Author(s): Ersegun Deniz Gedikli; Morten Bjerkås; Knut Vilhelm Høyland; Vegard Hornnes; Joshua Turner
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Abstract: In ice infested regions drift ice can cause 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 met-ocean 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 met-ocean conditions at the neighboring structures to understand how ocean environments differ in the region. For example, we find that the northern part of the Gulf of Bothnia has a typical crescent shaped wind profile and it is possible for 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, structural 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 met-ocean 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 met-ocean based FLI prediction method (Bjerkås and Gedikli, 2019) and discuss the results.
Year: 2020