Numerical Simulations of ice forces on the Kulluk: the role of ice confinement, ice pressure and ice management

Abstract The interaction of managed ice coverswith a wide structure is examined. Numerical simulations are used to simulatethe modes of ice cover deformation and forces on the structure. Theobjective of the present work is to validate the performance of the numericalmodel using historical data recorded during operations of the Kulluk in theBeaufort Sea during the 1980s and early 1990s. This paper is the last part ofan investigation aimed at developing an approach for modeling managed iceinteraction with wide moored structures. Previous papers examined the role ofthe mooring system (Sayed and Barker, 2011) and the effects of ice coverconfinement and managed floes sizes (Sayed et al., 2012). The focus of thepresent paper is on providing quantitative comparison between predicted iceforce statistics and observations. The numerical model is based on solving equations describing theconservation of mass and linear momentum together with a plastic yieldcriterion that describes ice properties. The managed ice cover consistsof a heterogeneous ensemble of relatively small floes. The floes are assignedvaried thickness values in order to reflect field conditions. The simulationsaddress a class of interaction scenarios corresponding to confined managed ice. As the ice cover is driven within confined boundaries, pressure conditionsarise. These conditions are of interest to designers since forces areconsiderably higher than those corresponding to unconfined ice covers. Thesolution of the governing equations simulate the evolution of the distributionsof ice thickness, concentration (or coverage) and stresses. The resulting iceforces, including peak values, averages and rise-time of forces, are comparedto field measurements. The influence of ice thickness and velocity on expectedice forces is also examined. Introduction Future offshore developments in ice covered zones will likely require icemanagement support. This has generated an interest in providing reliablepredictions of the modes of interaction of managed ice covers with widestructures and the resulting forces. This paper concerns validation of anumerical approach for modeling managed ice covers interaction with structures. To date, the historical data collected during operations of the Kulluk in theBeaufort Sea during the 1980s and early 1990s provide the best availableinformation on the interaction of managed ice covers with a wide mooredstructure. The observations and measurements were analyzed by Wright (1999) and(2000). The reports of Wright provide comprehensive information on measuredforces and the corresponding modes of ice interaction with the Kulluk, icecover characteristics and ice management operations.