Hybrid analysis of severe wave impact and hydroelastic effects on a rectangular vertical cylinder

This study investigates the most severe wave impact scenario documented by Abrahamsen et al. (2023a) on a rectangular vertical cylinder, mimicking a semisubmersible platform leg. Both flexible and rigid panels were tested under severe irregular waves, employing a hybrid analysis that combined signal-analysis techniques with use of a finite element method (FEM) and a simplified hydrodynamic model. Results revealed nearly two-dimensional impacts with gas-cavity entrapment causing peak pressure loads and subsequent oscillations. Maximum strain in the flexible panel occurred as a consequence of the cavity compression but the evolution of strain frequency content suggested a shorter permanence of the cavity at the structure and aero/hydroelastic effects. The forced-vibration stage connected maximum strain with peak pressures, highlighting the role of cavity compression for the excitation loads and for the hydrodynamic damping induced on the structure; this damping dominated over structural damping. A modal decomposition approach identified the deflection and strain modes, enabling the reconstruction of the distributed deflections, strains, and stresses, with the use of only five strain gauges.