EXPERIMENT-BASED RELATIONS BETWEEN LEVEL ICE LOADS AND MANAGED ICE LOADS ON AN ARCTIC JACK-UP STRUCTURE

摘要

Jack-ups have been constructed for numerous ocean environments, but to date there has been no operating experience under Arctic sea ice conditions. The current state of jack-up technology does not allow working outside the ice-free season and thus ice management will be needed to extend the drilling season. Currently, ice load calculations are reasonably well defined for level ice, while the ice loads due to managed ice are not known evenly well. In order to extend the drilling season for multi-legged jack-up structures by means of ice management, a better understanding of managed ice loads is required. To this purpose, the relation between level ice loads and managed ice loads on a multi-legged jack-up structure is investigated. Experiments for a 4-leg jack-up model were carried out in the ice tank of the Hamburgische Schiffbau-Versuchsanstalt (HSVA) in Germany, at a scaling ratio of 1:32. Two ice thicknesses (0.5 m and 1.0 m full scale) and three model orientations (0°, 22.5° and 45°) were tested. Additionally, ice concentration (level ice, 8/10th and 6/10th) and ice velocity (0.5 m/s and 1.0 m/s full scale) were varied. This paper reports on the model tests and the corresponding parametric study that was carried out with a focus on managed ice parameters. The relation between the observed level ice loads and the observed managed ice loads is quantified and discussed for varying orientations, ice velocities and ice thicknesses. Video and time series analyses were used to correlate ice loads to in-situ failure modes, and the results of these are summarised.