Research on the Offshore Structures for Deep Seas

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This joint research was organized between Japan and Brasil for the estimation of performance of floating offshore structures for deep seas, concerning to the development of ocean, especially for development of oil field in deep seas.For the first year study, we discussed on the way of conducting joint research, and inspected into the oil field off Brasilian coast.For the second year, we developed calculation model for estimating dynamic performance of offshore structures for deep sea considering the combined effect of wind, wave, current and mooring lines. We also conducted tank experiment for examining numerical calculation, and added model experiments in directional spectrum waves.For the final year, we continued the numerical calculation in long crested irregular waves and conducted experiments in directional spectrum waves.From the experiments in directional spectrum waves, estimation method of directional response function was studied.Summarizing the three years joint research, we obtained following main results.(1) Estimation of performance in waves of offshore structures for deep seas is possible.(2) Directional response function can be estimated from the measured results on motion in directional spectrum waves.(3) Motion responses in directional spectrum waves have a tendency to be decreased as the directional spreading become large.