Comparison between Dynamic Responses of Hollow and Solid Piles for Offshore Wind Turbine Foundations

The offshore wind energy industry is turning out ever larger numbers of offshore wind turbines every year. One way to achieve a cost-effective design is to have a better understanding of the dynamic response of offshore structures. That is why it is getting more and more important to understand the dynamic behavior of soil and interaction between soil and piles. To avert damage to offshore foundation, it becomes necessary to identify and quantify the soil-structure interaction and the related damping effects on the system. In this study, a single pile is investigated by means of boundary integral equations. The pile is modeled as a solid or hollow cylinder and the dynamic excitation is applied vertically. The surface along the entire interface is considered rough and with full contact between the soil and the structure. Somigliana’s identity, Betti’s reciprocal theorem and Green’s function are employed to derive the dynamic stiffness of pile, assuming that the soil is a linear viscoelastic medium. The dynamic stiffness is compared for solid and hollow cylinders by considering different values of material properties including the material damping. Modes of resonance and anti-resonance are identified and presented. It is observed that the absolute value of normalized dynamic stiffness is independent of Young’s modulus and Poisson’s ratio, whereas it is dependent on the soil’s damping.