Ice collars, development and effects

• Ice loads are vitally important for the Arctic offshore structures.
• Ice collar occurs around the structure during cold temperatures.
• Stefan Problem can be used for the formulation of the ice collar growth.
• Ice collar shape and size can be calculated numerically.
• Ice collars lead to an increase of the total load on the structure from the level ice.
• A number of preventive measures can be used to eliminate ice collar effect.

Ice interacts with offshore structure by number of ways. If structure is located in the stationary (or temporary stationary) level ice then structure freezes in the ice and ice collars occur during constant water level and cold temperatures. The duration of the freezing process and the temperature during it as well as structure thermal conduction properties are the main factors for the ice collar growth. Ice collar is an additional thermo-developed thick ice on the structure surface below level ice. Such additional ice is common for many structures and ships; however the basics are poorly described in the literature. Ice collars can lead to a significant increase of the total load on the structure and complicate moorage operations. The increase of the load on the structure appears as a result of the big ice-structure contact area and additional adhesion forces. The article goal is to provide overview on the main aspects related to the ice collars which should be considered. It includes mathematical formulation of the task, some aspects of the numerical modeling and possible preventive measures.