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Intermolecular potential energy functions for CO2 have been developed from first principles for use in heterogeneous systems, including one with explicit polarization. The intermolecular potentials have been expressed in a transferable form and parameterized from nearly exact electronic structure calculations. Models with and without explicit many-body polarization effects, known to be important in simulation of interfacial processes, are constructed. The models have been validated on pressure-density isotherms of bulk CO2 and adsorption in three metal-organic framework (MOF) materials. The present models appear to offer advantages over high quality fluid/liquid state potentials in describing CO2 interactions in interfacial environments where sorbates adopt orientations not commonly explored in bulk fluids. Thus, the nonpolar CO2-PHAST and polarizable CO2-PHAST* potentials are recommended for materials/interfacial simulations.

In electronic structure calculations the computational cost is of great importance because large systems can contain a huge number of electrons. One effective method to make such calculations is by density matrix purification. Although, the cost for this method is relatively low compared to other existing methods there is room for improvements. In this paper one method proposed by Emanuel Rubensson and one method proposed by Jaehoon Kim & Yousung Jung was compared to each other with respect to efficiency, simplicity and robustness. Both are improved methods to compute the density matrix by accelerated polynomial expansion. Rubensson’s method consists of two different algorithms and results showed that both performed better than Kim & Jung’s method in terms of efficiency, which is the property both methods directs their main focus on. The major differences between them was identified in terms of adaptivity. The methods require different inputs that demands separate levels of knowledge about the system. Kim & Jung’s method which require less knowledge can however benefit efficiency-wise from more information in order to optimize the algorithm for the system. Results also showed that both methods were stable, but since they only were tested with arbitrarily assumed input arguments no conclusion about their general stability could be drawn.

This Thesis presents the results of phase behavior calculations and simulation of asphaltene precipitation, flocculation, and deposition in five Middle-Eastern wells from different fields, based on a reliable experimental data provided for this purpose. The asphaltene precipitation, flocculation, and deposition have been simulated throughout the primary (pressure depletion), secondary (Waterflooding) and tertiary recovery (CO₂ injection) stages. Asphaltene precipitation becomes a serious problem especially when it causes plugging of the formation, wellbore, or production facilities, which will significantly affect the productivity and final recovery of the area. To help preventing asphaltene precipitation a bottomhole pressure higher than the asphaltene onset pressure (AOP) has been applied. Also, water and CO₂ injection has provided enough support for pressure maintenance, which helps in preventing asphaltene. Several scenarios were tested to investigate and identify the cases with lowest asphaltene precipitation and higher recovery. It has been considered obligatory to have a representative numerical simulation model that can predict the phase behavior of asphaltene precipitation, flocculation, and deposition accurately. The first part of this thesis includes a comprehensive literature review of asphaltene precipitation flocculation, and deposition that include asphaltene structure, models and prevention techniques. The second part of the thesis includes a detailed study of modeling asphaltene precipitation phase behavior utilizing experimental and real field data obtained from five Middle-Eastern wells from different fields. Experimental data include measurements of asphaltene onset pressure (AOP), saturation pressure, and PVT data. Asphaltene precipitation was modeled by using WinProp (a phase behavior utility from CMG) which uses Nghiem solid model. Saturation pressures, PVT, and AOP data were used to match Peng-Robinson EOS and the precipitation model was matched by the experimental data of AOP. The third part of the thesis includes a one-dimensional simulation comparison study of asphaltene precipitation between three different compositional simulators; UTCOMP, ECLIPSE and CMG/GEM. The last part of the thesis includes a full field scale study based on a heterogeneous three-dimensional cartesian single-well model. The objective of this study was to assess the effect of asphaltene precipitation, flocculation, and deposition in the well productivity and the economic impacts related to it. Different production practices were applied to define the most appropriate and efficient production strategy. This study includes a discussion and comparison of production rates with and without asphaltene precipitation, flocculation, and deposition and a comparison of asphaltene precipitation, flocculation, and deposition at different times using different bottomhole and production rate constraints. Several cases (i.e., WAG cycles, completion, target layers of injection, etc.) will be tested to come up with the optimum completion and operating strategy in the presences asphaltene. Despite the work devoted to understanding this subject, asphaltene still represents a challenging and unresolved problem. This thesis will help bridge the gap of this limited understanding in the field of asphaltene. / text

This thesis is intended to be a ground for the implementing of solid mechanics calculations of an expander axle in an existing CAD programme. The main parameters to be calculated are: effective stress, stress components in axial and radial direction, shear stress as well as maximum force and fatigue analysis. In order to achieve the above mentioned goal, calculations were made by hand. At the end of any of the chapters, a diagram on the input/output data and the equations needed for performing the calculations was drawn.

This thesis investigates the stabilization of divalent germanium using substituted diethanol amine ligands. Germylenes of type RN(CH2CH2OH)2Ge were obtained from N-heterocyclic germylenes and N-alkyl diethanol amines in yields of up to 94%. Single crystal X-ray diffraction confims the presence of a transannular Ge-N dative bond in all cases. In addition, intermolecular dimers containing Ge2O2 rings are formed for R = Me and Et. Reaction of the four germylenes L with nickel carbonyl yielded the respective germylene complexes L2Ni(CO)2 and LNi(CO)3. The germylenes and their complexes were investigated with DFT methods. Only four methods, SVWN, BB1K, MPWB1K and M062x gave acceptable Ge-N distances. Dimerization energies of the germylenes were examined with the thermochemically accurate M062x method. At the M062x/Def2-TZVP level, the dimerization energies of the germylenes are very small (ΔG° ≈ 0 kcal/mol). The experimentally observed dimerization or lack thereof may accordingly be determined by packing effects in the solid state or solvation energies in solution.

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This thesis handles the need for Volvo Logistics (VLC) to calculate their total carbon footprint of purchased transportations, i.e. the total carbon dioxide emissions by all vehicles employed by VLC to transport the goods of their customers. The purpose of the thesis is therefore to determine a method with which VLC can calculate the total carbon footprint. To be able to decide upon one method that can fulfil the purpose, the authors searched for various methods, both in the academia and within the transportation sector, with which the emissions can be determined. Simultaneously the available input at VLC was studied to determine what type of method would be best suited to the current state of the company. After gathering several methods and determine what input was available and what was not available at VLC, an analysis of the found methods was done. First matching them with the available input to see which were usable as is, and then a more thorough Analytical Hierarchical Process analysis using three main-criterions; credibility, comparability, and simplicity, each with several sub-criterions. The weighting of these criterions was done in a workshop together with VLC employees, particularly the Environmental Manager and an Environmental Analyst, but also with two employees at the Global Logistics Development department at VLC. Using the weighting and the author’s comparisons of the methods within each of the criterions it was possible to obtain the methods with which further analysis should be done. After further analysis was conducted, considering VLC’s situation and possible development, the final methods was decided upon, one for each mode of transport; air, rail, road, and sea. These had to be adapted to better suit VLC and the input that was available; the distances, the weight, and the transport mode, factors which are incorporated in the methods recommended by the authors. The adaptation was then done using expertise at VLC to be able to determine what input VLC could affect as to be able to work towards lowering the total carbon footprint once it was calculated the first time. This also led to a revaluation of the method for sea transportation, forcing a change from the previously chosen one to a more suited method. This meant that three of the four modes; air, road, and sea, was covered by the NTM method, while rail used the Green Cargo method. While adapting the methods; to make them ready to use for VLC, certain changes required to obtain all the input needed was encountered and forwarded to the environmental department, letting them include it in the annual supplier survey. The thesis was concluded by four sets of instructions to be used to calculate the carbon footprint, one two tiered set for each mode of transportation. The instructions are presented in a step by step fashion of how to perform the calculations. The first part; First time usage, depicts those changes needed before the calculations can be attempted, the second part; Annual usage, cover those steps which has to be gone through every time the total carbon footprint for a period is to be calculated.

In this thesis we investigate coupling and preconditioning techniques for 19D hybrid neutronics calculations. Each problem is represented by two spatial regions with Sn in one region and either Diffusion (P1) or P3 in the other region. For each of these two cases we define one coupling scheme and two different preconditioned systems. These systems are solved with both fixed9point iteration and the GMRES Krylov method. The solution techniques are compared in terms of iteration count and computational cost. Preconditioning with a global diffusion operator is found to be very effective for the most difficult problems.

Thesis (Ph. D.)--Virginia Commonwealth University, 2007. / Prepared for: Dept. of Biostatistics. Bibliography: leaves 179-181. Also available online via the Internet.