Local Heating Effect of Flow Past a Circular Cylinder

Heating effects of air flows past a two-dimensional circular cylinder at low Reynolds numbers and low Mach numbers are investigated by numerical simulation. The cylinder wall is heated partially rather than heated on the whole surface as with previous researches. The heating effects are completely different for various heating locations on the cylinder surface. Heating either windward or leeward side stabilizes the flow and reduces or completely suppresses vortex shedding from the cylinder at supercritical Reynolds numbers, which is consistent with previous results of heating on the whole surface of the cylinder. However, as the lateral sides of the cylinder （perpendicular to the stream-wise direction） are heated, an adverse effect is found for the first time in that the flow is destabilized and vortex shedding can be excited at subcritical Reynolds numbers. As the lateral sides of the cylinder are cooled, the flow is stabilized.     

圆柱体骰子最终面朝向概率的研究

下落物体的最终静止状态取决于物体的几何特征、运动状态、材料特性等多种因素.本文以圆柱体骰子为研究对象,基于动力学模型,探究了圆柱体骰子初始速度、角速度、高度、质量以及恢复系数等因素对骰子落地后最终面朝向的影响,并探讨了使圆柱体骰子每一面最终朝向概率相等时应具有的几何特征和物理条件.本文结果可为此类研究提供思路和借鉴.     

功能梯度厚壁中空圆柱体弹性动力学平面应变响应的解析解

研究了边界表面受均布动压力作用的功能梯度(FGM)厚壁中空圆柱体,给出了其平面应变响应下的弹性动力学解．假设材料性能(除Poisson比外)随厚度按幂律函数变化．为了得到一个精确解,将动力径向位移分为准静力部分和动力部分,导出了每个部分的一个解析解．先由Euler方程得到准静力学部分的解,再由分离变量法和正交展开法得到动力学部分的解．在不同动荷载作用下,对不同的FGM中空圆柱体,画出径向位移和应力图,并对本方法的优点进行了讨论．该解析解适用于中空圆柱体各种组合的FGM,厚度可以是任意的,初始条件也可以是任意的,壁面上均匀分布着任意形式的动压力．     

变厚度非均匀粘弹性复合圆柱体的旋转应力

在平面应变的假设下,给出了两个复合弹性圆柱体旋转时的解析解．外柱是由厚度按公式变化的正交各向异性材料所组成,它包裹着一个等厚度纤维增强粘弹性均匀各向同性的实心圆柱体．外圆柱体的厚度和弹性性质按半径方向的幂函数变化．应用边界和连续条件,确定复合圆柱体旋转时的径向位移和应力,应用等效模量和Illyushin逼近法,得到问题的粘弹性解．讨论了各向异性、厚度变化、本构参数以及时间参数,对径向位移和应力的影响．     

TRANSIENT THERMAL RESPONSE IN THICK ORTHOTROPIC HOLLOW CYLINDERS WITH FINITE LENGTH： HIGH ORDER SHELL THEORY

The transient thermal response of a thick orthotropic hollow cylinder with finite length is studied by a high order shell theory. The radial and axial displacements are assumed to have quadratic and cubic variations through the thickness, respectively. It is important that the radial stress is approximated by a cubic expansion satisfying the boundary conditions at the inner and outer surfaces, and the corresponding strain should be least-squares compatible with the strain derived from the strain-displacement relation. The equations of motion are derived from the integration of the equilibrium equations of stresses, which are solved by precise integration method （PIM）. Numerical results are.obtained, and compared with FE simulations and dynamic thermo-elasticity solutions, which indicates that the high order shell theory is capable of predicting the transient thermal response of an orthotropic （or isotropic） thick hollow cylinder efficiently, and for the detonation tube of actual pulse detonation engines （PDE） heated continuously, the thermal stresses will become too large to be neglected, which are not like those in the one time experiments with very short time.     

Funnel-Shaped Arrays of Metal Nano-Cylinders for Nano-Focusing

We analyse funnel-shaped arrays of metal nanocylinders that can be potentially used as waveguides for nanofocusing of light. The proposed structures consist of Ag nanocylinders with gradually changed radii and discrete spacing arranged like side-view funnels with different angles. Finite-difference and time-domain simulations demonstrate that the proposed structures with different spacings and funnel angles have versatile light propagation characteristics. These structures can focus the incident Gaussian light beam （200nm at its full width at half maximum） into beam sizes of 10hm, 15nm, and 20hm, respectively, which corresponds to the transmission efficiencies of 38%, 40%, and 80%.     

圆柱体对垂直其中轴并过其中心的转轴转动惯量的几种计算方法

由于取微元的不同,可通过几种方法计算圆柱体对垂直其中轴并过其中心的转轴的转动惯量.     

刚性圆柱体上圆阵波束形成性能分析

以环绕在刚性圆柱体上的均匀圆阵为阵列模型,分析了刚性圆柱体对圆阵响应的影响,在声场分解所得到的相位模式空间,推导了相位模式波束形成阵列和延迟求和波束形成阵列的白噪声增益和指向性指数的定量表达式,分析了它们在不同频率段的变化规律。在存在和不存在刚性圆柱体两种情况下,对两种阵列性能进行了对比分析。研究了圆阵与圆柱体之间存在间隙时对阵列接收信号及阵列性能的影响。仿真结果表明,在两种情况下相位模式波束形成处理都具有频率不变的指向性,但在低频段牺牲了阵列的鲁棒性;延迟求和波束形成处理在整个频率段具有较好的鲁棒性,但随频率的降低其波束指向性下降,直至变成各向同性阵列。存在刚性圆柱体时,两种阵列鲁棒性均有了一定的提高,前者的指向性不变,而后者的指向性得到了提高。圆阵与圆柱体之间的间隙会降低阵列在高频段的鲁棒性。      

Analytical solution of bending-compression column using different tension-compression modulus

Based on elastic theory of different tension-compression modulus, the analyttcal solution was deduced for bending-compression column subject to combined loadings by the flowing coordinate systemaxis, stress, strain andand phased integration methoddisplacement were developed,The formulations for the neutralthe finite element program was compiled for calculation, and the comparison between the result of finite element and analytical solution were given too. Finally, compare and analyze the result of different modulus and the same modulus, obtain the difference of two theories in result, and propose the reasonable suggestion for the calculation of this structure.     

功能梯度空心及实心圆柱体旋转时的弹性及粘弹性解

逐步分析了旋转的功能梯度空心及实心长圆柱体问题的解.假设圆柱体的弹性模量和材料密度沿径向呈指数变化,Poisson比为常数.由平衡方程、相容方程、弹性变形理论及应力-应变关系,导出了统一的控制方程.根据超几何函数,求解该二阶微分控制方程,得到旋转功能梯度圆柱体的弹性变形.检验并讨论了圆柱体中的应力与非均质参数、几何、边界条件之间的相互关系.将旋转功能梯度空心及实心圆柱体的分析结果,与旋转均质各向同性圆柱体的结果进行了对比分析.同时,提出了旋转粘弹性圆柱体的粘弹性解,并验证了空心及实心圆柱体中应力与时间参数间的依赖关系.