Nonlinear Simulation of a Spar Buoy Floating Wind Turbine

A computational model, developed in Nematbakhsh et al. [1], is used to predict the response of a spar buoy floating wind turbine to moderate amplitude waves. The method is based on solving the unsteady Navier-Stokes equations with a level set method to predict the free surface motion and an immersed boundary method for tracking the floating wind turbine. The tethers, tower, nacelle, and rotor are included using reduced order models, leading to a reasonably efficient computational approach. Wind is modeled as a constant thrust force. Results are presented for a full-scale 5 MW turbine mounted on a spar buoy platform. Pitch and surge response, as well as tethers tension are studied as a function of time for one incident wave frequency and amplitude and the results are discussed. The results show that for a spar buoy floating wind turbine with three taut tethers, there is a possibility of significant higher load on one tether.