Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Numerical simulation of the Vortex Induced Motion of a Semi-Submersible Platform
Submission Author:
Daniel Francisconi Oliveira , SP
Co-Authors:
Daniel Francisconi Oliveira, Bruno Carmo
Presenter: Daniel Francisconi Oliveira
doi://10.26678/ABCM.COBEM2021.COB2021-0425
Abstract
Wind energy on the onshore field is well established, and the new challenge is to apply this technology on the oceans. Although at offshore locations the wind resource is usually better, with less obstacles and huge empty areas, engineers must face the problem of waves and current. As the turbines get further from the coast, the depth makes it impossible to fix the structure on the ground, so a floating moored system is required, which adds much more complexity to the dynamic motion of turbines. One important consequence of currents around the immersed parts of floating bodies is the Vortex Induced Motion (VIM), when the structure experiences motion due to the alternate loads originated from the shed of vortices. In order to understand the effects of VIM on the floating offshore platforms and its consequences to the wind turbine operation and mooring system performance, it is essential to accurately model this phenomenon. For numerical investigations, Computational Fluid Dynamics (CFD) is a useful method for computing forces and visualizing the flow field. In this work, we investigate one of the most important floating offshore wind turbines available for the research community, the NREL 5 MW wind turbine mounted on the semi-submersible floating system OC4 Phase II. The platform consists basically of 3 columns disposed on a triangular configuration with one smaller main column at the center, on which the turbine tower is placed. The heave plates and smaller members may have limited effects on the VIM compared to the to the columns, so a two-dimensional computational model should be enough to obtain the structural response with acceptable uncertainty and low computational cost, which is fundamental due to the high number of simulations that are necessary to reach a thorough understanding of the dynamical behaviour of the system. Simulations with in-plane 3-DoF of the semi-submersible OC4 were conducted in the OpenFOAM software with the structure modelled as a single rigid body mounted on an elastic base. Results are compared with experimental and numerical available data, bounding the limits of the 2-D model, and will help to understand the interaction between columns in the offshore context and allow researchers to better model the VIM phenomenon.
Keywords
vortex-induced motion, Semi-submersible platform, Computational fluid dynamics (CFD), floating offshore wind turbine
