Parametric sensitivity analysis of soil properties for retrofitted offshore wind turbine jacket substructures under combined environmental loading

This research provides a comprehensive parametric evaluation of the retrofitting process for a 5.5 MW offshore wind turbine jacket substructure, designed to support an upgraded 15 MW turbine under various environmental loading conditions, which include the influences of wind, waves, and currents. Advanced nonlinear time history finite element analyses, featuring extensive soil–structure interaction modeling, were conducted across a diverse range of soil profiles, which included both uniform conditions and complex heterogeneous scenarios, exemplified by the Gunsan soil profile. The findings indicate that the retrofitted 15 MW jacket configuration substantially diminishes structural demands, with Von Mises stresses reduced by as much as 12 % in critical joint regions of the legs. Nonetheless, localized stress concentrations were noted near the top of the tower when exposed to stratified soil conditions. Furthermore, lateral accelerations at pivotal structural points were reduced by up to 73 %, consistently remaining below the operational threshold of 0.3 g. Logarithmic strains and lateral displacements significantly decreased, especially in low-stiffness soils, with reductions up to 88 % relative to the original 5.5 MW system. The research indicates that well-structured and efficient foundations improve dynamic performance, stability, and longevity, offering critical insights for future design and retrofitting in complex settings. • A parametric analysis was performed to modify a 5.5 MW jacket substructure for a 15 MW offshore wind turbine. • Retrofitting resulted in a reduction of Von Mises stresses by 12 % in leg joints under layered soil conditions. • Lateral accelerations were reduced by 73 %, remaining compliant with the 0.3 g operational threshold. • Logarithmic strains and displacements were diminished by 88 % in low-stiffness soils.