Advances in Sea Ice Mechanics in the USA

Abstract

A brief review of significant advances in the field of sea ice mechanics in the United States is presented in this paper. Emphasis is on ice forces on structures, as the subject relates to development of oil and gas resources in the southern Beaufort Sea. The main topics discussed here are mechanical properties, ice–structure interaction, modeling of sea ice drift, and oil industry research activities. Significant advances in the determination of ice properties are the development of testing procedures to obtain consistent results. Using stiff testing machines, researchers have been able to identify the dependence of tensile and compressive strengths on different parameters, eg, strain rate, temperature, grain size, c-axis orientation, porosity, and state of stress (uniaxial or multiaxial). Now reliable data exist on the tensile and compressive strengths of first-year and multi-year sea ice. Compressive strengths obtained from field testing of large specimens (6 × 3 × 2 m thick) were found to be within 30% of the strengths obtained from small samples tested in laboratory at the same temperature and strain rate as found in the field. Recent advances in the development of constitutive relations and yield criteria have incorporated the concept of damage mechanics to include the effect of microfracturing during the ice failure process. Ice forces generated during an ice–structure interaction are related to ice thickness and properties by conducting analytical or small-scale experimental studies, or both. Field measurements of ice forces have been made to assess the validity of theoretical and small-scale experimental results. There is good agreement between theoretical and small-scale experimental results for ice forces on conical structures. Theoretical elastic buckling loads also agree with the results of small-scale experiments. Though considerable insight has been achieved for ice crushing failure, estimation of ice forces for this mode is based on empirical relations developed from small-scale experiments. A good understanding of the ice failure process has been achieved when ice fails in a single failure mode, but our understanding of multi-modal ice failure still remains poor. Field measurements of effective pressure indicate that it decreases with increasing contact area. Research in fracture mechanics and nonsimultaneous failure is underway to explain this observed trend. Ice ridge formation and pile-up have been modeled, and the forces associated with these processes are estimated to be low. The modeling of sea ice drift has progressed to a point where it is able to determine the extent, thickness distribution, and drift velocity field of sea ice over the entire arctic basin. Components of this model relate to momentum balance, thermodynamic processes, ice thickness distribution, ice strength, and ice rheology.