On Forced-Vibroacoustic Component Analyses of an Arbitrarily Shaped Vibrating Structure

Abstract

This paper presents a methodology that enables one to trace back the forced-vibroacoustic components (F-VAC) that are responsible for acoustic radiation from an arbitrarily shaped structure. This methodology relies on a modified Helmholtz equation least-square (HELS) method that takes partial normal surface velocities obtained by using a laser vibrometer and partial acoustic pressures measured using a small array of microphones as input to reconstruct the distributions of the normal surface velocity and acoustic pressure over the entire source surface. Next, the normal component of the time-averaged acoustic intensity distribution is reconstructed and linked to the field acoustic pressure. Finally, the singular value decomposition (SVD) technique is used to reveal the most critical components of the structural vibrations that are responsible for acoustic radiation. The advantages of using partial normal surface velocities and acoustic pressures as input data are that: (1) it enables one to acquire the rich near-field information embedded in the normal surface velocities; (2) it is a noncontact and noninvasive measurement approach using a laser vibrometer or scanning laser and a small microphone array at a remote location; (3) it enables one to obtain a comprehensive picture of the vibroacoustic fields that traditional near-field acoustic holography (NAH) cannot offer; (4) it allows for correlating the near-field effects to the far-field acoustic pressures and revealing the root causes of structure-borne sound radiation; (5) it provides an insight into developing the most cost-effective noise reduction measures; and (6) it is suited for engineering applications since in practice there are always areas that are inaccessible for measurements. Finally, it is emphasized that although sound may be produced by structural vibrations, not all structural vibrations may produce sound. Therefore, all one needs to do is to suppress the most critical components of structural vibrations that can emit sound. Experimental validations of using F-VAC analyses to reduce sound radiation from an arbitrarily shaped structure are demonstrated.