基于高斯过程回归的大气进入段航天器飞行能力预测方法

轨迹优化技术是目前大气进入段研究的关键技术之一,如何在大气进入动力学复杂、航天器设计参数各异以及进入过程多约束的条件下,对进入轨迹性能参数进行评估是轨迹设计研究的重要问题。对此,以二维落点走廊为表征的大气进入段最大飞行航程作为性能指标,针对传统轨迹优化方法求解计算量庞大的问题,提出了一种基于高斯过程回归(Gaussian process regression, GPR)的大气进入段航天器飞行能力快速预测方法,挖掘航天器进入初始轨迹参量与轨迹包络特征参量之间的映射关系,求解航天器最大航程时避免了复杂的动力学建模以及大规模的迭代寻优过程。利用所提方法对1 000余组不同进入场景的进入轨迹最大航程进行快速预测,将预测结果用于进入段航天器飞行能力评估,为解决大气进入领域相关工程问题提供参考。     

大气环境中的亚轨道飞行器再入轨迹仿真

针对亚轨道再入飞行器的高精度轨迹仿真问题,采用了国际上最新的NRLMISISE00大气模式、HWM93水平风场建立了大气参数模拟系统,比较分析了不同模式下影响飞行器运动特性的各种大气参数的区别;利用查普曼公式建立了大气环境中亚轨道再入飞行器的运动方程;结合美国X-33演示验证实验样机,仿真分析了各种大气参数对亚轨道再入飞行器运动参数的影响.研究表明,大气环境对于再入飞行器的影响不容忽略,在实际应用中应该根据具体的任务需求来选择合理的大气模型.     

Penning阱中品质因数的提高

在Penning阱中提高品质因数对得到较高探测灵敏度和分辨率的离子谱有重要意义,本文对提高品质因数的可行性进行了分析,找到了提高品质因数的方案．     

Record of environmental change by α-cellulose δ13C of sphagnum peat at Shennongjia, 4000―1000 aBP

The Dajiuhu Basin at Shennongjia, located within typical East Asian Monsoon region, preserves a sub-alpine sphagnum peat deposition in its central area. The topmost 120 cm of the peat covers the last 4000 years according to AMS ^14C dating of pollen concentration. Carbon isotope of a-cellulose, extracted from sphagnum peat, provides a quantitative reconstruction of atmospheric relative humidity, based on transfer functions of C3 plants carbon isotopic fractionation equation and the bryophyte photosynthesis CO2 absorption rate equation. δ^13C, TOC and C/N variations reveal that the Dajiuhu area has experienced a long-term tendency to dry during 4000-1000 aBP, with a major transition happening around 3000 aBP. Four relative dry events are identified at 3400-3200, 3000-2600, 2200-2000 and 1600-1400 aBP, respectively, corresponding to those climate events documented in many global records. Three periodicities, 664 a, 302 a and 277 a enclosed in the atmospheric humidity of Dajiuhu are correlated to the cycles of solar activities. The weakening of East Asia summer monsoon during this period registered in the Dajiuhu peat is consistent with the synchronous weakening of Indian Monsoon. This trend may be attributed to gradual decrease of Northern Hemispheric summer solar insolation and the consequently southward migration of Intertropical Convergent Zone （ITCZ）.     

Effect of different atmospheres on dry friction behavior of steel sliding against brass at high speed

The atmosphere components have an influence on tribological behaviors of tribo-pairs. Through changing the atmosphere component, the effect of atmosphere component on the tribological behaviors of CrNiMo steel against brass at high sliding velocity was investigated. The wear test was carried out on a high-speed friction and wear test rig whose test atmosphere could be controlled. The tests were performed at four sliding velocities （30, 40, 50, 60 m/s）, one contact pressure （1.33 MPa） and two atmosphere components （N2 or O2）. The morphologies of the worn surfaces of various pins were observed with a scanning electron microscope. The chemical compositions of the surfaces and subsurfaces for steels were determined with an energy dispersion spectroscopy. The results showed that the wear rate of the steel pins were low all the time with the sliding velocity increasing in oxygen atmosphere, and that the wear rate of the steel pin in nitrogen atmosphere was higher than that of the steel pin in oxygen atmosphere. It was found that the thin and compact oxidation layer formed on the worn surface of the steel in oxygen atmosphere played a key role in wear resistance. However, the wear rate of the steel pin increased rapidly with the sliding velocity increasing in nitrogen atmosphere, which was attributed to the thick and loose surface layer formed on the worn surface of the steel.     

基于Mie理论的四种典型水云的光散射计算

在Mie理论的基础上,利用修正伽马函数来描述水云的粒子尺度分布,计算了一类层云、二类层云、一类层积云和二类层积云这四种典型水云的消光系数、单次散射反照率、不对称因子和散射相函数.结果表明,粒子的消光系数、单次散射反照率和非对称因子随着入射波长的增加有较大的起伏,后两者随着波长的增加其变化趋势基本一致;消光系数主要受云中液态水含量的影响;对于单次散射反照率来说,在可见光波段,反照率非常接近于1;在短波段,粒子的非对称因子变化较小,并且随着波长的增加,非对称因子会逐渐增大;Mie相函数随着散射角的增加呈现出先减小后增大的趋势,但相函数随着波长的增加,并没有呈现出简单的线性关系.     

数字化机载武器控制系统半实物仿真平台研究

基于HLA的框架和标准,设计了联邦的模型和各联邦成员,完成了由实时计算机、配线矩阵及信号调理单元、错误注入及中断单元组成的实时仿真部分和基于HLA的分布式数字仿真部分的开发,提出了基于软实时计算的方案对实时信息进行处理,并对实时仿真条件下HLA的时间管理机制和消息传递方式等关键问题进行了研究.仿真结果表明,该平台很好地实现了系统的仿真与测试.     

基于独立成分分析的超低频电磁探测信号滤波

将独立成分分析方法引入到超低频电磁探测曲线的滤波中。首先运用模拟数据来探讨运用独立成分分析方法进行滤波的可行性,然后运用实际的观测数据对基于独立成分分析的滤波方法进行了评价和比较。结果表明,运用独立成分分析方法进行探测曲线的噪声滤除是可行的,而且该方法可有效地滤除噪声、突出曲线的特征,有利于曲线的地质解译。同时,对相关问题进行了讨论。     

戈壁下垫面空气动力学参数确定的再研究

提出一种确定地表粗糙度z₀的方法。该方法仅需利用精细风廓线资料进行计算,误差较小,尤其适用于近中性层结观测较困难的情况。根据2006年夏季河西走廊戈壁地区的大气边界层观测资料,利用该方法确定的z₀为0.60mm左右,和前人方法计算结果0.78mm接近,证实了此方法和z₀数值的可靠性和可信度。此外,由于不同测量高度代表不同区域尺度上的特征,地表粗糙度的确定还应考虑风廓线的观测高度及分布状态。     

Q235碳钢在西沙大气暴晒的锈层特征

在西沙群岛高温、高湿的海洋大气环境下对Q235碳钢进行了3个月的暴晒实验,利用电子探针、激光拉曼等观察分析了暴晒后样品的锈层特征. 结果表明:Q235碳钢暴晒1个月后迅速形成较厚的锈层,锈层疏松多孔,多裂纹;当暴晒3个月时,锈层却明显减薄. Q235碳钢在西沙暴晒1个月后形成的外层腐蚀产物主要是γ-FeOOH、β-FeOOH、α-FeOOH及少量Fe3O4等,而锈层内部主要为Fe3O4、γ-Fe2O3等铁的氧化物. 暴晒3个月后,疏松锈层的内部电解液蒸发加剧,内层还原后的锈层重新被氧化,生成较多的FeOOH,同时部分γ-FeOOH转化成为α-FeOOH. Q235碳钢在西沙大气环境下的暴晒过程(也就是锈层的氧化还原反应的交替过程)中,钢基体不断地被腐蚀.