ASA 126th Meeting Denver 1993 October 4-8

3pPA5. Time, frequency, and thickness analysis of monostatic scattering from an infinite steel cylindrical shell immersed in water.

Timothy J. Yoder

SFA, Inc., 1401 McCormick Dr., Landover, MD 20785

Louis R. Dragonette Charles Gaumond

Naval Res. Lab., Washington, DC 20375

The monostatic scattering for an infinite cylindrical steel shell is analyzed for frequencies up to ka=10.0. The shell thickness is varied from h/a=0.001 to h/a=0.999. The time, frequency, and thickness dependence of the scattering is graphically analyzed to determine the physical process(es) responsible for the scattering. This analysis reveals the following processes: (a) The Lamb wave circumnavigating the cylinder; (b) a 180-deg phase shift in the specular scattering as the shell becomes thick; (c) the coincidence frequency of the flexural waves with the radiation medium; (d) a drastic decrease in the ``Q'' of the modes supporting the flexural waves caused when the circumnavigating flexural waves begin to radiate efficiently; (e) the onset of the creeping waves as the shell becomes thick; (f) the transition of flexural/Lamb wave behavior to Rayleigh wave behavior as the shell becomes a solid cylinder; (g) cancellation of the monopole and dipole modes for frequencies less than ka=3 occurring at thickness h/a=0.05; (h) the poles of the normal mode series solution coinciding with the highlights seen in the frequency domain.