A study of wave propagation on a cylindrical shell using fiber optic laser Doppler velocimetry

Abstract

A differential laser Doppler velocimeter (LDV) 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. It has been established that (1) the laser probe can be used to detect shear waves even in the presence of flexural waves; and (2) that wave-vector analysis of the recorded in-plane motion of the shell allows one to separate very clearly the types of waves propagating on the shell. 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 waves (slow waves, high wave numbers). The data were analyzed with both a two-dimensional spatial Fourier transform and a Prony spectral method. The analysis clearly reveals both type of waves separately. Experimentally measured mode shape and dispersion curves are in good agreement with theoretical predictions based on Donnell’s thin shell equations.