平面弹性力学问题的混合元法的泡函数稳定性及其后验误差估计

该文讨论平面弹性力学问题的混合元法的泡函数稳定性,并导出基于简化的稳定化格式的一种先验误差估计和后验误差估计．这种简化的稳定化格式较通常的格式节省自由度．     

二阶椭圆问题的混合有限元法的泡函数稳定性及其后验误差估计

本文讨论二阶椭圆问题的混合有限元逼近的一种泡函数稳定性,并给出其基于简化的稳定化格式的先验误差估计和后验误差估计.该方法较通常的格式(例如,Raviaxt-Thomas方法的同阶格式)节省大量的自由度.     

A reduced MFE formulation based on POD for the non-stationary conduction-convection problems

In this article, a reduced mixed finite element (MFE) formulation based on proper orthogonal decomposition (POD) for the non-stationary conduction-convection problems is presented. Also the error estimates between the reduced MFE solutions based on POD and usual MFE solutions are derived. It is shown by numerical examples that the results of numerical computation are consistent with theoretical conclusions. Moreover, it is shown that the reduced MFE formulation based on POD is feasible and efficient in finding numerical solutions for the non-stationary conduction-convection problems.     

Mixed finite element analysis for dissipative SRLW equations with damping term

In this paper a mixed finite element (MFE) formulation is proposed for the initial-boundary value problem of dissipative symmetric regularized long wave (SRLW) equations with damping. Existence and uniqueness of its generalized solution and of the fully discrete mixed finite element solution are proved. Error estimates based on energy methods are given. Numerical experiments verify the theoretical analysis.     

Stabilized Nonconforming Mixed Finite Element Method for Linear Elasticity on Rectangular or Cubic Meshes

Based on the primal mixed variational formulation, a stabilized nonconforming mixed finite element method is proposed for the linear elasticity on rectangular and cubic meshes. Two kinds of penalty terms are introduced in the stabilized mixed formulation, which are the jump penalty term for the displacement and the divergence penalty term for the stress. We use the classical nonconforming rectangular and cubic elements for the displacement and the discontinuous piecewise polynomial space for the stress, where the discrete space for stress are carefully chosen to guarantee the well-posedness of discrete formulation. The stabilized mixed method is locking-free. The optimal convergence order is derived in the $L^2$-norm for stress and in the broken $H^1$-norm and $L^2$-norm for displacement. A numerical test is carried out to verify the optimal convergence of the stabilized method.     

非粘性土壤中溶质运移问题的守恒混合有限元法及其数值模拟

奉文建立了非粘性土壤水中溶质运移问题的守恒混合元格式,讨论了广义解和混合元解的存在唯一性,并给出了误差估计.数值模拟结果表叫,用该方法模拟溶质运移问题是合理有效的,不仅提高了通量的模拟精度,而且使计算稳定.     

二阶椭圆问题基于泡函数的简化的稳定化二阶混合有限元格式

本文研究二阶椭圆方程基于泡函数的稳定化的二阶混合有限元格式,通过消去泡函数导出一种自由度很少的简化的稳定化的二阶混合有限元格式, 误差分析表明消去泡函数的简化格式与带有泡函数的格式具有相同的精度而可以节省6N_p个自由度(其中N_p三角形剖分中的顶点数目).       

包含泥沙冲淤的浅水方程的混合有限元法(Ⅱ)——时间沿特征方向离散的全离散情形

进一步研究由水动力学方程、泥沙输运方程和河床变化方程组成的浅水方程混合有限元法,给出时间沿特征方向离散的一种全离散格式,并证明全离散的水流速度、床底高度、水体厚度、水中泥沙含量的混合有限元解的存在性和收敛性(误差估计)．     

非饱和水流问题的混合元法及其数值模拟

1.引 言 均质土壤中的地下水流动可归结为非饱和土壤水的流动,是土壤水未完全充满孔隙时的流动,是多孔介质流体运动的一种重要形式.非饱和流动的预报在大气科学、土壤学、农业     

蒸汽沉淀化学反应方程混合元法的离散格式研究

蒸汽沉淀化学反应过程有着极其广泛的应用,其数学模型归结为一个包含流速场,温度场,压力场和气体溶质场的非线性偏微分方程组．用混合有限元方法研究蒸汽沉淀化学反应方程组,导出其半离散化和全离散化的混合元格式,并证明这些格式的解的存在性和收敛性(误差估计)．用混合元法处理究蒸汽沉淀化学反应方程组,可以同时求出流速场,温度场,压力场和气体溶质场的数值解. 因此该研究既具有重要的理论意义,又具有广泛的应用前景．     

Least squares moving finite elements

The moving finite element (MFE) method, when applied to purelyhyperbolic partial differential equation, moves nodes with approximatelycharacteristic speeds, which makes the method useless for steady-stateproblems. We introduce the least squares MFE method (LSMFE)for steady-state pure convection problems which corrects thisdefect. We show results for a steady-state pure convection problemin one dimension in which the nodes are no longer swept downstreamas in MFE. The method is then extended to two dimensions andthe grid aligns automatically with the flow, thereby yieldingfar greater accuracy than the corresponding fixed node leastsquares results, as is shown in two-dimensional numerical trials.     

包含泥沙冲淤的浅水方程的混合有限元法(Ⅰ)——时间连续的情形

研究由水动力方程、 泥沙输运方程和河床变化方程组成的浅水方程的初边值问题, 讨论其广义解和混合有限元解的存在性, 并导出半离散混合有限元解的误差估计, 这些估计是最优阶的．     

非定常Stokes方程的全离散稳定化有限元格式

本文研究二维非定常Stokes方程全离散稳定化有限元方法.首先给出关于时间向后一步Euler半离散格式,然后直接从该时间半离散格式出发,构造基于两局部高斯积分的稳定化全离散有限元格式,其中空间用P_1—P_1元逼近,证明有限元解的误差估计.本文的研究方法使得理论证明变得更加简便,也是处理非定常Stokes方程的一种新的途径.     

非定常Stokes方程的稳定化全离散有限体积元格式

本文研究非定常Stokes方程的有限体积元方法,给出一种基于两个局部高斯积分的稳定化全离散格式,并给其有限体积元解的误差分析.     

Wavelet stabilization of the Lagrange multiplier method

Summary. We propose here a stabilization strategy for the Lagrange multiplier formulation of Dirichlet problems. The stabilization is based on the use of equivalent scalar products for the spaces and , which are realized by means of wavelet functions. The resulting stabilized bilinear form is coercive with respect to the natural norm associated to the problem. A uniformly coercive approximation of the stabilized bilinear form is constructed for a wide class of approximation spaces, for which an optimal error estimate is provided. Finally, a formulation is presented which is obtained by eliminating the multiplier by static condensation. This formulation is closely related to the Nitsche's method for solving Dirichlet boundary value problems. Received December 4, 1998 / Revised version received May 7, 1999 / Published online April 20, 2000 –? Springer-Verlag 2000     

Stabilization by multiscale decomposition

We take advantage of the results of norm characterization by multiscale decomposition to introduce a stabilized formulation of an abstract noncoercive problem. The resulting stabilized problem is positive definite and can therefore be safely discretized by the Galerkin method.     

A stabilized Crank-Nicolson mixed finite element method for non-stationary parabolized Navier-Stokes equations

In this study, a time semi-discrete Crank-Nicolson (CN) formulation with second-order time accuracy for the non-stationary parabolized Navier-Stokes equations is firstly established. And then, a fully discrete stabilized CN mixed finite element (SCNMFE) formulation based on two local Gauss integrals and parameterfree with the second-order time accuracy is established directly from the time semi-discrete CN formulation. Thus, it could avoid the discussion for semi-discrete SCNMFE formulation with respect to spatial variables and its theoretical analysis becomes very simple. Finaly, the error estimates of SCNMFE solutions are provided.     

On the relationship between the moving finite-element procedure and best piecewise L2 fits with adjustable nodes

It is shown that, for a class of time-dependent partial differential equations of the form u_t = ??u, one step of the moving finite-element (MFE) procedure corresponds to one iteration of an algorithm for obtaining best L₂ fits with adjustable nodes to continuous functions. In the steady-state limit the MFE procedure gives the best fit of ??u, with adjustable nodes, to the null function. For first-order partial differential equations, the MFE procedure moves nodes with approximate characteristic nodal speeds. We identify an additional speed component arising directly from the L₂ projection which seeks a best fit in the sense described above. © 1994 John Wiley & Sons, Inc.     

A STABILIZED CRANK-NICOLSON MIXED FINITE VOLUME ELEMENT FORMULATION FOR THE NON-STATIONARY PARABOLIZED NAVIER-STOKES EQUATIONS

A time semi-discrete Crank-Nicolson(CN) formulation with second-order time accuracy for the non-stationary parabolized Navier-Stokes equations is firstly established.And then, a fully discrete stabilized CN mixed finite volume element(SCNMFVE) formulation based on two local Gaussian integrals and parameter-free with the second-order time accuracy is established directly from the time semi-discrete CN formulation so that it could avoid the discussion for semi-discrete SCNMFVE formulation with respect to spatial variables and its theoretical analysis becomes very simple. Finally, the error estimates of SCNMFVE solutions are provided.