Rotordynamic analysis of machines on active magnetic bearings: comparison to fluid film bearing machines and vibration specifications

This article considers rotordynamic modelling of a flexible rotor supported on active magnetic bearings (AMBs) and compares the process to a similar process for fluid film bearings (FFBs). Currently, vibration specification standards are good for industrial FFB supported rotors but are not adequate for active magnetic bearing supported rotors. This article discusses comparative studies of rotors on AMBs and FFBs involving critical speeds, AMB and FFB stiffness and damping values, mode shapes, and forced response. One objective is to assist in better communication between mechanical engineers who typically design and operate industrial machines and controls and engineers (usually electrical engineers) who design and produce AMBs. The stability of AMB machines subject to internal cross-coupled stiffness such as in seals is not considered in this work, except for the introduction.