Experimental investigation of freak wave actions on a floating platform and effects of the air gap

Unpredictable freak waves can reach up to 30 m and pose constantly a significant threat to shipping and oil/gas platforms. To provide further insights into the effects of freak waves on oceanic floating platforms, the present study conducts an experimental campaign focusing on two air-gap conditions (i.e. 0.35Hc and 0.2Hc, where Hc is the height of the platform column) and various wave impact patterns. Multiple quantities have been measured for each experimental test, including platform motions, tension forces in tethers and the wave impact pressure at numerous locations within the structure. By combining the experimental data of the air gap 0.55Hc presented in the authors' previous study, systematic comparisons were carried out for elaborating the characteristics of impact pressures, platform motions and tether forces, as well as the effects of air gap on these quantities. Within the experimental cases tested it is found that: i) with the reduction of the air gap, the impact pressure at the bottom wall of the upper deck increases while those at the vertical front wall reduce; ii) the air gap of 0.55Hc registers larger surge motions as compared to other air-gap conditions due to the combined effect of larger horizontal loads applied on the platform and the small resistance force of the system.