Physics-Based Modelling of Ice Actions and Action Effects on Marine Structures

Physics-based time-domain numerical modelling is a powerful approach to study ice-structure interactions and to accurately and effectively calculate ice actions and action effects on marine structures. In this study, we use the classical problem of ship resistance in level ice (continuous ice breaking mode) to demonstrate the advantages of this approach and to discuss current limitations and directions for future research. A case study comprising four different icebreakers transiting with constant speeds in level ice is presented. The Simulator for Arctic Marine Structures (SAMS) is used herein to generate the numerical results. In total 96 simulation runs are completed. In each simulation, the icebreaker under consideration transits at least twice its length in level ice. Beside varying the transit speed, the drag coefficients are also varied, and the simulations are run with and without including the ventilation effects. The numerical experiments reveal that the forces from the ice rubble are the major contributor to the ice resistance and that the increase of the ice resistance with speed comes mainly from the inertia of the ice rubble. Moreover, the ventilation effect is strongly influenced by the ship hull and it generally increases the total ice resistance independent of the transit speed. Further, the numerical experiments show that the rubble transport is largely influenced by the viscous forces of the ambient fluid flow, i.e., larger ice rubble coverage under the hull is achieved at higher transit speeds or when using large drag coefficients. Finally, the findings of the numerical experiments indicate that further improvements to our predictions can be achieved if processes like dynamic ice fracture, backfill effect and gap pressure are accounted for in the model.