Nonlinear dynamic of turbulent bearing-rotor system under quadratic damping with HSFD and active control

Traditional squeeze-film dampers are used in modern aircraft generators as vibration-suppressing devices. However, the conventional squeeze-film damper has the disadvantage of highly nonlinear oil film force. This study aims to improve the dynamic characteristics of the squeeze-film damper by changing its geometric structure, so a hybrid squeeze-film damper (HSFD) is proposed. Besides, the turbulent flow could also be found in lubrication analysis of high rotating speed turbo-machineries, and the ignorance of turbulent flow would lead to significant failure results. Accordingly, the study presents a nonlinear dynamic analysis of a turbulent bearing-rotor system under quadratic damping equipped with HSFD. The dimensionless speed ratio and dimensionless unbalance parameter are used to plot the bifurcation diagrams, and abundant harmonic, subharmonic, quasi-periodic, and even chaotic motions are found with dynamic trajectories, power spectrum, Poincaré maps, Lyapunov exponent, and fractal dimension, simultaneously. Finally, an active control method is applied to suppress the chaotic responses. The simulation results will provide valuable suggestions for designing and developing rotating machinery, such as rotor-bearing systems operating at high rotational speeds and nonlinearity.