Abstract
Passive magnetic bearings are known due to the excellent
characteristics in terms of friction and no requirement of additional
energy sources to work. However, passive magnetic bearings
do not provide damping, are not stable and, depending on
their design, may also introduce magnetic eccentricity. Such
magnetic eccentricities are generated by discrepancies in magnet
fabrication. In this framework the main focus of the work is
the theoretical as well as experimental investigation of the nonlinear
dynamics of a rotor-bearing system with strong emphasis
on the magnetic eccentricities and non-linear stiffness.
In this investigation passive magnetic bearings using axially-
aligned neodymium cylinder magnets are investigated. The
cylinder magnets are axially magnetised for rotor as well as
bearings. Compared to bearings with radial magnetisation, the
magnetic stiffness of axially-aligned bearings is considerably
lower, nevertheless they allow for asymmetric stiffness mounting,
and it could be beneficial for rotor stabilization.
A theoretical model is proposed to describe the non-linear
rotor-bearing dynamics. It takes into account non-linear behaviour
of the magnetic forces and their interaction with a multibody
system composed of rigid rotor and flexible foundation. The
magnetic eccentricities of the shaft magnets are modelled using
the distances (amplitudes) and directions (phase angles) between
the shaft axis and the centre of the magnetic fields generated. A
perturbation method, i.e. harmonic balancing, is used in order to
evaluate the frequency response of the non-linear system.
The experimental validation of the model is carried out us-
Address all correspondence to this author.
ing a dedicated rotor-bearing system set-up. The test set-up consists
of a vertical rigid shaft and disc supported by two passive
magnetic bearings using axially-aligned neodymium cylinder
magnets. The magnetic bearing housings are flexibly supported,
allowing horizontal motions. The housings are connected
to each other by means of elastic beams. The shaft is free in one
end and coupled to a DC motor on the other by means of a flexible
coupling. On the free end a disc is attached where imbalances
and gyroscopic effect can be generated.
Comparison between theory and experiment shows high
level of resemblance, which validates the theoretical model and
the explanations for the quasi-static and dynamic responses. The
magnetic eccentricities and mass imbalance effects are clearly
detected and distinguished.
detected and distinguished.
Original language | English |
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Title of host publication | Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition |
Number of pages | 10 |
Volume | 4A |
Publisher | The American Society of Mechanical Engineers (ASME) |
Publication date | 2014 |
Article number | IMECE2014-38032 |
ISBN (Print) | 978-0-7918-4647-6 |
DOIs | |
Publication status | Published - 2014 |
Event | ASME 2014 International Mechanical Engineering Congress & Exposition - Montreal, Canada Duration: 14 Nov 2014 → 20 Nov 2014 |
Conference
Conference | ASME 2014 International Mechanical Engineering Congress & Exposition |
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Country/Territory | Canada |
City | Montreal |
Period | 14/11/2014 → 20/11/2014 |