ASA 126th Meeting Denver 1993 October 4-8

4aSA6. Composite cylinder cross section tailoring for radiated noise reduction.

Colin P. Ratcliffe

Dept. of Mech. Eng., USNA, Annapolis, MD 21402-5008

Roger M. Crane Armando L. Santiago

NSWC, Annapolis, MD 21402-5067

This paper presents the results of an ongoing investigation into the reduction of transmitted noise for underwater cylindrical structures. A reduction in the radiated self-noise of cylindrical structures, compared with the conventionally utilized aluminum structures, was undertaken, investigating the use of composite materials with varying cross sections to meet the specified requirements. The cross sections investigated included several variations of a state-of-the-art triple skin construction, along with monolithic, constrained layer and a semi-debonded cross section. Cylinders have been fabricated and tested, comparing the dynamic vibration properties of the forced vibrations in air of the composite scaled cylinders to the baseline aluminum. The modal analysis determined mode shapes, natural frequencies, and damping loss factors. These were then tested in reverberant conditions under water to assess their acoustical performance. The in air and underwater tests were compared to identify similarities and differences between force excitation and acoustic excitation. The comparison showed where in air tests can be used as an aid to estimating underwater performance. The results also highlighted where in air tests are inadequate for predicting underwater behavior. The effect of the cross-sectional design for the tailoring of the acoustic signature will be discussed.