CoordenaÃÃo de AperfeÃoamento de Pessoal de NÃvel Superior / In reservoir simulation, the compositional model is one of the most used models for enhanced oil recovery. However, the physical model involves a large number of equations with a very complex interplay between equations. The model is basically composed of balance equations and equilibrium constraints. The way these equations are solved, the degree of implicitness, the selection of the primary equations, primary and secondary variables have a great impact on the computation time. In order to verify these effects, this work proposes the implementation and comparison of some implicit and semi-implicit methods. The following formulations are tested: an IMPEC (implicit pressure, explicit composition), an IMPSAT (implicit pressure and saturations), and two fully implicit formulations, in which one these formulations is being proposed in this work. However, the literature reports some intrinsic inconsistencies of the IMPSAT formulation mentioned. In order to verify it, an iterative IMPSAT is implemented to check the quality of the IMPSAT method previously mentioned. The finite volume method is used to discretize the formulations using Cartesian grids and unstructured grids in conjunction with the EbFVM (Element based finite volume method) for 2D and 3D reservoirs. The implementations have been performed in the UTCOMP simulator from the University of Texas at Austin. The results of several case studies are compared in terms of volumetric oil and gas rates and the total CPU time. It was verified that the FI approaches increase their performance, when compared to the other approaches, as the grid is refined. A good performance was observed for the IMPSAT approach when compared to the IMPEC formulation. However, as more complex stencils are used, the IMPSAT performance reduces. / Em simulaÃÃo de reservatÃrios, o modelo composicional à um dos mais usados para a recuperaÃÃo avanÃada de petrÃleo. Entretanto, o modelo fÃsico envolve um grande nÃmero de equaÃÃes com uma complexa interelaÃÃo entre elas. O modelo à basicamente composto por equaÃÃes de balanÃo e restriÃÃes de equilÃbrio. A forma como essas equaÃÃes sÃo resolvidas como, o grau de implicitude, a seleÃÃo das equaÃÃes primÃrias, variÃveis primÃrias e secundÃrias tem um grande impacto no tempo de computaÃÃo. Com o intuito de verificar esse efeito, esse trabalho propÃe a implementaÃÃo e comparaÃÃo de alguns mÃtodos implÃcitos e semi-implÃcitos. As seguintes formulaÃÃes sÃo testadas: uma IMPEC (implicit pressure, explicit composition), uma IMPSAT (implicit pressure and saturations), e duas formulaÃÃes totalmente implicitas, das quais uma destas està sendo proposta neste trabalho. Entretanto, a literatura relata algumas inconsistÃncias intrÃnsecas da formulaÃÃo IMPSAT mencionada. Para verificar isso, um IMPSAT iterativo foi implementado para verificar a qualidade nos resultados do mÃtodo IMPSAT prÃviamente mencionado. O mÃtodo de volumes finitos à usado para discretizar as formulaÃÃes usando malhas Cartesianas e nÃo-estruturadas em conjunto com o EbFVM (Element based finite volume method) para reservatÃrios 2D e 3D. A implementaÃÃo foi realizada no simulador UTCOMP da Univeristy of Texas at Austin. Os resultados de diversos casos de estudo sÃo comparados em termos das vazÃes volumÃtricas de Ãleo e gÃs e do tempo total de CPU. Verificou-se que as abordagens totalmente implÃcitas melhoram sua performance, quando comparado com os demais mÃtodos, a medidaque a malha à refinada. Um bom desempenho foi observado para as formulaÃÃes IMPSAT quando comparadas com a formulaÃÃo IMPEC. Entretando, com o uso de conexÃes mais complexas entre os blocos da malha, o desempho da formulaÃÃo IMPSAT reduziu.

abstract: 中国水环境行业当前正处在以质量驱动、效率提升为主导的发展阶段，为积极响应国家政策以及环境发展导向，平衡公众日益增长的公共品需求同公共品短缺、低效之间的矛盾，抓住市场发展机遇，提高企业市场竞争中的核心能力，水环境行业必须要明确资本驱动、效率导向、服务标准提高要求下的价值流方向，加快行业发展动力的创新改革。因此，本文立足政府充分授权下的水环境企业战略联盟模式（具体体现为BOT模式）影响因素研究，包括如下几部分内容： 第一，界定政府充分授权下水环境企业战略联盟内涵，分析其形成的理论基础、水环境企业战略联盟的类型、发展差异性及战略联盟动因。通过梳理战略联盟理论国内外研究现状回顾及评述，提出政府充分授权下水环境企业战略联盟模式研究的主要问题。 第二，探索政府充分授权下水环境企业战略联盟模式的影响因素。通过对水环境基础设施战略联盟项目合同关键内容的深入分析，识别出政府充分授权下水环境企业战略联盟模式的关键影响因素。 第三，实证分析各关键因素对政府充分授权下水环境企业战略联盟模式效果的影响。运用回归分析方法对项目规模、政府政策、监督管理、激励机制、风险分配和投资回报对联盟模式效果的影响进行实证检验，验证了各影响因素对政府充分授权下水环境企业战略联盟模式效果的正向作用。 最后，对政府充分授权下水环境企业战略联盟模式影响因素及作用研究的结论进行总结。 / Dissertation/Thesis / Doctoral Dissertation Business Administration 2019

In this thesis, results will be presented that pertain to the global regularity of solutions to boundary value problems having the general form \begin{align} F\left[D^2u-A(\,\cdot\,,u,Du)\right] &= B(\,\cdot\,,u,Du),\quad\text{in}\ \Omega^-,\notag\\ T_u(\Omega^-) &= \Omega^+, \end{align} where $A$, $B$, $T_u$ are all prescribed; and $\Omega^-$ along with $\Omega^+$ are bounded in $\mathbb{R}^n$, smooth and satisfying notions of c-convexity and c^*-convexity relative to one another (see [MTW05] for definitions). In particular, the case where $F$ is a quotient of symmetric functions of the eigenvalues of its argument matrix will be investigated. Ultimately, analogies to the global regularity result presented in [TW06] for the Optimal Transportation Problem to this new fully-nonlinear elliptic boundary value problem will be presented and proven. It will also be shown that the A3w condition (first presented in [MTW05]) is also necessary for global regularity in the case of (1). The core part of this research lies in proving various a priori estimates so that a method of continuity argument can be applied to get the existence of globally smooth solutions. The a priori estimates vary from those presented in [TW06], due to the structure of F, introducing some complications that are not present in the Optimal Transportation case.¶ In the final chapter of this thesis, the A3 condition will be reformulated and analysed on round spheres. The example cost-functions subsequently analysed have already been studied in the Euclidean case within [MTW05] and [TW06]. In this research, a stereographic projection is utilised to reformulate the A3 condition on round spheres for a general class of cost-functions, which are general functions of the geodesic distance as defined relative to the underlying round sphere. With this general expression, the A3 condition can be readily verified for a large class of cost-functions that depend on the metrics of round spheres, which is tantamount (combined with some geometric assumptions on the source and target domains) to the classical regularity for solutions of the Optimal Transportation Problem on round spheres.

A 2D fully nonlinear Numerical Wave Tank (NWT) is developed based on the potential theory, mixed Eulerian-Lagrangian (MEL) time marching scheme, and boundary element method (BEM). Nonlinear Wave deformation and wave forces on stationary and freely floating bodies are calculated using the NWT. For verification, the computed mean, 1st, 2nd, and 3rd order wave forces on a single submerged cylinder are compared with those of Chaplin's experiment, Ogilvie's 2nd-order theory, and other nonlinear computation called high-order spectral method. Similar calculations for dual submerged cylinders are also conducted. The developed fully nonlinear NWT is also applied to the calculations of the nonlinear pressure and force of surface piercing barge type structures and these obtained results agree with experimental and theoretical results. Nonlinear waves generated by prescribed body motions, such as wedge type wave maker or land sliding in the coastal slope area, can also be simulated by the developed NWT. The generated waves are in agreement with published experimental and numerical results. Added mass and damping coefficients can also be calculated from the simulation in time domain. For the simulation of freely floating barge-type structure, only fully nonlinear time-stepping scheme can accurately produce nonlinear body motions with large floating body simulations. The acceleration potential method, which was developed by Tanizawa (1996), is known to be the most accurate, consistent and stable. Using acceleration potential method, in the present study, the series of motions and drift forces were calculated over a wide range of incident wave frequencies including resonance region. To guarantitatively compare the nonlinear contribution of free-surface and body-boundary conditions, the body-nonlinear-only case with linearized free-surface condition is separately simulated. All the floating body motions and forces are in agreement with experimental results. Finally, the NWT is extended to fully nonlinear wave-body-current interactions of freely floating bodies, which has not been published in the open literature until now.

The overall objective is to improve the one-dimensional numerical prediction of the fine and non-cohesive bed material load in alluvial rivers, especially during high intensity episodes during which sediment beds are strongly remobilized. For this reason, we attempt to reduce the major inaccuracy sources coming from the alluvial resistance and bed material load relations needed to close the mathematical system. Through a shared parameter called the control factor m, the interactions occurring in alluvial rivers are incorporated more deeply into the mathematical model and more particularly into the closure laws: bed material load (SVRD, Suction-Vortex Resuspension Dynamics) and the energy slope (Verbanck et al. 2007). The control factor m is assumedly related to the Rossiter resonance modes of the separated flow downstream the bed form crest. To further improve the representation of the flow-sediment-morphology interactions, a fully coupled model approach has been naturally chosen. In this work the terminology fully coupled means that the three equations forming the system are solved synchronously and that the terms often neglected by more traditional decoupled models are kept. The feasibility of the new closure methodology has been drawn up by reproducing numerically the silt-flushing experiment conducted by the Yellow River Conservancy Commission (Y.R.C.C.) in the Lower Yellow River (LYR) in Northern China. The objective of the silt flushing experiment is to reverse the aggradation trend of the Lower Yellow River which, in the last decades, has become a perched river. The numerical simulation specifically reproduces the silt-flush effects in a reach of LYR located in the meandering part of the river. This reach (around 100 km) is delimited by Aishan and Luokou hydrometric stations. Since the SVRD formulation has been developed from flume observations, the law has first been confronted to river datasets. The confrontation has revealed that the SVRD law becomes less suitable for fine sediment fluxes (ratio of water depth over median particle size > 5000). Therefore, a modified equation SVRD-2 has been built to enlarge the validity range. The suitability of the SVRD-2 equation to predict fine sediment fluxes has been tested on data available from several hydrometric stations located in the meandering reach of the LYR: historical observations and measures collected during the flushes. The SVRD-2 has also been compared with relations specifically calibrated for this configuration. The comparison has pointed out that the performance of the two formulas is similar, which is encouraging for the SVRD-2 approach as it has not been calibrated on those data. The closed equation system has been written on its quasi-linear form and is solved by a Finite Volume Method combined with a linearized Riemann algorithm. The numerical model has been checked up on two test cases: deposition upstream of a dam and the aggradation experiment conducted by Soni 1975. As it is not yet possible to predict dynamically the value of the control factor m, a possible solution would be to extract its value from the measured data at the inlet cross section. Unfortunately, the necessary data are not measured locally. Moreover, a uniform value of the control factor m may not suffice to reproduce the flow along the whole reach. Therefore, it has been proposed to work temporarily in the reverse way. From the comparison between the numerical results and the experimental data, a time evolution of the control factor m has effectively been extracted and it has been shown that it varies along the reach. At Aishan, the evolution of the control factor m corresponds to the evolution expected from the data analysis previously conducted on other data sets: the value of the control factor m decreases during the flush as it tries to reach the optimal value m=1. The time evolution at Luokou behaves differently to the one at Aishan, but remains in agreement with m evolution patterns observed historically for the river section flowing round Jinan City walls. For Luokou, the highlighted differences may come from three dimensional effects coming from the meander bend upstream the station. Generally, the results obtained for the hydraulics, the sediment transport and bed adaptation are encouraging but still need improvements and additional feeding from the experimental data. The results for the concentration and therefore the bed elevation are very sensitive to the value of the control factor m as it influences most of the terms of the bed material load equation (SVRD-2). The major remaining difficulties are, firstly, to deal with the rapid transients for which the model is less suitable and, secondly, to improve the prediction of the value of control factor m. Before paying more attention into the transients, enhancements concerning the flow along the reach (initial condition and discharge rates during the first days of the flush) must be conducted in priority. Indeed as the prediction of the bed or the cross section evolutions depend directly on the quality of the prediction of the sediment concentration and the hydraulics, one should first improve these aspects. To perform this study, more information about the water levels or sediment concentrations is necessary at some intermediate stations. One solution is to lengthen the studied reach, upstream to Sunkou and downstream to Lijin, totaling a river length of 456 Km. A more entire signal of the energy slopes and the associated bed configurations at different stations would enlighten how the control factor m evolves along the reach during the silt-flush events.

In this paper, we discuss the viscosity solutions of the weakly coupled systems of fully nonlinear second order degenerate parabolic equations and their Cauchy-Dirichlet problem. We prove the existence, uniqueness and continuity of viscosity solution by combining Perron's method with the technique of coupled solutions. The results here generalize those in [2] and [3].

In the subject of Computational Fluid Dynamics (CFD), there seems to be small number of important progress in the pressure-based methods for several decades. Recent studies on the implicit coupled algorithms for pressure-based methods have brought a new insight. This method seems to provide a huge reduction in the solution times over segregated methods. Fully implicit coupled algorithm for pressure-based methods is very new subject with only few papers in literature. One of the most important work in this area is referenced as [1] in this thesis. Another source of information about the method comes from a commercially available code FLUENT which includes the algorithm as an option for pressure-based solver. However the algorithm in FLUENT does not seem to be a fully implicit with a little information in its manual. In this thesis, a fully implicit coupled pressure-based solver is developed mainly based on the available literature. The developed code is succesfully tested against some test cases.

<p>Large-scale, in vitro vaccine screening is an expensive and slow process, while rational vaccine design is faster and cheaper. As opposed to the emperical ways to design vaccines in biology laboratories, rational vaccine design models the structure of vaccines with computational approaches. Building an effective predictive computer model requires extensive knowledge of the process or phenomenon being modelled. Given current knowledge about the steps involved in immune system responses, computer models are currently focused on one or two of the most important and best known steps; for example: presentation of antigens by major histo-compatibility complex (MHC) molecules. In this step, the MHC molecule selectively binds to some peptides derived from antigens and then presents them to the T-cell. One current focus in rational vaccine design is prediction of peptides that can be bound by MHC.<p>Theoretically, predicting which peptides bind to a particular MHC molecule involves discovering patterns in known MHC-binding peptides and then searching for peptides which conform to these patterns in some new antigenic protein sequences. According to some previous work, Hidden Markov models (HMMs), a machine learning technique, is one of the most effective approaches for this task. Unfortunately, for computer models like HMMs, the number of the parameters to be determined is larger than the number which can be estimated from available training data.<p>Thus, heuristic approaches have to be developed to determine the parameters. In this research, two heuristic approaches are proposed. The rst initializes the HMM transition and emission probability matrices by assigning biological meanings to the states. The second approach tailors the structure of a fully connected HMM (fcHMM) to increase specicity. The effectiveness of these two approaches is tested on two human leukocyte antigens(HLA) alleles, HLA-A*0201 and HLAB* 3501. The results indicate that these approaches can improve predictive accuracy. Further, the HMM implementation incorporating the above heuristics can outperform a popular prole HMM (pHMM) program, HMMER, in terms of predictive accuracy.

Simulacó numérica directa de la dispersió turbulenta de plomalls amb flotació en un flux en un canal Alexandre Fabregat Tomás, Tarragona, octubre del 2006 1 IntroduccióL'objectiu d'aquest treball és estudiar la dispersió turbulenta de calor en diferents configuracions basades en el canal desenvolupat mitjançant DNS (Direct Numerical Simulations). Aquesta eina ha demostrat ser de gran utilitat a l'hora d'estudiar fluxos turbulents ja que permet, donada una malla computacional capaç de capturar totes les estructures del flux i un esquema que minimitzi els errors i la dissipació numérica, descriure acuradament l'evolució temporal del flux. Permet a més, donada la descripció tridimensional i temporal del flux, determinar amb precisió qualsevol quantitat que seria impossible d'obtenir experimentalment.En el flux en un canal, el fluid esmou entre dues parets planes, llises i paral·leles separades una distància 2d impulsat per un gradient constant mitjà de pressió. El flux s'anomena desenvolupat quan ja no hi ha efectes de regió d'entrada i la única inhomogeneïtat es troba en la direcció normal a la paret. Sota aquestes condicions, les quantitats promitjades esdevenen estacionàries en el temps.En aquest treball s'ha validat el codi computacional mitjançant la reproducció d'algunes configuracions de flux prèviament estudiades per altres autors. Els nous coneixements en l'estudi de la dispersió turbulenta de calor s'han obtingut a l'incloure, en un flux totalment desenvolupat en un canal, una font lineal centrada verticalment que provoca l'aparició d'un plomall amb una temperatura més alta que la del flux del fons i que per tant, al tenir una menor densitat, experimenta flotació i es deflecteix. L'amitjanament temporal del flux permet estudiar les diferents contribucions dels diferents termes rellevants en les equacions de transport.És d'especial interés la comparativa d'aquests resultats amb els corresponents a la formació d'un plomall a partir d'una font lineal d'un escalar passiu.Per altra banda també s'ha estudiat l'eficiència en paral·lel dels mètodes multigrid en la resolució d'equacions de Poisson. Aquestes equacions són d'especial interés ja que apareixen en el càlcul de la pressió i representen un coll d'ampolla en termes de costos computacionals. Aquest mètode numèric ha estat comparat amb els mètodes de gradient conjugat (anteriorment emprats en el codi 3DINAMICS) en la resolució de diferents problemes comparant els costos en termes de temps de CPU i la seua escalabilitat en la màquina multiprocessador de memòria distribuïda del grup de recerca de Mecànica de Fluids de Tarragona.2 Descripció matemàticaUn cop adimensionalitzades mitjançant les escales adequades, les equacions de transport de quantitat de moviment i energia han estat discretitzades sobre una malla desplaçada mitjançant el mètode de volums finits emprant un esquema centrat de segon ordre. La discretització dels termes advectius en els casos amb fonts lineals ha requerit, però, d'un cura especial ja que la no-linealitat d'aquests termes pot provocar oscil·lacions artificials en el camp dels escalars. La difusió numèrica dels mètodes upwind, com el QUICK, ha estat quantificada i comparada amb resultats obtinguts per a esquemes centrats de segon ordre. Les equacions han estat integrades en el temps mitjançant un esquema implícit de segon ordre tipus Crank-Nicholson. També ha estat necessari implementar condicions de sortida per a la temperatura en els casos A i C del tipus no reflectant per tal de garantir la conservació i evitar l'aparició d'estructures artificials en el flux.3 Descripció físicaLa figura 1 presenta un esquema del domini computacional corresponent al canal desenvolupat. De l'esquema es desprén que x, y i z corresponen a les direccions principal del flux, la perpendicular i la normal a les parets respectivament. Les configuracions del flux estudiades es troben resumides a la taula 1 on s'indica la resolució de la xarxa computacional, el nombre de Reynolds (basat en la velocitat de fricció ut) i en el casos amb flotació, el nombre de Grashof, la temperatura de referència i la direcció de flotació (la direcció del vector gravetat).Les dimensions del canal s´on 8pd×2pd×2d en les direccions x, y i z respectivament.En el cas A la temperatura representa un escalar de manera que el plomall format és passiu, és a dir, no hi ha acoblament entre les equacions de quantitat de moviment i energia. A diferència d'aquest, en els casos B i C totes dues equacions queden acoblades pel terme de flotació. Aquest terme apareix quan les diferències de temperatura en el si del fluid generen diferències de densitat. En el cas B, el canal vertical amb convecció mixta, cada paret del canal es troba a una temperatura constant però diferent. El vector gravetat i la direcció del corrent estan alineades de manera que aquesta direcció continua sent homogènia. En la zona propera a la paret calenta la flotació actua en la direcció del corrent imposada pel gradient mitjà de pressió. En canvi, en la zona propera a la paret freda, la flotació s'oposa al moviment del flux.El cas C és similar al cas A però en aquesta ocasió la temperatura no es considera un escalar passiu i per tant la flotació acobla el camp dinàmic amb el de temperatures. El vector gravetat actua en aquest cas en la direcció normal. La inhomogeneïtat en la direcció del flux no permet continuar emprant condicions de contorn periòdiques i per tant, al domini presentat en la figura 1, se li ha acoblat una regió auxiliar a l'entrada on es resolen únicament les equacions de quantitat de moviment. Els camps de velocitat i pressió per a un canal totalment desenvolupat obtinguts en aquest domini auxiliar s'empraran com a condició de contorn a l'entrada del domini de computació. No és necessari cap tipus d'interpolació ja que la resolució del a xarxa d'aquest domini auxiliar és la mateixa que l'emprada en el domini de computació.4 ResultatsEls resultats per a les simulacions presentades en la taula 1 contenen, principalment, els perfils de velocitat i temperatura mitjans així com la intensitat de les fluctuacions. A més, es presenten els perfils de les diferents contribucions dels termes relevants de les equacions de transport amitjanades. Per al cas C, els camps dinàmics i de temperatura no estan desenvolupats. Els perfils mitjans a diferents posicions aigües avall permeten estudiar l'evolució del plomall ascendent a més d'analitzar com la flotació afecta al balanç de les diferents contribucions. La figure 2 presenta el camp mitjà de temperatures per al cas C amb les tres posicions en la direcció principal del flux per a les quals s'han inclòs els perfils.Finalment, es presenten els resultats corresponents a la comparativa entre els diferents solvers per a una equació de Poisson. Tots els mètodes numèrics han es-3Figura 2: Camp mitjà de temperatures per al cas C tat paral·lelitzats mitjançant les llibreries Message Passing Interface. En la figura 3 es presenten com a exemple els resultats (en termes de temps de CPU i speedup) per a la resolució de l'equació de Poisson per al desacoblament de pressió i velocitat en el cas del flux desenvolupat en un canal.Els resultats de speed-up per als diferents mètodes mostren la baixa escalabilitat del solver multigrid comparat amb els altres mètodes del tipus gradient conjugat. La raó radica en les grans necessitats de comunicació d'un algoritme construït sobre un esquema de relaxació tipus SOR. Tanmateix, multigrid és el mètode numèric que requereix menys temps de CPU per concloure la tasca. El factor respecte als mètodes de gradient conjugat pot arribar a ser de 30 i per tant és el millor candidat per a la resolució d'aquests tipus de problemes. / The main goal of this work is to study the turbulent heat transfer in a developed channel flow using Direct Numerical Simulations (DNS). These simulations solve explicitly all the scales present in the turbulent flow so, even for moderate Reynolds numbers, the discretization grids need to be fine enough to capture the smallest structures of the flow and, consequently, DNS demands large computational resources. The flow, driven by a mean constant pressure gradient in the streamwise direction, is confined between two smooth, parallel and infinite walls separated a distance 2d.The turbulent heat transport is studied for three different flow configurations.Some of them are used as benchmark results for this work. The three cases reported can be summarized as:· case A: Scalar plume from a line source in a horizontal channel.· case B:Mixed convection with the gravity vector aligned with the streamwise direction (vertical channel).· case C: Buoyant plume from a line source in a horizontal channel.In addition, preliminary results for a turbulent reacting flow in a fully developed channel are also presented.In the case B heat flux results from a temperature difference between the channel walls. The gravity vector is aligned with the streamwise direction and the Grashof, Reynolds and Prandtl numbers are Gr = 9.6 · 106, Ret = 150 and Pr = 0.71 respectively. Close to the hot wall, buoyancy acts aligned to the flow direction imposed by the mean pressure gradient so velocities are generally increased in comparison with a purely forced convection flow. Oppositely, near the cold wall, buoyancy is opposed to the flow and consequently velocities are decreased.Cases A and C are similar because in both cases a hot fluid is released within a cold background flow through a line source vertically centered in the wall-normal direction located at the inlet. The height of the source is 0.054d. The injected hot fluid disperses forming a hot plume that is convected downstream between the two adiabatic walls of the channel.The difference between cases A and C lies in the fact that for case A heat and momentum are decoupled and temperature acts as an scalar. Advection and diffusion are the only phenomena responsible for the evolution of the plume. On the other hand, in case C, buoyancy couples heat and momentum and, consequently, the plume floats drifting upward as it advances in the channel due to its lower density. In case C, the streamwise direction is not homogenous because of the coupling between heat and momentum. To guarantee developed conditions at the inlet of the channel it has been necessary to attach a buffer domain just before the computational domain. In this buffer domain, the momentum transport equations for a fully developed channel are solved with the same resolution used in the main domain.The results of cases A and B have been used to validate the 3DINAMICS CFD code by comparison with data reported in the literature. This code is written in FORTRAN 90 and parallelized using the Message Passing Interface (MPI-CHlibrary). It uses the second order in time Crank-Nicholson scheme to integrate numerically the transport equations which are discretized spatially using the centered second-order finite volume approach.The analysis of averaged turbulent quantities and the contributions of the different terms of the time-averaged transport equations is used to show how buoyancy affects the turbulent transport of momentum and heat along the channel.Finally, following a similar configuration than that of case A, a chemical reactantA released through line source reacts with a background reactant B following a second order chemical reaction with Damkh¨oler number of 1. Preliminary results for turbulent species transport are also included in this work.Special attention have been devoted to the discretization of the advective terms to avoid non-realistic values of the variables because of the non-linearities of the transport equations. The conservative non-reflecting boundary conditions have been implemented at the outlet to simulate the convected outflow when the streamwise direction can not be considered homogeneous, as in case C. For homogeneous directions, periodic boundary conditions have been used.Large grid resolutions (up to 8 million grid nodes for case C including the buffer region) demand important computational resources. A parallel Multigrid solver has substituted the previous conjugate gradient method to solve the Poisson equation in the pressure calculation. This step was the most expensive in terms of CPU costs. The Multigrid method efficiency has been compared with two different versions of the conjugate gradient approach and it has been demonstrated that this method is the most efficient in terms of CPU time although the current algorithmcan be improved to enhance the scalability inmultiprocessor computers.

In this thesis we present results from quantum Monte Carlo for the fully-frustrated honeycomb lattice. The XXZ model is of interest in the classical limit, as there is a mapping between the classical fully-frustrated honeycomb Ising model groundstates and the classical hard-core dimer model groundstate. The aim of this work is to explore the effect of quantum fluctuations on the fully-frustrated honeycomb model to see what sort of interesting physics arises. One might expect unusual physics due to the quantum hard-core dimer model, where interesting physics are known to exist. This is because there is a duality mapping between the classical dimer model and the classical fully-frustrated honeycomb Ising model. Indeed, by studying the fully-frustrated honeycomb XXZ model we find that in some cases the system orders into crystal-like structures, a case of order-by-disorder. The most interesting case, when the frustrating bonds are chosen randomly, reveals to us a novel state without any discernible order while at the same time avoiding the freezing one would expect of a glass. This state is a featureless system lacking low temperature magnetic susceptibility---a candidate ``quantum spin liquid''. Future work that might more easily measure quantum spin liquid criteria is suggested.