椭圆型奇异摄动问题差分格式的一致收敛性分析

本文研究了一类椭圆型奇异摄动问题.利用Bakhvalov-Shishkin网格上的差分方法,获得了数值解一致一阶收敛于真解的结果.     

奇异摄动问题最优阶一致收敛的间断有限元分析

采用非对称内罚间断有限元方法(以下简称NIPG方法)求解一维对流扩散型奇异摄动问题.理论上证明了采用拉格朗日线性元的NIPG方法在Bakhvalov-Shishkin网格上具有最优阶的一致收敛性,即在能量范数度量下其误差估计为O(N~(-1)),其中N为网格剖分中单元个数.数值算例验证了理论分析的正确性.     

Bakhvalov-Shishkin网格上求解边界层问题的差分进化算法

该文在Bakhvalov-Shishkin网格上求解具有左边界层或右边界层的对流扩散方程,并采用差分进化算法对Bakhvalov-Shishkin网格中的参数进行优化,获得了该网格上具有最优精度的数值解.对三个算例进行了数值模拟,数值结果表明:采用差分进化算法求解具有较高的计算精度和收敛性,特别是边界层的数值解精度明显...     

奇异摄动问题在Bakhvalov-Shishkin 网格上的流线扩散有限元逼近

本文采用线性插值的流线扩散有限元在Bakhvalov-Shishkin网格上求解一维对流扩散型的奇异摄动问题. 在ε ≤ N^-1的前提下,可以得到,关于扰动参数ε 是一致收敛的. 在离散的SD范数下,其u-u_I的误差阶提高到N^-2,u-u_h的误差阶达到N^-2（lnN）^0.5. 最后,通过数值算例,验证了理论分析.     

奇异摄动问题SIPG方法的高阶一致收敛性分析

在Shishkin格上分析了高阶SIPG方法求解一维对流扩散型奇异摄动问题的一致收敛性.取k(k≥1)次分片多项式和网格剖分单元数为民时,在能量范数度量下Shishkin网格上可获得■((N~(-1)lnN)~k)的一致误差估计.在数值算例部分对理论分析结果进行了验证.     

否定非对合剩余格上基于正规模糊理想的一致拓扑空间

拓扑结构是逻辑代数研究领域的重要研究内容之一,为了揭示否定非对合剩余格上的拓扑结构,基于正规模糊理想诱导的同余关系在否定非对合剩余格上构造一致拓扑空间并讨论其拓扑性质.证明了:(1)一致拓扑空间是第一可数,零维,非连通,局部紧的完全正则空间;(2)一致拓扑空间是T_1空间当且仅当是T_2空间;(3)否定非对合剩余格中格运算和伴随运算关于一致拓扑都是连续的,从而构成拓扑否定非对合剩余格.同时,获得了一致拓扑空间是紧空间和离散空间的充分必要条件.最后,讨论了拓扑否定非对合剩余格中代数同构与拓扑同胚间的关系.对从拓扑层面进一步揭示否定非对合剩余格的内部特征具有一定的促进作用.     

偏序集上一致连续性的等价刻画与性质

将一致小于关系移植到一般偏序集上,同时引入了上界小于关系,定义了偏序集的一致连续性和上界连续性.给出了一致连续偏序集的等价刻画,探讨了一致连续偏序集所具有的性质.主要结果有:(1)证明了偏序集上的一致连续性,上界连续性与s-超连续性均等价;(2)在交半格条件下,偏序集的一致连续性等价于它的每一主理想一致连续;(3)在并半格条件下,偏序集的一致连续性蕴含连续性,反之不成立;(4)一致完备的一致连续偏序集均是连续bc-dcpo,且每个主理想均为完全分配格;(5)在一致完备的条件下,一致连续性对主滤子,对闭区间,对Scott S-集以及对一致连续投射像均是可遗传的.文中也构造了若干实用的反例.     

一致模的延拓

讨论一致模在有界格上的延拓,在有界格上引入收缩核,(r,s)-子格,收缩,e-算子等概念,并且利用收缩与e-算子方法对一致模进行延拓,使延拓后的一致模最大可能地保留原一致模的性质.同时还进一步讨论了一致模的共轭和它的延拓之间的关系.     

拟一致结构与拓扑

本文的目的是(1)指出分子格L上的拟一致结构既可在L上导出一个拓扑,又可在L上导出一个余拓扑,并研究二者的关系;(2)利用保交减值映射族来建立另一类拟一致结构理论;(3)研究两类拟一致结构之间的联系.     

求解带有移动界面的线性对流方程的浸入界面有限体积法（英文）

本文为一类带有移动界面的守恒律方程提出了耦合高分辨率格式的数值算法.这种算法是在一致大小的笛卡尔网格上导出而满足标准的双曲型稳定条件.文末列举数值算例研究这种算法的收敛性和数值精度.     

四阶奇异摄动边值问题在自适应网格上的一致收敛分析

we study a difference scheme for the fourth-order singular pertur-bation differential equation on the Bakhvalov-Shishkin grid by Green‘‘s function.The method is shown to be uniformly convergent with respect to the perturbation parameter,of order N^-2 in the maxmum norm on Bakhvalov-Shishkin meshes.Numerical results support our theoretical results.     

A posteriori error analysis for defect correction method for two parameter singular perturbation problems

Defect correction method is used for two parameter singular perturbation problem on Bakhvalov-Shishkin mesh. Use of defect correction method on Bakhvalov-Shishkin mesh gives a second order convergence. A posteriori error estimate is obtained. The numerical examples are given to establish the second order convergence in practice.     

Infinitesimally flexible meshes and discrete minimal surfaces

We explore the geometry of isothermic meshes, conical meshes, and asymptotic meshes around the Christoffel dual construction of a discrete minimal surface. We present a discrete Legendre transform which realizes discrete minimal surfaces as conical meshes. Conical meshes turn out to be infinitesimally flexible if and only if their spherical image is isothermic, which implies that discrete minimal surfaces constructed in this way are infinitesimally flexible, and therefore possess reciprocal-parallel meshes. These are discrete minimal surfaces in their own right. In our study of relative kinematics of infinitesimally flexible meshes, we encounter characterizations of flexibility and isothermicity which are of incidence-geometric nature and are related to the classical Desargues configuration. The Lelieuvre formula for asymptotic meshes leads to another characterization of isothermic meshes in the sphere which is based on triangle areas.     

Error analysis of staggered finite difference finite volume schemes on unstructured meshes

This work combines the consistency in lower‐order differential operators with external approximations of functional spaces to obtain error estimates for finite difference finite volume schemes on unstructured nonuniform meshes. This combined approach is first applied to a one‐dimensional elliptic boundary value problem on nonuniform meshes, and a first‐order convergence rate is obtained, which agrees with the results previously reported. The approach is also applied to the staggered Marker‐and‐Cell scheme for the two‐dimensional incompressible Stokes problem on unstructured meshes. A first‐order convergence rate is obtained, which improves over a previously reported result in that it also holds on unstructured meshes. For both problems considered in this work, the convergence rate is one order higher on meshes satisfying special requirements. © 2016 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 33: 1159–1182, 2017     

Infinitesimally flexible meshes and discrete minimal surfaces

We explore the geometry of isothermic meshes, conical meshes, and asymptotic meshes around the Christoffel dual construction of a discrete minimal surface. We present a discrete Legendre transform which realizes discrete minimal surfaces as conical meshes. Conical meshes turn out to be infinitesimally flexible if and only if their spherical image is isothermic, which implies that discrete minimal surfaces constructed in this way are infinitesimally flexible, and therefore possess reciprocal-parallel meshes. These are discrete minimal surfaces in their own right. In our study of relative kinematics of infinitesimally flexible meshes, we encounter characterizations of flexibility and isothermicity which are of incidence-geometric nature and are related to the classical Desargues configuration. The Lelieuvre formula for asymptotic meshes leads to another characterization of isothermic meshes in the sphere which is based on triangle areas. Authors’ addresses: Johannes Wallner (corresponding author), Institut für Geometrie, TU Graz, Kopernikusgasse 24, A 8010 Graz, Austria; Helmut Pottmann, Institut für Diskrete Mathematik und Geometrie, TU Wien, Wiedner Hauptstr. 8-10/104, A 1040 Wien, Austria     

Spline Surfaces over Arbitrary Topological Meshes: Theoretical Analysis and Application

Based on polyhedral splines, some multivariate splines of different orders with given supports over arbitrary topological meshes are developed. Schemes for choosing suitable families of multivariate splines based on pre-given meshes are discussed. Those multivariate splines with inner knots and boundary knots from the related meshes are used to generate rational spline shapes with related control points. Steps for up to $C^2$-surfaces over the meshes are designed. The relationship among the meshes and their knots, the splines and control points is analyzed. To avoid any unexpected discontinuities and get higher smoothness, a heart-repairing technique to adjust inner knots in the multivariate splines is designed.With the theory above, bivariate $C^1$-quadratic splines over rectangular meshes are developed. Those bivariate splines are used to generate rational $C^1$-quadratic surfaces over the meshes with related control points and weights. The properties of the surfaces are analyzed. The boundary curves and the corner points and tangent planes, and smooth connecting conditions of different patches are presented. The $C^1$−continuous connection schemes between two patches of the surfaces are presented.