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A Parallel High Order Discontinuous Galerkin Solver For The Unsteady Incompressible Navier Stokes Equations In Complex Geometries
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Book Synopsis A Parallel High-order Discontinuous Galerkin Solver for the Unsteady Incompressible Navier-Stokes Equations in Complex Geometries by : Khosro Shahbazi
Download or read book A Parallel High-order Discontinuous Galerkin Solver for the Unsteady Incompressible Navier-Stokes Equations in Complex Geometries written by Khosro Shahbazi and published by . This book was released on 2007 with total page 288 pages. Available in PDF, EPUB and Kindle. Book excerpt: We verify the accuracy and stability of the method on several two- and three-dimensional benchmarking problems. On the challenging Orr-Sommerfeld test problem, the equal-order polynomial approximation of the velocity and pressure (Pk - Pk) leads to a stable and accurate solution, while the mixed-order method (Pk - Pk-1) yields a non-physical instability. In simulating vortex shedding past a square cylinder at Re = 100 and in simulating a three-dimensional backward-facing step flow using the equal-order method, excellent agreement with other computational and experimental results are obtained. The developed solver is used to study flow through a two-dimensional bileaflet mechanical heart valve geometry. We conclude that the proposed discontinuous Galerkin method with the Pk - Pk formulation is a suitable scheme for simulations of flows through mechanical heart valve geometries. We develop a parallel method and corresponding code for the numerical solution of the unsteady incompressible Navier-Stokes equations, with application to the direct numerical simulation of transitional and turbulent flows through mechanical heart valves. The solver is based on a simple and efficient scheme, namely a high-order discontinuous Galerkin method on triangular and tetrahedral elements. Spatial discretization of the Stokes operator employed both equal-order (Pk - Pk) and mixed-order (Pk - Pk-1) velocity and pressure approximations. The interior penalty method and local Lax-Friedrichs fluxes are used for the discretizations of the viscous term and the nonlinear term in the divergence form, respectively. A second order approximate algebraic splitting is used to decouple the velocity and pressure calculations leading to an algebraic Helmholtz equation for each component of the velocity and a consistent Poisson equation for the pressure. The consistent Poisson operator is replaced by an equivalent operator, namely that arising from the interior penalty discretization of the standard Poisson operator with appropriate boundary conditions. An explicit lower bound is derived for the penalty parameter of the interior penalty method that ensures the coercivity of the bilinear form. Efficiency aspects of the scheme include knowing an explicit expression for the penalty parameter of the interior penalty method and compact stencil size for the discretizations of the velocity and pressure equations and the nonlinear term.
Book Synopsis A High Order Discontinuous Galerkin - Fourier Incompressible 3D Navier-Stokes Solver with Rotating Sliding Meshes for Simulating Cross-flow Turbines by : Esteban Ferrer
Download or read book A High Order Discontinuous Galerkin - Fourier Incompressible 3D Navier-Stokes Solver with Rotating Sliding Meshes for Simulating Cross-flow Turbines written by Esteban Ferrer and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis details the development, verification and validation of an unsteady unstructured high order (≥ 3) h/p Discontinuous Galerkin - Fourier solver for the incompressible Navier-Stokes equations on static and rotating meshes in two and three dimensions. This general purpose solver is used to provide insight into cross-flow (wind or tidal) turbine physical phenomena. Simulation of this type of turbine for renewable energy generation needs to account for the rotational motion of the blades with respect to the fixed environment. This rotational motion implies azimuthal changes in blade aero/hydro-dynamics that result in complex flow phenomena such as stalled flows, vortex shedding and blade-vortex interactions. Simulation of these flow features necessitates the use of a high order code exhibiting low numerical errors. This thesis presents the development of such a high order solver, which has been conceived and implemented from scratch by the author during his doctoral work. To account for the relative mesh motion, the incompressible Navier-Stokes equations are written in arbitrary Lagrangian-Eulerian form and a non-conformal Discontinuous Galerkin (DG) formulation (i.e. Symmetric Interior Penalty Galerkin) is used for spatial discretisation. The DG method, together with a novel sliding mesh technique, allows direct linking of rotating and static meshes through the numerical fluxes. This technique shows spectral accuracy and no degradation of temporal convergence rates if rotational motion is applied to a region of the mesh. In addition, analytical mappings are introduced to account for curved external boundaries representing circular shapes and NACA foils. To simulate 3D flows, the 2D DG solver is parallelised and extended using Fourier series. This extension allows for laminar and turbulent regimes to be simulated through Direct Numerical Simulation and Large Eddy Simulation (LES) type approaches. Two LES methodologies are proposed. Various 2D and 3D cases are presented for laminar and turbulent regimes. Among others, solutions for: Stokes flows, the Taylor vortex problem, flows around square and circular cylinders, flows around static and rotating NACA foils and flows through rotating cross-flow turbines, are presented.
Book Synopsis International Aerospace Abstracts by :
Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 974 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Nodal Discontinuous Galerkin Methods by : Jan S. Hesthaven
Download or read book Nodal Discontinuous Galerkin Methods written by Jan S. Hesthaven and published by Springer Science & Business Media. This book was released on 2007-12-18 with total page 507 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book offers an introduction to the key ideas, basic analysis, and efficient implementation of discontinuous Galerkin finite element methods (DG-FEM) for the solution of partial differential equations. It covers all key theoretical results, including an overview of relevant results from approximation theory, convergence theory for numerical PDE’s, and orthogonal polynomials. Through embedded Matlab codes, coverage discusses and implements the algorithms for a number of classic systems of PDE’s: Maxwell’s equations, Euler equations, incompressible Navier-Stokes equations, and Poisson- and Helmholtz equations.
Book Synopsis Discontinuous Galerkin Solution of the Navier-Stokes Equations on Deformable Domains by :
Download or read book Discontinuous Galerkin Solution of the Navier-Stokes Equations on Deformable Domains written by and published by . This book was released on 2009 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: We describe a method for computing time-dependent solutions to the compressible Navier-Stokes equations on variable geometries. We introduce a continuous mapping between a fixed reference configuration and the time varying domain, By writing the Navier-Stokes equations as a conservation law for the independent variables in the reference configuration, the complexity introduced by variable geometry is reduced to solving a transformed conservation law in a fixed reference configuration, The spatial discretization is carried out using the Discontinuous Galerkin method on unstructured meshes of triangles, while the time integration is performed using an explicit Runge-Kutta method, For general domain changes, the standard scheme fails to preserve exactly the free-stream solution which leads to some accuracy degradation, especially for low order approximations. This situation is remedied by adding an additional equation for the time evolution of the transformation Jacobian to the original conservation law and correcting for the accumulated metric integration errors. A number of results are shown to illustrate the flexibility of the approach to handle high order approximations on complex geometries.
Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1994 with total page 390 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Fast and Scalable Solvers for High-order Hybridized Discontinuous Galerkin Methods with Applications to Fluid Dynamics and Magnetohydrodynamics by : Sriramkrishnan Muralikrishnan
Download or read book Fast and Scalable Solvers for High-order Hybridized Discontinuous Galerkin Methods with Applications to Fluid Dynamics and Magnetohydrodynamics written by Sriramkrishnan Muralikrishnan and published by . This book was released on 2019 with total page 498 pages. Available in PDF, EPUB and Kindle. Book excerpt: The hybridized discontinuous Galerkin methods (HDG) introduced a decade ago is a promising candidate for high-order spatial discretization combined with implicit/implicit-explicit time stepping. Roughly speaking, HDG methods combines the advantages of both discontinuous Galerkin (DG) methods and hybridized methods. In particular, it enjoys the benefits of equal order spaces, upwinding and ability to handle large gradients of DG methods as well as the smaller globally coupled linear system, adaptivity, and multinumeric capabilities of hybridized methods. However, the main bottleneck in HDG methods, limiting its use to small to moderate sized problems, is the lack of scalable linear solvers. In this thesis we develop fast and scalable solvers for HDG methods consisting of domain decomposition, multigrid and multilevel solvers/preconditioners with an ultimate focus on simulating large scale problems in fluid dynamics and magnetohydrodynamics (MHD). First, we propose a domain decomposition based solver namely iterative HDG for partial differential equations (PDEs). It is a fixed point iterative scheme, with each iteration consisting only of element-by-element and face-by-face embarrassingly parallel solves. Using energy analysis we prove the convergence of the schemes for scalar and system of hyperbolic PDEs and verify the results numerically. We then propose a novel geometric multigrid approach for HDG methods based on fine scale Dirichlet-to-Neumann maps. The algorithm combines the robustness of algebraic multigrid methods due to operator dependent intergrid transfer operators and at the same time has fixed coarse grid construction costs due to its geometric nature. For diffusion dominated PDEs such as the Poisson and the Stokes equations the algorithm gives almost perfect hp--scalability. Next, we propose a multilevel algorithm by combining the concepts of nested dissection, a fill-in reducing ordering strategy, variational structure and high-order properties of HDG, and domain decomposition. Thanks to its root in direct solver strategy the performance of the solver is almost independent of the nature of the PDEs and mostly depends on the smoothness of the solution. We demonstrate this numerically with several prototypical PDEs. Finally, we propose a block preconditioning strategy for HDG applied to incompressible visco-resistive MHD. We use a least squares commutator approximation for the inverse of the Schur complement and algebraic multigrid or the multilevel preconditioner for the approximate inverse of the nodal block. With several 2D and 3D transient examples we demonstrate the robustness and parallel scalability of the block preconditioner
Book Synopsis A High-order Discontinuous Galerkin Solver for Incompressible and Low-mach Number Flows by : Benedikt Klein
Download or read book A High-order Discontinuous Galerkin Solver for Incompressible and Low-mach Number Flows written by Benedikt Klein and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Mechanics written by and published by . This book was released on 2002 with total page 500 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis A parallel discontinuous galerkin code for the navier-stokes and reynolds-averaged navier-stokes equations by : Björn Landmann
Download or read book A parallel discontinuous galerkin code for the navier-stokes and reynolds-averaged navier-stokes equations written by Björn Landmann and published by . This book was released on 2008 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis High-order Discontinuous Galerkin Methods for the Maxwell Equations by : Hassan Fahs
Download or read book High-order Discontinuous Galerkin Methods for the Maxwell Equations written by Hassan Fahs and published by Omniscriptum. This book was released on 2018-02-28 with total page 208 pages. Available in PDF, EPUB and Kindle. Book excerpt: This work is concerned with the development of a high-order discontinuous Galerkin time-domain (DGTD) method for solving Maxwell's equations on non-conforming simplicial meshes. First, we present a DGTD method based on high-order nodal basis functions for the approximation of the electromagnetic field within a simplex, a centered scheme for the calculation of the numerical flux at an interface between neighbouring elements, and a second-order leap-frog time integration scheme. Next, to reduce the computational costs of the method, we propose a hp-like DGTD method which combines local h-refinement and p-enrichment. Then, we report on a detailed numerical evaluation of the DGTD methods using several propagation problems. Finally, in order to improve the accuracy and rate of convergence of the DGTD methods previously studied, we study a family of high-order explicit leap-frog time schemes. These time schemes ensure the stability under some CFL-like condition. We also establish rigorously the convergence of the semi-discrete approximation to Maxwell's equations and we provide bounds on the global divergence error.
Book Synopsis Discontinuous Galerkin Methods for the Unsteady Compressible Navier-stokes Equations by : Gregor Gassner
Download or read book Discontinuous Galerkin Methods for the Unsteady Compressible Navier-stokes Equations written by Gregor Gassner and published by . This book was released on 2009 with total page 113 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Scientific and Technical Aerospace Reports by :
Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1994 with total page 836 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis Domain Decomposition Preconditioners for Higher-order Discontinuous Galerkin Discretizations by : Laslo Tibor Diosady
Download or read book Domain Decomposition Preconditioners for Higher-order Discontinuous Galerkin Discretizations written by Laslo Tibor Diosady and published by . This book was released on 2012 with total page 182 pages. Available in PDF, EPUB and Kindle. Book excerpt: Aerodynamic flows involve features with a wide range of spatial and temporal scales which need to be resolved in order to accurately predict desired engineering quantities. While computational fluid dynamics (CFD) has advanced considerably in the past 30 years, the desire to perform more complex, higher-fidelity simulations remains. Present day CFD simulations are limited by the lack of an efficient high-fidelity solver able to take advantage of the massively parallel architectures of modern day supercomputers. A higher-order hybridizable discontinuous Galerkin (HDG) discretization combined with an implicit solution method is proposed as a means to attain engineering accuracy at lower computational cost. Domain decomposition methods are studied for the parallel solution of the linear system arising at each iteration of the implicit scheme. A minimum overlapping additive Schwarz (ASM) preconditioner and a Balancing Domain Decomposition by Constraints (BDDC) preconditioner are developed for the HDG discretization. An algebraic coarse space for the ASM preconditioner is developed based on the solution of local harmonic problems. The BDDC preconditioner is proven to converge at a rate independent of the number of subdomains and only weakly dependent on the solution order or the number of elements per subdomain for a second-order elliptic problem. The BDDC preconditioner is extended to the solution of convection-dominated problems using a Robin-Robin interface condition. An inexact BDDC preconditioner is developed based on incomplete factorizations and a p-multigrid type coarse grid correction. It is shown that the incomplete factorization of the singular linear systems corresponding to local Neumann problems results in a nonsingular preconditioner. The inexact BDDC preconditioner converges in a similar number of iterations as the exact BDDC method, with significantly reduced CPU time. The domain decomposition preconditioners are extended to solve the Euler and Navier- Stokes systems of equations. An analysis is performed to determine the effect of boundary conditions on the convergence of domain decomposition methods. Optimized Robin-Robin interface conditions are derived for the BDDC preconditioner which significantly improve the performance relative to the standard Robin-Robin interface conditions. Both ASM and BDDC preconditioners are applied to solve several fundamental aerodynamic flows. Numerical results demonstrate that for high-Reynolds number flows, solved on anisotropic meshes, a coarse space is necessary in order to obtain good performance on more than 100 processors.
Book Synopsis A Parallel Reconstructed Discontinuous Galerkin Method for the Compressible Flows on Aritrary Grids by :
Download or read book A Parallel Reconstructed Discontinuous Galerkin Method for the Compressible Flows on Aritrary Grids written by and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: A reconstruction-based discontinuous Galerkin method is presented for the solution of the compressible Navier-Stokes equations on arbitrary grids. In this method, an in-cell reconstruction is used to obtain a higher-order polynomial representation of the underlying discontinuous Galerkin polynomial solution and an inter-cell reconstruction is used to obtain a continuous polynomial solution on the union of two neighboring, interface-sharing cells. The in-cell reconstruction is designed to enhance the accuracy of the discontinuous Galerkin method by increasing the order of the underlying polynomial solution. The inter-cell reconstruction is devised to remove an interface discontinuity of the solution and its derivatives and thus to provide a simple, accurate, consistent, and robust approximation to the viscous and heat fluxes in the Navier-Stokes equations. A parallel strategy is also devised for the resulting reconstruction discontinuous Galerkin method, which is based on domain partitioning and Single Program Multiple Data (SPMD) parallel programming model. The RDG method is used to compute a variety of compressible flow problems on arbitrary meshes to demonstrate its accuracy, efficiency, robustness, and versatility. The numerical results demonstrate that this RDG method is third-order accurate at a cost slightly higher than its underlying second-order DG method, at the same time providing a better performance than the third order DG method, in terms of both computing costs and storage requirements.
Book Synopsis Efficient Implementation of a Parallel High-order Accurate Incompressible Navier-Stokes Solver by : R. Steijl
Download or read book Efficient Implementation of a Parallel High-order Accurate Incompressible Navier-Stokes Solver written by R. Steijl and published by . This book was released on 2000 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Book Synopsis An Adaptive High Order Discontinuous Galerkin Method with Error Control for the Hamilton-Jacobi Equations by : Yanlai Chen
Download or read book An Adaptive High Order Discontinuous Galerkin Method with Error Control for the Hamilton-Jacobi Equations written by Yanlai Chen and published by . This book was released on 2007 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt:
