两参数非局部非线性反应扩散Robin问题的渐近解

研究了一类两参数非局部反应扩散奇摄动Robin问题.利用奇摄动方法,对该问题解的结构在两个小参数相互关联的情形下作了讨论.得到了该问题的渐近解.     

微分算子和边界双摄动的高阶椭圆型方程的狄立克雷问题

本文研究了在边界和算子摄动相结合的情况下高阶椭圆型方程解的渐近式的构造.如果非摄动问题A₀不在谱上,则摄动问题A_ε的渐近解可按小参数ε的次幂展开;如果A₀在谱上,则在A_ε的渐近解中出现有小参数ε的负幂;同时给出了有关的余项的估计.     

非Fourier温度场分布的奇摄动解

应用非Fourier热传导定律构建了单层材料中温度场模型，即一类在无界域上带小参数的奇摄动双曲方程，通过奇摄动展开方法，得到了该问题的渐近解.首先应用奇摄动方法得到了该问题的外解和边界层矫正项，通过对内解和外解的最大模估计和关于时间导数的最大模估计以及线性抛物方程理论，得到了内外解的存在唯一性，从而得到了解的形式渐近展开式.通过余项估计，给出了渐近解的L2估计，得到了渐近解的一致有效性，从而得到了无界域上温度场的分布.通过奇摄动分析，给出了非Fourier 温度场与Fourier 温度场的关系，描述了非Fourier温度场的具体形态.     

双曲-抛物型偏微分方程奇摄动混合问题的数值解法

构造了二阶双曲—抛物型方程奇摄动混合问题的差分格式，给出了差分解的能量不等式，并证明了差分解在离散范数下关于小参数一致收敛于摄动问题的解。     

具有多参数的奇摄动非线性边值问题的摄动解

讨论含多个参数的高阶非线性方程的摄动解,在适当的条件下,先构造出外部解,再根据不同的边界层,利用伸展变量和幂级数展开式理论,构造问题的形式渐近解,最后利用微分不等式理论证明渐近解的一致有效性和渐近形态,把奇摄动非线性问题中的参数推广到多个参数.     

一类热传导系数跳跃的非Fourier温度场分布的奇摄动双参数解

应用非Fourier热传导定律构建了温度场模型,即一类在有界域上带小参数的奇摄动双曲方程,由于温度急剧变化热传导系数出现跳跃的情况,得到了非线性的具有间断系数的奇摄动双参数双曲方程.通过奇摄动双参数展开方法,得到了该问题的渐近解;其次对热传导系数跳跃位置进行了定性分析,得到了确定热传导系数跳跃位置的计算公式,从而确定了解的形式渐近展开式;再通过余项估计,得到了渐近解的一致有效性,从而得到了完整温度场的分布.     

奇异摄动系统的一致稳定和镇定（英文）

针对一类线性时不变奇异摄动系统,研究其在稳定和镇定性方面关于小参数的一致性问题.当小参数处于有界而非闭区间时,将奇异摄动系统视为参数系统.同时,进一步地讨论该系统对小参数的依赖性.最后,利用线性矩阵不等式方法,给出了系统关于小参数具有一致性的稳定和镇定条件.     

双曲-双曲奇异摄动混合问题的一致收敛格式

本文构造了二阶双曲-双曲奇异摄动混合问题的差分格式,给出了差分解的能量不等式,并证明了差分解在离散范数下关于小参数一致收敛于摄动问题的解.     

区间参数结构振动问题的矩阵摄动法

当结构的参数具有不确定性时，结构的固有频率也将具有某种程度的不确定性．本文讨论了区间参数结构的振动问题，将区间参数结构的特征值问题归结为两个不同的特征值问题来求解．提出了求解区间参数结构振动问题的矩阵摄动方法．数值运算结果表明，本文所提出方法具有运算量小，结果精度高等优点．     

关于钱氏摄动法的高阶解的计算机求解和收敛性的研究

本文借助于中心受集中载荷圆板小挠度问题的积分方程,获得了摄动参数为中心挠度的任意n阶摄动解的解析式.于是,任意次摄动解的所有待定系数能用计算机求解.因此,获得了相当高阶的摄动解.在此基础上,讨论了钱氏摄动法的渐近性和适用区.     

THE BOUNDARY VALUE PROBLEMS FOR QUASILINEAR HIGHER ORDER ELLIPTIC EQUATIONS WITH A SMALL PARAMETER

In this paper we deal with the general boundary value problems for quasilinear higherorder elliptic equations with a small parameter before higher derivatives.By using themethod of multiple scales,we have proved that if the solution of degenerated boundary valueproblem exists,then under certain assumptions as the small parameter is sufficiently small,the solution of the origional boundary value problem exists as well and it is unique in a certainfunction space.Besides,the asymptotic expansion of the solution has been constructed.     

Perturbations for linear difference equations

In this paper we study boundary value problems for perturbed second-order linear difference equations with a small parameter. The reduced problem obtained when the parameter is equal to zero is a first-order linear difference equation. The solution is represented as a convergent series in the small parameter, whose coefficients are given by means of solutions of the reduced problem.     

A complete asymptotic expansion of a solution to a singular perturbation optimal control problem on an interval with geometric constraints

We consider an optimal control problem for solutions of a boundary value problem on an interval for a second-order ordinary differential equation with a small parameter at the second derivative. The control is scalar and is subject to geometric constraints. Expansions of a solution to this problem up to any power of the small parameter are constructed and justified.     

Asymptotics of eigenvalues of the Dirichlet boundary value problem for the Lame operator in a three-dimensional domain with a small cavity

A boundary value problem for the Lame operator in a bounded three-dimensional domain with a small cavity is studied. The domain is filled with an elastic homogeneous isotropic medium that is clamped at the boundary, which corresponds to the Dirichlet boundary condition. The leading term of an asymptotic expansion for the eigenvalue is constructed in the case of the Dirichlet limit problem. The asymptotic expansion is constructed in powers of a small parameter ? that is the diameter of the cavity.     

Asymptotic expansion of a solution to a singular perturbation optimal control problem on an interval with integral constraint

A control problem for solutions of a boundary value problem for a second-order ordinary differential equation with a small parameter at the second derivative is considered on a closed interval. The control is scalar and subject to integral constraints. We construct a complete asymptotic expansion in powers of the small parameter in the Erdélyi sense.     

Two boundary value problems for a strongly anisotropic inhomogeneous elastic ring

The second boundary value problem (displacements are given on the boundary) and the improper mixed problem for a cylindrically orthotropic ring are studied. It is assumed that the coefficients of elasticity are continuously differentiable functions of the coordinates and depend on a small parameter in a specific manner. The form of the dependence of the coefficients on the small parameter is selected in such a way that in the case of constant coefficients it describes bonding of the ring by two families of very rigid fibers located along the radius vectors and concentric circles, where the stiffness of the fiber families is of identical order. Consequently, the coefficients of elasticity are represented in the form of products of constants which will later be called provisionally the “stiffnesses”, and functions of the coordinates. It is assumed that the stiffnesses in the radial and circumferential directions are equal and exceed and shear stiffness considerably. The asymptotic form of the solution of the boundary value problems under consideration is constructed when the ratio between the shear stiffness and the stiffness in the radial direction is used as the small parameter. In the case of the second boundary value problem the limit boundary value problem is described by a hyperbolic system of equations and is not solvable uniquely, since one of the families of characteristics is parallel to the boundary. When constructing the asymptotic form the necessity arises to average the coefficients of elasticity with respect to the circumferential coordinate. In this respect, there is an analogy with the results obtained in /1/ where the boundary value problem was studied for a second-order elliptic equation.     

Analysis of Numerical Differentiation Formulas in a Boundary Layer on a Shishkin Grid

A problem of numerical differentiation of functions with large gradients in a boundary layer is investigated. The problem is that for functions with large gradients and a uniform grid the relative error of the classical difference formulas for derivatives may be considerable. It is proposed to use a Shishkin grid to obtain a relative error of the formulas that is independent of a small parameter. Error estimates that depend on the number of nodes of the difference formulas for a derivative of a given order are obtained. It is proved that the error estimate is uniform with respect to the small parameter. In the case of a uniform grid, a boundary layer region is indicated outside of which the numerical differentiation formulas have an error that is uniform with respect to the small parameter. The results of numerical experiments are presented.     

On an eigenvalue for the Laplace operator in a disk with Dirichlet boundary condition on a small part of the boundary in a critical case

A boundary-value problem of finding eigenvalues is considered for the negative Laplace operator in a disk with Neumann boundary condition on almost all the circle except for a small arc of vanishing length, where the Dirichlet boundary condition is imposed. A complete asymptotic expansion with respect to a parameter (the length of the small arc) is constructed for an eigenvalue of this problem that converges to a double eigenvalue of the Neumann problem.     

A Sturm-Liouville Inverse Spectral Problem with Boundary Conditions Depending on the Spectral Parameter

We consider a boundary value problem generated by the Sturm-Liouville equation on a finite interval. Both the equation and the boundary conditions depend quadratically on the spectral parameter. This boundary value problem occurs in the theory of small vibrations of a damped string. The inverse problem, i.e., the problem of recovering the equation and the boundary conditions from the given spectrum, is solved.     

合成展开法应用于球壳对称弯曲的边界层问题

本文推广钱伟长在[5]中提出的合成展开法分析双参数边界层问题. 对于受均布荷载作用的球壳对称变形问题,其非线性平衡方程可以写成(2.3a),(2.3b):式中ε与δ是待定参数.当δ=1,ε是小参数时,这是第一边界层问题:当δ与ε都县小参数时.这是第二边界层问题. 对于上述问题,我们假定ε,δ和p满足ε3pδ=1-ε在这个条件下,应用推广的合成展开法,求出上述问题具有固定边界条件情况的渐近解.