Analysis of the strength of deformed ice features over multiple scales: a comprehensive experimental and numerical analysis

Afzali, Soroosh (2023) Analysis of the strength of deformed ice features over multiple scales: a comprehensive experimental and numerical analysis. Doctoral (PhD) thesis, Memorial University of Newfoundland.

[English] PDF - Accepted Version Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission. Download (4MB)

Abstract

Ice ridges are one of the key concerns for the design and operation of ships and structures in ice prone areas. Little information on the flexural behavior of ridges is available. This body of research aimed to develop, calibrate, and validate a numerical tool based on data gathered during the last eight years in the Development of Ice Ridge Keel Strength (DIRKS) and the Mechanics of Ice Rubble (MIR) projects in the Centre for Arctic Resource Development (CARD) to gain a better understanding of the failure mechanism and loads arising during flexural failure of ice ridge. The flexural failure of an ice ridge is dependent on the failure of its consolidated layer and of its keel. This requires an understanding of not only the properties and modes of failure of these two layers but also the strength of the freeze-bonds between the submerged ice blocks of the keel. A new model for the 3D DEM modeling of ice was developed and implemented in an open-source codes WooDEM and LIGGGHTS. This ice model contains normal, shear, torsional, and flexural springs that operate between neighboring particles which are bonded or that overlap due to compressive stresses. Energy dissipation is accounted for using a hysteretic damping in WooDEM and viscous damping in LIGGGTHS. This program of research aimed to link physics of underpinning ice bond formation to the flexural failure of ice ridges with engineering simulations tools. This can be used for full-scale applications of intent for engineering design. To this end, this program has been executed in four phases: A testing method using a new apparatus was developed to examine the tensile strength of freeze-bonds under submerged, confined conditions. The experiments showed that the freeze-bonds exhibited brittle failure, with no degradation prior to failure. The tensile strength increased with higher confinement pressure during freeze-bond formation. The strength of the freeze-bond decreased by increasing the submersion time from 2 minutes to 3 hours. The second theme focused on the flexural failure of level ice and was based on in-situ experiments on side loaded ice beam specimen. The results of these tests were used to parameterize a discrete element model that simulates ice fracture under flexural loading. The simulations were carried out using the open-source DEM code WooDEM. Despite the limitations in simulating ice crushing behavior, the simulations captured the main features of beam failure reasonably well Next, using the newly developed 3D DEM model in the LIGGGHTS code, the strength and failure behavior of ice rubble beams and freeze-bonds were investigated. Rubble specimens were generated and compacted, and bonds between blocks were introduced based on freeze-bond experiments. Simulations of medium-scale freshwater ice rubble punch tests were conducted, considering two types of block shapes. The simulations aligned with experimental results, with empirical block simulations providing a more accurate estimation of the failure force compared to cuboid block simulations. The last research theme was the modeling of prismatic ice ridges composed of both a consolidated and a partially consolidated keel. Ice rubble blocks were created using spherical DEM particles and imported into the DEM domain with gravity and buoyancy forces. A simplified ice ridge, consisting of a rubble keel with a bonded consolidated layer on top, was modeled. From this study it was found that the freeze-bond strength between the rubble blocks has limited influence on the flexural failure of ice ridges when the keel to consolidated layer thickness ratio is less than around 7 and thickness of the consolidated layer is the main contributor to flexural strength. The DEM model introduced in this study can be used as a valuable tool to estimate the flexural load arising from the interaction of ice ridges and offshore structures in the ice prone area.

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