Abstract
This study investigates the sectional loads on an elastic semi-submersible platform for a 2 MW FOWT (floating offshore wind turbine) used in the Fukushima demonstration project. A water tank test is firstly carried out with an elastic model to study the dynamic responses and sectional loads of the platform in regular and irregular waves. Numerical simulations are then performed using multiple hydrodynamic bodies connected by elastic beams. The dynamic responses of the elastic model are compared to those of a rigid model to clarify the influence of the structural stiffness on the platform motion and mooring tension. The predicted sectional loads on the deck, brace and pontoon by the proposed nonlinear hydrodynamic models show good agreement with the experimental data obtained from the water tank test and a simplified formula is proposed to evaluate the distribution of the moments on the platform. Finally, the structural optimization of the elastic semi-submersible platform is conducted. The sectional moments and fatigue loadings on the pontoons are significantly reduced using the strut between the pontoons since the horizontal wave loads on the side column are dominant and the vertical wave loads acting on the platform are relatively small due to the deep draft.
Highlights
Floating offshore wind turbines (FOWTs) have been considered the best way to harvest wind energy in deep water regions
The conclusions are similar to those for the regular waves, that is, the bending moment M x decreases by the brace and deck, while the bending moment M y is primarily reduced by the strut
The nonlinear hydrodynamic coefficient models for the multibody are proposed considering the effects of Reynolds and KC numbers on the added mass and drag coefficients
Summary
Floating offshore wind turbines (FOWTs) have been considered the best way to harvest wind energy in deep water regions. To consider more accurate and efficient responses of the elastic platform, the distributed hydrodynamic loads obtained from BEM were widely used without consideration of hydroelasticity [18,19,20,21,22,23,24] In this approach, the platform was separated into multiple bodies connected by elastic beam elements. Cracks were found on the pontoons during demonstration due to fatigue This indicates that the elastic response prediction and structural analysis on the element of the platform is significant for cost reduction and safe design. The dynamic response of platform motion and sectional loads on the pontoon, brace and deck are analyzed and validated by the water tank test in regular and irregular waves.
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