Patient-specific anisotropic model of human trunk based on MR data

There are many ways to generate geometrical models for numerical simulation, and most of them start with a segmentation step to extract the boundaries of the regions of interest. This paper presents an algorithm to generate a patient-specific three-dimensional geometric model, based on a tetrahedral mesh, without an initial extraction of contours from the volumetric data. Using the information directly available in the data, such as gray levels, we built a metric to drive a mesh adaptation process. The metric is used to specify the size and orientation of the tetrahedral elements everywhere in the mesh. Our method, which produces anisotropic meshes, gives good results with synthetic and real MRI data. The resulting model quality has been evaluated qualitatively and quantitatively by comparing it with an analytical solution and with a segmentation made by an expert. Results show that our method gives, in 90% of the cases, as good or better meshes as a similar isotropic method, based on the accuracy of the volume reconstruction for a given mesh size. Moreover, a comparison of the Hausdorff distances between adapted meshes of both methods and ground-truth volumes shows that our method decreases reconstruction errors faster. Copyright © 2015 John Wiley & Sons, Ltd.Natural Sciences and Engineering Research Council (NSERC) of Canada and the MEDITIS training program (´Ecole Polytechnique de Montreal and NSERC)

Prospectives

Tiré de: Prospectives, vol. 19, no 4, déc. 1983.Titre de l'écran-titre (visionné le 24 janv. 2013

Prospectives

Tiré de: Prospectives, vol. 19, no 4, déc. 1983.Titre de l'écran-titre (visionné le 24 janv. 2013

Prospectives

Tiré de: Prospectives, vol. 19, no 4, déc. 1983.Titre de l'écran-titre (visionné le 24 janv. 2013

Controls on Mass and Thermal Loading to an Oil Sands End Pit Lake from Underlying Fluid Fine Tailings

End pit lakes (EPLs) are a relatively new strategy proposed for reclaiming oil sands surface mines. An EPL is formed within a depleted mine pit, with fluid fine tailings (FFT) stored below a water cover. Fluid fine tailings are a by-product of the oil sands bitumen extraction process with high water contents, low bearing capacities, and elevated concentrations of various constituents. This thesis considers mass and heat transfer between the FFT and overlying water cover at the first EPL, Base Mine Lake (BML). The study objectives were: (1) characterize the FFT thermal properties and the thermal regime in BML; (2) assess FFT settlement rates and characteristics; and (3) evaluate a range of potential mechanisms for mass and heat movement, including diffusion or conduction, and mixing of the FFT due to unstable density profiles or fluid movement within the water cover. These objectives were achieved through a combination of field investigations, laboratory testing, and numerical modelling, and the results were published in three manuscripts comprising the main body of the thesis. Overall, FFT is the largest (Cl) mass source to the BML water cover. The dominant transport mechanism was advective mass transport or convective heat transport due to tailings settlement; however, tailings disturbance near the FFT-water interface may also contribute to mass release. The predicted pore water fluxes based on the advective or convective regimes were similar to previously estimated FFT settlement rates and decreased throughout the studied period from approximately 1.46 m/a in 2013 to 2014, to 0.73 m/a in 2014 to 2015. Declining advection rates indicate that diffusive mass transport and conductive heat transfer will likely become more significant in the future. The results also confirmed that EPL design should consider the size of the water cover, volume and characteristics of the FFT, and operational controls, as these factors will likely influence EPL success as a sustainable reclamation landscape

An anisotropic mesh adaptation method for the finite element solution of heterogeneous anisotropic diffusion problems

Heterogeneous anisotropic diffusion problems arise in the various areas of science and engineering including plasma physics, petroleum engineering, and image processing. Standard numerical methods can produce spurious oscillations when they are used to solve those problems. A common approach to avoid this difficulty is to design a proper numerical scheme and/or a proper mesh so that the numerical solution validates the discrete counterpart (DMP) of the maximum principle satisfied by the continuous solution. A well known mesh condition for the DMP satisfaction by the linear finite element solution of isotropic diffusion problems is the non-obtuse angle condition that requires the dihedral angles of mesh elements to be non-obtuse. In this paper, a generalization of the condition, the so-called anisotropic non-obtuse angle condition, is developed for the finite element solution of heterogeneous anisotropic diffusion problems. The new condition is essentially the same as the existing one except that the dihedral angles are now measured in a metric depending on the diffusion matrix of the underlying problem. Several variants of the new condition are obtained. Based on one of them, two metric tensors for use in anisotropic mesh generation are developed to account for DMP satisfaction and the combination of DMP satisfaction and mesh adaptivity. Numerical examples are given to demonstrate the features of the linear finite element method for anisotropic meshes generated with the metric tensors.Comment: 34 page

Controls on Mass and Thermal Loading to an Oil Sands End Pit Lake from Underlying Fluid Fine Tailings

End pit lakes (EPLs) are a relatively new strategy proposed for reclaiming oil sands surface mines. An EPL is formed within a depleted mine pit, with fluid fine tailings (FFT) stored below a water cover. Fluid fine tailings are a by-product of the oil sands bitumen extraction process with high water contents, low bearing capacities, and elevated concentrations of various constituents. This thesis considers mass and heat transfer between the FFT and overlying water cover at the first EPL, Base Mine Lake (BML). The study objectives were: (1) characterize the FFT thermal properties and the thermal regime in BML; (2) assess FFT settlement rates and characteristics; and (3) evaluate a range of potential mechanisms for mass and heat movement, including diffusion or conduction, and mixing of the FFT due to unstable density profiles or fluid movement within the water cover. These objectives were achieved through a combination of field investigations, laboratory testing, and numerical modelling, and the results were published in three manuscripts comprising the main body of the thesis. Overall, FFT is the largest (Cl) mass source to the BML water cover. The dominant transport mechanism was advective mass transport or convective heat transport due to tailings settlement; however, tailings disturbance near the FFT-water interface may also contribute to mass release. The predicted pore water fluxes based on the advective or convective regimes were similar to previously estimated FFT settlement rates and decreased throughout the studied period from approximately 1.46 m/a in 2013 to 2014, to 0.73 m/a in 2014 to 2015. Declining advection rates indicate that diffusive mass transport and conductive heat transfer will likely become more significant in the future. The results also confirmed that EPL design should consider the size of the water cover, volume and characteristics of the FFT, and operational controls, as these factors will likely influence EPL success as a sustainable reclamation landscape