Search

In this work, a bound- and positivity-preserving quasi-conservative discontinuous Galerkin (DG) method is proposed for the γ -based model of compressible two-medium flows. The contribution of this paper mainly includes three parts. On one hand, the DG method with the extended Harten-Lax-van Leer contact flux is proposed to solve the γ -based model, and satisfies the equilibrium-preserving property which preserves uniform velocity and pressure fields at an isolated material interface. On the other hand, an affine-invariant weighted essentially non-oscillatory (Ai-WENO) limiter is adopted to suppress oscillations near the discontinuities. The limiter with the Ai-WENO reconstruction method to the conservative variables not only is able to maintain the equilibrium property, but also generates sharper results around the locations of shock waves in contrast to that applying to the primitive variables. Last but not least, a flux-based bound- and positivity-preserving limiting strategy is introduced and analyzed, which preserves the physical bounds for auxiliary variables in the non-conservative governing equations, and the positivity for density and internal energy. Extensive numerical experiments in both one and two space dimensions show that the proposed method performs well in simulating compressible two-medium flows with high-order accuracy, equilibrium-preserving and bound-preserving properties. [ABSTRACT FROM AUTHOR]

In this paper, a new limiter using weighted essentially non-oscillatory (WENO) methodology is investigated for the Runge–Kutta discontinuous Galerkin (RKDG) methods for solving hyperbolic conservation laws. The idea is to use the high-order DG solution polynomial itself in the target cell and the linear polynomials which are reconstructed by the cell averages of solution in the target cell and its neighboring cells to reconstruct a new high-order polynomial in a manner of WENO methodology. Since only the linear polynomials need to be prepared for reconstruction, this limiter is very simple and compact with a stencil including only the target cell and its immediate neighboring cells. Numerical examples of various problems show that the new limiting procedure can simultaneously achieve uniform high-order accuracy and sharp, non-oscillatory shock transitions. [ABSTRACT FROM AUTHOR]

In this work, we discuss an extension of the adaptive technique in Zhu and Qiu (J. Comput. Phys. 228, 6957-6976 2009) to design an h-adaptive Runge-Kutta discontinuous Galerkin (RKDG) method for the simulations of several classical one-dimensional detonation waves. The TVB troubled-cell indicator is employed to detect the troubled cells which are believed to contain the discontinuities. An adaptive mesh is generated at each time-level by refining the troubled cells and coarsening the others. A recursive multi-level mesh refinement technique is designed to avoid the problem that the detonation front moves so fast that there are not enough cells to resolve the detonation front before it leaves. We describe the numerical implementation in detail including the adaptive procedure, solution reconstruction method and troubled-cell indicator. Furthermore, a high order positivity-preserving technique is employed for the robustness of our algorithm. Extensive numerical tests are conducted to show the effectiveness of the adaptive strategy and advantages of our adaptive method over the fixed-mesh RKDG method in saving the computational storage and improving the solution quality. [ABSTRACT FROM AUTHOR]

In Zhu and Qiu (J Comput Phys 228:6957-6976, ), we systematically investigated adaptive Runge-Kutta discontinuous Galerkin (RKDG) methods for hyperbolic conservation laws with different indicators, with an objective of obtaining efficient and reliable indicators to obtain better performance for adaptive computation to save computational cost. In this follow-up paper, we extend the method to solve two-dimensional problems. Although the main idea of the method for two-dimensional case is similar to that for one-dimensional case, the extension of the implementation of the method to two-dimensional case is nontrivial because of the complexity of the adaptive mesh with hanging nodes. We lay our emphasis on the implementation details including adaptive procedure, solution projection, solution reconstruction and troubled-cell indicator. Extensive numerical experiments are presented to show the effectiveness of the method. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we systematically investigate adaptive Runge–Kutta discontinuous Galerkin (RKDG) methods for hyperbolic conservation laws with different indicators which were based on the troubled cell indicators studied by Qiu and Shu [J. Qiu, C.-W. Shu, A comparison of troubled-cell indicators for Runge–Kutta discontinuous Galerkin mehtods using weighted essentially non-osillatory limiters, SIAM J. Sci. Comput. 27 (2005) 995–1013]. The emphasis is on comparison of the performance of adaptive RKDG method using different indicators, with an objective of obtaining efficient and reliable indicators to obtain better performance for adaptive computation to save computational cost. Both h-version and r-version adaptive methods are considered in the paper. The idea is to first identify “troubled cells” by different troubled-cell indicators, namely those cells where limiting might be needed and discontinuities might appear, then adopt an adaptive approach in these cells. A detailed numerical study in one-dimensional case is performed, addressing the issues of efficiency (less CPU cost and more accurate), non-oscillatory property, and resolution of discontinuities. [Copyright &y& Elsevier]

The Newell–Whitehead–Segel type equations with time-dependent Dirichlet boundary conditions are solved by the local discontinuous Galerkin (LDG) method coupled with the implicit–explicit backward difference formulas (IMEX-BDF). With a suitable setting of numerical fluxes and by the aid of the multiplier technique and the a priori error assumption technique, the optimal error estimate for the corresponding fully discrete LDG-IMEX-BDF schemes is obtained by energy analysis, under the condition $ \tau \le C h^{1/s} $ τ≤Ch1/s, where h and τ are mesh size and time step, respectively, the positive constant C is independent of h, and $ s=1,\ldots, 5 $ s=1,…,5 is the order of the IMEX-BDF method. Numerical experiments are also presented to verify the accuracy of the considered schemes. [ABSTRACT FROM AUTHOR]

We propose a new family of asymptotic preserving (AP) discontinuous Galerkin (DG) schemes for kinetic transport equations under a diffusive scaling. They are built upon a characteristics-based model reformulation proposed in Zhang et al. (2023) [27]. The reformulated model comprises a convection-diffusion-like equation for the macroscopic density and another evolution equation for the distribution function. We employ the equations in a weak form to enjoy the advantages of a DG method. We also leverage a semi-Lagrangian (SL) approach to achieve higher efficiency than a fully implicit scheme without loss of unconditional stability. A damping technique is introduced to control spurious numerical oscillations for high-order DG methods. We establish formal AP and Fourier stability analyses for fully discrete schemes in a linear scenario. Numerical experiments, covering one-dimensional to three-dimensional in space problems, confirm the accuracy, AP property, uniformly unconditional stability, and high parallel efficiency of the proposed methods. • We proposed a new family of efficient AP DG methods for linear kinetic transport equations in the diffusive scaling. • We employ the weak form of a finite element method to enjoy the advantages of a DG method. • We leverage a semi-Lagrangian approach to achieve high parallel efficiency, without loss of unconditional stability. • We introduce a damping technique to control spurious numerical oscillations, which is very convenient and efficient. • Numerical experiments, confirm the accuracy, AP property, uniformly unconditional stability, and high parallel efficiency. [ABSTRACT FROM AUTHOR]