查询词典 finite difference approximation

In the method of numerical analysis, the spatial part of equation system in strong conservation form is first discretized by conventional central finite-difference approximation and then the system of partial differential equations becomes a system of ordinary difference equations.

本文所建数值方法的基本空间离散格式是中心差分，并用源于Jameson的标量耗散模型抑制数值波动；采用经典四阶龙格—库塔法积分经过空间离散后得到的常微分方程组当残差足够小时的解为稳态解。

The new method is a combination of characteristic approximation to handle the convection part, to ensure the high stability of the method in approximating the sharp fronts and reduce the numerical diffusion, a smaller time truncation is gained at the same time, and a mixed finite elementspatial approximation to deal with the diffusion part, the sealer unknown and the adjoint vector function are approximated optimally and simultaneously.

此方法即为对方程的对流项沿流体流动的方向即特征方向进行离散，从而保证格式在流动锋线前沿逼近的高稳定性，消除了数值弥散现象，并得到了较小的时间截断误差；另一方面，对方程的扩散项采用混合元离散，可同时高精度逼近未知函数及其伴随向量函数，理论分析表明，此方法是稳定的，具有最优的L~2逼近精度。

The characteristic approximation is used to handle the convection part along the direc-tion of fluid namely characteristic direction to ensure the high stability of the method in approximating the sharp fronts and reduce the numerical diffusion; The mixed finite element spatial approximation is employed to deal with diffusion part and approximate the scalar unknown and the adjoint vector function optimally and simultaneously; In order to preserve the integral conservation of the method, we introduce the modified characteristic method.

该方法对方程的对流部分沿流体流动的方向即特征方向离散以保证格式在流动的锋线前沿逼近的高稳定性，消除数值弥散现象；对方程的扩散部分采用最低次混合有限元方法离散、同时以高精度逼近未知函数及未知函数的梯度；为保证方法的整体守恒性，在格式中引入修正项。

Firstly, this paper investigated roundly the basic theory of the ambient vibration method, analyzed systematically the main methods of ambient vibration identification, and discussed their advantages and disadvantages. Then we established the finite element model of structural dynamics and test model and analyzed their mutual relation, improved MUSIC method and correlation function method in the harmonic identification, and gave the subspace method and correlation function method based on continuous model, which is multi-harmonic retrieve technique. And then, this paper also puts forward least-squares method to estimate directly structural physical and modal parameters; this approach replaced the derivative operator in the continuous time model with an equivalent approximation, and estimated the physical parameters of structures by the least-squares method. And then, we discussed the approximation methods of derivative and their convergence. Finally, this paper researched the modal parameters of a frame structure by the simulation and test. The results demonstrated that subspace method, correlation function method and the least-squares method are effective and stable respectively.

全面地研究环境振动识别方法的基本理论，系统地分析环境振动识别方法的主要方法，讨论它们的优点和不足；建立结(来源：6666AB44C论文网www.abclunwen.com)构动力学的有限元模型和试验模型，分析有限元模型与试验模型之间的相互关系；改进谐波识别中的MUSIC识别方法和相关函数识别方法，给出大型结构模态识别的连续型的子空间分解识别方法和相关函数识别方法，这个方法是多元谐波识别方法；提出直接识别结构的物理参数和模态参数的最小二乘方法，这个方法利用导数的近似值代替导数值，并运用最小二乘方法识别结构的物理参数，讨论导数近似值的选择方法，分析算法的收敛性；通过仿真计算和模型实验，研究高层框架结构的模态参数识别，验证子空间分解识别方法、相关函数识别方法和最小二乘识别方法的有效性，算法的稳定性；从理论和试验两个方面分析和研究噪声对识别精度的影响，影响识别精度的因素，以及部分模态成分的模态参数不能够被识别的原因。

Firstly, a two-dimension tensor product space is constructed, in which reproducing kernel exists. Secondly a multiresolution analysis is constructed in the reproducing kernel space. Then an orthonormal basis in is obtained. Thus,the reproducing kernel space can be expressed by wavelets spaces. Wavelets approximation formula and sampling formula can also be obtained in the space. Besides, the wavelets approximation formula is simple and easy for calculation. That completes the theory of multiresolution analysis in finite interval fully and provides theoretical base and algorithm for application.

首先，构造二维张量积空间，并证明该空间具有再生核；其次在再生核空间中，建立多尺度分析，获得该空间的一个标准正交基，使得再生核空间可以由小波空间来刻画，进而得到小波级数和相应的采样公式，而且给出的小波级数形式简单易于数值分析，进一步完善了有限区间上的多尺度分析方法，也为实际应用提供了良好的理论基础和算法。

In chapter 2,all kinds of numerical methods of computational fracturemechanics are summarized,the development histories and present situation ofboundary collocation method,boundary integral method,finite difference method,boundary element method and finite element method are expounded,and theapplication of finite element method in fracture mechanics are emphaticallydiscussed.

第二章 总结了计算断裂力学中各种数值方法，论述了边界配位法、边界积分法、有限差分法、边界元法及有限元法的发展历史和现状，并着重讨论了有限元法在断裂力学中的应用。

On the basis of experimental research, this thesis applies 2-dimensional non-linear finite element method to the analysis of transient temperature field on the section by means of relatively high precision triangular element of six joints. When the temperature field is analyzed, finite element reseaus are divided in space field and finite difference reseaus are divided in time field, and then the program is compiled. The computing results are in good agreement with the test data. It indicates that the program is stable and precise.

在试验研究的基础上，本文采用精度较高的三角形六结点单元对构件截面二维非线性瞬态温度场进行了有限元分析，即在空间域内采用有限元网格划分，在时间域内采用有限差分网格划分，据此编制了计算程序，计算结果与试验数据符合较好，程序稳定性好，精度满足要求。

This paper is devoted to solving linear saddle point problems, Specifically, We consider nonsymmetric systems, written as usual in block form, where the upper left block is an invertible linear operator with positive definite symmetric part. Such saddle point problems arise, for example, in certain finite element and finite difference discretizations of NavierStokes equations, Oseen equations, and mixed finite element discretization of second order convection-diffusion problems.

中文题名求解鞍点问题的迭代方法副题名外文题名论文作者冯丽红导师曹志浩教授学科专业计算数学研究领域\研究方向学位级别博士学位授予单位复旦大学学位授予日期2002 论文页码总数87页关键词鞍点问题迭代方法网格离散线性方程组馆藏号BSLW /2003 /O241 /15 论文针对鞍点问题的求解分析了一些典型的快速算法。

Finite element discretization was carried out on the mathematical model to get a fully coupled finite element equation with the parameters of element nodal displacement and element nodal pore pressure as unknown variables. Finally, the transient nonlinear finite element equation in incremental form for reservoir fluid-solid coupling is obtained by means of time discretization in implicit difference scheme.

基于与微分方程等价的加权余量公式，在空间域采用有限元离散，对时间域进行隐式差分格式离散，导出了以单元节点位移和单元节点孔隙压力为未知量的储层流固耦合的非线性有限元增量方程。

Firstly, the fully discrete standard finite element Galerkin method and the nonlinear finite element Galerkin method and the modified finite element Galerkin method in which time is discretized by the Euler implicit difference scheme are considered, and the - and - global relative errors and CPU time corresponding to the SG method, the NG method and the MNG method are computed respectively.

首先，对于全离散(时间离散是欧拉显式格式)标准有限元Galerkin方法和非线性有限元Galerkin方法以及修正有限元非线性Galerkin方法，分别进行数值计算，并比较了三种算法的计算解与精确解的误差估计及所耗费的CPU时间，结果验证了MNG方法要优于NG方法，而NG方法又优于SG方法。

The studies on the developing of new media are very important to the increasing of the area density of HDD and to the implementation of hybrid recoding technology.

光磁混合记录方法，是一种可以突破超顺磁极限的限制，并进一步提高硬盘记录密度和读写速率的一种新型超高密度信息存储方式。

In io, mTOR inhibition promotes T cell anergy under conditions that would normally induce priming.

体内研究中，在正常可激发免疫反应的条件下，抑制mTOR可促使T细胞无能。