Three-dimensional finite element analyses of monopiles in cohesive soil for offshore wind turbines

Resumo

In the vast majority of offshore wind farms, monopile-type foundations are the most used in the
construction of wind turbines, however, there are limited guidelines available for analysis and design of
foundation/support structures. Although it is a simple structure, its behavior under loads of wind, waves and
currents is very complex. As there is no design standard for offshore monopiles, offshore wind turbines are
designed based on the API standard, which has only been designed for small diameter monopiles; but, for the wind
industry, diameters greater than 4 m are used. Consequently, monopiles are commonly designed for an extreme
load scenario. For this reason, in this article a three-dimensional finite element analysis of the mechanical behavior
of offshore monopiles under vertical, horizontal and moment loads placed in cohesive soils is carried out, since
these soils, by presenting high plasticity, decrease their load capacity and increase their properties. A Modified
Drucker-Prager/Cap model (MDPC) and Mohr-Coulomb model (MC) is used to study the soil and its response to
complex loads. The results of the numerical simulations are presented and compared with the results of the vertical
bearing capacities predicted by the American Petroleum Institute (API) code method and the lateral displacement
at the pile top with the p–y curve method and the LAP GEOCALCS software. The analysis indicates that the
MDPC model has a better prediction of the load-displacement response than the MC model. The prediction of the
stress in the monopile in both models are very similar. The API method underestimated the lateral displacements
of the monopile at large forces and the LAP software predicts a flexible behavior of the monopile.