Session: 09-01-04 Wind Energy: Aero-hydrodynamics 4

Paper Number: 125799

125799 - Combination of Potential Theory and Morison-Like Viscous Drag Terms in the Hydrodynamic Model of a 12 Mw Semi-Submersible Floating Wind Turbine 

Semi-submersible platforms are widely adopted as support structures for floating wind turbines (FWT). Potential theory is effective for modelling the wave excitation at the wave-frequency (WF) range, but for low-frequency (LF) excitation viscous effects can become important, especially at harsher sea states. Viscosity also plays an important role in damping of the resonant horizontal motions.

Morison-like, quadratic drag terms are typically used for modelling viscous loads on the platform columns and pontoons, with drag coefficients obtained from model tests. When adopting this modelling approach, however, it can be challenging to achieve a simultaneous representation of damping effects and viscous excitation with the same set of coefficients.

In this paper, a systematic procedure is presented to calibrate the drag coefficients of a semi-submersible platform supporting a 12 MW FWT, based on model test results. First, drag coefficients for the pontoon are chosen based on the heave and pitch motions.

It is then assumed that viscous excitation in surge is mainly associated with the fluid-structure interaction at the upper part of the columns, which are subjected to more significant action of the waves. Thus, the coefficients at this portion of the columns are tuned to retrieve the low-frequency motion components not captured by potential theory alone. Meanwhile, the coefficients at the bottom of the columns are adjusted for achieving the necessary level of damping. The paper also discusses common assumptions in the modelling of the water particle kinematics at the wave zone.

Presenting Author: Petter Andreas Berthelsen SINTEF Ocean

Presenting Author Biography: Petter Andreas Berthelsen is currently a Senior Research Scientist at SINTEF Ocean in Marine Structures. He completed his MSc-degree in Offshore Engineering at Newcastle University, Dept. Marine Technology in 2000, before doing a PhD in fluid dynamics (multiphase flow, CFD) at the Norwegian University of Science and Technology (NTNU) in Trondheim (2000-2004). He continued with a post.doc. in Marine Hydrodynamics (CFD) at NTNU-CeSOS before he joined MARINTEK and SINTEF in 2007. In the period 2012 to 2014 he was the Chief Operating Officer at MARINTEK USA. And from early 2015 to 2017 he was the Research Manager of the Ocean Energy Group/Marine Structures at MARINTEK and then SINTEF Ocean.

Authors:

Carlos Eduardo Silva De Souza SINTEF Ocean
Nuno Fonseca SINTEF Ocean
Petter Andreas Berthelsen SINTEF Ocean