Improved modeling of the response of offshore wind turbines (OWTs) is key to optimizing design and reducing maintenance costs and downtime. A major challenge is the modeling of hydroelasticity, which is not yet well understood for non-uniform structures such as OWTs. Previous research on hydroelasticity during impact events focused on uniform systems, and the effect of non-uniformities on hydroelasticity has not been properly studied yet. Two characteristic non-uniformities of OWTs are the end mass (from the rotor-nacelle assembly) and the added mass around the base of the structure resulting from its submersion depth. The main research question in this thesis was: What is the effect of end mass and added mass on the hydroelasticity of non-uniform systems, such as offshore wind turbines, under breaking wave impact?

This question was answered through an experimental campaign. Experiments were conducted using a two-dimensional OWT model with varying end masses and submersion depths, which was impacted by a focused breaking wave in the wave tank at the Ship Hydromechanics lab of TU Delft. The force and structural response were measured and compared against a non-hydroelastic rigid model. Computational fluid dynamics simulations were performed using ComFlow, and a Finite Element Method model was created to get a quasi-static estimate of the model response used for comparison.

By increasing the end mass and added mass, the first natural period of the models approached the loading duration of the impact. This resulted in a peak force reduction of up to 30% compared to rigid models, indicating that the role of hydroelasticity increases as this ratio approaches 1.0. However, an effect on peak force reduction due to submersion depth for structures with similar period ratios was also seen, indicating the complexity of hydroelasticity for non-uniform structures. Comparing the structural response in the experiments against the quasi-static estimate showed larger errors for models with a period ratio close to 1.0, underestimating the response by up to 27% for the maximum deflection and 75% for the maximum acceleration. The results in this thesis show that the characteristic non-uniformities of offshore wind turbines significantly influence the hydroelastic behavior of such structures during breaking wave impacts.