1. State Key Laboratory of Tribology, Tsinghua University, Beijing 100084, China
2. Robotics Institute, School of Mechanical Engineering and Automation, Beihang University, Beijing 100191, China
3. Centre for Applied Dynamics Research, School of Engineering, University of Aberdeen, Aberdeen AB24 3UE, U.K.
4. Institute of Fluid Dynamics, Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstrasse 400, Dresden 01328, Germany
5. Department of Mechanical Engineering, Tsinghua University, Beijing 100084, China
6. School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, China