Coupled modeling of dynamic ice-structure interaction on offshore wind turbines

The offshore wind industry is growing at high pace and is already one of the major renewable energy sources in Europe. To support this growth, costs must be further decreased, amongst others by efficiently designing the support structure of the offshore wind turbines. This requires accurate prediction of environmental loading such as dynamic ice-structure interaction. From industry practice it is known, that current phenomenological models show results that are highly sensitive to the used input parameters. In this thesis it is investigated if the methodology used in industry practice, can be improved by coupled phe-nomenological modeling of dynamic ice-structure interaction. First, an introduction is given on the growing process and the properties of sea ice. These properties are related to the deformation and failure behavior of the ice. The failure behavior is divided into three regimes: the ductile regime, the transitional regime and the brittle regime. The ice load at which brittle failure occurs seems to decrease with increasing deformation rate. However, since this is debated in literature, a phenomenological approach is used to describe dynamic ice-structure interaction. The phenomena are related to the aspect ratio b/h and the ice velocity v ice and denoted as failure modes. The failure modes for ice failing against a vertical structure are: creep, crushing, and buckling. During crushing failure against a compliant structure, three ice-induced vibration regimes can occur: Intermittent crushing, frequency lock-in, and continuous brittle crushing. The ice-induced vibrations are often modeled in a phenomenological manner since the physics behind the phenomena are not well understood. A recently published phenomenological model by Hendrikse and Metrikine (2015a), is based on the variation of contact area at the interaction surface between the ice and the structure. The phenomenological model proposed by Hendrikse and Metrikine (2015a) is implemented and extended with creep and buckling. The model entails elastic-visco-plastic elements that deform inelastically at lower deformation rates, enabling the contact area to increase. Moreover, buckling is included to the model by the implementation of a finite element model. Here, the ice sheet is represented by a wedge-shaped beam on an elastic i Winkler foundation. The phenomenological model is implemented numerically to simulate dynamic ice-structure interaction in the time domain. The model uses a Newmark scheme for nonlinear dynamics to solve the system of equations iteratively. Moreover, a variable time stepping algorithm is created to increase the accuracy of the results. The input parameters of the model …