Effect of design parameters on the stability of multi-mass geared systems supported on fluid film bearings and subjected to unbalance and torsional excitation

Many high speed mechanical systems incorporate gearing for speed reduction. This study investigates the stability of multi-rotor geared systems supported on oil film bearings, taking into consideration the coupling between torsional and lateral dynamics.;The emphasis of the study is on the analysis of the interaction between the combined torsional and whirl instabilities.;The result of simulation in this study checked the previously published empirical approach for predicting nonharmonic whirl of geared systems which results from the inertial coupling at the gear mesh.;The feasibility of inducing a lateral and the torsional instability to neutralize an anticipated unstable condition is investigated. The possibility of suppressing the instabilities by controlling the parameters of the oil film bearings is also considered.;It is interesting to note that the coupling between the torsional and lateral oscillations can induce torsional instability due to unbalance excitation. Similarily, a torsional disturbance can induce whirl.;A procedure is given to guide the designer in selecting the system parameters which insure its safe operation in critical situations where instabilities or resonances are expected.;It is shown that torsional instability can be avoided by inducing a tuned whirl using an unbalance excitation in a system supported on either ball bearings or oil film bearings.