Reduction in drag and vortex shedding frequency through porous sheath around a circular cylinder

A numerical study on the laminar vortex shedding and wake flow due to a porous‐wrapped solid circular cylinder has been made in this paper. The cylinder is horizontally placed, and is subjected to a uniform cross flow. The aim is to control the vortex shedding and drag force through a thin porous wrapper around a solid cylinder. The flow field is investigated for a wide range of Reynolds number in the laminar regime. The flow in the porous zone is governed by the Darcy–Brinkman–Forchheimer extended model and the Navier–Stokes equations in the fluid region. A control volume approach is adopted for computation of the governing equations along with a second‐order upwind scheme, which is used to discretize the convective terms inside the fluid region. The inclusion of a thin porous wrapper produces a significant reduction in drag and damps the oscillation compared with a solid cylinder. Dependence of Strouhal number and drag coefficient on porous layer thickness at different Reynolds number is analyzed. The dependence of Strouhal number and drag on the permeability of the medium is also examined. Copyright © 2009 John Wiley & Sons, Ltd.     

Accurate quantum-chemical description of gold complexes with pyridine and its derivatives

Interaction of gold with pyridine and its derivatives was studied by means of different wavefunction-based correlation methods and standar DFT functionals as well as accounting for dispersion correction. Comparison of the calculated binding energies with benchmark CCSD(T)results allows us to find an appropriate computational method, when considering the two structures reflecting the interaction of gold with the lone pair at nitrogen, on the one hand, and with the π-system of pyridine, on the other hand. Additional binding sites were evaluated, when performing potential energy surface calculations and structure optimizations. The enhancement of the interaction energy due to donor substituents in the 4-position of the pyridine molecule has been investigated.     

近红外光谱测定人参与西洋参的主要皂甙总量

采用近红外光谱测定人参与西洋参的主要皂甙总量.采集人参与西洋参的漫反射光谱,分别对光谱进行正交信号校正(OSC)与常规预处理,建立了对应的偏最小二乘(PLS)回归模型.与常规最优预处理方法相比,OSC能很好地消除人参与西洋参的品种差异,显著提高了光谱与皂甙含量的相关系数,同时降低了PLS建模因子数,提高了模型的稳健性与...     

Improved Riemann solvers for complex transport in two-dimensional unsteady shallow flow

The numerical solution of advection–reaction–diffusion transport problems in two-dimensional shallow water flow is split in three subproblems in order to analyze them separately.     

Effects on spectroscopic parameters of several low-lying electronic states of GeS by core-valence correlation and relativistic corrections

The potential energy curves (PECs) of six low-lying electronic states (X¹Σ⁺, a³Σ⁺, b³Π, A¹Π, 1³Σ⁻ and 1⁵Σ⁺) of GeS molecule have been investigated employing the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach with large correlation-consistent basis sets for internuclear separations from 0.08 to 2.00 nm. The effects on the spectroscopic parameters by the core-valence correlation, relativistic and nonadiabatic corrections have been discussed in detail. The core-valence correlation correction is carried out at the aug-cc-pCVTZ basis set. The nonadiabatic correction is performed at the aug-cc-pVTZ basis set. And the relativistic correction is made at the level of cc-pV5Z basis set. The way to consider the relativistic correction is to employ the second-order Douglas-Kroll Hamiltonian (DKH2) approximation. To obtain more reliable PECs, the Davidson modification is also included in the present study. To reduce the incomplete basis set error, the PECs of these electronic states are extrapolated to the complete basis set (CBS) limit. With these PECs, the spectroscopic parameters of these low-lying electronic states are determined. On the one hand, analyses demonstrate that the effects on the spectroscopic parameters by the core-valence correlation correction, relativistic correction and Davidson modification are very obvious, whereas the effect on the spectroscopic parameters by the nonadiabatic correction is very small. On the other hand, comparison with the RKR data shows that the two-point total-energy extrapolation could improve the quality of spectroscopic parameters. On the whole, as expected, the most accurate spectroscopic parameters of GeS molecule are determined by the MRCI+Q/CV+DK+Q5 calculations.     

Boosting the accuracy of finite difference schemes via optimal time step selection and non-iterative defect correction

In this article, we present a unified analysis of the simple technique for boosting the order of accuracy of finite difference schemes for time dependent partial differential equations (PDEs) by optimally selecting the time step used to advance the numerical solution and adding defect correction terms in a non-iterative manner. The power of the technique, which is applicable to time dependent, semilinear, scalar PDEs where the leading-order spatial derivative has a constant coefficient, is its ability to increase the accuracy of formally low-order finite difference schemes without major modification to the basic numerical algorithm. Through straightforward numerical analysis arguments, we explain the origin of the boost in accuracy and estimate the computational cost of the resulting numerical method. We demonstrate the utility of optimal time step (OTS) selection combined with non-iterative defect correction (NIDC) on several different types of finite difference schemes for a wide array of classical linear and semilinear PDEs in one and more space dimensions on both regular and irregular domains.     

非自共轭椭圆特征值问题有限元插值校正

本文研究非自共轭椭圆特征值问题有限元插值校正方案.基于插值校正和广义Rayleigh商加速技巧,用三角形线性元二次插值、双二次元双四次插值得到了较好的结果,并用三线性元的三二次捕值将捅值校正推广到三维.     

Precision verification of a simplified three-dimensional DIC method

The traditional three-dimensional (3D) digital image measurement technique uses at least two images captured from different positions to determine the 3D coordinate of an object. One disadvantage of this method is that the mechanical and optical properties of the image capture devices are not fully identical, and the calibration procedure is quite complicated. This paper introduces a simplified 3D digital image correlation (DIC) method, in which only one image capture device is used. The theoretical measurement error equation is derived and experimentally verified. Experimental results show that distortion correction plays an important role in the improvement of measurement precision. After a radial distortion correction, the measurement precision of the object distance can reach 0.0043%. The optimal camera spacing should be set from 1/50 to 1/30 of the object distance, to obtain a satisfactory precision.     

120～180nm星载远紫外电离层成像光谱仪光学系统设计与研究

针对目前国内对星载电离层成像光谱仪研究,设计了一种适用于120～180 nm远紫外探测的光学系统,并开展了原理样机的研制工作.对比国外各种方案,分析其优劣性后提出了以离轴抛物镜为物镜,Czerny-Turner结构为成像光谱系统的方案.为解决传统Czerny-Turner结构像差校正不均匀、空间分辨率低等缺点,进行了像...     

求解对流扩散方程的紧致修正方法

提出了求解对流扩散方程的紧致修正方法,该方法是在低阶离散格式的源项中,引入紧致修正项,从而构造高阶紧致修正格式,并进行求解.采用紧致修正方法对典型的对流扩散方程进行计算.结果表明,紧致修正方法虽然与二阶经典差分方法建立在相同的结点数上,但紧致修正方法的精度与紧致方法的精度相同,均具有四阶精度.所以紧致修正方法可以在少网...