Stiffness and Damping related to steady state soil-structure Interaction of monopiles

The present thesis concerns soil–structure interaction affecting the dynamic structural response of offshore wind turbines with focus on soil stiffness and seepage damping due to pore water flow generated by cyclic motion of a monopile. The thesis aims to improve modelling of the dynamic interaction between the foundation and the soil and illustrates the dynamic response of offshore wind turbines at different load frequencies based on mathematical and numerical approaches.

The stiffness and seepage damping has been investigated using the concept of a Kelvin model which combines springs and dashpots. An appropriate model based on considering the effect of dynamic behaviour of soil–structure interaction has been explored. In this regard, the coupled equations for porous media have been employed in order to account for soil deformation as well as pore pressure. The effects of drained versus undrained behaviour of the soil and the impact of this behaviour on the stiffness and damping related to soil–structure interaction at different load frequencies have been illustrated. Based on the poroelastic and Kelvin models, more realistic dynamic properties have been presented by considering the effect of load frequency for the lateral loading of monopiles subjected to cyclic loads.