1. Lecturer, College of Aerospace Engineering, National Key Laboratory of Rotorcraft Aeromechanics, Nanjing Univ. of Aeronautics and Astronautics, Nanjing 210016, China.
2. Professor, College of Aerospace Engineering, National Key Laboratory of Rotorcraft Aeromechanics, Nanjing Univ. of Aeronautics and Astronautics, Nanjing 210016, China (corresponding author).