基于对偶混合变分形式的Uzawa型算法

基于弹性接触问题的三变量（应力，位移，接触边界位移）对偶混合变分形式，对混合有限元离散化的单边约束问题，提出了一种Uzawa型算法。首先证明了迭代算法的收敛性，然后用数值例子验证了迭代算法的有效性。     

弹性接触问题的一种新的混合变分形式

1．引言用混合有限元方法求解弹性力学问题,其优点在于可同时求解位移和应力．力学问题的混合变分形式是混合有限元方法的基础．对于弹性接触问题,文献问给出了一种混合变分形式,以及相应的混合有限元分析（也可见[6]）．本文考虑了弹性接触问题的一种新的混合变分形式,它是构造弹性接触问题的另一种混合有限元方法的基础．对于通常的静态弹性力学方程组的边界值（等式情形）问题,熟知可以有二种不同的混合变分形式（例如见门）．第一种混合变分形式中,对位移的求解空间为H‘（刚,对应力的求解空间为L‘（刚;而第二种混合变分形式…     

求解非单调变分不等式的一种半空间投影算法

本文提出了一种求解非单调变分不等式的半空间投影算法,在映射是连续和对偶变分不等式解集非空的假设条件下证明了该算法生成的无穷序列是全局收敛的,并在局部误差界和Lipschitz连续条件下给出了收敛率分析.通过数值实验验证了所提出算法的有效性和可行性.     

弹性接触问题的对偶混合有限元分析

１．引言用混合有限元方法求解弹性力学问题,其优点在于可同时求解位移和应力．力学问题的混合变分形式是混合有限元方法的基础．对于弹性接触问题,文献［６］给出了一种混合变分形式,以及相应的混合有限元分析（也可见［１０］）．其混合变分形式是直接从位移交分方程和Ｈｏｏｋ方程导出的,获得了应力ａ在Ｌ２（Ω）而位移、在Ｈ１（Ω）的一个闭凸子集上求解的混合变分问题．本文在［９］中提出的混合变分形式的基础上,再引入另一个Ｌａｐｒａｎｇｅ乘子,获得了三重组混合变分形式．它能同时求解物体内点的应力,位移和接触边界上的…     

一种新的求解拟单调变分不等式的压缩投影算法

2020年Liu和Yang提出了求解Hilbert空间中拟单调且Lipschitz连续的变分不等式问题的投影算法,简称LYA。本文在欧氏空间中提出了一种新的求解拟单调变分不等式的压缩投影算法,简称NPCA。新算法削弱了LYA中映射的Lipschitz连续性。在映射连续、拟单调且对偶变分不等式解集非空的条件下得到了NPCA所生成点列的聚点是解的结论。当变分不等式的解集还满足一定条件时,得到了NPCA的全局收敛性。数值实验结果表明NPCA所需的迭代步数少于LYA的迭代步数,NPCA在高维拟单调例子中所需的计算机耗时也更少。     

解可分离结构变分不等式的一种新的交替方向法

交替方向法是求解可分离结构变分不等式问题的经典方法之一, 它将一个大型的变分不等式问题分解成若干个小规模的变分不等式问题进行迭代求解. 但每步迭代过程中求解的子问题仍然摆脱不了求解变分不等式子问题的瓶颈. 从数值计算上来说, 求解一个变分不等式并不是一件容易的事情.因此, 本文提出一种新的交替方向法, 每步迭代只需要求解一个变分不等式子问题和一个强单调的非线性方程组子问题. 相对变分不等式问题而言, 我们更容易、且有更多的有效算法求解一个非线性方程组问题. 在与经典的交替方向法相同的假设条件下, 我们证明了新算法的全局收敛性. 进一步的数值试验也验证了新算法的有效性.     

一般混合似变分不等式的隐式迭代算法

对一般混合似变分不等式的若干隐式迭代算法进行了研究;利用一般混合似变分不等式与不动点问题和预解方程的等价关系,采用分裂技巧和自适应迭代技巧结合,提出了一个求解一般混合似变分不等式的新的隐式迭代算法;并证明了该算法在算子T是g-单调连续的条件下收敛．     

求解拟变分不等式问题的一种投影算法

拟变分不等式问题在经济、工程,最优化和控制等领域都有着广泛的应用,目前,对拟变分不等式问题的研究还处于初级阶段.在本文中,我们利用梯度投影技术,给出了一种求解拟变分不等式问题的投影类算法,证明了该算法的全局收敛性,并给出了数值试验结果.     

非线性最优控制问题的保辛多层次求解方法

将非线性系统的最优控制问题导向Hamilton系统,提出了求解非线性最优控制问题的保辛多层次方法．首先,以时间区段两端状态为独立变量并在区段内采用Lagrange插值近似状态和协态变量,通过对偶变量变分原理将非线性最优控制问题转化为非线性方程组的求解．然后,在保辛算法的具体实施过程中提出了多层次求解思想,以2N类算法为基础由低层次到高层次加密离散时间区段,利用Lagrange插值得到网格加密后的初始状态与协态变量作为求解非线性方程组的初值,可提高计算效率．数值算例验证了算法在求解效率与求解精度上的有效性．     

关于混合拟似变分包含问题的解的迭代算法

本文对混合拟似变分包含问题提出新的辅助变分不等式,首先证明辅助变分不等式存在唯一解.然后,通过这一辅助形式建立混和拟似变分包含问题解的迭代算法.最后讨论在新的算法下迭代解的收敛性.     

On Quasimonotone Variational Inequalities

In this paper, we study variational inequalities with multivalued mappings. By employing Fan's lemma, we establish the existence result for the dual formulation of variational inequalities with semistrictly quasimonotone mappings. We also show that similar results for quasimonotone variational inequalities do not hold.     

Variational formulation of the material failure process in solids by embedded discontinuities model

This work presents a variational formulation of the material failure process, idealized as strain or displacement discontinuities, by weak, strong, or discrete embedded discontinuities into a continuum. It is shown that the solution of the proposed variational formulation may be approximated by different types of finite elements with embedded discontinuities. The developed displacement approximation of a finite element split by the discontinuity leads to a symmetric stiffness matrix, which considers not only the continuity of tractions but also the rigid body relative motions of the portions in which the element is split. The variational formulation of a continuum with more than one discontinuity in its interior is developed. It is shown that this formulation may lead to finite elements with embedded discontinuities that can be classified as displacement, force, mixed, and hybrid models. To show the effectiveness of the proposed formulation, the classical example of a bar under tension is solved using one and 2D finite element approximations. © 2008 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq, 2009     

无单调性集值变分不等式的一种投影算法

本文给出了求解无单调性集值变分不等式的一个新的投影算法,该算法所产生的迭代序列在Minty变分不等式解集非空且映射满足一定的连续性条件下收敛到解.对比文献[10]中的算法,本文中的算法使用了不同的线性搜索和半空间,在计算本文所引的两个数值例子时,该算法比文献[10]中的算法所需迭代步更少.     

Uzawa iteration method for stokes type variational inequality of the second kind

In this paper,the Uzawa iteration algorithm is applied to the Stokes problem with nonlinear slip boundary conditions whose variational formulation is the variational inequality of the second kind.Firstly, the multiplier in a convex set is introduced such that the variational inequality is equivalent to the variational identity.Moreover,the solution of the variational identity satisfies the saddle-point problem of the Lagrangian functional ?.Subsequently,the Uzawa algorithm is proposed to solve the solution of the saddle-point problem. We show the convergence of the algorithm and obtain the convergence rate.Finally,we give the numerical results to verify the feasibility of the Uzawa algorithm.     

Variational formulation and efficient implementation for solving the tempered fractional problems

Because of the finiteness of the life span and boundedness of the physical space, the more reasonable or physical choice is the tempered power‐law instead of pure power‐law for the CTRW model in characterizing the waiting time and jump length of the motion of particles. This paper focuses on providing the variational formulation and efficient implementation for solving the corresponding deterministic/macroscopic models, including the space tempered fractional equation and time tempered fractional equation. The convergence, numerical stability, and a series of variational equalities are theoretically proved. And the theoretical results are confirmed by numerical experiments.     

Augmented Macro-Hybrid Mixed Finite Element Schemes for Elastic Contact Problems

On a setting of subdifferential models, variational augmented macro-hybrid mixed finite element schemes are formulated and analyzed for elastic unilateral contact problems with prescribed friction. Composition duality principles determine primal and dual mixed solvability, adopting coupling surjectivity for dualization. Macro-hybridization corresponds to nonoverlapping decompositions of elastic solid body systems, with displacement continuity and traction equilibrium transmission conditions dualized. In general, traction and displacement multipliers synchronize sub-bodies through nonmatching finite element interfaces. Three-field formulations give the basis for variational augmentation, in a sense of exact penalization, allowing speed-up of rates of convergence as well as proximation procedures of parallel numerical resolution algorithms.     

Primal-dual variational problems by boundary and finite elements

In this paper the primal-dual (or mixed) formulation is studied for self-adjoint elliptic problems coupled with a boundary integral equation. It is shown that, after introducing a suitable complementary variational principle, the problem is reduced to finding a stationarity point of a constrained functional. Some numerical examples are reported for a second-order differential equation on unbounded domains.