Estimation and Experimental Validation of Extreme Waves and Loads on a Large Monopile

Numerical wave analyses of extreme sea states have been performed for a large monopile subjected to 50 year and 500 year hurricane conditions. The numerical analyses have been established using the REEF3D::FNPF software. The wave kinematics has then been combined with a Morison type load model containing a modified inertia term, KC dependent drag and a Weynberg-Campbell slamming term. The line loads generated from the numerical hydrodynamic analyses are then implemented into the SIMA FE solver to establish the extreme WTG responses. The extreme statistics of hydrodynamic and structural response has been investigated and compared with results from model tests. The model test data sample is considerable and consist of 20 × 3h series of seed variations, including variations between sea states and mudline boundary conditions. When evaluating parameters such as crest height, steepness, we observe that the numerical wave tank approach allows for similar extreme behaviour as the observed in model tests. In general, the numerical and experimental results agree well when comparing the extreme statistics. Beyond this, we also compare the extreme events in the slamming zone. This implies that we sequence the max. load events for both experiments and numerical analyses and sort them by magnitude before making a direct time domain comparison of each of the sorted extreme events. The correspondence between model tests and numerics for the splash zone loads, is also observed for the overall response statistics. Finally, we conduct a comparison of waves between the REEF3D::FNPF-based models and more conventional constrained wave methods as outlined in IEC61400-3-1.