具有指数衰减振荡型概率密度变化规律的产品寿命分布模型

传统的机械产品可靠性模型大多忽略了周期性故障引起的概率密度的振荡特征,从而影响了模型的精度.在传统寿命模型的基础上,构建指数衰减振荡分布的可靠性模型及相应的可靠度、失效率以及平均寿命计算模型,并研究衰减系数、振荡幅值和振荡角频率等参数对概率分布特征的影响.运用建立的概率分布模型对某型叉车搭载的液力自动变速箱故障时间数据...     

Study on Microwave Dielectric Property of Carbon Black and Short Carbon Fibers

Carbon black and carbon fibers of different lengths were introduced in different matrices at different ratios to explore their micro-wave dielectric properties under 8.2 GHz-12.4 GHz. It is found that the actual dielectric constants of the samples containing carbon black are in a two-order function of the contents of carbon black (ε′, ε″=Av2 Bv C) and the complex dielectric constants show an obvi-ous frequency response. Of the added fibers of different lengths, the 4 mm-long one could well disperse in the matrices having not only good frequency response, but also larger real parts, imaginary parts and loss values. The imaginary parts and the loss values (tanδ) of the samples with 4 mm-long carbon fibers added increase linearly with the contents of fiber increasing. So it is practicable to adjust the di-electric parameters of the material in a wide range by changing the added amount of carbon black, and the carbon fiber or altering the lengths of the carbon fiber added.     

喷射液束电解-激光复合加工工艺试验研究

喷射液束电解 激光复合加工是一项新探索的加工技术,其特点是既发挥激光加工的高效率,又借助喷射电液束的冷却、冲刷、电解作用而实现在线去除再铸层。基于该加工原理的分析,在对激光电解液中衰减特性研究的基础上,研制了试验系统并对不锈钢片进行了打孔工艺试验。试验结果表明,应用液压1.5 MPa、浓度18%的NaNO₃电解液的喷射液束电解-激光复合加工可实现再铸层减少90%以上。通过对打孔形貌的对比以及加工工艺规律的初步分析,揭示了喷射液束电解-激光复合加工以激光加工为主,电解加工辅助去除再铸层的加工原理,证实了该复合加工工艺的可行性,可望在航空航天领域得到广泛工程应用。     

增益对星载微波辐射计系统线性度的影响分析

针对星载微波辐射计中检波器的工作特性进行分析. 观测固定目标时, 通过调节AGC (Automatic Gain Control)的大小, 定量分析系统伏安特性曲线, 对星载微波辐射计系统线性度进行定性分析. 结果表明, 通过调节AGC大小, 系统增益发生变化, 导致检波器工作区间发生微弱变化, 通过两点定标不能完全消除由于增益引起的非线性误差. 对一定亮温范围的观测目标进行分析, 结果证明, AGC变化时反算亮温与实际目标亮温差值随观测亮温的变化而成非线性变化. 从而证明, 系统增益变化导致的亮温变化通过两点线性定标并不能完全消除. 在系统正常工作或实时定标过程中, 要尽量避免调节AGC值, 保证微波辐射计系统工作在线性区间.      

VHF/UHF波段发射机互调抑制比测试方法研究

建立了发射机射频电路简化模型,并利用该模型和非线性多项式模型,研究了发射机互调(IM)发射电平与射频前端滤波器插入损耗、干扰信号功率和频率偏差之间的关系,对当前发射机互调抑制比的定义进行了修正;分析了传统发射机互调抑制比测试方法的局限性,设计了一种新型的发射机互调测试链路配置,分析了测试链路关键物理参数间的关联关系,建立了测试数据处理模型,该方法扩宽了测试带宽和功率范围,降低了对测试器件的要求。对实际电台的测试结果表明,本文提出的理论分析结论和发射机互调抑制比测试方法正确有效。     

用于辐射计定标源发射率测量的标定方法

针对用于风云系列卫星有效载荷微波辐射计的地面定标的定标源的双站测量系统进行建模,引入与待测的有限大周期方锥阵列定标源结构一致的锥形阵列金属标定体(标定锥),取代常规的标定金属平板(标定板).通过基于三维时域有限差分(FDTD,Finite-Difference Time-Domain)算法和等效时谐场外推理论的仿真,结果显示标定锥具有与定标源相似的散射分布特性,并通过基于天线近场耦合理论的分析,标定锥与定标源具有相近的天线耦合功率密度分布,因此,用标定锥作为标定体可有效地消减由天线口面带来的近场天线耦合的误差.对于文中给定的定标源模型,在不考虑收发天线直接耦合的条件下,采用标定锥取代标定板进行标定可以将定标源发射率的测量精度提高一个数量级.      

Generating precise and homogeneous orbits for Jason-1 and Jason-2

Driven by the GMES (Global Monitoring for Environment and Security) and GGOS (Global Geodetic Observing System) initiatives the user community has a strong demand for high-quality altimetry products. In order to derive such high-quality altimetry products, precise orbits for the altimetry satellites are a necessity. With the launch of the TOPEX/Poseidon mission in 1992 a still on-going time series of high-accuracy altimetry measurements of ocean topography started, continued by the altimetry missions Jason-1 in 2001 and Jason-2/OSTM in 2008. This paper contributes to the on-going orbit reprocessing carried out by several groups and presents the efforts of the Navigation Support Office at ESA/ESOC using its NAPEOS software for the generation of precise and homogeneous orbits referring to the same reference frame for the altimetry satellites Jason-1 and Jason-2. Data of all three tracking instruments on-board the satellites (beside the altimeter), i.e. GPS, DORIS, and SLR measurements, were used in a combined data analysis. About 7 years of Jason-1 data and more than 1 year of Jason-2 data were processed. Our processing strategy is close to the GDR-C standards. However, we estimated slightly different scaling factors for the solar radiation pressure model of 0.96 and 0.98 for Jason-1 and Jason-2, respectively. We used 30 s sampled GPS data and introduced 30 s satellite clocks stemming from ESOC’s reprocessing of the combined GPS/GLONASS IGS solution. We present the orbit determination results, focusing on the benefits of adding GPS data to the solution. The fully combined solution was found to give the best orbit results. We reach a post-fit RMS of the GPS phase observation residuals of 6 mm for Jason-1 and 7 mm for Jason-2. The DORIS post-fit residuals clearly benefit from using GPS data in addition, as the DORIS data editing improves. The DORIS observation RMS for the fully combined solution is with 3.5 mm and 3.4 mm, respectively, 0.3 mm better than for the DORIS-SLR solution. Our orbit solution agrees well with external solutions from other analysis centers, as CNES, LCA, and JPL. The orbit differences between our fully combined orbits and the CNES GDR-C orbits are of about 0.8 cm for Jason-1 and at 0.9 cm for Jason-2 in the radial direction. In the cross-track component we observe a clear improvement when adding GPS data to the POD process. The 3D-RMS of the orbit differences reveals a good orbit consistency at 2.7 cm and 2.9 cm for Jason-1 and Jason-2. Our resulting orbit series for both Jason satellites refer to the ITRF2005 reference frame and are provided in sp3 file format on our ftp server.     

固体火箭发动机排气羽流对微波衰减的计算方法

研究了弱电离的羽流等离子体对平面正弦微波的衰减机理,应用羽流等离子体电磁场标准Maxwell方程,结合颗粒相产物充放电的Shukla方程,给出有效用于微波衰减的预估方法;编制了(Radio fre-quency attenuation calculation,简称RFAC)羽流场微波衰减计算软件;分析了羽流场各特性参数对复电导率及微波衰减常数的影响规律,并结合ThermoCalc推进剂热力学评估系统计算了两种不同推进剂配方下,喷管出口羽流场对微波制导信号的衰减,计算结果与文献中的实验结果符合较好.      

高功率微波武器与反辐射导弹对抗研究

根据反辐射导弹和高功率微波武器的发展现状,从理论和技术上对高功率微波武器与反辐射导弹对抗的可行性进行了初步分析和探讨。     

“嫦娥三号”着陆缓冲机构的研究成果及其应用

“嫦娥三号”着陆器于2013年12月14日通过着陆缓冲机构在月面稳定着陆,表明中国已经突破并掌握了地外天体表面着陆缓冲技术,包括适合地外星体表面环境的缓冲方法、着陆缓冲机构设计方法和地面试验验证方法等。文章介绍了着陆缓冲方法的基本要求,对铝蜂窝缓冲特点进行了研究,提出了着陆缓冲机构关键几何参数确定及缓冲能力设计方法。此外,文章还介绍了着陆缓冲机构地面试验的主要验证项目和验证方案。这些研究成果不仅可以应用到未来火星等目标星体的着陆缓冲,而且在民用技术如桥梁的撞击防护、电梯抗坠毁及爆炸防护等领域中也具有十分广阔的应用前景。了解这些研究成果对于后续深空软着陆探测及相关民用技术的发展具有重要的意义。