Theoretical analysis of lateral response due to torsional excitation of geared rotors

Abstract

This paper is concerned with lateral response of geared rotors due to torsional excitation. Usually torsional response is determined due to excitation torque, such as short circuit torque, to determine the safety of a turbo generator set and the coupling of bending and torsion in such an analysis is ignored. Such an analysis gives an accurate prediction only when the bending natural frequencies are not close to the spin speed and its higher as well as lower orders. In this work, the coupling between bending and torsion due to gears as well as the effect of axial torque on bending vibrations is taken into account to determine the coupled lateral and torsional response due to torsional excitation. Examples are given which illustrate the importance of such coupling mechanism giving rise to large amplitudes of bending vibrations which may be harmful to the operation of geared turbine rotors. The effect of axial torque is shown to be less significant, even when the rotor runs at the bending natural frequency and is subjected to a short circuit torque.