The risks of ship besetting under ice pressure are examined. Hindcasts of ice dynamics examine the conditions that led to the besetting of two vessels in the Gulf of St. Lawrence on 9 March 2005. The analysis examines the distributions of potentially significant variables such as pressure (mean normal stress), ridge thickness and strain rates. A criterion for assessing the risk of besetting was then proposed. A preliminary parametric study was also done in order to illustrate a method for predicting the risk of besetting under different ice and environmental forcing conditions.
The interaction of managed ice covers with a wide structure is examined. Numerical simulations are used to simulate the modes of ice cover deformation and forces on the structure. The objective of the present work is to validate the performance of the numerical model using historical data recorded during operations of the Kulluk in the Beaufort Sea during the 1980s and early 1990s. This paper is the last part of an investigation aimed at developing an approach for modeling managed ice interaction with wide moored structures. Previous papers examined the role of the mooring system (Sayed and Barker, 2011) and the effects of ice cover confinement and managed floes sizes . The focus of the present paper is on providing quantitative comparison between predicted ice force statistics and observations.The numerical model is based on solving equations describing the conservation of mass and linear momentum together with a plastic yield criterion that describes ice properties. The managed ice cover consists of a heterogeneous ensemble of relatively small floes. The floes are assigned varied thickness values in order to reflect field conditions. The simulations address a class of interaction scenarios corresponding to confined managed ice. As the ice cover is driven within confined boundaries, pressure conditions arise. These conditions are of interest to designers since forces are considerably higher than those corresponding to unconfined ice covers. The solution of the governing equations simulate the evolution of the distributions of ice thickness, concentration (or coverage) and stresses. The resulting ice forces, including peak values, averages and rise-time of forces, are compared to field measurements. The influence of ice thickness and velocity on expected ice forces is also examined.
The paper examines ice compression (or pressure) build-up, which may pose a threat to navigation, over various zones of the Canadian Arctic and sub-Arctic waters. The results were obtained from a multi-year program conducted at the National Research Council of Canada. The objective of that program is to quantify the risks to navigation posed by compressive ice, and to develop predictive tools to aid shipping operations in an ice environment. The work consisted of a number of activities, including: the development of an ice dynamics model tailored for high-resolution simulations of ice cover drift and deformation; creating a database of besetting events and analysis of the conditions that influence the risk of besetting; hindcasting of ice and other environmental conditions that led to besetting over various geographic regions; and the development of forecasting tools to support offshore and shipping operations and training mariners. The present paper documents the governing equations of the ice dynamics and ridging model and discusses the high-resolution implementation that makes it possible to predict the risk of vessel besetting. A case of ice compression that took place in the southern Beaufort Sea is examined. The critical values of ice pressure and ridge thickness that posed a threat to vessels during that event were found compatible with estimates corresponding to besetting events in the Gulf of St. Lawrence and Frobisher Bay.
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