Multiple Melting Behavior of High-Speed Melt Spun Polylactide Fibers

High-speed melt spinning of polylactide (PLA) was conducted and the structure and multiple melting behavior of the as-spun fibers were investigated. In the analysis of temperature modulated differential scanning calorimetry (TMDSC) thermograms for the as-spun PLA fibers taken-up at 1 and 6 km/min, the peaks around the melting temperature region in the reversing heat flow (RHF) and nonreversing heat flow (NRHF) curves were mainly separated into (1) a pair of an endothermic peak (Peak L) in RHF and an exothermic peak (Peak R) in NRHF in a low temperature region, (2) an endothermic peak (Peak M) both in RHF and NRHF (only in RHF for PLA fiber spun at the low-speed) in an intermediate temperature region, and (3) an endothermic peak (Peak H) both in RHF and NRHF in a higher temperature region. Wide-angle X-ray diffraction (WAXD) measurements were conducted during the heating process of the as-spun fibers cut into powders. In the case of fibers obtained at 1 km/min, disordered crystals, i.e. α′-form crystals, were formed through cold crystallization followed by a disorder-to-order phase transition, i.e. α′ to α crystalline modification, with partial melting of the α′ crystals around 148.5°C in the temperature range of Peaks R and L. Finally, the α form crystals melted above 169.4°C, in the temperature range of Peak H. On the other hand, the PLA crystals generated by the orientation-induced crystallization during the spinning process at a spinning velocity of 6 km/min did not show a WAXD profile of perfect α form crystals but showed an intermediate structure having lattice spacings between the α′ and α forms. Such intermediate crystals did not transformed into α form crystals during the heating process.     

参考焓值法在高速槽道湍流中的修正

利用高来流马赫数为3, 5, 6, 7, 10的槽道湍流直接数值模拟(direct numerical simulations, DNS)数据, 评估和修正经典的参考焓值法. 研究表明在高来流马赫数槽道湍流中, 经典参考焓值法预测的壁面热流与DNS结果相差很大, 需要作适当的修正.修正参考焓值法Ⅰ和Ⅱ的预测结果明显优于经典参考焓值法;并且修正参考焓值法Ⅱ更加适用于高马赫数流动, 其壁面热流与DNS结果的相对误差在10%以内. 同时, 修正参考焓值法Ⅱ的普适性在超声速燃烧室隔离段热环境试验中得到了验证.     

路堤倾角变化对高速列车侧风运行气动特性影响

采用计算流体力学方法,探讨路堤倾角变化对高速列车侧风运行气动特性影响.结果表明:随着路堤倾角增大,头车侧向力系数先增加后减小,而中间车侧向力系数则持续减小.尾车上的侧向力系数先是略微减小,当路堤倾角达到47.5°时,侧向力系数随倾角增加而增加.作用在中间车上的负升力随着路堤倾角增加而增加.尾车的升力系数对路堤倾角变化非常敏感,变化幅度较大.路堤倾角变化时高速列车绕流流场变化,从而导致列车受到的气动力发生变化.     

千层塔提取物废液中3,4-二羟基肉桂酸和3,4-二甲氧基肉桂酸的提取

利用高速逆流色谱(HSCCC)对千层塔提取物废液中含量较高的2个同系物进行初步纯化分离, 再利用高效液相色谱(HPLC)对收集到的样品进行同系物分离, 得到8mg化合物A, 7mg化合物B, 纯度均在95%以上. 经核磁共振仪(NMR)鉴定2个组分的化学结构, 结果证明, 千层塔提取物废液所含的主要成分即2个同系物分别为3,4-二羟基肉桂酸和3,4-二甲氧基肉桂酸. 结论也同时证实高速逆流色谱与高效液相色谱联用能够有效分离样品所含同系物, 且工业提取千层塔有效成分后的废液中仍含有价值物质.     

高速列车空气动力学研究技术综述

随着我国高速铁路的快速发展,高速列车运行速度越来越快,包括气动阻力、横风效应、会车效应、隧道效应和气动噪声等一系列空气动力学问题日益突出. 利用模型试验、实车测量和数值计算等不同的研究手段,开展全面的高速列车空气动力学研究显得十分重要. 本文比较全面和系统地介绍了国内外高速列车空气动力学研究在模型试验、实车测量、数值计算等方面的技术现状和进展情况,对今后的发展方向和内容进行了展望.     

伴随超空泡产生的高速细长体入水实验研究

介绍了几种不同工况下高速细长体入水过程的实验研究工作. 用高速摄影仪实时记录了细长体高速入水时与自由液面之间的瞬态相互冲击作用, 清晰地观察了细长体高速入水后诱导生成的水中空泡流的形态及其演化过程. 具体分析了几种工况下高速细长体入水瞬间自由面的波动特性和细长体入水后运动的不稳定性. 从实时记录的照片中,测量出相邻2帧图片之间的细长体的位移差之后, 计算出细长体在入水过程中以及在水中的瞬时速度. 通过分析物体速度的变化趋势, 了解了超空泡流动的复杂过程.      

利用短波探测飞机目标的实验研究

利用自行研制的武汉电离层探测系统,使用改进的相位编码脉冲串信号,对武汉天河机场上空的飞机目标进行了探测.通过对回波的相干积累和谱分析,获得了机场上空的飞机目标回波,再利用时频分析方法得到了目标视向速度随时间的变化,并以此估计了目标的飞行状态.实验验证了利用相位编码脉冲体制短波雷达探测高速飞行目标的可行性,提出可使用时频分析方法来获取目标的运动特征.     

奥氏体回火温度对等温淬火球墨铸铁(ADI) 高速切削加工性能的影响研究

等温淬火球墨铸铁(Austempering Ductile Iron,以下简称ADI)是一种新型的耐磨球铁材料.结合现有ADI材料的生产情况,选取300、350、400 ℃3个奥氏体回火温度,制备3组试样并测定力学性能.通过高速切削试验,研究了CC650陶瓷刀具高速干式切削不同性能ADI材料时刀具磨损形态和磨损机理,探讨了奥氏体回火温度对ADI高速切削时刀具磨损性能的关系.试验结果表明,奥氏体回火温度对ADI材料组织和力学性能有较大影响;奥氏体回火温度和ADI试件材料与CC650刀具磨损之间具有相关性;高速切削时,CC650刀具对ADI切削的磨损机制以磨粒磨损和扩散磨损为主.     

An Improved Walk Model for Train Movement on Railway Network

In this paper, we propose an improved walk model for simulating the train movement on railway network. In the proposed method, walkers represent trains. The improved walk model is a kind of the network-based simulation analysis model. Using some management rules for walker movement, walker can dynamically determine its departure and arrival times at stations. In order to test the proposed method, we simulate the train movement on a part of railway network. The numerical simulation and analytical results demonstrate that the improved model is an effective tool for simulating the train movement on railway network. Moreover, it can well capture the characteristic behaviors of train scheduling in railway traffic.     

Simulating train movement in railway traffic using a car-following model

Based on a car-following model, in this paper, we propose a new traffic model for simulating train movement in railway traffic. In the proposed model, some realistic characteristics of train movement are considered, such as the distance headway and the safety stopping distance. Using the proposed traffic model, we analyse the space-time diagram of traffic flow, the trajectory of train movement, etc. Simulation results demonstrate that the proposed model can be successfully used for simulating the train movement. Some complex phenomena can be reproduced, such as the complex acceleration and deceleration of trains and the propagation of train delay.