1. School of Mechanical Engineering, Hebei University of Technology, Tianjin 300401, P. R. China
2. State Key Lab of Reliability and Intelligence of Electrical Equipment, Hebei University of Technology, Tianjin 300130, P. R. China
3. Department of Aerospace Engineering and Engineering Mechanics, University of Cincinnati, Cincinnati, OH 45221, USA
4. College of Aeronautics and Astronautics, Taiyuan University of Technology, Taiyuan 030024, P. R. China