一类奇摄动椭圆方程在摄动区域上的渐近解

研究了一类具有摄动边界的非线性椭圆方程摄动问题.经过极坐标变换,在适当的条件下,通过构建近似解以及校正项,利用上下解方法和微分不等式理论得到了解的渐近性态,并通过实际例子进行了验证.     

一类非线性离散系统的指数二分性及其在数值分析和计算中的应用

本文中我们考虑一类二阶非线性常微分方程的边值问题的迎风差分格式.我们运用奇异摄动方法构造了该迎风差分方程解的渐近近似,并利用指数二分性理论证明了有一个低阶方程其解是该迎风方程式的在边界外的一个良好近似.我们还构造了校正项,使校正项与低阶方程的解之和是一个渐近近似.最后一些数值例子用于显示本文方法的应用.     

参数展开摄动法

本文提出一个参数展开摄动法,作为一个应用,讨论了非线性项上带有的参数不是很小时的一般Duffing方程的解。求得了解的渐近展开式。 本文还讨论了广义Duffing方程λ~2x+ex~3=O,这个方程不宜用寻常的摄动法求其渐近解,但用参数展开摄动法可以求其渐近解,文中构造了解的渐近形式,提出了二次近似与一次近似渐近解的稳定判据。     

一类非线性双曲型发展方程的孤子解

研究了一类非线性发展方程.首先在无扰动情形下,利用待定函数和泛函同伦映射方法得到了非扰动发展方程的孤子精确解和扰动方程的任意次近似行波孤子解.接着引入一个同伦映射,并选取初始近似函数,再用同伦映射理论,依次求出非线性双曲型发展扰动方程孤子解的各次近似解析解.再利用摄动理论举例说明了用该方法得到的近似解析解的有效性和各次近似解的近似度.最后,简述了用同伦映射方法得到的近似解的意义,指出了用上述方法得到的各次近似解具有便于求解、精度高等优点.     

一类双参数非线性高阶反应扩散方程的摄动解法

研究了一类两参数非线性反应扩散奇摄动问题的模型.利用奇摄动方法,对该问题解的结构在两个小参数相互关联的情形下作了讨论.首先,构造问题的外部解; 之后在区域的边界邻域构造局部坐标系,再在该邻域中引入多尺度变量,得到问题解的边界层校正项; 然后引入伸长变量,构造初始层校正项,并得到问题解的形式渐近展开式;最后建立了微分不等式理论,并由此证明了问题的解的一致有效的渐近展开式.用上述方法得到的各次近似解,具有便于求解、精度高等特点.     

一类含小参数的Hill方程的自由振动

本文研究一类含小参数的Hill方程的初值问题,利用边值问题可解性条件及摄动理论中的伸缩参数法,给出寻求该初值问题近似周期解的方法,并以Mathieu方程为例作了具体计算.     

一类非线性兰彻斯特方程的摄动解

研究了一类非线性兰彻斯特方程,描述了现代化战争条件下的战斗模型.在分析实际交战过程中的损耗系数之间的关系的基础上,引入了摄动参数.利用摄动方法,得到了相应非线性方程组的渐近解,再利用微分不等式理论,证明了渐近解的一致有效性,并将得到的渐近解与数值解进行了精度比较.结果表明该摄动方法简单有效,而且它得到的解是近似解析解,能继续进行各种解析运算,这是数值解所无法媲美的优点.从而,所求的渐近解能够更准确地揭示出现代战争的特点和规律,还能为作战决策者提供更多有价值的信息.     

双参数半线性反应扩散方程的奇摄动解

讨论了一类具有双参数的半线性反应扩散方程奇摄动初始边值问题.利用微分不等式理论,研究了初始边值问题解的渐近性态.     

一类含慢变量奇摄动非线性系统初始层现象

研究含有慢变量的一类奇摄动非线性系统初始层现象,通过引进不同量级的伸长变量,构造不同“厚度”的初始层校正项,得到了摄动解关于小参数的N阶近似展开式,揭示了摄动解呈现的“层中层”现象,并利用不动点原理证明了摄动解的存在,给出了解的一致有效的渐近展开式．     

用加权残余法求解含大参数的Duffing方程

本文应用加权残余法分析了含大参数的 Duffing方程 ,并得到了整个区域内 (0 <ε<∞ )一致有效的近似解 ,得到的近似周期的最大相对误差小于 7.0 % ,当参数为小量时 (ε 1 ) ,得到的近似解和摄动解完全一致 .     

A semi‐discrete defect correction finite element method for unsteady incompressible magnetohydrodynamics equations

In this report, we give a semi‐discrete defect correction finite element method for the unsteady incompressible magnetohydrodynamics equations. The defect correction method is an iterative improvement technique for increasing the accuracy of a numerical solution without applying a grid refinement. Firstly, the nonlinear magnetohydrodynamics equations is solved with an artificial viscosity term. Then, the numerical solutions are improved on the same grid by a linearized defect‐correction technique. Then, we give the numerical analysis including stability analysis and error analysis. The numerical analysis proves that our method is stable and has an optimal convergence rate. In order to show the effect of our method, some numerical results are shown. Copyright © 2017 John Wiley & Sons, Ltd.     

Linearized perturbation method for stochastic analysis of a rill erosion model

The linearization and correction method (LCM) proposed by He is a simple and effective perturbation technique to solve nonlinear equations. To analyze the random properties of rill erosion model, a new stochastic perturbation technique called linearized perturbation method is developed by combining the traditional stochastic perturbation method with the LCM. Comparisons between the numerical results obtained by the linearized perturbation method and those obtained by Monte Carlo method indicated an excellent agreement. However, the calculation efficiency of the linearized perturbation method is higher.     

Convergence of a nonlinear finite difference scheme for the Kuramoto–Tsuzuki equation

A nonlinear finite difference scheme is studied for solving the Kuramoto–Tsuzuki equation. Because the maximum estimate of the numerical solution can not be obtained directly, it is difficult to prove the stability and convergence of the scheme. In this paper, we introduce the Brouwer-type fixed point theorem and induction argument to prove the unique existence and convergence of the nonlinear scheme. An iterative algorithm is proposed for solving the nonlinear scheme, and its convergence is proved. Based on the iterative algorithm, some linearized schemes are presented. Numerical examples are carried out to verify the correction of the theory analysis. The extrapolation technique is applied to improve the accuracy of the schemes, and some interesting results are obtained.     

Error estimate of a fully discrete defect correction finite element method for unsteady incompressible Magnetohydrodynamics equations

In this study, a fully discrete defect correction finite element method for the unsteady incompressible Magnetohydrodynamics (MHD) equations, which is leaded by combining the Back Euler time discretization with the two-step defect correction in space, is presented. It is a continuous work of our formal paper [Math Method Appl Sci. 2017. DOI:10.1002/mma.4296]. The defect correction method is an iterative improvement technique for increasing the accuracy of a numerical solution without applying a grid refinement. Firstly, the nonlinear MHD equation is solved with an artificial viscosity term. Then, the numerical solutions are improved on the same grid by a linearized defect-correction technique. Then, we introduce the numerical analysis including stability analysis and error analysis. The numerical analysis proves that our method is stable and has an optimal convergence rate. Some numerical results [see Math Method Appl Sci. 2017. DOI:10.1002/mma.4296] show that this method is highly efficient for the unsteady incompressible MHD problems.     

Maximum norm error bound of a linearized difference scheme for a coupled nonlinear Schrödinger equations

In this article, a linearized conservative difference scheme for a coupled nonlinear Schrödinger equations is studied. The discrete energy method and an useful technique are used to analyze the difference scheme. It is shown that the difference solution unconditionally converges to the exact solution with second order in the maximum norm. Numerical experiments are presented to support the theoretical results.     

Two grid discretizations with backtracking of the stream function form of the Navier-Stokes equations

We analyze a two grid finite element method with backtracking for the stream function formulation of the stationary Navier—Stokes equations. This two grid method involves solving one small, nonlinear coarse mesh system, one linearized system on the fine mesh and one linear correction problem on the coarse mesh. The algorithm and error analysis are presented.     

Lyapunov functions in justification theorems for asymptotics

A formal asymptotic solution is considered for a nonlinear system of ordinary differential equations in a neighborhood of a singular point. The problem of existence of an exact solution with such an asymptotics and the problem of stability of this solution are solved. The main tool in these studies is the Lyapunov function for a system linearized on a formal solution.     

Behavior of cylindrical panels made of composite materials subjected to longitudinal impact in a gas flow

The dynamic properties of plates and cylindrical panels made of composite materials subjected to axial impact in a supersonic gas flow are investigated on the basis of a geometrically nonlinear orthotropic model and a linear wave equation for a one-dimensional medium. A solution is obtained by applying the Bubnov—Galerkin procedure with respect to the arc coordinate and a finite-difference method with respect to the axial coordinate and time. The aerodynamic pressure is found by means of an improved variant of linearized piston aerodynamics with a correction for curvature. Numerical results are presented and analyzed.     

Local and parallel finite element algorithm based on the partition of unity method for the incompressible MHD flow

Based on the partition of unity method (PUM), a local and parallel finite element method is designed and analyzed for solving the stationary incompressible magnetohydrodynamics (MHD). The key idea of the proposed algorithm is to first solve the nonlinear system on a coarse mesh, divide the globally fine grid correction into a series of locally linearized residual problems on some subdomains derived by a class of partition of unity, then compute the local subproblems in parallel, and obtain the globally continuous finite element solution by assembling all local solutions together by the partition of unity functions. The main feature of the new method is that the partition of unity provide a flexible and controllable framework for the domain decomposition. Finally, the efficiency of our theoretical analysis is tested by numerical experiments.     

Numerical analysis of nonlinear model of excited carrier decay

This paper presents a mathematical model for photo-excited carrier decay in a semiconductor. Due to the carrier trapping states and recombination centers in the bandgap, the carrier decay process is defined by the system of nonlinear differential equations. The system of nonlinear ordinary differential equations is approximated by linearized backward Euler scheme. Some a priori estimates of the discrete solution are obtained and the convergence of the linearized backward Euler method is proved. The identifiability analysis of the parameters of deep centers is performed and the fitting of the model to experimental data is done by using the genetic optimization algorithm. Results of numerical experiments are presented.