From Egg-Code to Actual Ice Field Flow Definition

Abstract

The Arctic Operations Handbook JIP [1] is an initiative of the Dutch offshore industry to investigate available existing standards and guidelines related to typical offshore contractor operations in Arctic conditions. The JIP identified that guidelines are required for the evaluation of the flow of ice around floating structures, and eventually to predict the resulting ice loads as input to workability studies. A pilot study called IceStream was set up as a first step towards developing guides and tools for ice flow behaviour prediction. This paper describes ice field definition and visualization as conducted within this pilot project. In the process of developing guides and tools, the objective of IceStream is to obtain a description of the geometry of an ice field, similar to open water conditions. These definitions, indicating the severity of the conditions, are needed as a basis for the determination of operational limits, and serve as an input for numerical prediction models. The ‘egg-code’ [2] principle is identified to be a good starting point when focussing on level ice, as it contains a limited but sufficient number of parameters to indicate the ice field characteristics. The applicability of the egg-code in numerical modelling is demonstrated by the development of an algorithm which translates egg-code parameters together with floe size distribution parameters into an ice field visualisation that complies with these parameters. The floe size distribution parameters are established from field observation studies. The ice field is defined by a set of ice particles, each particle represented by its area and ice thickness. Other properties (such as bending and crushing strength) can be assigned to the ice particles as well. Based on the ice field definition, Voronoi Treemapping is used to visualize the ice field. An additional parameter in this treemapping is required to indicate the distribution of ice floes over the domain (or ice cluster formation). Sea ice fields with any ice concentration between open water and 10/10th can be generated in this way. The result is an ice field consisting of random shaped (convex) ice particles with individual properties that comply with the given egg-code. The generated set of ice floes has shown to be a suitable input in the numerical modelling of an ice field approaching a floating structure.