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 co upling-rotor system capable of describing the mechanical vibration res ulting from misalignment and unbalance was developed. The universal jo int effect was included in the model to take the misalignment effect i nto account. Generalized system equations of motion for a system under misalignment and unbalance conditions were derived using the componen t mode synthesis technique. The derived equations indicate that the fo rcing frequencies due to shaft misalignment are even multiple frequenc ies 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 reso nance condition occurs. As a result of this, the vibrations induced by misalignment are amplified into major vibration sources.