Laser-Assisted Reconstruction of Vibro-Acoustic Behaviors of an Arbitrarily Shaped Vibrating Structure

Abstract

This paper presents a new method known as laser-assisted, modified Helmholtz Equation Least Squares method-based reconstruction to determine vibro-acoustic quantities of an arbitrarily shaped vibrating structure subject to a noncontact acoustic excitation. Unlike the traditional near-field acoustical holography (NAH) that relies on the acoustic pressures measured in the near-field, this new methodology enables one to collect the input data at a remote distance by using a laser vibrometer, making measurement setup much easier than all previous NAH approaches. Most importantly, by measuring the normal components of the surface velocities at the accessible areas, one can acquire near-field information of a vibrating structure directly, rather than indirectly through reconstruction based on the acoustic pressures measured in the near field. To ensure the accuracy in reconstruction of all the vibro-acoustic characteristics of a structure, the acoustic pressures at a few points in space are also measured. By combining these partial input data, one can acquire a complete picture of the vibro-acoustic field of an arbitrarily shaped vibrating structure, which includes operation deflection shapes, distributions of the acoustic pressures and the normal component of the acoustic intensities on a source surface, and the time-averaged acoustic power of the structure. When the input power is specified, one may determine the frequency response functions, the natural modes, the structural damping ratios of the structure, sound transmission loss, sound transmission path, etc. Examples of using this technology to acquire an in-depth understanding of the vibro-acoustic characteristics of an automobile front dash panel are presented.