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.

Abstract-The harmonic aggregation in wind power generation is widely concerned in engineering practice. In this paper, large volumes of voltage and current data in wind farm was measured and analyzed for exploring the distribution rules of harmonic current amplitude and phase, based on which, the probabilistic statistical model of harmonic current in wind farm was set up. And the superposition of harmonic in wind farm was predicted and evaluated with Monte-Carlo method. Simulation shows that the calculation of harmonic superposition with Monte-Carlo method has strong reliability and maneuverability. This method can be used to calculate the mean value of the superposition of harmonic and predict the harmonic aggregation at extreme situations.

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