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H. Ecker:
"Beneficial effects of parametric excitation in rotor systems";
Talk: IUTAM Symposium on Emerging Trends in Rotor Dynamics, New Delhi, India (invited); 2009-03-23 - 2009-03-26; in: "IUTAM Symposium on Emerging Trends in Rotor Dynamics", Indian Institute of Technology Delhi, India, (2009), 10 pages.

For a long time parametric excitation in rotor systems was associated only
with the gravity effect on the bending vibration of rotors with anisotropic shafts.
Parametric excitation seemed to have only negative effects on the dynamics of rotating
systems and therefore the focus of research studies was on how to avoid or at
least minimize the adverse consequences of parametric excitation.
However, recent research results have shown that parametric excitation may not
only cause harmful instabilities in a dynamical system but can also improve the capability
of a system to suppress vibrations. In particular it is possible to avoid the
onset of an instability by introducing parametric excitation to the system. These
findings are quite new and the numerous possibilities of making use of it still need
to be explored and discussed.
This article presents the basics of parametric excitation as a means to suppress
vibrations in rotating machines. Several theoretical and experimental studies are reviewed.
The potential of this novel design concept is discussed and directions for
further research and future practical applications are outlined.

Rotor instability, vibration damping, time-periodic stiffness variation