Optical measurements of shear waves on a point-driven cylindrical shell excited radially

Abstract

A differential laser Doppler velocimeter (LDV) [Lee et al., Proceedings of the 3rd International Congress on Intensity Techniques, Senlis, France, pp. 181–188 (1990)] has been used to measure in-plane motion associated with waves propagating on a thin cylindrical shell excited radially at a single frequency by a shaker. The endcaps of the shell approximate the case of a simply supported shell with axial constraints at both ends. The fiber optic technology used in the LDV system allows the optical probe head, located at a distance of about 30 cm from the shell, to be scanned over the entire surface of the shell. Data were recorded along an array of 32 points circumferentially and 16 points axially, enough to sample spatially both extensional (fast waves, low wave numbers) and flexural (slow waves, high wave numbers) waves. The data were analyzed with both a two-dimensional spatial FFT algorithm and a Prony algorithm. The analysis clearly reveals both type of waves separately. Theoretical predictions are obtained from the analysis of a point-driven infinite shell and from Forsberg's original paper [AIAA J. 2 (12), 2150 (1964)]. Both theoretical and experimental results clearly show the presence of shear waves propagating on the structure. [Work supported by ONR.]