Behavior of Soil in OWT Monopile Foundation Subjected to Torsion

Wind energy is one of the most promising renewable energy sources. Offshore wind turbines (OWTs) are now used in many countries. Most OWT farms use driven monopiles as their foundation. The purpose of this study was to investigate the behavior of monopile under torsional load. Quasi-static analysis using finite element analysis is performed in PLAXIS3D. The performed study is used to evaluate the deformation and frictional mobilization of the surrounding soil. The rotor axis of an OWT rotor is usually not aligned with the wind since the wind is continuously changing its direction. The yaw mechanism, which rotates the nacelle around the tower axis, can help to increase energy capture. Any failure in the power control units, torsional loading is added to the monopile foundation. It initiates a twist (ɵ) at the pile head, reduces its axial capacity, and increases the settlement of the foundation. This study includes the torsional effect caused by the failure of the yaw and bearing system, and thus, the corresponding strength mobilization of soil is being done. The experimental investigation was done by varying the relative density of the sandy soil. Parametric studies are also done by changing the embedded length of the monopile and varying the soil stratum. Through the numerical studies, the effect of cyclic loads on the rate of accumulated displacements, shear stress variation with respect to the depth, and changes in soil–pile stiffness were discussed.