Junction between a 3-D Stokes flow and a 2-D thin film with pressure boundary conditions

A 3-D Stokes equation modelling the flow in the inlet region of a lubricated device is studied. Boundary conditions on both the pressure and the velocity are considered. The geometry induces that the flow region is divided into two parts: the first one is a thin gap with height ?h, where a change of scale is performed, and the second one is a cavity whose dimensions are large with respect to ?. Two equivalent variational formulations are proposed and lead to accurate a priori estimates. The resulting asymptotic equation for the pressure in the thin gap is the currently used Reynolds equation, whose boundary conditions are obtained via the junction with the 3-D cavity. Both hydrostatic and hydrodynamic cases are considered.     

Delta-Wave in a Simple 1-D 2x2 Hyperbolic Problem

A simple one-dimensional $2\times 2$ hyperbolic system is considered in the paper. The model contains a linear hyperbolic equation, as well as a hyperbolic equation of which the coefficients are about the solution of the linear one. The exact solution is presented and discussed, then numerical experiments are given by TVD (or MmB) type schemes for Riemann problems. From the results, we know that the solutions do have $\delta-$waves for some suitable initial data.     

The transonic shock in a nozzle, 2-D and 3-D complete Euler systems

In this paper, we study a transonic shock problem for the Euler flows through a class of 2-D or 3-D nozzles. The nozzle is assumed to be symmetric in the diverging (or converging) part. If the supersonic incoming flow is symmetric near the divergent (or convergent) part of the nozzle, then, as indicated in Section 147 of [R. Courant, K.O. Friedrichs, Supersonic Flow and Shock Waves, Interscience Publ., New York, 1948], there exist two constant pressures P₁ and P₂ with P₁<P₂ such that for given constant exit pressure Pe∈(P₁,P₂), a symmetric transonic shock exists uniquely in the nozzle, and the position and the strength of the shock are completely determined by Pe. Moreover, it is shown in this paper that such a transonic shock solution is unique under the restriction that the shock goes through the fixed point at the wall in the multidimensional setting. Furthermore, we establish the global existence, stability and the long time asymptotic behavior of an unsteady symmetric transonic shock under the exit pressure Pe when the initial unsteady shock lies in the symmetric diverging part of the 2-D or 3-D nozzle. On the other hand, it is shown that an unsteady symmetric transonic shock is structurally unstable in a global-in-time sense if it lies in the symmetric converging part of the nozzle.     

Exact-gradient shape optimization of a 2-D Euler flow

The optimization of an obstacle shape immersed in an Eulerian flow is investigated. In order to construct a descent method, we consider the differentiation of the flow solution with respect to the shape. In the continous case, the Hadamard variational formula yields the formal derivatives. In the discrete case, we choose an upwind method with flux splitting, and proved that an exact gradient can be derived using the adjoint state. The behavior of a gradient method is studied for a family of nozzle flows.     

Forms of Unsteady Flow in a 2-D Channel

The paper describes results of a numerical simulations of air flow in a turned off, 2D channel with the plain nozzle. Simulations are based on an earlier experiment, carried out by Dyban, Mazur and Epik (1971). In the featured channel it has been observed several bifurcation forms, depending on the flow velocity and geometry relations. Basing on the numerical simulations results, the integral characteristics of the flow areas has also been presented. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

On the stochastic 2-D motion of a Bingham fluid

We establish the existence and uniqueness of a strong solution to the initial boundary value problem associated with the motion of a Bingham fluid in a two-dimensional domain with random noise. We also prove the existence of an invariant measure for a certain class of noise. When the deterministic forcing is sufficiently small and the multiplicative noise is almost linear, it is shown that extinction of a solution occurs in a finite time almost surely.     

单稳型二维格微分方程的整体解

通过解一个以-κ为初始时刻的初值问题序列,并且利用比较原理证明了单稳型二维格微分方程整体解的存在性和一些定性性质.     

$\delta-$Wave for 1-D and 2-D Hyperbolic Systems

Here a new kind of nonlinear wave, which is called $\delta-$wave, is described by some high resolution difference solutions for Riemann problems of one-dimensional (1-D) and two-dimensional (2-D) nonlinear hyperbolic systems in conservation laws. Some phenomena are numerically shown for the solutions of Riemann problems for 2-D gas dynamics systems.     

一类带约束的二维弱奇异积分方程的解*

本文找出二维弱奇异第一类积分方程作用着约束方程的解p.p=p(r,θ)={2/[π2k(φ₀]}√F(r,θ)-c_*(0≤r≤r_*)其中是(s,φ)原点在M(r,θ)的局部极坐标,(r,θ)是原点在O(0,0)的总体极坐标:k和F是给出的连续函数;φ₀是一常数;F(_*,θ)=c_*(常数)是研究域Q的边界围线。所用方法可推广到三维情形。     

Inference for 2-D GARCH models

The purpose of this paper is, in the first step, to consider a class of GMM estimators with interesting asymptotic properties and a reasonable number of computations for two dimensionally indexed Generalized Autoregressive Conditional Heteroscedasticity (GARCH) model. In the second step, we use the central limit theorem of Huang (1992) for spatial martingale differences to establish the LAN property for general two-dimensional discrete models on a regular grid with Gaussian errors. We then apply this result to the spatial GARCH model and derive the limit distribution of the maximum likelihood estimators of the parameters. Results of numerical simulations are presented.     

Convergence and Compactness Properties for a Family of 2-D Discontinuous Signals

In this paper, convergence and compactness properties for sets of possibly discontinuous functions on ² are discussed. The issue appears to be relevant with respect to optimization and identification problems for 2-D images.Several convergence properties are provided and compared for a class of discontinuous 2-D functions with sufficiently regular discontinuity sets.Two sufficient compactness criteria are given; the first one extends to the 2-D case previously known results on the 1-D Skorohod topology.     

Periodic Structure of 2-D Navier-Stokes Equations

We study in this article both the structure and the structural evolution of the solutions of 2-D Navier-Stokes equations with periodic boundary conditions and the evolution of their solutions. First the structure of all eigenvectors of the corresponding Stokes problem is lassified using a block structure, and is linked to the typical structure of the Taylor vortices. Then the structure of the solutions of the Navier-Stokes equations forced either by eigenmodes or by potential forcing is classified.     

SPIRALS IN 2-D GAS DYNAMICS SYSTEMS

1.Preliminaries(I)ModelsConsiderthetwomodels:iselltropicandadiabaticflows,(a)2-Disentropicflow(b)2-Dadiabaticflowwherep,(u,v)andpisdensity,velocityandpresure,respectively.andwiththe2-DRiemanndatawhere(i)-statesaredescribedtoProblem(1.1)(1.3)and(1.2)...     

Stochastic 2-D Navier—Stokes Equation

   Abstract. In this paper we prove the existence and uniqueness of strong solutions for the stochastic Navier—Stokes equation in bounded and unbounded domains. These solutions are stochastic analogs of the classical Lions—Prodi solutions to the deterministic Navier—Stokes equation. Local monotonicity of the nonlinearity is exploited to obtain the solutions in a given probability space and this significantly improves the earlier techniques for obtaining strong solutions, which depended on pathwise solutions to the Navier—Stokes martingale problem where the probability space is also obtained as a part of the solution.     

有关二维Euler方程的一些估计

首先得到Ｌｏｒｅｎｔｚ空间中的一些结果,然后在此基础上得到了有关二维Ｅｕｌｅｒ方程解的一些估计。这些估计与该方程当初始旋度ω０∈Ｌ＾－１∩Ｌ＾ｐ（ｐ〉１）时解的唯一性有关。     

2-D Systems,an Algebraic Approach

Journal of the Operational Research Society -     

一个带有小参数的二维椭圆方程的渐近性分析

通过数值方法研究在边界充分(逐段)光滑区域上的带有小参数的二维椭圆方程在部分Dirichlet边界控制下的渐近性问题.对于一维的情形求解析解的结果,对高维问题提出类似的问题.但高维问题解析求解一般不可能,因此采用数值分析的方法.数值结果表明,在所选的条件下,边界值对小常数仍然不是解析的.     

Density symmetries for a class of 2-D diffusions with applications to finance

We study densities of two-dimensional diffusion processes with one non-negative component. For such diffusions, the density may explode at the boundary, thus making a precise specification of the boundary condition in the corresponding forward Kolmogorov equation problematic. We overcome this by extending a classical symmetry result for densities of one-dimensional diffusions to our case, thereby reducing the study of forward equations with exploding boundary data to the study of a related backward equation with non-exploding boundary data. We also discuss applications of this symmetry for option pricing in stochastic volatility models and in stochastic short rate models.