Numerical simulation of fluid flow caused by buoyancy forces during vacuum arc remelting process

The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting (VAR) process have important effect on the subsequent mechanical processes like forging, rolling and welding. In order to determine the fluid motion of molten pool, a 2D finite element model is established using ANSYS10.0 software, combined with the turbulent fluid flow and heat transfer. The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study. The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile. It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.     

某型平台罗经专家故障诊断系统知识库和推理机研究

某型平台罗经是大型复杂精密机械电子设备,为了快速提高维修速度,需建立一套高效适用的专家诊断系统,而专家知识库是系统的关键组成部分。在充分分析平台罗经各种故障类型的基础上,选择采用故障树诊断方法、专家系统方法、神经网络方法相结合,建立了一套高效的故障诊断系统知识库。     

跨河城市桥梁群体景观规划浅析——以郑东新区龙湖地区为例

桥梁群体的景观规划是当前跨河城市建设面临的重要课题,桥梁群体的景观设计与单体桥梁的景观设计相比设计过程更为复杂,内涵更加丰富,需要与城市规划、建筑设计、景观风貌结合得更加紧密。以郑东新区龙湖地区桥梁群为研究对象,通过对该地区35座桥梁群的景观规划分析,对桥梁群景观规划进行一些方法上的探讨。     

Method of estimating human error probabilities in construction for structural reliability analysis based on analytic hierarchy process and failure likelihood index method

Partial safety factors must be evaluated precisely for the given target reliability index to ensure the certain level of structural reliability due to uncertain factors. The current studies of partial safety factors do not consider human error in construction for structural reliability. A mathematically model should be improved to simulate the partial safety coefficient concerned uncertainty factors which concern the effect of human error in construction. We employ the contaminated distribution to obtain the realistic mean value and standard variance of variable of structural parameters which coexist with random error human error. The reasonable partial safety coefficient can be calculated based on the realistic value of structural parameters concerned the effects of random error and gross error.     

反映车辆污染物排放水平的指标研究

机动车排放受车辆类型、车龄、燃料类型、油品质量等多种因素的影响,这些因素也直接或间接反映车辆的污染物排放水平。本文系统梳理了反映单个车辆污染物排放水平的指标,并分为直接和间接指标两类,其中车辆的燃料类型、车辆大小、车龄、行驶里程、行驶速度以及车辆满足的环保排放标准等指标是间接指标,间接反映车辆的排放水平。车辆实时尾气排放检测结果是直接指标,能够直接反映车辆的污染物排放水平。反映车辆污染物排放水平的指标研究是车辆污染物排放研究的基础性研究,也是机动车污染减排的重要支撑。     

高速铁路“四电”集成技术与管理

我国铁路建设企业在高速铁路快速发展的时期面临新的机遇与课题，而解决新课题无疑是一项长期和艰巨的任务。综合介绍了高速铁路“四电”新技术发展的特点，并分析了当今铁路建设企业在发展中应该注意技术及管理上的问题，以及采用的应对措施。     

MQ软件在TMIS应用中存在的问题及解决方法

Message Queue(MQ)作为应用和网络之间的界面,实现了信息的异步传输,同时也保证了信息的可靠性.针对MQ的特点,介绍了MQSeries软件在铁路计算机系统中的应用和维护.     

Wind turbine gearbox reliability analysis based on the system level stress-strength model

In order to estimate the reliability of wind turbine gearbox based on the system level, a generalized stress-strength model is introduced. Considering that the system works properly under a variety of random stresses which affect every component, the total stress on the system is given by a known linear combination of the stresses of all components. Then the strength of the system can be viewed as a linear combination of the strengths of relative components. In this model, stress and strength are independent of each other. Reliability of the system is the probability that strength exceeds stress. Finally, the reliability of wind turbine gearbox is estimated by the multivariable reliability calculation method. The corresponding result is compared with the results of reliability in the extreme cases(completely dependent and completely independent) by the traditional evaluation method.     

太中银铁路大理河沿岸黄土工程特性及防治措施

结合太中银铁路大理河沿岸的工程地质勘察实例,对该区的黄土工程特性及发生在黄土中的陷穴、错落、崩塌、坡面坍滑及滑坡等不良地质现象进行了分析,并结合铁路工程特点,提出了相应的处理方法。     

可口可乐、AD钙奶等食品中常见防腐剂测定

样品前处理采用传统的液-液萃取。样品酸化后用乙醇提取,取上清液进样分析。使用日本岛津公司2010型气相色谱仪,氢火焰离子化检测器(FID)可测得五种防腐剂的平均回收率为98.63%(n=3),平均相对标准偏差小于3%,标准曲线的线性回归系数也均在0.9918以上。仪器稳定性好,重现性也能够满足分析实验的要求。