Xie, Lei (2009)
Numerical and Experimental Investigation of AMBs Supported Rotor System with Auxiliary Bearings.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung

Kurzbeschreibung (Abstract)

In case of active magnetic bearing power failures or high transient overloads, the fast spinning rotor interacts with the auxiliary bearing. A critical motion is possible, called backward whirl. It can produce very high loads on rotor and bearings, which can lead to the destruction of the machine. Therefore, it is important to make numerical and experimental investigations of active magnetic bearings (AMBs) supported rotor system with auxiliary bearings. The models for the AMBs supported rotor with auxiliary bearing system are introduced. The theoretical method for estimation equivalent stiffness and damping of the AMB is developed in this work. The dynamic equivalent stiffness and damping of the AMB-rotor system is calculated from the knowledge of frequency response of the digitally controlled AMB. In this work, plenty experiments have been made to explore which factors or parameters are essential for the system performance. Some modifications and extensions of the hardware and software of the test rig have been done. Several important parameters of system such as stiffness and damping have been estimated through frequency domain and time domain methods by analyzing the experimental results. These parameters were used in numerical simulations. Under some specific designed cases, it is found that the rotor undergoes a complicated motion behavior, the backward whirl. The experiment results have been presented and analyzed. The detailed models of the AMBs supported rotor interacting with the auxiliary bearing system are introduced, which considered discontinuous stiffness caused by bearing clearance effect, nonlinear Hertzian contact and Coulomb friction forces. Furthermore, according to the real test rig, the auxiliary bearings could be modeled as fixed and compliant mounted. The rotor is modeled as rigid mass or rigid beam by paying regard to its operation range. Several groups of differential equations are presented and the numerical simulation method is developed for the nonlinear time variant ODEs based on event functions in MATLAB. Numerical investigations as time history, orbit diagram, Poincar\'{e} section diagram and waterfall spectrum diagram are proposed to study the complex dynamic response of the system. It is found that the AMB-rotor-auxiliary bearing system undergoes complicated motion behaviors including chaotic motion. The bifurcation analysis results are presented, to explore which factors or parameters are essential to system performance then find an appropriate optimized design to prevent it. The important parameters studies on the rotor driving frequency, the support and contact stiffness are carried out through bifurcation analysis. The complicated motions of rotor are observed by changing the control parameters.

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