Abstract
Freak waves have great peak energy, short duration, great contingency, and strong nonlinear characteristics, and can cause severe damage to ships and marine structures. In this study, numerical simulations in conjunction with experimental tests are applied to study air gap response and wave slamming loads of a semi-submersible offshore platform under a freak wave. A three-dimensional wave tank, which is created based on the computational fluid dynamics (CFD) method, is applied to study the hydrodynamic responses of a semi-submersible platform. The numerical model of the tank and offshore platform system are checked according to the experimental results. A typical freak wave is modelled in numerical wave tanks by the linear superposition method, and its significant wave height is 13.03 m. It is found that the freak wave is closely associated with the wave slamming. The appearance of the freak wave gives rise to a negative air, gap which appears on the side of the back wave surface at the bottom of the deck box, and considerable slamming pressure is generated. Furthermore, the wave run up at the junction of the column and the buoyancy tank is also seen due to the freak wave.
Highlights
Much maritime distress indicates that freak waves cause severe damages to ocean platforms
The generation mechanism of freak waves and their interactions with floating structures have been well studied by numerical simulations or experimental methods in previous researches
Liu et al [8] reviewed the slamming pressure of a semi-submersible platform in different waves by the model test method
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The generation mechanism of freak waves and their interactions with floating structures have been well studied by numerical simulations or experimental methods in previous researches. Liu et al [8] reviewed the slamming pressure of a semi-submersible platform in different waves by the model test method. Zhang et al [19] generated freak waves by utilizing wave superposition theory They studied the effect of freak waves on motions of a rigid plate and the slamming pressure. Based on the improved double wave train superposition model of the Longuet-Higgins’s theory, Zhang et al [20] carried out numerical simulation to study freak waves. The air gap response to motion and wave slamming characteristics of offshore platform under freak wave are studied by combining numerical simulation with experimental tests. This study is organized as follows: a theoretical study on numerical wave tanks, the establishment and verification of a numerical model, and a study on the load distribution of a platform under a freak wave in numerical simulation
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