求解静电场偏微分方程的新代数多重网格法

多重网格法是求解偏微分方程大规模离散化方程最有效的方法,针对静电场偏微分方程,讨论一致线性有限元剖分下的拉格朗日有限元方程的代数多重网格法,给出了一种新的粗化算法和构造插值算子的途径。数值实验表明,新的代数多重网格法的有效性。     

RKDG有限元法求解一维拉格朗日形式的Euler方程

描述一种新的求解Euler方程的拉格朗日格式,该格式用Runge-Kutta Discontinuous Galerkin(RKDG)方法在拉格朗日坐标系求解Euler方程,剖分网格随流体运动.新格式不仅保证流体的质量、动量和能量守恒,而且能够在时间和空间上同时达到二阶精度.数值算例表明在一维情况,随着拉氏网格的移动和改变,格式在时间和空间上仍保持二阶精度,并且没有数值震荡.     

求解Euler方程的高精度的空间--时间守恒格式

空间-时间守恒(STC)格式是近年来发展出的一种计算格式,在现有的STC格式构造过程中,流动变量在解元中的分布都用其一阶Taylor展开式来表示.STC格式的精度与所采用的Taylor展开式的阶数有关.该文采用流动变量的二阶Taylor展开式来表示其在解元上的分布、构造出了求解一维Euler方程的STC格式.用该格式对几个问题进行了计算,将计算结果与精确解进行了比较,比较表明该格式有较高的精度.     

完全多重网格法求解光强度传播方程的相位恢复方法

一般多重网格算法求解光强度传播方程是从精细网格层开始计算,精细网格层的初值选择影响算法的收敛速度和求解精度.提出了一种完全多重网格方法求解光强度传播方程的相位恢复方法.基于限制法将最细网格上的方程转化为最粗网格上的方程,求解该方程得到最粗网格上的解;然后对此解用延拓法得到上一层细网格上的解,以得到的解作为此层网格上的初解,利用V循环解此层上的方程,得到此层网格的精确解.依次,直到得到最细网格上的精确解.模拟相位恢复实验结果表明,本文方法具有较快的收敛速度,能够恢复复杂相位分布.     

多重网格法在反应堆扩散方程中的应用分析

该文叙述的是把多重网格法应用于反应堆扩散方程的一个准备性工作。我们应用V循环和W循环的多重网格法求解一个模型问题,并与SOR方法进行了比较。数值结果表明,W循环的多重网格法要比SOR方法快四倍。     

代数多重网格法在排队理论中的应用

提出一种校正ＡＭＧ方法来求解排队模型。该方法对一般ＡＭＧ方法的限制算子进行了改进，从而在求解过程中保留了问题的奇异性。计算结果表明改进后的方法加快了收敛速度，提高了解的精度。     

在代数多重网格法中的新插值公式

推导出代数多重网格法的一个新的插值公式。理论分析和数值计算表明这个公式很有效,且适用性强。推广了原代数多重网格法的应用范围,能够求解一些很病态的代数方程组。     

采用多重网格法进行电子结构的计算

采用多重网格法(MG)和对称性理论以及密度泛函理论中著名的Kohn-Sham 方程,开发了一种计算具有一定对称性的原子簇的电子结构的方法,并对H₂ 分子的基态能进行了实际的计算,并与用其他理论计算得到的结果进行了比较。     

Research of the Algebraic Multigrid Method for Electron Optical Simulator

At present, electron optical simulator (EOS) takes a long time to solve linear FEM systems. The algebraic multigrid preconditioned conjugate gradient (AMGPCG) method can improve the efficiency of solving systems. This paper is focused on the implementation of the AMGPCG method in EOS. The aggregation-based scheme, which uses two passes of a pairwise matching algorithm and the K-cyle scheme, is adopted in the aggregation-based algebraic multigrid method. Numerical experiments show the advantages and disadvantages of the AMG algorithm in peak memory and solving efficiency. The AMGPCG is more efficient than the iterative methods used in the past and only needs one coarsening when EOS computes the particle motion trajectory.     

一类三维等代数结构面剖分下的代数多重网格算法

对一类等代数结构面的三维非结构网格剖分,针对光滑变系数和各向异性系数的偏微分方程,给出两种非结构代数多重网格算法,数值试验表明算法的有效性和健壮性.     

二维半线性扩散反应方程的高精度全隐格式及其多重网格方法

针对二维非定常半线性扩散反应方程，空间导数项采用四阶紧致差分公式离散，时间导数项采用四阶向后Euler公式进行离散，提出一种无条件稳定的高精度五层全隐格式.格式截断误差为O（τ⁴+τ²h²+h⁴），即时间和空间均具有四阶精度.对于第一、二、三时间层采用Crank-Nicolson方法进行离散，并采用Richardson外推公式将启动层时间精度外推到四阶.建立适用于该格式的多重网格方法，加快在每个时间层上迭代求解代数方程组的收敛速度，提高计算效率.最后通过数值实验验证格式的精确性和稳定性以及多重网格方法的高效性.     

An Algebraic Multigrid Method for Nearly Incompressible Elasticity Problems in Two-Dimensions

In this paper, we discuss an algebraic multigrid (AMG) method for nearly incompressible elasticity problems in two-dimensions. First, a two-level method is proposed by analyzing the relationship between the linear finite element space and the quartic finite element space. By choosing different smoothers, we obtain two types of two-level methods, namely TL-GS and TL-BGS. The theoretical analysis and numerical results show that the convergence rates of TL-GS and TL-BGS are independent of the mesh size and the Young's modulus, and the convergence of the latter is greatly improved on the order $p$. However, the convergence of both methods still depends on the Poisson's ratio. To fix this, we obtain a coarse level matrix with less rigidity based on selective reduced integration (SRI) method and get some types of two-level methods by combining different smoothers. With the existing AMG method used as a solver on the first coarse level, an AMG method can be finally obtained. Numerical results show that the resulting AMG method has better efficiency for nearly incompressible elasticity problems.     

求解Euler方程的隐式无网格算法

研究了求解Eluer方程的稳式无网格算法，用点云离散计算区域，代替通常的网格划分；在当地点云上，引入二次平方极小曲面逼近计算空间导数，用Roe的近似Riemann解确定通量；并用LU-SGS算法求解离散得到的Euler方程稳式时间后差联立方程组，数值模拟了二维翼型跨音速绕流，由于无网格算法区域离散只涉及点云，具有灵活性，适合处理复杂的气动外形。     

A New General Algebraic Method and Its Application to Shallow Long Wave Approximate Equations

A new general algebraic method is presented to uniformly construct a series of exact solutions for nonlinear evolution equations （NLEEs）. For illustration, we apply the new method to shallow long wave approximate equations and successfully obtain abundant new exact solutions, which include rational solitary wave solutions and rational triangular periodic wave solutions. The method is straightforward and concise, and it can also be applied to other nonlinear evolution equations in mathematical physics.     

Extended Fan's Algebraic Method and Its Application to KdV and Variant Boussinesq Equations

An extended Fan's algebraic method is used for constructing exact traveling wave solution of nonlinear partial differential equations. The key idea of this method is to introduce an auxiliary ordinary differential equation which is regarded as an extended elliptic equation and whose degree r is expanded to the case of r ＞ 4. The efficiency of the method is demonstrated by the KdV equation and the variant Boussinesq equations. The results indicate that the method not only offers all solutions obtained by using Fu's and Fan's methods, but also some new solutions.     

Extended Fan's Algebraic Method and Its Application to KdV and Variant Boussinesq Equations

An extended Fan's algebraic method is used for constructing exact traveling wave solution of nonlinear partial differential equations. The key idea of this method is to introduce an auxiliary ordinary differential equation which is regarded as an extended elliptic equation and whose degree r is expanded to the case of r>4. The efficiency of the method is demonstrated by the KdV equation and the variant Boussinesq equations. The results indicate that the method not only offers all solutions obtained by using Fu's and Fan's methods, but also some new solutions.     

多级轴流透平气动特性计算方法研究

在多级轴流透平子午面中线上建立1.5维欧拉方程组,其中叶片作用力、流体的黏性作用、冷气的作用以源项的形式考虑到方程中,控制方程采用一步时间推进TVD-LW格式进行离散和求解.计算结果表明,该方法能够预测多级轴流透平的平均气动参数分布和气动性能,具有快速、灵活的特点,可以用于求解透平的特性曲线或进行气动优化.