ABSTRACT:

In this paper, the finite element analysis of collision between a supply vessel and semi-submersible platform is presented. LS-DYNA generalpurpose explicit finite element code, which is a product of ANSYS software, is used to model and analyze the non-linear response of the platform due to ship collision. Due to the importance of damage to the platform, the ship hull is assumed rigid. Most probable impact locations and impact geometries are studied based on the dimensions and geometry of the platform and vessel, operational sea-states and relative motions of the vessel and platform. Then, various impact scenarios are considered. The worst impact scenarios are modeled and analyzed. At the end, based on the results, the mechanics of energy absorption and the extent of damage is presented and discussed.

INTRODUCTION

Semi-submersibles are often employed in deep waters and hostile environments instead of drilling rigs as mobile drilling platforms. They can also be used as floating production systems (ABS, 2001). Ship collision is one of the major hazards to offshore platforms. Columns of floating platforms that play a crucial role in platform" s stability are more vulnerable to the collision. In recent years, the growing demand of offshore structures and increasing maritime traffic has increased the risk of collisions. In this regard, several incidents have been reported during the last few years. The most likely events are happened between supply vessels and captive boats servicing the platform during its installation and operation. For example, in United Kingdom Continental Shelf (UKCS), supply vessel collisions, have a rather high probability of occurrence, approximately 17 percent per platform in year (Serco Assurance, 2003). Most of these events have occurred during operational mode of platform. Local indentation is most likely to occur in members with large diameter/thickness ratio such as semi-sub columns.

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