Ice and conical structure interactions

The pursuit of energy in Arctic waters drives people to design ocean structures applying new concepts.Conical structures which shift the ice failure mode from crushing to bending could reduce the total iceload. Moreover, its symmetric geometry naturally achieves the requirement of ice-vaning and reduces the risk of possible large ice loads induced by the failure of ice-vaning that might be encountered by other shapes of floaters. The thesis is based on the model test results of a group of conical structures in different ice conditions. All the tests were conducted in the Hamburg Ship Model Basin (HSVA) in Germany.The thesis comprises two parts. In the first part, the ice basin test results of the SEVAN FPU-Ice Buoy were analyzed. Based on the test data, the structure’s responses and load transferring characteristics were examined using the computer software Diadem. And the hydrodynamic and hydro-static characteristics were calculated by using Hydro-D. Then this dynamic system was analyzed in the surge direction. Based on the calculation results, explanations concerning the dominant pitch response coinciding with the pitch natural frequency were given in a descriptive way. Furthermore, alow-frequency ice accumulation volume was visually observed. This was thought to be the cause of the dominant low frequency surge displacement. The relationships between different structural responses with different ice load components were also identified. It was pointed out that the surge displacement was mainly influenced by the ice sliding load while pitch displacement was mainly influenced by the ice rotating load. According to the analysis of this system in surge direction, it was further found that the mooring force was mainly to counter balance the ice sliding load while the ice rotating load was mainly counter balanced by the inertia force and mooring force.Furthermore, based on a discussion about level ice-conical structure interaction processes, a numerical model concerning the level ice and moored structure interaction was developed using MATLAB in the first part of this thesis. The calculation results were compared with the test data. It is found that this numerical model gives good predictions of the surge and heave displacements. And it was also found that the ice accumulation load (a part of ice sliding load) and ventilation load (a part of ice rotatingload) are two major contributors to the total ice load.In the second part, the analysis was based on the test data of five conical structures designed by AkerSolutions. Both moored and fixed structures with different geometries were tested in different ice conditions (level ice, managed ice, and ice ridges) with different ice speeds (0.1 m/s, 0.5 m/s and 1 m/sNTNU, Trondheim, Norwayiiat full-scale). Extensive comparisons of the test results in different ice conditions with different ice speeds are discussed in Part II of my thesis.In conclusion, the thesis discusses the ice-conical structure interaction processes, loading characteristics, and response characteristics, based on which a numerical model was developed.Furthermore the influences of the geometry of the structure, different ice conditions, and different ice speed were also discussed based on experiment data and theoretical analysi