Extreme Wave-structure Interaction And
Directional Spreading Effects On The Air-gap
Design Of An Offshore Platform
Author(s)
M. Chen
Abstract
Accurate prediction on the behaviour of the largest waves in an ocean
environment is vital to the safe design and performance of offshore platforms.
This paper is concerned with the description of extreme waves, and includes both
linear and nonlinear modelling of the largest water waves arising within
directionally spread sea-state. The statistical description of the most probable
temporal shape of the free surface in the vicinity of a large crest, for a given
wave period and wave direction is found to correspond to the statistics of an
extreme wave event. A variety of time-frequency analysis techniques is used to
demonstrate that the free surface elevation time histories of focused wave groups
are in close agreement with linear theory. A deterministic nonlinear correction is
proposed for isolated extreme storm events. The NewWave formulation
associated with this proposed nonlinear correction coefficient is employed to
simulate the interactions between an extreme wave event and an idealized
platform loading column. Statistics of the predicted maximum crest elevation are
obtained using an exact linear interaction formulation of the scattering of water
waves by a vertical circular cylinder in conjunction with a unidirectional
Bretschneider spectrum. The results show that the second-order coefficient of the
Stokes-type wave component is affected by directional spreading. Statistical
analyses suggest that second-order wave theory describes the wave field very
accurately even for extreme events. The present study provides a critical insight
into the free surface elevation maxima of random seas containing waves of
different frequencies and various energies, thus safeguarding the air-gap design
of the offshore platform.
Keywords: extreme wave, wave-structure interaction, air-gap design, nonlinear
modelling, directional spreading.
Keywords
extreme wave, wave-structure interaction, air-gap design, nonlinear
modelling, directional spreading
Related Book
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