Lab. d'Acoust. Ultrason. et d'Electron., LAUE URA CNRS 1373, Univ. Le Havre, Place Robert Schuman, 76610 Le Havre, France
Tallinn Tech. Univ., Tallinn EE 0026, Estonia
The method of isolation and identification of resonances (MIIR) has allowed plotting of resonance spectra that characterize the shape, the structure, and the material of an object. On the spectra, the resonance peaks are related to surface waves propagating around the object. The backscattering, from thin-walled cylindrical shell stiffened by internal lengthwise rib and insonified normally to its axis, is studied. In the explored frequency band, the frequencies of S[sub 0] wave resonances are not much affected by the presence of stiffener. Measurements made during transient state after quasiharmonic excitation of the stiffened shell have shown that, at the S[sub 0] wave resonances, backscattering is maximum when the rib is located at the vibration nodes. In the total backscattered pressure, considering also forced vibration, the maxima are detected when the rib is in the antinodes. In the stiffened shell, other additional resonances appear that are not detected in the case of the unstiffened shell. These resonances are attributed to the flexural waves. They are the result of interaction of the rib and the shell at their structural joint. These additional resonances are better observed when the joint is located at the illuminated part.