基于相似理论的飞机实际着陆距离预测方法

为防止飞机着陆时冲出跑道事件的发生,提出一种基于相似理论的飞机实际着陆距离预测方法.首先,通过量纲分析法结合影响飞机实际着陆距离的主要因素,推导出表征实际着陆距离的无量纲方程;然后,利用真实飞行数据,得出不同接地俯仰角条件下飞机实际着陆距离的预测方程;最后,对比分析方程预测结果与由真实数据所得的飞机实际着陆距离.结果 ...     

Bio-economic evaluation of implementing trawl fishing gear with different selectivity

The paper develops a biological-economic evaluation tool to analyse the consequences for trawl fishers of implementing more selective fishing technologies. This is done by merging a dynamic biological population model and an economic cost–benefit evaluation framework to describe the consequences for the fish stocks, fishermen and society. The bio-economic evaluation is applied to the case of the Danish trawl fishery in Kattegat and Skagerrak, which experiences a high level of discards and bycatches of several species. Four different kinds of selectivity scenarios are evaluated in comparison with a baseline. The results from the evaluation are indicators for the consequences on ecological and economic levels. The results show that implementation of different selective fishing gear in the Kattegat and Skagerrak mixed trawl fisheries generally implies a trade off over time between rebuilding the stocks and economic loss. Moreover, the analysis shows that implementation of more selective gear is not always beneficial.     

The conspicuity of first-responder safety garments

Introduction

This study compared the conspicuity of three types of first-responder safety garments (NFPA 1971-2007 turnout gear coats, and ANSI/ISEA 107 and 207 safety vests).

Method

Participants drove instrumented vehicles on a closed track during both daytime and nighttime, indicating when they could first detect pedestrians in a simulated emergency response scene. Pedestrians wore one of the safety garments and stood on either side of the emergency scene, facing or perpendicular to oncoming traffic, and either stationary or walking in place.

Results

All three garment standards provided equal levels of conspicuity, in that the distances at which the pedestrians were detected were equivalent. Time of day was a significant factor, with longer mean detection distances being observed in daytime. Pedestrian orientation was significant, with mean detection distances being longest when facing traffic. Pedestrian motion did not result in significant differences in detection distance.

Discussion

The results suggest that all three garment types studied are equivalent in making first responders conspicuous as pedestrians when working an emergency response scene in close proximity to traffic.

Impact on Industry

Whether an NFPA or ANSI/ISEA compliant is worn, first responders are equally likely to be detected by passing motorists, and as such these garments should be considered to be equivalent.     

京津冀机场群飞机LTO大气污染物排放清单

基于国际民航组织(ICAO)标准排放模型,调查搜集京津冀机场群9个机场实际航班情况,充分考虑了大气混合层高度的影响,采用EPA方法修正运行时间,精确估算了2018～2019航季年(364 d)京津冀机场群飞机起飞着陆循环(LTO)大气污染物排放清单.结果表明, 2018～2019航季年京津冀机场群飞机LTO循环NO_x、 CO、 SO_2、 HC和PM排放总量分别为10 720.5、 3 972.2、 407.8、 508.0和53.7 t.其中,冬春航季排放量分别为4 290.2、 1 646.7、 168.3、 220.1和22.4 t;夏秋航季排放量分别为6 430.3、 2 325.5、 239.5、 287.9和31.3 t.从空间分布来看,北京首都机场是该机场群大气污染物排放量最多的机场.从时间分布来看,07:00～08:00处于排放量最高峰, 12:00～20:00处于中等偏高排放水平, 21:00之后排放量相对较低.飞机在LTO循环中NO_x和CO排放量较多,PM排放量最少.各污染物不同工作模式下的排放情况差异明显.在该机场群起降所有机型中,B777单位LTO循环排放污染物最多,B737最少,B787单位LTO循环排放HC最低.     

基于Monte Carlo的海洋平台圆柱落物落点分析及危险区快速评价*

为实现海洋平台落物风险快速精确评价，针对传统推荐性规范经验化、过于简化、平面化及未体现工程随机性等问题，以圆柱落物为研究对象开展先导研究，基于3D运动理论模型，提出1种采用Monte Carlo方法表征工程随机性以实现危险区快速精确评价的方法，自主开发形成海洋平台圆柱落物危险区快速评价工具（MREDP），着重分析落点分布规律和危险区等级划分。结果表明:落点分布整体呈现“倒工字圆弧型”、两端“一密一疏”、关于X轴对称特点；MREDP快速评价结果可信，评价周期大幅降低；MREDP快速评价危险区相对较大、存在多峰值点，DNVGL-RP-F107推荐危险区相对保守、存在单峰值点。     

基于民航安全信息文本挖掘的进近着陆致险因素分析

为有效识别飞行进近着陆阶段致险因素,以进近着陆不安全事件为对象,利用Python语言和文本挖掘方法对文本进行预处理,获取包含关键特征值和特征权重的高维稀疏原始特征向量集合;利用卡方统计对致险因素原始特征项进行降维,得到30个维度文本特征项,借助词云图将文本挖掘结果可视化;通过人为因素、飞机故障、环境因素和管理因素4个层...     

汽车转向螺母精锻成形技术的研究开发

对汽车转向螺母精锻的成形工艺、模具及电极的设计与制造技术等方面进行了研究探讨,阐述了所解决的主要问题。试生产表明,采用所开发的精锻成形工艺取代转向螺母齿形及外形的切削加工工艺是合理、可行的。     

带毂直齿圆柱齿轮精锻的计算机模拟

此文利用上限法建立带毂直齿圆柱齿轮精锻过程的数学模型,并利用该模型对带毂直齿圆柱齿轮精锻过程中坯料外形尺寸和力一行程曲线进行了计算机模拟。对所得结果作了实验校核。实验结果与模拟结果吻合得较好,证明此文所建立的数学模型和模拟方法是可行的。     

圆柱直齿轮温挤压精密成形工艺研究

采用温挤压精密成形技术,成功地研制出直齿圆柱齿轮零件,理论和实验证明,新工艺具有优质高效节材节能的特点,非常适合圆柱直齿轮,特别是大模数齿轮的精密成形。     

圆柱齿轮冷锻成形技术探讨

探讨了几种圆柱齿轮冷锻成形技术 ,对圆柱齿轮冷锻特性进行了分析 ,并运用系统的观点对提高冷锻圆柱齿轮的轮齿精度做了探讨