Abstract:
The response of a ribbed shell with many attached internal oscillators to a point force has been measured by near-field acoustic holography and compared to similar measurements of a ribbed shell with no oscillators. The total mass of the attached oscillators is significant, of order of the mass of the ribbed shell. The measurements show that the internal attachments have a very significant and complex impact both on the local response of the shell and on the propagation of vibration along the shell. At low frequencies the range of propagation is reduced, consistent with an increase in the effective ``damping,'' while at high frequencies, the range of propagation is increased. Examination of the input impedance of the system reveals a frequency dependence consistent with this behavior. These observations and their implications on the underlying scattering and absorption mechanisms resulting from the internal structure will be discussed.