Limite asymptotique pour le modèle de BGK

We present, for the BGK equation, asymptotic limits leading to various equations of incompressible and compressible fluid mechanics: the Navier-Stokes equations, the linearized Navier-Stokes equations, the Euler equation, the linearized Euler equation, and the compressible Euler equation. We state a convergence theorem for the nonlinear Navier-Stokes, as well as a result for the linear Navier-Stokes case, and for the compressible Euler equation.     

On the stability of the solutions to the compressible Navier-Stokes equations when the Mach number goes to zero

In this paper an asymptotic stability result is estabilished for the compressible navier-Stokes equations. Since the Mach number tends to zero, the incompressible limit solution of compressible Navier-Stokes equations is proved to be stable exponentially. Some results of Stokes' problem are used.     

The Asymptotic Expansion of Solutions for the Navier-Stokes Equations with Large Parameters

In this paper, we decomposite the coefficient matrix of the Navier-Stokes equations with large parameter in λ power. By factor analysis and energy estimation, the long time existence and asymptotic expansion of the solution tor the system are obtained. Key words Navier-Stokes equations; expansion; approximation.     

On dependence of dynamical structure of numerical solutions of fluid simulations on forcibly added randomness

In the present paper, the dependencies of the numerical results of fluid simulations on forcibly added randomness are discussed. The incompressible Navier-Stokes equations and the continuity equation are solved numerically by using the MAC (Maker-And-Cell) method and implicit temporal scheme. The model adopted in the present study is a flow around a two-dimensional circular cylinder and the Reynolds number is 1500. The randomness which is given by using the pseudo-random number is forcibly added in the time marching step of the discretized Navier-Stokes equations. Dependencies of the averaged structure of asymptotic numerical solutions on the randomness are discussed. Furthermore, the dependence of the qualitative structure of the asymptotic solution of each sample calculation on the amplitude of randomness is also studied. It is clarified that forcibly added random errors may cover the nonlinear errors which make the system unstable.     

Stochastic differential equations in fluid dynamics

Stochastic Navier-Stokes equations are investigated. Preliminary results of existence of solutions are summarized, and open questions on the well posedness are discussed. Uniqueness and ergodicity of the asymptotic regime (invariant measure) is also presented.     

Asymptotic Analysis of Steady and Nonsteady Navier-Stokes Equations for Barotropic Compressible Flow

We study the asymptotic behavior of solutions to steady and nonsteady Navier-Stokes equations for barotropic compressible fluids with slip boundary conditions in small channels whose diameters converge to zero. We also derive the corresponding asymptotic one-dimensional equations and we analyze the sets, where L ¹-weak convergence of the pressure terms fails.     

Convergence to rarefaction waves for the nonlinear Boltzmann equation and compressible Navier-Stokes equations

The main purpose of this paper is to study the asymptotic equivalence of the Boltzmann equation for the hard-sphere collision model to its corresponding Euler equations of compressible gas dynamics in the limit of small mean free path. When the fluid flow is a smooth rarefaction (or centered rarefaction) wave with finite strength, the corresponding Boltzmann solution exists globally in time, and the solution converges to the rarefaction wave uniformly for all time (or away from t=0) as ?→0. A decomposition of a Boltzmann solution into its macroscopic (fluid) part and microscopic (kinetic) part is adopted to rewrite the Boltzmann equation in a form of compressible Navier-Stokes equations with source terms. In this setting, the same asymptotic equivalence of the full compressible Navier-Stokes equations to its corresponding Euler equations in the limit of small viscosity and heat conductivity (depending on the viscosity) is also obtained.     

A combination of energy method and spectral analysis for study of equations of gas motion

There have been extensive studies on the large time behavior of solutions to systems on gas motions, such as the Navier-Stokes equations and the Boltzmann equation. Recently, an approach is introduced by combining the energy method and the spectral analysis to the study of the optimal rates of convergence to the asymptotic profiles. In this paper, we will first illustrate this method by using some simple model and then we will present some recent results on the Navier-Stokes equations and the Boltzmann equation. Precisely, we prove the stability of the non-trivial steady state for the Navier-Stokes equations with potential forces and also obtain the optimal rate of convergence of solutions toward the steady state. The same issue was also studied for the Boltzmann equation in the presence of the general time-space dependent forces. It is expected that this approach can also be applied to other dissipative systems in fluid dynamics and kinetic models such as the model system of radiating gas and the Vlasov-Poisson-Boltzmann system.      

Justification of Asymptotic Two-dimensional Model for Steady Navier-Stokes Equations for Incompressible Flow

We study the asymptotic behavior of solutions to steady Navier-Stokes equations for incompressible flow in thin three-dimensional deformed cylinders. We prove that a sequence of the solutions converges strongly to a solution of a corresponding two-dimensional asymptotic model if the thickness of the cylinders converges to zero.     

ZERO DISSIPATION LIMIT OF THE COMPRESSIBLE HEAT-CONDUCTING NAVIER-STOKES EQUATIONS IN HE PRESENCE OF THE SHOCK

The zero dissipation limit of the compressible heat-conducting Navier-Stokes equations in the presence of the shock is investigated. It is shown that when the heat ε→ 0 (see (1.3)), if the solution of the corresponding Euler equations is piecewise smooth with shock wave satisfying the Lax entropy condition, then there exists a smooth solution to the Navier-Stokes equations, which converges to the piecewise smooth shock solution of the Euler equations away from the shock discontinuity at a rate of ε. The proof is given by a combination of the energy estimates and the matched asymptotic analysis introduced in [3].     

Viscous incompressible free-surface flow down an inclined perturbed plane

The plane stationary free boundary value problem for the Navier-Stokes equations is studied. This problem models the viscous fluid free-surface flow down a perturbed inclined plane. For sufficiently small data the solvability and uniqueness results are proved in Hölder spaces. The asymptotic behavior of the solution is investigated.     

Asymptotic solutions of the Navier-Stokes equations and systems of stretched vortices filling a three-dimensional volume

We construct asymptotic solutions of the Navier-Stokes equations describing periodic systems of vortex filaments entirely filling a three-dimensional volume. Such solutions are related to certain topological invariants of divergence-free vector fields on the two-dimensional torus. The equations describing the evolution of of such a structure are defined on a graph which is the set of trajectories of a divergence-free field.     

A principle of linearization and the uniform asymptotic stability of solutions of the Navier–Stokes equations for compressible isothermic fluids

We prove the correctness of a principle of linearization in the investigation of the uniform asymptotic stability of a sufficiently smooth, but generally non-steady, solution of the Navier-Stokes equations for compressible fluids in the case of a constant temperature.     

Ergodicity and asymptotic stability of Feller semigroups on Polish metric spaces

We provide some sharp criteria for studying the ergodicity and asymptotic stability of general Feller semigroups on Polish metric spaces. As an application, the 2D Navier-Stokes equations with degenerate stochastic forcing will be simply revisited.     

Asymptotic solutions of Navier-Stokes equations and topological invariants of vector fields and Liouville foliations

We construct asymptotic solutions of the Navier-Stokes equations. Such solutions describe periodic systems of localized vortices and are related to topological invariants of divergence-free vector fields on two-dimensional cylinders or tori and to the Fomenko invariants of Liouville foliations. The equations describing the evolution of a vortex system are given on a graph that is a set of trajectories of the divergence-free field or a set of Liouville tori.     

Exact solutions for the Cauchy problem to the 3D spherically symmetric incompressible Navier-Stokes equations

In this article, we establish exact solutions to the Cauchy problem for the 3D spherically symmetric incompressible Navier-Stokes equations and further study the existence and asymptotic behavior of solution.     

Navier－Stokes方程组的一个一致有效渐近解

本文利用多重尺度法[1,2]研究了大雷诺数情况下的平板绕流问题,得到了Navier-Stokes方程的一个一致有效渐近解。     

Asymptotic solutions of the Navier-Stokes equations describing periodic systems of localized vortices

We construct asymptotic solutions of the Navier-Stokes equations describing the two-phase Taylor-scale structures consisting of periodic systems of localized vortex filaments. Such solutions are related to certain topological invariants of divergence-free vector fields on the two-dimensional cylinder or the torus. The equations describing the evolution of the vortex system are defined on a graph which is the set of trajectories of a divergence-free field.     

两个非同心旋转圆柱间粘性流动的广义雷诺方程及其基本流

运用张量分析方法及修正双极坐标系,建立了轴承润滑流动所应满足的广义Reynolds方程.应用薄流层中的Navier-Stokes方程的渐近分析方法和张量分析工具,得到了两个非同心旋转圆柱之间粘性流动的基本流所应满足的方程.这个基本流可以表示为两个同心旋转圆柱之间的Taylor流加上一个扰动项,并且给出了数值计算例子.     

An elementary approach to the analysis of exact solutions for the Navier-Stokes stagnation flows with slips

We deal with the exact solutions of the Navier-Stokes equations for stagnation flows with slips. The problem becomes the solvability of certain third-order ordinary differential equations (ODEs). Reducing the order of ODEs, we exhibit another elementary proof of the existence and asymptotic behavior of solutions. Numerical investigations are also provided. Received: 14 August 2003