ABSTRACT:

Each ice floe within a marginal ice zone reflects a proportion of incoming ocean wave energy and allows the balance to pass further into the ice cover. Thus the synthesis of the transmission characteristics of the discrete floes making up the ice field determines the wave energy at any point within its interior. A new model to represent the wave-forced motion and flexure of a single elastic ice floe of constant thickness is reported. The model predicts that resonance, i.e., perfect transmission, occurs when the ratio of the ice wavelength to the floe diameter assumes certain values. This is observed; it is analogous to the propagation of electromagnetic radiation through an homogeneous slab. Features in the reflexion and transmission coefficients, and strain fields are discussed.

INTRODUCTION

The passage of ocean waves through an ice field composed of many discrete floes of various sizes and thicknesses arranged in zones of different concentrations has attracted the interest of polar engineers and scientists for over a century. Even earlier, the observational records of sealing and whaling ships operating in Arctic and Antarctic waters describe the sheltering effect of the interior of the pack ice and the dangers of the very active zone of ice floes near the edge. The first attempt to model the phenomenon was that of Greenhill (1887), who proposed an elastic beam as a suitable surface boundary condition to represent the ice-it is unclear whether Greenhill was thinking of pack ice, i.e., a marginal ice zone (MIZ), or shore fast ice. Remarkably, Greenhill's model with only slight modification is used to this day. The first serious systematic attempt to measure wave penetration into and through pack ice was carried out during the Weddell Sea passage of RRS John Biscoe in 1959–60 using a ship-borne wave recorder (Robin, 1963).

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