The paper focuses on CFD modeling of random breaking extreme wave events and resulting impact loads on a vertical structure. CFD simulations of wave impacts can be a valuable tool in the design stage of offshore structures. In the present paper the wave impact forces on a buoyant offshore structure has been analyzed. It is important to validate CFD model against experimental data in relevant sea conditions. Based on an extensive model test program at irregular sea state conditions, three extreme wave impact events were identified and selected as candidates to be modeled by means of CFD methods. The method applies a numerical model which reproduces the experimental conditions as close as possible. The two flap wave generation mechanism is modeled as moving wall boundaries in the CFD simulation, using a morphing mesh technique for the deformation of the computational mesh in vicinity to the moving wall boundaries. The motions of the flaps are based on the wave generator control signal used during the model tests. The time series of the waves are compared against model test results at several longitudinal positions. At the location of the extreme wave event, approximately 35 m from the wave generation flaps, the steepness of the wave event is reasonably well reproduced, while the height of the wave is slightly smaller than in the experiments. The time history of the wave impact force is also in reasonably agreement with experiments, although with a smaller peak value. The effect of the design modification is well captured in the CFD simulations.

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