Experimentelle Modalanalyse und aktive Schwingungsdämpfung eines biegeelastischen Rotors

Strohschein, Daniel

kassel university press, ISBN: 978-3-89958-561-2, 2011, 217 Pages
(Berichte des Instituts für Mechanik 2/2011)

Zugl.: Kassel, Univ., Diss. 2011

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Content: The present dissertation makes a contribution to the experimental modal analysis and active vibration control of elastic rotors. The experimental modal analysis is an established method to identify modal parameter in the machine- and structural dynamics. These also apply for the active vibration control, in which robust applications are still in development process. In the rotor dynamic both cases need particular requirements. The transmission for vibration excitation and for active damping forces in the rotor, the practical implementation, recording and analysis of measurement data are some of this context to be named reasons.

For the experimental modal analysis a twin Magnetic-Exciter-System is developed, which is based on the principle of magnetic bearings. With this system a contactless and measurable excitation of the rotor and the measurement of the vibration response in two orthogonal directions are possible. Furthermore the Magnetic-Exciter is also able to produce the necessary forces to do the active vibration damping of the rotor.

The used rotor test stand consists of a 1.4 m long rotor shaft, which is plaint on hydrodynamic bearings. On the shaft two discs with different diameters are mounted. The larger disc is positioned on cantilevered to create large gyroscopic forces. In the examined frequency range of up to 500 Hz 10 elastic bending natural frequencies are found. The associated mode shapes divide due to gyroscopic forces mostly into clear forward and backward modes.

For the identification of modal parameters the nonparametric identification is used to identify the frequency responces from the measured excitation and response signals. With the frequency responces and the parametric identification the modal parameters natural frequencies, mode shapes and viscouse damping are calculated.

The closed loop model for the active vibration damping consists mainly of the rotor, the Magnetic-Exciter-System and the current amplifiers. In the hybrid rotor model, the shaft is discretized into finite elements and the discs are modeled as rigid bodies. The hydrodynamic bearings with their speed dependent elastic and damping characteristics are also considered. The experimentally determined modal parameters are adapted to the rotor model with a model-updating process. Afterward the degrees of freedom of the rotor model are reduced by the method of modal condensation. In this context, the occurring problem of spillover is
described in a special meaning. The analysis of the close loop model results in a Positive-Position-Feedback (PPF-)controller that meets the requirements of the active vibration damping. The active vibration damping is shown on the stationary and the run-up and rundown rotor through simulations and experimental results.

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