ABSTRACT:

The non-linear interaction of steep waves with an FPSO is discussed in the paper. The study of numerical analysis and experiments for a steep wave group interaction with a simplified FPSO has shown that the second-order free surface components at the bow of the ship are very significant, and cannot be neglected; otherwise a major underestimation of the wave impact on the structure could occur. By applying the same wave group to a few non-head on wave directions, the effect of the wave heading on the non-linear free surface elevations and run-up on the ship has been examined and discussed.

INTRODUCTION

The use of ship-shaped floating oil production systems is becoming commonplace around the world, even in areas with severe wave environments, with the offshore industry moving into deeper and deeper water. Non-linear wave interactions with such a ship-shaped body then become more of a concern to engineers and researchers. Fixed and floating offshore production units are very much prone to the effects of the weather, in particular as a result of their requirement to remain in the same position. FPSOs have a ship-like form with one axis of symmetry and with the longitudinal dimension much larger than the transverse one, which make them particularly sensitive to the direction of the incoming waves. A recent report of structural damage from green water on deck has shown that four of five production ships on the Norwegian continental shelf have experienced damage due to green water, and the incidents have occurred in the bow area, amidships and aft (Ersdal & Kvitrud, 2000). Recent research undertaken in Oxford has demonstrated the importance of non-linear effects for both wave loads and the surface run-up around the bow of an FPSO in random seas (Zang et al 2006).

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