NUMERICAL SIMULATION OF THREE-DIMENSIONAL INCOMPRESSIBLE FLOW BY A NEW FORMULATION

A new mathematical formulation, called the pseudovorticity–velocity formulation, of the three-dimensional incompressible Navier–Stokes equations is presented as an alternative to the vorticity–velocity approach. For the model lid-driven cavity flow problem in two and three dimensions, combined with an explicit mixed spectral /finite different numerical scheme the proposed formulation is found to be efficient and very accurate as compared with the results available in the literature. In particular, the simulation results demonstrate an attractive feature of the present formulation compared with the vorticity–velocity approach, namely that the divergence-free condition of the velocity field can always be achieved on a non-staggered mesh.     

正常金属-铁磁绝缘层-dx2-y2+idxy混合波超导结中的磁散射对隧道谱的影响

在正常金属铁磁绝缘层dx2-y2 idxy混合波超导隧道结中,考虑到铁磁绝缘层的磁散射和界面的粗糙散射效应,运用BogoliubovdeGennes(BdG)方程和BlonderTinkhamKlapwijk(BTK)理论,计算了隧道结中的准粒子传输系数和微分电导.研究表明:(1)磁散射和界面粗糙散射均可以压低电导峰,其中磁散射能使电导峰滑移,而粗糙界面散射却能阻止这种滑移,且两散射的共同作用可抑制由混合波两序参数的幅值比不同所导致的电导峰滑移;(2)随铁磁层离超导表面距离的增加,隧道谱在零偏压处由凹陷变成了零偏压电导峰,继而又演化为凹陷中的中心峰;(3)当铁磁层离开超导表面有若干相干长度时,隧道谱中将呈现一些子能级谐振峰.     

金属冲击温度的辐射法测量问题

 金属的冲击温度及熔化温度测量对构建其完全状态方程具有重要意义。简要综述了用于金属冲击温度及熔化温度辐射法测量的一维热传导理想界面模型和非理想界面模型,并着重对模型中明示或隐含的关键假定的合理性、影响金属冲击温度与熔化温度结果的主要因素进行了分析、讨论,以期对实验数据有一个合理的评估。还讨论了求解理想和非理想界面模型一维热传导方程界面温度时所隐含的冲击压缩下热导率不随温度而变、冲击压缩下金属样品/窗口界面辐射的灰体假定,以及窗口材料的透明性、非理想界面模型中表观界面温度的修正、动载条件下金属高压熔化温度的测量、界面的非Flourier热传导等问题。分析结果表明,目前采用辐射法测量大致可以得到冲击温度,在发生熔化的情况下可获得熔化温度,但离精密测量的要求还有较大差距。     

一种新型手性功能单体的合成

以手性芳胺为母体,丙烯酰氯为酰化试剂,合成了新型手性功能单体(1)。用1合成了一系列手性分子印迹聚合物。1的结构经1H NMR,IR,MS及元素分析确证。     

随机生长误差对双腔型平顶法布里-珀罗滤波器的影响

在光网络中平顶滤波器可以有效地提高信道光检测的快速性和准确性。利用两个法布里珀罗腔间的串联耦合,可以构建出具有平顶透射特性的双腔型法布里珀罗滤波器。采用传输矩阵的方法,研究了随机生长误差对双腔型平顶滤波器透射特性的影响。模拟分析表明,当两个法布里珀罗腔的物理厚度差超过一个纳米时,在透射谱中就会出现两个高度不同的透射峰;解释了实测器件的透射谱中的双峰不对称性;用界面起伏的概念解释了实测滤波器带宽大于理论值的原因。理论分析与实验结果取得了较好的一致。     

ZnS Nanospheres for Optical Modulator in an Erbium-Doped Fiber Laser

Zinc sulfide (ZnS), which belongs to transition metal monochalcogenides, is a semiconductor material with wide direct band gap. It can potentially show some special applications (such as luminescence, phosphor, sensors, infrared window materials, photocatalysis) by changing the morphology, size, and crystal structure of semiconductor materials. However, ZnS nanospheres have not been studied as optical modulators until now. Herein, ZnS nanospheres are synthesized by the hydrothermal method and are used to realize optical modulators in an Er-doped fiber laser. The evanescent field effect is utilized to incorporate the ZnS nanospheres on a tapered fiber. Furthermore, with the increase in pump power, the modulation interval gradually decreases to a minimum of 34.36 ns corresponding to the modulation frequency of 29.1 MHz, which is the highest modulation frequency to our knowledge in a ring cavity all-fiber laser. These results demonstrate ZnS nanospheres together with the interaction of dispersion and nonlinearity in optical fibers can modulate the proposed lasers. This not only provides a new method for controlling the power and frequency of all optical modulators, but also marks an important step for ZnS materials in optics research and device applications.     

Finite element modelling of natural-convection-controlled change of phase

The problem of phase change in the presence of natural convection has been investigated. A model has been proposed based on the treatment of the release/absorption of latent heat as a heat source/sink in combination with the standard Galerkin finite element method with a primitive variable formulation on a fixed grid. To demonstrate the capabilities of the model, three cases of phase change of an aluminium alloy in the presence of natural convection arc considered, i.e. solidification, melting and combined solidification and melting. The solidification of water in a square cavity is modelled as another example, taking into account the density extremum, and the results are compared with a previously published work.     

流-固界面波的激光激发与光偏转检测

基于光偏转原理,研制了可用于流-固界面波探测的光纤传感装置.在此基础上,建立了以调Q Nd∶YAG激光为流-固界面波激发光源的实验系统.实验上探测了激光在空气-铝、水-铝和酒精-铝等界面上激发的界面波波形.根据实验波形,算得在这三种界面上的泄漏Rayleigh波和Scholte波的速度分别为2889 m/s和339 m/s、2916 m/s和1512 m/s、2872 m/s和1184 m/s,此实验值与理论计算值相比,偏差小于5％.     

黏弹性接触界面端附近的奇异应力场

研究蠕变加载条件下线黏弹性材料接触界面端附近的奇异应力场问题.考虑接触界面的摩擦,假设界面端的滑移方向不改变,相对滑移量微小,且其与位移同量级,由此线性化局部边界条件,根据对应原理得到Laplace变换域中的界面端应力场,导出时域中奇异应力场的卷积积分表达式.对卷积积分核函数进行数值反演,考虑接触材料的两类组合,一是持久模量具有量级上的差异,另一是持久模量接近相同.算例结果证实核函数可以用准弹性法求得的解析式较准确地近似.在此基础上,利用积分中值定理,并引入各应力分量的修正系数,得到黏弹性奇异应力场的简化式.结合核函数的数值反演结果分析修正系数表达式的取值范围,得到如下结论,若两相接触材料的持久模量相差很大,可以采用准弹性解的解析式较准确地描述界面端的奇异应力场;一般情况下,应力场不存在统一的奇异值和应力强度系数,当采用类似于准弹性解的表达式近似给出黏弹性应力场时,可以估计此近似描述的误差限.文中最后采用有限元分析黏弹性板端部嵌入部位的应力场,算例包括了黏弹性板与弹性金属支承、黏弹性板与黏弹性垫层所形成的滑移接触界面端,利用黏弹性有限元的数值结果验证理论分析所得结论的有效性.      

含非完整界面的功能梯度压电材料Ⅲ型裂纹问题

本文研究了含非完整界面的功能梯度压电复合材料的Ⅲ型裂纹问题．此裂纹垂直于非完整界面,采用弹簧型力电耦合界面模型模拟非完整界面．界面两侧材料的性质,如弹性模量、压电常数和介电常数均假定呈指数函数形式且沿着裂纹方向变化．运用积分变换法将裂纹面条件转换为奇异积分方程,并使用Gauss-Chebyshev方法对其进行数值求解．根据算例结果讨论了一些退化问题并分析了裂纹尖端强度因子与材料的非均匀系数和非完整界面参数的关系．