Affiliations: [a] School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China | [b] State Key Laboratory of Technologies in Space Cryogenic Propellants, Beijing 100028, China | [c] Technical Institute of Physics and Chemistry of Chinese Academy of Sciences, Beijing 100190, China
Correspondence:
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Corresponding author: Li Wang, School of Mechanical Engineering, University of Science and Technology Beijing, Beijing 100083, China. E-mail:liwang@me.ustb.edu.cn
Abstract: This paper uses finite element method to analyze the
effect of brace stiffness and damping of an electromagnetic bearing on the
critical speed of a flexible rotor for the rotor system of a high-speed
turbo-expander. Result shows that eight orders of critical speed and eight
modal shapes exist in the range of the calculation speed for the flexible
rotor system of an electromagnetic bearing. The first six orders of
vibrations are swing of rigid body, in which the critical speed increases
with increase of the brace stiffness of the bearing. The seventh and eighth
orders are first-order bending, in which the stiffness of the bearing has
little influence on the critical speed of the rotor. Adjusting the stiffness
of magnetic bearing can significantly change the corresponding critical
speed of the rotor during rigid body swing. However, doing so has little
influence on the critical speed of the first-order bending. The rotor system
experimental test results of turbo-expander electromagnetic bearing show
that adjusting the brace stiffness and damping of electromagnetic bearing
through the control system can change the distribution of each order of the
critical speed of the rotor system to maintain a steady working speed of
30000 r/min. Moreover, the movement tracks of the rotor axis center can be
maintained within 6 μ m when external influences interfere with the rotor
during operation.
Keywords: Active electromagnetic bearing, rotor dynamics, stiffness and damping, stability
