复合目标电磁散射的高效混合计算方法

传统混合法在计算目标与粗糙面的耦合场时,需要耗费大量内存与时间。以计算复合目标后向电磁散射为目的,提出一种更为高效的混合计算方法。该混合法在单独处理粗糙面与目标方面与传统混合法一致,即使用基尔霍夫近似法（Kirchhoff approach,KA）处理粗糙面区域;使用矩量法（method of moment, MoM）并结合多层快速多极子（multilevel fast multipole algorithm, MLFMA）技术处理目标区域。与传统混合法所不同的是：根据大尺度粗糙面镜向散射最强的特点,只在粗糙面上截取一块很小的区域进行耦合场计算,从而极大减少内存与时间。大量数值实验表明,该方法在保证较高精度的同时,效率要远高于传统混合法。     

电特大目标散射的多层快速多极子高性能计算

针对电特大目标散射的并行多层快速多极子计算中出现的构造几何信息树所需资源过多、保存远场模式所需内存过大及计算雷达散射截面时间长等问题,根据主流并行计算机架构以及电特大目标的特点,提出了解决方案,实现了电特大目标散射的高效精确计算。通过对未知数超过5亿、电尺寸达到几千个波长的电特大目标的数值实验,表明本文方案的精确性和高效性。     

多层快速多极子法的内存占用与控制分析

从多层快速多极子算法的内存组成出发,建立了内存与未知数之间的关系,首次提出了网格划分尺寸与入射波长之比和多极子模式数对内存的影响。入射频率不变而网格划分尺寸减小时,聚合配置量内存与总未知数成正比,稀疏矩阵内存与相关未知数数目成平方关系,总内存迅速增加。网格不变而频率降低时,若分层数相同,稀疏矩阵内存不变,聚合配置量内存随频率降低而减小;若分层数降低,稀疏矩阵内存平方递增;若频率成偶数倍关系,聚合配置量占用内存不变,总内存振荡增加。改进模式数的精度控制后,提高了精度,但聚合配置量内存相应增加,总内存随之增加。     

Fast 3D EM scattering and radiation solvers based on MLFMA

As the fastest integral equation solver to date, the multilevel fast multipole algorithm （MLFMA） has been applied successfully to solve electromagnetic scattering and radiation from 3D electrically large objects. But for very large-scale problems, the storage and CPU time required in MLFMA are still expensive. Fast 3D electromagnetic scattering and radiation solvers are introduced based on MLFMA. A brief review of MLFMA is first given. Then, four fast methods including higher-order MLFMA （HO-MLFMA）, fast far field approximation combined with adaptive ray propagation MLFMA （FAFFA-ARP-MLFMA）, local MLFMA and parallel MLFMA are introduced. Some typical numerical results demonstrate the efficiency of these fast methods.     

三维局部多层快速多极子算法

为了进一步加速多层快速多极子算法求解电大尺寸目标电磁散射,提出了一种基于局部耦合技术计算矩阵矢量相乘的多层快速多极子方法。通过在迭代过程中设置与迭代误差相关的最初层,每次迭代仅仅需要考虑局部的耦合区域。该方法在保证合理计算精度的同时大大降低了迭代过程中矩阵矢量相乘的计算复杂度,提高了多层快速多极子方法计算效率。数值结果说明了所提方法的有效性。     

多层快速多极子算法中修正多极子模式数技术

为了提高多层快速多极子算法求解电磁散射问题的效率,提出了两种修正多极子模式数的方法。与传统的多层快速多极子相比,该方法通过有效地减少多极子模式数,从而减少了迭代求解矩阵方程时的矩矢相乘时间和内存存储需求。计算结果表明,该方法提高了电磁散射问题求解的计算效率,保留了原有方法的精度,同时保持了多层快速多极子算法的计算复杂度,并且简单易于实现,十分适于三维电大结构电磁散射问题的求解。     

电各向异性介质目标散射分析的快速偶极子法

提出一种求解电场体积分方程的快速算法--快速偶极子法 (fast dipole method, FDM),并用其求解了三维非均匀电各向异性介质目标的电磁散射问题。该方法基于等效偶极矩法 (equivalent dipole-moment method, EDM) 和Schaubert-Wilton-Glisson (SWG)基函数。在EDM中,将SWG基函数的体元对用偶极子等效,加快了阻抗矩阵元素的计算速度,但是并不能降低内存需求和矩阵求解时间。快速偶极子法通过简单的泰勒级数展开将阻抗矩阵元素的计算自然地转化为聚集-转移-发散的过程,有效地缓解了矩阵求解时间和内存消耗的矛盾。数值结果表明该方法的高效性以及令人满意的数值精度。     

快速多极子算法在电流步进法中的应用

基于电流步进法利用双表面磁场积分方程有效计算三维导体电磁散射的优点,提出了一种结合快速多极子和电流补步进法的改进算法。根据电流步进法前向-后向迭代以及使用新值进行计算的高斯-塞得尔迭代的特点,算法将修改后快速多极子算法引入到电流步进法的计算中,加快了原始算法的计算速度。在迭代的过程中,通过快速多极子方法降低了原有的计算量。给出了算法的具体步骤,通过仿真实验证明了算法的有效性。     

复杂目标电磁散射计算软件的改进

在计算复杂目标的电磁散射中 ,图形电磁计算方法 (graphicelectromagneticcomputing,GRECO)可用来实时计算电大尺寸复杂目标的RCS。在考察了原有的GRECO计算内核之后 ,结合计算机图形学方面的理论 ,对GRE CO的内核代码进行了改进 ,从而使得对于目标的棱边判定更加充分、准确。对于PTD绕射系数f和g表达式中的奇异点 ,通过求取平均值的方法给出了准确的结果 ,整体上使得绕射场的计算结果更加准确。     

改进的特征基函数法分析电磁散射问题

目标电磁散射特性分析具有重要意义,矩量法等数值方法是求解该类问题的重要工具。当待分析目标的电尺寸增大时,矩量法的内存需求和计算量随之快速增加,极大地限制了可求解问题的规模。宏基函数类方法通过在宏域上构造各种宏基函数,减少未知量数目,实现最终矩阵方程规模的缩减,使分析大规模问题变为可能。重点研究该类方法中近期获得较大发展的特征基函数法,结合物理光学法和球谐函数展开-多层快速多极子技术分析电磁散射问题。数值结果验证了改进的特征基函数法的准确性与高效性。     

Improvement and performance of parallel multilevel fast multipole algorithm

The method of establishing data structures plays an important role in the efficiency of parallel multilevel fast multipole algorithm(PMLFMA).Considering the main complements of multilevel fast multipole algorithm(MLFMA) memory,a new parallelization strategy and a modified data octree construction scheme are proposed to further reduce communication in order to improve parallel efficiency.For far interaction,a new scheme called dynamic memory allocation is developed.To analyze the workload balancing performance of a parallel implementation,the original concept of workload balancing factor is introduced and verified by numerical examples.Numerical results show that the above measures improve the parallel efficiency and are suitable for the analysis of electrical large-scale scattering objects.     

Efficient analysis of dielectric radomes using multilevel fast multipole algorithm with CRWG basis

A full-wave analysis of the electromagnetic problem of a three-dimensional （3-D） antenna radiating through a 3-D dielectric radome is preserued. The problem is formulated using the Poggio-Miller-Chang-Harrington- Wu（PMCHW） approach for homogeneous dielectric objects and the electric field integral equation for conducting objects. The integral equations are discretized by the method of moment （MoM）, in which the conducting and dielectric surface/interfaces are represented by curvilinear triangular patches and the unknown equivalent electric and magnetic currents are expanded using curvilinear RWG basis functions. The resultant matrix equation is then solved by the multilevel fast multipole algorithm （MLFMA） and fast far-field approximation （FAFFA） is used to further accelerate the computation. The radiation patterns of dipole arrays in the presence of radomes are presented. The numerical results demonstrate the accuracy and versatility of this method.     

Fast and accurate analysis of electromagnetic scattering from targets situated in dielectric half space

Electromagnetic scattering from targets situated in half space is solved by applying fast inhomogeneous plane wave algorithm combined with a tabulation and interpolation method. The integral equation is set up based on derivation of dyadic Green’s functions in this environment. The coupling is divided into nearby region and well-separated region by grouping. The Green’s function can be divided into two parts: primary term and reflected term. In the well-separated region, the two terms are both expressed as ...