弹性理论中的临界变分及消除方法

临界变分现象是拉氏乘子法的固有特性，钱伟长应用高阶拉氏乘子消除了临界变分现象。本文将提出一种新的方法－凑合反推法，这种方法摒充了拉氏乘子法，把拉氏乘子所在的项目一个待定函数Ｆ代替。这样构成的泛函，作者称之为试泛函。而待定函数Ｆ的识别类似于拉氏乘子的识别。通过该法可以方便地构造出各种多变量广义变分原理，并且可以消除临界变分现象。     

非线性问题的变分迭代方法及其应用

本文应用变分的概念，提出了求解非线性问题的加速迭代方法．这一方法的基本思想是：先给出问题的近似解，再引进一乘子校正其近似解；而乘子可用变分的概念最优确定，几个例子说明这种方法是有效的．     

建议一种非线性弹性论的约束变分原理及其与广义变分原理的协调性

本文建议一种新的约束变分原理,通过拉氏乘子法构成广义变分原理,其拉氏乘子不为零值.     

关于拉氏乘子的识别

本文讨论了在消元识别和换元识别过程中拉氏乘子的不唯一性问题，拉氏乘子表达方式的不唯一性反映了消元或换元方式的多样性，由于不同的消元或换元方式不改变问题，拉氏乘子的解仍是唯一的，因而由不同的拉氏乘子表达式可以得到一族具有价驻值条件的无约束驻值问题，本文用换元识别法，推导了Ｈｅｌｌｉｎｇｅｒ－Ｒｅｉｓｓｎｅｒ变分原理和胡一鹫变分原理及其更多样的形式。     

论拉氏乘子法及其唯一性问题

本文指出文[13](1985)对于拉氏乘子法的最近论点仍旧是先验的,并不是国际上大家所公认而又证实了的“古老的数学概念”(1983),该文所赖以立论的三个实例,都不成立。所说明的,不是象文中所称的那样,“在力学问题中正确应用拉氏乘子法的要点”,恰好相反,文[13]很不正确地应用了拉氏乘子法,从而达到了错误结论,甚至只能求助于所谓“猜谜语“的方法。 本文也指出拉氏乘于是可以根据拉氏乘子法唯一地识別的,文[10]、文[16]说拉氏乘子的不唯一性应是对拉氏乘子法的误解所引起的。 本文讨论的弹性力学问题是非线性弹性体的一般弹性力学问题,其应力应变关系是非线性的,当应变很小可以略去其非线性项时,其结果可以还原为线性弹性体的各种广义变分原理。因此,不论Hellinger-Reissner 原理或胡-鹫原理都是本文所讨论的非线性弹性体的广义变分原理的近似特例。     

粘性流动动力学有限元变分原理

本文把建立有限元变分原理的一种新方法“Ｎ〉２直接方法”从固体力学推广到流体力学，并用该方法把粘性流体动力学的广义功率消耗原理＾［２］和广义变分原理＾［２］发展成为有限元变分原理。还在论证中发现，相邻有限元交界面上的应力协调条件会自然地满足而无需引进任何拉氏乘子。本文还建立了混合杂交非协调元的变分原理和广义变分原理，它解除了全部协调性约束条件和其它的边界性约束条件，但是并不增加待定的拉氏乘子，因此使     

粘性流体动力学有限元变分原理

本文把建立有限元变分原理的一种新方法“N>2直接方法”从固体力学推广到流体力学,并用该方法把粘性流体动力学的广义功率消耗原理和广义变分原理发展成为有限元变分原理。还在论证中发现,相邻有限元交界面上的应力协调条件会自然地满足而无需引进任何拉民乘子。本文还建立了混合杂交非协调元的变分原理和广义变分原理,它解除了全部协调性约束条件和其它的边界性约束条件,但是并不增加待定的拉氏乘子,因此使有限元计算得到简化。本文结果可以作为粘性流体动力学有限元计算的基础定理。     

关于拉格朗日乘子法及其它

本文通过推理和举例,说明了在力学问题中正确应用拉氏乘子法的要点。指出了对应于一个力学问题可能有多个不等价的和等价的变分原理,说明了有些所谓更一般的广义变分原理乃是众所周知的变分原理的简单组合。     

非线性薄壁复合曲梁广义变分原理之研究

应用拉氏乘子法建立了两端边界均为完全约束的复合材料自然弯曲闭口薄壁细长梁大位移变形弹性理论的非完全广义变分原理的泛函￣［１，２］，其中考虑了对叠层复合材料变得敏感的横向剪切变形以及和扭转有关的翘曲变形的影响，分析中还包括了拉压、弯曲和扭转的相互耦合。由泛函驻值条件可以导出所给问题的平衡方程及全部边界条件。上述方法还可以方便地推广到其它各种非完全约束边界的情况。此外，广义变分原理建立也有助于扩大有限元法和其它近似方法在薄壁复合曲梁中的应用。     

一种新的三维动力接触约束单元

本文应用广义变分原理，利用拉氏乘子法和罚函数法计入接触约束条件修正，建立了分析三维动力接触问题的一般有限元分析的理论模式；推导了处理这类问题的一种新的接触约束单元的接触刚度矩阵；采用增量求解模型解，研编了实施程序３ＤＤＣＦ；处理了方程中的病态问题、碰撞及能量释放条件问题。进行了算例考核，还首次给出了一个三维动力接触问题的算例结果。     

Note on the critical variational state in elasticity theory

Recently Prof. Chien Wei-zang pointed out that in certain cases, by means of ordinary Lagrange multiplier method, some of undetermined Lagrange multipliers may turn out to be zero during variation. This is a critical state of variation. In this critical state, the corresponding variational constraint can not be eliminated by means of simple Lagrange multiplier method. This is indeed the case when one tries to eliminate the constraint condition of strain-stress relation in variational principle of minimum complementary energy by the method of Lagrange multiplier.By means of Lagrange multiplier method, one can only derive, from minimum complementary energy principle, the Hellinger-Reissner Principle, in which only two type of in-dependent variables, stresses and displacements, exist in the new functional. Hence Prof. Chien introduced the high-order Lagrang multiplier method bu adding the quadratic terms.to original functions. The purpose of this paper is to show that by adding to original functionals one     

Further study of the equivalent theorem of Hellinger-Reissner and Hu-Washizu variational principles

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Involutory transformations and variational principles with multi-varoables in thin plate bending problems

In this paper, the generalizd variational principles of plate bending, froblems are established from their minimum potential energy principle and minimum complementary energy principle through the elimination of their constraints by means of the method of Lagrange multipliers. The involutory transformations are also introduced in order to reduce the order of differentiations for the variables in the variation. Funhermore, these involutory transformations become infacl the additional constraints in the varialion. and additional Lagrange multipliers may be used in order to remove these additional constraints. Thus, various multi-variable variational principles are obtained for the plate bending problems. However, it is observed that. nol all the constrainls ofva’iaticn can be removed simply by the ordinary method of linear Lagrange multipliers. In such cases, the method of high-order Lagrange multipliers are usedto remove iliose constrainls left over by ordinary linear multiplier method. And consequently. some funct ionals of more general forms are oblained for the generaleed variational principles of plate bending problems.     

Variational principles and generalized variational principles in hydrodynamics of viscous fluids

In this paper, the variational principles of hydrodynamic problems for the incompressible and compressible viscous fluids are established. These principles are principles of maximum power losses. Their generalized variational principles are also discussed on the basis of Lagrangian multiplier methods.     

Method of high-order lagrange multiplier and generalized variational principles of elasticity with more general forms of functionals

It is known[1]that the minimum principles of potential energy andcomplementary energy are the conditional variation principles underrespective conditions of constraints.By means of the method of La-grange multipliers,we are able to reduce the functionals of condi-tional variation principles to new functionals of non-conditionalvariation principles.This method can be described as follows:Mul-tiply undetermined Lagrange multipliers by various constraints,andadd these products to the original functionals.Considering these un-determined Lagrange multipliers and the original variables in thesenew functionals as independent variables of variation,we can see thatthe stationary conditions of these functionals give these undeter-mined Lagrange multipliers in terms of original variables.The sub-stitutions of these results for Lagrange multipliers into the abovefunctionals lead to the functionals of these non-conditional varia-tion principles.However,in certain cases,some of the undetermined Lagrangemultipliers ma     

Numerical solution of the Klein–Gordon equation via He’s variational iteration method

In this paper, we present the solution of the Klein--Gordon equation. Klein--Gordon equation is the relativistic version of the Schrödinger equation, which is used to describe spinless particles. The He’s variational iteration method (VIM) is implemented to give approximate and analytical solutions for this equation. The variational iteration method is based on the incorporation of a general Lagrange multiplier in the construction of correction functional for the equation. Application of variational iteration technique to this problem shows rapid convergence of the sequence constructed by this method to the exact solution. Moreover, this technique reduces the volume of calculations by avoiding discretization of the variables, linearization or small perturbations.     

New applications of variational iteration method using Adomian polynomials

In this paper, we discuss a new application of the variational iteration method considering Adomian’s polynomials on nonlinear physical equations. Two models of interest in physics are considered and solved by means of the variational iteration method. The behavior of the variational iteration method and the effects of different values of t are investigated. Comparisons are made among the standard Adomian decomposition method, exact solutions, and the proposed method. He’s variational iteration method is introduced to overcome the difficulty arising in calculating the Adomian polynomial in Adomian decomposition method. The results reveal that the proposed method is very effective and simple and can be applied to other nonlinear problems.