Transient dynamic analysis of brushless direct current motors by coupling electromagnetic and hydrodynamic forces

Vibration of a crankshaft-journal bearing system driven by an electric motor is a coupled phenomenon between hydrodynamic characteristics and magnetic origins through the motor air gap. With the advent of new high-energy magnets together with variable speed motor applications, magnetic sources of vibration are becoming more serious. This article investigates the transient whirl responses of a rotor system with purely hydrodynamic origins and compares it with that of magnetically coupled origins. Results show that magnetically coupled sources significantly affect the vibration of the rotor-motor system.