DIRKS & Enhancements (Dr. Eleanor Bailey)
Sea ice ridges pose a hazard to offshore operations, offshore structures, pipelines and subsea equipment. DIRKS (Development of Ice Ridge Keel Strength) was a four-year project (April 2011 – March 2015) which investigated the failure mechanisms of gouging ice ridge keels through a series of near full-scale tests that involved pushing a first-year ice keel into an artificial seabed.
A proposal was submitted to significantly enhance the original DIRKS program with additional laboratory experiments and numerical modelling to investigate the thermo-mechanical properties of sea ice ridges. It paid particular attention to the effects of compression and associated sintering and bonding on the strength of an ice keel.
Compressive Ice Failure and Distributed Damage (Perry Moore)
A constitutive model of ice for finite element analysis. The model, coded in FORTRAN and used within the ABAQUS software, was based on damage mechanics and took microcracking, pressure softening, dynamic recrystallization, and pressure melting into account. This damage-based model was successfully recreated experimentally-observed ice behaviour. The model code was refined and modernized, producing better performance in modelling high-speed events, such as the formation of high-pressure zones (hpzs) believed to induce vibrations in structures.
Fracture and Scale Effect (Dr. Rocky Taylor)
Ice has one of the lowest values of fracture toughness on earth. Fractures occur during all ice–structure interactions and cause the scale effect whereby global pressures decrease with interaction area. Despite scientific advances, fundamental questions remain regarding the influence of flaw structure, interaction geometry, temperature, time, and the interplay between fracture and microstructural damage. To help answer these questions, CARD developed programs of experimental and theoretical fracture research.
Data Analysis (Chris Rossiter with Dr. Martin Richard)
A model developed to analyze ship–ice interaction which was used to study a ship’s response when impacting a single ice feature. The program solved the surge and heave equations of motion, using a Runge-Kutta numerical integration scheme, and can take a variety of inputs ranging from floe parameters to ship characteristics. The load developed from the ship-ice interaction was modelled using a pressure-area curve where the pressure developing on the ship hull is related to the hull global contact area through an exponential relationship. The results of this work were intended to be important input into the managed ice model (see next section).
Modelling Ice Management (Dr. Martin Richard with Dr. Richard McKenna)
Ice Management (IM) has an important role in enabling vessel movement through heavy ice conditions and in reducing the likelihood and severity of ice-structure interactions for floating systems. CARD launched a project aimed at enhancing IM capability. The three initial tasks were (i) development of an icebreaking and management model, (ii) studies of ice drift data and physical processes, and (iii) development of a discrete floe model. This model used the Discrete Element Method (DEM) and accounted for the movement of a field of broken ice floes interacting together and with ice-breaking and production or drilling vessels.
It was used to obtain ice loads on the vessel of interest, to investigate the performance of different IM methods, to develop decision-support tools for real-time operations and for training purposes.
Scale-Model Testing of Floating Systems
Fundamental questions remain regarding the scaling of results from model ice basins to predict full-scale behaviour. For issues such as the prediction of loads, ice clearing, and ice accumulation for vessels operating in ice, research is needed to evaluate and improve methodology and scaling of results for scale-models of floating structures. Scale-model testing of ice-induced loads on mooring systems and dynamically positioned floating systems have been identified as areas for further research.
Modelling of Loads on Moored Floating Platforms
Modelling ice-induced loads on mooring systems for different loading scenarios, ice features, types of ice, metocean conditions, vessel designs, anchor systems and mooring configurations is needed. To aid in the assessment of mooring loads used in design of systems for selected development concepts and locations, probabilistic models must be developed. Research is also needed to improve understanding of issues associated with the disconnection of turrets under high ice loads, reconnection of mooring in ice conditions, or interactions of individual mooring lines with ice features.
Modelling of Loads on Dynamically Position Platforms
The response of DP systems to loads from managed and unmanaged ice is complex and at present is not well understood. To improve understanding of such systems, models of ice-induced loads and dynamic positioning system response for different loading scenarios, ice features, types of ice, metocean conditions, vessel designs and DP system configurations are needed. The development of a probabilistic framework for studying and evaluating DP system response has been identified as an area for further research.
Concept Evaluation and Downtime Reduction Tools
To aid in the evaluation of different floating system concepts for a range of environmental conditions and design configurations, new tools have been developed. This includes decision-support tools to assess expected downtime for different design concepts, which helps assess the required number and types of support vessels, and the optimal platform concept to reduce operational downtime.