VIBRATION ANALYSIS OF A MOTOR FLEXIBLE COUPLING ROTOR SYSTEM SUBJECT TO MISALIGNMENT AND UNBALANCE .1. THEORETICAL-MODEL AND ANALYSIS

Shaft misalignment and rotor unbalance are major concerns in rotating machinery. In order to understand the dynamic characteristics of these machinery faults, a theoretical model of a complete motor-flexible coupling-rotor system capable of describing the mechanical vibration resulting from misalignment and unbalance was developed. The universal joint effect was included in the model to take the misalignment effect into account. Generalized system equations of motion for a system under misalignment and unbalance conditions were derived using the component mode synthesis technique. The derived equations indicate that the forcing frequencies due to shaft misalignment are even multiple frequencies of the motor rotational speed. The system response depends heavily on the relation between the system natural frequencies and the motor rotational speed. If any of the even multiples of the motor rotational speed is at or close to one of the system natural frequencies, a resonance condition occurs. As a result of this, the vibrations induced by misalignment are amplified into major vibration sources.