混合通量差分格式的比较

系统研究了几种混合通量差分格式的构造方法和耗散模型,分别对低速平板绕流、二维跨音速喷管流动和高超音速钝头体无粘绕流进行了数值模拟,结合先进的EASM湍流模型对格式的粘性分辨率和激波稳定性进行了细致的比较分析.结果表明混合通量差分格式兼顾了FDS和FVS格式的优点,具有较高的间断分辨率和数值稳定性.     

High-temperature current conduction through three kinds of Schottky diodes

Fundamentals of the Schottky contacts and the high-temperature current conduction through three kinds of Schottky diodes are studied. N-Si Schottky diodes, GaN Schottky diodes and AlGaN/GaN Schottky diodes are investigated by I--V--T measurements ranging from 300 to 523~K. For these Schottky diodes, a rise in temperature is accompanied with an increase in barrier height and a reduction in ideality factor. Mechanisms are suggested, including thermionic emission, field emission, trap-assisted tunnelling and so on. The most remarkable finding in the present paper is that these three kinds of Schottky diodes are revealed to have different behaviours of high-temperature reverse currents. For the n-Si Schottky diode, a rise in temperature is accompanied by an increase in reverse current. The reverse current of the GaN Schottky diode decreases first and then increases with rising temperature. The AlGaN/GaN Schottky diode has a trend opposite to that of the GaN Schottky diode, and the dominant mechanisms are the effects of the piezoelectric polarization field and variation of two-dimensional electron gas charge density.     

基于模糊故障树的动车组空调系统性能可靠性

空调系统是动车组上的车载设备之一,其可靠性程度直接关系到乘客的生命安全。本文在对CRH5型动车组空调系统的故障数据统计与分析的基础上,结合模糊数学理论以及故障树方法,对空调系统可靠性进行了分析。首先建立空调系统的模糊故障树,以定量分析的方法进行分析计算,可得系统的故障概率区间,然后计算了28个底事件的重要度,得到影响空调系统的薄弱环节,最后通过对比分析,证明该方法的有效性,为动车组空调系统的故障预测和诊断提供参考。     

基于FTA-FPN的动车组塞拉门系统可靠性分析

基于动车组塞拉门系统故障的多样性以及故障征兆的模糊性,本文提出故障树(FTA)定性分析和模糊Petri网(FPN)定量分析相结合的可靠性分析方法,将Petri网理论和模糊推理规则有效结合,具有快速准确的并行推理能力。结合兰新客专动车组实际的运维记录,首先建立基于FTA的塞拉门系统模型,再根据FTA-FPN的转换规则,得到基于FPN的可靠性分析模型。当系统正常工作时,利用历史故障数据和FPN的正向矩阵推理对塞拉门系统进行可靠性分析得到了塞拉门系统的薄弱环节,并对各底事件进行了排序,这不仅能够为动车组塞拉门系统的维护与预防工作提供理论依据,还能更好的保证动车组安全运营。