改进的Whipple防护结构与相关数值模拟方法研究进展

基于弹丸在超高速撞击薄板时破碎形成碎片云的机理,Whipple防护结构能够对航天器所面临的空间碎片及微流星体等威胁形成有效防护。通过回顾Whipple防护结构的研究和发展历程,对多层板结构、填充式防护结构、夹芯板结构等进行对比,分析其力学效应和防护性能;总结可应用于含泡沫、蜂窝、梯度和编织等材料的防护结构超高速撞击的数值模拟方法及其改进方法;结合相关材料的超高速撞击试验及数值模拟结果,为防护结构未来的研究方向提出建议。     

用于空间碎片清除的高功率激光器（英文）

虽然人类的太空活动已经考虑了尽量减少空间碎片的措施,但近地轨道碎片的数量仍呈指数增长,特别是中小型碎片的现有数量已对在轨卫星构成了实质性的威胁。作为具有较高期待的消除碎片办法,用地基DF激光器和空基Nd∶YAG激光器消除碎片的方案令人关注,它们可以以低成本和非破坏性的方式清除空间轨道的危险碎片。本文介绍了使用平均功率为100 kW的高功率、高重复频率P-P Nd∶YAG激光器和平均功率约为1.5 MW的DF激光器来保护在轨飞行器和清除直径为1～10 cm空间轨道危险碎片涉及的相关工作。     

"神舟"五号的空间环境保障

空间环境安全保障是载人航天器飞行安全和航天员生命安全保障的一个重要部分．文章从高层大气、高能辐射环境、流星体空间碎片和重大空间环境扰动事件等四个方面空间环境要素对载人航天的影响，介绍了空间环境预报中心为“神舟”五号载人飞行任务所作的空间环境保障工作．     

Determination of the debris produced from poly(ethylene terephthalate) during KrF excimer laser ablation

Pulsed UV laser beams, which are widely used in the processing of polymers, have many advantages because their photon energy is higher than the binding energy of polymers. Fabricating polymers with a UV laser process is faster, cleaner, and more convenient than with other processes. Nevertheless, some problems occur in the precision microprocessing of polymers. For example, the formation and deposition of surface debris, which is produced from the breakdown of either polymer chains or radical bonds.To determine the formation and origin of surface debris, a KrF excimer laser beam (248 nm) was used in the processing of poly(ethylene terephthalate) (PET). The investigation of the debris formation was facilitated by UV-vis spectroscopy, ATR FT-IR spectroscopy, and NMR spectroscopy. The UV-vis absorption peak indicates that the primary chromophore in the PET is benzoate. Furthermore, because benzoate causes the primary absorption, the absorbed energy is transferred by heat generation to an unsaturated ester. The ATR FT-IR spectrometer measurements show that the phenyl systems in the benzoate are demolished by ablation. This phenomenon indicates that the photochemical reaction causes the benzoate bonds to break down, and this breakdown in turn causes the carbonization to leave debris on the PET.     

Experimental study of transient heat transfer characteristics of single-phase natural convection in multidimensional porous bed with volumetric heat generation

Natural convection in an internally heated porous bed of height and diameter of 450 mm and 500 mm, respectively, and superposed with the fluid layer has been experimentally investigated. The onset of natural convection in the bed is indicated by change in the rate of temperature rise within the bed. An empirical model based on local Nusselt number and local Rayleigh number has been developed. A comparison of the present model with the models in literature is made to draw out the differences between the local heat transfer of large multidimensional beds and the average heat transfer of small beds.     

Modeling method and preliminary model of Asteroid Toutatis from Chang’E-2 optical images

Shape modeling is fundamental to the analysis of dynamic environment and motion around asteroid. Chang＇E- 2 successfully made a flyby of Asteroid 4179 Toutatis and obtained plenty of high-resolution images during the mis- sion. In this paper, the modeling method and preliminary model of Asteroid Toutatis are discussed. First, the optical images obtained by Chang＇E-2 are analyzed. Terrain and silhouette features in images are described. Then, the modeling method based on previous radar model and preliminary information from optical images is proposed. A preliminary polyhedron model of Asteroid Toutatis is established. Finally, the spherical harmonic coefficients of Asteroid Toutatis based on the polyhedron model are obtained. Some parameters of model are analyzed and compared. Although the model proposed in this paper is only a preliminary model, this work offers a valuable reference for future high-resolution models.     

Tunable magnetophoretic method for distinguishing and separating wear debris particles in an Fe-PDMS-based microfluidic chip

Wear debris analysis provides an early warning of mechanical transmission system aging and wear fault diagnosis, which has been widely used in machine health monitoring. The ability to detect and distinguish the ferromagnetic and nonmagnetic debris in oil is becoming an effective way to assess the health status of machinery. In this work, an Fe-poly(dimethylsiloxane) (PDMS)-based magnetophoretic method for the continuous separation of ferromagnetic iron particles by diameter and the isolation of ferromagnetic particles and nonmagnetic particles with similar diameter by type is developed. The particles experience magnetophoretic effects when passing through the vicinity of the Fe-PDMS where the strongest gradient of the magnetic fields exists. By choosing a relatively short distance between the magnet and the sidewall of the horizontal main channel and the length of Fe-PDMS with controlled particles flow rate, the diameter-dependent separation of ferromagnetic iron particles, that is, smaller than 7 µm, in the range of 8–12 µm, and larger than 14 µm, and the isolation of ferromagnetic iron particles and nonmagnetic aluminum particles based on opposite magnetophoretic behaviors by types are demonstrated, providing a potential method for the detection of wear debris particles with a high sensitivity and resolution and the diagnostic of mechanical system.     

泥石流研究述评

泥石流这一特殊的二相流体是山区常见的一种自然灾害,一般可分为稀性泥石流(颗粒碰撞及离散力起主导作用)和粘性泥石流(粘性力起主导作用)两大类。本文概略地评述了泥石流的几个问题,即泥石流形成学、分类学、动力学等,指出急需解决的问题有泥石流汇流理论、泥石流阻力规律等。文中还根据近年来的动态和趋向,推断更加深入的理论研究和以数学模型为核心的泥石流流域管理模式将会成为泥石流学科发展的主要方向。      

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根据实验结果,将泥石流的流变关系分为稀性和粘性泥石流两类情况进行了分析,并由流变模型绘出明渠中泥石流的垂向速度分布．     

泥石流反粒径分布的一种定性解释

假设泥石流中的粗颗粒（如石块等）以跳跃的方式前进,通过分析单个颗粒在定常充分发展的流场中的运动,给出了单一起跳速度下以及具有一定分布的起跳速度下,颗粒数密度随高度的分布,并给出了起跳粒径有分布时颗粒的平均粒径随高度的分布,定性地解释了泥石流中的反粒径分布现象。