Abstract This study presents a modal analysis of a jacket-type substructure supporting a 15 MW offshore wind turbine, aiming to assess the influence of geotechnical soil variability on the foundation’s dynamic response. Three representative soil profiles from the Brazilian coast were considered, incorporating different stiffness and stratification conditions. According to offshore engineering guidelines, the soil-pile interaction was modeled using manually inserted nonlinear springs along the pile shaft, based on P-Y, T-Z, and Q-Z curves. These curves were generated using the geotechnical software PILELAT and PILEAXL and integrated into a three-dimensional finite element model developed in ANSYS. The structural model included tubular elements and concentrated masses representing the rotor-nacelle assembly. Two boundary conditions were analyzed: a conventional model with distributed springs along the depth and a simplified model with fixed supports at the jacket base. The modal results indicated that all configurations operate outside the critical resonance bands associated with rotational excitation frequencies, classifying the system as semi-rigid. Even in low-stiffness soils, the jacket system demonstrated satisfactory dynamic performance, provided proper geotechnical characterization is carried out. The findings highlight the importance of integrated modeling between foundation and structure and contribute to the safe and efficient implementation of offshore turbines in Brazilian waters, enhancing the technical feasibility of exploiting the country’s offshore wind energy potential.
Garcia et al. (Thu,) studied this question.