Wave run-up and secondary load cycle on a rounded square column in focused waves

The wave–column interaction under extreme waves is a key issue affecting the safety of marine structures. This study investigates the wave run-up and wave load characteristics on a rounded square column under focused waves using a combination of physical experiments and numerical simulations. The results showed that the increase in wave steepness and period significantly intensifies the wave–column interactions, leading to greater wave run-ups along the column surface. When the focus position is located at the rear surface of the column, the wave run-up height is greater than those at other focus positions. Due to the diffraction effect of the column's rounded corners on wave energy, the wave run-up height is notably reduced under quartering waves. Additionally, the phenomenon of secondary load cycle (SLC) was identified and investigated to explore its underlying mechanism during the interaction between focused waves and the rounded square column. The results indicated that the complex motion of scattered waves behind the column is the primary cause of the secondary load cycle. Furthermore, the presence of a reverse slamming force on the rear side of the column is confirmed, with wavelet analysis revealing that this force contains a high-frequency component. This study provides new insights into the design and safety assessment of column structures under extreme wave conditions.