A study on the sealing performance of bolted flange joints with gaskets using finite element analysis

Gaskets play an important role in the sealing performance of bolted flange joints, and their behaviour is complex due to nonlinear material properties combined with permanent deformation. The variation of contact stresses due to the rotation of the flange and the material properties of the gasket play important roles in achieving a leak proof joint. In this paper, a three-dimensional finite element analysis (FEA) of bolted flange joints has been carried out by taking experimentally obtained loading and unloading characteristics of the gaskets. Analysis shows that the distribution of contact stress has a more dominant effect on sealing performance than the limit on flange rotation specified by ASME.     

碟式抛物面太阳能聚能器焦面特性数值仿真

结合太阳能聚能器的光学特性,同时考虑了太阳不平行度、跟踪指向误差、镜面的反射误差以及焦面位置误差等误差因素,采用蒙特卡罗法对碟式抛物面太阳能聚能器的焦面特性进行了数值模拟分析,获得在等口径和等焦距条件下,边缘角对焦平面热流分布的影响,为碟式太阳能聚能器的设计和安装提供参考依据。     

Nanoscale Characterization of Energy Generation from Piezoelectric Thin Films

We report on the use of nanoindentation to characterize in situ the voltage and current generation of piezoelectric thin films. This work presents the controlled observation of nanoscale piezoelectric voltage and current generation, allowing accurate quantification and mapping of force function variations. We characterize both continuous thin films and lithographically patterned nano­islands with constrained interaction area. The influence of size on energy generation parameters is reported, demonstrating that nanoislands can exhibit more effective current generation than continuous films. This quantitative finding suggests that further research into the impact of nanoscale patterning of piezoelectric thin films may yield an improved materials platform for integrated microscale energy scavenging systems.     

基于双色光刀的三维扫描仪标定方法的研究

为了解决双色光刀三维扫描仪的标定问题,分别采用直线对应法和基于最小二乘的标定方法对摄像机和光刀进行标定,设计并实现了三维扫描仪系统的标定,经试验表明,此方法简单易行,计算结果精度高,对数据测量的精确性和可靠性提供了保障。也为后续口腔修复CAD／CAM软件系统的开发奠定了基础。     

Experimental and theoretical investigation of defects at (1 0 0) Si1−xGex/oxide interfaces

The identification of a nontrigonal Ge dangling bond at SiO₂/Si_1−xGe_x/SiO₂ heterostructures and its electrical activity are discussed, both from experimental and theoretical points of view. This dangling bond is observed from multifrequency electron-spin resonance experiments performed at 4.2 K, for typical Ge concentrations in the range 0.4 ≤ x ≤ 0.85. The electrical activity of this defect is revealed from capacitance-voltage characteristics measured at 300 and 77 K, and is found to behave like an acceptor defect. First-principles calculations of the electronic properties of this Ge dangling bond indicate that its energy level approaches the valence band edge of the Si_1−xGe_x layer as the Ge content increases, confirming its acceptor-like nature.     

Micro-Raman characterization of Germanium thin films evaporated on various substrates

We perform an extensive micro-Raman analysis of Germanium thin films physically evaporated on several substrates including silicon, silicon oxide and glass. We investigate the dependence of crystal quality on thin film deposition parameters such as substrate temperature and growth rate. We also study the continuous transitional change of the material structure from amorphous to crystalline phases. Ge films obtained by this simple and low cost technique are a viable solution towards the realization of virtual substrates and devices.     

Ellipsometric study of thermally induced redistribution and crystallization of Ge in Ge:SiO2 mixture layers

Mixture layers of Ge:SiO₂ of 40:60 mol% respectively, have been prepared by co-sputtering. The thermally induced change of optical properties of the layers was studied by variable angle spectroscopic ellipsometry. The mixture was modelled as an unknown material with optical constants described by multiple oscillators. The optical parameters determined from ellipsometric measurements can be well correlated with structural changes in the mixture. The results indicate that Ge in the mixture deposited or annealed up to 600 °C is in an amorphous state and it redistributes with increase of temperature, changing refractive index through the layer. The crystallization starts between 600 and 650 °C, at first next to the substrate. Crystallites size grows with temperature. Results were compared with findings of grazing incidence wide angle X-ray scattering measurements and a good agreement was found. Ellipsometry has been shown to be an appropriate non-invasive technique for characterization of this kind of layers.     

三维激光扫描仪球形靶标测量方法与精度评定

球形靶标是三维激光扫描仪检定、坐标系转换等测量任务中的主要手段,通过获取球形靶标的中心坐标可以评定三维激光扫描仪的测量精度.本文结合三维激光扫描仪野外测量和室内检定的要求,提出了四种球形靶标球心测量方案,并结合某三维激光扫描仪检定场,对不同测量方案的特点和精度进行了分析.     

大孤山铁矿边坡岩体结构数字识别及力学参数研究

针对目前岩体结构面信息获取主要以人工现场接触测量为主,劳动强度大、效率低下的现状,借助于先进的ShapeMetrix 3D三维数字摄影测量系统,对大孤山铁矿边坡岩体结构面进行摄影测量,对获取到的结构面进行分组、分析,得到结构面各种几何信息的详细数据,并对其进行数理统计计算、分析,拟合出结构面各种几何信息的概率分布模型。采用蒙特卡洛方法编制的程序和根据数字摄影测量系统得到的统计数据,模拟岩体内部结构面三维分布情况。在此基础之上,采用修正广义Hoek-Brown准则,估计节理化岩体强度,得到岩体强度指标。根据已获得的结构面三维分布情况和岩体强度指标综合评价了大孤山铁矿边坡岩体稳定性。     

三维激光扫描在测量中的应用现状

简要介绍了三维激光扫描系统的研究背景和分类,着重阐述了三维激光扫描系统在逆向工程、历史古建筑的保护、变形监测、减灾等方面的应用,指出三维激光扫描的普及应用将给测绘学科带来新的发展机遇。