Numerical assessment of the behaviour of a fixed offshore platform subjected to ship collision

Abstract

According to the International Association of Oil and Gas Producers Report [1] one of the main accidental situations endangering offshore Jacket platforms is a ship collision. Such scenario may induce severe damage level and is therefore addressed in the Norwegian standards, Norsok N-003 and N-004 [2,3], which provide a series of guidelines and methodologies to establish the resistance and ductility of framed structures. The ship-platform collision is characterized by the ship's kinetic energy, due to its carrying mass and velocity, and also by the deformation capacity of both structure and ship. As two bodies collide their deformation stiffness can lead to different responses: a near elastic collision (in which case the two bodies travel in opposite directions after the collision), a perfectly inelastic (both bodies travel together), or a situation in-between. The Norsok standards establish three different design cases: strength design, in which the energy is dissipated by the ship; ductile design in which the energy is dissipated by the structure; or a halfway compromise shared-energy design, which is rather troublesome to quantify. In this way, the main purpose of this paper is to perform a sensible numerical analysis of the behaviour of a steel offshore platform based on the Merluza-1, located in Bacia de Santos, São Paulo, Brazil, under an impact loading of a stiff and a soft 5000 ton ships, traveling at a speed of 0.5 m/s and, as prescribed in the standards, at a speed of 2 m/s. The finite element software ABAQUS is used to determine the deformation and dissipated energy in both the ship and the structure during the local collision.