Laboratory simulation of waves in an ice floe

Abstract

An attempt is made to determine whether the complex natural phenomenon of the interaction of pack ice and ocean waves can be studied effectively in a laboratory model. Owing to the large number of variables involved in such a study, this paper considers mainly the relatively easier problem of the study of the dynamic behavior of ocean waves and an ice floe. Ocean waves and ice floes are simulated by waves in a laboratory channel and by thin floating sheets of polyethylene. From theoretical considerations, the phase velocity of waves through the sheet and the factors that influence wave reflection and transmission are developed. Phase velocity can be expressed as a function of the effective modulus of elasticity, density and thickness of polyethylene, the density of water, and the velocity of waves on a free water surface. Reflection and transmission depend on a number of dimensionless parameters, such as the ratio of sheet thickness to the incident wave height and the ratio of the elastic wave energy in the sheet to the incident gravitational wave energy. The reflection and transmission coefficients of the system and the phase velocity of waves propagating through the sheet are determined experimentally. A comparison of the theoretical predictions and results from model test indicates that a reasonable agreement exists between theory and experiment. Measurements of spectral energy density in open sea and results from model studies of this kind, which, however, take into account the patchiness of floes, may be applied to predict the attenuation experienced by waves that pass into pack ice. Values of effective viscosities determined from the simple model are applied to predict wave attenuation based on Robin's measurements in the south polar sea. The limitations of the model study are discussed.