An investigation into the behaviour of rotating shaft systems, incorporating oil film bearings and gyroscopic effects

The aim of the work presented in this thesis was to investigate the behaviour of rotating shaft systems which are supported on oil film bearings and which have a significant amount of gyroscopic inertia associated with the rotating parts. A computer program was written to predict the non-linear behaviour of a general rotor incorporating flexibility and gyroscopic inertia, the rotor being carried on a number of oil film bearings. The bearing characteristics were established by successive over-relaxation of a finite difference form of Reynolds’ Equation, while the characteristics of the elements of the rotor were described by classical mechanics. The dynamic stiffness matrix was built up from these characteristics using a routine and general method invented by Kron(5) and using the resultant set of equations of motion were solved by a forward integration technique. If only small amplitude movement of the journal within the clearance space is assumed, then the bearing stiffness and damping characteristics can be assumed to be linear. The stability of a wide range of systems was tested making this assumption, the stability being established by an eigenvalue analysis. It was found that the small amplitude stability was in general worsened by the presence of gyroscopic inertia, but that for some very particular combinations of system parameters, the stability could be greatly improved (relative to no gyroscopic inertia) by a very small amount of gyroscopic inertia. It was anticipated that for these cased, the stabilising effect would not operate if the amplitude of motion was large, and this was found to be the case when checked with the non-linear analysis program described earlier. It was also anticipated that from some systems, the while amplitudes would settle down to a particular value, regardless of the starting conditions. Again, the anticipated results and the program output agreed