Feasibility of Offshore Wind Substructures in Arctic Environments

Environmental research and in-situ measurements have shown that most regions of the Baltic Sea harnesses a large wind energy potential. The Finnish government has outlined a policy to generate a rapid increase in the use and production of renewable wind energy. In order to achieve these goals, the need arises for the construction of full scale offshore wind farms with a total capacity of around 2,500 MW. However, large parts of the northern basins of the Baltic Sea are covered with ice during the winter season, which is something that to offshore wind farms operational to this date have not yet been subjected to. The scope of this thesis is to provide an insight into the overall feasibility and the preliminary design process of an offshore wind substructure suitable for the conditions as found along to the Northeastern coastline of the Bay of Bothnia. An extensive literature study has been performed, which focusses on the recent development of offshore wind farms, offshore wind substructure concepts, the environment of the Bay of Bothnia and on aspects related to arctic engineering. Using the literature study as a reference, the case study was outlined in further detail, by establishing the design basis regarding the NREL 5MW reference turbine and tower. Governing environmental parameters such as the on-site wind speeds, wave heights and ice conditions are determined, along with the on-site geotechnical parameters such as water depth and soil composition. Based on the case study, the various offshore wind substructure concepts are compared to determine to most suitable concept for application in the Bay of Bothnia. Based on this assessment, the monopile foundation was considered the most suitable for application within the boundaries of the case study. In order to examine the effects of ice loads on the overall feasibility of offshore wind monopile foundations in arctic environments, the increase in structural dimensions and design weight of the monopile foundation due to ice loading is analyzed. For this structural analysis, use will be made of static load cases and a static analysis methodology. Using the case study and determined design loads, three monopile design iterations are presented, ranging from the exclusion of ice loading, including global level ice loading and a design including global ice ridge loading. Each design has been optimized regarding the structural dimensions required to withstand the applicable load cases, by using allowable cross section stresses and deflections as design criteria.Steel, Hybrid and Composit StructuresStructural EngineeringCivil Engineering and Geoscience