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We describe a shock-capturing streamline diffusion space-time discontinuous Galerkin (DG) method to discretize the shallow water equations with variable bottom topography. This method, based on the entropy variables as degrees of freedom, is shown to be energy stable as well as well-balanced with respect to the lake at rest steady state. We present numerical experiments illustrating the numerical method. [ABSTRACT FROM AUTHOR]

A large-eddy simulation (LES) framework is developed for simulating the dynamics of clouds and boundary layers with closed water and entropy balances. The framework is based on the anelastic equations in a formulation that remains accurate for deep convection. As prognostic variables, it uses total water and entropy, which are conserved in adiabatic and reversible processes, including reversible phase changes of water. This has numerical advantages for modeling clouds, in which reversible phase changes of water occur frequently. The equations of motion are discretized using higher-order weighted essentially nonoscillatory (WENO) discretization schemes with strong stability preserving time stepping. Numerical tests demonstrate that the WENO schemes yield simulations superior to centered schemes, even when the WENO schemes are used at coarser resolution. The framework is implemented in a new LES code written in Python and Cython, which makes the code transparent and easy to use for a wide user group. [ABSTRACT FROM AUTHOR]

We design schemes for the approximation of entropy solutions to nonlinear hyperbolic conservation laws in the regime where small-scale effects drive the dynamics of nonclassical shock waves in these solutions. Typically, the small-scale effects are modeled by adding higher-order dissipation terms taking into account the viscosity, capillarity, the Hall coefficient, etc., of the material under consideration. We analyze a strategy for the design of numerical methods adapted to these problems, referred to as schemes with well-controlled dissipation (WCD). Nonclassical entropy solutions are approximated by (small-scale) consistent and converging schemes with high accuracy--the main challenge being to capture physically relevant shocks. Following earlier works by LeFloch and collaborators, we rely on the equivalent equation, which provides a suitable tool in order to guarantee that small-scale dependent shocks are computed in a consistent and accurate way. WCD schemes are also intended to capture (nonclassical) shocks with arbitrary large strength. Our strategy is exemplified with examples and numerical experiments encompassing the cubic conservation law, the nonlinear elasticity system, and a reduced magnetohydrodynamics model. We compute the kinetic functions associated with the schemes and, as the order of the WCD schemes is increased, we observe convergence toward the exact kinetic function--even for strong shocks. [ABSTRACT FROM AUTHOR]

We consider initial-boundary-value problems for systems of conservation laws and design entropy stable finite difference schemes to approximate them. The schemes are shown to be entropy stable for a large class of systems that are equipped with a symmetric splitting, derived from the entropy formulation. Numerical examples for the Euler equations of gas dynamics are presented to illustrate the robust performance of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract: We deal with a single conservation law with discontinuous convex–concave type fluxes which arise while considering sign changing flux coefficients. The main difficulty is that a weak solution may not exist as the Rankine–Hugoniot condition at the interface may not be satisfied for certain choice of the initial data. We develop the concept of generalized entropy solutions for such equations by replacing the Rankine–Hugoniot condition by a generalized Rankine–Hugoniot condition. The uniqueness of solutions is shown by proving that the generalized entropy solutions form a contractive semi-group in . Existence follows by showing that a Godunov type finite difference scheme converges to the generalized entropy solution. The scheme is based on solutions of the associated Riemann problem and is neither consistent nor conservative. The analysis developed here enables to treat the cases of fluxes having at most one extrema in the domain of definition completely. Numerical results reporting the performance of the scheme are presented. [Copyright &y& Elsevier]

We deal with a single conservation law in one space dimension whose flux function is discontinuous in the space variable and we introduce a proper framework of entropy solutions. We consider a large class of fluxes, namely, fluxes of the convex-convex type and of the concave-convex (mixed) type. The alternative entropy framework that is proposed here is based on a two step approach. In the first step, infinitely many classes of entropy solutions are defined, each associated with an interface connection. We show that each of these class of entropy solutions form a contractive semigroup in L1 and is hence unique. Godunov type schemes based on solutions of the Riemann problem are designed and shown to converge to each class of these entropy solutions. The second step is to choose one of these classes of solutions. This choice depends on the Physics of the problem being considered and we concentrate on the model of two-phase flows in a heterogeneous porous medium. We define an optimization problem on the set of admissible interface connections and show the existence of an unique optimal connection and its corresponding optimal entropy solution. The optimal entropy solution is consistent with the expected solutions for two-phase flows in heterogeneous porous media. [ABSTRACT FROM AUTHOR]