Rogue wave impact on a tension leg platform: The effect of wave incidence angle and mooring line tension

Abstract

An understanding of the interaction between extreme ocean conditions and floating offshore platforms is required for their design and safe operation. Rogue wave impacts cannot easily be handled by traditional analytic or computational techniques. Here we use Smoothed Particle Hydrodynamics (SPH) to simulate the fully non-linear dynamics of a large breaking wave on a semi-submersible tension leg platform. We consider the effect of wave impact angle and mooring line pre-tension on the subsequent motion of the platform, and predict the maximum tension in each mooring line. The primary effect of wave impact angle is to determine the peak mooring line tension and line “slackness” during wave impact. A 45° impact results in the maximum tension on the leading line. The maximum heave, surge and pitch vary only slightly with wave angle. As mooring line pre-tension is increased, the duration of heave and pitch excursions is reduced. Peak mooring tension increases only slightly, but the incidence of mooring line “slack” decreases significantly for higher pre-tension. Properly applied, SPH has a wide application in predicting non-linear wave–structure interactions. Genuine opportunity exists for using SPH in the design of structures and mooring systems exposed to extreme ocean events such as rogue wave impact.