FACTORS INFLUENCING MANAGED SEA ICE LOADS

摘要

Sea ice management has an important role in enabling the movement of vessels through heavy ice conditions and in reducing the severity of ice interactions with floating systems. Except for analyses of managed ice conditions and loads from the Kulluk drilling vessel, the factors influencing loads from managed ice have received relatively little attention. Ice thickness, the presence of pressure ridges and the average floe size of managed ice are important factors while other features of the ice cover such as floe size distribution and station-keeping system characteristics are also important. This paper focuses on the dynamics of a broken ice field and the displacements of a station-keeping vessel in the horizontal plane using a new two-dimensional discrete element model. The discrete element approach simulates the complex dynamics of the broken ice field and is used here to assess the sensitivity of different scenarios on loads experienced by the station-keeping system. The model approximates the shape of managed sea ice floes by circular discs of random diameters. The mechanics of the broken ice field is driven by the contact forces between individual floes. A viscoelastic contact model is used with boundary conditions and environmental forcings that vary both in time and space. The influence on loads of (1) floe size distribution; (2) stiffness of the station-keeping system; and (3) changes in ice drift direction are examined. The ability to correctly model these factors is critical for effective ice management operations. The results of the study highlight the relative importance of those factors for evaluating operational ice management strategies and for defining operating envelopes.