On the ice and wind conditions in the northern part of the Gulf of Bothnia leading ice-induced vibrations
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In ice infested regions drift ice can give serious damage to offshore structures and ships. The origin of the drifting ice is the winds and the currents. However, it is known that the Gulf of Bothnia does not have strong currents; therefore, it is the wind conditions and wind force that drive large ice sheets. In this study, we analyze the metocean data including measured wind speeds, wind directions, ice speeds, ice directions and ice concentrations on the Norströmsgrund lighthouse for the years of 2001-2003. We also examine the metocean conditions on the neighboring structures to understand how ocean environment differ in the region. For example, we find that northern part of the Gulf of Bothnia has a typical crescent shaped wind profile and it is possible ice floes to change their direction suddenly depending on the stable wind directions both in early and late seasons where large ice sheets are not present. However, vibration can occur in any direction depending on the ice concentration near the structure, severity of the winter and the sea ice extent in the Bay. Because all metocean data are eventually coupled with the structural motions, it is important to understand how these parameters interact with each other and how they vary when large vibrations are observed so that one could use them for forecasting. In the end, we also present the results of the updated version of the metocean-based FLI prediction method (Bjerkås and Gedikli, 2019) and discuss the results.