CALCULATED NATURAL FREQUENCIES AND NORMAL MODES OF THE GUIDED MISSILE CRUISER USS LONG BEACH (CG(N)-9)
1966
Robinson, Donald C.
Calculations were performed to determine the first six modes of vertical and horizontal flexural vibration, the first three modes of torsional vibration, and the first five modes of coupled torsion-horizontal bending vibration for the guided missile cruiser USS LONG BEACH (CG(N)9) at a displacement of 16,103 tons. A calculation coupling propulsion system longitudinal vibration with vertical flexural hull vibration was performed on an electrical analog computer in an attempt to simulate the excitation of flexural hull modes by vibratory forces transmitted longitudinally through the propulsion-shafting system. Flexural calculations of hull horizontal vibrations were performed with the large forward superstructure deckhouse considered both as rigidly and flexibly attached to the hull. Included in the results are the hull response to a sinusoidal force of 1000 lb acting at the stern in a vertical direction. The vertical flexural modes and natural frequencies were computed using both the standard two-node Lewis virtual mass coefficient and a variable virtual mass coefficient. The parameters used for the calculations are discussed in detail. Results of the calculations are compared with measured hull frequencies.
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