Effects of Unbalance and Controller Gains on Nonlinear Dynamic of a Coaxial Rotor in Active Magnetic Bearings and Contact with Auxiliary Bearings

The main purpose of this study is to predict the nonlinear dynamic behavior of a coaxial rotor system supported by two active magnetic bearings (AMBs) and contact with two auxiliary bearings. The system is modeled by ten degrees of freedom in two perpendicular lateral planes. In this model, gyroscopic moments of disks and geometric coupling of the magnetic actuators are included. The nonlinear equations of motion are developed using the Lagrange’s equation and solved by the Rung-Kutta method. Then, the effects of unbalance, proportional and differential controller gain on the dynamic behavior of the coaxial rotor-AMB system are investigated by the dynamic trajectories, power spectra, Poincare´ maps and bifurcation diagrams. The results indicate that the unbalance and controller gains have significant effects on the dynamic responses of the coaxial rotor-AMB system. Also, the results of analysis reveal a variety of nonlinear behavior such as period-2, quasi-periodic motions, as well as jump phenomena that can give some insight to engineers and researchers in designing and studying coaxial rotor-AMB systems or some turbo-machinery in the future.