Visualization of underwater structural vibration using generalized near-field acoustical holography (GENAH)

Abstract

The principle and signal-processing method of generalized near-field acoustical holography (GENAH) to visualize the vibration of radiating surface are described. While the conventional acoustical holography is based on the acoustic pressure in far field, GENAR on that in near field. Much higher completeness of transformation of the measured field pressure to the surface vibration is then achieved by back-propagating evanescent waves in near field onto the surface. GENAH signal-processing utilizes the K-space analysis on the basis of the spatial Fourier trans-form, and it is able to "visualize" the correspondence between theory and experiment on vibroacoustical problems. As a specific example, it is illustrated how GENAH was applied to the study on the vibration of two concentric submerged cylindrical shells coupled by the entrained fluid.