一类一维的辐射流体力学方程组激波的存在性

该文主要讨论一维空间中一类辐射流体力学方程组的激波. 由Rankine-Hugoniot条件及熵条件得此问题可表述为关于辐射流体力学方程组带自由边界的初边值问题. 首先通过变量代换, 将其自由边界转换为固定边界, 然后研究关于此非线性方程组的一个初边值问题解的存在唯一性. 为此先构造了此问题的一个近似解, 然后分别通过Picard迭代与Newton迭代对此非线性问题构造近似解序列. 通过一系列估计与紧性理论得到此近似解序列的收敛性, 其极限即为原辐射热力学方程组的一个激波.     

可渗透壁面上Falkner-Skan磁流体动力学流动的近似解

研究了可渗透壁面上Falkner-Skan磁流体动力学(MHD)边界层流动问题.利用结合了微分变换法(DTM)和Padé近似的DTM-Padé方法,得到了边界层问题的近似解和壁摩擦因数值.通过建立一个迭代程序,边界层问题的近似解被表示为幂级数的形式,而且以图和表形式对不同参数下的近似解结果与打靶法得到的数值结果进行了对比,近似解和数值解结果高度吻合,从而验证了所得问题近似解和结论的可靠性和有效性.并且,对求得的边界层问题近似解结果进行了讨论,分析了不同物理参数对边界层流动的影响.     

Helmholtz方程Cauchy问题的间接积分方程方法

 本文处理二维和三维Helmholtz方程的边界数据复原问题.通过利用位势理论近似问题的解,导出了解决Cauchy问题的一种非迭代积分方程方法.为了处理形成问题的不适定性,采用了Tikhonov正则化结合Morozov偏差原理的方法,并且给出了算法的收敛性和误差估计,最后给出了二维和三维的数值算例.通过数值算例我们检验了源点和边界之间距离的关系,算法关于噪声、源点数目的数值收敛性,稳定性.     

献给马富明教授60华诞 Helmholtz方程Cauchy问题的间接积分方程方法

本文处理二维和三维Helmholtz方程的边界数据复原问题.通过利用位势理论近似问题的解,导出了解决Cauchy问题的一种非迭代积分方程方法.为了处理形成问题的不适定性,采用了Tikhonov正则化结合Morozov偏差原理的方法,并且给出了算法的收敛性和误差估计,最后给出了二维和三维的数值算例·通过数值算例我们检验了源点和边界之间距离的关系,算法关于噪声、源点数目的数值收敛性,稳定性.     

广义强非线性拟补问题

利用本文中的算法，我们证明了广义强非线性拟补问题解的存在性及由算法产生的迭代序列的收敛性，改进和发展了Ｎｏｏｒ．Ｃｈａｎｇ－Ｈｕａｎｇ等人的结果。此外，也给出了求广义强非线性拟补问题的近似解的另一更一般的迭代算法并证明了由此迭代格式获得的近似解收敛于此补问题的精确解。     

Banach空间内涉及H-η-单调算子的集值混合拟似变分包含组

在没有光滑性的一般Banach空间内引入和研究了涉及H-η-单调算子的集值混合拟似变分包含组(SSMQVLI).利用与H-η-单调算子相联系的预解算子技巧,建议和分析了一类寻求SS-MQVLI的近似解的新的迭代算法.在适当假设下,证明了由算法生成的迭代序列强收敛于SS-MQVLI的精确解.这些结果是新的,改进和推广了这一领域的相应结果.     

广义Lyapunov方程A~TX+X~TA=C的一般解及其最佳逼近解

本文讨论矩阵方程ATX+XTA=C的一般解及其最佳逼近解的正交投影迭代解法.首先,利用矩阵的结构特点及相关性质,并借助矩阵空间的相关理论,给出求该矩阵方程一般解正交投影迭代算法;其次,根据奇异值分解、F-范数正交变换不变性证明算法的收敛性并推导出算法的收敛速率估计式,当方程相容时,该算法收敛于问题的极小范数解,且对该算法稍加修改,就可得到相应最佳逼近解;最后,用数值实例验证算法的有效性.     

Banach空间中集值混和变分不等式问题解的迭代算法

介绍了集值映象的伪单调定义，并在Banach空间中构造了集值混和变分不等式问题近似解的迭代算法．应用伪单调映象定义，证明了该迭代算法收敛于集值混和变分不等式问题的近似解．特别值得注意的是：在文章中对集值映象没有Lipschitz连续性假设．     

基于近似一阶信息的加速的bundle level算法

本文提出了四种加速的BL(bundle level)算法来分别求解凸光滑函数、强凸光滑函数的极小值问题和一类鞍点(saddle-point)问题.这些算法可以运用目标函数的近似的一阶信息来得到上述几类问题的近似解.本文重点研究了在一阶信息误差上界可自由选取和给定不变的两种情形下,所提出的算法中近似解能达到的最佳精度以及相应的迭代复杂度.     

一类Riccati矩阵方程广义自反解的双迭代算法

本文研究了一类Riccati矩阵方程广义自反解的数值计算问题.利用牛顿算法将Riccati矩阵方程的广义自反解问题转化为线性矩阵方程的广义自反解或者广义自反最小二乘解问题,再利用修正共轭梯度法计算后一问题,获得了求Riccati矩阵方程的广义自反解的双迭代算法.拓宽了求解非线性矩阵方程的迭代算法.数值算例表明双迭代算法是有效的.     

On Neumann - Dirchlet coupling strategy of Finite Element and Boundary Element method in elastodynamics

The Finite Element Method (FEM) and the Boundary Element Method (BEM) are the most used numerical tools for solid mechanics analysis. Each one of these methods has advantages and drawbacks in different cases. In order to take advantage of both methods, a nonoverlapping domain decomposition method FEM - BEM in elastodynamics is presented. The domain is divided in two subdomains and each one of them is analyzed separately and only the interface information is exchanged. An iterative Neumann - Dirchlet algorithm with relaxation is used, to get continuity and the equilibrium conditions at the interface. The FEM time integration is carried out using the Newmark's method and the BEM approach in time domain is based in the Convolution Quadrature Method developed by Lubich. Numerical examples are presented to show agreement with other available numerical results. (© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

A boundary element method in elastodynamics for geometrically axisymmetric problems

A direct boundary element method (BEM) in elastodynamics is developed for geometrically axisymmetric problems subjected to arbitrary external loads. Traction and displacement components are expressed in terms of Fourier series. Unlike classical BEMs, the kernel functions in the resulting integral governing equations in the present method are expanded as implicit functions of the difference of the polar angles at two field points. The new BEM is therefore capable of solving a wider variety of elastodynamic problems. Two numerical examples in foundation engineering show that the present BEM is also accurate and computationally efficient.     

一种有限元-边界元耦合分域算法

提出了一种有限元．边界元耦合分域算法．该算法将所分析问题的区域分解成有限元和边界元子域，在满足两子域界面上位移和面力协调连续的条件下，通过迭代求解得到问题的解．在迭代求解过程中，引入动态松弛系数，使收敛得以加速．该方法在两子域界面上有限单元结点和边界单元结点的位置相互独立，无需协调一致，对诸如裂纹扩展过程的模拟具有独特的优势．用所提出的耦合算法分析算例，得到的结果与有限元法、边界元法和另一种耦合算法的数值计算结果一致，验证了这种算法的正确性和可行性．     

Adaptive FEM–BEM coupling with a Schur complement error indicator

In this paper an a-posteriori error estimate for non-linear coupled FEM–BEM equations is derived by using the Steklov–Poincaré operator and hierarchical basis techniques. We obtain “local” error indicators which are based on two-level subspace decompositions with the additive Schwarz operator. We present an algorithm for adaptive error control which is driven by these error indicators and numerical results are included.     

Coupling of FEM and BEM in Shape Optimization

In the present paper we consider the numerical solution of shape optimization problems which arise from shape functionals of integral type over a compact region of the unknown shape, especially L ²-tracking type functionals. The underlying state equation is assumed to satisfy a Poisson equation with Dirichlet boundary conditions. We proof that the shape Hessian is not strictly H ^1/2-coercive at the optimal domain which implies ill-posedness of the optimization problem under consideration. Since the adjoint state depends directly on the state, we propose a coupling of finite element methods (FEM) and boundary element methods (BEM) to realize an efficient first order shape optimization algorithm. FEM is applied in the compact region while the rest is treated by BEM. The coupling of FEM and BEM essentially retains all the structural and computational advantages of treating the free boundary by boundary integral equations.This research has been carried out when the second author stayed at the Department of Mathematics, Utrecht University, The Netherlands, supported by the EU-IHP project Nonlinear Approximation and Adaptivity: Breaking Complexity in Numerical Modelling and Data Representation     

Finite element method in the solution of the Euler and Navier-Stokes equations for internal flow

Finite element solutions of the Euler and Navier-Stokes equations are presented, using a simple dissipation model. The discretization is based on the weak-Galerkin weighted residual method and equal interpolation functions for all the unknowns are permitted. The nonlinearity is iterated upon using a Newton method and at each iteration the linear algebraic system is solved by a direct solver with all unknowns fully coupled. Results are presented for two-dimensional transonic inviscid flows and two- and three-dimensional incompressible viscous flows. Convergence of the algorithm is shown to be quadratic, reaching machine accuracy in very few iterations. The inviscid results demonstrate the existence of nonunique numerical solutions to the steady Euler equations.     

A pod reduced-order spdmfe extrapolating algorithm for hyperbolic equations

In this article, a proper orthogonal decomposition (POD) method is used to study a classical splitting positive definite mixed finite element (SPDMFE) formulation for second-order hyperbolic equations. A POD reduced-order SPDMFE extrapolating algorithm with lower dimensions and sufficiently high accuracy is established for second-order hyperbolic equations. The error estimates between the classical SPDMFE solutions and the reduced-order SPDMFE solutions obtained from the POD reduced-order SPDMFE extrapolating algorithm are provided. The implementation for solving the POD reduced-order SPDMFE extrapolating algorithm is given. Some numerical experiments are presented illustrating that the results of numerical computation are consistent with theoretical conclusions, thus validating that the POD reduced-order SPDMFE extrapolating algorithm is feasible and efficient for solving second-order hyperbolic equations.     

A POD REDUCED-ORDER SPDMFE EXTRAPOLATING ALGORITHM FOR HYPERBOLIC EQUATIONS

In this article, a proper orthogonal decomposition （POD） method is used to study a classical splitting positive definite mixed finite element （SPDMFE） formulation for second- order hyperbolic equations. A POD reduced-order SPDMFE extrapolating algorithm with lower dimensions and sufficiently high accuracy is established for second-order hyperbolic equations. The error estimates between the classical SPDMFE solutions and the reduced-order SPDMFE solutions obtained from the POD reduced-order SPDMFE extrapolating algorithm are provided. The implementation for solving the POD reduced-order SPDMFE extrapolating algorithm is given. Some numerical experiments are presented illustrating that the results of numerical computation are consistent with theoretical conclusions, thus validating that the POD reduced-order SPDMFE extrapolating algorithm is feasible and efficient for solving second-order hyperbolic equations.     

A meshless scaling iterative algorithm based on compactly supported radial basis functions for the numerical solution of Lane‐Emden‐Fowler equation

In this article, we combine the compactly supported radial basis function (RBF) collocation method and the scaling iterative algorithm to compute and visualize the multiple solutions of the Lane‐Emden‐Fowler equation on a bounded domain Ω ? R² with a homogeneous Dirichlet boundary condition. This novel method has the advantage over traditional methods, which approximate the spatial derivatives using either the finite difference method (FDM), the finite element method (FEM), or the boundary element method (BEM), because it does not require a mesh over the domain. As a result, it needs less computational time than the globally supported RBF collocation method. When compared with the reference solutions in (Chen, Zhou, and Ni, Int J Bifurcation Chaos 10 (2000), 565–1612), our numerical results demonstrate the accuracy and ease of implementation of this method. It is therefore much more suitable for dealing with the complex domains than the FEM, the FDM, and the BEM. © 2010 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 28: 554‐572, 2012     

AN ITERATIVE HYBRIDIZED MIXED FINITE ELEMENT METHOD FOR ELLIPTIC INTERFACE PROBLEMS WITH STRONGLY DISCONTINUOUS COEFFICIENTS

An iterative algorithm is proposed and analyzed based on a hybridized mized finite element method for numerically solving two-phase generalized Stefan interface problems with strongly discontinuous solutions,conormal derivatives,and coefficients.This algorithm iteratively solves small problems for each single phase with good accuracy and exchange information at the interface to advance the iteration until convergence ,following the idea of Schwarz Alternating Methods,Error estimates are derived to show that this algorithm always converges provided that relaxation parameters are suitably chosen,Numeric exper-iments with matching and non-matching grids at the interface from different phases are performed to show the accuracy of the method for capturing discontinuities in the solutions and coefficients.In contrast to standard numerical methods,the accuracy of our method does not seem to deteriorate as the coefficient discontinuity increases.