1. School of Aerospace Engineering, Xi’an Jiaotong Univ., Xi’an, Shaanxi 710049, PR China.
2. Professor, State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong Univ., Xi’an, Shaanxi 710049, PR China; Professor, School of Aerospace Engineering, Xi’an Jiaotong Univ., Xi’an, Shaanxi 710049, PR China (corresponding author).