Free convection of nanofluid filled enclosure using lattice Boltzmann method （LBM）

The lattice Boltzmann method (LBM) is used to examine free convection of nanofluids. The space between the cold outer square and heated inner circular cylinders is filled with water including various kinds of nanoparticles: TiO₂, Ag, Cu, and Al₂O₃. The Brinkman and Maxwell-Garnetts models are used to simulate the viscosity and the effective thermal conductivity of nanofluids, respectively. Results from the performed numerical analysis show good agreement with those obtained from other numerical methods. A variety of the Rayleigh number, the nanoparticle volume fraction, and the aspect ratio are examined. According to the results, choosing copper as the nanoparticle leads to obtaining the highest enhancement for this problem. The results also indicate that the maximum value of enhancement occurs at λ = 2.5 when Ra = 10⁶ while at λ = 1.5 for other Rayleigh numbers.     

ANALYTICAL SOLUTION OF THE FREE VIBRATION OF VISCOELASTIC SANDWICH ANNULAR PLATE

基于薄板小挠度理论和Kelvin-Voigt 黏弹性本构方程,建立了黏弹性夹层环形薄板振动控制方程.采用分离变量法计算了内边固支、外边自由黏弹性夹层环形薄板的固有频率和振型,并与有限元计算结果进行比较. 分别讨论了夹心层比和内外半径比对固有频率及衰减系数的影响. 研究表明:系统频率随夹心层厚度增大,先增大后减小,而衰减系数一直增大;系统频率和衰减系数随内外半径比增大而增大.     

Thermal analysis of annular fins with temperature-dependent thermal properties

The thermal analysis of the annular rectangular profile fins with variable thermal properties is investigated by using the homotopy analysis method （HAM）. The thermal conductivity and heat transfer coefficient are assumed to vary with a linear and power-law function of temperature, respectively. The effects of the thermal-geometric fin parameter and the thermal conductivity parameter variations on the temperature distribution and fin efficiency are investigated for different heat transfer modes. Results from the HAM are compared with numerical results of the finite difference method （FDM）. It can be seen that the variation of dimensionless parameters has a significant effect on the temperature distribution and fin efficiency.     

变角度纤维复合材料环扇形层合板的自由振动分析

与传统的直线纤维增强复合材料相比,变角度纤维复合材料具有更强的可设计性,为改善结构性能提供了更大的可能．鉴于此,本文将研究纤维的变角度铺设对复合材料环扇形层合板的自振频率及振动模态的影响．假设纤维的方向角沿环扇形板的径向线性变化,基于经典的层合板理论,采用微分求积法获得了环扇形层合板自由振动问题的数值解．通过与现有文献及ABAQUS有限元结果的比较验证了本文模型及方法的正确性和收敛性,并详细分析了纤维起始角和终止角的变化对层合板的自振频率及振动模态的影响．研究结果表明：与常刚度层合板相比,变角度纤维复合材料层合板的基频具有更大的调整空间,通过合理选择纤维起始角和终止角可有效提高层合板的基频．研究结果可为该种新型复合材料结构的优化设计提供一定的参考．     

基于球面透视投影约束的全景环形透镜畸变校正

全景环形透镜将折反射面集成到一起,能无扫描地瞬时得到围绕光轴的360度超大视场,在机器人导航、视频监控和虚拟现实领域得到了广泛的应用.其成像机理是将围绕光轴的视场二次反射投影到环形平面上,图像存在严重的切向和径向畸变.本文根据全景环形透镜的特点采用基于球面透视投影模型对图像进行校正.首先建立含有畸变参量的全景环形透镜校正模型,将空间直线点映射为球面点,然后使用遗传算法将球面点拟合为球面上的最佳大圆,求出变形校正参量,进而校正全景环形像.仿真和真实图像实验表明,环形图像的切向和径向畸变得到了很好的校正.     

高负荷压气机叶栅分离与流场结构研究

通过流动显示及静压测量,对不同冲角下、三种叶型弯角的环形压气机直、弯叶栅近壁面区域的流动分离及旋涡结构进行了实验研究.结果表明,近吸力面的气泡分离与转捩取决于叶栅型面静压分布;随叶栅负荷增大,流动分离形式由闭式分离逐渐向开式分离发展,流动分离的对称性逐渐减弱;减少涡系与涡系、涡系与附面层之间的相互作用及掺混可以有效拓宽正弯叶片的应用范围.     

Displacement fields around Guinier–Preston 1 zones in Al–Cu alloys: investigations using MD and ADF-STEM image simulations

The displacements of atoms around Guinier–Preston 1 (GP1) zones in Al–Cu alloys at a temperature of 295?K have been investigated using molecular dynamics (MD) simulations. The magnitude of the displacements at the first Al layer adjacent to a GP1 zone reached 24% strain and this value decreased with distance from the zone to zero at about 40th Al layer. Strain fields near a GP1 zone were evaluated by calculating strain tensors around individual atoms. The obtained strain maps suggested that the equilibrium Cu content in a GP1 zone should be 100%. The atomic configurations determined by MD simulations were utilised for multislice image simulations of annular dark-field scanning transmission electron microscopy (ADF-STEM) to investigate the effect of foil thickness and the depth position of a GP1 zone in a foil on ADF-STEM images. The atomic displacements in ADF-STEM images were smaller than the MD result due to foil thickness and electron channelling.     

粘弹性夹芯层合旋转圆板的气动弹性动力稳定性分析

基于哈密尔顿原理,考虑作用于圆板上的空气动力载荷以及粘弹性复模量本构模型,本文建立了含有粘弹性夹芯层的旋转圆板的空气动力学模型,并给出了相应的稳定性的控制方程及边界条件。运用Galerkin方法,文中数值求解并给出了夹芯层合旋转圆板的动力学基本特征,以及结构几何参数、材料参数对于其前、后行波振动频率、阻尼和动力稳定性的影响。结果表明：通过优化合理选取粘弹性夹芯层合旋转圆板的几何参数和材料参数,可提高旋转圆板的临界转速和颤振速度,从而增强其稳定性。     

Laboratory investigation of annular denuders as sampling system for the determination of aliphatic primary and secondary amines in stack gas

A method for the sampling and analysis of aliphatic amines ranging from C₁ to C₅ and some diamines in exhaust gas is described. Two different annular denuder systems coated with phosphoric acid were used for the laboratory investigation of sampling gaseous amines. The denuder sampling systems were tested under different conditions for their readiness to work in stack gas.The reagent 2,4-dinitrofluorobenzene (DNFB) was used in pre-column derivatization of the amines investigated. The amino derivatives were separated using high performance liquid chromatography (HPLC) in conjunction with UV-detection. This method has been used for the examination of emissions from a landfill waste disposal and from animal husbandry with respect to traces of aliphatic amine emissions.     

EXISTENCE OF POSITIVE RADIAL SOLUTIONS FOR SOME QUASILINEAR ELLIPTIC EQUATIONSIN ANNULAR OMAINS

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