ABSTRACT
The dynamic response of offshore wind turbines e.g. eigen frequencies and eigen modes, are affected by the properties of the foundation. The purpose of this paper is to evaluate the dynamic soil-structure interaction of embedded foundations for offshore wind turbines, with the intention that the dynamic properties of the embedded foundation can be properly included in a composite structure-foundation system. The investigation concerns the determination of the vertical dynamic stiffness for surface footings, skirted foundations and solid embedded foundations. The soil surrounding the foundation is homogenous with linear viscoelastic properties. The dynamic stiffness of the foundations is expressed by dimensionless frequency dependent dynamic stiffness coefficients corresponding to the vertical degree of freedom. The dynamic stiffness coefficients for the foundations are evaluated by means of a dynamic three-dimensional coupled Boundary Element Method/Finite Element Method model. Benchmark tests have been performed for analytical half-space solutions for rigid surface footings and there is good agreement between the analytical solution and the BEM/FEM model. The frequency dependent dynamic vertical stiffness of skirted foundations has been investigated and compared with the solutions for the rigid surface footing and the solid embedded foundation.
