33,283 research outputs found
A theory of -dissipative solvers for scalar conservation laws with discontinuous flux
We propose a general framework for the study of contractive semigroups
of solutions to conservation laws with discontinuous flux. Developing the ideas
of a number of preceding works we claim that the whole admissibility issue is
reduced to the selection of a family of "elementary solutions", which are
certain piecewise constant stationary weak solutions. We refer to such a family
as a "germ". It is well known that (CL) admits many different contractive
semigroups, some of which reflects different physical applications. We revisit
a number of the existing admissibility (or entropy) conditions and identify the
germs that underly these conditions. We devote specific attention to the
anishing viscosity" germ, which is a way to express the "-condition" of
Diehl. For any given germ, we formulate "germ-based" admissibility conditions
in the form of a trace condition on the flux discontinuity line (in the
spirit of Vol'pert) and in the form of a family of global entropy inequalities
(following Kruzhkov and Carrillo). We characterize those germs that lead to the
-contraction property for the associated admissible solutions. Our
approach offers a streamlined and unifying perspective on many of the known
entropy conditions, making it possible to recover earlier uniqueness results
under weaker conditions than before, and to provide new results for other less
studied problems. Several strategies for proving the existence of admissible
solutions are discussed, and existence results are given for fluxes satisfying
some additional conditions. These are based on convergence results either for
the vanishing viscosity method (with standard viscosity or with specific
viscosities "adapted" to the choice of a germ), or for specific germ-adapted
finite volume schemes
Compact Central WENO Schemes for Multidimensional Conservation Laws
We present a new third-order central scheme for approximating solutions of
systems of conservation laws in one and two space dimensions. In the spirit of
Godunov-type schemes,our method is based on reconstructing a
piecewise-polynomial interpolant from cell-averages which is then advanced
exactly in time. In the reconstruction step, we introduce a new third-order as
a convex combination of interpolants based on different stencils. The heart of
the matter is that one of these interpolants is taken as an arbitrary quadratic
polynomial and the weights of the convex combination are set as to obtain
third-order accuracy in smooth regions. The embedded mechanism in the WENO-like
schemes guarantees that in regions with discontinuities or large gradients,
there is an automatic switch to a one-sided second-order reconstruction, which
prevents the creation of spurious oscillations. In the one-dimensional case,
our new third order scheme is based on an extremely compact point stencil.
Analogous compactness is retained in more space dimensions. The accuracy,
robustness and high-resolution properties of our scheme are demonstrated in a
variety of one and two dimensional problems.Comment: 24 pages, 5 figure
Hybrid Riemann Solvers for Large Systems of Conservation Laws
In this paper we present a new family of approximate Riemann solvers for the
numerical approximation of solutions of hyperbolic conservation laws. They are
approximate, also referred to as incomplete, in the sense that the solvers
avoid computing the characteristic decomposition of the flux Jacobian. Instead,
they require only an estimate of the globally fastest wave speeds in both
directions. Thus, this family of solvers is particularly efficient for large
systems of conservation laws, i.e. with many different propagation speeds, and
when no explicit expression for the eigensystem is available. Even though only
fastest wave speeds are needed as input values, the new family of Riemann
solvers reproduces all waves with less dissipation than HLL, which has the same
prerequisites, requiring only one additional flux evaluation.Comment: 9 page
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