某导弹发射箱箱盖开盖角度优化研究

采用求解三维、非定常、雷诺平均的N-S方程的方法,对某车载导弹发射过程中的燃气流场进行了非定常数值模拟。紊流模型采用标准的k-ε二方程模型,计算方法为有限体积法,计算网格为结构化网格。在此基础上研究了箱盖受力与开盖角度之间的关系,给出了最优开盖角度。     

大型稀疏线性方程组新的ICCG方法

有限元线性方程组的系数矩阵一般具有稀疏性和对称性的特点,全稀疏存贮方法就是利用这些特点,只存贮对称部分的非零元素,采用链表式管理,即节省存贮空间,又便于动态更改．在完全Cholesky分解的基础上,构造出了新的预处理方法,应用适当的对角元修正策略,得到了一种新的ICCG方法,能够确保方程组高效准确的分解和求解．数值算例证明该算法在时间和存贮上都较为占优,可靠高效,能够应用于有限元线性方程组的求解．     

广义预测控制中 Diophantine矩阵多项式方程的显式解

直接利用被控对象的离散差分方程推导出多变量广义预测控制中Diophantine矩阵多项式方程的显式解,从而避免了其递推求解或迭代求解,使广义预测控制的应用更加方便．     

导体-介质组合体散射分析两种积分方程法比较

采用耦合积分方程和单积分方程两种方法,分析了三维导体-介质组合体目标的电磁散射问题.与传统的耦合积分方程法相比,单积分方程法使介质体表面的未知量数目减少一半,并且能获得更快的迭代解.讨论了导体-介质交界线上RWG基函数的正确处理问题.对介质锥-导体柱组合体、导体-介质组合球和某导弹模型的雷达截面(RCS)进行了计算和比较,验证了两种积分方程方法的正确性,且数值结果表明单积分方程法更加有效.     

A bridge between projection methods and SIMPLE type methods for incompressible Navier–Stokes equations

A bridge is built between projection methods and SIMPLE type methods (Semi‐Implicit Method for Pressure‐Linked Equation). A general second‐order accurate projection method is developed for the simulation of incompressible unsteady flows by employing a non‐linear update of pressure term as Θⁿ?pⁿ⁺¹+(I?Θⁿ)?pⁿ, where Θⁿ is a coefficient matrix, which may depend on the grid size, time step and even velocity. It includes three‐ and four‐step projection methods. The standard SIMPLE method is written in a concise formula for steady and unsteady flows. It is proven that SIMPLE type methods have second‐order temporal accuracy for unsteady flows. The classical second‐order projection method and SIMPLE type methods are united within the framework of the general second‐order projection formula. Two iteration algorithms of SIMPLE type methods for unsteady flows are described and discussed. In addition, detailed formulae are provided for general projection methods by using the Runge–Kutta technique to update the convective term and Crank–Nicholson scheme for the diffusion term. Copyright © 2007 John Wiley & Sons, Ltd.     

光纤布拉格光栅非线性孤子的特性分析

以非线性耦合模理论为基础，用数值计算的方法分析了光纤光栅非线性孤子的特性。结果表明，在较弱光脉冲输入时，脉冲被展宽幅度降低；在强光脉冲输入时，脉冲的幅度，速度和脉宽保持不变，孤子形成；当更强光脉冲输入时，脉冲被压缩同时产生随距离而变的线性啁啾。当波长位于负色散区的弱脉冲和位于正常色散区的强泵浦脉冲共同传输时，输入弱脉冲被压缩。     

捷联惯性测量装置全温度标定方法

为了提高捷联惯性测量装置(SIMU)的测量精度,在使用前必须对其进行标定,以确定SIMU的参数及性能指标.为此研究了一种SIMU的全温度标定方法,利用专用的测试设备对SIMU进行全温度标定试验.给出了SIMU的静态模型方程,详细介绍了模型方程中各参数的标定方法及具体的误差补偿计算方法,最后给出了SIMU综合性能指标的计算.经过多发SIMU的标定实验,结果表明:该标定方法有效地提高了SIMU的实际实用精度.     

Finite Element Analysis for Wave Propagation in Double Negative Metamaterials

In this paper, we develop both semi-discrete and fully-discrete mixed finite element methods for modeling wave propagation in three-dimensional double negative metamaterials. Here the model is formed as a time-dependent linear system involving four dependent vector variables: the electric and magnetic fields, and the induced electric and magnetic currents. Optimal error estimates for all four variables are proved for Nédélec tetrahedral elements. To our best knowledge, this is the first error analysis obtained for Maxwell’s equations when metamaterials are involved.      

Modelling and effective modification of smooth boundary geometry in boundary problems using B-spline curves

To create curves in computer graphics, we use, among others, B-splines since they make it possible to effectively produce curves in a continuous way using a small number of de Boor’s control points. The properties of these curves have also been used to define and create boundary geometry in boundary problems solving using parametric integral equations system (PIES). PIES was applied for resolution 2D boundary-value problems described by Laplace’s equation. In this PIES, boundary geometry is theoretically defined in its mathematical formalism, hence the numerical solution of the PIES requires no boundary discretization (such as in BEM) and is simply reduced to the approximation of boundary functions. To solve this PIES a pseudospectral method has been proposed and the results obtained were compared with both exact and numerical solutions.     

Identifying a control function in parabolic partial differential equations from overspecified boundary data

Determination of an unknown time-dependent function in parabolic partial differential equations, plays a very important role in many branches of science and engineering. In the current investigation, the Adomian decomposition method is used for finding a control parameter p(t) in the quasilinear parabolic equation u_t=u_xx+p(t)u+, in [0,1]×(0,T] with known initial and boundary conditions and subject to an additional condition in the form of which is called the boundary integral overspecification. The main approach is to change this inverse problem to a direct problem and then solve the resulting equation using the well known Adomian decomposition method. The decomposition procedure of Adomian provides the solution in a rapidly convergent series where the series may lead to the solution in a closed form. Furthermore due to the rapid convergence of Adomian’s method, a truncation of the series solution with sufficiently large number of implemented components can be considered as an accurate approximation of the exact solution. This method provides a reliable algorithm that requires less work if compared with the traditional techniques. Some illustrative examples are presented to show the efficiency of the presented method.