Evaluation of load-carrying capacity of a submersible platform subjected to accidental ice impacts

Abstract

Floating glacial ice features of various sizes pose great threats to the structural integrity of offshore structures in arctic regions. Potential collisions with large icebergs should generally be avoided through proper ice management, but smaller glacial ice features such as bergy bits or growlers (with a characteristic water line < 15 m) may be overlooked by radar in high sea states, and are likely to hit the platform accidentally. This paper evaluates the load carrying capacity of a semi-submersible platform to accidental ice impacts. The shared energy approach is adopted as done in ship collision analysis, assuming collision scenarios with rigid platform-deformable ice on the one hand, and rigid ice-deformable structures on the other hand. Both ice and the platform should deform and dissipate energy under the same force level. For structural analysis, non-linear finite element code LS-DYNA is used. An alternative approach is the simplified analytical method, which allows for fast and reasonable prediction of structural damage. Simplified expressions for stiffened panels under ice pressure patch loading are introduced. The resulting resistance curves compare reasonably with LS-DYNA simulations.