导管螺旋桨叶梢泄漏涡机理研究及一种推迟梢涡空化的方法

文章运用数值模拟研究了导管螺旋桨叶梢泄漏涡机理,并提供了一种推迟泄漏涡空化的方法。通过分析不同间隙时的泄漏涡的空泡数发现,随着间隙增大,最小空泡数发生了位置向下游移动,靠近桨叶吸力面,其数值减小。间隙尺寸影响梢涡空泡数的机理很复杂,可以从三个方面来解释：第一、间隙大小改变了泄漏流动速度,从而影响了泄漏涡水动力参数;第二、间隙大小影响叶梢区域压强分布,泄漏涡压强随之改变;第三、间隙大小改变了间隙内黏流的产生和发展,影响泄漏涡黏性分布。而且叶梢泄漏涡核是导管螺旋桨空泡初生位置。文中研究一种叶梢喷射流方法降低叶梢涡核压降,推迟空化初生,探究了不同喷射速度和喷射间隙高度、喷射角度对泄漏涡空泡数的影响。从模拟结果看,叶梢喷射可以降低叶梢翼型载荷,改善泄漏涡核压强分布,推迟泄漏涡空化。比较不同喷射速度,发现速度越高,越能有效提高泄漏涡核压强,速度足够高时甚至可以“吹掉”涡核;研究不同喷射间隙高度发现,间隙越高,越能有效提高泄漏涡核压强,但由于会降低了叶梢更大区域的载荷,降低了桨叶推力;喷射角度的研究表明,轻微的正向预旋对推迟叶梢空化有利。     

地铁列车晚点分析与控制

着重分析地铁列车晚点的产生原因和时空分布特征,从故障预防与应急处理角度,提出减少列车初始延误发生、控制连带延误影响范围的建议和措施.     

带随机延滞的衍生的ARCH模型的几何遍历性

引入了带随机延滞的门限自回归滑动平均一自回归条件异方差模型,讨论了这个模型的极限行为,并给出了该模型以几何速率收敛的充分条件．该模型将固定延滞的衍生的门限自回归滑动平均一自回归条件异方差模型推广为延滞受到一个有限状态马氏链控制的衍生的门限自回归滑动平均一自回归条件异方差模型,能更好的拟合现实世界中的诸多实际问题．同时,推广了自回归条件异方差模型,增强了模型的适应性,能够更好的拟合金融市场中价格行为波动的现象．     

Combustion and emission characteristics of BD20 reformed by ultrasonic energy for different injection delay and EGR rate in a diesel engine

The purpose of this study is to understand the operational characteristics of a diesel engine that uses BD20 reformed by ultrasonic energy irradiation. In particular we study the effects of tuning injection delay and EGR rate. BD containing about 10% oxygen has attracted attention due to soaring crude oil prices and environmental pollution. This oxygen decreases soot by promoting combustion, but it also increases NOx. To solve this problem, injection timing may be delayed or an EGR system may be applied. These adjustments normally lower engine power and increase exhaust emission but, in using fuel reformed by ultrasonic energy irradiation (which is changed physically and chemically to promote combustion), we may hope to circumvent this problem. To control the duration of the ultrasonic energy irradiation, the capacity of the chamber in an ultrasonic energy fuel supply system was tested at 550cc and 1100cc capacities. As for the results of the experiment, we could identify the optimum EGR rate by investigating the engine performance and the characteristics of exhaust emissions according to the injection timing and the EGR rate while ultrasonically irradiated BD20 was fed to a commercial diesel engine. With UBD20 (at an injection timing of BTDC 16°), the optimum EGR rate, giving satisfactory engine performance and exhaust emissions characteristics, was in the range of 15∼20%.     

基于社会力模型的邮船舱段疏散滞后性分析

针对邮船遭遇紧急事件时乘客疏散过程中的滞后问题,基于社会力模型并应用逐段分析法分析在不同情景下的人员疏散过程。计算结果表明,随着滞后时间的增长,舱室内乘客的疏散效率逐渐降低。最危险的情况是在疏散开始时滞后3个舱段,人员疏散有效时间在平均疏散时间中占比不及50%,总时间是无滞后疏散的2倍。研究方法对邮船及其他类型客船的人员疏散流线设计具有一定的参考意义。