ASA 126th Meeting Denver 1993 October 4-8

4pSA12. On the acoustic advantages of a helical-ring stiffener in a thin cylindrical shell.

Y. F. Hwang

David Taylor Model Basin, Carderock Div., Naval Surface Warfare Ctr., Bethesda, MD 20084-5000

A conventional circular-ring stiffener in a thin cylindrical shell may cause undesirable sound radiation due to the scattering of subsonic flexural waves. Vibration in each of a set of disjointed circular rings may stay within the ring, which results in a resonant buildup that acts as a localized excitation of the shell. Furthermore, elastic waves in a cylindrical shell tend to propagate, having a plate-wave front, along the axis of the cylinder. A circular ring is oriented in the plane normal to the direction of wave propagation and therefore it sees the elastic wave as a normal incident wave. These rings are separated at a certain distance in tandem. An incident wave in the shell may be reflected back and forth between a pair of adjacent rings. Therefore, a circular ring may not only be an efficient scattered, it could also scatter the same wave several times causing a reverberant buildup in the shell between rings, and, consequently, enhance acoustic radiation from the shell. This paper discussed the technical rationale to alleviate these shortcomings by using a continuous helical-ring stiffener in a thin cylindrical shell.