Resonance analysis of the acoustic response of a water-filled cylindrical shell

Abstract

The resonance analysis approach developed for characterizing free-field air-filled cylindrical shells in terms of geometrical and mechanical pararneters is extended to fluid-filled shells either in the freefield or proud on the sea bottom. The resonance phenomena generated when a target is unsonified at broadside, by broadband, low-frequency, incident pulses are investigated in the ka range (2,25). Attention is focused on those scattering phenomena common to free-field and proud cases. A comparison is also drawn between the resonance behavior of the same cylindrical target filled with either air or sea water. From the study of a set of fluid-borne and shell-borne wave families, equations

are formulated which relate their characteristics to the target elastic properties. Resonance

frequencies are detected and localized by the algorithm presented earlier, identified and used for

parameter estimation by an automatic multihypothesis method of model-data fitting. The approach was tested on real acoustic data backscattered by a water-filled finite cylinder either suspended in

free-field, or lying proud on a sandy sea bottom and insonified at very low grazing angle (below the

seabed critical angle). A good agreement between theory and experiment was found in terms of

model-data fit and target parameter estimates. The results achieved encourage the extension of target echo analysis to objects buried in bottom sediment. The extension to multi-aspect resonance scattering analysis of the same and more complex objects is also planned.