| Abstract | Numerical simulations (using LS-Dynaᵀᴹ) were initially conducted to show two scenarios for a naval vessel, one where little-to-no-damage occurs during an ice collision and the other where substantial damage occurs. NRC’s crushable-foam ice model was used for all simulations. One instance of the first scenario corresponded to the vessel moving at a given vessel speed of 1.5 m/s and experiencing a bow-side collision with a block-shaped ice mass of approximately 181 tonnes that caused a relatively small amount of plastic damage to the vessel’s hull (i.e. a widearea shallow-depth plating dent with depth of ~ 11 mm). In contrast, the second scenario corresponded to the vessel colliding at the same speed with a 524 tonne similar-shaped ice mass at the same hull location that caused extensive, non-holing, plastic damage to the vessel grillage. That is, the hull plating experienced substantial plastic indentation (~ 60 mm) and the stiffener and frame in the region of impact underwent bending and buckling. Following those simulations, others were performed using progressively smaller ice masses in order to determine what the size of an ice mass would be that would cause no damage at all to the vessel. The results indicated that some level of damage, albeit diminishingly small, occurred (in a linear trend) as the ice masses and associated peak loads get smaller until eventually an ice mass of 8 tonnes produced no damage at all, where the peak load was 25 kN. The next ice-mass size up from that was 17 tonnes, that produced a tiny amount of damage during a simulation. An important observation from all the simulations concerns where the ice impact occurs with respect to supporting stiffeners and frames behind the plating. This can influence the peak loads and pressures that occur, and the extent of local damage. The 524 tonne ice mass collision simulation yielded average and peak contact pressures that were in reasonable agreement with average and hardzone pressure values obtained in large double pendulum ice impact lab tests. This, and favorable comparisons with other lab and field data, bolster confidence in the ice model used. |
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