A moving ice field or ice feature hitting a fixed offshore structure will cause different ice load actions as ice can be breaking in different ways depending on ice velocity. At low ice velocities loads are pseudo static or intermittent load fluctuations, and at high ice velocities exhibit random variations. In between is a velocity range where the most severe dynamic ice loading on structure may occur: the frequency lock-in range where ice failures repeat continuously close to a natural frequency in a resonant type of a loading. The capricious frequency lock-in vibrations were encountered already 50 years ago, but even now, the true understanding of the ice-structure interaction based on physical and mechanical properties of both the ice and the structure are not fully understood. Recent advances in scale model testing and numerical analysis of measurement results provide deeper insight on what is really happening in dynamic ice-structure interaction. This development provides a refined understanding on the phenomena during ice failure process against the structure, and how the structure is responding. The final proof is still ahead: acquiring dedicated full-scale data to verify the findings of scale-model tests and the predictions of numerical analysis.
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