Active modal control of a flexible rotor

This study explores the applicability of a novel approach by applying a dual-level control for modal vibration suppression of a rotor possessing repeated rigid body modes. Independent modal space control (IMSC) of undamped or proportionally damped systems has been well established. However, the technology was not correctly developed for non-classically damped systems by the pioneer researchers. For non-proportionally damped systems with repeated rigid body modes, the problems of orthogonality and singularity must be treated in a different fashion to facilitate modal vibration control. The present approach applies a first level control to remove any combination of flutter, divergence, rigid body, and/or repeated modes by enabling positive definiteness of the augmented system. A second level control is then applied for the augmented system with complex modes. Ordinary decoupling procedure by using the orthogonality of the left and right eigenvectors can thus be applied for subsequent modal control to suppress excessive vibration of the complex dynamic systems. It is demonstrated that a mode switching approach by directing control to the modes with higher vibration contribution can be beneficial in alleviating the higher mode residual vibration.