Fractional-order model and nonlinear vibration analyses of hybrid gas journal bearing-rotor system

It is important to propose a reasonable nonlinear dynamic model of gas dynamic bearing-rotor system for the stable operation of turbocharger. This paper presents a hybrid gas journal bearing (HGJBs)-rotor system with flexible supporting structure. A fractional-order dynamic model of the symmetrical flexible HGJB-rotor system is established. A trackingalarming method is proposed to obtain the rotational speed ratio at the bifurcation point. The stable and unstable regions of the rotational speed ratio Omega(omega) for both the rigid bearing-rotor system and flexible HGJB-rotor system are analyzed. The nonlinear dynamic behaviors of HGJB-rotor system versus the fractional order alpha(d) and rotational speed ratio Omega(omega) are studied. Results show the fractional-order dynamic model can realize the reasonable prediction of nonlinear dynamic behaviors. An increase in the rotational speed ratio Omega(omega) and the decrease of fractional order alpha(d) result in a growth of the vibration amplitude. The adoption of flexible supporting structure is a good strategy to increase the size of stable region.