Macroscopic Transport Equations for Rarefied Gas Flows

Progress of the unified wave-particle methods for non-equilibrium flows from continuum to rarefied regimes

Complex macroscopic systems (like for instance those encountered in nanotechnology
and biology) need to be investigated in a family of mesoscopic theories involving varying
amount of details. In this paper we formulate a general thermodynamics providing a uni-
versal framework for such multiscale viewpoint of mesoscopic dynamics. We then discuss
its role in making extensions (i.e. in lifting a mesoscopic theory to a more microscopic
level that involves more details).

methods

/pdf/role-of-thermodynamics-in-extensions-of-mesoscopic-dynamical-4ogti6v1b6.pdf

Role of thermodynamics in extensions of mesoscopic dynamical theories

Heat transfer in rarefied binary gas-mixtures confined in a bottom-heated squared cavity is investigated through the Grad’s moment equations for gaseous mixtures composed of Maxwell molecules. The numerical method based on finite differences is presented and the convergence of the numerical method is studied. Some preliminary results on heat transfer are presented.

http://www.mathcces.rwth-aachen.de/_media/5people/gupta/paper.pdf

Heat transfer in binary gas-mixtures confined in a square cavity

Highly efficient energy-conserving moment method for the multi-dimensional Vlasov-Maxwell system

This work applies the moment method onto a generic form of kinetic equations to simplify kinetic models of particle systems. This leads to the moment closure problem which is addressed using entropy-based moment closure techniques utilizing entropy minimization. The resulting moment closure system forms a system of partial differential equations that retain structural features of the kinetic system in question. This system of partial differential equations generate balance laws for velocity moments of a kinetic density that are symmetric hyperbolic, implying well-posedness in finite time. In addition, the resulting moment closure system satisfies an analog of Boltzmann's H-Theorem, i.e. solutions of the moment closure system are entropy dissipative. Such a model provides a promising alternative to particle methods, such as the Monte Carlo approaches, which can be prohibitive with regard to computational costs and inefficient with regard to error decay. However, several challenges pertaining to the analytical formulation and computational implementation of the moment closure system arise that are addressed in this work. The entropy minimization problem is studied in light of the classical results by Junk [18] showing that this technique suffers from a realizability problem, i.e. there exists realizable moments such that the entropy minimizer does not exist. Recent results by Hauck [17], Schneider [31] and Pavan [29] are used to investigate and circumvent this issue. The resulting moment closure system involves moments of exponentials of polynomials of, in principle, arbitrary order. In the context of numerical approximations, this is regarded as a complication. A novel and mathematically tractable moment system is developed that is based on approximating the entropy minimizing distribution. It will be shown that the resulting system retains the same structural features of the kinetic system in question. This system can be seen as a refinement of Grad's original moment system [15, 32]. Finally, a numerical approximation of the resulting moment systems is devised using discontinuous Galerkin (DG) finite elements method. Energy analysis based on the work of Barth [1, 2] is employed to investigate energy stable numerical flux functions to be used for the DG discretization of the moment systems. In contrast to the work of Barth [1], the numerical flux function suggested for the tractable system does not require a simplified construction since it is computable. In addition, higher order (approximated) moment systems, beyond the 10-moment system investigated by Barth [1], can be considered.

/pdf/numerical-approximation-of-the-boltzmann-equation-moment-1akv6elp3i.pdf

Numerical approximation of the Boltzmann equation : moment closure

/pdf/macroscopic-transport-equations-for-rarefied-gas-flows-36pljxyd8k.pdf

Macroscopic Transport Equations for Rarefied Gas Flows

Citations

Progress of the unified wave-particle methods for non-equilibrium flows from continuum to rarefied regimes

Role of thermodynamics in extensions of mesoscopic dynamical theories

Heat transfer in binary gas-mixtures confined in a square cavity

Highly efficient energy-conserving moment method for the multi-dimensional Vlasov-Maxwell system

Numerical approximation of the Boltzmann equation : moment closure

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