The ice melting and lateral cavity formation caused by in situ burning (ISB) of liquid fuels in ice-infested waters was studied in order to improve predictions on the removal efficiency of this oil spill mitigation method. For this purpose, several experimental studies were conducted to increase the fundamental understanding of the mechanisms that lead to ice melting and lateral cavity formation. The findings of the experimental studies provided the required knowledge to mathematically formulate the ice melting problem. Mathematical scaling analysis of ice melting during burning of oils in the vicinity of ice was performed to create a tool to estimate the extent of melting that occurs during ISB in ice-infested waters. A series of lab-scale experiments were designed to systematically investigate the ice melting problem. The first set of experiments were conducted in cylindrical shaped ice cavities with a 5.7 cm diameter. Burning of n-octane from ignition to natural extinction and the subsequent geometry change of the ice, fuel thickness, and fuel temperature were measured. The preliminary experimental observations showed that the melting of the ice walls was higher in areas where the fuel layer was in contact with ice compared with places of flame exposure. Based on these observations, a hypothesis that suggested the convective flows in the liquid fuel (driven mainly by surface tension and buoyancy) were contributing in melting of the ice was proposed to explain the origins of the lateral cavity. To evaluate this hypothesis, two dimensionless numbers (Marangoni and Rayleigh) were calculated as the indicators of the mechanisms of convection in the fuel layer. The comparison between the melting speed and these dimensionless numbers indicated surface tension driven flow was dominant while the role of buoyancy was negligible. In another set of experiments, Particle Image Velocimetry (PIV) was used to study the flow structure within the liquid-phase of n-octane pool fire bound on one side by an ice wall. Experiments were conducted in a square glass tray (9.6 cm × 9.6 cm × 5 cm) with a 3 cm thick ice wall placed on one side of the tray. Burning rate, flame height, and melting front velocity were measured to analyze the effect of heat feedback on melting of the ice. The melting rate of the ice increased from 0.6 cm/min for the first 50 seconds after ignition to 1 cm/min for the rest of burning period. Meanwhile, the measurement of the burning rates and flame heights showed two distinctive behaviors; a growth period from self-sustained ignition to the peak mass loss rate (first 50 seconds after ignition) followed by a steady phase from the peak of mass loss rate until the manual extinguishment. Similarly, the flow field measurements by a 2-dimensional PIV system indicated the existence of two different flow regimes. In the moments before ignition of the fuel, coupling of surface tension and buoyancy forces led to a combined one roll structure in the fuel. This was when a single large vortex was observed in the flow field. After ignition the flow field began transitioning toward an unstable flow regime (separated) with an increase in number of vortices around the ice wall. As the burning rate/flame height increased the velocity and evolving flow patterns enhanced the melting rate of the ice wall. Experimentally determined temperature contours showed that a hot zone with thickness of approximately 3 mm was present below the free surface, corresponding to the multi-roll location. The change in the flow field behavior was found to relate to the melting front velocity of ice. To further study the lateral cavity phenomena, a parametric experimental study on melting of ice adjacent to liquids exposed from above to various heat fluxes was conducted in order to understand the role of liquid properties in formation of cavities in ice. Multiple liquids with wide variety and range of thermophysical properties were used in order to identify the key influential properties on melting. The melting rate of the ice and penetration speed of the liquid in a transparent glass tray (70 mm × 70 mm × 45 mm) with a 20 mm thick ice wall (70 mm × 50 mm × 20 mm) was measured. The melting front velocities obtained from experiments were then compared to surface flow velocities of liquids obtained through a scaling analysis of the surface flow to elucidate the influence of the various thermophysical properties of the liquids on ice melting. The surface velocity of the liquids correlated well to the melting front velocities of the ice which showed a clear relationship between the flow velocity and melting front velocity. As the final step of this work, to extend the findings of the experimental studies conducted herein to larger sizes comparable to realistic situations in the Arctic, an order of magnitude scaling analysis was performed to obtain the extent of ice melting. The scaling considered the heat feedback from the flame to fuel surface, the convective heat transfers toward the ice, and the melting energy continuity of ice. The existing experimental data on the size of lateral cavity were also collected and were correlated to the results of the scaling analysis using a nonlinear regression fitting technique. The mathematical correlation that was obtained by the scaling analysis can be used to predict the size of the lateral cavity for a given fuel, pool fire diameter, and burning time. This correlation will provide a predictive tool to estimate the size of a potential lateral cavity formed during ISB of a given spill scenario. In general, the ability to predict the ice melting caused by burning of spilled oil in ice-infested waters is of great practical importance for assessment of the response outcome. This would assist with quantifying the geometry change of the burning medium which in turn will define oil burning rate and extinction condition. Knowledge of burning behavior and extinction condition indicate the burned volume which can directly be used to define the removal effectiveness of ISB. Nevertheless, this analysis was conducted on a generic interaction of oil and ice and the specific details that are observed in actual application of ISB in ice-infested waters were neglected for simplicity. Extending the outcome of this study to more specific (scenario-based) oil-in-ice situation and improving the predictability of the melting correlation with large-scale experiments are the next steps to develop this work.

<p> The thaw rates of the active layer above the permafrost zone from a series of sites along the Hudson Bay coastline at lat. 56° have been examined with respect to temperature and moisture gradients, the characteristics of the surface layer and the bulk thermal properties for each profile. The thermal properties have been examined using firstly a Fourier approach with the parameter of degree days and using secondly a graphical approach employing thermal relationships obtained in the laboratory analyses by Kersten (1949).</p> <p> It was found that thaw rates are controlled by the interaction of a number of environmental factors of which vegetation appears to be the most important.</p> <p> The two approaches to the derivation of thermal properties give quite different results, such that the graphical approach is deemed to be unsuitable to field application.</p> / Thesis / Bachelor of Science (BSc)

The primary objective of this work is to propose a state-of-the-art physics based multiscale modeling framework for simulating material phase change problems. Both ice melting and copper crystallization problems are selected to demonstrate this multiscale modeling and simulation. The computational methods employed in this thesis include: classical molecular dynamics, finite element method, phase-field method, and multiscale (nano/micro coupling) methods. Classical molecular dynamics (MD) is a well-known method to study material behaviors at atomic level. Due to the limit of MD, it is not realistic to provide a complete molecular model for simulations at large length and time scales. Continuum methods, including finite element methods, should be employed in this case. In this thesis, MD is employed to study phase change problems at the nanoscale. In order to study material phase change problems at the microscale, a thermal wave method one-way coupling with the MD and a phase-field method one-way coupling with MD are proposed. The thermal wave method is more accurate than classical thermal diffusion for the study of heat transfer problems especially in crystal based structures. The second model is based on the well-known phase-field method. It is modified to respond to the thermal propagation in the crystal matrix by the thermal wave method, as well as modified to respond to temperature gradients and heat fluxes by employing the Dual-Phase-Lag method. Both methods are coupled with MD to obtain realistic results. It should be noted that MD simulations can be conducted to obtain material/thermal properties for microscopic and/or macroscopic simulations for the purpose of hierarchical/sequential multiscale modeling. These material parameters include thermal conductivity, specific heat, latent heat, and relaxation time. Other type of interfacial parameters that occur during the phase change process, such as nucleus shape, interfacial energy, interfacial thickness, etc., are also obtained by MD simulation since these have so far been too difficult to measure experimentally. I consider two common phase change phenomena, ice melting and copper crystallization, in this thesis. For the case of ice melting, MD is first employed to study its phase change process and obtain thermal properties of ice and water. Several potential models are used. I conduct simulations of both bulk ice and ice/water contacting cases. It is found that various potential models result in similar melting phenomena, especially melting speed. Size effects are also studied and it is found that the melting time is longer for larger bulk ice segments but that the average melting speed is size dependent. There is no size effect for the melting speed at ice/water interface at the nanoscale if the same temperature gradient is applied. The melting speed of ice should depend on the temperature gradient. To study ice melting at the microscale, the thermal wave model is employed with parameters obtained from MD simulations. It is found that ice melting speed is scale, for both length scale and time scale, dependent. For the case of copper crystallization, an EAM potential is first employed to conduct MD simulations for studying the copper crystallization process at the nanoscale. I obtain thermal properties and interfacial parameters, including thermal diffusion coefficient, latent heat, relaxation time, interfacial thickness, interfacial energy and the anisotropy coefficients, and nucleus shape etc. A central symmetry parameter is used to identify an atom in solid state or liquid state. And then an initial nucleus shape is obtained and used as the input for microscale simulation, in which the phase-field method is used to study copper crystallization at the microscale.

The Greenland Ice Sheet is the largest ice sheet in the northern hemisphere. Ongoing melting of the ice sheet, resulting in increased mass loss relative to the longer term trend, has raised concerns about the stability of the ice sheet. Melt water generated at the surface is temporarily stored in supra-glacial lakes on the ice sheet. Connections between melt water generation, storage and ice sheet dynamics highlight the importance of the surface hydrological system. In this thesis different methods are used that improve our ability to observe the supra-glacial lake system on the west Greenland Ice Sheet. This region of the Greenland Ice Sheet has the most extensive supra-glacial hydrological system with a dense network of streams connecting lakes that can exceed several square kilometres in area. Synthetic Aperture Radar (SAR) and visible-near infrared (VNIR) images are used to explore the potential of different sensor systems for regular observations of the supra-glacial lakes. SAR imagery is found to be a useful complement to VNIR data. VNIR data from moderate resolution sensors are preferred as these provide high temporal resolution data, ameliorating problems with cloud cover. The dynamic nature of the lakes makes automated classification difficult and manual mapping has been widely used. Here a new method is proposed that improves on existing methods by automating the identification and classification of lakes, and by introducing a flexible system that can capture the full range of lake forms. Applying our new method we are better able to analyse the evolution of lakes over a number of melt seasons. We find that lakes initiate after approximately 40 positive degree days. Most lakes exist for less than 20 days before draining, or later in the season, and less often, freezing over. Using the automated method developed in this thesis lakes have been mapped in imagery from 2001–2010 at approximately five day intervals. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript. Paper 5: Manuscript.</p>

Title: Dynamics of icy satellites with a liquid phase Author: Klára Kalousová Department: Department of Geophysics Department: Laboratoire de Planétologie et Géodynamique de Nantes Supervisors: Doc. RNDr. Ondřej Čadek, CSc. upervis ors: Dr. Gaël Choblet Abstract: Jupiter's moon Europa has a young surface with a plethora of unique terrains that indicate recent endogenic activity. Morphological models and spectral observations suggest that it possesses an internal ocean as well as shallow pockets of liquid water within its outer ice shell. Presence of water in a chemically rich environment and a longterm energy source ensured by tidal heating, make Europa one of the best candidates for habitability, for which the material exchange between the surface and the ocean is critical. In this thesis, we investigate internal melting and subsequent meltwater evolution within Europa's ice shell by using a two-phase formalism developed for this context. Results of a parametric study for a temperate ice shell indicate that the time scale of water transport by porous flow is governed by the ice permeability, while the ice viscosity affects the solution wavelength. We then consider a polythermal ice shell with two melting scenarios: (i) In a tidally-heated convecting ice shell, melting occurs mainly in its lower half and...