Exploring the Relationship Between Grain Configuration and the Movement Of Capillary-Held Water in Unsaturated Porous Media

The air-water interface in porous media has been studied for decades, and is important for understanding the distribution and movement of water, solutes and suspended colloids and nanoparticles in the unsaturated zone. The spatial configuration of individual grain surfaces plays a central role in defining the shapes of capillary-held water films in porous media, as well as influencing how flow and transport occur in unsaturated media. An accurate description of grain surface is essential for the simulation of the configuration of air-water interface. The objectives of this work were to explore algorithms related to reconstruction of grain surfaces from scanning electron microscopy (SEM) images, and then to simulate configuration and flow in unsaturated media at different scales. To obtain grain surface configuration, a new hybrid method was developed to reconstruct three-dimensional (3D) grain surfaces from two dimensional (2D) images taken by scanning electron microscopy (SEM). The hybrid method combines stereoscopic reconstruction with shape-from-shading calculations, and is able to capture detail from complex natural surfaces. shadows are universal in SEM images, and can complicate reconstruction. A machine-learning method based on boosted decision trees was used to identify shadows in SEM images based on a training set of shadows in photographic images. The influence of shadows on the hybrid reconstruction method was analyzed. Previous studies examining the configuration of air-water interfaces have been based on calculations for surfaces whose elevations can be defined by z=f(x,y). This made existing methods unsuitable for calculations in more complex geometries, such as around the outsides of grains. A numerical simulation method was developed to calculate air-water interface in three-dimensional space around the outsides of grains. The method was then extended to allow simulation of flow during evaporation. Finally, work was conducted to explore the flow and transport of nanoparticles in a cluster of sand grains experiencing evaporation. Experiments involved filling a cluster of sand grains with water containing fluorescein sodium and sulfate-modified polystyrene nanospheres, and using confocal microscopy to image water flow between sand grains and deposition of fluorescent nanoparticles during evaporation. A model was developed to explain the flow behavior observed

Mathematical techniques for shape modelling in computer graphics: A distance-based approach.

This research is concerned with shape modelling in computer graphics. The dissertation provides a review of the main research topics and developments in shape modelling and discusses current visualisation techniques required for the display of the models produced. In computer graphics surfaces are normally defined using analytic functions. Geometry however, supplies many shapes without providing their analytic descriptions. These are defined implicitly through fundamental relationships between primitive geometrical objects. Transferring this approach in computer graphics, opens new directions in shape modelling by enabling the definition of new objects or supplying a rigorous alternative to analytical definitions of objects with complex analytical descriptions. We review, in this dissertation, relevant works in the area of implicit modelling. Based on our observations on the shortcomings of these works, we develop an implicit modelling approach which draws on a seminal technique in this area: the distance based object definition. We investigate the principles, potential and applications of this technique both in conceptual terms (modelling aspects) and on technical merit (visualisation issues). This is the context of this PhD research. The conceptual and technological frameworks developed are presented in terms of a comprehensive investigation of an object's constituent primitives and modelling constraints on the one hand, and software visualisation platforms on the other. Finally, we adopt a critical perspective of our work to discuss possible directions for further improvements and exploitation for the modelling approach we have developed