Wave decomposition of the vibrations of a cylindrical shell with an automated scanning laser vibrometer

Elastic waves propagating in a cylindrical shell have been detected by an a utomated scanning laser vibrometer designed to record both in-plane and out -of-plane surface motion over the surface of the shell (32 points axially a nd 32 points circumferentially). The structure was freely suspended in air and excited radially by a shaker at a single frequency, either below or abo ve the ring frequency of the shell. A wave vector analysis of the data was performed with a fast Fourier transform and an overdetermined modified exte nded Prony method. The results clearly show the presence of longitudinal, s hear, and flexural waves above the ring frequency. In addition, the Prony m ethod reveals the presence of evanescent waves due to mode conversion of th e propagating waves near the ends of the shell. Below the ring frequency, t wo types of in-plane waves and flexural waves were identified. The results are in excellent agreement with predictions from the dispersion curves for thin shells. (C) 1998 Acoustical Society of America. [S0001-4966(98)01211-9 ].