The improved element-free Galerkin method for three-dimensional wave equation

The paper presents the improved element-freeGalerkin(IEFG) method for three-dimensional wave propagation.The improved moving least-squares(IMLS) approximation is employed to construct the shape function,whichuses an orthogonal function system with a weight function asthe basis function.Compared with the conventional movingleast-squares(MLS) approximation,the algebraic equationsystem in the IMLS approximation is not ill-conditioned,andcan be solved directly without deriving the inverse matrix.Because there are fewer coefficients in the IMLS than in theMLS approximation,fewer nodes are selected in the IEFGmethod than in the element-free Galerkin method.Thus,theIEFG method has a higher computing speed.In the IEFGmethod,the Galerkin weak form is employed to obtain a discretized system equation,and the penalty method is appliedto impose the essential boundary condition.The traditionaldifference method for two-point boundary value problems isselected for the time discretization.As the wave equationsand the boundary-initial conditions depend on time,the scaling parameter,number of nodes and the time step length areconsidered for the convergence study.     

An h-adaptive modified element-free Galerkin method

In this work an h-adaptive Modified Element-Free Galerkin (MEFG) method is investigated. The proposed error estimator is based on a recovery by equilibrium of nodal patches where a recovered stress field is obtained by a moving least square approximation. The procedure generates a smooth recovered stress field that is not only more accurate then the approximate solution but also free of spurious oscillations, normally seen in EFG methods at regions with high gradient stresses or discontinuities.The MEFG method combines conventional EFG with extended partition of unity finite element (EPUFE) methods in order to create global shape functions that allow a direct imposition of the essential boundary conditions.The re-meshing of the integration mesh is based on the homogeneous error distribution criterion and upon a given prescribed admissible error. Some examples are presented, considering a plane stress assumption, which shows the performance of the proposed methodology.     

无网格伽辽金法求解平面偶应力问题

提出采用无网格伽辽金法(EFGM)求解偶应力问题,以避免有限元求解中因C¹连续要求可能引起的不便。推导了基于二次基和移动最小二乘技术的EFGM计算公式,通过计算受轴向均匀拉伸的带中心小孔无限大板和细长杆的偶应力问题,对所提方法进行了数值验证,与解析解相比结果令人满意,此外还讨论了节点密度和权函数对计算结果的影响。数值结果表明,所提算法可有效地求解平面偶应力问题。     

复合材料层合板的谱随机无网格伽辽金法

针对基于摄动理论的计算方法不适用于分析随机结构参数大变异问题,提出谱随机无网格伽辽金法,该方法基于随机场正交分解理论,将随机场采用Karhunen-Loève级数展开为一系列不相关随机变量,再引入结构位移随机响应的混沌多项式分解,结合无网格伽辽金法,从而导出含随机变量的复合材料层合板的谱随机无网格伽辽金法,给出结构响应的统计特征值的计算公式,该方法既适用于随机参数大变异情况,又具有无网格法的优势;数值算例结果表明该方法是正确有效的。     

波前法在无网格伽辽金法中的应用

有别于有限元法,无网格法采用基于点的近似,可彻底或部分地去除网格(只保留积分所需的背景网格),在保证计算精度同时降低计算难度.无网格伽辽金法(Element Free Galerkin Method,EFG)是一种基于移动最小二乘近似(Moving Least-Squares,MLS)的全局弱式无网格法,广泛应用于计算力学等领域,该方法的一个缺点是:计算过程中产生的系数矩阵含有的非零元数量比有限元法多,即使处理中等规模模型时,也要求计算机有很大的存储空间,并且计算时间长.波前法在有限元法中已有很成熟的应用,但至今没有应用于无网格方法.论文介绍了波前法在无网格伽辽金法中的应用方法,编写了相应的计算程序,并以弹性力学为例做了验算.     

完全变换法在无网格伽辽金方法中的应用

由于移动最小二乘形函数一般不具有常规有限元或边界元形函数所具有的插值特征，本质边界条件的处理成为无网格伽辽金法实施中的一个难点。本文通过建立节点位移和广义位移之间的关系对移动最小二乘形函数进行修正，给出了修正的移动最小二乘形函数；以二维问题为例，对完全交换法在无网格伽辽金方法中的应用进行了研究，实现了本质边界条件在节点处的精确施加。数值计算结果表明该方法不仅简单合理，而且具有较高的精度、收敛性和稳定性。     

无网格Galerkin法与非协调元方法的耦合

无网格Galerkin法(EFGM)处理不可压缩问题时不存在自锁现象,有限元方法(FEM)也常被用来与其耦合以方便地施加边界条件和提高计算效率。在有限元方法中使用等参元,EFGM与FEM的耦合方法在处理不可压缩问题时仍然存在自锁现象。本文在有限元方法中,采用非协调元,将无网格kGalerkin法与非协调元耦合,保留了耦合方法的优点,且避免了求解不可压缩问题时的自锁现象。算例显示本文方法在分析平面应变不可压缩问题时能得到合理的结果。     

反平面断裂问题的无单元伽辽金比例边界法

将比例边界法与无单元伽辽金法相结合,建立了反平面断裂分析的无单元伽辽金比例边界法。这是一种边界型无网格法,在环向方向上采用无单元伽辽金法进行离散,因此计算时仅需要边界上的节点信息,不需要边界元所要求的基本解。为了便于施加本质边界条件,通过建立节点值和虚拟节点值之间的关系给出了修正的移动最小二乘形函数。在径向方向上,该方法利用解析的方法求解,因此是一种半解析的数值方法。最后,给出了数值算例,并验证了所提方法后处理简单和计算精度高的特点,适合于求解反平面断裂问题。     

A three-dimensional explicit element-free galerkin method

The formulation and implementation of a three-dimensional meshless method, the element-free Galerkin (EFG) method, are described. The formulation is intended for dynamic problems with geometric and material non-linearities solved with explicit time integration, but some of the developments are applicable to other solution methods. The mechanical formulation is posed in the reference configuration so that the shape functions and their derivatives need to be computed only once. A method for speeding up the calculation of shape functions and their derivatives is presented. Results are presented for sloshing problems and Taylor bar impact problems, including an impact problem in which the bar impacts with an angle of obliquity. © 1997 John Wiley & Sons, Ltd.     

弹塑性大变形分析的一致性高阶无单元伽辽金法

采用无单元伽辽金法求解弹塑性大变形问题。充分利用无单元法易于建立高阶近似函数的优点,位移采用二阶移动最小二乘近似。在更新拉格朗日方法的框架下,通过对控制方程弱形式的线性化建立了内力率的表达式,并区分为材料和几何两部分。采用Hughes-Winget算法更新应力,建立了Newton-Raphson迭代求解所需的一致切线刚度阵。刚度阵的数值积分采用近来针对小变形分析建立的二阶一致三点积分格式QC3（Quadratically Consistent 3-point integration scheme）。数值结果证明了本文方法分析弹塑性大变形问题的有效性和优越性。     

A higher-order boundary element method for three-dimensional potential problems

A method of eliminating the singularities involved in boundary element methods for three-dimensional potential problems is presented and the non-singular expressions of integrals on an element on which the singular point is situated are given for linear and quadratic interpolation functions. Numerical examples are compared with analytical solutions to show that the higher-order interpolations have better precision.     

NEW ALGORITHM OF COUPLING ELEMENT-FREE GALERKIN WITH FINITE ELEMENT METHOD

IntroductionMeshless methods, as a special numerical method, originated from1970s. Since thediffuse element method was proposed by Nayroleset al.[1]in1992, the meshless methodshave received wide attentions in the mechanics area, and have shown obvious adv…     

弹塑性体脆断相场模型的一致性无单元伽辽金法

采用无单元伽辽金法（EFG）对弹塑性体脆性断裂的相场模型进行了数值实现。利用无单元法便于构建高阶近似函数的优势,位移和相场均采用二阶移动最小二乘（MLS）近似。刚度阵的数值积分采用更为高效的二阶一致三点积分格式QC3（Quadratically Consistent 3-point integration scheme）。本构算法采用Newton-Raphson迭代和弹塑性一致性切线模量。数值结果表明了本文方法模拟弹塑性体脆性断裂的有效性。     

局部正交无网格伽辽金法的研究及其在含多裂纹多孔结构中的应用

通过对无网格法中正交基函数的研究,提出局部正交无网格伽辽金法,局部正交基函数保持原正交基函数的性质,但其导数具有了通式,简洁明了,易于编程实现,计算效率高,并将其应用到求解含多裂纹多孔均匀拉伸板的应力强度因子中,计算结果与用正交无网格伽辽金法和有限元法得到的结果进行比较,证明了局部正交无网格伽辽金法的可行性和正确性。     

A proper orthogonal decomposition variational multiscale meshless interpolating element-free Galerkin method for incompressible magnetohydrodynamics flow

In the recent decade, the meshless methods have been handled for solving most of PDEs due to easiness of the meshless methods. One of the popular meshless methods is the element-free Galerkin (EFG) method that was first proposed for solving some problems in the solid mechanics. The test and trial functions of the EFG are based on the special basis. Recently, some modifications have been developed to improve the EFG method. One of these improvements is the variational multiscale EFG procedure. In the current article, the shape functions of interpolation moving least squares approximation have been applied to the variational multiscale EFG technique for solving the incompressible magnetohydrodynamics flow. In order to reduce the elapsed CPU time of simulation, we employ a reduced-order model based on the proper orthogonal decomposition technique. The current combination can be referred to as the reduced-order variational multiscale EFG technique. To illustrate the reduction in CPU time used as well as the efficiency of the proposed method, we applied it for the two-dimensional cases.     

The Galerkin method as applied to problems in viscoelasticity

This paper establishes the convergence of the continuous-time Galerkin technique as applied to quasi-static, linear viscoelasticity.     

A 3D shell-like approach using element-free Galerkin method for analysis of thin and thick plate structures

A new efficient meshless method based on the element-free Galerkin method is proposed to analyze the static deformation of thin and thick plate structures in this paper. Using the new 3D shell-like kinematics in analogy to the solid-shell concept of the finite element method, discretization is carried out by the nodes located on the upper and lower surfaces of the structures. The approximation of all unknown field variables is carried out by using the moving least squares (MLS) approximation scheme in the in-plane directions, while the linear interpolation is applied through the thickness direction. Thus, different boundary conditions are defined only using displacements and penalty method is used to enforce the essential boundary conditions. The constrained Galerkin weak form, which incorporates only displacement degrees of freedom (d.o.f.s), is derived. A modified 3D constitutive relationship is adopted in order to avoid or eliminate some self-locking effects. The numeric efficiency of the proposed meshless formulation is illustrated by the numeric examples.     

The analytical method for three-dimensional elastic problems in finite deformations

The three-dimensional elastic problems in finite deformations are not known to have been analyzed by the usual stress function and displacement function. By applying Hasegava's presentation and Adkins perturbation method, we propose a new analytical method for three-dimensional elastic problems for compressible materials and incompressible materials, using the displacement function for axisymmetrical elastic problems in finite deformations with surface force or body force. Further, this analytical method is examined by two simple examples.     

A Newton method for three-dimensional fretting problems

The present paper concerns the numerical treatment of fretting problems using a finite element analysis. The governing equations resulting from a formal finite element discretization of an elastic body with a potential contact surface are considered in a quasi-static setting. The constitutive equations of the potential contact surface are Signorinis contact conditions, Coulombs law of friction and Archards law of wear. Using a backward Euler time discretization and an approach based on projections, the governing equations are written as an augmented Lagrangian formulation which is implemented and solved using a Newton algorithm for three-dimensional fretting problems of didactic nature. Details concerning the implementation are provided.