圆锥形零件冲压成形皱曲破裂成形极限的变化规律性

由外皱曲模型给出外不皱曲判据,依据它可计算出防外皱曲最小压边力的大小,作为防外皱曲的极限判据。由内皱曲模型给出内不皱曲判据,依据它可计算出防内皱曲最小压边力的大小,作为防内皱曲的极限判据。由破裂模型给出不破裂判据,依据它可计算出最大压边力的大小,作为防破裂的极限判据。结合上述外不皱曲判据、内不皱曲判据和不破裂判据,给出圆锥形零件冲压成形的成形判据和圆锥形零件冲压成形皱曲破裂成形极限的变化规律性。它们是材料参数M(n,r,σb,K,E)、设计参数D(D0,δ0,m,Kd,rd)和过程参数P(fb,fd,fα,η)的函数。     

板料成形过程系统分析

此文从系统的角度就板料性能、板料毛坯的展开计算、模具设计与制造、摩擦与润滑、应力应变分析等诸多方面对板料成形过程作了一般分析.可知板料成形过程是一复杂的,需要考虑系统中各个因素之间的相互关系和影响才能得到合理的板料成形件.并从有限元法的角度,建立了板料成形过程模型.     

氨气敏电极法测定大气中氨

以Ｈ２ＳＯ４（０．０５ｍｏｌ／Ｌ）和ＮＨ３（１．００ｍｇ／Ｌ）的混合溶液作吸收液，采用气敏电极测定大气中氨，发挥了离子选择电极所具有的快速、灵敏及测定范围宽等优点，保证了大气中低浓度氨测定的准确性和可靠性。实验表明，该方法检测限为０．０１４～０．０１８ｍｇ／ｍ＾２，精密度约为１４．３％（相对标准偏差），回收率在９７％～１０２％之间，经６个月实验室验证的结果，无论是精密度的变异系数或回收率的置信系数     

Driver speed selection on high-speed two-lane highways: Comparing speed profiles between uniform and differential speed limits

Objective: Although a considerable amount of prior research has investigated the impacts of speed limits on traffic safety and operations, much of this research, and nearly all of the research related to differential speed limits, has been specific to limited access freeways. The unique safety and operational issues on highways without access control create difficulty relating the conclusions from prior freeway-related speed limit research to 2-lane highways, particularly research on differential limits due to passing limitations and subsequent queuing. Therefore, the objective of this study was to assess differences in driver speed selection with respect to the posted speed limit on rural 2-lane highways, with a particular emphasis on the differences between uniform and differential speed limits.

Methods: Data were collected from nearly 59,000 vehicles across 320 sites in Montana and 4 neighboring states. Differences in mean speeds, 85th percentile speeds, and the standard deviation in speeds for free-flowing vehicles were examined across these sites using ordinary least squares regression models.

Results: Ultimately, the results of the analysis show that the mean speed, 85th percentile speed, and variability in travel speeds for free-flowing vehicles on 2-lane highways are generally lower at locations with uniform 65 mph speed limits, compared to locations with differential limits of 70 mph for cars and 60 mph for trucks.

Conclusions: In addition to posted speed limits, several site characteristics were shown to influence speed selection including shoulder widths, frequency of horizontal curves, percentage of the segment that included no passing zones, and hourly volumes. Differences in vehicle speed characteristics were also observed between states, indicating that speed selection may also be influenced by local factors, such as driver population or enforcement.     

混合气体爆炸性现场测试实验研究

为测定现场可燃混合气体的爆炸性,对比分析了国内外实验室爆炸极限的测定装置及爆炸性判定方法,设计研制了混合气体爆炸性现场测试装置。装置实现了爆炸性环境现场的自动采样、超高温点火、高速压力和温度测定及爆炸性自行判定。开展了丙烷、乙烯和液化石油气等典型可燃气体爆炸性实验,提出了基于压力和火焰温度变化相结合的气体爆炸性判定指标,改变了传统目测判定方式。研究结果表明:20 L球和1 L爆炸腔以爆炸压力提升来判定,比管式法测定的爆炸极限范围窄,以压力提升量5%~10%判定较适宜;1 L爆炸腔以爆炸过程温度提升量来判定,爆炸极限范围比以爆炸压力提升量判定宽,与目测观察的管式测定法相比,略宽于管式测定法和大部分文献数据。     

Reducing the risk of rear-end collisions with infrastructure-to-vehicle (I2V) integration of variable speed limit control and adaptive cruise control system

Objective: Adaptive cruise control (ACC) has been investigated recently to explore ways to increase traffic capacity, stabilize traffic flow, and improve traffic safety. However, researchers seldom have studied the integration of ACC and roadside control methods such as the variable speed limit (VSL) to improve safety. The primary objective of this study was to develop an infrastructure-to-vehicle (I2V) integrated system that incorporated both ACC and VSL to reduce rear-end collision risks on freeways.

Methods: The intelligent driver model was firstly modified to simulate ACC behavior and then the VSL strategy used in this article was introduced. Next, the I2V system was proposed to integrate the 2 advanced techniques, ACC and VSL. Four scenarios of no control, VSL only, ACC only, and the I2V system were tested in simulation experiments. Time exposed time to collision (TET) and time integrated time to collision (TIT), 2 surrogate safety measures derived from time to collision (TTC), were used to evaluate safety issues associated with rear-end collisions. The total travel times of each scenario were also compared.

Results: The simulation results indicated that both the VSL-only and ACC-only methods had a positive impact on reducing the TET and TIT values (reduced by 53.0 and 58.6% and 59.0 and 65.3%, respectively). The I2V system combined the advantages of both ACC and VSL to achieve the most safety benefits (reduced by 71.5 and 77.3%, respectively). Sensitivity analysis of the TTC threshold also showed that the I2V system obtained the largest safety benefits with all of the TTC threshold values. The impact of different market penetration rates of ACC vehicles in I2V system indicated that safety benefits increase with an increase in ACC proportions.

Conclusions: Compared to VSL-only and ACC-only scenarios, this integrated I2V system is more effective in reducing rear-end collision risks. The findings of this study provide useful information for traffic agencies to implement novel techniques to improve safety on freeways.     

限速值对信号交叉口交通安全的影响分析

为研究交叉口进口道车辆限速值对交叉口的安全和运行产生的影响,通过微观仿真平台,分析车辆在交叉口限速分别为30,38和46 km/h时的车均延误、车均行程时间,并将车辆行驶轨迹输入安全辅助评价(SSAM)软件中展开分析。结果表明,车辆限速值的提高对车均延误的影响不大,但会减小车辆在进口道的车均行程时间。另外,限速值从30 km/h提高到46 km/h,引起的碰撞时间(TTC)、后侵占时间(PET)数值变化不显著,但使总冲突数从42个增加到59个。     

环氧氯丙烷工艺中分离罐气相出口的燃爆危险性分析

环氧氯丙烷生产工艺中双氧水分解产生的氧气与含氯丙烯、环氧氯丙烷、甲醇的可燃气体混合存在燃爆危险,为预防燃爆发生,利用5L爆炸极限测试仪测定分离罐气相出口可燃气在不同氧气浓度条件下的爆炸极限,并以此绘制爆炸极限三元图,得到不同工况条件下"可燃气-氧气-氮气"混合体系的燃爆区域。结果表明:随着氧气浓度的升高,可燃气爆炸上限明显提高,但爆炸下限变化不明显;随温度上升,气相出口组分发生变化,LOC值逐渐降低;正常冷却条件下极限氧含量为12%,冷却效果差时为10%,冷却失效时为9.3%;设置氧浓度报警时参考最小LOC值,留出裕度空间,控制体系氧含量小于5%有助于预防燃爆发生。     

Populations of orchids at the northern limit of their distribution (Murmansk Oblast): Effect of climate

The effect of climatic conditions on the dynamics of 21 populations of 10 species of the family Orchidaceae at the northern limit of their range in Europe was studied between 1992 and 2004. The abundance of orchid populations proved to depend primarily on air temperature during the previous and current growing seasons.     

浮顶油罐油气惰化防火防爆实验研究

对浮顶油罐的油气空间进行惰化,是一种新的油罐防火防爆方法。向浮顶油罐一、二次密封间的油气空间中加入氮气,可缩小浮顶油罐的一、二次密封之间环形空间油气的爆炸极限的范围。根据这一原理,通过模型实验对大型双重密封型浮顶油罐的油气空间进行了氮气惰化保护实验研究。实验结果表明油气空间内氮气的体积分数会随着氮气通入时间的增长而逐渐升高,油气的体积分数则逐渐降低。氮气通入开始一段时间,环形空间内氮气的体积分数会迅速上升,油气体积分数迅速下降。但随着氮气通入时间的增长,氮气体积分数的上升和油气体积分数的下降速度都会趋于平缓。另外当入口处氮气流量从27Nm3/h变化到54Nm3/h时,为使油气体积分数下降至油气爆炸下限1%所需氮气持续通入的时间也从300分钟左右下降至200分钟左右。