NATURE OF SCHOLTE INTERFACE WAVES ON CYLI NDRICAL-SHELLS

The theoretical and experimental studies of the ultrasonic scattering by cylindrical shells filled with air and immersed in water show, on t he backscattering spectra, large amplitude variations. These variation s are related to an interface wave called ''A wave''. The resonances o f this wave are detected in a frequential window that depends on the r adius ratio (inner radius b/outer radius a). They are observed for cyl indrical shells with a radius ratio superior to 0.6. This wave that pr opagates in the water around the pipe is still not very well know in s pite of the investigations which have been devoted to it. In this nume rical study, it is proposed a study of the evolution of the frequency of different resonances for cylindrical shells with the radius ratio b etween 0.2 and 0.95. The interaction between the flexural wave A0 in t he shell and the creeping wave in the fluid around the pipe is studied in greater detail. The dispersion curves of the phase velocity for th ese waves are presented. They show a repulse area between these two cu rves. This area is translated toward the high frequencies when the rad ius ratio tends toward 1. This phenomenon is related to the contact co ndition at the liquid/shell interface.