Global solution of the initial value problem for the Boltzmann equation near a local Maxwellian

For molecules with a cut-off, we solve the initial value problem for the non-linear, spatially dependent Boltzmann equation when the initial density is sufficiently close to a locally Maxwellian function. The result is obtained for Maxwellian and weak interactions and achieved through a suitable application of the iteration scheme of Kaniel & sHinbrot.     

Upper Maxwellian Bounds for the Spatially Homogeneous Boltzmann Equation

For the spatially homogeneous Boltzmann equation with cutoff hard potentials, it is shown that solutions remain bounded from above uniformly in time by a Maxwellian distribution, provided the initial data have a Maxwellian upper bound. The main technique is based on a comparison principle that uses a certain dissipative property of the linear Boltzmann equation. Implications of the technique to propagation of upper Maxwellian bounds in the spatially-inhomogeneous case are discussed.     

L2-stability near equilibrium of the solution of the homogeneous Boltzmann equation in the case of Maxwellian molecules

Summary The problem of L²-stability for the homogeneous Boltzmann equation in the case of Maxwellian molecules is studied, for initial data close to equilibrium.

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Sommario Si studia il problema della stabilità in L² per l'equazione di Boltzmann omogenea, nel caso delle molecole Maxwelliane, per dati iniziali vicini all'equilibrio.

     

The Boltzmann Equation for a Multi-species Mixture Close to Global Equilibrium

We study the Cauchy theory for a multi-species mixture, where the different species can have different masses, in a perturbative setting on the three dimensional torus. The ultimate aim of this work is to obtain the existence, uniqueness and exponential trend to equilibrium of solutions to the multi-species Boltzmann equation in \({L^1_vL^\infty_x(m)}\), where \({m\sim (1+ |v|^k)}\) is a polynomial weight. We prove the existence of a spectral gap for the linear multi-species Boltzmann operator allowing different masses, and then we establish a semigroup property thanks to a new explicit coercive estimate for the Boltzmann operator. Then we develop an \({L^2-L^\infty}\) theory à la Guo for the linear perturbed equation. Finally, we combine the latter results with a decomposition of the multi-species Boltzmann equation in order to deal with the full equation. We emphasize that dealing with different masses induces a loss of symmetry in the Boltzmann operator which prevents the direct adaptation of standard mono-species methods (for example Carleman representation, Povzner inequality). Of important note is the fact that all methods used and developed in this work are constructive. Moreover, they do not require any Sobolev regularity and the \({L^1_vL^\infty_x}\) framework is dealt with for any \({k > k_0}\), recovering the optimal physical threshold of finite energy \({k_0=2}\) in the particular case of a multi-species hard spheres mixture with the same masses.     

Global Well-Posedness in Spatially Critical Besov Space for the Boltzmann Equation

The unique global strong solution in the Chemin–Lerner type space to the Cauchy problem on the Boltzmann equation for hard potentials is constructed in a perturbation framework. Such a solution space is of critical regularity with respect to the spatial variable, and it can capture the intrinsic properties of the Boltzmann equation. For the proof of global well-posedness, we develop some new estimates on the nonlinear collision term through the Littlewood–Paley theory.     

Regularity Theory for the Spatially Homogeneous Boltzmann Equation with Cut-Off

We develop the regularity theory of the spatially homogeneous Boltzmann equation with cut-off and hard potentials (for instance, hard spheres), by (i) revisiting the L^p theory to obtain constructive bounds, (ii) establishing propagation of smoothness and singularities, (iii) obtaining estimates on the decay of the singularities of the initial datum. Our proofs are based on a detailed study of the regularity of the gain operator. An application to the long-time behavior is presented.     

L 1 and BV-type stability of the inelastic Boltzmann equation near vacuum

The L ¹ and BV-type stability to mild solutions of the inelastic Boltzmann equation is given in this paper. The result is an extension of the stability of the classical solution of the elastic Boltzmann equation proved in Ha (Arch. Ration. Mech. Anal. 173:25–42, 2004 [16]). The observation relies on the energy loss of the inelastic Boltzmann equation. This is a continuity work of Alonso (Indiana Univ. Math. J. [1]), where the author obtained the global existence of a mild solution for the inelastic Boltzmann equation. The proof is based on the mollification method and constructing some functionals as the one in Chae and Ha (Contin. Mech. Thermodyn. 17(7):511–524, 2006 [9]).     

Solution of a Model Boltzmann Equation via Steepest Descent in the 2-Wasserstein Metric

We study a model Boltzmann equation closely related to the BGK equation using a steepest-descent method in the Wasserstein metric, and prove global existence of energy-and momentum-conserving solutions. We also show that the solutions converge to the manifold of local Maxwellians in the large-time limit, and obtain other information on the behavior of the solutions. We show how the Wasserstein metric is natural for this problem because it is adapted to the study of both the free streaming and the collisions.     

The Acoustic Limit for the Boltzmann Equation

The acoustic equations are the linearization of the compressible Euler equations about a spatially homogeneous fluid state. We first derive them directly from the Boltzmann equation as the formal limit of moment equations for an appropriately scaled family of Boltzmann solutions. We then establish this limit for the Boltzmann equation considered over a periodic spatial domain for bounded collision kernels. Appropriately scaled families of DiPerna-Lions renormalized solutions are shown to have fluctuations that converge entropically (and hence strongly in L ¹) to a unique limit governed by a solution of the acoustic equations for all time, provided that its initial fluctuations converge entropically to an appropriate limit associated to any given L ² initial data of the acoustic equations. The associated local conservation laws are recovered in the limit. Accepted: October 22, 1999     

BV-Regularity of the Boltzmann Equation in Non-Convex Domains

We consider the Boltzmann equation in a general non-convex domain with the diffuse boundary condition. We establish optimal BV estimates for such solutions. Our method consists of a new W^1,1-trace estimate for the diffuse boundary condition and a delicate construction of an \({\varepsilon}\)-tubular neighborhood of the singular set.     

Convergence of Discrete-Velocity Schemes for the Boltzmann Equation

In this paper we prove the convergence of two discrete-velocity deterministic schemes for the Boltzmann equation, namely, Buet's scheme and a new finite-volume scheme that we introduce here. We write the discretized equation in the form of a Boltzmann continuous equation in order to be in the framework of the DiPerna-Lions theory of renormalized solutions. In order to prove convergence we have to overcome two difficulties: the convergence of the discretized collision kernel is very weak and the lemma on the compactness of velocity averages can be recovered only asymptotically when the parameter of discretization tends to zero. (Accepted February 6, 1996)     

Nonlinear Stability of Rarefaction Waves for the Boltzmann Equation

It is well known that the Boltzmann equation is related to the Euler and Navier-Stokes equations in the field of gas dynamics. The relation is either for small Knudsen number, or, for dissipative waves in the time-asymptotic sense. In this paper, we show that rarefaction waves for the Boltzmann equation are time-asymptotic stable and tend to the rarefaction waves for the Euler and Navier-Stokes equations. Our main tool is the combination of techniques for viscous conservation laws and the energy method based on micro-macro decomposition of the Boltzmann equation. The expansion nature of the rarefaction waves and the suitable microscopic version of the H-theorem are essential elements of our analysis.     

Global Lp-properties for the spatially homogeneous Boltzmann equation

This paper studies the L ^p-behavior for 1p of solutions of the nonlinear, spatially homogeneous Boltzmann equation for a class of collision kernels including inverse k ^th-power forces with k>5 and angular cut-off. The following topics are treated: differentiability in L ^p together with global boundedness in time for L ^p-moments that exist initially, translation continuity in L ^p uniformly in time, and strong convergence to equilibrium.     

Lattice Boltzmann simulation of flow past a circular cylinder near a moving wall

The two‐dimensional flows past a circular cylinder near a moving wall are simulated by lattice Boltzmann method. The wall moves at the inlet velocity and the Reynolds number ranges from 300 to 500. The influence of the moving wall on the flow patterns is demonstrated and the corresponding mechanism is illustrated by using instability theory. The correlations among flow features based on gap ratio are interpreted. Force coefficients, velocity profile and vortex structure are analyzed to determine the critical gap ratio. Copyright © 2011 John Wiley & Sons, Ltd.     

Decay and Continuity of the Boltzmann Equation in Bounded Domains

Boundaries occur naturally in kinetic equations, and boundary effects are crucial for dynamics of dilute gases governed by the Boltzmann equation. We develop a mathematical theory to study the time decay and continuity of Boltzmann solutions for four basic types of boundary conditions: in-flow, bounce-back reflection, specular reflection and diffuse reflection. We establish exponential decay in the L ^∞ norm for hard potentials for general classes of smooth domains near an absolute Maxwellian. Moreover, in convex domains, we also establish continuity for these Boltzmann solutions away from the grazing set at the boundary. Our contribution is based on a new L ² decay theory and its interplay with delicate L ^∞ decay analysis for the linearized Boltzmann equation in the presence of many repeated interactions with the boundary.     

The L1-Stability of Boundary Layers for Scalar Viscous Conservation Laws

Let v=v(x) be a non-trivial bounded steady solution of a viscous scalar conservation law u _t+f(u) _x =u _xx on a half-line R⁺, with a Dirichlet boundary condition. The semi-group of this IBVP is known to be contractive for the distance d(u, u)u–u₁ induced by L ¹(R⁺). We prove here that v is asymptotically stable with respect to d: if u ₀–vL ¹, then u(t)–v₁0 as t+. When v is a constant, we show that this property holds if and only if f(v)0. These results complement our study of the Cauchy problem [2].