巨大箱型浮体構造の動的弾性挙動に関する研究 : 梁モデルによる水平撓み挙動特性の検討

抄録

A number of studies on the dynamic structural analysis of huge floating structures with length or breadth to the order of several thousands of meters have been done by several authors. Most of these studies deal with the basic characteristics of vertical deflections of the structure modeled as a beam or plate on elastic foundation. Eigen frequencies for vertical vibrations of very large and comparatively flexible floating structures exist continuously in relatively high frequency zone due to buoyancy effect. On the other hand, the lowest eigen frequency for horizontal vibrations may appear in the lower frequency zone than the heave-mode frequency, because of no effect of buoyancy on the horizontal deflection behaviour. Therefore, it is important to investigate the dynamic response in the lower frequency zone than the heave-mode frequency. This paper deals with the dynamic behaviour for the horizontal deflection of a huge floating structure (about 4,600m×1,000m) using the beam model cosidering shearing rigidity by the analytical method. Effects of mooring characteristics and structural parameters on the dynamic response and strength of such structures are discussed. The results obtained in this study are summarized as follows: (1)It is comfirmed that the lowest eigen frequency for horizontal vibrations of the huge floating structure is comparatively lower than the heave-mode frequency and intervals of eigen frequencies are wide. (2)It is pointed out that not only vertical deflection behaviours but horizontal deflection behaviours should be also considered at the lower frequency zone. (3)It is neccessary to consider effects of shearing rigidity on the horizontal deflection behaviour.