In the present work we implemented parallel version of a computational fluid dynamics code. This code is based on Discontinuous Galerkin Method (DGM), which is due to its favourable properties suitable for parallelization. In the work we describe the Navier-Stokes equations and their discretization using DGM. We explain the advantages of usage of the DGM and formulate the serial algorithm. Next we focus on the parallel implementation of the algorithm and several particular issues connected to the parallelization. We present the numerical experiments showing the efficiency of the parallel code in the last chapter.

This thesis is concerned on the simulation of wet steam flow using discontinuous Galerkin method. Wet steam flow equations consist of Naviere-Stokes equations for compressible flow and Hill's equations for condensation of water vapor. The first part of this thesis describes the mathematical formulation of wet steam model and the derivation of Hill's equations. The model equations are discretized with the aid of discontinuous Galerkin method and backward difference formula which leads to implicit scheme represented by nonlinear algebraic system. This system is solved using Newton-like method. The derived scheme was implemented in program ADGFEM which is used for solving non-stationary convective-diffusive problems. The numerical results are presented in the last part of this thesis. 1

O presente trabalho de pesquisa tem por objetivo estudar a paralelização de algoritmos voltados à solução de equações diferenciais parciais. Esses algoritmos são utilizados para gerar a solução numérica das equações de Navier-Stokes em um escoamento bidimensional incompressível de um fluido newtoniano. As derivadas espaciais são calculadas através de um método de diferenças finitas compactas com a utilização de aproximações de altas ordens de precisão. Uma vez que o cálculo de derivadas espaciais com alta ordem de precisão da forma compacta adotado no presente estudo requer a solução de sistemas lineares tridiagonais, é importante realizar estudos voltados a resolução desses sistemas, para se obter uma boa performance. Ressalta-se ainda que a solução de sistemas lineares também faz-se presente na solução numérica da equação de Poisson. Os resultados obtidos decorrentes da solução das equações diferenciais parciais são comparados com os resultados onde se conhece a solução analítica, de forma a verificar a precisão dos métodos implementados. Os resultados do código voltado à resolução das equações de Navier-Stokes paralelizado para simulação de escoamentos incompressíveis são comparados com resultados da teoria de estabilidade linear, para validação do código final. Verifica-se a performance e o speedup do código em questão, comparando-se o tempo total gasto em função do número de elementos de processamento utilizados / The objective of the present work is to study the parallelization of partial differential equations. The aim is to achieve an effective parallelization to generate numerical solution of Navier-Stokes equations in a two-dimensional incompressible and isothermal flow of a Newtonian fluid. The spatial derivatives are calculated using compact finite differences approximations of higher order accuracy. Since the calculation of spatial derivatives with high order adopted in the present work requires the solution of tridiagonal systems, it is important to conduct studies to solve these systems and achieve good performance. In addiction, linear systems solution is also present in the numerical solution of a Poisson equation. The results generated by the solution of partial differential equations are compared to analytical solution, in order to verify the accuracy of the implemented methods. The numerical parallel solution of a Navier-Stokes equations is compared with linear stability theory to validate the final code. The performance and the speedup of the code in question is also checked, comparing the execution time in function of the number of processing elements

Orientador: João Batista Campos Silva / Banca: Cassio Roberto Macedo Maia / Banca: Elcio Nogueira / Resumo: Neste trabalho, desenvolveu-se, implementou e testou-se um modelo numérico para simular escoamentos incompressíveis de fluidos viscosos em regime transiente, usando o Método de Elementos Finitos baseado em Volumes de Controle (CVFEM) para a discretização espacial e o Método de Passo Fracionado (time-splitting) para a discretização temporal, levando em consideração as características parabólicas, elípticas e hiperbólicas das equações de Navier-Stokes. Para a implementação computacional do método numérico, foi desenvolvido um código em linguagem fortran para simulação dos escoamentos. Depois da obtenção do código computacional e verificada a estabilidade e convergência da técnica de passo fracionado, foram feitas aplicações para simulação de casos de escoamentos internos em cavidades. Também insvestigou-se o modelo de viscosidade turbulenta de Smagorinsky com o CVFEM em passo fracionado, através da metodologia de Simulação de Grandes Escalas (LES - Large Eddy Simulation). / Abstract: In this work, the main purpose has been the development, implementation and test of a numeric model to simulate unsteady, incompressible, viscous fluid flows. The Finite Element Method based on Volumes of Control (CVFEM) has been used for the space discretization and the Fractional Step Method (time-splitting) for the time discretization, taking in consideration the parabolic, elliptic and hyperbolic characteristics of Navier-Stokes equation. For the computational implementation of the numeric method, it was developed a computational code in fortran language. After obtaining the computational code and verified the stability and convergence of the technique of fractional step, simulations for the lid-driven cavity flow have been done for low Reynolds number. The turbulence effect has been considered by the model of turbulent viscosity of Smagorinsky with CVFEM in fractional step, through the methodology of Large Eddy Simulation. / Mestre

Dans cette thèse nous étudions trois modèles décrivant la dynamique de l’écoulement d’un fluide à densité variable, dans des échelles spatio-temporelles grandes. Dans ce cadre, le mouvement relatif induit par des forces extérieures,comme la force de Coriolis ou la poussée hydrostatique, s’avère être beaucoup plus important que le mouvement intrinsèque du fluide induit par le transport des particules. Une tel déséquilibre contraint ainsi le mouvement, induisant des structures persistantes dans l’écoulement du fluide.D’un point de vue mathématique, l’une des difficultés consiste en l’étude des perturbations induites par les forces extérieures, qui se propagent à grande vitesse.Ce type d’analyse peut être effectué au moyen de plusieurs outils mathématiques ;on choisit ici d’employer des techniques caractéristiques de l’analyse de Fourier,comme l’analyse des propriétés dispersives des intégrales oscillantes.Tout au long de cette thèse, on se restreint à considérer des domaines spatiaux sans frontière : c’est le cas de l’espace entier, ou encore de l’espace périodique. Les modèles considérés sont donc les suivants: équations primitives dont les nombres de Froude et de Rossby sont comparables,et pour lesquelles la diffusion verticale est nulle, fluides stratifiés dans un régime à faible nombre de Froude, fluides faiblement compressibles et tournants dans un régime où les nombres de Mach et de Rossby sont comparables.On prouve que ces systèmes propagent globalement dans le temps des donnés peu régulières. Nous n’imposons jamais de condition de petitesse sur les données initiales. Toutefois, on prendra en compte certaines hypothèses spécifiques de régularité, lorsque des raisons techniques l’imposent. / In this thesis we discuss three models describing the dynamics of density-dependent fluids in long lifes pans and on a planetary scale. In such setting the relative displacement induced by various external physical forces, such as the Coriolis force and the stratification buoyancy, is far more relevant than the intrinsic motion generated by the collision of particles of the fluid itself. Such disproportion of balance limits hence the motion, inducing persistent structures in the velocity flow.On a mathematical level one of the main difficulties relies in giving a full description of the perturbations induced by the external forces, which propagate at high speed. This analysis can be performed by the aid of several tools, we chose here to adopt techniques characteristic of harmonic analysis, such as the analysis of the dispersive properties of highly oscillating integrals.All along the thesis we consider boundary-free, three-dimensional domains, and inspecific we study only the case in which the domain in either the whole space or the periodic space . The models we consider are the following ones : primitive equations with comparable Froude and Rossby number and zero vertical diffusivity, density-dependent stratified fluids in low Froude number regime, weakly compressible and fast rotating fluid in a regime in which Mach and Rossbynumber are comparable. We prove that these systems propagate globally-in-time data with low-regularity. Nosmallness assumption is ever made, specific constructive hypothesis are assumed on the initial data when required.

The Seattle District wants to better manage the Ballard Locks and structures along the Lake Washington Ship Canal (LWSC) in a way that will maintain the environmental sustainability and biodiversity in the area. Due to strict salt water intrusion regulations in the LWSC, the Seattle District is working on upgrading their management practices such that they will resolve two inter-related problems. First, to improve the fish passage conditions for migrating salmon; and second, to learn how to better manage the salt wedge that forms and intrudes upstream. Based on the hydrodynamic and water quality results that are produced by this research, the Engineer Research and Development Center (ERDC) Portland Office will use their Eulerian-Lagrangian-Agent-Model (ELAM) to analyze fish patterns, looking for the most beneficial management schemes that assist salmon in migrating upstream. This research implemented CFD engineering techniques to help better understand the effectiveness of the hydraulic structures in the area, as well as come up with management practices that both mitigate the salt water intrusion from Puget Sound, and improve the migrating passages for salmon.

<p>This thesis describes a system for dealing with free surface fluid simulations, and the components needed in order to construct such a system. It builds upon recent research, but in a computer graphics context the amount of available literature is limited and difficult to implement. Because of this, the text aims at providing a solid foundation of the mathematics needed, at explaining in greater detail the steps needed to solve the problem, and lastly at improving some aspects of the animation process as it has been described in earlier works. </p><p>The aim of the system itself is to provide visually plausible renditions of animated fluids in three dimensions in a manner that allows it to be usable in a visual effects production context. </p><p>The novel features described include a generalized interaction layer providing greater control to artists, a new way of dealing with moving objects that interact with the fluid and a method for adding source and drain capabilities.</p>

Control of the transition of laminar flow to turbulence would result in lower drag and reduced energy consumption in many engineering applications. A spectral state-space model of linearised plane Poiseuille flow with wall transpiration ac¬tuation and wall shear measurements is developed from the Navier-Stokes and continuity equations, and optimal controllers are synthesized and assessed in sim¬ulations of the flow. The polynomial-form collocation model with control by rate of change of wall-normal velocity is shown to be consistent with previous interpo¬lating models with control by wall-normal velocity. Previous methods of applying the Dirichlet and Neumann boundary conditions to Chebyshev series are shown to be not strictly valid. A partly novel method provides the best numerical behaviour after preconditioning. Two test cases representing the earliest stages of the transition are consid¬ered, and linear quadratic regulators (LQR) and estimators (LQE) are synthesized. Finer discretisation is required for convergence of estimators. A novel estimator covariance weighting improves estimator transient convergence. Initial conditions which generate the highest subsequent transient energy are calculated. Non-linear open- and closed-loop simulations, using an independently derived finite-volume Navier-Stokes solver modified to work in terms of perturbations, agree with linear simulations for small perturbations. Although the transpiration considered is zero net mass flow, large amounts of fluid are required locally. At larger perturbations the flow saturates. State feedback controllers continue to stabilise the flow, but estimators may overshoot and occasionally output feedback destabilises the flow. Actuation by simultaneous wall-normal and tangential transpiration is derived. There are indications that control via tangential actuation produces lower highest transient energy, although requiring larger control effort. State feedback controllers are also synthesized which minimise upper bounds on the highest transient energy and control effort. The performance of these controllers is similar to that of the optimal controllers.

Aquesta tesi doctoral proposa formulacions de Galerkin discontinu (DG) d'alt ordre per fluxos viscosos incompressibles. Es desenvolupa un nou mètode de DG amb penalti interior (IPM-DG), que condueix a una forma feble simètrica i coerciva pel terme de difusió, i que permet assolir una aproximació espacial d'alt ordre. Aquest mètode s'aplica per resoldre les equacions de Stokes i Navier-Stokes. L'espai d'aproximació de la velocitat es descompon dins de cada element en una part solenoidal i una altra irrotacional, de manera que es pot dividir la forma dèbil IPM-DG en dos problemes desacoblats. El primer permet el càlcul de les velocitats i de les pressions híbrides, mentre que el segon calcula les pressions en l'interior dels elements. Aquest desacoblament permet una reducció important del número de graus de llibertat tant per velocitat com per pressió. S'introdueix també un paràmetre extra de penalti resultant en una formulació DG alternativa per calcular les velocitats solenoidales, on les pressions no apareixen. Les pressions es poden calcular com un post-procés de la solució de les velocitats. Es contemplen altres formulacions DG, com per exemple el mètode Compact Discontinuous Galerkin, i es comparen al mètode IPM-DG. Es proposen mètodes implícits de Runge-Kutta d'alt ordre per problemes transitoris incompressibles, permetent obtenir esquemes incondicionalment estables i amb alt ordre de precisió temporal. Les equacions de Navier-Stokes incompressibles transitòries s'interpreten com un sistema de Equacions Algebraiques Diferencials, és a dir, un sistema d'equacions diferencials ordinàries corresponent a la equació de conservació del moment, més les restriccions algebraiques corresponent a la condició d'incompressibilitat. Mitjançant exemples numèrics es mostra l'aplicabilitat de les metodologies proposades i es comparen la seva eficiència i precisió. / This PhD thesis proposes divergence-free Discontinuous Galerkin formulations providing high orders of accuracy for incompressible viscous flows. A new Interior Penalty Discontinuous Galerkin (IPM-DG) formulation is developed, leading to a symmetric and coercive bilinear weak form for the diffusion term, and achieving high-order spatial approximations. It is applied to the solution of the Stokes and Navier-Stokes equations. The velocity approximation space is decomposed in every element into a solenoidal part and an irrotational part. This allows to split the IPM weak form in two uncoupled problems. The first one solves for velocity and hybrid pressure, and the second one allows the evaluation of pressures in the interior of the elements. This results in an important reduction of the total number of degrees of freedom for both velocity and pressure. The introduction of an extra penalty parameter leads to an alternative DG formulation for the computation of solenoidal velocities with no presence of pressure terms. Pressure can then be computed as a post-process of the velocity solution. Other DG formulations, such as the Compact Discontinuous Galerkin method, are contemplated and compared to IPM-DG. High-order Implicit Runge-Kutta methods are then proposed to solve transient incompressible problems, allowing to obtain unconditionally stable schemes with high orders of accuracy in time. For this purpose, the unsteady incompressible Navier-Stokes equations are interpreted as a system of Differential Algebraic Equations, that is, a system of ordinary differential equations corresponding to the conservation of momentum equation, plus algebraic constraints corresponding to the incompressibility condition. Numerical examples demonstrate the applicability of the proposed methodologies and compare their efficiency and accuracy.

We consider the stabilized finite element method for solving the incompressible Navier-Stokes equations and the magnetohydrodynamic (MHD) equations in two dimensions. The well-known instabilities arising from the application of standard Galerkin finite element method are eliminated by using the stabilizing subgrid method (SSM), the streamline upwind Petrov-Galerkin (SUPG) method, and the two-level finite element method (TLFEM). The domain is discretized into a set of regular triangular elements. In SSM, the finite-dimensional spaces employed consist of piecewise continuous linear interpolants enriched with the residual-free bubble functions. To find the bubble part of the solution, a two-level finite element method with a stabilizing subgrid of a single node is described and its applications to the Navier-Stokes equations and MHD equations are displayed. This constitutes the main original contribution of this thesis. Numerical approximations employing the proposed algorithms are presented for some benchmark problems. The results show that the proper choice of the subgrid node is crucial to get stable and accurate numerical approximations consistent with the physical configuration of the problem at a cheap computational cost. The stabilized finite element method of SUPG type is applied to the unsteady Navier-Stokes equations together with a finite element discretization in the time domain. Thus, oscillations in the solution and the need of very small time increment are avoided in obtaining stable solutions.