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H. Ecker:
"Experimental results on parametric excitation damping of an axially loaded cantilever beam";
Talk: ASME 2009 International Design Engineering Technical Conferences & Computers and Information in Engineering (IDETC09), San Diego, California, USA; 2009-08-30 - 2009-09-02.

Slender beam structures as design elements are found in various areas as e.g. in aerospace applications and in robotics. The blading of a rotor as
used in turbomachinery is another example and shares a common problem with many other applications - insufficiently damped bending vibrations
due to little structural or material damping. Therefore, new solutions to increase damping and reduce the level of structural vibrations are always
sought for.
This contribution investigates experimentally a novel method to enhance damping of beam vibrations. A slender and inextensible cantilever beam is
loaded with a controlled force, which acts on the tip of the beam and always points to the root of the beam. Only in the undeflected state of the beam
this force represents exactly an axial load. A test rig was designed and built to test this new concept.
To achieve a damping effect by applying an external force at the tip of the beam, a suitable control law is needed. The concept uses an open-loop
control, which needs no measured vibration signals. This method is based on the stabilization effect that can be achieved for parametrically excited
systems next to a certain characteristic frequency. By the open-loop control the (almost) axial force is changed harmonically in time, which leads to a
time-periodic stiffness matrix of the system and, hence, a parametrically excited system.
Experimental results are presented and show that the control method can suppress the free vibrations of the beam much faster, compared to the
uncontrolled system. The open-loop control works very well for initial first mode vibrations. When the initial conditions are second mode vibrations,
the performance is somewhat decreased, but still remarkable results are obtained.