Methodology for Analysing Controllability and Observability of Bladed Disc Coupled Vibrations

Many bladed rotating machines such as helicopters, turbines and compressors are susceptible to blade faults due to vibration problems. Typically, blade vibrations in this kind of machines are suppressed by using passive mechanical components. However, when passive control techniques are not efficient enough to suppress vibration problems, active control techniques might become the only feasible way of avoiding vibration problems.

Implementing effectively active vibration control into any machine implies that the controllability and observability have to be analysed in order to determine where to place sensors and actuators so that all vibration levels can be monitored and controlled. Due to the special dynamic characteristics of rotating coupled bladed discs, where disc lateral motion is coupled to blade flexible motion, such analyses become quite complicated.

The dynamics is described by a time-variant mathematical model, which presents parametric vibration modes and centrifugal stiffening effects resulting in increasing blade natural frequencies. In this framework the objective and contribution of this paper is to present a methodology for analysing the modal controllability and observability of bladed discs.

The aim is to determine where to locate actuators and sensors in order to be capable of controlling and monitoring both disc lateral and blade vibrations. The analysis methodology is based on the time-variant modal analysis. A numerical example of the methodogy is provided. A tuned rotating bladed disc is analysed.

The analysis shows that blade actuators and sensors are inevitable in order to control and monitor the vibrations. Moreover, it shows that the controllability and observability depends very strongly on the rotational speed.