Finite-discrete element modelling of sea ice sheet elasticity, sea ice sheet fracture, and ice-structure interaction: A three-dimensional, lattice-based approach

In this thesis, the elastic and inelastic properties of an ice sheet modelled by a new hybrid, three-dimensional finite-discrete element (FE-DE) method were examined. Ice-structure interaction between an ice sheet and a conical offshore structure was studied as well. By this new method, an ice sheet is modelled with undeformable, i.e. rigid, discrete elements. The mass centroids of the discrete elements connect then via an in-plane beam lattice of co-rotational, viscously damped, de-cohesive Timoshenko beam finite elements. A centroidal-Voronoi-tessellation-based iterative scheme (CVT) was applied in creating the studied FE-DE meshes, i.e. the modelled ice sheets. Due to the internally damped, de-cohesive, lattice-based construction, the mechanical response of a modelled ice sheet turns out to be both strain rate- and size-dependent (dependent on both the absolute and relative sizes), the investigation of which formed an integral part of the present study. A general objective of this thesis was to study the applicability of the new, hybrid FE-DE method in modelling the elasticity and fracture of sea ice sheets. In order to understand the effects of scale and to demonstrate the feasibility of the approach in studying ice mechanics applications in general, i.e. the ice-structure interaction, several conceptually simple constitutive tests with square FE-DE sheet samples of varying side lengths, thicknesses, and discrete element sizes were performed. The results presented gave a partial guideline for choosing the microscale material parameters of a CVT-tessellated, lattice-based FE-DE model of an ice sheet in order to achieve a desired macroscale response, both elastic and inelastic. Furthermore, the results provided substantial insight into the functional dependencies each studied physical quantity has. In addition, the elastic bending tests showed that the model is able to emulate a free Kirchhoff-Love plate in bending on a Winkler-type foundation with a good accuracy. Finally, a new in-direct approach to compute ice-breaking loads on a conical offshore structure was proposed. The novelty of the approach lies in its simplicity. It provides a device not only to compute cone ice loads but also to investigate the ability of a numerical method to produce both radial and circumferential cracking. While the contents of this thesis were strictly restricted to applications that are closely related to ice mechanics, i.e. the modelling of intact sea ice sheets, their fracture, and ice-structure interaction, the results presented should apply to other cohesive, lattice-based models on other application areas as well, in the ab initio-type constitutive modelling of ceramic matrix composites or concrete for instance.