Abstract
Magnetic bearing systems are commonly used for high speed rotor applications, having particular advantages in low pressure or vacuum environments. They provide an alternative to conventional journal, rolling element and gas bearings. The benefits of using magnetic bearing systems are well documented in terms of low fiction and controllable stiffness and damping. In order to protect the magnetic bearings in cases of power failure, intermittent faults and unexpected external disturbances, secondary back-up or touchdown bearings are usually included so that rotor and stator contact is prevented. If, for any reason, the rotor should make contact with a touchdown bearing, the rotor dynamic response will depend on many operational parameters and the rotor unbalance distribution. Contact between the rotor and touchdown bearings could cause relatively high contact forces, potentially damaging in terms of direct mechanical stresses and through induced heat inputs when slip occurs.In this thesis, parameters that allow rotor contact-free orbits and persistent contact orbits to co-exist are investigated. These include rotational speed, unbalance distribution, disturbance force, magnetic bearing and touchdown bearing axial alignment. In order to alleviate the contact problem, an active controlled touchdown bearing is used to reduce contact and friction forces with the aim of returning the rotor to a contact-free orbit.
It is found that using active touchdown bearing motion control to achieve contact-free levitation from a persistent contact condition is possible when suitable touchdown bearing control strategy is applied. The effect of magnetic bearing and touchdown bearing misalignment on rotor contact dynamics is also analysed and found to have little effect on the effectiveness of touchdown bearing control. The control strategies through an active touchdown bearing have been implemented experimentally; they are demonstrated as being effective in returning a rotor to its contact-free levitation from a persistent contact condition.
| Date of Award | 11 Jun 2015 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Patrick Keogh (Supervisor) |