Development of a 3-legged jacket substructure for installation in the southwest offshore wind farm in South Korea

A suitable substructure for Offshore Wind Turbines plays an important role since it can efficiently reduce the financial costs of wind power projects. According to the track record of the Korean offshore wind farms, the 4-Legged Jacket (4LJ) substructure is the most utilized system; however, this design is still limited, specifically in the economic aspects. Thus, this study aims to design a more cost-effective substructure to enable large-scale deployment for Korean offshore projects. To achieve this objective, the new 3-Legged Jacket (3LJ) substructures together with various bracing topological forms (i.e., Pratt, Warren, and X-bracing) are developed. Results show that under the environment loads, dynamic responses obtained from the developed 3LJs are almost independent to the loading directionality; while there is a strong polarization in the case of 4LJ. Among the three cases of the 3LJs, the X-type topological form has the highest flexural stiffness together with the largest manufacturing and fabrication costs, while the Warren bracing system reaches ultimate strength earlier than the Pratt system. Therefore, the 3LJ substructure with a Pratt bracing system is suggested as a good alternative to the existing 4LJ system for Korean offshore wind farms, with reductions of up to 21% and 25% in total weight and number of weld joints, respectively.