Numerical Simulation of Ice-Rubble Mound Breakwater Interactions

Offshore activity in energy production, fishing, shipping, and tourism is projected to increase in the Arctic and SubArctic. This projected increase in offshore activity means the supporting coastal infrastructure needs to be expanded. All human activity in ice-prone regions requires a specialized knowledge and understanding of ice mechanics and how to properly design against ice forces and ice-structure interactions. Analyzing ice-structure interactions is a prerequisite for any successful venture into areas where sea ice can occur. This thesis studied numerically modeling the interaction between pre-broken, rigid ice sheets and wide, sloping structures. The thesis focused on adapting a numerical model and validating the base phenomena of the simulated ride-up and pile-up. The numerical model used in this study is the Simulator for Arctic Marine Structures (SAMS). SAMS has previously been validated for ship-shape structures, and individual modules within SAMS has been validated for a wider range of applications. However, coastal structures with wide, upward slopes were previously unanalyzed, and SAMS required a few modifications before simulations could proceed. Due to limitations in the version of SAMS used for this study, level sheet ice was approximated with a section of pre-broken, rigid bodies being driven by a significantly larger, unbroken sheet. Ice was driven by simulated current and wind, thus a limit-force scenario could theoretically be reached. Side confinement was used to reduce the three dimensional (3D) effects introduced in the rigid-body approximation. For ride-up, 36 test conditions were used with ice thicknesses between 0.5 and 1 m, velocities between 1.0 and 2.0 m/s, and the slopes of 1:4 to 1:6. Each test combination was repeated 40 times for a total 1440 simulations. Results from the tests show ride-up is both qualitatively and quantitatively well represented with an 18.9% difference between the simulations and Christensen's analytical model for ride-up. For pile-up, 22 tests conditions were used with values similar to those found in the North Caspian Sea. The ice thickness was 0.15 m, the velocity was 0.5 m/s, and the slope was 1:3. Simulations were designed to test the effects of ice-ice friction, ice-structure friction, and rubble geometry on the pile-up behavior of SAMS. Qualitatively, pileup simulations showed 5 distinct stages of simulation: 1) initial ride-up, 2) initial pile-up, 3) rubble-pile development, 4) ice-sheet failure away from the pile, and 5) the unbroken ice sheet directly influencing the pile. Stages 1-3 correspond with the expected behavior of pile-up, but stages 4 and 5 represent unrealistic behavior caused by the rigid-body approximation. Quantitatively, ice loads ranged between 3 and 9 kN/m, porosity between 0.35 and 0.65, the pile sail from 1-3 m, and the pile keel was not consistently grounded. Sensitivity tests have shown pile-up in SAMS is: 1) sensitive to changes in ice-ice friction for lower friction coefficients and relatively insensitive for higher friction coefficients, 2) small increases in ice-structure friction can exaggerate the aberrant stages, and 3) triangular rubble geometry can exaggerate the aberrant stages.