1. College of Mechanical Engineering and Beijing, Key Laboratory of Measurement and Control of Mechanical and Electrical System, Beijing Information Science and Technology University, Beijing 100192, P. R. China
2. Department of Mechanics, Guangxi University, Nanning 530004, P. R. China
3. Department of Mechanics, Inner Mongolia University of Technology, Hohhot 010051, P. R. China
4. Institute of Magnetic Levitation and Electromagnetic Propulsion, China Aerospace Science and Industry Corp., Beijing 100143, P. R. China