Sean Feng Wu photo

Sean F. Wu, Ph.D.
Fellow, ASME, ASA
University Distinguished Professor
Department of Mechanical Engineering
Wayne State University
Detroit, MI 48202

Sean F. Wu received his BSME from Zhejiang University (China); MSME and Ph.D. from Georgia Institute of Technology, U.S.A. Dr. Wu joined the Department of Mechanical Engineering at Wayne State University (WSU) as an Assistant Professor for Research in 1988; became a tenure-track Assistant Professor in 1990; Associate Professor in 1995, and a Professor in 1999. He was voted unanimously as the Charles DeVlieg Professor of Mechanical Engineering in 2002; and was appointed and re-appointed by the Board of Governors to the rank of University Distinguished Professor every year since 2005. Dr. Wu holds the rank of Fellow in the Acoustical Society of America (ASA) and the American Society of Mechanical Engineers (ASME), and is a member of the Society for Automotive Engineering (SAE). Currently, Dr. Wu serves as an Associate Editor for the Journal of the Acoustical Society of America (JASA), Express Letters Editor for JASA, Managing Editor and Co-Editor-in-Chief for the Journal of Computational Acoustics (JCA).
Dr. Wu’s areas of interest are acoustics, vibration, and noise control. He has over 60 refereed journal articles, 13 U.S. and International Patents, and is the author of the book, “The Helmholtz Equation Least Squares Method for Acoustic Radiation and Reconstruction,” published by Springer (2015) in the Modern Acoustics and Signal Processing book series. Dr. Wu has mentored supervised more than 40 Ph.D. and MS students, who have won 24 the Best Student Papers Competitions at the professional conferences sponsored by the ASME, ASA, Institute of Noise Control Engineering International, and SAE. He was a co-founder of SenSound, LLC in 2003. In 2015, Dr. Wu founded Signal-Wise, LLC, a private company to provide disruptive technologies for tackling complex noise and vibration issues, and for conducting in-line and end-of-line product quality control tests.

Interrelationships Among Force Excitation, Structural Vibration, and Sound Radiation

Sean F. Wu  
Department of Mechanical Engineering
Wayne State University
Detroit, MI 48202
Pan Zhou  
College of Power and Energy Engineering  
Harbin Engineering University  
Harbin, Heilongjiang Province  
P. R. China, 150001  

Received: 2 April 2017


This paper presents the general theory of using NAH to uncover the root causes of sound and vibration of a structure, namely, the excitation force acting behind a vibrating structure. The input data are the acoustic pressures collected on a hologram surface in the near field in front of the structure. These data are utilized to reconstruct the normal surface velocity distribution. Once this is done, the excitation force acting behind the vibrating surface is determined by synthesizing the normal modes of the structure. Specifically, the characteristics of the excitation force such as its location, type, and amplitude distribution are identified, as if one could “see” the force acting behind a structure based on the acoustic pressure measured on the opposite side. It is shown that such an approach is of generality because vibro-acoustic responses on the surface of a vibrating structure can always be reconstructed, exactly or approximately by using NAH. With these vibro-acoustic responses, the excitation forces acting behind the structure can always be determined, analytically or numerically, given any set of boundary conditions. The second part of this paper examines the interrelationships among excitation, structural vibration and acoustic radiation. For simplicity yet without loss of generality, we consider a finite plate mounted on an infinite rigid baffle subject to an arbitrary force acting on its backside. We demonstrate that the excitation force is not the direct cause of acoustic radiation, but rather the source of mechanical energy supply to a vibrating plate. The direct cause of acoustic radiation is the normal component of the surface velocity, which can be obtained by synthesizing the normal modes of a structure. It is emphasized that these normal modes do not contribute equally to acoustic radiation however. In other words, at any excitation frequency, only a small number of natural modes can produce sound effectively, and the rest do not, including resonance modes. Therefore, the conventional thinking that because the amplitudes of structural vibrations at resonances are maximal, they are primarily responsible for resultant acoustic radiation is not true at all. 


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