ABSTRACT
To ensure safety of marine operations during ice management in arctic seas, it is essential to understand an iceberg's stability. Stable icebergs can be towed away from offshore facilities using standard vessels and procedures. Unstable icebergs create high risks and can easily capsize during the vessel's maneuvering and towing. As is known, an iceberg capsize event could lead to iceberg destruction into several pieces. The total danger from the parts often would exceed the initial one. Especially dangerous are large icebergs that may capsize and damage the towing vessel.
Due to interaction with the seawater, the icebergs have their natural oscillations, which under certain environmental conditions can significantly complicate the towing process due to resonance phenomena. We should also notice that during the melting, icebergs will change form and motion characteristics.
The paper presents calculations of icebergs' stability criteria (metacentric height) based on iceberg towing experiments conducted in 2016–2017 in the Barents and Kara seas. Longitudinal and roll oscillations of various icebergs are considered. The appearance of resonance phenomena during iceberg drift is studied for characteristic periods of waves of the Kara and Laptev seas.
Periods of natural oscillations are defined using 3D models of icebergs constructed from aerial and sonar surveys. The results obtained show the dependencies of the iceberg's stability criteria on the iceberg's above-water parameters – and demonstrate that unstable icebergs may be identified without sonar surveys.
Due to significant mass of icebergs and sophisticated underwater geometries that are hard to determine, aspects of icebergs stability significantly affect the tactics of ice management operations. On the one hand, an iceberg can overturn during towing (Efimov et al., 2019) or even while a tow rope or net is being deployed requiring prompt vessel maneuvering, and in the worst case, causing some damage to a towing vessel. On the other hand, an unstable iceberg may breakup due to wave action from the vessel without direct contact with vessel or rope (Kornishin et al., 2019).
