### ASA 127th Meeting M.I.T. 1994 June 6-10

## 5aUW4. Structural resonance contributions to scattering cross sections of
cylindrical shells: Mode and frequency dependence.

**Miguel C. Junger
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*Cambridge Acoust. Associates, Inc., 200 Boston Ave., Ste. 2500, Medford,
MA 02155-4243
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H. Lamb's compact formulation of resonance contributions to the scattered
field of elastic, lossless spheres (1900) was generalized by P. W. Smith, Jr.
to structurally damped scatterers of arbitrary shape (1962). Excluding
axisymmetric modes, modal configurations of cylindrical shells are identified
by a pair of axial/circumferential wave numbers associated with a predominantly
flexural, poorly radiating resonance and two supersonic (membrane and shear)
resonances. Implementing Smith's solution for the latter two yields a simple
expression for the familiar ``chalice'' resonance peak loci in the
aspect/frequency plane. A peak's height is proportional to the square of the
ratio of the modal radiation resistance over the combined radiation and
structural resistance. With increasing wave numbers, modal configurations
gradually become tangential, thereby reducing radiation damping as compared to
total damping (an effect overlooked in this speaker's 1993 publication, which
unrealistically neglected structural as compared to radiation resistance).
Consequently, though associated with supersonic wave numbers, resonance peaks
fade with increasing mode order and frequency. Results are compared with
Rummerman's (1993) detailed analysis and measurements. [Work sponsored by Naval
Undersea Warfare Center.]