8. Higher Mode Vertical Vibration of Giant Tanker

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The preliminary analysis has been made on the hull vertical vibration of tankers in which the ship hull is simulated by the model of two parallel beams elastically connected. Each beam represents the side shell and the longitudinal bulkhead respectively, and the connecting springs the transverse structural members. The result shows that the relative deformation between these two beams is remarkable in the modes higher than 5- or 6-noded mode which means the elastic deformation of the cross section of the ship is significant, contrary to the assumption in the beam-theory calculation. As the mode becomes higher than these modes, there appear new modes in which the deflection of one beam is out of phase by 180゜ to that of another beam. To testify the phenomena mentioned above, the experiments on full scale ships have been carried out on two large tankers and the following phenomena are observed. (a) The relative deflection between the longitudinal bulkhead and the side shell becomes significant in the modes higher than 4-, 5-noted modes. (b) In the modes higher than 7- or 8-noded ones, the deflection of the side shell is remark-ably different from that supposed from the beam theory. In these modes the deflection of the longitudinal bulkhead is similar to that derived from the beam theory. (c) In the region higher than 10- to 12-noded modes, the deflection of the longitudinal bulk-head as well as that of the side shell becomes very complex and shows no longer the clear nodal point. (d) On the other hand, the phase difference of the deflection is very significant and irregular, possibly due to the effect of damping. To explain these facts the new theory above-mentioned has been extended including studies on the hydrodynamic inertia and applied to the ship. The result shows that the calculated natural frequency agrees with the measured one in a full scale ship with 5% of errors, and that although the calculated response agrees with experiment qualitatively, more study is necessary to acquire the precise result.
社団法人日本船舶海洋工学会の論文

8. Higher Mode Vertical Vibration of Giant Tanker

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