Experimental study on surface wave modifications by different ice covers

A laboratory experimental study conducted in a freshwater wave flume installed in a refrigerated room characterized the modifications of wave propagation along on-site manufactured ice covers. Monochromatic surface waves of various amplitudes and frequencies were generated and propagated through three types of ice covers: sheet ice, broken ice floes, and grease ice. This study characterized the spatial evolutions of wave height attenuation and phase speed changes. Wave phase speed increased significantly in sheet ice relative to open water values while no significant changes in phase speed were present with other ice covers. The modifications by sheet ice are consistent with thin plate model predictions based on the elasticity of ice, using measured mechanical properties of sheet ice. Attenuation was strongest for shorter waves in sheet ice followed by grease ice and ice floes. Attenuation under grease ice is shown to be related to the surface wave orbital velocity, similar to dissipation by bottom friction and swell dissipation. The attenuation coefficient of grease ice normalized by wavenumber is proportional to wave steepness with a coefficient varying with ice properties. This laboratory experimental study examined and characterized wave dispersion and attenuation under these different ice properties and wave characteristics, which could be useful in understanding and modeling wave-ice interaction processes in open waters.