Assessment of ship collision according to new NORSOK N-003 criteria
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Abstract
In 2017 the NORSOK N-003 code action and action effects was revised regarding energy requirementsfor ship collision with offshore installations. Previous energy requirements for ship collision with anoffshore installation were set to be 11 MJ and 14 MJ for head-on/stern and broadside. Now the revisedversion allows for 50 MJ impact for all events. This stems from advancements in ship design over thepast decades, which have introduced larger supply vessels and bows such as bulbous bows and X-bow.This study inquires into ship collision with a semi-submersible offshore platform with the revised energy.Simulated collision events include bow, stern and broadside for bulbous bow and X-bow. The platformcolumn and vessel are modelled to simulate the collision interaction for the various events. The vesselrepresents a 10 000 tonnes offshore service vessel including added mass during impact and impact velocityis set to achieve an impact energy of 50 MJ. A Non-Linear Finite Element Analysis (NLFEA) is conductedand numerical results are discussed herein. The results primarily focus on the penetration and deformationof the semi-submersible platform that causes flooding of compartments. Where a strain-based failurecriterion is applied to represent the failure of the elements. The analysis focuses on a shared energydesign using mean material properties for both ship and platform with no added safety factors. Findingsfrom the analysis suggest that the impact location greatly affects the number of penetrated compartments.As well as increased energy does not satisfy the original acceptance criteria which allow for 2 penetratedcompartments. Results also suggest that low-energy collision does not distinguish bulbous bow or X-bowas more critical in terms of damage to the platform. However, large energy impacts indicate that X-bowcollisions have a greater damage potential than the bulbous bow. Penetration of compartments has aclose relation to the fracture of the platform shell. This study has applied the simplest representationas strain-based criteria. More advanced criteria such as strain-dependent failure criteria would moreaccurately represent the fracture of elements.