Analysis of whirl speeds for rotor-bearing systems supported on fluid film bearings

摘要

There are several numerical approximations for vibration analysis of rotor bearing systems and the most popular approach is the Finite Element Method. In the light of the above it is proposed to undertake a study on the dynamic behaviour of Timoshenko beam supported on hydrodynamic bearings incorporating internal damping using FEM model. Critical speeds are estimated for synchronous whirl at different operating conditions using Campbell diagrams. It is observed in the analysis that in addition to the natural whirl frequencies, for every spin speed another whirling frequency appears in the solution, which is around half the spin speed. In case of fluid film bearings, half whirl is very common phenomenon. In case of dynamic coefficients evaluated using short bearing approximation, it is observed that these additional frequencies are of the same order as that of the synchronous whirling frequencies. The additional frequencies around half the spin speeds are found using only finite bearing dynamic coefficients; this clearly indicates the deficiency in the use of short bearing approximation in similar work.