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Publications in Scientific Journals:

T. Pumhössel, B. Hopfner, H. Ecker:
"Enhanced Utilization of Structural Damping of Rotating Machines Using Impulsively Shaped Torsional Moments";
Technische Mechanik, 37 (2017), 2-5; 208 - 217.



English abstract:
The reduction of torsional vibrations of rotating machines is an important issue, as they may Lead to a decrease of
the pe,formance, or in the warst case, to a damage of the machinery. In particular, self-excited vibrations have to
be suppressed in any case due to their hazardous nature.
In this contribution, a method is proposed, which allows utilizing the structural damping inherent to every rotating
machine much more ejfectively by introducing impulsively shaped torsional moments, resulting in repeated modal
transfers of vibration energy. Depending on the chosen impulsive strength, the energy transfers are accompanied
by feeding external energy to, or extracting energy from the mechanical system. lt is shown theoretically by approximating
the impulses by Dirac-delta functions that an impulsive strength exists, where no energy crosses the
system boundary, i.e. energy extracted from one mode is fed entirely to another mode of vibration. In the case
of a conservative system, a repeated application of such impulses induces a periodic exchange of energy between
lower and higher modes. Taking into account the structural damping reveals the advantages of transferring energy
across modes. As higher modes possess higher damping ratios than lower ones, the structural damping of the
rotating machine can be utilized much more ejfectively, which Leads to a significant reduction of torsional vibrations.
The underlying equations of motion ofthe impulsively excited system can be written as recursive difference
equations with constant coefficients. Hence, the stability properties of the system can be investigated according to
the Floquet theory. lt is shown that the proposed concept is capable of suppressing seif-excited vibrations. Stability
charts are presented which allow to identify stable areas of operation. Finally, some numerical results of a test-rig
are shown, underlining the effectivity of the proposed method.

Keywords:
Impulsive parametric excitation

Created from the Publication Database of the Vienna University of Technology.