ASA 125th Meeting Ottawa 1993 May

2aPA6. The effect of periodically attached substructures on the excitation of submerged cylindrical shells.

S.-H. Choi

J. D. Achenbach

T. Igusa

Dept. of Civil Eng., Northwestern Univ., Evanston, IL 60208

The presence of substructures in a cylindrical shell gives rise to dynamic interactions that influence the axial distribution of vibration along the shell. In this paper, Lagrange's equations are used to develop the equations governing the forced harmonic vibration of a submerged cylindrical shell with periodically attached internal substructures that is subjected to periodically placed loads. Modal expansions are used to describe the response of the shell and the fields in the fluid. First a shell without substructures but subjected to periodically placed ring loads is considered. The method of this paper is found to be nearly as accurate as a traveling-wave-based method for an infinite shell subjected to a single ring load. Two types of substructures are examined: circular panels with hinge connections and circular ribs with rigid connections. It is shown that the substructures confine the flexural motion to a region near the location of the applied forces. The localization effect decreases when the forcing frequency is close to the substrate's natural frequencies, and becomes more pronounced when within a periodic segment the ribs have a varying impedance. [Work supported by ONR.]