Abstract:
The presence of internal structure can greatly alter the acoustic behavior of elastic systems. Many structures of interest are comprised of reinforced shells where a periodic placement of the stiffeners lead to well-known stop- and passbands for the long-range transport of vibrational energy. Various degrees of disorder are typically the norm in real systems and the phenomenon of localization can dominate the structural dynamics and lead to high degrees of apparent damping even for frequencies well inside passbands. Generally speaking, localization can result from a number of physical mechanisms that include: radiation damping, structural damping, local resonances, and Anderson localization. Experiments have been conducted on a 1.02-m-long stainless steel cylindrical shell with 80 ring stiffeners attached with a small degree of irregularity in their placement (on average (delta)z/d is (plus or minus)2.5). Out-of-plane structural velocities in the midfrequency band were derived by employing nearfield acoustic holography (NAH) for the case of radial point excitation. The experimental evidence of Anderson localization on a fluid-loaded two-dimensional system is reported here for the first time. [Work supported by NRL and ONR.]