Study of offshore monopile behaviour due to ocean waves

Abstract

Offshore monopile foundations are one of the most commonly used foundation structures in offshore renewable energy, especially in areas with relatively shallow water. They are characterised by relatively large geometric dimensions compared with other offshore pile foundations and differ from onshore piles in that they suffer from more dynamic ocean environments during their lifetime. One of the most significant aspects is associated with the wave effect on the structural behaviour of monopile foundations. In this study, a three-dimensional scaled boundary finite element model (SBFEM) is proposed to investigate structural responses of monopile foundations when exposed to ocean waves. Unlike other numerical techniques, SBFEM provides an analytical solution in the radial direction with numerical approximation along the discretised faces of the monopile foundation. The SBFEM model is validated by an equivalent finite element model, by which favourable computational efficiency and reliable accuracy are demonstrated. Subsequently, a parametric study is carried out focussing on various wave properties to gain an insight into monopile behaviour. Results show that the lateral displacement of the monopile foundation increases as wave numbers, wave amplitudes or water depths increase. This study aims at improving the design of offshore monopile foundations, when wave load is a dominant factor.