# Dynamics Investigation on Axial-Groove Gas Bearing-Rotor System with Rod-Fastened Structure
## 1 Introduction  
Oil-free lubrication provides many unique characteristics for gas bearings, such as low friction, high positioning precision and low pollutant emission. As a result, the rotor system supported in a gas bearing is frequently employed within the high-speed rotating machinery, whether in civilian, agriculture, or military aerospace fields. The characteristic of rotor dynamics is one key factor for the stable operation of high-speed rotating machinery. It is necessary to carry out more research about the stability analysis and dynamic performance of the gas bearing-rotor system [1; 2; 3; 4]. [PERSON] et al. [5] studied the effects of the circumferential and axial surface waviness on the nonlinear dynamic characteristics of a gas-lubricated bearing-rotor system; the dynamic stability of the bearing-rotor system can be improved with the increase of amplitude of circumferential waviness. Based on the finite difference method, perturbation method, and mixing method, [PERSON] et al. [6] investigated the nonlinear dynamic performance of the flexible rotor system with opposed high-speed gas bearing support; by changing the parameters of the bearing, chaos phenomena and the system loss produced by the irregular vibration can be reduced. [PERSON] et al. [7] analyzed numerically the unbalance response and dynamic stability of the rotor system supported on a micro gas bearing with a gas rarefaction effect; the influence of mass eccentricities of rotor on the stability of rotor system supported on the micro gas bearing was discussed. [PERSON] et al. [8] analyzed the nonlinear dynamic behavior of a hybrid active aerostatic and aerodynamic bearing-rotor system by using a mixed numerical method, and the complex dynamic phenomena underdifferent parameters and conditions were obtained. These gas bearings are cylindrical bearings, which have a simple structure and high-load-carrying capacity, but the rotor system supported by the cylindrical gas bearing is prone to instability under higher speed. The application of grooved gas bearings ensures the stable operation and improves the work performance of high-speed machinery; many research results were obtained on the lubrication performance of the grooved bearings. [PERSON] et al. [PERSON] et al. (2018) focused on gas bearings with a micro spherical spiral groove, and the thermohydrodynamic performance of the bearings was analyzed by considering the surface roughness and air rarefaction, the effects of surface roughness and slip flow were obtained by using the Weierstrass-Mandelbrot function and [PERSON]'s slip model. [PERSON] et al. [PERSON] et al. (2018) studied the contact characteristics of a gas-lubricated thrust micro-bearing with a spiral-groove by considering the gas rarefaction, and the effects of the standard deviation of asperity height and the groove depth on the surface contact forces of the gas-lubricated bearing were discussed. [PERSON] et al. [PERSON] et al. (2018, 2020) built a mathematical model of spherical spiral-groove hybrid-gas bearings rotor system coupled with the analysis of nonlinear dynamic lubrication. The critical speed of the rotor-bearing system was calculated and the stability of the hybrid gas bearings was predicted; they then forced the dynamic variation rule of the gas film damping and stiffness under different states of motion, and the vortex motion and oscillation phenomenon of the gas film was analyzed. [PERSON] et al. (2020) studied the nonlinear dynamic characteristics of a rigid rotor system with herringbone-grooved-journal gas bearings support, the onset speed and the whirl frequency ratio of subsynchronous vibration in the gas bearings-rotor system were estimated and analyzed. [PERSON] et al. [PERSON] et al. (2020) investigated the whirl motion of a rigid rotor system with spiral-grooved opposed-hemisphere gas bearing support; the complicated rotor responses under the initial disturbance were analyzed, and the synchronous and nonsynchronous excitations were obtained.