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Active Magnetic Bearings (AMB) are a relatively recent innovation in bearing technology. Unlike conventional bearings, which rely on mechanical forces originating from fluid films or physical contact to support bearing loads, AMB systems utilize magnetic fields to levitate and support a shaft in an air-gap within the bearing stator. This design has many benefits over conventional bearings. The potential capabilities that AMB systems offer are allowing this new technology to be considered for use in state-of-the-art applications. For example, AMB systems are being considered for use in jet engines, submarine propulsion systems, energy storage flywheels, hybrid electric vehicles and a multitude of high performance space applications. Many of the benefits that AMB systems have over conventional bearings makes them ideal for use in these types of vehicular applications. However, these applications present a greater challenge to the AMB system designer because the AMB-rotor system may be subjected to external vibrations originating from the vehicle's motion and operation. Therefore these AMB systems must be designed to handle the aggregate vibration of both the internal rotor dynamic vibrations and the external vibrations that these applications will produce. This paper will focus on the effects of direct base excitation to an AMB/rotor system because base excitation is highly possible to occur in vehicular applications. This type of excitation has been known to de-stabilize AMB/rotor systems therefore this aspect of AMB system operation needs to be examined. The goal of this research was to design, build and test a test rig that has the ability to excite an AMB system with large amplitude base excitation. Results obtained from this test rig will be compared to predictions obtained from linear models commonly used for AMB analysis and determine the limits of these models. / Master of Science

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The subject of this thesis is about the balancing of large flexible rotors which exhibit mixed modal characteristics. The objective of the research was to develop a balancing procedure to determine correction masses without trial runs. This required the determination of(a) the modal vibration vectors for each resonance, (b) the modal damping ratios,(c) the mode shapes and(d) the equivalent mass of the rotor for each mode. It was made clear from the beginning that trial runs are unavoidable either, when the mode shapes cannot be determined using an analytical or numerical method, or when there is dual vibration at normal operating speed, produced by the influence of higher unbalanced modes, is too high to allow continuous operation of the machine. Therefore, the scope of the project was limited to the possible determination of correction masses without trial runs for the vibration modes included within the normal operating range. Some studies about the minimisation or complete elimination of trial runs have been published by several authors, but a literature search revealed no reports of systematic application of these procedures to field balancing of large turbo generators. This suggested that some practical difficulties had still to be overcome, opening the possibility for further research on this area. Analysis of the rotor response demonstrated the necessity of considering the angular position of the transducers when registering the rotor vibration. It was shown that measuring in a direction other than those of the principal axes of stiffness introduces errors when determining the magnitude and phase of the correction masses. That is to say, failing to consider the effects of the transducer angular position eliminates the possibility of balancing the rotor without trial runs. This is the first time that this problem has been recognised. The procedure developed was verified using an experimental rotor rig. The successful application of the procedure to the balancing of this rotor demonstrates that balancing withouttrialrunsisnotonlyatheoreticalbutalsoapracticalpossibility. The dynamic characteristics of the rotor rig, however, were some what limited and did not cover all the possibilities considered during the project. Therefore, a more complete numerical example was also successfully solved using the computer model of a rotor with characteristics similar to those of a real turbine, and whose unbalanced distribution was not initially known by this author.