Abstract:

Consider the meridional plane which contains the axis of a circular cylinder and the incident acoustic wave vector. The meridional leaky rays which lie in this plane may be excited for certain tilt angles. Radiation resulting from the reflection of such rays off truncations on a cylinder gives strong high-frequency backscattering enhancements [Kaduchak et al., J. Acoust. Soc. Am. 100, 67--71 (1996)]. The present work gives ray approximations for such backscattering contributions and for the related contributions to scattering by tilted infinite cylinders. These are evaluated using a general convolution integral formulation [P. L. Marston, J. Acoust. Soc. Am. 100, 2820(A) (1996)]. The infinite cylinder results for radiation by Rayleigh waves on a solid cylinder agree with the partial-wave series solution. The truncation enhancement for a finite cylinder causes a backward-directed three-dimensional wavefront possessing a vanishing Gaussian curvature. The amplitude from the far-field propagation integral associated with the caustic due to this wavefront can significantly exceed the amplitude for reflection off a rigid sphere having the same radius as the cylinder. The analysis does not rely on thin shell assumptions. [Work supported by the Office of Naval Research.]