Bifurcation and nonlinear dynamic behaviours of a metal mesh damped flexible pivot tilting pad gas bearing system

Abstract

The nonlinear dynamics of a rigid rotor supported on two identical metal mesh damped flexible pivot tilting pad gas bearings is investigated. This new type gas bearing is used because of high effective damping level and adequate compliance with variations in rotor geometry or misalignment. Time domain simulation that couples rotor motion equations, unsteady Reynolds equation and pad motion (considering dampers) equations is used. The nonlinear dynamic responses are analysed using rotor trajectories, fast Fourier transform plots, Poincare maps and bifurcation plots. The effects of different system parameters, including operating speed, rotor mass, imbalance radius, pad radial stiffness and pad preload, on nonlinear characteristics of the rotor–bearing system are studied. The numerical results reveal that rich and complex nonlinear behaviours are contained in the rotor responses. The rotor experiences T-periodic motion, KT-periodic motion and quasi-periodic motion with the variations of different system parameters. The bifurcation diagrams for different damper mesh densities are compared. For the bearing system with larger damper mesh density, both the speed range of subsynchronous vibrations and the amplitudes of rotor orbits are smaller. As rotor mass increases, the subsynchronous amplitudes increase. Quasi-periodic motion occurs when the imbalance radius is within the interval of $$0.2\times 10^{-6}\,\hbox {m}\le r_u \le 2\times 10^{-6}\,\hbox {m}$$ . Moreover, smaller pad radial stiffness and pad preload lead to larger subsynchronous vibration peaks. These studies can be used as guideline for designing and selecting suitable rotor, bearing and operating parameters of rotor–bearing system.