A STUDY OF WAVE-PROPAGATION ON A CYLINDRICAL-SHELL USING FIBER OPTIC LASER-DOPPLER VELOCIMETRY

A differential laser Doppler velocimeter (LDV) has been used to measur e in-plane motion associated with waves propagating on a thin cylindri cal shell excited radially at a single frequency by a shaker. It has b een established that (1) the laser probe can be used to detect shear w aves 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 se parate very clearly the types of waves propagating on the shell. The f iber 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 scann ed over the entire surface of the shell. Data were recorded along an a rray of 32 points circumferentially and 16 points axially, enough to s ample spatially both extensional (fast waves, low wave numbers) and fl exural waves (slow waves, high wave numbers). The data were analyzed w ith both a two-dimensional spatial Fourier transform and a Prony spect ral 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.