The modal analysis of a double disc flexible rotor-bearing system with isotropic stiffness and damping properties

Abstract

This paper shows the analysis of the modal characteristics of a flexible rotor system having two non-identical discs mounted on it using the finite element method. It uses the Timoshenko beam elements theory including shear deformation, rotary bending effects and gyroscopic effects. The bearing is considered to be isotropic having translational stiffness and damping values constant in x and y directions. There are no cross-coupling terms. The conduct of the framework is investigated by reference to natural frequency maps and mode shape diagrams. A comparative study has been conducted between this system having isotropic bearings of stiffness and damping properties and the one in which the bearings have only stiffness keeping other parameters same. The gyroscopic effect is seen to be prominent at higher rotating speeds for both the cases which cause the splitting of frequency pairs into forward and backward whirls. The Campbell diagram is computed which helps in finding the critical speeds associated with each pair of diverging natural frequencies. The bearing system represented by stiffness and damping properties shows a comparatively better control over the critical speed range.