1. Department of Mechanical and Electrical Engineering, Ocean University of China, Qingdao 266100, People's Republic of China
2. Key Laboratory of Ocean Engineering of Shandong Province, Ocean University of China, Qingdao 266100, People's Republic of China
3. Center for Structural Acoustics and Machine Fault Diagnosis, Qingdao University of Technology, Qingdao 266520, People's Republic of China