Shah, Arpi (2016) Design and simulation of magnetic thrust and radial bearing system. (MSc(R) thesis), Kingston University, .
Abstract
Active magnetic bearings (AMBs) are used in many high speed machinery applications because of their advantages of no contact, no wear, no need for lubrications and ability to operate in high rotational speeds. AMBs represent an alternative solution to traditional mechanical bearing due to their contactless working principle. Touchdown bearings are needed in AMBs to prevent system damage under certain conditions such as sudden impact or sudden change of unbalance. In these conditions, rotor may make contact with touchdown bearings. AMBs may have the capability to accommodate sudden impact without contact though this will require novel design of control strategy for thrust and touchdown bearing. The purpose of this work is to provide platform for the robust control design research of flexible rotor-AMB touchdown systems. To this end research work concentrates on the design, construction and simulation of magnetic thrust and touchdown system. The report begins with the identifications of flexible rotor AMB system configuration. In this content accurate rotor system model considering AMB, thrust and touchdown discs was obtained using FEM technique according to Timoshenko beam theory. Design of flexible rotor AMB system requires careful attention towards rotordynamic design aspect such as observability and controllability and it is important that actuator and sensor location are away from the nodal point. Identification of flexible rotor-AMB system model is achieved in a series of steps. Free-free undamped mode shapes were obtained in this work which predicts the dynamic behaviour of the flexible rotor. The plot of the free-free mode shapes and natural frequencies results have shown that the system is controllable and observable. Second, Campbell diagram was generated to see the effect of gyroscopic behaviour on the splitting of natural frequencies into forward and backword modes. Campbell diagram results showed satisfactory behaviour of flexible rotor. The second goal of this work is to acquire technical design, modelling of electromechanical components and control unit. Magnetic actuator design specifications were obtained based on magnetic circuit analysis. Unigraphics software was used to carry out detail design and 3D modeling/assembly of electromechanical components. In this context purchase cost estimation was identified based on quotations. Purchase of rotor model components were made outside. The third goal of a thesis work is to verify the flexible rotor system model using experimental test. Hammer used as a force transducer was used in the test as excitation of the system and accelerometer used to measure response of the system. The experimental result validates the FEM technique because it is in reasonably good agreement with simulation results. The experimental mode shape results showed rotor will perform well within design speed range.
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