Abstract
This study presents a generic method to upscale a semi-submersible substructure and tower-nacelle-blade for a floating offshore wind turbine from 5 MW to 15 MW and beyond. The effects of upscaling the column radius and/or distance of the floating base are investigated, and a comparison is made with a 15 MW reference design. It is found that scaling column radius increases the mass of the platform and the heave natural period, while scaling column distance raises the center of gravity and metacentric height of the floating system and slightly decreases the heave natural period. The 15 MW reference design addresses these issues through design changes that increase the ballast mass to lower the center of gravity, and increase the added mass to raise the heave natural period. Finally, a method for estimating the scaling of platform parameters with different assumptions is proposed.
Highlights
The scaling up of floating offshore wind turbines (FOWT) may be one of the most significant factors in reducing their LCOE
A generic method for upscaling a semi-submersible-type floating offshore wind turbine has been presented, with two variations that highlight the different effects of scaling the semi-submersible’s column radius and column distance. This upscaling was done in the range of 5 MW to 15 MW, as reference semi-submersible designs are available for reference wind turbines at those power ratings, and because the scaling of the floating substructure represents an important area of potential cost savings as new wind turbines are being developed and reaching the 15 MW mark
Turbine upscaling using mass and overturning moment exponents less than cubic was shown to have good agreement with the reference 10 MW and 15 MW wind turbines, with an exception for nacelle mass at 15 MW that is explained by assumptions for a more advanced generator cooling system in the reference design
Summary
The scaling up of floating offshore wind turbines (FOWT) may be one of the most significant factors in reducing their LCOE (levelized cost of energy). Linear scaling laws for wind turbines developed in the UpWind project [7] are often used as a starting point, such as in the work of Leimeister et al [8], which upscaled the 5 MW OC4 semi-submersible to 7.5 MW by scaling the floater dimensions with the square root of the power rating ratio between turbines. Kikuchi and Ishihara [10] upscaled a 2 MW floating wind turbine used in the Fukushima FORWARD project to 5 MW and 10 MW by scaling the floater column radius with the cubic root of the mass ratio between turbines, and scaling the column distance to preserve the static balance in pitch between overturning moment and pitch restoring moment They found the overturning moment to scale roughly proportional to the power rating between turbines, or with the square of the turbine scale factor rather than the cubed scaling that would be expected in linear upscaling
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