Abstract
When implementing active control into bladed rotating machines aiming at reducing blade vibrations, it can be shown that blade as well as rotor vibrations can in fact be controlled by the use of only shaft-based actuation. Thus the blades have to be deliberately mistuned. This paper investigates the dynamical characteristics of a mistuned bladed rotor and shows how, why and when a bladed rotor becomes controllable and observable if properly mistuned. As part of such investigation modal controllability and observability of a tuned as well as a mistuned coupled rotor-blade system are analysed. The dependency of the controllability and observability on varying rotational speed and mode shape interaction phenomena between parametric and basis mode shape components are also analysed. Numerical results reveal a limitation of the achievable controllability and observability, once quantitative measures of modal controllability and observability converge toward steady levels as the degree of mistuning is increased. Finally, experimental control results are presented to prove the theoretical conclusions and to show the feasibility of controlling rotor and blade vibrations by means of shaft-based actuation in practice.
Highlights
The implementation of active vibration control into bladed rotating machines, such as for instance turbo machinery, implies that sensors and actuators will have to be built-in the blades monitoring their vibration levels and applying proper control action based on the measurements
Active controlled bearings for rotor vibration control have been developed for many years, applied for various purposes and shown their effectivenes in practical applications
One could ask: Can rotating blade vibrations be controlled using such active controlled bearings? Are actuators built into the blades absolutely required in order to control rotor blade vibrations? Can the rotor as well as blade vibrations be monitored and controlled by means of shaft-based sensing and actuation solely?
Summary
The implementation of active vibration control into bladed rotating machines, such as for instance turbo machinery, implies that sensors and actuators will have to be built-in the blades monitoring their vibration levels and applying proper control action based on the measurements. From the theoretical viewpoint the main contributions are: i) the modal controllability and observability and their dependency on stiffening and frequency veering effects [15] are carefully quantified in the absence of periodic excitation induced by the gravity; ii) it is shown how and why the introduction of deliberate blade mistuning makes the bladed rotor controllable and observable using only shaft-based actuation and sensing; iii) the influence of the rotational speed on the degrees of controllability and observability is investigated; iv) the influence of mistuning patterns on the controllability of vertical bladed rotors with different number of blades is examined. The feasibility of controlling blade vibrations in a vertical bladed rotors by means of shaft-based active control is tested, achieving significant better performances than those delivered by the controllers presented in [20,21]
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