Resonant Frequencies and Mode Shapes for Single and Double Cylindrical Shells

Resonant frequencies and mode shapes for single and double cylindrical shells are identified from measurements made with the shells in air and in water. The single shell assembly consists of five ribbed sections bolted together and closed at each end with watertight endcaps. Outer shells are wrapped around the inner shell assembly to produce the double shell assembly. The space between the inner and outer shells is free flooded. Resonant frequencies are reported for frequencies up to 1000 Hz. For frequencies above 1000 Hz the resonant modal density is too high to allow separation of all of the resonant frequencies. Because of the limited number of accelerators inside the shell assembly, only the first eight resonant bending modes are identified. It is shown that submerging the shell assembly in water reduces the resonant frequencies of the lowest bending modes to nearly one half of the frequencies for the shell assembly in air. (Author)