A Model Study of the Wave-Induced Motion of Small Icebergs and Bergy Bits

Wave tank studies were conducted to determine the kinematics of “small” ice masses in storm waves typical of the Grand Banks region (10–14-s periods, 12–15-m heights). The models tested spanned the range of full-scale masses from growlers and bergy bits (10–10³ tonnes), to small icebergs (10⁴–10⁵ tonnes). In open water, models smaller than 1/13 wavelength behaved essentially as particles of fluid. The corresponding full-scale kinetic energies associated with such motions could exceed 10⁷ J. Models approximately 1/2 wavelength in size could attain energies in the surge direction in excess of 10⁹ J, largely through wave diffraction effects. Significant heave resonance motions were also seen. Tank studies additionally revealed that wave-driven ice-structure impacts of substantial energy could occur, although wave diffraction from the structure could also have a considerable influence on nearby ice motion. The conclusion is reached that wave-induced motion of small ice masses represents a significant environmental hazard to the operation of offshore structures in ice-infested waters.