Investigation of structure-soil-pile interaction of a monopile based offshore wind turbine subjected to environmental loads

Today, energy demand is steadily increasing, and the demand for renewable energy and interest in energy technologies have gained significant industrial importance in recent years. Offshore wind turbines, particularly those constructed in open sea areas, are highly preferred due to their high energy production capacity. Offshore wind turbines can generate energy thanks to the constant flow of wind. To ensure the safety of these structures in the marine environment, load transfer is achieved through pile foundations. This study investigates the interaction between the soil and a 5 MW offshore tower structure based on a monopile foundation, taking into account the effects of environmental loads. To investigate the interaction between offshore wind turbine structure with monopile and the soil, saturated dense sand, loose sand, and clay soil profiles were considered. The soil was modeled based on the Mohr-Coulomb criterion. Nonlinear dynamic analyses were performed, considering different time-dependent ground motions, to determine the system's behavior under seismic effects. Wave analysis was performed using the Airy wave theory method, considering the offshore structure-interconnection element (transient piece) and the steel monopile system in the marine environment. The values obtained from the numerical analyses were examined and interpreted. The first section provides information on offshore structures, while the second section summarizes studies in the literatüre. The third chapter provides general information about earthquakes, including past earthquakes and earthquakes applied to the system during nonlinear dynamic analyses. The fourth chapter provides information about wave theories due to the investigation of the behavior of the ground pile structure system under sea wave effects. In chapter fifth, information is provided on soil models, analysis methods, and shear strength and Mohr failure criterion in soil stability. Additionally, this chapter provides information on seismic analysis methods. Chapter sixth provides information on the behavior of the soil pile system under dynamic loads. Chapter seventh provides information on the techniques and data used. Time-dependent ground motions were applied to the offshore wind turbine monopile soil system to perform nonlinear dynamic analyses of the system under different soil conditions. During the seismic analyses, time-dependent acceleration values from different earthquakes that occurred in the past were applied to the structure-soil pile system. The eighth chapter contains the research findings section, where the obtained values are evaluated comparatively. The ninth chapter provides a general evaluation of the results obtained from the analyses performed. This study aims to determine the behavior of offshore structures exposed to different environmental loads and to investigate the interaction between piles and soil, considering different soil conditions.