Modal balancing of flexible rotors with gyroscopic effects using kalman filter

Abstract

At present day, rotating machinery is being used at numerous different fields. Looking to its development so far, demand from the rotating components is evolving towards becoming lighter and spinning faster by still keeping the same or higher amount of life cycles. The mentioned trend makes rotating components less stiff and increases their operating speed range. This can possibly introduce vibration driven problems such as noise, excessive wear or shortened fatigue life. One topic related with vibrations is the balancing of the rotating hardware. Balancing approach of rotating components differ depending on the classification of a rotor being "rigid" or "flexible". The difference between the two is, a rigid rotor operates significantly less than its first critical bending speed and a flexible rotor operates close to or above its first critical bending speed. Balancing of rigid rotors are very well-known theoretically and practically. On the other hand, flexible rotor balancing is not standardized and there are various approaches for the process. This study will try to develop a robust and precise flexible balancing procedure considering the gyroscopic effect which is usually neglected at many flexible balancing techniques. The developed approach will be suitable for both test rig and in-site balancing. The approach hosts a FE model to be used and does not require any trial mass. It is necessary to collect displacement data from the rotating hardware at close to critical speeds. FE model and sensor data are adequate to generate the unbalance values and positions using a series of calculations. These calculations require a force reconstruction method to be used and it is decided to use Augmented Kalman Filter. A regular Augmented Kalman Filter is not suitable for capturing the desired phenomena's, thus, some additional tweaks are made so that it fits better for the nature of rotordynamics. When the forces are generated, it is an easy effort to obtain unbalance masses and positions. The balancing can be done at close to critical speeds, mode by mode using modal approach and without upsetting the previously balanced modes. An important point on setting the balancing criteria is using the complex eigenvalue analysis to obtain modal properties due to existence of gyroscopic effect.