472 research outputs found
Finite volume schemes for diffusion equations: introduction to and review of modern methods
We present Finite Volume methods for diffusion equations on generic meshes,
that received important coverage in the last decade or so. After introducing
the main ideas and construction principles of the methods, we review some
literature results, focusing on two important properties of schemes (discrete
versions of well-known properties of the continuous equation): coercivity and
minimum-maximum principles. Coercivity ensures the stability of the method as
well as its convergence under assumptions compatible with real-world
applications, whereas minimum-maximum principles are crucial in case of strong
anisotropy to obtain physically meaningful approximate solutions
Computational fluid dynamics for aerospace propulsion systems: an approach based on discontinuous finite elements
The purpose of this work is the development of a numerical tool devoted to the
study of the flow field in the components of aerospace propulsion systems. The
goal is to obtain a code which can efficiently deal with both steady and unsteady
problems, even in the presence of complex geometries.
Several physical models have been implemented and tested, starting from Euler
equations up to a three equations RANS model. Numerical results have been compared
with experimental data for several real life applications in order to understand
the range of applicability of the code. Performance optimization has been
considered with particular care thanks to the participation to two international
Workshops in which the results were compared with other groups from all over the
world.
As far as the numerical aspect is concerned, state-of-art algorithms have been implemented
in order to make the tool competitive with respect to existing softwares.
The features of the chosen discretization have been exploited to develop adaptive
algorithms (p, h and hp adaptivity) which can automatically refine the discretization.
Furthermore, two new algorithms have been developed during the research
activity. In particular, a new technique (Feedback filtering [1]) for shock capturing
in the framework of Discontinuous Galerkin methods has been introduced. It is
based on an adaptive filter and can be efficiently used with explicit time integration
schemes. Furthermore, a new method (Enhance Stability Recovery [2]) for
the computation of diffusive fluxes in Discontinuous Galerkin discretizations has
been developed. It derives from the original recovery approach proposed by van
Leer and Nomura [3] in 2005 but it uses a different recovery basis and a different
approach for the imposition of Dirichlet boundary conditions. The performed numerical
comparisons showed that the ESR method has a larger stability limit in
explicit time integration with respect to other existing methods (BR2 [4] and original
recovery [3]). In conclusion, several well known test cases were studied in order
to evaluate the behavior of the implemented physical models and the performance
of the developed numerical schemes
Spectral and High Order Methods for Partial Differential Equations ICOSAHOM 2018
This open access book features a selection of high-quality papers from the presentations at the International Conference on Spectral and High-Order Methods 2018, offering an overview of the depth and breadth of the activities within this important research area. The carefully reviewed papers provide a snapshot of the state of the art, while the extensive bibliography helps initiate new research directions
Multiresolution strategies for the numerical solution of optimal control problems
Optimal control problems are often characterized by discontinuities or switchings in the control variables. One way of accurately capturing the irregularities in the solution is to use a high resolution (dense) uniform grid. This requires a large amount of computational resources both in terms of CPU time and memory. Hence, in order to accurately capture any irregularities in the solution using a few computational resources, one can refine the mesh locally in the region close to an irregularity instead of refining the mesh uniformly over the whole domain. Therefore, a novel multiresolution scheme for data compression has been designed which is shown to outperform similar data compression schemes. Specifically, we have shown that the proposed approach results in fewer grid points in the grid compared to a common multiresolution data compression scheme.
The validity of the proposed mesh refinement algorithm has been verified by solving several challenging initial-boundary value problems for evolution equations in 1D. The examples have demonstrated the stability and robustness of the proposed algorithm. Next, a direct multiresolution-based approach for solving trajectory optimization problems is developed. The original optimal control problem is transcribed into a nonlinear programming (NLP) problem that is solved using standard NLP codes. The novelty of the proposed approach hinges on the automatic calculation of a suitable, nonuniform grid over which the NLP problem is solved, which tends to increase numerical efficiency and robustness. Control and/or state constraints are handled with ease, and without any additional computational complexity. The proposed algorithm is based on a simple and intuitive method to balance several conflicting objectives, such as accuracy of the solution, convergence, and speed of the computations. The benefits of the proposed algorithm over uniform grid implementations are demonstrated with the help of several nontrivial examples. Furthermore, two sequential multiresolution trajectory optimization algorithms for solving problems with moving targets and/or dynamically changing environments have been developed.Ph.D.Committee Chair: Tsiotras, Panagiotis; Committee Member: Calise, Anthony J.; Committee Member: Egerstedt, Magnus; Committee Member: Prasad, J. V. R.; Committee Member: Russell, Ryan P.; Committee Member: Zhou, Hao-Mi
Contributions to the development of residual discretizations for hyperbolic conservation laws with application to shallow water flows
In this work we review 12 years of developments in the field of residual based discretizations and their application to the solution of the shallow water equations. Fundamental concepts related to the topic are recalled and he construction of second and higher order schemes for steady problems is presented. The generalization to time dependent problems by means of multi-step implicit time integration, space-time, and genuinely explicit techniques is thoroughly discussed. Finally, the issues of C-property, super consistency, and wetting/drying are analyzed in this framework showing the power of the residual based approach
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