Study on bearing performance and reliability of modified monopiles for OWTs using deterministic and probabilistic analysis methods

Abstract

Existing studies mainly focus on the bearing capacity of monopiles, with less emphasis on reliability analysis, which is an important aspect of the performance of offshore wind turbine (OWT) foundations. This paper investigates the bearing capacity and reliability of traditional and hybrid monopiles using deterministic and probabilistic analyses. The three-dimensional finite element model (FEM) considering the structure-soil interaction is established and its accuracy is verified through comparisons with existing research findings. The responses of monopiles under wind and wave loads are compared in detail, including the rotation angle at the mudline, structural stress, and soil displacement. The environmental design parameters are obtained based on the 30-year annual extreme data, and the correlation between these environmental parameters is considered to obtain a large amount of random environmental parameter data. Then, the back propagation neural network (BPNN) and the response surface method (RSM) are combined to construct the failure response surface. Research shows that the reliability index of the plated monopile does not improve significantly, while the skirted-monopiles perform much better than the traditional monopile. The proposed FEM-BPNN-RSM coupled methodology provides a more comprehensive understanding of the monopile bearing capacity, and can be used for the future monopile structure design of OWTs.