共查询到19条相似文献,搜索用时 156 毫秒
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为了克服传统的基于合成孔径雷达(SAR)图像局部统计特性的降斑算法的缺点,提出了基于区域分类、自适应滑动窗和结构检测的联合降斑算法.首先,联合降斑算法对当前区域进行区域分类,并直接保留强边缘结构和点目标.接着,联合降斑算法对均匀区域和弱边缘结构区域进行滑动窗的自适应增长,从而获得合适的滤波窗口.最后,联合降斑算法对新的滤波窗口使用区域分类.如果滤波窗口属于均匀区域,则直接使用均值滤波;如果滤波窗口属于边缘结构区域,则进一步使用结构检测,并且选择窗口内的均匀子区域作为最终的滤波区域.降斑实验表明,联合降斑算
关键词:
区域分类
自适应滑动窗
结构检测
联合降斑算法 相似文献
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基于几何型扩展有限元离散方法,研究含静态裂缝线弹性问题的高效区域分解预条件算法。为了构造Schwarz型预条件算法,采用一种特殊的裂尖型区域分解策略,将计算区域分解为包含所有分支增强自由度的裂尖子区域和仅包含标准有限元自由度与Heaviside增强自由度的常规子区域。基于该区域分解策略,推导一类高效的乘性和限制型乘性Schwarz区域分解预条件子,对裂尖子问题进行精确求解,而对常规子问题则非精确求解。数值实验验证了算法的有效性。 相似文献
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对有限区域进行旋转风和辐散风的分解,是中尺度系统结构分析的一种诊断方法,可提高对中尺度系统动力结构的认识. 一方面,有限区域风场的分解可以给出总风场中无辐散风与无旋转风的不同分布,还可根据这两种风场的分布特征进行不同要求的分析;另一方面,由于耦合边界条件不能直接计算,计算过程中必须简化处理,使有限区域风场分解本身还有许多问题没有很好解决. 目前,对风场进行有效分解的方法是对有限区域里的流函数和速度势进行求解,然后对流函数和速度势求导得到对应的无辐散风与无旋转风. 有限区域流函数和速度势求解的准确程度主要以分解后的风场能否还原到原始风场(即风场重建)为标准. 本文总结了有限区域风场分解和重建的方法,重点介绍了调和正弦/余弦方法,该方法可较准确有效地解决有限区域风场的分解和重建问题,对进一步研究天气系统的动力结构有较好效果. 相似文献
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对有限区域进行旋转风和辐散风的分解,是中尺度系统结构分析的一种诊断方法,可提高对中尺度系统动力结构的认识. 一方面,有限区域风场的分解可以给出总风场中无辐散风与无旋转风的不同分布,还可根据这两种风场的分布特征进行不同要求的分析;另一方面,由于耦合边界条件不能直接计算,计算过程中必须简化处理,使有限区域风场分解本身还有许多问题没有很好解决. 目前,对风场进行有效分解的方法是对有限区域里的流函数和速度势进行求解,然后对流函数和速度势求导得到对应的无辐散风与无旋转风. 有限区域流函数和速度势求解的准确程度主要以分解后的风场能否还原到原始风场(即风场重建)为标准. 本文总结了有限区域风场分解和重建的方法,重点介绍了调和正弦/余弦方法,该方法可较准确有效地解决有限区域风场的分解和重建问题,对进一步研究天气系统的动力结构有较好效果.
关键词:
有限区域
风场分解和重建
调和正弦/余弦方法
流函数和速度势 相似文献
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非结构网格的并行生成 总被引:1,自引:0,他引:1
研究了非结构网格的并行生成方法.改进了R.Lohner的"波阵面"区域分裂算法以使子网格及其边界更有益于网格并行生成,提出了边界并行优化策略,改善了边界的光滑性;完善了子区域内生成网格时接受新点及新单元的条件,在界面网格生成过程中提出只接受新单元而拒绝新点的策略,节省了机时. 相似文献
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提出了一维广义Fibonacci准周期结构的声子晶体模型. 对弹性波通过该一维准周期结构声子晶体的透射系数进行数值计算,并与周期结构和标准Fibonacci准周期结构声子晶体的透射系数进行比较. 结果表明,利用一维广义Fibonacci准周期结构的声子晶体可获得比周期结构和标准Fibonacci准周期结构声子晶体更大的带隙范围,同时在带隙内有更丰富的局域模式存在. 对局域模性质的研究有助于声波或弹性波滤波器的制作.
关键词:
广义Fibonacci准周期结构
声子晶体
局域化 相似文献
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从梁的弯曲振动方程出发,利用传递矩阵法,给出了无限周期结构的一维多振子声子晶体梁的弯曲振动能带结构,并利用有限元方法计算了有限周期结构梁的弯曲振动频率响应.建立了多振子声子晶体梁的简化模型,推导出带隙起始截止频率公式.结果表明:一维多振子声子晶体梁具有比单振子声子晶体梁更宽更丰富的振动带隙,可应用于呈倍频关系的减振降噪中;振动在带隙频率范围内频率响应具有明显的衰减;所建立的简化模型与理论模型结果符合较好.研究工作为梁类结构的减振提供一种新的思路. 相似文献
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在采用无网格方法进行数值计算时,常常涉及到结点搜索问题.在处理复杂区域问题时,求解区域中分布的结点数量非常大.如果用传统的全局结点搜索算法时计算量将十分巨大,因此,提出了求解域分解法以减小结点搜索的计算量.采用该方法时,结点搜索的范围就可以由整个求解域缩减到几个相关的子域中,从而大大地减少了无网格方法计算中的结点搜索时间.用该方法对理想流体的位势流动进行了数值模拟,发现:随结点数的增加,无网格方法所用时间与有限元方法相比越来越大;但与全局结点搜索无网格方法相比,本方法大大节省了计算时间. 相似文献
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Bruno Stupfel 《Journal of computational physics》2010,229(3):851-874
The scattering problem of a time-harmonic electromagnetic wave from a perfect electric conductor (PEC) coated with materials is considered, and solved by coupling a finite element method with an integral equation prescribed on the outer boundary of the computational domain. To reduce the numerical complexity, a one-dimensional domain decomposition method (DDM) is employed: the computational domain is partitioned into concentric subdomains (SDs), and Robin transmission conditions (TCs) are prescribed on the interfaces. For some configurations and/or materials, the convergence of the corresponding DDM algorithm happens to be slow. A possible remedy is to enhance the efficiency of the TCs by approximating the exact ones more accurately. To this end, we first consider the simplified 2D problem of a circular PEC cylinder with an homogeneous coating and up to four SDs with circular interfaces, thus allowing to obtain the exact TCs in closed-form. Approximate local or non-local TCs are derived from these exact ones, and numerical examples demonstrate their superiority over the standard Robin TCs. Then, the case of an elliptical PEC cylinder with one interface in free-space is investigated. Also, the issues pertaining to the uniqueness of the solutions and convergence of the algorithm are addressed. 相似文献
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采用间断有限元法(discontinuous finite element method,DFEM)求解非规则形状介质内的辐射导热耦合传热问题,得到了典型非规则形状介质内辐射导热耦合传热问题的高精度数值结果.和传统连续型有限元方法不同,DFEM将计算区域划分成相互独立的离散单元,形函数的构造、未知量的加权近似以及控制方程的求解均在每一个离散单元上进行.通过在单元之间施加迎风格式的数值通量,DFEM保证了整个计算区域的连续性,因此这种方法兼具良好的几何灵活性和局部守恒性.推导了辐射传输方程和能量扩散方程的射导热耦合传热问题,得到了典型非规则形状介质内辐射导热耦合传热的高精度数值结果. 相似文献
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M. Barrault B. Lathuilière P. Ramet J. Roman 《Journal of computational physics》2011,230(5):2004-2020
A reactivity computation consists of computing the highest eigenvalue of a generalized eigenvalue problem, for which an inverse power algorithm is commonly used. Very fine modelizations are difficult to treat for our sequential solver, based on the simplified transport equations, in terms of memory consumption and computational time.A first implementation of a Lagrangian based domain decomposition method brings to a poor parallel efficiency because of an increase in the power iterations [1]. In order to obtain a high parallel efficiency, we improve the parallelization scheme by changing the location of the loop over the subdomains in the overall algorithm and by benefiting from the characteristics of the Raviart–Thomas finite element. The new parallel algorithm still allows us to locally adapt the numerical scheme (mesh, finite element order). However, it can be significantly optimized for the matching grid case. The good behavior of the new parallelization scheme is demonstrated for the matching grid case on several hundreds of nodes for computations based on a pin-by-pin discretization. 相似文献
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Some theoretical aspects of elastic wave modeling with a recently developed spectral element method 总被引:1,自引:0,他引:1
SERIANI Geza 《中国科学G辑(英文版)》2007,50(2):185-207
A spectral element method has been recently developed for solving elastodynamic problems. The numerical solutions are obtained by using the weak formulation of the elastodynamic equation for heterogeneous media, based on the Galerkin approach applied to a partition, in small subdomains, of the original physical domain. In this work, some mathematical aspects of the method and the associated algorithm implementation are systematically investigated. Two kinds of orthogonal basis functions, constructed with Legendre and Chebyshev polynomials, and their related Gauss-Lobatto collocation points are introduced. The related integration formulas are obtained. The standard error estimations and expansion convergence are discussed. An element-by-element pre-conditioned conjugate gradient linear solver in the space domain and a staggered predictor/multi-corrector algorithm in the time integration are used for strong heterogeneous elastic media. As a consequence, neither the global matrices nor the effective force vector is assembled. When analytical formulas are used for the element quadrature, there is even no need for forming element matrix in order to further save memory without losing much in computational efficiency. The element-by-element algorithm uses an optimal tensor product scheme which makes this method much more efficient than finite-element methods from the point of view of both memory storage and computational time requirements. This work is divided into two parts. The first part mainly focuses on theoretical studies with a simple numerical result for the Che-byshev spectral element, and the second part, mainly with the Legendre spectral element, will give the algorithm implementation, numerical accuracy and efficiency analyses, and then the detailed modeling example comparisons of the proposed spectral element method with a pseudo-spectral method, which will be seen in another work by Lin, Wang and Zhang. 相似文献
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In this paper, we introduce a parallelized version of a novel, non-iterative domain decomposition algorithm, called Characteristic Basis Finite Element Method (CBFEM-MPI), for efficient solution of large-scale electromagnetic scattering problems, by utilizing a set of specially defined characteristic basis functions (CBFs). This approach is based on the decomposition of the computational domain into a number of non-overlapping subdomains wherein the CBFs are generated by employing a novel procedure, which differs from all those that have been used in the past. Clearly, the CBFs are obtained by calculating the fields radiated by a finite number of dipole-type sources, which are placed hypothetically along the boundary of the conducting object. The major advantages of the proposed technique are twofold: (i) it provides a substantial reduction in the matrix size, and thus, makes use of direct solvers efficiently and (ii) it enables the utilization of parallel processing techniques that considerably decrease the overall computation time. We illustrate the application of the proposed approach via several 3D electromagnetic scattering problems. 相似文献
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A highly efficient numerical algorithm using the multigrid method (MGM) is introduced to solve a three-dimensional (3-D)field distribution. Taking advantage of the restriction and prolongation in MGM computation, a more accurate field distribution can be acquired rapidly. According to the MGM algorithm, a 3-D program is accomplished, which can solve the field distributions in electron optical systems for various electrostatic lenses. The 3-D field distribution in an electrostatic concentric spherical model is tested with the MGM algorithm and with an algorithm based on the finite difference method (FDM). Comparing these two results in terms of computational efficiency and computational accuracy, it appears that MGM is superior to FDM, which is now used the most in field computations. This paper shows that the 3-D field computation using MGM greatly improves the computational efficiency of field distributions in electron optical systems and shortens the computational time. 相似文献
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三维粗糙面电磁双站散射的直接型区域分解计算 总被引:3,自引:0,他引:3
提出三维粗糙面双站电磁散射的直接型有限元-区域分解方法.首先建立含有迭代Robin边界条件(IRBC)的区域分解法耦合模型,再用内视法导出高度稀疏分块的分区耦合矩阵,之后给出缩减耦合矩阵带宽的子区域排序方法和IRBC的FFT加速算法.用有限元-完全匹配层和未分区的有限元-IRBC方法验证数值结果. 相似文献
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A Fast High Order Iterative Solver for the Electromagnetic Scattering by Open Cavities Filled with the Inhomogeneous Media
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Meiling Zhao 《advances in applied mathematics and mechanics.》2013,5(2):235-257
The scattering of the open cavity filled with the inhomogeneous
media is studied. The problem is discretized with a fourth order
finite difference scheme and the immersed interface method,
resulting in a linear system of equations with the high order
accurate solutions in the whole computational domain. To solve the
system of equations, we design an efficient iterative solver, which
is based on the fast Fourier transformation, and provides an ideal
preconditioner for Krylov subspace method. Numerical experiments
demonstrate the capability of the proposed fast high order iterative
solver. 相似文献