球头铣刀铣削球面的表面形貌建模与仿真研究

基于齐次坐标矩阵变换原理和矢量运算法则，建立了工件坐标系下球头铣刀扫掠面的数学模型，基于Z-MAP法设计了球形表面形貌的生成算法，利用该算法对球头铣刀分别采用3D环绕法和放射加工法这两种典型走刀路线加工凸球面，并对加工后的表面形貌进行了仿真，通过分析对比仿真结果，发现3D环绕法更有利于减小表面粗糙度。同时，仿真结果和试验结果具有较高的吻合度，表明该仿真方法是可靠的，可以用于实际生产中球头铣刀铣削球面表面形貌的预测。     

变厚度板中水平剪切波的传播特性分析

为研究超声导波在储罐壁板等变壁厚结构中的传播特性，建立了SH波在空间自由边界中的传播模型，基于各向同性弹性介质Navier-Stokes方程，推导了变厚度板中SH波的频散方程，分析了变厚度板中水平剪切波走时t与倾斜角θ间的相互作用关系；通过简谐点源的远场响应并引入板厚与传播位移的非线性关系，得出了变厚度板中SH波的远场响应方程。在此基础上，仿真分析和实验验证了水平剪切波在不同倾斜角变厚度板中的传播特性，结果表明：在变厚度板的薄端激励水平剪切波并沿结构表面传播时，无频散现象，且无波包分离现象；但随着变厚度板倾斜角θ增大，水平剪切波的走时和接收信号幅值均逐渐递减，且呈非线性关系。     

Effect of Moving Speed of Charged Metallic Spherical Electrode on Electrostatic Discharge

In this investigation, the nature of the electrostatic discharge (ESD) that occurs when a charged object moves toward a stationary grounded object is experimentally clarified. The spark lengths, discharge currents, and induced voltages in a magnetic probe were measured when a charged metallic spherical electrode connected to a 422 pF capacitor approached a stationary grounded object, which was the current target, for different moving speeds of the charged metallic spherical electrode in a range of 1 mm/s to 100 mm/s. The charge voltages of the capacitor were +6.5 kV and +10 kV. Based on the results, the average gap length shortened with the speed of the spherical electrode. The average peak values of the discharge current and the induced voltage were likely to increase with the speed of the spherical electrode. The average rise times of the discharge current and the induced voltage were likely to drop with the speed of the spherical electrode. The relation between the spark length and the discharge current due to the ESD can be explained qualitatively by using an equation derived from the spark resistance formula proposed by Rompe and Weizel.     

Mathematical Modeling of a Simulated Moving‐Bed Adsorption Process: Parex™ Technology as a Case Study

A simplified dynamic mathematical model for a simulated moving‐bed adsorption process is presented. The model is adopted to simulate the separation process of p‐xylene from the other 8‐carbon aromatics by means of the Parex^? technology. Operating conditions and the moving‐bed structure for a commercial plant were used and the performance of the unit was simulated. The model results are in good agreement with the findings of similar existing studies. Comparison of the results of this simplified model with those obtained by other researches indicates a considerable decrease in central processing unit (CPU) time.     

Fluidization Characteristics of Air Dense Medium Agitated Separation Fluidized Bed with Different Distributors

ABSTRACT

The distribution plate structure plays an important role in the stability of air dense medium fluidized beds (ADMFB). Optimization of the distribution plate structure can reduce the generation of large bubbles. In the present work, the influence of the distribution plate structure on the fluidization characteristics of fluidized bed with agitator was investigated. Two different feedstock samples with the size fraction of 25–13 and 13–6 mm were tested individually. The experimental results showed that the fluidized bed density fluctuation was relatively small and the dead zone of gas-solids fluidized bed was significantly reduced by adding the stirring device into the fluidized bed under the optimal working conditions. Through a study of the sorting test, it was revealed that the separation performance can be effectively improved. This indicates that there is an obvious interrelationship between the structure of distribution plate and other process parameters, which affects the fluidization characteristics of ADMFB.     

Uplift capacity of horizontal anchor plate in geocell reinforced sand

The paper investigates the uplift performance of horizontal anchor plate in geocell reinforced sand through a series of model tests. It is noted that the unreinforced anchor plate undergoes a clear failure at a displacement of about 3% of its width, whereas with the provision of geocell and a layer of geotextile right below the geocell mattress significantly increases the uplift capacity by about 4.5 times higher than that of unreinforced sand and could sustain anchor displacement of more than 60%. Results indicates that the geocell mattress by virtue of its rigidity distributes the uplift load in the lateral directions to a larger area, thereby reducing the stress in the overlying soil mass and hence increases the performance of anchor plate system. The provision of the additional geotextile layer right below the geocell mattress is found to be very effective in increasing the stiffness as well as load carrying capacity of anchor plate system. The optimum size (i.e., width and length) of geocell mattress giving adequate load carrying capacity of anchor plate is found to be 5.4 times of anchor width (5.4B). The comparison of model tests results with 3D numerical analysis shows good agreement, indicating that the proposed model is able to capture the uplift load-displacement behaviour of geocell reinforced anchor plate system.     

基于压缩机-支架系统的异常噪声研究

针对某乘用车发动机转速在1 573 r/min，压缩机开启时车内噪声异常的问题，对样车进行试验分析与诊断，对压缩机-支架系统进行仿真分析，提出改进方案并验证改进效果。利用LMS声振信号采集系统采集振动噪声数据，采用频谱分析、阶次追踪等方法，并结合压缩机-支架系统模态仿真结果，确定车内异常噪声是压缩机轴频21阶与压缩机-支架系统3阶模态频率接近发生共振造成的。通过优化支架结构来提高压缩机-支架系统3阶模态频率以此来避免共振，并换装橡胶驱动盘缓和压缩机输入扭矩波动。将改进结构进行整车试验，结果表明：匀速工况空调开启时问题转速下，车内噪声降低了2.5 dB(A)；匀加速工况空调开启时发动机转速1 500~1 650 r/min区间，车内噪声无峰值，其余转速空调开启时改进前/后车内噪声基本不变，噪声波动趋势平缓。     

移动加热源法制备单层硒化镓晶体

为了解决硒化镓(GaSe)晶体制备困难、化学性能差的问题,对GaSe晶体传统的化学汽相沉积制备方法进行了改进,采用移动加热源法制备GaSe晶体。搭建了GaSe晶体的制备装置,通过单片机精确调控制备晶体的高温炉的加热温度、移动位置等参数,并采用光学显微镜和原子力显微镜对所制备的GaSe晶体进行辅助表征。研究表明,利用移动加热源法可以制备出表面光滑且尺寸较大的单层二维GaSe晶体。由于对机电设备实现了自动精密移动,可对单层二维GaSe晶体实现高质量大批量的制备,有利于GaSe晶体在光电子学和纳电子学中的广泛应用。     

Ti70合金板的组织与力学性能的各向异性

通过拉伸及低温冲击试验、光学显微镜、扫描电镜及X射线衍射仪,对Ti70合金板的组织与力学性能的各向异性进行了研究。结果表明,Ti70合金板热轧及退火后组织未出现明显差异,退火过程中主要以回复为主,但在高密度位错的剪切带上出现了一定数量的再结晶晶粒。退火态Ti70合金板横向屈服强度及低温冲击吸收能量都高于纵向,但抗拉强度低于纵向,表现出了明显的各向异性。退火后Ti70合金板形成了较强的{0002}基面织构,其晶面法向向RD方向(纵向)偏转±30°,向TD(横向)方向偏转±41°。由于基面织构更向RD方向集中,因此造成了Ti70合金板力学性能的各向异性。     

退火温度对EB熔炼低成本TC4钛合金宽厚板组织和性能的影响

采用EB炉一次熔炼TC4合金扁锭作为直轧坯料,在4200 mm宽厚板轧机上成功制备出规格46 mm×2650 mm×8700 mm的低成本TC4合金宽厚板,研究了退火温度对低成本TC4合金板材显微组织和力学性能的影响。结果表明:EB熔炼TC4合金扁锭经过两火换向轧制,粗大铸态组织得到充分破碎,热轧态TC4合金板材显微组织中等轴α或条状α含量较高,横纵向室温拉伸性能差异小,横向室温冲击吸收能量小于纵向,横纵向心部强度均高于表层。TC4合金板材经750~900 ℃退火,横纵截面为等轴组织,经950 ℃退火,横纵截面为双态组织,经980 ℃退火,横截面为双态组织,纵截面为魏氏组织。随着退火温度升高,TC4合金板材抗拉强度和规定塑性延伸强度呈下降趋势,伸长率基本不变,室温冲击吸收能量先升高后降低,900 ℃退火后,强度、伸长率和冲击吸收能量达到最佳匹配。