1. Beijing Institute of Technology, School of Mechanical Engineering, Beijing 100081, China
2. University of Virginia, Mechanical and Aerospace Engineering Department, Rotating Machinery and Controls (ROMAC) Laboratory, 122 Engineer's Way, Charlottesville, VA 22904-4746 e-mail:
3. University of Virginia, Mechanical and Aerospace Engineering Department, Rotating Machinery and Controls (ROMAC) Laboratory, 122 Engineer's Way, Charlottesville, VA 22904-4746