Fuzzy variational principle and its applications

Linear and non-linear peaky fuzzy numbers and their arithmetic operations are constructed for the analysis of engineering structures with fuzzy characteristic quantities. Fuzziness of the corresponding quantities is consistently incorporated into the functional of the total potential energy. A set of deterministic recursive equations is obtained as the alternative expressions of the fuzzy variational principle by means of the second-order perturbation technique. The fuzzy Ritz method and the fuzzy finite element method are presented as the applications of the fuzzy variational principle. Accordingly, the roundabout procedures frequently used in the formulations of the fuzzy finite element method are avoided. A benchmark problem of a bending beam with fuzzy Young's modulus under fuzzy external loading is solved by the developed fuzzy numerical methods. Numerical examples show that results determined by these two fuzzy methods are both little conservative, and are in good agreement with those obtained by the analytical method. Moreover, the fuzzy Ritz method or the fuzzy finite element method can provide more valuable information than the conventional deterministic methods.     

A variational principle for the dynamic problem of linear coupled thermoelasticity

Summary A functional is constructed by whose stationarity the mixed problem for linear and dynamic thermoelasticity is obtained. In contrast with previous results[2], [4], [8], neither constrained variations nor previous transformations upon the equations of the problem are used. The unrestricted variational formulation is made possible by means of a convolutive bilinear form.

---

Sommario Si costruisce un funzionale dalla cui stazionarietà si ricava il problema misto della termoelasticità lineare accoppiata. A differenza di precedenti risultati[2], [4], [8] non si ricorre né a variazioni bloccate né a preliminari trasformazioni del problema. La formulazione variazionale non ristretta è resa possibile dall'uso di una forma bilineare convolutiva.

---

---

Work done in the sphere of activity of the Group for Mathematical Research of the (Italian) C.N.R.     

The parametric variational principle for elastoplasticity

A parametric variational principle, the parametric minimum potential energy principle (abbreviated to PMPEP), is presented for the elastoplastic problems. The principle proposed is free from the restraint of Drucker's postulate and consequently suitable for solving the nonassociated plastic flow problems in rock, soil, concrete and other geomaterials.     

???????????????嶯???????????

针对充黏性液体的刚体,给出了一种应用Jourdain变分原理推导系统动力学方程的方法.将流体微团上所受的表面力合力视为质点系的主动力,出现在系统内力的虚功率中,代入系统的动力学普遍方程,从而获得充液刚体系统的Newton-Euler方程及腔内液体的Navier-Stokes方程.该方法不仅可以导出充黏性液体系统的动力学方程,还可以退化为充理想液体的系统动力学方程.     

The variational principle of thin shell in stability

ＴＨＥＶＡＲＩＡＴＩＯＮＡＬＰＲＩＮＣＩＰＬＥＯＦＴＨＩＮＳＨＥＬＬＩＮＳＴＡＢＩＬＩＴＹＨｕａｎｇｙａｎ黄炎,ＨｕａｎｇＲｅｉｆａｎｇ黄瑞芳（ＲｅｃｅｉｅｄＮｏｖ．１８．１９９４ＣｏｍｍｕｎｉｃａｔｅｄｂｙＣｈｉｅｎＷｅｉｚａｎｇ）Ａｂｓｔｒａｃｔ...     

The random variational principle and finite element method

In this paper, we introduced the random materials, geometrical shapes, force and displacement boundary condition directly into the functional variational formulations and developed a unified random variational principle and finite element method with the small parameter perturbation method. Numerical examples showed that the methods have the advantages of the simple and convenient program implementation, and are effective for the random mechanics problems.     

On Chien's question to the Hu-Washizu three-field functional and variational principle

There is an open question,namely Chien’s question,in construction of a generalized functional in elasticity,i.e.,why the stress-strain relation can still be derived from the Hu-Washizu generalized variational principle while the Lagrangian multiplier method is applied in vain?This study shows that the generalized variational principle can only be understood and implemented correctly within the framework of thermodynamics.This investigation finds that as long as the functional has one of the comb...     

薄板理论的正交关系及其变分原理

利用平面弹性与板弯曲的相似性理论，将弹性力学新正交关系中构造对偶向量的思路推广到 各向同性薄板弹性弯曲问题，由混合变量求解法直接得到对偶微分方程并推导了对应的变分 原理. 所导出的对偶微分矩阵具有主对角子矩阵为零矩阵的特点. 发现了两个独立的、对称 的正交关系，利用薄板弹性弯曲理论的积分形式证明了这种正交关系的成立. 在恰当选择对 偶向量后，弹性力学的新正交关系可以推广到各向同性薄板弹性弯曲理论.     

COUPLED VARIATIONAL PRINCIPLES AND GENERALIZED COUPLED VARIATIONAL PRINCIPLES IN PHOTOELASTICITY

ＦｕＢａｏｌｉａｎ（付宝连）（ＲｅｃｅｉｖｅｄＮｏｖ．２２，１９９３；ＣｏｍｍｕｎｉｃａｔｅｄｂｙＣｈｉｅｎＷｅｉｚａｎｇ）ＣＯＵＰＬＥＤＶＡＲＩＡＴＩＯＮＡＬＰＲＩＮＣＩＰＬＥＳＡＮＤＧＥＮＥＲＡＬＩＺＥＤＣＯＵＰＬＥＤＶＡＲＩＡＴＩＯＮＡＬＰＲＩ...     

The parametric variational principle for Perzyna model in viscoplasticity

This paper presents the parametric variational principle for Perzyna model which isone of the main constitutive relations of viscoplasticity.The principle,by which the potentialenergy function is minimized under a constrained condition transformed by the constitutiverelations of viscoplasticity,is free from the bound of Drucker’s postulate of plastic flow andconsequently suitable for solving the nonassociated plastic flow problems.Furthermore,the paper has proven the presented principle and discussed the creep problem.     

The variational principles of coupled systems in photoelasticity

ＴＨＥＶＡＲＩＡＴＩＯＮＡＬＰＲＩＮＣＩＰＬＥＳＯＦＣＯＵＰＬＥＤＳＹＳＴＥＭＳＩＮＰＨＯＴＯＥＬＡＳＴＩＣＩＴＹＦｕＢａｏ－ｌｉａｎ（付宝连）（ＹａｎｓｈａｎＵｎｉｖｅｒｓｉｔｙ,Ｑｉｎｈｕａｎｇｄａｏ）（ＲｅｃｅｉｖｅｄＮｏｖ．８,１９８９,Ｃｏ...     

一类铁电模型的参变量变分原理及其应用

将参变量变分原理引入铁电问题。对一类借用了经典弹塑性理论中的概念和方法的多轴铁电模型建立基于Helmholtz自由能的参变量变分原理,可以有效处理传统变分原理中由非关联流动法则或屈服面不考虑材料系数变化所引起的切线模量非对称困难。相应于参变量变分原理,引入参数二次规划算法,可获得具有可靠数值稳定性的一套铁电算法。将该算法应用于一个具体的铁电模型,数值计算结果表明本文方法的有效性。     

Symplectic solution for three dimensional couple stress problem and its variational principle

A new state vector is presented for symplectic solution to three dimensional couple stress problem. Without relying on the analogy relationship, the dual PDEs of couple stress problem are derived by a new state vector. The duality solution methodology in a new form is thus extended to three dimensional couple stress. A new symplectic orthonormality relationship is proved. The symplectic solution to couple stress theory based a new state vector is more accordant with the custom of classical elasticity and is more convenient to process boundary conditions. A Hamilton mixed energy variational principle is derived by the integral method.     

On a variational principle in thermodynamics

The dynamic principle is proposed that a thermodynamic system evolves in time so that the total energy balance including the energy drawn from the environment becomes stationary for all admissible variations of thermodynamic states. It is shown that this principle allows to obtain variational characterizations of contact Hamiltonian equations (even in presence of ports), reaction equations and doubly nonlinear reaction–diffusion equations. Further, examples are discussed which support this principle.     

Fuzzy stochastic variable and variational principle

ＩｎｔｒｏｄｕｃｔｉｏｎＩｎｄｅｆｉｎｉｔｅｎｅｓｉｎｃｌｕｄｅｓｆｕｚｉｎｅｓａｎｄｒａｎｄｏｍｎｅｓｗｈｉｃｈａｒｅｔｈｅｇｅｎｅｒａｌｎａｔｕｒｅｏｆｅｎｇｉｎｅｒｉｎｇｓｔｒｕｃｔｕｒｅｓ．Ｉｎｔｈｅｎｕｍｅｒｉｃａｌａｎａｌｙｓｉｓｏｆｓｔ...     

复固有频率问题的模糊变分原理

模糊变分原理是模糊有限元重要的理论基础之一,模糊有限元的研究已经比较成熟了,然而关于模糊变分原理的研究却非常少.为研究复固有频率问题的模糊变分原理,首先介绍了一些模糊数学的概念,之后推导了非保守系统的拟Hamilton变分原理.接着通过将模糊参数引入到拟Hamilton变分原理,推导了复固有频率问题的模糊变分原理.作为模糊变分原理的应用,又推导了模糊有限元法.该方法可以直接得到问题的模糊解.与传统的模糊有限元方法相比,它避免了先将模糊参数转化为区间形式求解,之后再由区间解构造模糊解的过程.因此,该方法可以很大程度上减少计算量.最后通过数值算例表明了所提方法的可行性.     

The application of generalized variational principle in finite element-semianalytical method

The method developed in this paper is inspired by the viewpoint in ref. [1] that sufficient attention has not been paid to the value of the generalized variational principle in dealing with the boundary conditions in the finite element method. This method applies the generalized variational principle and chooses the series constituted by spline function multiplied by sinusoidal function and added by polynomial as the approximate deflection of plates and shells. By taking the deflection problem of thin plate, it shows that this method can solve the coupling problem in the finite element-semianalytical method. Compared with the finite element method and finite stripe method, this method has much fewer unknown variables and higher precision. Hence, it proposes an effective way to solve this kind of engineering problems by minicomputer.     

A generalized variational principle in micromorphic thermoelasticity

Recently Nappa obtains a Gurtin-type variational principle for micromorphic thermoelasticity. However, the use of convolutions is of course restricted to the linear case, which sets a limit to the rang of applicability. This paper establishes a classic variational principles for the discussed problem by the semi-inverse method.     

Subspace variational principle of rods and shells

This paper builds the general forms of subspace variational principles of rods andshells which are taken as the controlled equations of the constitutive theories developedfrom the three-dimensional (non-polar) continuum mechanics. And the constitutiveequations of rods and shells using the principles are satisfactory.