强不定问题的变分方法

本文概述作者承担的国家自然科学基金项目所获得的部分成果,特别是从源头出发系统地培育强不定问题变分方法的特色方向,并开启一些应用问题的研究,包括(1)建立强不定问题的变分框架的基本方法;(2)建立局部凸拓扑线性空间的形变理论,相应得到处理强不定问题的临界点定理;(3)首次研究非自治稳态Dirac系统解的存在性,特别是突破强不定困难获得其半经典解的存在性、集中现象和指数衰减性;(4)首次得到非线性(非自治、无界Hamilton型)反应-扩散系统整体解的存在性和多重性,特别是奇异扰动下其基态解的存在性、集中现象和衰减性;(5)深入研究Hamilton系统的同宿轨和Schrdinger方程的全局解;(6)其他初始性工作,如自旋流形上的Dirac方程的分歧现象.     

广义集值强非线性混合似变分不等式解的迭代逼近

延拓辅助原理的技巧研究一类取非紧值的集值映象的广义强非线性混合似变分不等式．证明了这类广义强非线性混合似变分不等式的辅助问题解的存在性．利用该存在性结果,给出了解这类广义强非线性混合似变分不等式的迭代算法,最终证明了这类广义强非线性混合似变分不等式解的存在性及由算法生成的迭代序列的收敛性．     

广义集值强非线性混合似变分不等式的辅助原理和三步迭代算法

使用辅助原理技巧研究了一类广义集值强非线性混合变分不等式．证明了此类集值强非线性混合变分不等式辅助问题解的存在性和唯一性;构建了一个新的三步迭代算法,通过辅助原理技巧,构建并计算此类非线性混合变分不等式的近似解,进一步证明非线性混合变分不等式解的存在性以及由算法产生的三个序列的收敛性．所得结论推广了近年来许多混合变分不等式和准变分不等式以及他们的有关结果．     

资料变分同化中的若干理论问题

对变分同化中的若干理论问题进行了研究,具体讨论了一类简单模式在整体和局部观测资料下的变分同化问题．对于整体观测资料下的变分同化问题,利用变分同化方法对预报模式中的初值、参数以及模式进行了修正,从理论上作出了变分同化方法的误差估计及收敛精度的估计,证明了变分同化方法的有效性．对于局部观测资料下的变分同化问题,由于得到的解往往不适定,因而通常的变分同化方法失效．为了克服问题的不适定性所带来的困难,利用变分同化结合正则化方法对预报模式中的初值、参数以及模式进行修正,同样作出了变分同化方法的误差估计及收敛精度估计,证明了变分同化与正则化方法结合的必要性和有效性,并对正则化参数的选择提供了理论判据．最后,举了一个实例说明所提出的方法的有效性．     

细长杆的Cosserat动力学模型和变分原理

利用Cosserat理论建立了细长杆的三维非线性动力学模型,借助伪刚体法和变分原理得到了Cosserat杆的包括各种形变的三维空间运动方程.     

含有锥约束的多目标变分问题的广义对称对偶性

本文研究了一类含有锥约束多目标变分问题的广义对称对偶性.利用函数的(F,ρ)-不变凸性的条件,得出了多目标变分问题关于有效解的弱对偶定理、强对偶定理和逆对偶定理,将多目标变分问题的对称对偶性理论推广到含有锥约束的广义对称对偶性上来.     

电动力学电磁场边值问题的广义变分原理

给出了线性各项异性电磁场边值问题的广义虚功原理表达式,运用钱伟长教授提出的方法建立了该问题的广义变分原理,可直接反映该问题的全部特征,即4个Maxwell方程、2个场强-位势方程、2个本构方程和8个边界条件．继而导出了一族有先决条件的广义变分原理．作为例证,导出了两个退化形式的广义变分原理,和已知的广义变分原理等价．此外还导出了两个修正的广义变分原理,可为该问题提供杂交有限元模型．建立的各广义变分原理可为电磁场边值问题的有限元应用提供更为完善的理论基础．     

一类ψ-强增生型变分包含问题解的存在性与迭代逼近

本研究Banach空间中一类新的ψ-强增生型变分包含问题．在实的自反的光滑Banach空间中．证明了这类变分包含问题解的存在唯一性及其带误差的Ishikawa迭代程序的收敛性．本结果是张石生教授等人的早期与最近的结果的改进与推广．     

大应变固结理论的分区变分原理及其广义变分原理

土体材料本构特性的差异问题与大变形问题是分析岩土材料变形特性的基本问题．根据有限变形的描述方法构筑土体结构大变形固结方程,证明了大变形固结的变分原理A·D2应用分区子结构的连续条件,推导固结理论的分区变分原理．引用Lagrange乘子法构筑并证明了大变形固结问题在无约束状态下的广义分区变分原理．     

一类新的Ф-强增生型变分包含问题

本文研究了Banach空间中一类新的Ф-强增生型变分包含问题．在实自反Banach空间中，证明了这类变分包含问题解的存在唯一性及其带有混合误差项的Ishikawa迭代程序的收敛性．本文结果是张石生教授和曾六川教授等人的早期与最近的结果的改进与推广．     

Nontrivial solutions for resonant noncooperative elliptic systems

In this paper, by introducing some new conditions, we study the nontrivial (multiple) solutions for resonant noncooperative elliptic systems. Our main ingredients are using a new version of Morse theory for strongly indefinite functionals and precisely computing the critical groups of the associated variational functionals at zero and at infinity. © 2000 John Wiley & Sons, Inc.     

Dirichlet problems with double resonance and an indefinite potential

We consider semilinear Dirichlet problems with an unbounded and indefinite potential and with a Carathéodory reaction. We assume that asymptotically at infinity the problem exhibits double resonance. Using variational methods, together with Morse theory and flow invariance arguments, we prove multiplicity theorems producing three, five, six or seven nontrivial smooth solutions. In most multiplicity theorems, we provide precise sign information for all the solutions established.     

Bifurcation for strongly indefinite functional and applications to Hamiltonian system and noncooperative elliptic system

In this paper, we discuss the bifurcation problems for strongly indefinite functional via Morse theory. The generalized topological degree for a class of vector fields is defined. As applications, we study the bifurcation problems for Hamiltonian system and noncooperative elliptic system.     

The effects of concave and convex nonlinearities in some noncooperative elliptic systems

We consider a class of elliptic systems leading to strongly indefinite functionals, with nonlinearities which involve a combination of concave and convex terms. Using variational methods, we prove the existence of infinitely many large and small energy solutions. Our approach relies on new critical point theorems which guarantee the existence of infinitely many critical values of a wide class of strongly indefinite even functionals. Our abstract critical points theorems generalize the fountain theorems of T. Bartsch and M. Willem.     

Asymptotic behaviour of ground states

We derive the asymptotic behaviour of the ground states of a system of two coupled semilinear Poisson equations with a strongly indefinite variational structure in the critical Sobolev growth case.

     

Solitary waves for the Klein–Gordon–Dirac model

We study the existence of solitary waves for non-autonomous Klein–Gordon–Dirac equations with a subcritical nonlinear term via variational methods. The problem is strongly indefinite and lacks compactness. To overcome these difficulties, we use the linking and concentration-compactness arguments.     

T-coercivity and continuous Galerkin methods: application to transmission problems with sign changing coefficients

To solve variational indefinite problems, one uses classically the Banach–Ne?as–Babu?ka theory. Here, we study an alternate theory to solve those problems: T-coercivity. Moreover, we prove that one can use this theory to solve the approximate problems, which provides an alternative to the celebrated Fortin lemma. We apply this theory to solve the indefinite problem $\text{ div}\sigma \nabla u=f$ set in $H^1_0$ , with $\sigma $ exhibiting a sign change.     

A new morse index theory for strongly indefinite functionals

In this paper, a new Morse index theory for strongly indefinite functionals was developed via Gălerkin approximation. In particular, the abstract theory is valid for those kinds of strongly indefinite functionals corresponding to wave equation and beam equation.     

General fractional variational problem depending on indefinite integrals

In this report, we consider two kind of general fractional variational problem depending on indefinite integrals include unconstrained problem and isoperimetric problem. These problems can have multiple dependent variables, multiorder fractional derivatives, multiorder integral derivatives and boundary conditions. For both problems, we obtain the Euler-Lagrange type necessary conditions which must be satisfied for the given functional to be extremum. Also, we apply the Rayleigh-Ritz method for solving the unconstrained general fractional variational problem depending on indefinite integrals. By this method, the given problem is reduced to the problem for solving a system of algebraic equations using shifted Legendre polynomials basis functions. An approximate solution for this problem is obtained by solving the system. We discuss the analytic convergence of this method and finally by some examples will be showing the accurately and applicability for this technique.     

On a class of elliptic problems with indefinite nonlinearities

In this paper we apply variational and sub-supersolution methods to study the existence and multiplicity of nonnegative solutions for a class of indefinite semilinear elliptic problems that depend on a parameter. The results on the existence of solutions do not impose any growth condition at infinity on the term which depends on the parameter. To derive such results, first we find a positive supersolution by solving an auxiliary problem. Then we use a truncation argument and a global minimization method. The main hypothesis for the existence of two nonzero solutions is that the indefinite term is the product of a weight function, having a thick zero set, and a nonlinear function which satisfies the Ambrosetti–Rabinowitz superlinear condition. Results for some corresponding indefinite problems are also established.