Extraordinary Dynamic Responses of Huge Floating Offshore Structures in Directional Spectrum Waves

在横滨国立大学的拖曳池中，对系泊在深海的巨型浮式海工结构体进行了不规则波浪下的半弹性模型实验研究。用张力式单点系泊浮标系泊了一个很长的模型，并使用了能很好地模拟真实海浪的方向谱波。这样的实验在世界上还没有进行过。本研究得到的结果如下：1。经试验证明，新研制的4根张紧索单点系泊浮筒具有足够的性能，可在深海和波涛汹涌的海域使用。此外，该浮标系统所系泊的大型海上浮式结构物的运动非常小，完全满足人工浮岛等的使用要求。另一方面，与大型船舶相比，大型海上浮式结构的纵向刚度有明显的偏小趋势。虽然作为刚体的运动，如上文所述，更小的可以忽略不计，但波浪中的弹性响应表现得非常明显。特别是当弹性结构的固有频率存在于波谱的频率阶时，会发生共振现象，与输入的波激力相比，弹性结构的响应变得非常高。多种振动模式同时产生，且存在相位差。因此，由于在结构中的位置不同，弹性响应特性也有很大的不同。从所获得的结果可以清楚地看出，巨大的海上浮动结构对于人工浮岛的许多用途都是有价值的，即使这些人工浮岛是在波涛汹涌的深海中定居的。并给出了一点式张力浮筒系泊超长浮岛的实例。研究结果再次表明，巨型浮岛结构的弹性响应是设计初期的重要研究项目之一。并为此类大型海上结构的设计提供了一些实用的数据。少

On huge floating offshore structures mooring in deep seas, experimental researches in irregular waves using semi-elastic models were carried out at the towing tank of Yokohama National University.A very long model was moored by the one point mooring buoy of a tension type and directional spectrum waves simulating satisfactorily real ocean waves were also used. Such experiments have not been carried out in the world. Obtained results of this study are as follows.1. It is certified that newly developed one point mooring buoy using 4 tensioned wires has enough performances for usage in deep and rough seas.2. Furthermore, motions of the huge floating offshore structure moored by this buoy system are very small and satisfy completely the demands for use of artificial floating islands etc.3. On the other hand, there is a notable tendency that the longitudinal rigidity of the huge floating offshore structures is small compared with that of the huge ships. Although the motions as a rigid body … More are negligible small as above mentioned, the elastic responses in waves appear remarkably. Especially when the natural frequency of elastic structure exist in the frequency order of wave spectra, resonance phenomena are occurred and those elastic responses become extraordinary high value to compared with wave exciting forces as input.4. Several vibration modes are induced simultaneously and there are phase differences. Therefore elastic response characteristics are quite different due to the position in the structure.From the obtained results, it become clear that the huge floating offshore structure is valuable for the artificial floating islands to many purposes, even if those are settled at the rough deep ocean. And this study shows a practical example of the very long floating island moored by one point tension buoy system. Moreover the results of this investigation newly indicate that the elastic structural response of the huge floating island is one of the important investigation item in the initial design stage. And some practical useful data for design of such huge offshore structure are also shown in this research. Less