关于中子扩散方程的一个变分方法

本文对中子扩散方程提出了一个变分方法,这个方法使不同扩散区域间的边界条件在泛函的变分中自然地得出。为了说明这方法的可靠程度,我们用这个方法对具有解析解的球对称反应堆方程求解,用变分法算得结果与解析解的值十分接近。     

一类带停时的奇异型随机控制问题的研究

以随机分析的知识和最优控制理论为基础,讨论了一类带停时的奇异型随机控制的折扣费用模型,在原模型的状态过程的基础上添加了漂移因子和扩散因子,并在λ＜δα的情况下讨论了该问题相应的变分方程的解,给出了此随机控制问题的最优策略,即最优控制和最优停时,并且证明了变分方程的解即为最优费用函数.     

一类渐进线性Kirchhoff方程解的多重性

研究一类全空间上的Kirchhoff型方程.当非线性项在无穷远处渐进线性增长时,利用变分方法建立方程解的多解性及非存在性结果,改进了相关文献中的结论.     

变质量高阶非ЧeTaeB型非完整约束系统动力学

本文给出了高了阶非ЧｅＴａｅＢ约束加在广义虚位移上的限制条件，建立了变质量高阶非ЧｅＴａｅＢ型非线性非完整系统的Ｒｏｕｔｈ方程，ЧａПЛЫГИН方程、Ｎｉｅｌｓｅｎ方程，给出了高阶非ЧｅＴａｅＢ型约束系统“ｄ”与“δ”之间的产换关系，建立了其积分变分原理，并得到了变质量高阶非ЧｅＴａｅＢ型约束系统的广义Ｎｏｅｔｈｅｒ守恒律。     

一类具有变号位势的超二次Kirchhoff方程解的多重性

本文研究一类全空间上的Kirchhoff型方程.当非线性项是凹凸混合项且f在无穷远处满足超二次增长时,利用变分方法获得方程解的多重性结果,改进和推广了相关文献中的结论.     

一个扩散问题的自然边界元法与有限元法组合

本文讨论由Helmholtz方程描述的扩散问题的自然边界元法与有限元法的组合．取一个圆作为公共边界，用Fourier展开建立边界积分方程，将无界区域上的问题化为有界区域上的非局部边值问题．在变分方程中公共边界上的未知量只包含函数本身而不包含其法向导数，从而减少了未知数的数目，并且边界元剐度矩阵只有极少量不同的元素，有利于数值计算．这种组台方法优越于建立在直接边界元法基础上的组合方法．文中证明了变分解的唯一性，数值解的收敛性和误差估计．最后讨论了数值技术并给出一个算倒．     

变质量高阶非Четаев型非完整约束系统动力学

本文给出了高阶非型约束加在广义虚位移上的限制条件，建立了变质量高阶非型非线性非完整系统的Ｒｏｕｔｈ方程、方程、Ｎｉｅｌｓｅｎ方程和Ａｐｐｅｌｌ方程；给出了高阶非型约束系统“ｄ”与“δ”之间的交换关系，建立了其积分变分原理；并得到了变质量高阶非型约束系统的广义Ｎｏｅｔｈｅｒ守恒律．     

二阶中立型变时滞差分方程解的振动性

研究了二阶中立型变时滞差分方程Δ2(xn+pxn-l)+qnf(xσ(n))=0解的振动性,获得了该类方程全部非平凡解振动的三个定理.所得结果将二阶中立型差分方程已有的振动性的相应结论推广到了二阶中立型变时滞差分方程.     

一类带有组合非线性项Kirchhoff方程解的多重性

本文研究一类全空间上的Kirchhoff型方程.当非线性项在无穷远处是线性有界时,利用变分方法建立方程解的多解性结果,并讨论次线性项对问题解的多重性的具体影响,改进了相关文献中的结论.     

一类非线性抛物型方程广义差分法的变分原理及H~1模误差估计

和有限元方法类似,广义差分法属于基于变分原理的差分格式,是解偏微分方程的一种有效的数值方法.因此,寻求对应于定解问题的广义差分法的变分原理是很重要的,本文第一部分内容即属此.本文还给出了用此方法解一类非线性抛物型方程的H~1模误差估计.     

与随机控制有关的一类变分方程(Ⅰ)

本文讨论了一些有关微分方程的复杂的分析问题并得到一系列结论,这些结论在本文（Ⅱ）中变分方程问题的研究中起关键作用．     

Applications of He’s principles to partial differential equations

This paper applies the variational iteration method (VIM) and semi-inverse variational principle to obtain solutions of linear and nonlinear partial differential equations. The nonlinear model is considered from gas dynamics, fluid dynamics and Burgers equation. The linear model is the heat transfer (diffusion) equation. Results show that variational iteration method is a powerful mathematical tool for solving linear and nonlinear partial differential equations, and therefore, can be widely applied to engineering problems.     

Boundedness of a Derived Function of a Solution About a Class of Diffusion Variational Equations

In this paper the boundedness of a derived function of a solution about a class of diffusion variational equations is discussed. The application of it to related stochastic analysis problems is also illustrated. What should be emphasized is that the problem discussed and the ways proved in this paper are fundamentally new and the conclusion of this paper is fairly profound.     

Necessary conditions for stochastic optimal control problems in infinite dimensions

The purpose of this paper is to establish the first and second order necessary conditions for stochastic optimal controls in infinite dimensions. The control system is governed by a stochastic evolution equation, in which both drift and diffusion terms may contain the control variable and the set of controls is allowed to be nonconvex. Only one adjoint equation is introduced to derive the first order necessary optimality condition either by means of the classical variational analysis approach or, under an additional assumption, by using differential calculus of set-valued maps. More importantly, in order to avoid the essential difficulty with the well-posedness of higher order adjoint equations, using again the classical variational analysis approach, only the first and the second order adjoint equations are needed to formulate the second order necessary optimality condition, in which the solutions to the second order adjoint equation are understood in the sense of the relaxed transposition.     

对流扩散方程一类改进的特征线修正有限元方法

１引言在地下水污染,地下渗流驱动,核污染,半导体等问题的数值模拟中,均涉及抛物型对流扩散方程（或方程组）的数值求解问题．这些对流扩散型偏微分方程（或方程组）具有共同的特点：对流的影响远大于扩散的影响,即对流占优性,对流占优性给问题的数值求解带来许多困难,因此对流占优问题的有效数值解法一直是计算数学中重要的研究内容．用通常的差分法或有限元法进行数值求解将出现数值振荡．为了克服数值振荡,提出各种迎风方法和修正的特征方法并在这些问题上得到成功的实际应用、８０年代,Ｄｏｕｇｌａｓ和Ｒｕｓｓｅｌｌ［２］等…     

A system of boundary integral equations for the transmission problem in acoustics

In this paper, we reduce the classical two-dimensional transmission problem in acoustic scattering to a system of coupled boundary integral equations (BIEs), and consider the weak formulation of the resulting equations. Uniqueness and existence results for the weak solution of corresponding variational equations are established. In contrast to the coupled system in Costabel and Stephan (1985) [4], we need to take into account exceptional frequencies to obtain the unique solvability. Boundary element methods (BEM) based on both the standard and a two-level fast multipole Galerkin schemes are employed to compute the solution of the variational equation. Numerical results are presented to verify the efficiency and accuracy of the numerical methods.     

Multi-valued,singular stochastic evolution inclusions

We provide an abstract variational existence and uniqueness result for multi-valued, monotone, non-coercive stochastic evolution inclusions in Hilbert spaces with general additive and Wiener multiplicative noise. As examples we discuss certain singular diffusion equations such as the stochastic 1-Laplacian evolution (total variation flow) in all space dimensions and the stochastic singular fast-diffusion equation. In case of additive Wiener noise we prove the existence of a unique weak-⁎ mean ergodic invariant measure.     

Application of He's variational iteration method for solving the Cauchy reaction–diffusion problem

In this paper, the solution of Cauchy reaction–diffusion problem is presented by means of variational iteration method. Reaction–diffusion equations have special importance in engineering and sciences and constitute a good model for many systems in various fields. Application of variational iteration technique to this problem shows the rapid convergence of the sequence constructed by this method to the exact solution. Moreover, this technique does not require any discretization, linearization or small perturbations and therefore it reduces significantly the numerical computations.     

The variational iteration method for analytic treatment for linear and nonlinear ODEs

In this work, the variational iteration method (VIM) is used for analytic treatment of the linear and nonlinear ordinary differential equations, homogeneous or inhomogeneous. The method is capable of reducing the size of calculations and handles both linear and nonlinear equations, homogeneous or inhomogeneous, in a direct manner. However, for concrete problems, a huge number of iterations are needed for a reasonable level of accuracy.     

Application of He's variational iteration method to nonlinear Jaulent–Miodek equations and comparing it with ADM

Instead of finding a small parameter for solving nonlinear problems through perturbation method, a new analytical method called He's variational iteration method (VIM) is introduced to be applied to solve nonlinear Jaulent–Miodek, coupled KdV and coupled MKdV equations in this article. In this method, general Lagrange multipliers are introduced to construct correction functionals for the problems. The multipliers can be identified optimally via the variational theory. The results are compared with exact solutions.