Experimental study on hydrodynamic characteristics of a moored square cylinder under freak wave (II: Frequency-domain study)

Previous studies indicated that the occurrence of freak wave has a significant impact on the time-domain characteristics of a moored floater dynamic response. In this study, extensive investigations have been performed to figure out further dynamic response characteristics of a moored square cylinder under freak wave in frequency-domain. In the experiments, the wave sequences with and without the freak wave are defined as freak and random waves, respectively. The results show that, the freak wave parameter α1 and spectral peak period have significant impacts on the dynamic response characteristics of the moored floater in frequency-domain. The effect of freak wave on surge and mooring tension of the floater is figured out through the low frequency components (0–0.5fp) which leads to significant increase with α1. Followed the occurrence of freak wave, surge increases sharply and oscillates for longer than 20 wave periods in low frequency. Without the occurrence of freak wave, however, both amplitude and oscillating of surge is significantly weaker. The mooring tension response is subjected to surge and hence the trend of variation is similar to surge.