Performance of an example jack-up platform under directional random ocean waves

Abstract

This article presents the results of nonlinear dynamic analyses that explore the effects of directionality and the random nature of ocean waves on the overall structural performance of a sample jack-up platform. A finiteelement model is developed which rigorously includes the effects of the material and geometrical nonlinearities in the structure and the nonlinear soil-structure interaction. Two wave theories, NewWave and Constrained NewWave, are adopted to simulate the water surface and water particle kinematics, which are implemented in the numerical model developed. Analyses are performed for both two and three-dimensional wave models, and the results are compared in terms of the deck and spudcan foundation displacements. The results obtained from the analyses indicate that the inclusion of wave spreading can result in reductions in the deck displacements of the sample jack-up platform. The level of reduction is greater when considerable plasticity occurs in the foundation. Furthermore, the probability of failure can be significantly decreased when the wave-spreading effects are included. In addition, it is shown that the effects of wave-spreading on the response and failure of the sample jack-up is increased when wave period is decreased.

Effects of irregular nonlinear ocean waves on the dynamic performance of an example jack-up structure during an extreme event

“…The structural response is evaluated in terms of the deck displacement of the jack-up which is representative of all nonlinearities in the structure and the foundation and the dynamic reaction of the structure to the applied wave loads [5]. In this study, the horizontal deck displacement at x ¼ 0.0 m (centre of the hull) is used to investigate the effects of wave nonlinearity and irregularity on the overall performance of the jack-up structure.…”

“…B n cosðk n X À u n t þ 4 n Þ þ gA n cosðk n X À u n tÞ þ dA n u n sinðk n X À u n tÞ (8) Detail description and sample application of linear CNW with its NewWave and random wave are presented by Mirzadeh et al [5] and [22].…”

“…This effect reduces the width of the crests (perpendicular to mean wave direction) and decreases the particle kinematics of the water in the mean wave direction [5].…”

“…Considering the limitations in the current practices, a more rigorous numerical method is required to accurately and realistically simulate extreme ocean waves. In a previous study [5], the authors broadly investigated the effects of the directionality of ocean waves. In this study, only the effects of the nonlinearity and the randomness of ocean waves are considered.…”

Various methods of simulating wave kinematics on the structural members of 100-year responses

“…The most widely used and accepted method for determining hydrodynamic wave loads on offshore structure members is known as the Morison's equation [1,[24][25][26]. The Morison's equation can be defined as follow,…”