Numerical analysis of the long-term performance of offshore wind turbines supported by monopiles

• Published in: Ocean engineering 2017-05, Vol.136, p.94-105
• Main Authors: Ma, Hongwang, Yang, Jun, Chen, Longzhu
• Format: Article
• Language: English
• Subjects: Cyclic loading; Long-term performance; Monopile; Soil-structure interaction; Wind turbine
• ISSN: 0029-8018; 1873-5258
• DOI: 10.1016/j.oceaneng.2017.03.019

Offshore wind turbines (OWT) are often supported on large-diameter monopiles and subjected to cyclic loading such as wind and wave actions. The cyclic loading can lead to an accumulated rotation of the monopile and a change in the foundation stiffness. This long-term effect is not yet well understood. This paper presents a three-dimensional finite element model for analyzing the long-term performance of offshore wind turbines on large-diameter monopiles in sand in a simple way. In this model the characteristics of pile-soil interaction under long-term cyclic lateral loading, observed from well-controlled laboratory model tests, are taken into account. A parametric study has been conducted for a full-scale wind turbine supported on a large-diameter monopile, with focus on the influence of several design parameters on the deformations of the monopile and the tower supporting the wind turbine. The study shows that under the serviceability limit state, the deflection and rotation at pile head in the case of considering the effect of long-term cyclic loading are notably greater than that computed in the case where this long-term effect is ignored. This significant difference suggests that the long-term cyclic loading effect cannot be overlooked in design and analysis. •A 3D FEM is presented for analysis of the long-term performance of monopiles supported offshore wind turbine.•The validity of the basic 3D model was examined against results from full-scale tests.•A parametric study was conducted for a full-scale 3MW offshore wind turbine supported on a monopile in sand.•The deformation of the monopile and the tower computed with and without considering the long-term cyclic loading effect were compared.•The influence of several design factors on the long-term performance of the pile and tower was investigated.