Acoustic scattering from an isotropic elastic hollow cylindrical shell of infinite length excited by an obliquely incident plane acoustic wave is investigated. The form functions of an aluminum c3/lindrical shell immersed in water have been calculated by the direct summation of the Rayleigh series. Computations are made at angles (with the normal to the cylinder axis) between a = 0 ø and a = 35 ø. The results of the theoretical calculation are in good agreement with the results of experiments. The experimental results have shown in a frequency range of kl a = 0-20 that the resonances are related to three wave families: the circumferential wave (l = 2) detected for angles smaller than the "angle of longitudinal wave in thin rods" (a•), the guided wave (p = 1 ) detected for angles smaller than the second critical angle (at), and the Scholte-Stoneley wave (l = 0). The evolution of the resonance frequencies is followed for different angles and one can note experimentally, that at an angle superior to the Rayleigh critical angle (a = 30.3ø), resonances of the Scholte-Stoneley wave have been observed.
The complex eigenfrequencies of a fluid-immersed evacuated infinite cylindrical shell, when plotted in the complex frequency plane, can be grouped into families corresponding to different types of circumferential waves. The dispersion curves versus frequency of the phase velocities of these circumferential waves are analogous to those of the Lamb waves on a plate A0, A1,… and S0, S1,…, but contain an additional branch reminiscent of the fluid-borne Scholte–Stoneley wave. This branch together with the A0-analog forms an interacting pair of dispersion curves A0+ (upper branch) and A0− (lower branch) which exhibit a repulsion phenomenon near the ambient fluid sound speed. Results of a recent numerical study of this phenomenon are here explained by perturbation theory, showing that during repulsion the wave character gets exchanged so that at frequencies above repulsion A0+ is a flexural and A0− a fluid-borne wave, and vice versa below repulsion.
A modal theory is developed for investigating the acoustic scattering by elastic cylinders of arbitrary cross section immersed in a fluid. Numerical results are presented for a plane wave incidence normal to the axis of an elliptical cylinder but arbitrary with respect to the noncircular cross section. Experimental results are obtained for an aluminum elliptical cylinder with the use of an impulse method. Comparisons between theoretical and experimental data are performed in the broad frequency range 8.5рkaр30 ͑k is the wave number in the fluid and a the major axis radius of the elliptic cylinder͒. The experimental observations are in good agreement with the theoretical predictions.
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