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Thu, 17 Aug 2000 00:00:00 +0200Thu, 17 Aug 2000 00:00:00 +0200On the approximation of kinetic equations by moment systems
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1115
The aim of this article is to show that moment approximations of kinetic equations based on a Maximum Entropy approach can suffer from severe drawbacks if the kinetic velocity space is unbounded. As example, we study the Fokker Planck equation where explicit expressions for the moments of solutions to Riemann problems can be derived. The quality of the closure relation obtained from the Maximum Entropy approach as well as the Hermite/Grad approach is studied in the case of five moments. It turns out that the Maximum Entropy closure is even singular in equilibrium states while the Hermite/Grad closure behaves reasonably. In particular, the admissible moments may lead to arbitrary large speeds of propagation, even for initial data arbitrary close to global eqilibrium.Wolfgang Dreyer; Michael Junk; Matthias Kunikpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1115Thu, 17 Aug 2000 00:00:00 +0200Exponentially exact hyperbolic systems
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1111
Starting with general hyperbolic systems of conservation laws, a special sub - class is extracted in which classical solutions can be expressed in terms of a linear transport equation. A characterizing property of this sub - class which contains, for example, all linear systems and non - linear scalar equations, is the existence of so called exponentially exact entropies.Michael Junkpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1111Mon, 14 Aug 2000 00:00:00 +0200Consistency analysis of mesh-free methods for conservation laws
https://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1112
Based on general partitions of unity and standard numerical flux functions, a class of mesh-free methods for conservation laws is derived. A Lax-Wendroff type consistency analysis is carried out for the general case of moving partition functions. The analysis leads to a set of conditions which are checked for the finite volume particle method FVPM. As a by-product, classical finite volume schemes are recovered in the approach for special choices of the partition of unity.Michael Junk; Jens Struckmeierpreprinthttps://kluedo.ub.uni-kl.de/frontdoor/index/index/docId/1112Mon, 14 Aug 2000 00:00:00 +0200