David P. Mackovjak
Arthur B. Baggeroer
Dept. of Ocean Eng., Rm. 204, MIT, Cambridge, MA 02139
The structural acoustic interaction of model cylindrical shells with different structural discontinuities and internal loading configurations is studied using the maximum-likelihood method (MLM). Three different finite fluid-loaded cylindrical shells are insonified with a midfrequency broadband pulse. The original MLM algorithm is modified using time windowing and slowness steering to exploit the transient nature of the backscattered field. This allows for a detailed investigation of different propagating waves along the shell surface and internal subsystem. Results show that propagating helical membrane waves are important contributors to the scattered field and are frequency dependent. Frequencies below ka=5.5 result in a coupled system where the shell and the internal structures interact dispersively. Above this frequency, the membrane waves interact with the shell's discontinuities creating almost continuously radiating localized point scatters. The source location proves to be an important parameter in the creation of these localized radiation fields. The MLM array processing appears to identify weak flexural resonances established by the shell's physical geometry. [Work supported by ONR and Charles Stark Draper Laboratory, Inc.]