对流-扩散方程的hp-局部间断Galerkin有限元方法的最优L∞(H^1)误差估计北大核心

通过使用Arnold等人和Perugia等人对于椭圆问题引入的提升算子方法以及不同的处理非线性对流项的方法,得到了对流-扩散方程的hp-局部间断Galerkin有限元(hp-LDG)方法的最优L∞(H^1)误差估计.对于非线性Burgers方程进行了数值试验,计算结果验证了文中得到的理论结果.     

对流扩散方程的三层WENO-MMOCAA差分方法

本文把三层修正特征线法,MMOCAA 差分方法及WENO 插值相结合,提出了求解对流扩散方程的三层WENO-MMOCAA 差分格式.此格式关于时间具有二阶精度,关于空间具有二阶以上精度且可避免基于二次以上Lagrange 插值的三层MMOCAA 差分方法在解的大梯度附近所产生的振荡.本文使用新的分析方法,给出了格式的误差估计.本文的数值算例表明新格式可消除振荡.     

对流扩散方程的时空间断有限元方法

研究对流扩散方程的时空间断Galerkin有限元方法,该方法采用时,空两个变量都允许间断的基函数,更适用于移动网格,自适应算法以及并行计算.本文利用拉格朗日欧拉方法,采用F.Brezzi数值流通量,给出对流扩散方程的间断时空有限元离散格式,并证明格式的相容性,强制性,稳定性,解的存在唯一性,以及总体误差估计.     

对流扩散方程的三层UNO-MMOCAA差分方法

By combing the three-step modified method of characteristics and MMOCAA difference method with UNO interpolation, the three-step UNO-MMOCAA finite difference method is established for convection-dominated diffusion problems in this paper. The scheme is two-order accurate in space and time and is free from the oscillation near the steep front, with which the problem is solved by three-step MMOCAA finite difference method based on two-order Lagrange interplation. Using the new method, we give an estimate analysis of the scheme and a numerical example.     

一种推广的对流扩散方程的局部化间断Galerkin方法

研究求解一种产生于径向渗流问题的推广的对流扩散方程的局部化间断Galerkin方法，对一般非线性情形证明了方法的L^2稳定性；对线性情形证明了，当方法取有限元空间为κ次多项式空间时，数值解逼近的L^∞（0，T；L^2)模的误差阶为κ。     

对流扩散方程的一种显式有限体积——有限元方法

本文给出非线性对流扩散问题的一种有限体积的有限元方法相结合的显式离散方法,证明了数值解的稳定性,并给出了一个实际算例。     

非定常线性对流扩散问题的算子分裂半显式有限元分析

在现代科学及工程领域中,存在着许多同时伴有物质传输和动力耗散两种过程的物理系统.在数学上,它们常归结为对流占优的对流扩散方程或以这种方程占主导的方程组.这类方程具有殆双曲性质,其解函数常呈现局部大梯度变化,使得传统的求解抛物问题的数值方法常常     

对流扩散方程的间断时空有限元方法的误差估计

研究了一类线性对流扩散方程的间断时空有限元方法,即空间连续,时间允许间断的时空有限元方法.将有限元方法和有限差分方法相结合,在每一时间层上充分利用Lagrange插值多项式在Radau点处的特性,给出了有限元解的最优阶L∞(L2)模误差估计.     

线性对流占优Sobolev方程的流线扩散有限元方法

Abastract. In this paper,a streamline-diffusion F. E. M. for linear Sobolev equations with con-vection-dominated term is given. According to the range of space-time F. E mesh parameter h,two choices for artifical diffusion parameter are presented,and for the corresponding computa-tion schemes the stability and error estimates in suitable norms are estabilished.     

对流扩散方程的混合时间间断时空有限元方法

构造并分析二阶对流扩散方程的混合时间间断时空有限元格式．利用混合有限元方法将二阶方程降阶,利用空间连续而时间允许间断的时空有限元方法离散低阶方程．证明数值解的稳定性、存在唯一性和收敛性．最后通过数值结果验证该算法的有效性和可行性．     

Time discontinuous Galerkin space-time finite element method for nonlinear Sobolev equations

This article presents a complete discretization of a nonlinear Sobolev equation using space-time discontinuous Galerkin method that is discontinuous in time and continuous in space. The scheme is formulated by introducing the equivalent integral equation of the primal equation. The proposed scheme does not explicitly include the jump terms in time, which represent the discontinuity characteristics of approximate solution. And then the complexity of the theoretical analysis is reduced. The existence and uniqueness of the approximate solution and the stability of the scheme are proved. The optimalorder error estimates in L²(H¹) and L²(L²) norms are derived. These estimates are valid under weak restrictions on the space-time mesh, namely, without the condition k_n≥ch², which is necessary in traditional space-time discontinuous Galerkin methods. Numerical experiments are presented to verify the theoretical results.     

High accuracy error estimates of a Galerkin finite element method for nonlinear time fractional diffusion equation

In this work, an effective and fast finite element numerical method with high-order accuracy is discussed for solving a nonlinear time fractional diffusion equation. A two-level linearized finite element scheme is constructed and a temporal–spatial error splitting argument is established to split the error into two parts, that is, the temporal error and the spatial error. Based on the regularity of the time discrete system, the temporal error estimate is derived. Using the property of the Ritz projection operator, the spatial error is deduced. Unconditional superclose result in H¹-norm is obtained, with no additional regularity assumption about the exact solution of the problem considered. Then the global superconvergence error estimate is obtained through the interpolated postprocessing technique. In order to reduce storage and computation time, a fast finite element method evaluation scheme for solving the nonlinear time fractional diffusion equation is developed. To confirm the theoretical error analysis, some numerical results are provided.     

The Euler-Galerkin finite element method for nonlocal diffusion problems with a p-Laplace-type operator

This paper is devoted to the study of the finite element method for a class of non-linear nonlocal diffusion problems associated with p-Laplace-type operator. Using the Euler–Galerkin finite element method, the convergence and a priori error estimates for the semi-discrete as well as fully-discrete formulations are established.     

The characteristic finite difference streamline diffusion method for convection-dominated diffusion problems

In this paper, we consider the characteristic finite difference streamline diffusion method for two-dimensional convection-dominated diffusion problems. The scheme is combined the method of characteristics with the finite difference streamline diffusion (FDSD) method to create the characteristic FDSD (C-FDSD) procedures. Stability analysis and error estimate of the C-FDSD method are deduced. The scheme not only realizes the purpose of lowering the time-truncation error, using larger time step for solving the convection-dominated diffusion problems, but also keeps the favorable stability and high precision of the FDSD method. Finally, numerical experiments are presented to illustrate the availability of the scheme.     

A projection-based stabilized finite element method for steady-state natural convection problem

We formulate a projection-based stabilization finite element technique for solving steady-state natural convection problems. In particular, we consider heat transport through combined solid and fluid media. This stabilization does not act on the large flow structures. Based on the projection stabilization idea, finite element error analysis of the problem is investigated and optimal errors for the velocity, temperature and pressure are established. We also present some numerical tests which both verify the theoretical predictions and demonstrate the method?s promise.     

On discontinuous Galerkin finite element method for singularly perturbed delay differential equations

A nonsymmetric discontinuous Galerkin FEM with interior penalties has been applied to one-dimensional singularly perturbed problem with a constant negative shift. Using higher order polynomials on Shishkin-type layer-adapted meshes, a robust convergence has been proved in the corresponding energy norm. Numerical experiments support theoretical findings.     

A high order finite difference method with Richardsonextrapolation for 3D convection diffusion equation

In this paper, we extend the Sun and Zhang’s [24] work on high order finite difference method, which is based on the Richardson extrapolation technique and an operator interpolation scheme for the one and two dimensional steady convection diffusion equations to the three dimensional case. Firstly, we employ a fourth order compact difference scheme to get the fourth order accurate solution on the fine and the coarse grids. Then, we use the Richardson extrapolation technique by combining the two approximate solutions to get a sixth order accurate solution on coarse grid. Finally, we apply an operator interpolation scheme to achieve the sixth order accurate solution on the fine grid. During this process, we use alternating direction implicit (ADI) method to solve the resulting linear systems. Numerical experiments are conducted to verify the accuracy and effectiveness of the present method.