Probabilistic Assessment and Comparison of Scour Protections at Horns Rev 3 and Egmond aan Zee Offshore Wind Farms

Abstract

Offshore wind foundations have seen a remarkable growth in over the last three decades. Up to date, this growth has been mainly registered in North Sea locations, where water depths do not exceed 30 m and monopile diameters typically range between 4 to 9 m. In these cases, scour phenomena can be a main reason for structural instability and fatigue induced damage, thus there is often a need to apply scour protection. Given the complexity and uncertainties of scour phenomena, the design of scour protection is mostly based on semi-empirical formulations. These often result in conservative design, which in turn leads to excessive costs when installing offshore wind foundations. To account for the uncertainty in scour protection design and to assess the reliability of existing solutions, recent developments have been made regarding the application of probabilistic based analysis, which aim to either quantify the protection’s reliability or to derive the median stone size associated to a target value for the probability of failure. However, there are few to almost no case studies reported in the literature concerning the reliability analysis of scour protection for offshore wind monopiles. Hence there is a need to extend this probabilistic analysis to a broad range of locations, to further improve their application for both design and median stone size optimization purposes. This research provides a study on the probabilities of failure at Horns Rev 3 and Egmond aan Zee offshore wind farms. The results show that the values of the probability of failure of a scour protection for the same design criterion can vary significantly depending on the site-specific conditions. Variations can be of two orders of magnitude, from 10^-4 to 10^-6. Still, the probabilistic assessment is able to provide indications on the potential optimization of the median stone size. Based on the comparison between both locations, this study also provides guidelines for future applications to other locations.