Implications of iceberg dynamics for iceberg stability estimation: Fid-Bau Portal

Implications of iceberg dynamics for iceberg stability estimation

Bailey, R.C

AbstractMethods of estimating when an iceberg is likely to become unstable and roll over are potentially useful (e.g. in iceberg towing). Iceberg stability assessment and prediction can be done using surveys of the underwater geometry of the iceberg; this however is is not fast enough to be ideal for working conditions. Real-time monitoring of the dynamic response of icebergs to ocean wave excitation can be used as the basis of three alternative stability assessment methods which work in real time. An iceberg becomes unstable to rolling when its resonant rolling frequency diminishes to zero, typically as a result of changes in geometry produced by ablation. The first assessment method is based on the Weeks-Mellor iceberg stability criterion, and translates to a requirement that $f r √ W g$ be small compared with unity, where W and fr are observed iceberg width and roll frequency, and g is the acceleration of gravity. Secondly, the time evolution of the roll frequency may be used to predict time remaining to capsize, without knowledge of iceberg geometry. Thirdly, the development of higher harmonics of the fundamental roll frequency in the motion is diagnostic of incipient rollover. Finally, the dependence of roll frequency and higher harmonic development on towing force may make possible estimates of the maximum stable tow force.