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Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

The Streamline Upwind/Petrov-Galerkin (SU/PG) method is applied to higher-order finite-element discretizations of the Euler equations in one dimension and the Navier-Stokes equations in two dimensions. The unknown flow quantities are discretized on meshes of triangular elements using triangular Bezier patches. The nonlinear residual equations are solved using an approximate Newton method with a pseudotime term. The resulting linear system is solved using the Generalized Minimum Residual algorithm with block diagonal preconditioning. The exact solutions of Ringleb flow and Couette flow are used to quantitatively establish the spatial convergence rate of each discretization. Examples of inviscid flows including subsonic flow past a parabolic bump on a wall and subsonic and transonic flows past a NACA 0012 airfoil and laminar flows including flow past a a flat plate and flow past a NACA 0012 airfoil are included to qualitatively evaluate the accuracy of the discretizations. The scheme achieves higher order accuracy without modification. Based on the test cases presented, significant improvement of the solution can be expected using the higher-order schemes with little or no increase in computational requirements. The nonlinear system also converges at a higher rate as the order of accuracy is increased for the same number of degrees of freedom; however, the linear system becomes more difficult to solve. Several avenues of future research based on the results of the study are identified, including improvement of the SU/PG formulation, development of more general grid generation strategies for higher order elements, the addition of a turbulence model to extend the method to high Reynolds number flows, and extension of the method to three-dimensional flows. An appendix is included in which the method is applied to inviscid flows in three dimensions. The three-dimensional results are preliminary but consistent with the findings based on the two-dimensional scheme. / Ph. D.

Ce travail porte sur le développement d’une nouvelle méthode numérique intitulée « Meshless local Petrov Galerkin (MLPG) combinée à la méthode des volumes finis (MVF) » appliquée au calcul de structures. Elle est basée sur la résolution de la forme faible des équations aux dérivées partielles par une méthode de Petrov Galerkin comme en éléments finis, mais par contre l’approximation du champ de déplacement introduite dans la forme faible ne nécessite pas de maillage. Seul un ensemble de nœuds est réparti dans le domaine et l’approximation du champ de déplacement en un point ne dépend que de la distance de ce point par rapport aux nœuds qui l’entourent et non de l’appartenance à un certain élément fini. Les déformations et les déplacements sont déterminés aux différents nœuds par interpolation locale en utilisant les moindres carrés mobiles (MLS). Les valeurs des déformations aux nœuds sont exprimées en termes de valeurs nodales interpolées indépendamment des déplacements, en imposant simplement la relation déformation déplacement directement par collocation aux points nodaux. La procédure de calcul pour cette méthode est implémentée dans un programme de calcul développé sous MATLAB. Le code obtenu a été validé sur un certain nombre de cas tests par comparaison avec des solutions analytiques de référence et des calculs éléments finis comme ABAQUS. L’ensemble de ces tests a montré un bon comportement de la méthode (environs 0.0001% d’erreurs par rapport à la solution exacte). L’approche est étendue pour l’étude des poutres minces et pour l’analyse dynamique et stabilité. / This work concerns the development of a new numerical method entitled “Meshless Local Petrov- Galerkin (MLPG) combined with the Finite Volumes Method (FVM)” applied to the structural analysis. It is based on the resolution of the weak form of the partial differential equations by a method of Petrov Galerkin as in finite elements, but the approximation of the field of displacement introduced into the weak form does not require grid. The displacements and strains are given with the various nodes by local interpolation by using moving least squares (MLS). The values of the nodal strains are expressed in terms of interpolated nodal values independently of displacements, by simply imposing the strain displacement relationship directly by collocation at the nodal points. The procedure of calculation for this method is implemented in a computer code developed in MATLAB. The developed code was validated on a certain number of test cases by comparison with analytical solutions and finite elements results like ABAQUS. The whole of these tests showed a good behaviour of the method (about 0.0001% of errors in compared to the exact solution). The approach is also extended for the study of the thin beams and the dynamic analysis and stability.

一維的無粘Burgers方程是最簡單的非線性雙曲守恆型方程，在本篇論文中，我們提出一個交錯間斷伽遼金方法去解Burgers方程。交錯間斷伽遼金方法融合了標準有限元方法和標準間斷伽遼金方法，此方法會求兩個間斷函數的解，而這對函數間斷的地方是不同的，所以在其中一個函數間斷的位置，另外的函數加強了該函數的連續性。對於Burgers方程來說，要求的解及通量組成了一對交錯對，我們將構造這個交錯間斷伽遼金格式和證明這格式是能量守恆的。 / 典型Burgers方程的解常存有衝擊波和間斷的地方，在這些情況下，我們的格式不再是能量守恆，並且出現了數值振蕩的問題，我們會提出兩個方案去除掉數值解中的數值振蕩。第一個方法是把一個人工的擴散性通量加在數值格式裏，這個人工的擴散性通量是從一個解粘性Burgers方程的交錯間斷伽遼金格式中求得的，這個格式的構造過程跟構造原格式的過程是類似的。為確保數值解的準確度，擴散性通量只會在存有數值振蕩的地方才加上。第二個方法是一個全變差正則化方法，在某些保留數值解的準確性的條件下，振蕩性數值解的全變差會被減至最小。這個步驟只用於存在振蕩的地方，以減小計算成本和多餘的誤差。另外，處理最小化問題時會用到Bregman算法。本篇論文將記述有關這兩個方法的細節和數值驗証。 / The 1D inviscid Burgers' equation is the simplest nonlinear hyperbolic conservation law. In this thesis, a staggered discontinuous Galerkin method for the Burgers' equation is proposed. Staggered discontinuous Galerkin method is a kind of DG method that compromise conforming finite element method and standard DG method. Two unknown functions that are discontinuous at different points are solved, thus extra continuity is imposed at the points of discontinuity of the discontinuous function by the staggered counter part. For the Burgers' equation, the unknown function and the flux form the staggered pair. We will derive this staggered DG scheme and show that the scheme is energy conserving. / Typical problems concerning the Burgers' equation involve shock waves and discontinuous solutions. In such cases, the scheme is no longer energy conserving and the problem of numerical oscillations arises. Two approaches are presented to eliminate the numerical oscillations in the solution. The rst one is based on adding an artificial diffusive flux to the scheme. The artificial diffusive flux is derived from a staggered DG scheme for the viscid Burgers' equation for which the derivation is similar. To preserve accuracy, the artificial diffusive flux is added only at regions with oscillations. The second approach is a TV regularization method. The total variation of the oscillatory numerical solution is minimized under certain constraints that preserve the accuracy of the solution. To reduce computation cost and redundant error, the TV minimization process is induced locally in regions with oscillations. Bregman algorithm is applied for numerical implementation of the minimization problem. Detailed description of the two methods and the numerical results are presented in this thesis. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Chan, Hiu Ning. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2012. / Includes bibliographical references (leaves 71-73). / Abstracts also in Chinese. / Chapter 1 --- Introduction --- p.7 / Chapter 2 --- Inviscid scheme --- p.10 / Chapter 2.1 --- Space discretization and element spaces --- p.10 / Chapter 2.2 --- Derivationofinviscidscheme --- p.11 / Chapter 2.3 --- Conservationofenergy --- p.13 / Chapter 2.4 --- Piecewiseconstantcase --- p.17 / Chapter 2.5 --- Problemwithdiscontinuity --- p.18 / Chapter 3 --- Mixed method --- p.21 / Chapter 3.1 --- Viscidscheme --- p.22 / Chapter 3.1.1 --- Derivation of viscid scheme --- p.22 / Chapter 3.1.2 --- Conservationofenergy --- p.24 / Chapter 3.1.3 --- Piecewiseconstantcase --- p.26 / Chapter 3.2 --- Relations between the inviscid scheme and the viscid scheme --- p.27 / Chapter 3.3 --- Mixed method with piecewise constant elements --- p.32 / Chapter 3.4 --- Mixed method with piecewise linear elements --- p.35 / Chapter 3.5 --- Numericalresults --- p.40 / Chapter 3.5.1 --- Figures --- p.40 / Chapter 3.5.2 --- Error --- p.49 / Chapter 4 --- A local TV regularization method --- p.56 / Chapter 4.1 --- LocalTVminimizationproblem --- p.56 / Chapter 4.2 --- Oscillationvector --- p.57 / Chapter 4.3 --- Methoddescription --- p.59 / Chapter 4.4 --- Implementation --- p.61 / Chapter 4.5 --- Remarkon’global’method --- p.63 / Chapter 4.6 --- Numericalresults --- p.63 / Chapter 5 --- Conclusion --- p.69 / Bibliography --- p.71

published_or_final_version / Civil and Structural Engineering / Master / Master of Philosophy

Thesis (Ph.D.)--University of Tulsa, 1975. / Bibliography: leaves 38-43.

Zugl.: Heidelberg, Univ., Habil.-Schr., 2004. / Also available in print.

Zugl.: Heidelberg, University, Habil.-Schr., 2004. / Description based on print version record.