Abstract

When designing oil and gas platforms for offshore arctic and subarctic regions, operators may need to consider the influence of iceberg impacts on optimal structure configuration and ice strengthening requirements. Icebergs have complex and varied shapes, are mostly underwater and are usually moving in currents and waves. Previous iceberg profiles developed from sonar profiles and above water measurements have varying limitations in accuracy, necessitating approximations in modeling both the overall and local shape of the icebergs. A field program was conducted to obtain high resolution full three dimensional (3D) iceberg profiles that allow for detailed modeling of icebergs. Following the field program, a number of studies were conducted to utilize this data to develop improved tools both for calculating design iceberg impact loads for offshore structures and for improving ice management. One of these studies, described here, entails development of a full 3D timedomain simulation model for icebergs impacting fixed and floating platforms in 6 and 12 degrees of freedom (DOF) respectively. A key requirement of the model is that existing scale dependent models for global ice crushing failure pressure can be incorporated. The main objective in developing the model was to provide a tool for evaluating specific iceberg impact scenarios that considers 3D effects and requires fewer assumptions regarding interaction mechanics than previous methods.

In this paper, the basic framework of the 3D time-domain model is described, and initial model results are presented for several example applications: icebergs impacting a cylindrical GBS, a stepped cylindrical GBS and a moored spar floating production unit (FPU), the probability of iceberg pinnacles impacting a platform topsides, and subsea interactions. For the cylindrical Gravity Base Structure (GBS), sensitivity analyses are presented for ice strength, friction, drag coefficient, damping coefficients, platform diameter and iceberg velocity.

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