Analysis of Bottom Damage Caused by Ship Grounding Available to Purchase

A last resort for a ship in disabled condition is to set it aground in a controlled manner for later salvage. A prerequisite for proper handling of this action are tools for reliable, structural analysis with respect to local damage and global hull integrity. The paper addresses advances made in the course of an EU funded project. An important issue is the size and shape of the sea floor in grounding analysis. As little information is generally available, the paper discusses sea floor shape in view of the resistance to indentation of the ship bottom and characteristic scenarios are defined. The resistance to indentation is analyzed for a typical oil tanker for various positions of contact. The interaction between global hull bending and local indentation is also addressed. In dynamic grounding a large part of the ship bottom or the entire bottom may be subjected to damage and a complete nonlinear finite element simulation is very demanding, A new, simplified approach is presented, where the horizontal and vertical components of the contact forces are derived from numerical simulation of lateral indentation, only. Very good agreement has been obtained between the simplified procedure and complete numerical simulation. Force indentation relationships are used as input to rigid body simulation of ship motion. The method is illustrated by a numerical simulation of damages to double bottom of a shuttle tanker. As reliable prediction of rupture initiation and crack growth in cargo tanks is essential with respect to oil spill estimation, advanced rupture criteria have been developed and implemented in the numerical tools. For verification purposes lateral indentation tests of unstiffened and stiffened plates have been carried out in laboratory. Initial results are being presented in the paper.