A Freestream-Preserving High-Order Finite-Volume Method for Mapped Grids with Adaptive-Mesh Refinement PDF Download
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Author:
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ISBN:
Category :
Languages : en
Pages : 12
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Book Description
A fourth-order accurate finite-volume method is presented for solving time-dependent hyperbolic systems of conservation laws on mapped grids that are adaptively refined in space and time. Novel considerations for formulating the semi-discrete system of equations in computational space combined with detailed mechanisms for accommodating the adapting grids ensure that conservation is maintained and that the divergence of a constant vector field is always zero (freestream-preservation property). Advancement in time is achieved with a fourth-order Runge-Kutta method.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 12
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Book Description
A fourth-order accurate finite-volume method is presented for solving time-dependent hyperbolic systems of conservation laws on mapped grids that are adaptively refined in space and time. Novel considerations for formulating the semi-discrete system of equations in computational space combined with detailed mechanisms for accommodating the adapting grids ensure that conservation is maintained and that the divergence of a constant vector field is always zero (freestream-preservation property). Advancement in time is achieved with a fourth-order Runge-Kutta method.
Author: Pawel Buchmüller
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Author: Xueshang Feng
Publisher: Springer
ISBN: 9811390819
Category : Science
Languages : en
Pages : 772
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Book Description
The book covers intimately all the topics necessary for the development of a robust magnetohydrodynamic (MHD) code within the framework of the cell-centered finite volume method (FVM) and its applications in space weather study. First, it presents a brief review of existing MHD models in studying solar corona and the heliosphere. Then it introduces the cell-centered FVM in three-dimensional computational domain. Finally, the book presents some applications of FVM to the MHD codes on spherical coordinates in various research fields of space weather, focusing on the development of the 3D Solar-InterPlanetary space-time Conservation Element and Solution Element (SIP-CESE) MHD model and its applications to space weather studies in various aspects. The book is written for senior undergraduates, graduate students, lecturers, engineers and researchers in solar-terrestrial physics, space weather theory, modeling, and prediction, computational fluid dynamics, and MHD simulations. It helps readers to fully understand and implement a robust and versatile MHD code based on the cell-centered FVM.
Author: Joe Antoine Rached
Publisher:
ISBN:
Category :
Languages : en
Pages : 266
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Book Description
The aim of this thesis is divided into two parts. The first part consists of imp lementing and testing the accuracy of polygonal grids in the Finite Volume Metho d (FVM) context, a method usually used in Computational Fluid Mechanics (CFD). T he use of polygonal elements instead of triangular or quadrilateral elements lie s behind the nature of the FVM, which adapts to any Control Volume (CV) shape. P ure advection and real flow test cases were conducted for this end. Results show ed that more insight should be made in developing a tailored differencing scheme to be used on polygonal grids. The accuracy was acceptable but the solution tim e was not enhanced. The second part of this thesis is to implement Adaptive Mesh Refinement (AMR) us ing the hanging nodes method, a technique that resolves cells in regions where n eeded. Since the computational cost is directly related to the number of element s used in the numerical simulation, AMR is capable of automatically refining the grid where large gradients are present and hence the accuracy of the solution i s increased with less computational cost and time, compared to uniform refinemen t. Mesh refinement alone is not sufficient because previously refined grids migh t not be needed anymore, especially in transient problems. To this end, a new me sh coarsening method was developed in order to decrease the density of the grid in regions where large gradients are not present anymore. AMR and Coarsening (AM RC) are usually implemented in a tree-structure, using a children-parent sort of linkage. In the developed method, the tree structure is abandoned and AMRC is d one locally without the need to store the history of the refined element. In order to speed up the simulation on adapted grids, a good initial guess on th e refined grid is needed. To this end, the solution of the original grid is mapp ed on the initial grid, leading to less time and computational cost in reaching a converged solution. Pure advection and real flow problems for fluid flows at a ll speeds where conducted. The method proves accuracy especially in the compress ible flow regime.
Author: Lucian Ivan
Publisher:
ISBN: 9780494778326
Category :
Languages : en
Pages :
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Author: Jenmy Zimi Zhang
Publisher:
ISBN: 9780494766118
Category :
Languages : en
Pages : 224
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Book Description
A novel anisotropic adaptive mesh refinement (AMR) technique is proposed and de- scribed. A block-based AMR approach is used which permits highly efficient and scalable implementations on parallel computer architectures and the use of multi-block, body-fitted computational grids for the treatment of complex geometries. However, rather than adopting the more usual isotropic approach to the refinement of the grid blocks, the proposed approach uses a binary hierarchical tree data structure that allows for anisotropic refinement of the grid blocks in each of the coordinate directions in an inde- pendent fashion. This allows for more efficient and accurate treatment of narrow layers, discontinuities, and/or shocks in the solutions which occur, for example, in the thin boundary and mixing layers of high-Reynolds-number viscous flows and in the regions of strong non-linear wave interactions of high-speed compressible flows with shocks. The anisotropic AMR technique is implemented within an existing finite-volume framework, which encompasses both explicit and implicit solution methods, and is capable of per- forming calculations with both second- and higher-order spatial accuracy. To clearly demonstrate the potential and feasibility of the proposed AMR technique, it is applied to the unsteady and steady-state solutions of both a model system, the advection diffusion equation, as well as the Euler equations governing compressible, inviscid, gaseous flows, both in two space dimensions.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages : 29
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We present a fourth-order accurate finite-volume method for solving time-dependent hyperbolic systems of conservation laws on Cartesian grids with multiple levels of refinement. The underlying method is a generalization of that in [5] to nonlinear systems, and is based on using fourth-order accurate quadratures for computing fluxes on faces, combined with fourth-order accurate Runge?Kutta discretization in time. To interpolate boundary conditions at refinement boundaries, we interpolate in time in a manner consistent with the individual stages of the Runge-Kutta method, and interpolate in space by solving a least-squares problem over a neighborhood of each target cell for the coefficients of a cubic polynomial. The method also uses a variation on the extremum-preserving limiter in [8], as well as slope flattening and a fourth-order accurate artificial viscosity for strong shocks. We show that the resulting method is fourth-order accurate for smooth solutions, and is robust in the presence of complex combinations of shocks and smooth flows.
Author: Andrew Giuliani
Publisher:
ISBN:
Category : Conservation laws (Mathematics)
Languages : en
Pages :
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This thesis is concerned with the parallel, adaptive solution of hyperbolic conservation laws on unstructured meshes. First, we present novel algorithms for cell-based adaptive mesh refinement (AMR) on unstructured meshes of triangles on graphics processing units (GPUs). Our implementation makes use of improved memory management techniques and a coloring algorithm for avoiding race conditions. The algorithm is entirely implemented on the GPU, with negligible communication between device and host. We show that the overhead of the AMR subroutines is small compared to the high-order solver and that the proportion of total run time spent adaptively refining the mesh decreases with the order of approximation. We apply our code to a number of benchmarks as well as more recently proposed problems for the Euler equations that require extremely high resolution. We present the solution to a shock reflection problem that addresses the von Neumann triple point paradox. We also study the problem of shock disappearance and self-similar diffraction of weak shocks around thin films. Next, we analyze the stability and accuracy of second-order limiters for the discontinuous Galerkin method on unstructured triangular grids. We derive conditions for a limiter such that the numerical solution preserves second order accuracy and satisfies the local maximum principle. This leads to a new measure of cell size that is approximately twice as large as the radius of the inscribed circle. It is shown with numerical experiments that the resulting bound on the time step is tight. We also consider various combinations of limiting points and limiting neighborhoods and present numerical experiments comparing the accuracy, stability, and efficiency of the corresponding limiters. We show that the theory for strong stability preserving (SSP) time stepping methods employed with the method of lines-type discretizations of hyperbolic conservation laws may result in overly stringent time step restrictions. We analyze a fully discrete finite volume method with slope reconstruction and a second order SSP Runge-Kutta time integrator to show that the maximum stable time step can be increased over the SSP limit. Numerical examples show that this result extends to two-dimensional problems on triangular meshes. Finally, we propose a moment limiter for the discontinuous Galerkin method applied to hyperbolic conservation laws in two and three dimensions. The limiter works by finding directions in which the solution coefficients can be separated and limits them independently of one another by comparing to forward and backward reconstructed differences. The limiter has a precomputed stencil of constant size, which provides computational advantages in terms of implementation and runtime. We provide examples that demonstrate stability and second order accuracy of solutions.
Author: Shawn Shamendra Prasad
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Kui Ou
Publisher:
ISBN:
Category :
Languages : en
Pages :
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A comprehensive study of discontinuous finite element based high-order methods has been performed in this thesis, addressing a wide range of important issues related to high-order methods. The thesis starts with a detailed discussion of nodal based high-order methods and careful analysis of their stability properties. In particular, the formulations of nodal Discontinuous Galerkin method, Spectral Difference method, and Flux Reconstruction method for the scalar conservation laws are discussed first. The differences and similarities among these high-order schemes are carefully examined and effectively used to establish the linear stability of these methods. Stability proofs of nodal Discontinuous Galerkin method, Spectral Difference method, and Flux Reconstruction method subsequently lead to a new type of energy stable high-order scheme called Energy Stable Flux Reconstruction scheme. The extension of this new scheme from linear advection equation to the diffusion equation is formulated and discussed. The fundamental study of the high-order methods for scalar conservation laws lays the theoretical foundation for the subsequent extension to include conservation laws for fluid dynamics. The formulation of spectral difference method for the Navier-Stokes equations is first discussed. Validation tests to verify the resulting flow solver are presented. The extension of the spectral difference based Navier-Stokes flow solver from static fixed computational mesh to include dynamic moving deforming mesh is discussed next. An efficient mesh deformation algorithm that can handle substantial boundary movement is proposed and examined. The invariance of conservation laws mapping between coordinate systems allows the high-order scheme to be formulated on dynamic deforming meshes without deteriorating the formal order of accuracy of the underlying scheme. Detailed formulation, analysis, and validation results are presented. As a result of mesh deformation, the issue of geometric conservation needs to be addressed. The definition and origin of the geometric conservation law are discussed. The differential form of the geometric conservation law is derived from first principles for both the scalar conservation law and the fluid dynamic conservation laws. Subsequently a geometric conservative high-order scheme is formulated. The significance of geometric conservation on the stability and accuracy of the flow solution is examined. Finally a wide range of interesting fluid dynamic phenomena have been studied using the resulting high-order flow solver based on dynamic unstructured meshes. The representative test cases cover fluid dynamic phenomena ranging from completely laminar flows, to unsteady vortex dominated flows, and to flows exhibiting mixed regions of laminar, transitional, and turbulent structures. Other work that has been completed in this thesis is included in the appendix. In particular, continuous unsteady adjoint equations for advection and Burger's equations have been derived and solved using the high-order methods. The method of mesh deformation is reformulated as an optimization problem and used to achieve adaptive mesh refinement.
