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 have shown , on the backscattering spectra, large amplitude variations. These var iations are related to an interface wave called the ''Scholte-Stoneley wave'' or ''A wave''. The resonances of this wave are detected in a f requency window that depends on the radius ratio (inner radius b/outer radius alpha). They are observed for cylindrical shells with a radius ratio greater than 0.6. This wave that propagates in the water around the pipe is still not very well known in spite of the investigations which have been devoted to it. This numerical study is concerned with the evolution with frequency of different resonances for cylindrical s hells with the radius ratio between 0.2 and 0.95. The interaction betw een the flexural wave A(0) in the shell and the creeping wave in the f luid around the pipe, called the Stoneley wave in a thick shell, and w ith a pole near the pole of the Franz 1 wave for a rigid cylinder in t he complex plane defined by the Sommerfeld-Watson transform, is studie d in greater detail. The dispersion curves of the phase velocity for t hese waves are presented. They show a repulsive area between the two c urves. This area is translated toward the high frequencies when the ra dius ratio tends towards 1. This phenomenon is related to the contact condition at the liquid/shell interface. To verify it, another paramet er of the contact condition is modified: the density ratio.