Finite element analysis and optimization of active magnetic bearings for contra-rotating coaxial rotor system

Abstract

This paper presents the design, analysis and optimization of active magnetic bearings (AMBs) to support the inner rotor in a contra-rotating coaxial rotor system. An FEM based rotordynamic model is developed using 8-dof Timoshenko beam elements assuming both inner and outer rotors to be flexible. The dynamic response of this system due to an unbalanced force is used in one of the constraints of a multi-objective genetic algorithm for controlling the vibration amplitude within 10% of the air gap. A maximum reduction of 46.9% in the amplitude peak is obtained under the present conditions. Hence, this work also offers a tool useful in touch-down bearing design. The PD controller gains are found to govern the stiffness and damping properties of the AMB. On increasing the mass unbalance by a factor of 2.5, number of turns, pole width and maximum current are found to increase by 52.9%, 29.4% and 71.67% respectively.