Basic Integrative Models for Offshore Wind Turbine Systems

Abstract

This research study developed basic dynamic models that can be used to accurately predict the response behavior of a near-shore wind turbine structure with monopile, suction caisson, or gravity-based foundation systems. The marine soil conditions were modeled using apparent fixity level, Randolph elastic continuum, and modified cone models. The offshore wind turbine structures were developed using a finite element formulation. A two-bladed 3.0 megawatt (MW) and a three-bladed 1.5 MW capacity wind turbine were studied using a variety of design load, and soil conditions scenarios. Aerodynamic thrust loads were estimated using the FAST Software developed by the U.S Department of Energy’s National Renewable Energy Laboratory (NREL). Hydrodynamic loads were estimated using Morison’s equation and the more recent Faltinsen Newman Vinje (FNV) theory. This research study addressed two of the important design constraints, specifically, the angle of the support structure at seafloor and the horizontal displacement at the hub elevation during dynamic loading. The simulation results show that the modified cone model is stiffer than the apparent fixity level and Randolph elastic continuum models. The effect of the blade pitch failure on the offshore wind turbine structure decreases with increasing water depth, but increases with increasing hub height of the offshore wind turbine structure.