Behaviour of Suction Bucket Foundations for Offshore Wind Energy Converters under Cyclic Loading

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Suction buckets are an alternative type of foundation for offshore wind energy converters. Due to their widely proved noise-emission-free installation, they can be used instead of the usual offshore foundations with driven piles. Cyclic loads, induced by wind and water waves, play a special role in the design of suction bucket foundations. These loads can lead to changes in foundation behaviour. Due to lack of experience on cyclic response, extensive studies are required to ensure the stability of suction bucket foundations throughout their planned service-life time. Therefore, the subject of the proposed research project is the numerical and experimental investigation of the suction bucket foundations in order to quantitatively determine the changes in their behaviour caused by the cyclic loads. In the framework of the finite element analyses, the response of suction buckets subjected to cyclic axial and lateral loads will be investigated, taking into account the accumulation of permanent soil deformations and excess pore water pressures in saturated soil. Therefore, a fully coupled two-phase model combined with a hypoplastic constitutive model will be used for the modelling of the saturated sandy soil. In the model test, the long-term changes in foundation response, which are induced by cyclic axial and lateral loads, will be studied. The investigations should lead to important findings with which the effects of cyclic-dynamic loadings on the behaviour of suction buckets can be reliably determined. Based on these results, a design method for the estimation of the displacements and rotations of cyclic loaded suction buckets will be developed. Thus, an economic dimensioning of suction buckets subjected to cyclic loads, as well as a significant increase in the operational reliability of offshore wind energy converters can be achieved.