An optimization-based approach for high-order accurate discretization of conservation laws with discontinuous solutions

JOURNAL OF COMPUTATIONAL PHYSICS

卷:365

Article

Zahr, M. J.^1,2  Persson, P. -O.^1,3 

[1] Lawrence Berkeley Natl Lab, Math Grp, 1 Cyclotron Rd, Berkeley, CA 94720 USA

[2] Univ Notre Dame, Dept Aerosp & Mech Engn, Notre Dame, IN 46556 USA

[3] Univ Calif Berkeley, Dept Math, Berkeley, CA 94720 USA

关键词: r-Adaptivity;    Shock tracking;    High-order methods;    Discontinuous Galerkin;    Full space PDE-constrained optimization;    Transonic and supersonic flow;   

DOI  :  10.1016/j.jcp.2018.03.029

来源: Elsevier

【 摘 要 】

This work introduces a novel discontinuity-tracking framework for resolving discontinuous solutions of conservation laws with high-order numerical discretizations that support inter-element solution discontinuities, such as discontinuous Galerkin or finite volume methods. The proposed method aims to align inter-element boundaries with discontinuities in the solution by deforming the computational mesh. A discontinuity-aligned mesh ensures the discontinuity is represented through inter-element jumps while smooth basis functions interior to elements are only used to approximate smooth regions of the solution, thereby avoiding Gibbs' phenomena that create well-known stability issues. Therefore, very coarse high-order discretizations accurately resolve the piecewise smooth solution throughout the domain, provided the discontinuity is tracked. Central to the proposed discontinuity-tracking framework is a discrete PDE-constrained optimization formulation that simultaneously aligns the computational mesh with discontinuities in the solution and solves the discretized conservation law on this mesh. The optimization objective is taken as a combination of the deviation of the finite-dimensional solution from its element-wise average and a mesh distortion metric to simultaneously penalize Gibbs' phenomena and distorted meshes. It will be shown that our objective function satisfies two critical properties that are required for this discontinuity-tracking framework to be practical: (1) possesses a local minima at a discontinuity-aligned mesh and (2) decreases monotonically to this minimum in a neighborhood of radius approximately h/2, whereas other popular discontinuity indicators fail to satisfy the latter. Another important contribution of this work is the observation that traditional reduced space PDE-constrained optimization solvers that repeatedly solve the conservation law at various mesh configurations are not viable in this context since severe overshoot and undershoot in the solution, i.e., Gibbs' phenomena, may make it impossible to solve the discrete conservation law on non-aligned meshes. Therefore, we advocate a gradient-based, full space solver where the mesh and conservation law solution converge to their optimal values simultaneously and therefore never require the solution of the discrete conservation law on a non-aligned mesh. The merit of the proposed method is demonstrated on a number of one- and two-dimensional model problems including the L-2 projection of discontinuous functions, Burgers' equation with a discontinuous source term, transonic flow through a nozzle, and supersonic flow around a bluff body. We demonstrate optimal O(h(P+1)) convergence rates in the L-1 norm for up to polynomial order p = 6 and show that accurate solutions can be obtained on extremely coarse meshes. (C) 2018 Elsevier Inc. All rights reserved.

【 授权许可】

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