Broadband 3-D high spatial density structural response measurements of a pair of framed air-loaded cylinders of differing internal complexity

Abstract

The presence of internal structure can greatly alter the acoustic behavior of elastic structures. The effect of a large number of internal oscillators on the vibrational response of an air-loaded framed cylindrical shell has been examined experimentally. This examination included the construction of two shells of the same design, one of which has 880 attached oscillators. Spatially dense (200 axial points by 80 azimuthal =16 000 points) 3-D laser Doppler vibrometer measurements have been collected for both of these structures for the case of broadband radial point excitation. Comparisons made between these two visually identical structures reveal dramatic differences. These include a modification of the participation factors between the three displacement polarizations and strong spatial confinement of the vibration response due to complexity. These results are presented together with a discussion of mechanisms which may account for these observations. [Work sponsored by ONR.]