频域有限元计算的扩展面向目标误差估计

研究了针对频域有限元直接动态分析的面向目标误差估计以及误差范围估计计算方法．面向目标的误差估计方法就是专门针对如何准确和经济地估算特定值误差的一种方法,利用原问题的共轭偶问题进行计算．频域有限元的直接动态分析是模拟频域扫描实验的一种计算方法,专门针对谐振激励的线性动态响应问题,利用将原自由度分解为实部和虚部描述频率的变化,从而计算变形体的动态响应．利用扩展针对有限元的面向目标误差估计的自由度,将该方法应用到直接动态分析中进行误差估计．通过建立同时包含实部和虚部自由度的能量弱形式及偶问题,并将其数值实现,估算频域直接动态分析有限元解的误差及误差范围,并通过悬臂梁的激振算例进行了验证．     

A Review of Unified a Posteriori Finite Element Error Control

This paper aims at a general guideline to obtain a posteriori error estimates for the finite element error control in computational partial differential equations. In the abstract setting of mixed formulations, a generalised formulation of the corresponding residuals is proposed which then allows for the unified estimation of the respective dual norms. Notably, this can be done with an approach which is applicable in the same way to conforming, nonconforming and mixed discretisations. Subsequently, the unified approach is applied to various model problems. In particular, we consider the Laplace, Stokes, Navier-Lamé, and the semi-discrete eddy current equations.     

三维守恒律有限元方法逼近光滑解的误差估计

我们对一个三维守恒律的显式有限元方法证明了H^1范数的二阶误差估计。     

Unconditionally Optimal Error Analysis of the Second-Order BDF Finite Element Method for the Kuramoto-Tsuzuki Equation

This paper aims to study a second-order semi-implicit BDF finite element scheme for the Kuramoto-Tsuzuki equations in two dimensional and three dimensional spaces. The proposed scheme is stable and the nonlinear term is linearized by the extrapolation technique. Moreover, we prove that the error estimate in $L^2$-norm is unconditionally optimal which means that there has not any restriction on the time step and the mesh size. Finally, numerical results are displayed to illustrate our theoretical analysis.     

Mixed Finite Element Methods for the Ferrofluid Model with Magnetization Paralleled to the Magnetic Field

Mixed finite element methods are considered for a ferrofluid flow model with magnetization paralleled to the magnetic field. The ferrofluid model is a coupled system of the Maxwell equations and the incompressible Navier-Stokes equations. By skillfully introducing some new variables, the model is rewritten as several decoupled subsystems that can be solved independently. Mixed finite element formulations are given to discretize the decoupled systems with proper finite element spaces. Existence and uniqueness of the mixed finite element solutions are shown, and optimal order error estimates are obtained under some reasonable assumptions. Numerical experiments confirm the theoretical results.     

A Finite Element Algorithm for Nematic Liquid Crystal Flow Based on the Gauge-Uzawa Method

In this paper,we present a finite element algorithm for the time-dependent nematic liquid crystal flow based on the Gauge-Uzawa method.This algorithm combines the Gauge and Uzawa methods within a finite element variational formulation,which is a fully discrete projection type algorithm,whereas many projection methods have been studied without space discretization.Besides,error estimates for velocity and molecular orientation of the nematic liquid crystal flow are shown.Finally,numerical results are given to show that the presented algorithm is reliable and confirm the theoretical analysis.     

淬火过程中具有非线性表面系数考虑相变时温度场的有限元分析

温度场的计算对淬火过程中热应力和热应变的分析有较大影响，对淬火后试件的残余应力和微观结构分析也有较大影响·本文以４２ＣｒＭｏ钢圆柱体试件为研究对象，从相变等温动力学ＴＴＴ图，给出了连续冷却相变动力学ＣＣＴ图的数学模拟计算式，计算了钢淬火过程中相变组织成分百分比，将热物性系数处理为温度和相变体积百分比的函数，用有限单元法计算了淬火过程中具有非线性表面系数考虑相变时的温度场·并建立了相应的泛函，为以后计算淬火的热应力和热应变做好准备工作     

线性对流占优扩散方程的扩展特征混合有限元法

本文针对线性对流占优扩散方程提出了一种新型数值模拟方法一扩展特征混合有限元法,即对对流部分沿特征线方向离散,而对扩散部分采用扩展混合有限元方法,同时高精度逼近未知函数,未知函数的梯度及伴随向量函数,通过严格的数值分析,得到其最优L^2模误差估计。     

Lagrange四边形单位分解有限元法的最优误差分析

用构造最优局部逼近空间的方法对Lagrange型四边形单位分解有限元法进行了最优误差分析.单位分解取Lagrange型四边形上的标准双线性基函数,构造了一个特殊的局部多项式逼近空间,给出了具有2阶再生性的Lagrange型四边形单位分解有限元插值格式,从而得到了高于局部逼近阶的最优插值误差.     

水污染问题特征有限元方法的数值计算及理论分析

本文研究了水污染二维对流占优数学模型特征有限元方法的计算问题，导出的计算格式对时间变量用特征线方法离散，对空间变量用Galerkin有限元方法离散，得到的H^1－模和L^2－模误差估计是最优阶的。     

A Variational Analysis for the Moving Finite Element Method for Gradient Flows

By using the Onsager principle as an approximation tool, we give a novel derivation for the moving finite element method for gradient flow equations. We show that the discretized problem has the same energy dissipation structure as the continuous one. This enables us to do numerical analysis for the stationary solution of a nonlinear reaction diffusion equation using the approximation theory of free-knot piecewise polynomials. We show that under certain conditions the solution obtained by the moving finite element method converges to a local minimizer of the total energy when time goes to infinity. The global minimizer, once it is detected by the discrete scheme, approximates the continuous stationary solution in optimal order. Numerical examples for a linear diffusion equation and a nonlinear Allen-Cahn equation are given to verify the analytical results.     

二维热传导型半导体器件的特征有限体积元方法和H1模分析

将特征线方法与有限体积元方法相结合,采用分片线性函数和分片常数函数分别作为有限体积元方法的试探函数和检验函数空间,构造了热传导型半导体器件的全离散特征有限体积元格式.并进行收敛性分析,在一般的条件下得到了最优阶H1模误差估计结果.     

裂缝孔隙介质中二相驱动问题的交替方向有限元方法及理论分析

考虑裂缝孔隙介质中二相驱动问题的数值方法及理论分析。对压力方程采用混合有限元方法,对裂缝和岩块系统上的饱和度方程采用交替方向有限元方法,证明了交替方向有限元格式具有最优Ｌ２模和Ｈ１模误差估计。     

细菌模型的非协调有限元分析

将非协调元应用于描述细菌传播的反应扩散方程组的初边值问题.借助单元的一些特性和非协调误差估计技巧,分别在半离散和全离散有限元格式下,研究了其数值解与精确解的误差估计,得到了最优的误差估计以及超逼近结果.     

A Posteriori Error Analysis of a Fully-Mixed Finite Element Method for a Two-Dimensional Fluid-Solid Interaction Problem

In this paper we develop an a posteriori error analysis of a fully-mixed finite element method for a fluid-solid interaction problem in 2D. The media are governed by the elastodynamic and acoustic equations in time-harmonic regime, respectively, the transmission conditions are given by the equilibrium of forces and the equality of the corresponding normal displacements, and the fluid is supposed to occupy an annular region surrounding the solid, so that a Robin boundary condition imitating the behavior of the Sommerfeld condition is imposed on its exterior boundary. Dual-mixed approaches are applied in both domains, and the governing equations are employed to eliminate the displacement u of the solid and the pressure $p$ of the fluid. In addition, since both transmission conditions become essential, they are enforced weakly by means of two suitable Lagrange multipliers. The unknowns of the solid and the fluid are then approximated by a conforming Galerkin scheme defined in terms of PEERS elements in the solid, Raviart-Thomas of lowest order in the fluid, and continuous piecewise linear functions on the boundary. As the main contribution of this work, we derive a reliable and efficient residual-based a posteriori error estimator for the aforedescribed coupled problem. Some numerical results confirming the properties of the estimator are also reported.     

热传导对流问题的自适应最小二乘Galerkin/Petrov混合有限元法

对热传导对流问题提出了自适应Galerkin/Petrov最小二乘混合有限元法．该算法对任何速度和压力有限元空间的组合是相容和稳定的(不需要满足Babuka-Brezzi稳定性条件)．利用Verfürth的一般理论,得到了热传导对流问题的残量型的后验误差估计．最后通过几个数值算例验证了方法的有效性．     

浅水中污染物扩散的自适应有限元分析法

介绍浅水中污染物扩散分析中的有限元法.分析包括两个部分:1)流场速度、水面高度的计算;2)根据扩散模型计算污染物浓度场.联合使用了自适应网格技术以期提高解的精度,同时减少计算时间和计算机内存的消耗.通过几个有已知解的实例验证了有限元公式和计算机程序.最后,使用这种联合方法分析泰国Chao Phraya河附近海湾中的污染物扩散.     

一维有限元后处理的EEP法的数学分析

利用一维投影型插值与有限元超收敛基本估计,对一类两点边值问题,严格证明了袁驷等人由单元能量投影(EEP)法获得的节点恢复导数,当有限元空间的次数不超过4时,具有最佳阶超收敛．理论分析圆满地解释了已有的数值结果．     

非协调有限元的全塑性分析

本文采用满足相容条件的非协调有限元模型以解决全塑性分析中有限元解的数值精度问题.文中讨论了该模型适用于全塑性分析的机理和判据,还设计了一个确定塑性极限载荷的算法.     

自适应有限元方法在凹角域线性椭圆方程的应用(续)

作为序列文章自适应有限元方法在凹角域线性椭圆方程的应用的第三篇,在本文我们将给出并详细论证一个重要结论即 |?(u(x)-U(x))|≤Ch(x)|x|^β-2,|x|≥C′h且进一步分析说明在本序列文章的第一部分和地二部分得出方法都是以此为基础作出的。