Higher Mode Vertical Vibration of Giant Tanker (1st Report)

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For the purpose of clarifying the nature of the hull vertical vibration in the higher mode, the preliminary analysis has been made in which the ship hull is simulated by the two parallel beams model elastically connected. Each beam represents the side shell and the longitudinal bulkhead respectively, and the connecting springs the transverse structural members. The result obtained shows that the relative deformation of longitudinal bulkhead to side shell is remarkable, in the modes higher than 5- or 6-noded mode which means the elastic deformation of the cross section of 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 the longitudinal bulkhead is out of phase by 180° to that of the side shell.To testify the phenomenon above mentioned, the experiments on full scale ships have been carried out on two 150,000 D/W class tankers and the following phenomena are observed.(a) The diffence of deflection of longitudinal bulkhead from that of the side shell becomes significant in the modes higher than 4-, 5-noded modes. The difference becomes larger in the higher modes.(b) In the modes higher than 7-, 8-noded, the deflection of the side shell is remarkably diferent 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 bulkhead 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 and applied to the ship. Calculation of the natural frequency, normal mode and the vibratory response to the sinusoidal exciting force has been made and the results can explain the experimental facts (a)〜(c). Though the calculation partly explains (d), additional study is necessary.
社団法人日本船舶海洋工学会の論文

Higher Mode Vertical Vibration of Giant Tanker (1st Report)

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