The foil-air bearing (FAB) plays a key role in the development of high speed, economical and environmentally friendly oil-free turbomachinery. However, FABs are known to be capable of introducing undesirable nonlinear effects into the dynamic response of a rotor-bearing system. This necessitates a means for calculating the nonlinear response of rotor systems with FABs. Up to now, the computational burden introduced by the interaction of the dynamics of the rotor, air film and foil structure has been overcome by uncoupling these three subsystems, introducing the potential for significant error. This paper performs the time domain solution of a simple rotordynamic system without uncoupling the state variables. This solution is then used as a reference for the verification of two proposed novel methods for reducing the computational burden: (a) use of harmonic balance; (b) use of Galerkin transformation. The applicability and accuracy of these two methods is illustrated on a simple symmetric rotor-FAB system.
A nonlinear model for rotor-shaft joints of high speed rotor systems with internal damping