大型公共建筑风险评估框架研究

大型公共建筑是开放复杂系统,其风险由可靠性风险、安全性风险和可持续发展性风险构成.大型公共建筑的风险评估、需要从系统的角度,针对3类风险的不同特性,采用定性与定量结合的方法,进行系统的风险评估.针对可靠性风险侧重系统的可靠程度评估,安全性风险侧重风险源和系统脆弱性评估,可持续发展性风险侧重关联风险事件评估.大型公共建筑...     

双随机下刚性索穹顶结构的可靠性灵敏度分析

针对目前索穹顶结构研究中没有考虑荷载的随机性和结构本身的随机性的问题,采用基于正交设计响应面的Monte Carlo法对刚性索穹顶结构进行了双随机下的可靠性灵敏度分析.以一个跨度为60m,承受轴对称均布荷载作用的肋环型刚性索穹顶结构为例进行分析,得到了结构功能函数的响应面,进而采用Monte Carlo方法得到结构的失效概率以及各随机变量对于结构失效的灵敏度矩阵.结果表明,刚性索穹顶结构的失效概率较小,且应力控制的失效概率小于位移控制的失效概率,最外圈斜索的预应力水平、荷载、刚性杆件截面积对于结构失效较为敏感.在此基础上,与相应索穹顶结构比较,两种索穹顶结构的失效主要都是位移控制,且在位移控制下,最外圈斜索的预应力水平对于刚性索穹顶结构失效的敏感程度要比整体预应力水平对于相应索穹顶结构失效的敏感程度低,刚性索穹顶结构较相应索穹顶结构更为可靠.     

毛细管辐射末端的防结露控制系统可靠性分析

介绍了毛细管温湿度独立调节系统的防结露控制原理,分析了防结露控制系统的工作状态以及故障状态,运用可靠性的理论,对系统的可靠性进行了分析,对系统的可靠性指标进行了求解,并对防结露控制系统的可靠性提出了优化的方法.     

环境振动试验和高储液箱的有限元分析

介绍了带盖、固定于地面的钢储液箱的动力参数、自振频率及振型的试验和数值研究结果。考虑了3个不同高宽比钢储液箱。3个储液箱高度均为12.190m,半径分别为6.095,8.000,9.144m。讨论了不同高宽比和不同液体高度所引起的动力参数对试验的影响。利用ANSYS软件建立了储液箱的有限元模型。尽管模型中限制了流体与结构的相互作用,但是在运用数值模型分析储液箱-液体体系之前,应利用试验明确这种作用。因此,做了一系列环境振动试验得到自振频率和振型。数值分析和试验结果吻合较好。还考虑了储液箱盖子对自振频率和振型的影响,结果显示:储液箱钢盖对自振频率的影响可以忽略不计,但对储液箱顶部的径向变形和振型有着显著影响。     

低酸催化水解稻草制备腐植酸的工艺研究

试验采用低酸催化水解工艺,从稻草中提取腐植酸.根据单因素试验设计,通过测定水解过程中稻草纤维素转化率和腐植酸产率的变化指标,来寻求较佳工艺参数.结果表明,初始阶段反应条件为温度220℃、0.1%硫酸溶液、固液比1∶12、压力4 MPa、转速300 r/min、时间20 min,将反应釜的反应条件调整为温度70℃、转速3...     

Investigation of the effect of disulfiram on corrosion of mild steel in hydrochloric acid solution

The corrosion inhibition properties of disulfiram (DSR) for mild steel in HCl solution were analyzed by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, atomic force microscopy, scanning electron microscopy and gravimetric methods. Physical adsorption is proposed for the inhibition and the process followed the Langmuir adsorption isotherm and kinetic/thermodynamic model of El-Awady et al. Constant phase elements describing the non-ideal characteristics of the electrochemical interface are introduced. The occurrence of inductive loop is also dealt with, through the introduction of an inductive element L. The use of these elements significantly improved the quality of fit of simulation to the EIS data.     

Oxidation behaviour of Al2O3–TiC–Co composites at 800–1000 °C in air

The oxidation behaviour of nanometre and micrometre sized Al₂O₃–TiC–Co composites is investigated at 800–1000 °C in air for 25 h. The oxidation resistance of nanometre sized samples is better than of micrometre sized. Phase compositions and microstructures were studied by XRD and SEM. The values of general rate constant k and oxidation exponent n are dependent on oxidation temperature and composites. The oxidation kinetics followed a rate that is slightly faster than the parabolic-rate law at 800–1000 °C. The activation energy of the nanometre sized is higher than of micrometre sized in the range of 800–1000 °C.     

基于ANSYS模拟预测S45C钢轴感应加热工艺参数

基于ANSYS有限元法对感应加热过程中电磁场和温度场进行了耦合分析,通过模拟得到了感应加热过程中频率f、电流密度Js和加热时间t等重要工艺参数之间的关系曲线,制定了预测工艺参数的确定方法。针对S45C钢轴类工件的技术性能要求提出了试制工艺参数,进行了感应淬火试验及相应的ANSYS有限元模拟,结果表明轴径向的温度模拟结果与硬度梯度曲线试验结果存在一致性。     

Experimental study on ultrasonic elliptical vibration cutting of hardened steel using PCD tools

Diamond tools cannot usually be applied for machining hardened steels while applying conventional cutting technique. As an alternative, ultrasonic elliptical vibration cutting (UEVC) technique was successfully applied for obtaining mirror surface on such steels using single crystal diamond (SCD) tools. In order to reduce production cost without compromising mirror surface quality, polycrystalline diamond (PCD) tools may be tested against highly expensive SCD tools. However, study on machining of hardened steel using PCD tools applying the UEVC technique has not yet been reported. The current research presents an experimental study on UEVC of hardened stainless steel (a typical Stavax, hardness 49 HRC) using the PCD tools. Face turning experiments were carried out to investigate the effects of three machining parameters: nominal depth of cut, feed rate, and nominal cutting speed on output performances such as cutting force, tool flank wear, surface roughness, and chip formation. Experimental results show that nominal cutting speed has very strong influence on the output performances, compared to the other two parameters. The surface roughness improves with a decrease in cutting speed. A mirror-like surface of approximately 804 mm² with a roughness value R_a of 11 nm was achieved at a lower cutting speed. Theoretical explanations have been given to support the results drawn from the UEVC experiments. It can be concluded that, while applying the UEVC technique, the inexpensive PCD tools instead of the SCD tools can be effectively applied to obtain optical surface for producing precise molds from the hardened steel.     

基于正交试验及MoldFlow模拟优化扶手盖板注塑工艺

以某汽车扶手盖板为研究对象,综合评价了多个工艺参数对注射翘曲变形的影响.通过正交试验法,并基于MoldFlow注射模流动分析软件,分析最佳浇口位置,获取试验数据,研究试验范围内各工艺参数对翘曲的影响,从而获得最优工艺参数组合.