Heave and pitch motions of a ship in model ice: An experimental study on ship resistance and ice breaking pattern

Ice model tests with an ice going tanker are carried out to investigate the impact of heave and pitch motions on the resistance peak values and on the breaking pattern. Therefore, the tests have been conducted in two different modes: Firstly the model is freely allowed to heave and pitch and secondly the model is constrained in vertical direction. The resistance in ice, in the continuous ice breaking mode, is characterized by peak values, which are referring to the amplitudes of the sinusoidal-like resistance-time histories. With increasing speed the heave and pitch motions decrease and the average resistance of the free model converges to the average resistance of the constrained model. The impact of the heave and pitch motions on the average resistance decays with increasing speed, but it will be shown that this impact is still present in the resistance peak values. Furthermore, the relation between the resistance and the breaking pattern leads to the hypothesis that the heave and pitch motions affect the resistance and the breaking pattern. Therefore, the breaking pattern is analyzed and put in context with the frequency analysis of the measured signals of the motions and the resistance. Additionally, it is indicated that the resolution of the frequency spectrum can have a significant influence on the analysis results. Further frequency analysis of the resistance time histories discloses the problem of surge resonance of the test setup, which highlights the change of the added mass for surge in ice compared to open water. Further frequency analyzes of the resistance and motion time histories disclose the problem of surge resonance of the test setup and the change of the added masses in ice compared to open water.