Assessment of the consequences of the Fengyun-1C breakup in low Earth orbit

On 11 January 2007, the People’s Republic of China conducted a successful anti-satellite test against one of their defunct polar-orbiting weather satellites. The target satellite, called Fengyun-1C, had a mass of 880 kg and was orbiting at an altitude of about 863 km when the collision occurred. Struck by a direct-ascent interceptor at a speed of 9.36 km/s, the satellite disintegrated, spreading the cataloged fragments between 200 and 4000 km, with the highest concentration near the breakup height. By the end of April 2008, 2377 pieces of debris, including the original payload remnant, had officially been cataloged by the US Space Surveillance Network. Of these, nearly 1% had reentered the Earth’s atmosphere. This deliberate act is the largest debris-generating event on record, and its consequences will adversely affect circumterrestrial space for many years.     

堆焊在液压支架立柱中缸中的应用

分别采用CO2气体保护焊和埋弧自动焊对立柱中缸活塞段进行了堆焊试验研究,确定了合理的工艺流程和焊接规范参数,为中缸活塞段采用堆焊新工艺代替整体加工的旧工艺提供了技术支持。     

机床立柱高比刚度结构仿生设计

提高机床运动结构的比刚度对于提高机床加工精度以及系统动力学性能具有重要作用.基于结构仿生的原理和方法,在分析骨架对生物体刚度的贡献以及体现了最佳的载荷路径这一思想的基础上,对叶片抛磨机立柱内部的筋板结构进行重新设计,使其发挥骨架的作用.对原型及仿生型立柱进行了静力、模态及瞬态动力学分析,经过有限元分析发现,立柱的质量减小,比刚度结构效能得到了较大的提高,其静动力学性能也有明显的改善.      

垂直对天顶测量的紫外前向散射探测臭氧总量的可行性研究

选用SBDART模式作为大气辐射传输计算模式,通过模拟计算和结果分析探讨无云的晴天、垂直对天顶观测的紫外前向散射反演大气臭氧总量的可行性.计算表明,穿透能力与探测灵敏度之间的复杂联系使得探测波长应随着sΩ0的增大而波长变长,若用波长对探测,则波长对中较短的波长也应随着sΩ0的增大而增大.另外大气的臭氧总量越少,反演结果受下垫面反照率、气压和仪器精度的影响越大,因而反演误差越大.当强度Ii的测量精度为±1%时,下垫面反照率R和气压P0的分辨率分别达到±0.05和±50 hPa,若用单波长探测,则在大气臭氧总量Ω0和s都较小时,反演结果大于5%;若选用波长对进行探测,由于R和P0的误差对反演结果的影响降低,故精度大大提高.Ii,R和P0在上述精度下,选取适当的波长对进行探测,精度至少可达±4%,当臭氧总量高于350 DU时,可达±2%.      

在落震试验中起转和回弹载荷的模拟情况对试验结果的影响

起转和回弹载荷的模拟是影响起落架落震试验结果的重要因素。通过在立柱式落震试验台上进行不同模拟跑道的起落架带转落震试验,得到了某些典型起转和回弹载荷模拟情况下的落震试验结果。通过对这些落震试验结果进行分析和讨论,得出了在立柱式落震试验台上进行落震试验时合理的起转和回弹载荷的模拟方式。研究结果表明 :在立柱式落震试验台上进行起落架落震试验时,使用合理的起转和回弹载荷的模拟方式,可以将机轮与模拟跑道之间定点摩擦对试验结果的影响减到最小。     

柱形等离子体辐射场的数值计算和分析

参照金属辐射场的求解方法,在简化条件下计算出柱形等离子体行波传输和驻波传输的辐射图．当改变等离子体密度以及相关参数时,对应的辐射图会相应地发生变化,得出与信号在金属介质中传输相类似的结果．根据理想柱形等离子体表面波的色散关系得到波矢,求出的柱形等离子体辐射方向图与金属介质的辐射方向图相比,会发生较大的变化,因此利用等离子体进行信号传输有一定的价值．     

Space Debris Reentry Analysis Methods and Tools

The reentry of uncontrolled spacecraft may be broken into many pieces of debris at an altitude in the range of 75-85 km. The surviving fragments could pose great hazard and risk to ground and people. In recent years, methods and tools for predicting and analyzing debris reentry and ground risk assessment have been studied and developed in National Aeronautics and Space Ad-ministration (NASA), European Space Agency (ESA) and other organizations, including the group of the present authors. This paper reviews the current progress on this topic of debris reentry briefly. We outline the Monte Carlo method for uncertainty analysis, breakup prediction, and parameters affecting survivability of debris. The existing analysis tools can be classified into two categories, i.e. the object-oriented and the spacecraft-oriented methods, the latter being more accurate than the first one. The past object-oriented tools include objects of only simple shapes. For more realistic simulation, here we present an object-oriented tool debris reentry and ablation prediction system (DRAPS) developed by the present authors, which introduces new object shapes to 15 types, as well as 51 predefined motions and relevant aerodynamic and aerothermal models. The aerodynamic and aerothermal models in DRAPS are validated using direct simulation Monte Carlo (DSMC) method.     

双悬臂式三坐标测量机误差补偿研究

根据双悬臂式三坐标测量机的结构特点,在刚体模型的基础上推出测量机的非刚体模型的误差补偿公式。通过对横梁和立柱的受力分析,推导出附加函数的回归方程,从而确定整机的误差补偿模型。最后补偿结果证明误差公式能有效进行补偿。     

火箭发动机燃气射流驱动液柱降噪实验

为了研究单兵火箭燃气射流噪声抑制的方法,设计了液体水柱放置在尾管中,采用高速摄影系统观察了高温高压燃气驱动液体水柱在大气环境中的扩散过程,并对气液混合物射流噪声声压进行了测量,对比了有无液体水柱两种状态下射流的测试结果.实验结果表明,在尾管中放置液体水柱后,由于气液之间的相互作用,改变了燃气射流流场结构以及降低了射流特征参数.通过与无液体水柱的燃气射流对比,发现有液体水柱时整个测点区域的噪声声压级峰值均有较大幅度的降低,且地面对声波的反射也减弱,噪声声压级峰值随着测点偏离射流中心轴线角度的增大而逐渐减小.因此,放置液体水柱后起到了明显的降噪效果,在偏离角为45°位置声压级峰值降低了6.4dB,验证了此方案的可行性.      

高速水流冲击弹性边界结构问题的试验研究

针对水下航行体出水过程空泡溃灭问题,依据水发射试验装置,设计一套试验方案,研究高速水流冲击弹性边界结构的现象.研究结果表明:高速水流冲击弹性边界时,随着弹性边界工装厚度的增加,压力脉冲脉宽逐渐减小,压力脉冲幅值逐渐增大,其增大部分主要是由于刚度较大产生的高频振荡部分.将数据分析频率窗口降低至500Hz,去掉高频振荡成分...