Hydrodynamic Phenomenon and Its Effects in Large Scale Floating Structures

本文首先通过与半潜船模型试验的对比，讨论了本课题组实验室发展的波浪荷载分析方法的准确性。在数值模拟中发现了一个有趣的驻波现象，并在入射波具有特定方向和频率的情况下得到了实验的证实。在大尺度半潜体的情况下，竖直方向的变形刚度一般比水平方向小得多。为此，将三维矩阵方法与波浪荷载分析方法相结合，提出了一种考虑刚体运动的竖向弹性变形分析方法，并通过与模型试验的比较，验证了该方法具有较高的精度。从计算结果可以看出，对于大型半潜式结构，柱单元数量较多时，应考虑水弹性的影响。另一方面，对风荷载进行了试验研究。利用东京大学土木工程系全跨模型风洞，对某大型半潜器模型的单元阻力和升力进行了测量。特别是在某些情况下，采用半潜水结构和高波高固体波面的组合模型来测量波浪的存在对风荷载的影响。结果表明，风荷载并不是很小，特别是在上述组合模型的情况下，风荷载可能会相当大，因此，进一步研究风对大尺度半潜体运动特性的影响具有重要意义。

In this study, first of all, the accuracy of the analysis method of wave load, which has been developed in the laboratory of the head investigator, was discussed by comparison with experiments of a model of semisubmersible with a large number of columns connected by lower hulls. An interesting phenomenon of generation of standing wave was found out in the numerical simulation by the above analysis method and confirmed by the experiments in the case where the incident wave has some particular direction and frequency for the model composed of densely allocated large number columns with large diameter.In the case of large scale semisubmersibles, the rigidity with respect to deformation in the vertical direction is, generally speaking, much smaller than that in the horizontal direction. Therefore, an analysis method for vertical elastic deformation including rigid motion was developed by combining the 3D-matrix method with the wave load analysis method mentioned above and the high accuracy was confirmed by comparison with experiments of a model. It can be said from the results obtained that hydroelasticity should be taken into account in the case of large scale semisubmersible with a large number of column elements.On the other hand, regarding wind, an experimental study on wind load was carried out. Using the wind tunnel for full span model test belonging to the department of Civil Engineering of the University of Tokyo, element-wise drag and lift foyces of a model of a large scale semisubmersible were measured. Especially, in some cases, combination models of the semisubmersible structure and a solid wave surface with high wave height were used to measure the effect of existence of waves on wind loads. The results showed that the wind load is not so small and may be considerably large especially, in the case of combined model mentioned above.Therefore, it is considered to be important to study further the effect of wind on behaviors of large scale semisubmersibles.