Modelling of Breaking Focused Wave Interaction with an Offshore Wind Turbine Support Structure in Intermediate Water

Abstract

Offshore wind turbine (OWT) substructures are exposed to extreme waves under severe environmental conditions especially in intermediate and shallow waters. These extreme waves are highly nonlinear, which cause high intensity short duration impact forces on OWTs. The main objective of the study is to investigate numerically and experimentally wave impact forces on a vertical slender cylinder which resembles a monopile substructure for offshore wind turbines subjected to focused breaking waves in intermediate water depth. Both laboratory measurements and numerical simulations are performed in order to obtain more insights into the breaking wave impact problem. The total response forces on a monopile substructure were measured at higher resolution in a well-controlled programmable wave flume. In addition, acceleration of the monopile, the wave surface elevations around the breaking region were measured for different intensities of breaking wave impacts. Further, the evolution of focused breaking waves along the tank and their characteristics were examined. Numerical experiments are carried out in a computational fluid dynamics based three-dimensional numerical wave tank, REEF3D. The model is based on the incompressible Reynolds-averaged Navier–Stokes equations together with the k − ω for turbulence and the level set method for free surface. The experimentally measured main wave crest of the breaking focused wave group is fairly well captured in the numerical simulation.