偶应力问题的杂交／混合元分析

将弹性力学中Hellinger—Reissner交分原理推广到偶应力理论中，并以罚函数的形式引入其约束条件，提出了一种有效的杂交／混合单元。文中分别分析了带中心小孔平板在轴向均匀加载时的应力集中情况，以及含中问裂纹的无限平板单轴拉伸时的位移场和应力场。算例表明，该单元计算效率高，精度好，即使在材料本征长度很小时，仍然能够得到相当理想的结果。     

An efficient iteration algorithm of mixed boundary/finite element method and application to free torsional vibration analysis of bodies of revolution

In this paper,the general formulation of a new proposed iteration algorithm of mixedBEM/FEM for eigenvalue problems of elastodynamics is described.Approximatefundamental solutions of elastodynamics are adopted in the normal mixed BEM/FEMequations.The accuracy of solutions is progressively improved by the iteration procedure.Not only could the awkwar dness of non-algebraic eigenvalue equations be avoided but alsothe accuracy of numerical solutions is almost independent of the interior meshing.All thesegive many advantages in numerical calculation.The algorithm is applied to free torsionalvibration analysis of bodies of revolution.A few cases are studied.All of the numericalresults are very good.     

APPLICATION OF PENALTY FUNCTION METHOD IN ISOPARANIETRIC HYBRID FINITE ELEMENT ANALYSIS

IntroductionSince T.H.H.Pain firstly puts forward hybrid element method[1]in1964, the researchand application of hybrid element have got great development. T.H.H.Painet al.havemade important pioneer works in the domain of the research on incompatible displacementstructure hybrid elementstress pattern[2,3]in recentdecades. Reference [4] had provided theoptimizing design concept of hybrid element further and established standardization methodof incompatible displacement structure hybrid eleme…     

Introduction of turbulent model in a mixed finite volume/finite element method

The aim of this work is to present a new numerical method to compute turbulent flows in complex configurations. With this in view, a k-? model with wall functions has been introduced in a mixed finite volume/finite element method. The numerical method has been developed to deal with compressible flows but is also able to compute nearly incompressible flows. The physical model and the numerical method are first described, then validation results for an incompressible flow over a backward-facing step and for a supersonic flow over a compression ramp are presented. Comparisons are performed with experimental data and with other numerical results. These simulations show the ability of the present method to predict turbulent flows, and this method will be applied to simulate complex industrial flows (flow inside the combustion chamber of gas turbine engines). The main goal of this paper is not to test turbulence models, but to show that this numerical method is a solid base to introduce more sophisticated turbulence model.     

Development of an optimal hybrid finite volume/element method for viscoelastic flows

A cell‐vertex hybrid finite volume/element method is investigated that is implemented on triangles and applied to the numerical solution of Oldroyd model fluids in contraction flows. Particular attention is paid to establishing high‐order accuracy, whilst retaining favourable stability properties. Elevated levels of elasticity are sought. The main impact of this study reveals that switching from quadratic to linear finite volume stress representation with discontinuous stress gradients, and incorporating local reduced quadrature at the re‐entrant corner, provide enhance stability properties. Solution smoothness is achieved by adopting the non‐conservative flux form with area integration, by appealing to quadratic recovered velocity‐gradients, and through consistency considerations in the treatment of the time term in the constitutive equation. In this manner, high‐order accuracy is maintained, stability is ensured, and the finer features of the flow are confirmed via mesh refinement. Lip vortices are observed for We>1, and a trailing‐edge vortex is also apparent. Loss of evolution and solution asymptotic behaviour towards the re‐entrant corner are also discussed. Copyright © 2003 John Wiley & Sons, Ltd.     

Coarse-mesh-accuracy improvement of bilinear Q<Subscript>4</Subscript>-plane element by the combined hybrid finite element method

The combined hybrid finite element method is of an intrinsic mechanism of enhancing coarse-mesh-accuracy of lower order displacement schemes. It was confirmed that the combined hybrid scheme without energy error leads to enhancement of accuracy at coarse meshes, and that the combination parameter plays an important role in the enhancement. As an improvement of conforming bilinear Q₄-plane element, the combined hybrid method adopted the most convenient quadrilateral displacements-stress mode, i. e., the mode of compatible isoparametric bilinear displacements and pure constant stresses. By adjusting the combined parameter, the optimized version of the combined hybrid element was obtained and numerical tests indicated that this parameter-adjusted version behaves much better than Q₄-element and is of high accuracy at coarse meshes. Due to elimination of stress parameters at the elemental level, this combined hybrid version is of the same computational cost as that of Q₄-element. Foundation item: the National Tianyuan Yourth Funds of China (TY10126027) Biography: Xie Xiao-ping (1970≈)     

拉索穹顶结构非线性分析的混合有限元增量法

拉索穹顶结构是由受压桅杆和拉索组成的新型柔性大跨度空间组合结构,几何上表现为极强的非线性特性,计算困难,本文应用有限元法,结合拉索穹顶结构特征,假定拉索和桅杆的受力满足虎克宣定律,建立了可以直接考虑拉索垂度影响的两节点索单元模型,并与两节点直杆单元相结合,基于修正的拉格朗日描述方法和虚功原理建立了拉索穹顶结构非线性分析的混合有限元增量方程。采用荷载增量法与Ｎｅｗｔｏｎ－Ｒａｐｈｓｏｎ法相结合的求解     

Mixed compatible element and mixed hybrid incompatible element variational methods in dynamics of viscous barotropic fluids

ＭＩＸＥＤＣＯＭＰＡＴＩＢＬＥＥＬＥＭＥＮＴＡＮＤＭＩＸＥＤＨＹＢＲＩＤＩＮＣＯＭＰＡＴＩＢＬＥＥＬＥＭＥＮＴＶＡＲＩＡＴＩＯＮＡＬＭＥＴＨＯＤＳＩＮＤＹＮＡＭＩＣＳＯＦＶＩＳＣＯＵＳＢＡＲＯＴＲＯＰＩＣＦＬＵＩＤＳＳｈｅｎＸｉａｏ－ｍｉｎｇ（沈孝明...     

Least-squares mixed finite element method for a class of stokes equation

ＩｎｔｒｏｄｕｃｔｉｏｎＡｇｅｎｅｒａｌｔｈｅｏｒｙｏｆｔｈｅｌｅａｓｔ＿ｓｑｕａｒｅｓｍｅｔｈｏｄｈａｓｂｅｅｎｄｅｖｅｌｏｐｅｄｂｙＡＫＡｚｉｚ,ＲＢＫｅｌｌｏｇｇａｎｄＡＢＳｔｅｐｈｅｎｓｉｎ[1].Ｔｈｅｍｏｓｔｉｍｐｏｒｔａｎｔａｄｖａｎｔａｇｅｌｅａｄｓｔｏａｓｙｍｍｅｔｒｉｃｐｏｓｉｔｉｖｅｄｅｆｉｎｉｔｅｐｒｏｂｌｅｍ.ＪＨＢｒａｍｂｌｅａｎｄＪＡＮｉｔｓｈｅｐｒｅｓｅｎｔｅｄａｌｅａｓｔ＿ｓｑｕａｒｅｓｍｅｔｈｏｄｆｏｒＤｉｒｉｃｈｌｅｔｐｒｏｂｌｅｍｓｉｎ[2].Ｔｈｅｍｅｔｈｏｄｇｅ…     

Adaptive mixed least squares Galerkin/Petrov finite element method for stationary conduction convection problems

An adaptive mixed least squares Galerkin/Petrov finite element method (FEM) is developed for stationary conduction convection problems. The mixed least squares Galerkin/Petrov FEM is consistent and stable for any combination of discrete velocity and pressure spaces without requiring the Babuska-Brezzi stability condition. Using the general theory of Verfürth, the posteriori error estimates of the residual type are derived. Finally, numerical tests are presented to illustrate the effectiveness of the method.     

基于Hellinger-Reissner变分原理的应变梯度杂交元设计

从一般的偶应力理论出发,基于Hellinger-Reissner变分原理,通过对有限元 离散体系的位移试解引入非协调位移函数,得到了偶应力理论下有限元离散系统的能量相容 条件,并由此建立了应变梯度杂交元的应力函数优化条件. 根据该优化条件,构造了一 个C0类的平面4节点梯度杂交元,数值结果表明,该单元对可压缩和不可压缩状态的 梯度材料均可给出合理的数值结果,再现材料的尺度效应.     

Adaptive mixed least squares Galerkin/Petrov finite element method for stationary conduction convection problems

An adaptive mixed least squares Galerkin/Petrov finite element method (FEM) is developed for stationary conduction convection problems. The mixed least squares Galerkin/Petrov FEM is consistent and stable for any combination of discrete velocity and pressure spaces without requiring the Babuska-Brezzi stability condition. Using the general theory of Verfürth, the posteriori error estimates of the residual type are derived. Finally, numerical tests are presented to illustrate the effectiveness of the method.     

A potential-hybrid/mixed finite element scheme for analysis of plates and cylindrical shells

Based on the potential-hybrid/mixed finite element scheme,4-node quadrilateralplate-bending elements MP4,MP4a and cylindrical shell element MCS4 are derived with,the inclusion of splitting rotations.All these elements demonstrate favorable convergencebehavior over the existing counterparts,free from spurious kinematic modes and do notexhibit locking phenomenon in thin plate/shell limit.Inter-connections between the existingmodified variational functionals for the use of formulating C~0-and C~1-continuous elementsare also indicated.Important particularizations of the present scheme include Prathap’sconsistent field formulation,the RIT/SRIT-compatible displacement model and so on.     

A hybrid/mixed model finite element analysis for eigenvalue problem of moderately thick plates

The buckling and free vibration problems of moderately thick plate are considered in this paper by using the hybrid/mixed finite element model. A modified Reissner principle which only requires C⁰ continuity is derived. No lockling phenomenon is observed. Linear interpolation is used for all independent unknown function. Finally a displacement generalized eigenvalue equation is obtained, in which the stiffness matrix is symmetric and positively definite. The calculated results show that the method proposed is simple, reliable and satisfactory.     

Theoretical basis and general optimal formulations of isoparametric generalized hybrid/mixed element model for improved stress analysis

By the modified three-field Hu-Washizu principle, this paper establishes a theoretical foundation and general convenient formulations to generate convergent stable generalized hybrid/mixed element (GH/ME) model which is invariant with respect to coordinate, insensitive to geometric distortion and suitable for improved stress computation. In the two proposed formulations, the stress equilibrium and orthogonality constraints are imposed through incompatible displacement and internal strain modes respectively. The proposed model by the general formulations in this paper is characterized by including assumed stress/strain, assumed stress, variable-node, singular, compatible and incompatible GH/ME models. When using regular meshes or the constant values of the isoparametric Jacobian Det in the assumed strain interpolation, the incompatible GH/ME model degenerates to the hybrid/mixed element model. Both general and concrete guidelines for the optimal selection of element shape functions are suggested. By means of the GH/ME theory in this paper, a family of new GH/ME can be and have been easily constructed. The software can also be developed conveniently because all the standard subroutines for the corresponding isoparametric displacement elements can be utilized directly. Modified version of a conference paper presented at Int. Conf. on EPMESC IV, July 29–Aug. 3, 1992, Dalian, China     

Development of a hybrid finite volume/element solver for incompressible flows

In this paper, we report our development of an implicit hybrid flow solver for the incompressible Navier–Stokes equations. The methodology is based on the pressure correction or projection method. A fractional step approach is used to obtain an intermediate velocity field by solving the original momentum equations with the matrix‐free implicit cell‐centred finite volume method. The Poisson equation derived from the fractional step approach is solved by the node‐based Galerkin finite element method for an auxiliary variable. The auxiliary variable is closely related to the real pressure and is used to update the velocity field and the pressure field. We store the velocity components at cell centres and the auxiliary variable at cell vertices, making the current solver a staggered‐mesh scheme. Numerical examples demonstrate the performance of the resulting hybrid scheme, such as the correct temporal convergence rates for both velocity and pressure, absence of unphysical pressure boundary layer, good convergence in steady‐state simulations and capability in predicting accurate drag, lift and Strouhal number in the flow around a circular cylinder. Copyright © 2007 John Wiley & Sons, Ltd.     

Difference scheme and numerical simulation based on mixed finite element method for natural convection problem

ntroductionLetΩ R2 beaboundeddomain .Weconsiderthefollowingnon_stationarynaturalconvectionproblem :Problem (Ⅰ )　Findu =(u1,u2 ) ,p ,andTsuchthat,foranyt1>0 ,ut- μΔu +(u· )u + p=λjT　　 ((x ,y ,t) ∈Ω× (0 ,t1) ) ,divu =0　　　　　　　　　 ((x ,y,t) ∈Ω× (0 ,t1) ) ,Tt-ΔT +λu· T =0　　 ((x,y,t) ∈Ω× (0 ,t1) ) ,u =0 ,T =0　　　　　　 ((x,y,t)∈ Ω× (0 ,t1) ) ,u(x ,y ,0 ) =0 ,　T(x,y,0 ) =f(x,y)　　 ((x,y) ∈Ω) ,whereuisthefluidvelocityvectorfield ,pthepressurefield ,Tthet…     

A mixed finite element method for the generalized Stokes problem

We present and analyse a new mixed finite element method for the generalized Stokes problem. The approach, which is a natural extension of a previous procedure applied to quasi‐Newtonian Stokes flows, is based on the introduction of the flux and the tensor gradient of the velocity as further unknowns. This yields a two‐fold saddle point operator equation as the resulting variational formulation. Then, applying a slight generalization of the well known Babu?ka–Brezzi theory, we prove that the continuous and discrete formulations are well posed, and derive the associated a priori error analysis. In particular, the finite element subspaces providing stability coincide with those employed for the usual Stokes flows except for one of them that needs to be suitably enriched. We also develop an a posteriori error estimate (based on local problems) and propose the associated adaptive algorithm to compute the finite element solutions. Several numerical results illustrate the performance of the method and its capability to localize boundary layers, inner layers, and singularities. Copyright © 2005 John Wiley & Sons, Ltd.     

A study of the hybrid element methods for stress analysis

A new functional which forms the basis of an improved hybrid element formulation is proposed. The variables for the functional include stresses, strains and displacements, and the displacements and stresses are further decomposed into two parts respectively. The proposed new formulation appears to be particularly suitable for improving conforming models.The relationship between the new hybrid elements and the conventional displacement elements are also explored in this paper.     

A finite element method on the plane elastic material analysis

Based on the finite element displacement method, a finite element method on the analysis of mechanical behaviour of plane elastic materials is proposed in this paper. By using this method and the corresponding computational program, the material behaviour of any unknown plane elastic material can be determined and all the elastic constants can be calculated.