Holistic Assessment of Survival Time after Ship Collision

Licentiate thesis, 2010

Collisions between ships contribute to ship losses even in modern time, and the International Maritime Organization (IMO) strives towards a more risk-based view on addressing the damage stability of ships. This thesis presents a holistic methodology for computing the consequences of ship collisions. It is comprised of structural analysis of a collision scenario followed by dynamic damage stability simulations of the struck ship. The time to capsize is determined and studied with regard to uncertainties in the choice of failure model and material parameters in the structural computations as well as the variation in sea state representation in the stability simulation. The emphasis of this thesis is on structural computations of the collision event. Results from material testing recorded with a digital image correlation technique are presented; tensile tests have been carried out to study dependence on length scale, and forming limit tests have been conducted to study the dependence of the failure of the material on multiaxial strain state. Based on these results, recommendations for constitutive and failure modelling are given, taking scatter of material data into account. Explicit finite element analyses are presented for a case study of a collision scenario in which the consequences from uncertainties in material properties and failure model in terms of shape and size of the damage opening are studied. This variation also has an impact on the time to capsize of the vessel, which is studied in the subsequent damage stability computations. One conclusion is that the holistic methodology that has been used is important for future efforts in the research on safety at sea. The study presented demonstrates the importance of incorporating uncertainties in the analysis chain and studying the effect of these on the final results: the time to capsize.