, ao invés do sistema tradicional com oito pólos, um conceito diferente é adotado. Neste, uma máquina primitiva bearingless é excitada com corrente contínua e usada como mancal magnético. Os resultados experimentais obtidos com o protótipo em funcionamento mostram que o sistema em malha fechada é estável e apresenta uma resposta transitória satisfatória. / A tubular linear induction motor applied to onshore oil exploitation, named MATÆOS (which is in the Portuguese acronym for Tubular Asynchronous Motor for Onshore Oil Exploitation) was built at Escola Politécnica da Universidade de São Paulo (EPUSP). Its purpose is to directly drive the sucker-rod pump installed in the down hole of the oil well. In continuing the research accomplished at EPUSP concerning magnetic levitation systems, an Active Magnetic Bearing (AMB) was developed and applied to the prototype of the motor in substitution to the existing traditional bearing. The design includes the construction of the magnetic bearing prototype composed of mechanical, electric and software components required to the operation of the system. The electromagnet design was accomplished using the Finite Element Method (FEM) in the analysis of both the flux density and the relationship between the radial force and the suspension winding current. The magnetic bearing levitation control is executed by a digital controller using an AD/DA converter and a control algorithm implemented in FPGA hardware. Using the system model, the controllers are tuned to provide both stability and rejection of disturbances that tend to move the air gap from its nominal value. Instead of the usual eight-pole AMB, a different concept is adopted where a DC-excited primitive bearingless machine is used as a magnetic bearing. The experimental results obtained with the prototype in operation show that the closed-loop system is stable and exhibits a satisfactory transient response.

No description available.

Η παρούσα διδακτορική διατριβή αναφέρεται σε έδρανα ολίσθησης. Συγκεκριμένα, αναφέρεται στο σχεδιασμό και την κατασκευή ενός νέου, πρωτότυπου υβριδικού εδράνου ολίσθησης, το οποίο έχει τη δυνατότητα να λειτουργεί είτε ως υδροδυναμικό, είτε ως ενεργό ηλεκτρομαγνητικό, είτε ως υβριδικό, δηλαδή υδροδυναμικό και ενεργό ηλεκτρομαγνητικό ταυτόχρονα. Προκειμένου να πραγματοποιηθεί ο σχεδιασμός και η κατασκευή του συγκεκριμένου υβριδικού εδράνου ολίσθησης, έγιναν υπολογισμοί και προσομοίωση του υδροδυναμικού πεδίου για τα υδροδυναμικά έδρανα ολίσθησης και του ηλεκτρομαγνητικού πεδίου για τα ηλεκτρομαγνητικά έδρανα στο πρόγραμμα ANSYS. Η προσομοίωση των υβριδικών εδράνων ολίσθησης έγινε με επαναληπτική διαδικασία μεταξύ του υδροδυναμικού και του ηλεκτρομαγνητικού πεδίου προκειμένου να υπολογίζεται το κάθε επιθυμητό μέγεθος. Για το σχεδιασμό του υβριδικού εδράνου ολίσθησης χρησιμοποιήθηκε το σχεδιαστικό πρόγραμμα CATIA. Για την προσομοίωση του ελέγχου του υβριδικού εδράνου ολίσθησης, χρησιμοποιήθηκε το πρόγραμμα Matlab, το οποίο ενεργοποιεί το πρόγραμμα Ansys για τον υπολογισμό των χαρακτηριστικών του υδροδυναμικού και του ηλεκτρομαγνητικού πεδίου του εδράνου και το Simulink module του Matlab για τον υπολογισμό των χαρακτηριστικών του ελέγχου, ώστε να γίνονται όλοι οι απαραίτητοι υπολογισμοί αυτοματοποιημένα. Τέλος, έγιναν υπολογισμοί και προσομοίωση δυναμικής περιστρεφόμενων αξόνων, με στήριξη του ρότορα σε δύο έδρανα και δίσκο προσαρμοσμένο στον ρότορα, στο πρόγραμμα Matlab, με σύνδεση με το Ansys για τον υπολογισμό των συντελεστών ελαστικότητας και απόσβεσης και το Simulink module του Matlab για τον υπολογισμό των χαρακτηριστικών του ελέγχου, με σκοπό την ολοκληρωμένη ανάλυση του συστήματος. Συμπερασματικά, μέσω της συγκεκριμένης διδακτορικής διατριβής αποδεικνύεται πως ο σχεδιασμός, η λειτουργία και η κατασκευή του συγκεκριμένου πρωτότυπου υβριδικού εδράνου ολίσθησης είναι εφικτά, και από τα αποτελέσματα προκύπτει πως η λειτουργία ενός τέτοιου υβριδικού εδράνου ολίσθησης, έχει πολλά πλεονεκτήματα σε σχέση με άλλα έδρανα στήριξης περιστρεφόμενων αξόνων, είτε αυτά είναι απλά είτε υβριδικά και μπορεί να εφαρμοστεί είτε σε εργαστηριακό επίπεδο είτε σε βιομηχανικές εφαρμογές. / The present doctoral thesis refers to hydrodynamic journal bearings. Specifically, it refers to the design and construction of a new, innovative hybrid journal bearing, which has the ability to function either as hydrodynamic or active magnetic or hybrid, i.e. both hydrodynamic and active magnetic, at the same time. In order to be performed the design and construction of the specific hybrid journal bearing, calculations and simulation of the hydrodynamic field for the hydrodynamic journal bearings in the program ANSYS, have been made. The simulation of the hybrid journal bearings has been made with iterative process, between the hydrodynamic and active magnetic field, so that every desired magnitude can be calculated. For the design of the hybrid journal bearing, the designing program CATIA has been used. For the simulation of the control of the hybrid journal bearing, the program Maltab has been used, which activates the program Ansys, for the calculation of the features of the hydrodynamic and active magnetic field of the bearing and the Simulink module of Maltab, for the calculation of the features of control, so that all necessary calculations can be made automated. Finally, calculations and simulation of rotor dynamics, with support of the rotor in two bearings and disc adjusted to the rotor, in Maltab, in connection to Ansys, for the calculation of the elastic and damping coefficients and the Simulink module of Maltab, for the calculation of the features of control, have been made, having as a purpose the complete analysis of the system. In conclusion, through the specific doctoral thesis, it is proved that the design, function and construction of the specific, new hybrid journal bearing, can be achieved and the results show that the function of such a hybrid journal bearing, has many advantages compared to other bearings of support of rotors, either they are simple or hybrid and it can be applied either to laboratory level or industrial applications.

The McTronX research group at the North-West University is currently researching self-sensing techniques for Active Magnetic Bearings (AMB). The research is part of an ongoing effort to expand the knowledge base on AMBs in the School of Electrical, Electronic and Computer Engineering to support industries that make use of the technology. The aim of this project is to develop an integrated co-processor based power electronic drive with the emphasis placed on the ability of the co-processor to execute AMB self-sensing algorithms. The two primary techniques for implementing self-sensing in AMBs are state estimation and modulation. This research focuses on hardware development to facilitate the implementation of the modulation method. Self-sensing algorithms require concurrent processing power and speed that are well suited to an architecture that combines a digital signal processor (DSP) and a field programmable gate array (FPGA). A comprehensive review of various power amplifier topologies shows that the pulse width modulation (PWM) switching amplifier is best suited for controlling the voltage and current required to drive the AMB coils. Combining DSPs and power electronics to form an integrated co-processor based power electronic drive requires detail attention to aspects of PCB design, including signal integrity and grounding. A conceptual design is conducted and forms part of the process of compiling a subsystem development specification for the integrated drive, in conjunction with the McTronX Research Group. Component selection criteria, trade-off studies and various circuit simulations serve as the basis for this essential phase of the project. The conceptual design and development specification determines the architecture, functionality and interfaces of the integrated drive. Conceptual designs for the power amplifier, digital controller, electronic supply and mechanical layout of the integrated drive is provided. A detail design is performed for the power amplifier, digital controller and electronic supply. Issues such as component selection, power supply requirements, thermal design, interfacing of the various circuit elements and PCB design are covered in detail. The output of the detail design is a complete set of circuit diagrams for the integrated controller. The integrated drive is interfaced with existing AMB hardware and facilitates the successful implementation of two self-sensing techniques. The hardware performance of the integrated coprocessor based power electronic drive is evaluated by means of measurements taken from this experimental self-sensing setup. The co-processor performance is evaluated in terms of resource usage and execution time and performs satisfactorily in this regard. The integrated co-processor based power electronic drive provided sufficient resources, processing speed and flexibility to accommodate a variety of self-sensing algorithms thus contributing to the research currently underway in the field of AMBs by the McTronX research group at the North-West University. / Thesis (M.Ing. (Electrical Engineering))--North-West University, Potchefstroom Campus, 2009.