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

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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