A single point mooring (SPM) system is one of the possible mooring systems in the field of Arctic floating production. It consists of a moored buoy to provide its anchoring unit with the capacity of mooring and ice sheltering. In the preliminary design phase, the performance of the mooring buoy must be assessed. This can be done by numerical modeling. This thesis provides a model for the two-dimensional numerical simulation of a moored buoy under ice loading, and it optimizes the buoy design based on the results of the numerical simulation.

The model is constructed based on the discrete element method (DEM), where the elements consist of the elements describing the level ice, and one element describing the buoy. The numerical model is capable of simulating several ice-structure interaction mechanisms, including the ice compressive failure, the ice bending failure, and friction.

The model consists of three parts. A compliant contact formulation describes the behavior of contacts between elements. Contact forces are solved implicitly using a Lagrange multiplier formulation. Lastly, the mooring system is described using the catenary equation.

The model is validated against a number of analytical solutions, demonstrating that the model is capable of simulating the buoy-ice interaction. An example of the buoy design optimization process is demonstrated. The optimization aims to obtain a concept design of a satisfactorily performing moored buoy with minimized dimensions under a specific ice condition. Design criteria were determined for the maximum pitch angle and the maximum horizontal displacement of the buoy. Given the desired design criteria, one can obtain the most optimized buoy design after several phases of selection.

Offshore wind energy has very recently begun expanding into subarctic regions with seasonally ice-infested waters like the Baltic Sea. For offshore wind turbines with conventional support structures such as monopiles and jackets that are typically flexible and vertically sided, the phenomenon known as ice-induced vibrations can develop. In response to the growing interest in offshore wind in the Baltic Sea and in further validating a state-of-the-art numerical model for ice-structure interaction, the Ice-induced Vibrations of Offshore Structures
(IVOS) project has been coordinated with the Hamburg Ship Model Basin (HSVA) and many academic and industry partners—including TU Delft and NTNU—in order to enhance understanding of the topic via a comprehensive laboratory testing campaign.
In this thesis, specific data are selected fromthe extensive IVOS Phase 2 tests such that a comparative analysis is performed between two different model-scale structures, one with circular cross-section and another with rectangular cross-section, that were subjected to ice-induced vibrations in the frequency lock-in regime. Preceding the comparative analysis, the data from the IVOS Phase 2 tests are organized into a database and post-processing tools are developed to facilitate further research by supplying analysis-ready data sets. Included in the post-processing tools is an attempt to determine ice-induced global loads from uncalibrated tactile sensor data, which offers insight into the relationship between the relative pressure distributions along the ice-structure interface and the ice-induced global forces on the model structure.
The comparative analysis garnered qualitative information about the frequency lock-in regime and buckling failure of ice. It is observed that frequency lock-in vibrations usually persisted regardless of buckling events. For the frequency lock-in regime, the ice-induced global loads on the circular cross-section structure are generally lower than those for the rectangular cross-section structure. It is unclear whether the difference in global loads between the structures is caused by the difference in cross-sectional shape, other structural properties, ice properties, or combinations thereof. The analysis of the energy of the system is intriguing but does not offer lucid conclusions. However, the quasi-figure-eight pattern from the x-direction and derived y-direction structural displacements is an enlightening discovery that may explain inconsistencies in the energy of the system. Based on the general configuration of the test apparatus from the IVOS Phase 2 tests and the results from the comparative analysis, it can be concluded that ice-induced vibrations of the model-scale structures in the frequency lock-in regime should be regarded as a two-dimensional problem.