Experimental Verification of Magnetic Bearing System Rotordynamics Code

Modeling of magnetically levitated rotors presents unique challenges to the rotordynamicist. The active control system means that bearing characteristics cannot simply be modeled as stiffness and damping coefficients. They must be modeled as closed loop systems that include all elements of the control system as well as the phySical characteristics of the shaft. This technique is important in order to properly identify the system to determine appropriate tuning parameter values. Of equal importance is the modeling of the physical shaft including such items as the radial rotors which can be complex laminated sleeves. The impact of these sleeves on the overall rotordynamics can be substantial, especially in smaller shafts where the relative mass of the rotors is high. This paper describes our experience with experimental verification of the accuracy of the model. Three case studies are presented for three substantially different equipment types. Gyroscopic effects and control system interaction with higher order bending modes are also considered.