Hyun-Gwon Kil
Jacek Jarzynski
School of Mech. Eng., Georgia Inst. of Technol., Atlanta, GA 30332
The surface displacement of a vibrating shell has been directly measured by laser interferometry. The system is designed to measure the two in-plane components of the surface displacement: the axial and the circumferential components. The system is completely automated for scanning around the cylindrical shell both circumferentially and axially, for focusing at each point until the detected signal is stable and sufficiently above the noise level, and for recording and transferring the data to a computer. The data are analyzed in the frequency-wave-number domain with fast Fourier transforms and Prony decomposition to separate the extensional waves (fast waves, low wave numbers) from the flexural waves (slow waves, high wave numbers). The shell under consideration is 0.94 m long and 1.6 mm thick. It is freely suspended in air and it is excited radially by a shaker at various frequencies up to twice the ring frequency which is about 10 kHz. The optical probe head is very compact (about 4 by 4 cm) and it is designed to take full advantage of optical fiber technology. [Work supported by ONR.]