ABSTRACT:

The present paper summarizes a set of experiments relating to the drift of an iceberg in the vicinity of a large offshore structure which is induced by regular waves and a colinear current. Results for various iceberg dimensions and wave-current conditions are presented and compared with the predictions of a numerical model. The influence of the structure on the flow field and on the associated iceberg motions is found to be significant for wave driven drift motions when the iceberg diameter is less than approximately half the structure diameter. Agreement between the physical and numerical models is reasonable for some conditions, but relatively poor when negative wave drift forces act on an iceberg in front of the structure.

INTRODUCTION

The evaluation of loads arising from iceberg collisions is important in the design of offshore structures located where icebergs may be present. This may be predicted on the basis of observed iceberg trajectories, or from a consideration of current and wave forces acting on an iceberg at a given location. For the case of a large structure subjected to impacts by small icebergs, the influence of the structure on the wave-current flow field and on the resulting iceberg motions should be considered when evaluating iceberg impact velocities. A numerical model for evaluating iceberg drift motions in the modified current and wave fields in the vicinity of a large structure has been developed by Isaacson (1987). This is based on the assumptions of potential flow and linear, regular waves and utilizes a boundary element method to determine the flow field as an iceberg approaches a structure. Numerical results from the model have indicated that the influence of the structure on iceberg motions can be significant when the iceberg diameter is less than half the structure diameter.

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