Insight into modelling offshore monopiles via 3D finite element analyses - Considérations pour la modélisation de monopieux par élément finis 3D

Offshore wind farms have been attracting the attention of both researchers and practitioners over the past few decades, due to the growing interest in renewable energy. The choice of a particular foundation, which depends on several factors such as the mechanical properties of soil, depth to bedrock and bathymetry, may influence the overall wind farm cost by up to about 20%. Monopiles are the most used foundation system in the market, whose design can be further refined with advanced numerical analyses, provided that input parameters are properly calibrated. This paper shows the main results of a nonlinear static analysis of a monopile subjected to a horizontal load and embedded in a layered deposit. The analysis was performed using a 3D Finite Element model, where the foundation was represented with plate elements, and the soil mechanical behaviour was described with advanced constitutive models. The obtained pushover curves are shown and discussed, from which a reference design condition was selected. Then, the bending moment profile was obtained following three approaches, listed in a descending order of complexity: (1) integration of the stresses at the soil-plate interface; (2) derivation of the monopile rotation profile of the plate elements; (3) direct output from a dummy beam element located at the centreline of the monopile. It is shown that the dummy beam provides results in good agreement with those from the other two approaches, suggesting that it may be successfully adopted in practice to speed up the post-processing in the design of monopiles. The methodology presented in this paper would be useful for industrial projects.