Using Discrete Element Model to Simulate Keel-Gouging: A Sensitivity Analysis

A three-dimensional discrete element model is under development to simulate a number of different keel-gouge and subsea interaction scenarios. The model is being validated against controlled tests conducted in the National Research Council’s ice tank facility under the Pipeline Ice Risk and Mitigation (PIRAM) Joint Industry Project, which was led by C-CORE on behalf of a number of oil and gas companies. To investigate the influence of certain key parameters on the failure behaviour of the keel, a sensitivity analysis has been carried out. Best results were achieved when Young’s modulus of the keel was 5 MPa, the shear-to-tensile ratio of the freeze bonds was set to 1.2, the internal friction angle of the ice was 9°, the bond breakage ratio 0.8 % and Young’s modulus of the gravel 0.01 MPa. A low modulus for the gravel was needed to prevent premature failure of the keel, a consequence of the model not accounting for soil deformations. Using these parameters the model was able to accurately reproduce the loads on the soil tray during peak loading. Future developments in the model include using ‘clumps’ to give more representative ice block shapes, which will allow interlocking between ice pieces and the development of force chains.