Dynamic Analysis of Geared Rotors-A Review
Rotor dynamics plays an important role in many engineering fields such as gas turbine, steam turbine, reciprocating and centrifugal compressors, the spindle of machine tools, and so on. Owing to the growing demands for high power, high speed, and light weight of the rotor-bearing system, computations of critical speeds and steady-state response at synchronous and sub critical resonances become essential for system design, identification, diagnosis, and control. The present paper reviews some of the approaches that have been developed to provide a means for understanding and simulations of the characteristics of a geared rotor dynamic system. More emphasis is given on the lateral vibrations of the rotors, effect of coupling of torsional and lateral vibration of rotors especially when the rotors are coupled with gears. Keywords—Critical speed, Geared rotors, Lateral vibrations, Rotor dynamics, Torsional vibrations.
Theoretical analysis of lateral response due to torsional excitation of geared rotors
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.
Dynamic Characteristics of a Gear train System with Softly Supported Shafts
Coupled torsional-lateral vibration of softly supported shafts in a spur geared system is investigated. Taking torsional flexibility and bearing stiffness into consideration, dynamic characteristics of a countershaft in a geared system are discussed. It is shown in this paper that the dynamic characteristics of a countershaft are affected not only by the angle between the two power transmitting directions on the shaft but also by the angle between power transmitting direction and elastic principle axis of the support. In this study, the relationships between these factors and dynamic characteristics including natural frequencies are discussed numerically and experimentally.