1. College of Aerospace Engineering, Chongqing University, Chongqing 400044, P. R. China
2. State Key Laboratory of Reliability and Intelligence Electrical Equipment, National Engineering Research Center for Technological Innovation Method and Tool, School of Mechanical Engineering, Hebei University of Tchnology, Tianjin 300401, P. R. China
3. Department of Mechanical Engineering, National University of Singapore, Singapore 117575, Singapore