Measured dynamics of a thin cylindrical shell subject to axial excitation

One source of structural vibration in a submarine is the fluctuating axial thrust force applied to the thrust block by the propeller shaft. This paper describes the initial stages of experimental work being undertaken to validate an existing mathematical model for the sound radiation from a submarine excited by this mechanism. A thin cylindrical shell 1500mm long and 400mm in diameter made of 2mm thick steel with its ends capped by 20mm thick steel discs is examined. The shell was suspended from eyelets welded at either end and was excited axially by a modal shaker mounted inside the cylinder on one of the end caps. The first few modes with significant axial content were extracted from frequency-response functions measured at a number of points on the surface of the cylinder and the end caps and are described. This work will lead into the development of a sound radiation model suitable for use in the active vibration control of the cylinder.