Development of Vibration Control System for Helium Expander Turbines with Gas Bearings

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The purpose of this study is to develop an intelligent tilting-pad gas bearing system for helium liquefier expander by actively controlling the position and rotation angle of the pads in the bearings. The investigators of this project made the active control of pad position and rotation possible by improving the design of a helium liquefier developed by the project team. In detail, the pad position and rotation were actively controlled by the piezoelectric actuators which had been embedded in two of the three pivots used to support the 3 pads in the bearing. The robust control theory was used in the design of controller. By using this method, the vibration amplitude of the two rigid modes was effectively suppressed. The mechanism of instability phenomenon which occurred in an uncontrolled gas bearing above 230,000rpm was theoretically clarified and the simulation results show that the critical rotation speed can be rajsed to 300,000 by the active control method proposed in this research.The project team also succeeded in the vibration control experiment of the helium expender rotor by integating the developed active gas bearings into the expander. The experimental results were compared with the simulation results and their agreement was verified. A simulation program for a gas bearing system with elastic rotors was also developed.