| Popis: |
In most of the available literature in grounding analysis, the ship is supposed to run aground over a rock following a prescribed horizontal trajectory. However, in situations where the vessel is navigating in presence of waves, its oscillating heave motion sometimes leads to multiple breaches in the bottom plating, as observed in some real grounding events [1]. Recent numerical studies [2] showed that resulting overall damage of the hull can extend up to 4 times the one obtained by assuming only a horizontal movement for the ship. Despite the increase in computing capacity of computers, nonlinear finite element simulations are very time consuming, and consequently not well suited for probabilistic damage stability analyses that may involve hundreds or thousands of grounding scenarios. In the present paper, a simplified analytical model based on plastic analysis is developed for the response of an unstiffened bottom plating, with the aim to rapidly assess the damage of a ship grounding on a rock idealised as an elliptic paraboloid. At the moment of impact, the ship is supposed to have both heave and surge velocities. Sliding and raking situations are considered and the criterion used to switch from one mode to the other is discussed. The model is then confronted to finite element simulations for different rock shapes, velocities, and friction coefficients. Although the proposed approach is shown to give a good prediction of the dissipated energy in most cases, some limitations are also highlighted. |
