A Method to Upgrade Iceberg Velocity Statistics to Include Wave-Induced Motion

Iceberg impact design loads for offshore structures can be estimated by incorporating an ice/structure interaction model in a probabilistic framework, or risk analysis. The relevant iceberg and environmental parameters are input in statistical form. Iceberg velocity statistics are usually compiled from drilling rig radar reports, and hence represent estimates of average hourly drift speeds. Yet it is the instantaneous ice velocity which is the relevant input to the simulation of the iceberg/structure collision process. Thus, risk analyses based on mean drift speed distributions will only yield valid results for the subset of conditions where wave-induced iceberg motion is negligible. This paper describes a method which, for the first time, systematically accounts for wave-induced motion in iceberg impact risk analyses. A linear three-dimensional potential flow model is utilized to upgrade iceberg velocity statistics to include the influence of Grand Banks sea-state conditions on instantaneous ice motion. The results clearly demonstrate the importance of including wave-induced motion in iceberg impact risk analyses.