Abstract

Many offshore operations are today located in the so called marginal ice zone (MIZ) in which ice is broken up and moved by waves. The impact of ice and waves will cause high loads on offshore structures. Typical operations as vessel approach and launching of rescue and evacuation crafts can also be affected negatively. The correlation of wave parameters and resulting ice field properties is one key factor for the prediction and simulation of such processes. First results of the laboratory test campaigns have shown that they can fill gaps left in the description and quantification of wave ice interaction processes by theoretic models, satellite observation and field measurement campaigns.

A model testing campaign with wave propagation into a solid ice field has been carried out in a 70m by 10m ice model basin. The wave parameters (length and height) were increased stepwise and the interaction process with the ice sheet was monitored and documented. Relevant parameters like the crack length and orientation and resulting floes size distribution after different runs of wave application were measured and analysed by image processing. The relation between controlled wave parameters and ice field properties in the basin are compared to theoretic approaches which are based on linear wave- and elasticity theory.

The interaction processes of waves and model ice result in a typical pattern with areas of smaller floes at the ice edge and increasing floe size with distance from the first contact zone. The floe size decreases with duration of wave application until reaching a minimum which can be related to the wave length and height (wave steepness). The first breakup of the ice sheet is observed at certain wave amplitude depending on the ice thickness.

The main purpose of the test campaign was to assess the feasibility of combined wave ice tests in a model basin. Thereby the focus was to compare observations and results of the model tests to observations in nature and theoretic descriptions of wave ice interaction. This analysis provides valuable information on scaling problems, limitations of testing range and model ice behavior in cyclic loading. The information can be used to evaluate the significance of such model tests for ice scenarios and load investigations for offshore installations.

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