A large eddy lattice Boltzmann simulation of magnetohydrodynamic turbulence

Large eddy simulations (LES) of a lattice Boltzmann magnetohydrodynamic (LB-MHD) model are performed for the unstable magnetized Kelvin–Helmholtz jet instability. This algorithm is an extension of Ansumali et al. [1] to MHD in which one performs first an expansion in the filter width on the kinetic equations followed by the usual low Knudsen number expansion. These two perturbation operations do not commute. Closure is achieved by invoking the physical constraint that subgrid effects occur at transport time scales. The simulations are in very good agreement with direct numerical simulations.     

Morphisms Cohomology and Deformations of Hom-algebras

The purpose of this paper is to define cohomology complexes and study deformation theory of Hom-associative algebra morphisms and Hom-Lie algebra morphisms. We discuss infinitesimal deformations, equivalent deformations and obstructions. Moreover, we provide various examples.     

利用霍尔效应测磁场实验的数据处理

推导了亥姆霍兹线圈产生磁场的全空间分布的普遍公式,讨论了如何确定磁感应强度的方向。就实验内容进行了实例分析,利用Matlab软件进行了相关计算,提出了利用霍尔效应测磁场实验的数据处理方法。最后,详细讨论了亥姆霍兹线圈所在平面处磁场强度相关参数的分布曲线。     

有满单分解态射的加权Moore-Penrose逆

研究了范畴C中有满单分解态射ψ关于态射h,k的加权Moore-Penrose逆ψ hk的存在性问题,给出了ψ hk存在的几个充分必要条件,推广了态射的Moore-Penrose逆的相应结果.其次,讨论了态射乘积的加权Moore-Penrose逆,得到了乘积公式成立的一个充要务件.     

关于一般范畴中态射的加权Moore-Penrose逆

讨论了带有对合＊的一般范畴C中态射的加权Moore-Penrose逆,给出了加权Moore-Penrose逆存在的几个充要条件以及若干性质.     

A METHOD FOR SOLVING THE INVERSE SCATTERING PROBLEM FOR SHAPE AND IMPEDANCE

The inverse problem considered in this paper is to determine the shape and the impedance of an obstacle from a knowledge of the time-harmonic incident field and the phase and amplitude of the far field pattern of the scattered wave in two-dimension. Single-layer potential is used to approach the scattered waves. An approximation method is presented and the convergence of the proposed method is established. Numerical examples are given to show that this method is both accurate and easy to use.     

一种求解三维声腔声压分布问题的无网格法

利用传统有限元法求解声压分布问题常常受到污染误差和色散误差的困扰.加权最小二乘无网格法(MWLS)是一种基于移动最小二乘(MLS)近似的无网格方法,求解声腔声压分布问题具有低色散、高精度的特点.然而传统的MLS近似有时容易产生病态矩阵,利用加权正交基函数构建改进的移动最小二乘(IMLS)近似,得到的系统方程为非病态的.论文基于改进的加权最小二乘无网格法(IMWLS)求解三维声腔内部声压分布.计算得到的声压分布和声压频响曲线都与参考值十分吻合,峰值误差和污染误差都比FEM的小,计算成本相比无单元伽辽金法显著降低.计算结果表明IMWLS相比传统的FEM,能在更高的频段内达到高精度,并且相比EFGM能大幅提高计算效率.     

关于态射集中的Γ-逆与星序

研究态射集中的Г-逆的存在条件与星序的刻划．利用Г-环的方法得到了Г—Moore-Penrose逆存在的一些条件．给出了Г—Moore-Penrose逆与星序的联系以及星序的一些Г-逆刻划．     

Intuitive understandings of negative bulk modulus of metamaterials composed of Helmholtz resonators

We present theoretical and experimental results to obtain an intuitive understanding of bulk modulus of metamaterials composed of Helmholtz resonators (HR). Using transmission line theory, we introduce an intuitive method to determine the frequency domain in which the negative bulk modulus appears. The results obtained by simulations and experiments are consistent with theoretical results found using transmission line theory. The results suggest that wider negative (BNG) areas of bulk modulus can be obtained using two HRs than one HR of the same total cavity volume.     

Second-order efficient nonlinear filter stabilization for high Reynolds number flows

In this article, we develop a second-order nonlinear filter based stabilization scheme for high Reynolds number flows. We prove the unconditional stability of the method, establish the second order consistency and discuss the dynamical tuning of the relaxation parameter. The scheme is then validated against experimental data for an isothermal turbulent flow in a Staggered Tube Bundle at Reynolds number of 18,000. Numerical results are found to be in an overall good qualitative and quantitative agreement with the benchmark results.