Plume aerodynamic effects of cushion engine in lunar landing

 During the second period of China "Tanyue" Project, the explorer will softland on the moon. The cushion engines are used to decelerate the explorer and reduce the impact on the lunar ground. It is necessary to study its plume effects on the explorer component. The self-developed PWS (Plume WorkStation) software based on direct simulation Monte Carlo (DSMC) method is used to simulate the plume effects of two 150 N engines. Due to the complex structure of the explorer, PWS uses a decoupling method to treat the boundary mesh, which mainly interacts with simulation particles, and has no relation with the computational grids. After the analytical expressions of plane surfaces and curved surfaces of each boundary block are given, the particle position within or without the boundary blocks can be easily determined. Finally the 3D plume field of two 150 N engines is simulated. The pressure, temperature and velocity distributions of plume field are clearly presented by three characteristic slices. The aerodynamic effects on the explorer bottom, the landfall legs and antenna are separately shown. The compression influence on the plume flow of four landfall legs can be observed.     

浅议大学生讲诚信

近年来诚信缺失普遍存在于社会生活各个领域,甚至影响到在校的大学生,因此加强高校自身诚信环境建设,加强对学生的诚信意识教育,完善社会信用评价体系,建立学生个人信用档案,使大学生树立诚信理念和准则,肩负起时代赋予的历史使命,具有十分重要的意义。     

粉末涂装系统的选择及维护

如果对粉末涂装系统技术或合作缺乏足够认识，生产不出高质量的产品，势必有被淘汰的一天。本文叙述了粉末涂料、喷粉设备、施工环境及设备使用维护等有关问题，以帮助使用者作出正确地选择。     

Impact effects from small size meteoroids and space debris

When the impact risk from meteoroids and orbital debris is assessed the main concern is usually structural damage. With their high impact velocities of typically 10–20 km/s millimeter or centimeter sized objects can puncture pressure vessels and other walls or lead to destruction of complete subsystems or even whole spacecraft. Fortunately chances of collisions with such larger objects are small (at least at present). However, particles in the size range 1–100 μm are far more abundant than larger objects and every orbiting spacecraft will encounter them with certainty. Every solar cell (8 cm² area) of the Hubble Space Telescope encountered on average 12 impacts during its 8.25 years of space exposure. Most were from micron sized particles.     

Comparative study between crack closure model and Willenborg model for fatigue prediction under overload effects

A comparative study is performed between a crack closure model and the Willenborg model, which can calculate the fatigue crack growth rate under the overload effects. The modified virtual crack annealing (VCA) model is briefly reviewed, which is based on the equivalent plastic zone concept. In this method, the retardation phenomenon is explained by the crack closure level variation, which is derived from the interactions between forward and reverse plastic zones ahead of the crack tip. As a comparison, the Forman equation in conjunction with the Willenborg model is also reviewed. The retardation phenomenon is described by directly modifying the stress intensity factor. It is known that the large plastic zone created by the overload can decelerate the fatigue crack growth rate until the crack grows beyond this region. A relationship between the plastic zone and the modified stress intensity factor is developed, which is a mathematical fitting equation instead of physical-based formulation. The experimental data in aluminum alloys are used to val-idate these two models. Overall, good agreement is observed between the model predictions and the testing data. It is noted that the approach based on modified VCA model can give more accurate prediction curves than the Willenborg model.     

Technology review of aeroengine pollutant emissions

The Environmental effects issue of air traffic has been gaining increasing public attention. This has led to a considerable world-wide effort to reduce aircraft emissions. The task encompasses a broad variety of scientific and technological problems which are reviewed.The concerns about atmospheric effects have been based largely on laboratory information and experience from weather and climatic simulations. Research carried out over the past few years will improve the understanding of physical and chemical interaction phenomena and will support regulatory activities. Operational changes of airline flight profiles would be of benefit to the reduction of NO_x released into the stratosphere but would probably involve a major economic penalty. Emissions reductions through improved engine technology offer an overall potential of 10 % lower fuel burn but will also require a considerable component development effort and investment.Combustion technology appears most promising and industry is concentrating research in this area. Over the past two decades smoke emissions have become negligible and oxides of nitrogen have been reduced by 50 %. Staged combustion and emerging lean premix and rich-burn quick-quench lean-burn technologies are potentially good for another 50 % reduction. Alternative gaseous fuels will become of interest only in the context of a necessity to generally replace crude oil fuels.     

我国国债宏观经济效应的实证研究

采用多元Granger因果测试模型和1980～2003年的相关数据实证检验我国国债的宏观经济效应。实证结果表明，我国国债融资实际上并未对宏观经济产生显著影响。这主要是因为我国利用国债融资的时间较短，国债的宏观经济效应尚未显现；利用国债融资的多为基础设施项目，周期较长，真正发挥效应尚需一段时间；尤其是国债资金管理不到位，使得国债融资未对实体经济作出积极贡献。因此，政府当务之急是完善国债投资管理和审批体制，增加国债资金运用的透明度，加大对国债资金管理和使用的监督和检查力度，提高国债项目的投资效益。     

奥运会对北京经济的挤出效应

举办2008年奥运会,是发展北京经济强有力的助推器,对北京经济具有巨大的提升作用.然而,奥运对北京经济同时也具有不利的影响--挤出效应.文章具体分析了奥运对北京经济的挤出效应,以便更好的利用这次机遇促进北京经济的进一步发展.     

压力探针临壁效应的试验研究

在窄通道中测量时（如全台压气机试验），临壁效应会使压力探针的测量结果发生误差。对几种常用型式的压力探针的试验研究表明，由于探针多属非流线形物体，所以其临壁效应的机理与流线形的机翼不同，不应简单套用机翼临壁效应的结论。临壁效应所造成的测量误差与探针的形状有关。     

论疲劳短裂纹

 <正> 1.裂纹扩展阶段划分及影响因素 总结已有的实验分析表明,影响短裂纹扩展的可能因素有:(1)微观结构因素和微观力学因素;(2)力学因素和环境因素。微观因素是影响晶粒量级裂纹扩展的主要因素;远大于晶粒量级的裂纹则主要受宏观因素的影响。因此将短裂纹按其控制因素的性质分为微观结构短裂纹(MSC)和物理短裂纹(PSC)较为科学(图1)。 通过对许多实验结果的分析表明:MSC的上界视局部应力,晶界和夹杂的性质等的不同为1～3M(M为微观结构特征尺寸)。