To reduce computational costs, an improved form of the frequency domain boundary element method（BEM） is proposed for two-dimensional radiation and propagation acoustic problems in a subsonic uniform flow with arbitr...To reduce computational costs, an improved form of the frequency domain boundary element method（BEM） is proposed for two-dimensional radiation and propagation acoustic problems in a subsonic uniform flow with arbitrary orientation. The boundary integral equation（BIE） representation solves the two-dimensional convected Helmholtz equation（CHE） and its fundamental solution, which must satisfy a new Sommerfeld radiation condition（SRC） in the physical space. In order to facilitate conventional formulations, the variables of the advanced form are expressed only in terms of the acoustic pressure as well as its normal and tangential derivatives, and their multiplication operators are based on the convected Green＇s kernel and its modified derivative. The proposed approach significantly reduces the CPU times of classical computational codes for modeling acoustic domains with arbitrary mean flow. It is validated by a comparison with the analytical solutions for the sound radiation problems of monopole,dipole and quadrupole sources in the presence of a subsonic uniform flow with arbitrary orientation.展开更多
传统聚类算法进行混叠矩阵估计时存在的聚类中心个数不确定和初始聚类中心的随机选取导致陷入局部最优的问题,为此提出一种基于密度峰值的改进模糊聚类算法进行欠定盲源分离的混叠矩阵估计。通过短时傅里叶变换提取信号在频域中的稀疏特...传统聚类算法进行混叠矩阵估计时存在的聚类中心个数不确定和初始聚类中心的随机选取导致陷入局部最优的问题,为此提出一种基于密度峰值的改进模糊聚类算法进行欠定盲源分离的混叠矩阵估计。通过短时傅里叶变换提取信号在频域中的稀疏特性,利用寻找密度峰值聚类算法(clustering by fast search and find of density peaks,CFSFDP)自动获取聚类簇的数目和初始聚类中心;将获得的聚类数目和聚类结果作为模糊聚类算法(fuzzy c-means clustering,FCM)的初始输入参数,提高FCM聚类结果的精度。实验结果表明,该算法可以准确估计源信号的数目,相比传统FCM、层次聚类、基于密度峰值改进的粒子群等聚类算法,可以有效提高欠定盲源分离的混叠矩阵估计精度。展开更多
An adaptive mesh refinement strategy is proposed in this paper for the Immersed Boundary and Immersed Interface methods for two-dimensional elliptic interface problems involving singular sources.The interface is repre...An adaptive mesh refinement strategy is proposed in this paper for the Immersed Boundary and Immersed Interface methods for two-dimensional elliptic interface problems involving singular sources.The interface is represented by the zero level set of a Lipschitz functionϕ(x,y).Our adaptive mesh refinement is done within a small tube of|ϕ(x,y)|δwith finer Cartesian meshes.The discrete linear system of equations is solved by a multigrid solver.The AMR methods could obtain solutions with accuracy that is similar to those on a uniform fine grid by distributing the mesh more economically,therefore,reduce the size of the linear system of the equations.Numerical examples presented show the efficiency of the grid refinement strategy.展开更多
基金supported by National Engineering School of Tunis (No.13039.1)
文摘To reduce computational costs, an improved form of the frequency domain boundary element method（BEM） is proposed for two-dimensional radiation and propagation acoustic problems in a subsonic uniform flow with arbitrary orientation. The boundary integral equation（BIE） representation solves the two-dimensional convected Helmholtz equation（CHE） and its fundamental solution, which must satisfy a new Sommerfeld radiation condition（SRC） in the physical space. In order to facilitate conventional formulations, the variables of the advanced form are expressed only in terms of the acoustic pressure as well as its normal and tangential derivatives, and their multiplication operators are based on the convected Green＇s kernel and its modified derivative. The proposed approach significantly reduces the CPU times of classical computational codes for modeling acoustic domains with arbitrary mean flow. It is validated by a comparison with the analytical solutions for the sound radiation problems of monopole,dipole and quadrupole sources in the presence of a subsonic uniform flow with arbitrary orientation.
基金国家自然科学基金(the National Natural Science Foundation of China under Grant No.60674003No.60505005)+4 种基金国家杰出青年基金(the National Science Fund of China for Distinguished Young Scholar under Grant No.60325310)广东省自然科学团队研究项目(No.04205783)广东省自然科学基金(the Natural Science Foundation of Guangdong Province of China under Grant No.05006508 No.05103553)科技部重大基础前期研究专项(No.2005CCA04100)。
文摘传统聚类算法进行混叠矩阵估计时存在的聚类中心个数不确定和初始聚类中心的随机选取导致陷入局部最优的问题,为此提出一种基于密度峰值的改进模糊聚类算法进行欠定盲源分离的混叠矩阵估计。通过短时傅里叶变换提取信号在频域中的稀疏特性,利用寻找密度峰值聚类算法(clustering by fast search and find of density peaks,CFSFDP)自动获取聚类簇的数目和初始聚类中心;将获得的聚类数目和聚类结果作为模糊聚类算法(fuzzy c-means clustering,FCM)的初始输入参数,提高FCM聚类结果的精度。实验结果表明,该算法可以准确估计源信号的数目,相比传统FCM、层次聚类、基于密度峰值改进的粒子群等聚类算法,可以有效提高欠定盲源分离的混叠矩阵估计精度。
文摘An adaptive mesh refinement strategy is proposed in this paper for the Immersed Boundary and Immersed Interface methods for two-dimensional elliptic interface problems involving singular sources.The interface is represented by the zero level set of a Lipschitz functionϕ(x,y).Our adaptive mesh refinement is done within a small tube of|ϕ(x,y)|δwith finer Cartesian meshes.The discrete linear system of equations is solved by a multigrid solver.The AMR methods could obtain solutions with accuracy that is similar to those on a uniform fine grid by distributing the mesh more economically,therefore,reduce the size of the linear system of the equations.Numerical examples presented show the efficiency of the grid refinement strategy.
