Ice island creation, drift, recurrences, mechanical properties, and interactions with arctic offshore oil production structures. Final report.

摘要

Research and engineering studies on first-year sea ice for over two decades has resulted in the design, construction, and operation of jacket platforms, of artificial islands, and of massive gravity structures which routinely withstand moving sea ice of thickness up to 2 meters. However, the less-common interactions between such structures and moving multiyear ice ((ge)3 meters thick), and also moving ice islands (10 to 60 meters thick) remain as the unknown and potentially most serious hazard for Arctic offshore structures. In this study, research was addressed across the complete span of remaining questions regarding such features. Ice island components, thickness distributions, scenarios and models for the interactions of massive ice features with offshore structures, all were considered. Ice island morphology and calving studies were directed at the cluster of 19 ice islands produced in a calving from the Ward Hunt Ice Shelf on Ellesmere Island in 1983, and also at a calving from the Milne Ice Shelf in 1988. The statistics of ice island dynamics, on both a short-term small-scale basis and also on a long-term basis, were studied. Typical wind velocities of 5 to 7.5 meters per second led to ice island speeds of about 0.014 of the wind speed, at an angle of 20(degrees) to the right of the wind direction. Ice island samples were tested for their stress/strain characteristics. Compressive strength values ranged from 1.64 MPa at a strain rate of 2 (times) 10(sup (minus)7) s(sup (minus)1) to 6.75 MPa at a strain rate of 1 (times) 10(sup (minus)3) s(sup (minus)1). Scenarios for ice island/structure interactions were developed, and protective countermeasures such as spray ice and ice rubble barriers were suggested. Additional computer modeling of structure/ice interactions for massive ice features is recommended.