Modal Controllability and Observability of Bladed Disks and their Dependency on the Angular Velocity

Abstract

Rotating bladed disks are characterized by time-variant mathematical models presenting vibration coupling among rotor lateral motion and blade flexible motion. Moreover, they present parametric vibration modes and the blade natural frequencies may change depending on the angular velocity due to centrifugal stiffening. Consequently, the degree of controllability and observability of bladed disks also becomes time-varying, dependent on angular velocity, and a difficult task to analyze. In this paper we present a methodology for analyzing the modal controllability and observability of a bladed disk, based on time-variant modal analysis. The method takes into account time-variant parametric vibration mode shapes, and quantitative measures of modal controllability and observability are calculated. Numerical results show that, in order to control blade and shaft vibrations of a tuned bladed disk, by means of active control, blade-based as well as shaft-based sensing and actuation are required to monitor and control all vibration levels. If rotor blades are properly mistuned, the results show that disk as well as blade vibrations are monitorable and controllable by using only shaft-based sensing and actuation. The analysis shows why the mistuned disk becomes theoretically controllable and observable, via the presence of parametric mode shape components. Finally, the results show that the levels of controllability and observability depend significantly on the angular velocity, no matter the number of applied sensors and actuators used or their positioning.