缩放管内自旋流强化传热的场协同分析

建立了周期性单元模型,采用数值模拟方法分析了缩放管内带衰减性自旋流的三维湍流流动中的场协同现象,研究轴向不同位置速度场与温度场的演变过程。结果表明,切向速度对强化传热影响很大,自旋流纵向涡使轴向速度和切向速度在同一数量级;自旋流改善了湍流中心区与边壁区流体速度场与温度梯度场的协同程度,使传热得到了强化。     

自持式智能浮标的低功耗悬停控制方法

针对自持式智能浮标悬停精度与能耗之间的矛盾,借助地转海洋学实时观测阵(Array for real-time geo strophic oceanography,Argo)计划所观测的历史数据,提出了一种低功耗的浮标悬停控制方式。由浮标运动学模型可知,悬停时浮标外油囊体积只与悬停深度的海水密度、温度相关,因此利用Argo历史数据对目标海域进行密度、温度拟合曲线提取,得到了悬停深度与外油囊体积的关系。采用遗传算法对悬停过程进行了能耗最优的运动规划,最终得到悬停控制过程的具体运动控制方式。与双闭环模糊PID控制方法和径向基(Radial basis function,RBF)神经网络PID方法对比,在定深精度相当的情况下,所提出的方法能够将能耗降至1/50。最后,利用半实物仿真系统,对上述方法进行了实物验证,在不考虑拟合曲线带来的误差时,悬停的平均误差为2.62 m,能耗为3.214×10⁴J,能耗与理论值的误差仅为0.65%。表明了该方法的有效性和可靠性,以及综合考虑精度和能耗上的优势。     

基于RANS对考虑风向随高度偏转的大气边界层自保持研究

从基本方程出发,通过调整k-ε模型基本参数,对考虑风向随高度偏转的不可压缩中性层结水平均匀稳态正压大气边界层进行了模拟。通过少量网格预前模拟、主模拟和近地面物理量调整三个步骤,对风场的自保持实现方法进行了探讨。研究表明,通过调整k-ε模型基本参数,可以取得与实测较一致的模拟结果。少量网格预前模拟得到的风场应用于主模拟中,各物理量均可以在流域中得到较好的保持。通过ANSYS Fluent中的FixedValues操作进行近地面物理量调整,可以取得更加理想的自保持结果。     

超大直径圆形薄壁地下连续墙围护结构研究

地下连续墙筑成的圆形围护结构,由混凝土来承受其外部荷载作用而产生的环向压应力,具有较好的自身稳定性、较强的整体刚度和较小的径向变形特点,是一种较为经济合理的地下空间结构型式.环球金融中心101层塔楼深基坑工程采用100m超大直径圆形薄壁地下连续墙自立式围护结构,结合这一成功工程实例进行的研究,得出了一些对圆形深基础工程理论研究与设计施工非常有价值的结论.     

高职物理形象法教学中电磁场概念的解读

不同的教学内容可以采用不同的教学方法,作为教学的一种尝试,本文试图采用简单直观的图示法,解说电磁场理论的基本概念,以期避免学生因物理和数学知识的不足而导致理解的困难。     

The Effect of Frequency in the Problem of Interface Crack Under Harmonic Loading

The breakage of a tiny tail on a head of solid glass just removed from a glass bath and treated by fluoric acid (a “Batavian tear") makes the tear explode into a cloud of dust with the sound like that of a shot. This explosion reminds that of TNT but TNT disintegrates into molecules of the order of 10⁻⁹ m while the glass particles of dust are of the order of 10⁻⁶ m and have the same chemical composition as the solid glass. Rock bursts in deep mines of South Africa and Russia represent another example of the sudden, explosive self-destruction. To explain this phenomenon the theory of self-sustaining fracture waves was suggested earlier by Galin and Cherepanov (1966). This theory was based on the analogy with detonation waves later criticized as insufficiently substantiated. The approach presented below is based only on the conservation laws and does not use any analogies. It proves that the self-sustaining fracture wave can propagate only in compressed structures at the speed of longitudinal elastic waves.     

Processing of Fe3Al and FeAl alloys by reaction synthesis

The effects of powder particle size, alloy composition, and reaction atmosphere on reaction synthesis of binary Fe---Al alloys were studied. Reactions were observed in an open (air) furnace, under static vacuum (in an evacuated quartz tube) and in a dynamic vacuum furnace. Reactions occurring in the open furnace and in the evacuated quartz tube were recorded using high-speed video equipment. High-speed videotapes of reaction synthesis of compacts formed from 45 μm Fe and 10 μm Al particles reacted in air and under static vacuum revealed that an unusual ‘two-stage’ reaction exists in this system under these conditions. Compacts formed from 9 μm Fe and 3 μm Al powder particles do not exhibit a two-stage reaction under any of the conditions examined in this work. The first stage of the two-stage reaction lasts several seconds and starts at round 650 °C. The second stage begins at about 900 °C, reaching temperatures between 1250 and 1350 °C. The progress of the reaction to the second stage is sensitive to the alloy composition and reaction atmosphere. The reaction behavior is explained in terms of thermodynamics and heat transfer, which control the delicate balance between heat accumulation and heat loss during reaction synthesis.     

几例乌托邦式建筑实例剖析

建筑需要创造力,更需要深刻地揭示和探索更本质的东西,需要从更高角度和更广阔的视角进行乌托邦式的构想;而这些构想源于社会、科技和城市问题,源于对自然要素的体验.     

The feasibility of synthesis tungsten nitride in magnesium‐tungsten oxide‐melamine ternary system via mechanochemical method

Different routes have been investigated to synthesize tungsten (W) – tungsten nitride (W₂N) nanocomposite powder by mechanochemical method in magnesium–tungsten oxide–melamine ternary system. In stoichiometric mixture, reduction of tungsten oxide by magnesium took place after 30 minutes of milling in mechanically induced self‐sustaining reaction (MSR). A large amount of heat generated from magnesiothermic reaction, makes the used melamine unstable which causes the formation of undesirable tungsten carbide phase. By separating magnesiothermic reduction from nitride formation reaction, no thermal degradation of melamine occurred; however, milling alone has not brought much change in the used melamine to form tungsten nitride. Dispersion of reaction heat by adding magnesium in three‐stages (during 3 hours of milling) has been capable of preparing maximum value of tungsten nitride phase. According to scanning and transmission electron microscope images, the range of particle size was within 100 nanometer.