An experimental study on convective heat transfer performance of steam and air flow in V-shaped rib roughened channels

An experimental study on heat transfer characteristics of steam and air flows in a V-shaped ribbed channels was conducted. The effects of Reynolds numbers and rib angles on heat transfer of steam and air were obtained. The area-averaged Nusselt numbers of steam flow at a Reynolds number of 12,000 were 13.9%, 20.6%, 27.1%, and 27.9% higher than those of air flow for rib angles of 90°, 75°, 60°, and 45°, respectively. The correlations for Nusselt number in terms of Reynolds number and rib angle for steam and air in V-shaped ribbed channels were developed.     

Influence of Si doping on the structural and optical properties of InGaN epilayers

Influences of the Si doping on the structural and optical properties of the InGaN epilayers are investigated in detail by means of high-resolution X-ray diffraction （HRXRD）, photolumimescence （PL）, scanning electron microscope （SEM）, and atomic force microscopy （AFM）. It is found that the Si doping may improve the surface morphology and crystal quality of the InGaN film and meanwhile it can also enhance the emission efficiency by increasing the electron concentration in the InGaN and suppressing tile formation of V-defects, which act as nonradiative recombination centers in the InGaN, and it is proposed that the former plays a more important role in enhancing the emission efficiency in the InGaN.     

Stop band characteristics of a TESLA cavity coaxial-type HOM coupler

A TTF-type coaxial higher order modes (HOM) coupler has been used in a TESLA 9 cell cavity. It is impossible to measure the stop band characteristics of the HOM coupler with the cavity. A measurement device for the coaxial transmission line type for the HOM coupler has been designed at Peking University. Experimentally it was shown that the average voltage standing wave ratio of the coaxial transmission line is smaller than 1.08. The experimental results of the stop band characteristics of the TTF-type HOM coupler have been fitted for the simulation. This paper describes the design of the measurement device and discusses the experimental and simulation results of stop band characteristics of the HOM coupler.     

Elastic analysis of an elliptic notch in quasicrystals of point group 10 subjected to shear loading

Based on the stress potential and complex variable function method, this paper makes an elastic analysis of an elliptic notch subjected to uniform shear stress at infinity in quasicrystals with point group 10. With the aid of conformal transformation, an exact solution for the elliptic notch of the quasicrystals is obtained. The solution of the mode {\rm II} Griffith crack as a special case is constructed. The stress intensity factor and energy release rate have been also obtained as a direct result of the crack solution.     

腐蚀与缺口对LY11铝合金疲劳极限影响的试验研究与分析

以飞机螺旋桨叶常用材料ＬＹ１１ＣＺ铝合金锻件的材料试件、腐蚀试件和缺口试件的疲劳极限实验结果为依据,研究了腐蚀与缺口对疲劳极限的影响,给出腐蚀试件和缺口试件疲劳极限的关系,并建立起一种只用材料疲劳极限来确定严重腐蚀情况对应的疲劳极限分布的方法,以适应螺旋桨叶等按无限寿命准则设计的构件评估腐蚀后疲劳可靠性的工程需求．     

自发极化强度对VFLC电光迟滞曲线影响的电路级模拟

提出了关于V字型铁电液晶(V-shaped Ferroelectric Liquid Crystal,VFLC)的等效电路模型,旨在将EDA技术引入对VFLC光电集成系统进行研究、开发和设计。该模型考虑了由铁电液晶盒多层结构和驱动电路引起的阻抗分配效应,以及极化与非极化锚定能对VFLC光电响应特性的影响。演示了电光迟滞曲线的反常迟滞、V字型及正常迟滞状态,并着重就自发极化强度对电光迟滞曲线的影响给出了模拟结果和分析。结果表明:强制电压随驱动信号频率的提高而增加,但增加速度随自发极化强度的提高而减慢;强制电压和迟滞反转频率随自发极化强度的变化均存在一个拐点,强制电压在自发极化强度为80nC/cm2时取到最小值(-0.084V),迟滞反转频率在自发极化强度为90nC/cm2时达到最大值(6.4Hz);自发极化强度小于80nC/cm2时,迟滞反转频率随自发极化强度准线性增加。模拟结果从量级和趋势上均与实验结果吻合。     

复合材料反平面切口端部奇性研究

基于复合材料切口尖端位移场的渐近展开,将切口的反平面平衡控制方程转化为关于切口奇性指数的特征微分方程,采用一种变换将其化为线性特征微分方程组,引入插值矩阵法计算相应边界条件下方程组的特征值以获取切口尖端的应力奇性指数.研究单相材料切口、双相材料切口及止于异质界面切口的奇异性,算例表明该方法可以一次性计算出多阶奇性指数.对所取得的非奇异指数尽管切口不表现出奇性状态,但却是描述切口尖端完整应力场必不可少的参量.     

A NOVEL APPROACH TO TESTING THE DYNAMIC SHEAR RESPONSE OF Ti-6Al-4V

Modifications were made on the traditional split Hopkinson pressure bar (SHPB) system to conduct dynamic shear tests. The shear response of Ti-6Al-4V was acquired at a shear strain rate of 10 4 s 1 by using this modified apparatus. The geometry as well as the clamping mode of the double-notch specimen was optimized by commercial FEM software ABAQUS, and the feasibility of the experiment set-up was validated. A shear stress calibration coefficient of τ = 1.03 and a shear strain calibration coefficient of Γ = 0.50 were obtained.We have employed high-speed photography to record the deformation process, especially the initiation and propagation of adiabatic shear band (ASB), during the dynamic shear test. The frames show that the time duration from ASB initiation to its completion is less than 2 μs, from which we can estimate that the propagation speed of ASB within Ti-6Al-4V is more than 1250 m/s under such loading conditions. The temperature rise within ASB is also estimated to be T 2 ≈ 1460℃ based on energy balance. Such high temperature has led to softening of the material within the ASBs, and has intensified the shear localization and finally resulted in fracture of the material.     

Notch filter feedback controlled chaos in buck converter

A method of controlling chaos in the voltage-mode buck converter is presented by using an improved notch filter feedback control in this paper. The proposed control part comprises a notch filter and a low-pass filter. The discrepancy between the outputs of the two filters is introduced into the control prototype of the power converter. In this way, the system period-1 solution is kept unchanged. The harmonic balance method is applied to analysing the variation law of the system bifurcation point, and then the stable range of the feedback gain is ascertained. The results of simulation and experiment are also given finally.[第一段]