四元数分析中正则函数与非齐次n阶方程(■~n F)/(■z~n)=f的某些边值问题

主要讨论了四元数空间中正则函数与非齐次n阶方程(■~n F)/(■z~n)=f在超球上的Dirichlet问题和双圆柱上具有任意整数指标的Riemann-Hilbert问题,给出了可解条件和解的积分表示式.     

Vibration characteristics of FGM circular cylindrical shells filled with fluid using wave propagation approach

The vibration characteristics of a functionally graded material circular cylindrical shell filled with fluid are examined with a wave propagation approach. The shell is filled with an incompressible non-viscous fluid. Axial modal dependence is approximated by exponential functions. A theoretical study of shell vibration frequencies is analyzed for simply supported-simply supported, clamped-simply supported, and clamped-clamped boundary conditions with the fluid effect. The validity and the accuracy of the present method are confirmed by comparing the present results with those available in the literature. Good agreement is observed between the two sets of results.     

Generalized elastic curves in the Lorentz flat space <Emphasis Type="Italic">L</Emphasis><Superscript>4</Superscript>

In this paper, we study the extremals of the curvature energy actions on non-null curves in the four-dimensional Lorentz-Minkowski space. We derive the motion equations and find three Killing fields along the generalized elastic curves. We also construct a cylindrical coordinate system using these Killing fields and express the generalized elastic curves by means of quadratures.     

壳体翻滚失准角模型最小二乘辨识方法

为了提高空间稳定惯性导航系统的姿态角测量精度,建立了壳体翻滚失准角模型,给出了从壳体翻滚失准角幅值和初始相位到当地水平坐标系下的姿态转换矩阵的传递规律.利用静态下平台运动学方程中壳体翻滚失准角与框架角的定量关系,进行了壳体翻滚失准角模型最小二乘辨识方法仿真,结果表明模型系数估计精度是足够的.针对实验系统,经过模型补偿,姿态角计算误差峰峰值小于0.5′.     

Vibrations of FGM thin cylindrical shells with exponential volume fraction law

In this paper, the influence of an exponential volume fraction law on the vibration frequencies of thin functionally graded cylindrical shells is studied. Material properties in the shell thickness direction are graded in accordance with the exponential law. Expressions for the strain-displacement and curvature-displacement relationships are taken from Love＇s thin shell theory. The Rayleigh-Ritz approach is used to derive the shell eigenfrequency equation. Axial modal dependence is assumed in the characteristic beam functions. Natural frequencies of the shells are observed to be dependent on the constituent volume fractions. The results are compared with those available in the literature for the validity of the present methodology.     

串列双圆柱同步测压实验结果的相关分析

本文在雷诺数2×104下,同步测量了12个不同间距下串列双圆柱的表面压力分布,积分得到脉动升、阻力的时间历程,并对前、后柱之间的脉动升、阻力以及脉动升阻力和圆柱表面的脉动压力进行了相关分析.在本实验中,串列双圆柱流态切换的临界间距比在3.5～4.0之间,在临界间距前后,相关曲线的形态差别很明显.当串列双圆柱之间的距离小于临界间距时,前后柱之间的影响显著,造成脉动升/阻力和脉动压力之间的相关程度下降.串列双圆柱之间的距离大于临界距离时,前、后柱的脉动升力之间的相位差随间距线性增加.分离点的脉动压力和脉动升力之间以及背压和脉动阻力之间都有较好的相关性,可以用分离点的脉动压力和背压来分别表征脉动升力和脉动阻力.     

Elasticity solutions for functionally graded plates in cylindrical bending

The plate theory of functionally graded materials suggested by Mian and Spencer is extended to analyze the cylindrical bending problem of a functionally graded rectangular plate subject to uniform load. The expansion formula for displacements is adopted. While keeping the assumption that the material parameters can vary along the thickness direction in an arbitrary fashion, this paper considers orthotropic materials rather than isotropic materials. In addition, the traction-free condition on the top surface is replaced with the condition of uniform load applied on the top surface. The plate theory for the particular case Of cylindrical bending is presented by considering an infinite extent in the y-direction. Effects of boundary conditions and material inhomogeneity on the static response of functionally graded plates are investigated through a numerical example.     

三维编织复合材料圆柱壳在外压作用下的屈曲分析

提出一种三维四向编织复合材料圆柱壳的细观力学模型,宏观上基于Reddy高阶剪切变形理论和广义Kármán型方程,采用奇异摄动法求解在固支边界条件下三维四向编织复合材料圆柱壳在外压作用下的屈曲和后屈曲.分析中同时考虑非线性前屈曲、大挠度和初始几何缺陷的影响.讨论了纤维体积含量、壳体几何参数等因素对圆柱壳屈曲行为的影响.     

纳米尺度圆柱绕流尾迹区流动形式模拟研究

采用非平衡分子动力学模拟方法,对微尺度低{Re}数下的圆柱绕流问题进行了研究,模拟结果表明:当{Re}<12时,圆柱下游形成对称、无分离的定常流;当{Re}>20时,圆柱下游形成周期性交替出现的对称涡;当12相似文献   

利用声波干涉抑制旋转式压缩机的辐射噪声

压缩机是制冷设备的主要噪声源之一,其辐射噪声的抑制很有必要.理论分析了两列声波在自由场和管道中传播特性,证实了在管道中的两列声波能够产生有效干涉从而降低声压幅值.将压缩机储液器内的双管吸气改为了单吸气,数值分析表明了改进后壳体辐射噪声得到了明显抑制.声学实验验证了数值计算结果和理论分析,单吸气压缩机总声压级降低了约1.2dB(A).