1. Department of Power Engineering, North China Electric Power University , Baoding 071003 , China
2. Department of Aerospace Engineering and Engineering Mechanics, University of Cincinnati , Cincinnati , OH 45221-0070 , United States of America
3. Department of Engineering Mechanics, Tsinghua University , Beijing 100084 , China
4. Department of Electronic Engineering, North China Electric Power University , Baoding 071003 , China