舱壁打孔的环肋圆柱壳振动性能分析

为研究舱壁打孔对结构振动性能的影响,以环肋圆柱壳为研究对象,采用有限元法,计算结构在不考虑开孔加强结构的条件下,改变圆形孔的大小、位置、数量以及含圆形孔的舱壁数量时的均方法向速度级,得到不同工况下整个结构的均方法向速度级频率响应曲线。数值计算结果的比较和分析表明:激振频率在150～350Hz时,4种工况对模型均方法向速度级影响不大;350～1 000 Hz时,在部分激振频率下,4种工况对模型均方法向速度级的影响变大。可见舱壁开孔在满足工程需求的同时,也可有效减少艇体质量,但同时也会一定程度地改变结构振动特性,须在潜艇实际设计中予以考虑。     

十里长街上“流动之家”的暖心人--记北京公交集团客四分公司常洪霞

随着社会经济的快速发展,人们的生活水平日益提高,乘客的出行需求,也从最初的能上去车,车厢里不太拥挤的需求向着安全、快捷、方便、准时、舒适等方面转变。如何为乘客提供更精准的服务,让乘客在短暂的乘车体验中,留下对公交美好的印象,是常洪霞一直思考的问题,为此她立足乘客需求,从安全行车、暖心服务上创新方法,为乘客提供更加精准的服务。     

靠港船舶应用大功率变频器供电仿真与分析

针对目前的岸电供电趋势,设计了一种大功率变频器供电的岸电供电模型。并根据理论研究在MATLAB/Simulink中搭建船舶岸电供电的仿真模型,对实际应用中靠港船舶应用大功率变频器供电易出现的故障类型进行模拟仿真,得到了靠港船舶供岸电过程中的故障动态参数并对其进行分析,对靠港船舶应用大功率变频器供电的岸电供电技术在我国港口的推广研究很有意义。     

Experimental study on the resistance of a transport ship navigating in level ice

This study investigates the resistance of a transport ship navigating in Arctic waters by conducting a series of model tests in an ice tank at Tianjin University. The laboratory-scale model ship was mounted on a rigid carriage using a one-directional load cell and then towed through an ice sheet at different speeds. We observed the ice-breaking process at different parts of the ship and motion of the ice floes and measured the resistances under different speeds to determine the relationship between the ice-breaking process and the ice resistance. The bending failure at the shoulder area was found to cause maximum resistance. Furthermore, we introduced the analytical method of Lindqvist (1989) for estimating ice resistance and then compared these calculated results with those from our model tests. The results indicate that the calculated total resistances are higher than those we determined in the model tests.     

Review on Theoretical Delay Estimation Model for Signalized Intersections

Traffic delay is an effective index for estimating the performance of a signalized intersection. In this study, we provide a comprehensive review of the theoretical delay estimation model over the last ca. 90 years. For fixed-time signalized intersections, we classified the estimation development process into three stages. Stage 1 covered 1920s–1970s, when approaches based on steady-state theory were derived. These methods obtain accurate predictions with low degrees of saturation, but overestimate the delay with higher saturation and cannot provide reasonable results for oversaturated conditions. To accommodate high saturation, time-dependent models were proposed and improved in Stage 2, 1970s–2000s, using coordination transformation techniques. Progression factors to account for the filtering impact from upstream intersections were also introduced during this period. Due to inaccurate approximation of certain specific traffic conditions, some modified approaches and supplementary terms were derived from 2000 onwards (Stage 3), which facilitate the evolution of the delay estimation method and improved approximation results. Some new techniques, including artificial intelligence algorithms, were also introduced into delay estimation in this era. We also describe theoretical delay measurement methods for actuated control intersections with a similar time line. From our summary of the evolution of theoretical delay models, we highlight some deficiencies and future research directions.     

自升式钻井平台结构动力响应研究与等效建模要点讨论

随着油气开采作业水深的不断增加,自升式平台的动力敏感性愈发明显,对其进行结构动力响应研究十分有必要,而结构动力响应研究的重点在于平台固有周期的计算。以某400英尺自升式钻井平台为研究对象,分析并探讨了平台结构动力响应的计算方法,重点对平台等效建模中的关键要点进行了讨论与总结,并提出新的观点。以此为依据,基于SESAM GeniE软件进行建模,计算了平台的一阶固有周期,与基本设计数据进行对比,验证了建模中关键点处理的正确性,可为自升式平台的结构动力响应研究提供参考。     

多电平电力变换器主电路拓扑分析与调制仿真

大容量是电力电子技术未来的主要发展方向,多电平变换技术是实现高电压大容量的关键,多电平变换装置主电路拓扑是研究重点。文章详细分析了多电平变换装置的几种具体主电路拓扑结构,指出了几种拓扑结构的优缺点,分析研究了级联多电平变换装置的可靠性,并对三相级联11电平变换装置进行了载波相移脉宽调制(CPSPWM)仿真分析。     

基于区间数学理论和贝叶斯网络指标灵敏度分析

针对航空公司安全质量管理体系(SQMS)中风险识别与可靠性改进问题,文中提出基于区间数学与贝叶斯网络的灵敏度分析方法.给出了衡量航空公司安全状况的指标;借助贝叶斯网络建立指标关联网络,结合先验知识进行参数学习以获取条件概率;通过贝叶斯双向推理机制和区间数学理论分析不同区间内重要指标与系统整体安全状况间的扰动关系;基于扰动分析结果对各指标进行灵敏度排序以识别风险并指导可靠性改进工作.实例分析验证了基于区间数学与贝叶斯网络的指标灵敏度分析方法的有效性.     

桥头跳车对路面结构的冲击效应研究

基于车-路耦合动力学模型,研究桥头跳车对路桥过渡段路面结构的冲击效应.分析了考虑车-路耦合作用对路面冲击效应的影响,研究了车辆冲击系数和路面振动响应随路面弹性模量、路基反应模量的变化规律,提出了路桥过渡段的道路设计建议.结果表明:考虑车-路耦合作用后,车辆冲击系数和有效影响范围均有所减小;路面弹性模量、路基反应模量对车辆冲击系数影响不大,但对路面振动响应影响较大;路桥过渡段的路面结构设计应考虑路面动力响应,采用车辆冲击系数作为标准轴载的放大系数偏危险,建议采用路面动力反应系数;从控制路面振动角度出发,路桥过渡段宜选择柔性路面,同时路基反应模量应超过200 MPa/m.     

钢箱梁疲劳裂纹安全性等级评价方法

参考现有评价方法,将模糊综合评价法应用在钢箱梁疲劳裂纹安全性等级评价上。根据钢箱梁的结构特点,确定相应的因素集和评价集,建立数学模型,确定各评价指标的权重,并划分了相应的评价等级标准。根据此标准可对钢箱梁疲劳裂纹的安全性等级作出评价。