Explosions of gasoline–air mixture in the tunnels containing branch configuration

In order to investigate the effects of branch tunnels on explosion propagation, experiments were performed in five different configuration tunnels (straight configuration and configurations with 1 branch, 2 branches, 3 branches and 4 branches). Pressure and flame transducers were used to record the history of the pressure development and track the velocity of the flame front. It was shown that the branch tunnels had ability to enhance the maximum overpressure, rate of overpressure rise, and deflagration index (K_G) of the gasoline–air mixture explosion due to the turbulence induced by the branch tunnels. The overpressure rise rate and K_G of the explosion increased as a function of the number of branch tunnels. Experiments also showed that the maximum flame speed increased as the branch number increasing from 0 to 3 due to the enlargement of turbulence induced by the branch tunnels. However, an increase of branch number did not always lead to an enhancement of flame speed because the heat loss was intensified resulting from the increase of flame surface caused by the branch tunnels. When the number of branch tunnels exceeded 3, the maximum flame speed dropped.     

南水北调穿越北京地铁13号线清河桥施工优化分析

以南水北调工程盾构施工穿越北京地铁13号线清河桥工程为背景,采用有限元分析方法,针对不同施工加固措施及行车速度条件下所引起的桥面竖向变形、桥墩竖向变形和地表沉降等问题进行了研究。总结了预加固旋喷桩配比参数、注浆配比参数及行车速度等因素对各结构变形的影响程度。结果表明:水灰比为1.00时的旋喷桩,既能控制结构变形,又具有较高的经济和施工效益;水泥浆与水玻璃浆之比为1.0∶1.0时的注浆参数最优;行车速度控制在50 km/h以下时,能较好地控制结构变形的发展。最后通过对施工过程中各结构的变形进行监测,验证了优化结果的合理性。     

模糊神经网络钳式吊车行走力矩跟随系统

主要根据主机参数设计一个模糊神经网络控制器，利用模糊神经网络使从机的速度和力矩都跟随主机，从而达到主从跟随模式。然后根据设计参数仿真和运行，成功地应用于钳式吊控制系统。     

基于心电的铁路列车驾驶压力检测研究

为实时检测列车司机压力水平,基于高铁驾驶行为与安全仿真平台,获取16名被试不同驾驶速度下的主观压力量表和心电(ECG)信号。首先,通过分析主观压力量表,探究不同速度下司机的压力水平;其次,统计分析不同压力水平下的心率变异性(HRV)特征;最后,比较最邻近算法(KNN),支持向量机(SVM),随机森林(RF)3种机器学习算法在压力检测方面的表现,并分析不同输入特征对分类器性能的影响。研究表明:随着速度的增加,司机的压力增大。连续R波之间的时间差间隔大于50 ms的数量(NN50),连续R波之间的时间差间隔大于50 ms的数量占比(PNN50),低频段功率值与高频段功率值之比(LF/HF),心脏交感神经指数(CSI)在不同的压力条件下具有显著性差异。在高速条件下,PNN50、HF、LF/HF减小,NN50增加,其中LF/HF值显著降低。此外,特征选择和特征标准化均有助于提高模型的表现;相比KNN和RF,径向基为核函数(RBF)的SVM分类器模型在检测驾驶压力方面的效果最好,准确度为71.2%。     

泡沫金属对甲烷/空气爆燃火焰的淬熄实验研究

为研究多孔材料对甲烷/空气预混气体爆燃火焰的抑制淬熄效果,运用一套自主设计的管道爆炸抑制系统进行实验研究。在实验中运用高速摄像机记录爆燃火焰在穿过多孔材料板时的淬熄过程,采用20,40,60,80PPI (孔目数) 的4种多孔材料,研究不同孔目数的多孔材料对爆燃火焰传播的形态结构、火焰传播速度以及抑制淬熄等特性的影响。结果表明:多孔材料的孔目数对爆燃火焰传播的早期阶段影响较小,爆燃火焰都经历了半球形火焰和指形火焰阶段;当火焰传播到多孔材料板时,孔目数越大对火焰的降速作用越强,80PPI工况下爆燃火焰不能穿过多孔材料板,即发生淬熄。实验结果揭示了多孔材料对火焰的淬熄作用与微孔通道和火焰的相互作用有关。     

梯形巷道平均风速分布特征的数值与实验研究

为实现矿井巷道内风量的准确监测,基于3D数值模型,对梯形截面巷道内平均风速的分布规律进行了数值分析,并通过实验研究对模拟结果进行对比验证,同时在不同断面尺寸及不同通风风速条件下,数值分析了梯形巷道内紊流充分发展截面上平均风速点的分布特征。结果表明:平均风速分布呈现环状连续分布,数值结果与实验结果符合良好;梯形截面上平均风速点的分布与通风风速无关,仅与巷道截面特征和参数有关;得到了梯形截面平均风速分布曲线在巷道顶部的特征方程。     

Heavier birds react faster to predators: individual differences in the detection of stalking and ambush predators

The relationship between body mass and reactions speed in response to a predatory threat is poorly understood. Theory predicts that different vigilance patterns are optimal for the detection of different predator types. We suggest that birds of different individual state might also differ in their speed of response dependent upon predator type. We used laboratory trials of wild caught chaffinches (Fringilla coelebs) to determine how between individual differences in chaffinch behaviour and state correlate with latency to react to a ground predator model (domestic cat), thus providing a comparison with previous work in the same model system using aerial predator models. In experiment 1, we observed chaffinch responses to a moving cat model, simulating a stalking predator. In experiment 2, we used a camouflaged cat model simulating an ambush predator. Both experiments show evidence suggesting heavier individuals (which previous literature has linked to impaired flight performance) responded more quickly to the model cat. Heavier individuals also had shorter interscan intervals. In contrast to a previous study, both experiments found individuals with a higher intake rate were not faster at responding to the cat model. In addition, individuals in experiment 1 that head turned more while scanning were slower to respond to the stalking cat model. Our work suggests that although heavier individuals may have impaired escape performance they appear to show behavioural compensation by allocating more attention to anti-predator behaviour and by modifying their interscan intervals, resulting in faster response times to a ground predator. We suggest more experiments investigating response time to different predatory types and explicitly manipulating state to elucidate cause and effect.     

黑河流域参考蒸散量的时空变化特征及影响因素的定量分析

利用黑河流域及周边地区14个气象站的1960—2009年逐日气象资料,基于FAO推荐的 Penman-Monteith模型分析了黑河流域近50 a来潜在年、 季参考蒸散量ET₀的时空分布特征,同时利用敏感分析计算了流域内不同区域典型气象站ET₀对各气候要素的敏感系数,并结合各气候要素的多年相对变化定量探讨了导致ET₀变化的主导因素。结果表明:黑河流域年ET₀表现出明显的南北差异,亦即从南到北呈增大趋势,上游祁连山区年ET₀约568~700 mm,中游走廊平原约800~900 mm,下游的金塔、 鼎新一带约1 000 mm,额济纳地区则高达1 150 mm以上。各季节ET₀亦呈北多南少特征,且ET₀的年内分布以夏季最多,春季次之,秋冬最少。近50 a来,黑河流域年、 季平均ET₀整体呈减小趋势,但亦存在区域差异,其中上游ET₀略有增加,而中下游以减小趋势为主。就年平均敏感系数而言,上游的托勒站和中游的高台站皆对相对湿度敏感性最强,而下游的额济纳旗对平均风速最为敏感。不同站点各季节/月ET₀对气候要素的敏感性有所差异。风速是引起ET₀变化的主导因素,相对湿度和日照时数的贡献则较小。     

自动扶梯曳引机由静态元件供电的拖动线路及PLC控制

文章分析了GBI6899—2011《自动扶梯和自动人行道的制造与安装安全规范》中曳引电机由静态元件供电的要求,讨论了使用两个和一个电源接触器切断曳引机供电的线路。并优先使用一种两个电源接触器切断供电的线路,设计了该线路的一种PLC控制电路,讨论了其起动和停止的控制过程。并给出了PLC控制梯形图程序的结构图。     

双怠速法机动车尾气排放检测结果的影响因素分析

针对双怠速法机动车尾气排放检测过程中经常大量出现过量空气系数(λ)不合格现象,结合相关标准和工作实践对影响检测结果的因素进行分析。结果显示,取样管路的气密性差、系统响应时间未达标准、测试软件程序设置错误、高怠速转速设置不合理及由于车辆特性导致的选用标准及操作错误均会导致λ测试结果超标,影响双怠速检测法的准确性。