Design of a Shipboard Local Load Measurement System to Collect Managed Ice Load Data

Abstract

Abstract Due to a lack of data, currently (and justifiably) conservative ice load assumptions are made in rig assessments allowing only very small floe sizes to contact non-Polar classed drilling rigs. In September 2015, in cooperation with the Norwegian University of Science and Technology (NTNU) and the Swedish Polar Research Secretariat (SPRS), ExxonMobil and C- CORE participated in the Oden Arctic Technology Research Cruise. A distinguishing aspect of this Cruise was: (a) performing ice management trials using two icebreakers, the Oden and the Frej; and (b) instrumenting the Frej, i.e. the secondary icebreaker and therefore collecting first-of-a-kind local ice load data during stationkeeping in managed ice. Unlike all prior data behind code pressure-area curves, which are based on transit in unmanaged ice and ship ramming, the new data are in managed ice field, representing true pressures and forces on a drilling or production vessel in a stationkeeping mode (moored, dynamically positioned (DP) or DP assist). This paper describes the design, installation and calibration of the Frej load measurement system. The system consists of an array of over 160 strain gauges installed over three panels on the bow and shoulder of the vessel. Prior to sailing, physical calibrations were performed as quality checks of the gauge installation and to benchmark finite element (FE) models used afterwards to convert measured strains into hull local ice pressures. More than 260 hours of local ice load data were collected throughout the program including measurements while stationkeeping in managed ice conditions in addition to actively managing ice and transit. The system remained operational through the entire field program without loss or damage to a single strain gauge. The data collected can contribute toward demonstrating the ability of existing rigs to resist some degree of managed ice, and hence can open the possibility for drilling season extension beyond open water, which can have a significant economic impact on arctic drilling. The resulting pressure-area curves will be the subject of a follow-up publication.