单喷管火箭自由喷流噪声数值模拟

利用非定常燃气流场数值模拟方法，研究超声速喷流核心区及其外围亚声速区燃气流动态分布和流动特性，在此基础上利用欧拉方程条件的伽辽金有限元方法以及FWH方法，实现并完成喷流噪声传播特性、辐射特性数值模拟。喷流噪声数值模拟结果显示：燃气流推进初期，强喷流噪声区域紧随燃气流前锋；燃气流场相对稳定后，强喷流噪声区域主要位于燃气流等能区末稍，一些小尺度试验的燃气流激波系附近也存在较强喷流噪声。这些强喷流噪声主要由燃气流前锋带动的大涡动态卷吸、燃气流强湍流脉动以及激波扰动引起。受数值模拟网格分辨率影响，当前仅能保持中低频段声压级数值模拟结果与实测结果总体接近。     

Viscoelastic characterization of polymers for deployable composite booms

Deployable space structures are being built from thin-walled fiber-reinforced polymer composite materials due to their high specific strength, high specific stiffness, and designed bistability. However, the inherent viscoelastic behavior of the resin matrix can cause dimensional instability when the composite is stored under strain. The extended time of stowage between assembly and deployment in space can result in performance degradation and in the worst case, mission failure. In this study, the viscoelastic properties of candidate commercial polymers consisting of difunctional and tetrafunctional epoxies and thermoplastic and thermosetting polyimides were evaluated for deployable boom structures of solar sails. Stress relaxation master curves of the candidate polymers were used to predict the relaxation that would occur in 1 year at room temperature under relatively low strains of about 0.1%. A bismaleimide (BMI) showed less stress relaxation (about 20%) than the baseline novolac epoxy (about 50%). Carbon fiber composites fabricated with the BMI resin showed a 44% improvement in resistance to relaxation compared to the baseline epoxy composite.     

光电编码器模拟测速机在转台控制系统中的应用

在转台的可靠性设计中, 常用测速机输出作为转台限速报警的触发信号, 但传统的测速机在安装、成本及精度上都不具有优势。利用美国AD 公司生产的AD650 芯片,对被广泛用于转台测角系统中的Heidenhain 公司的RON886C 型增量式旋转编码器 信号进行电压频率(V/ F) 和频率电压(F/V) 转换, 实现利用编码器输出模拟测速机电路, 不仅可以满足限速保护要求,并且较测速机具有成本低,安装使用方便,且精度较高的 优点,在实际应用中效果良好。     

复合材料桁架胶接装配技术

叙述了某型号卫星碳纤维复合材料桁架胶接装配过程的配套条件、工艺方法和质量控制等内容.研究表明,杆件和接头的配合间隙介于0.1～0.3 mm时胶接强度较高;桁架的精度完全依靠高精度胶接工装保证,且最终精度能控制在0.2mm之内;合适的工艺方法和质量控制方法,能够满足碳纤维桁架结构的高精度和胶接质量要求,并且这些方法具有通用性.     

基于FM-1密封材料低温性能研究

氟醚材料因其优良性能,广泛地应用于航天产品密封,文章选取火工装置常用的FM-1密封材料作为研究对象,着重研究了其低温性能数据。通过设计试验测量了低温下FM-1材料密封圈的回弹性数据和回弹量随时间变化的曲线,并通过进一步计算得出了低温下的FM-1材料密封圈压缩率远低于设计值的结论,这会对密封性造成较大影响。最后,结合火工装置实例分析了低温下密封圈对火工装置工作性能的影响,通过研究发现虽然低温对密封圈回弹性有较大影响,但对整体密封性影响有限。     

Signatures of the Sudden Stratospheric Warming events of January–February 2008 in Seoul,S. Korea

The period January–February 2008 was characterized by four Sudden Stratospheric Warmings (SSWs) in the Northern Hemisphere, of which the last warming, at the end of February 2008, was a major warming. A significant decrease in mesospheric water vapour (H₂O) of more than 2 ppmv (∼40%) was observed by the ground-based microwave (GBMW) radiometer in Seoul, S. Korea [37.3°N, 126.3°E] during the major SSW. A comparison with ground-based mesospheric H₂O observations from the mid-latitude station in Bern [46.9°N, 7°E] revealed an anticorrelation in the mesospheric H₂O data during the major SSW. In addition, prior to the major warming, strong periodic fluctuations were recorded in the Aura MLS vertical temperature distribution between 15 and 0.05 hPa at Seoul. The mesospheric temperature oscillation was found to have a period of ∼10–14 days with a persistency of 3–4 cycles.     

机载嵌入式软件可靠性设计研究

机载航电系统的可靠性问题越来越受到关注,软件可靠性设计要抓住两个方面,软件开发过程和软件开发方法。本文根据机载嵌入式系统软件的特点,讨论了软件开发过程在可靠性方面的考虑,还有在需求、设计、编码阶段使用的相关设计方法和技术。     

一种从混合表面的明暗变化恢复形状的新算法

针对传统的混合表面形状恢复算法存在较大误差的问题,提出了一种基于透视投影的从混合表面的明暗变化恢复形状的新算法.首先,建立了一种改进的Ward反射模型来描述混合表面的反射特性,其次,采用更接近摄像机实际拍摄的透视投影方式,并且假定光源位于摄像机的光心处,构造了新模型下的图像辐照度方程,然后将该方程转化为包含物体表面深度信息的Hamilton-Jacobi偏微分方程,使用Fixed-point Iterative Sweeping方法和2D Central Hamiltonian函数逼近该微分方程的黏性解,进而得到物体表面的三维形状.与同类算法相比,新算法恢复的结果更加准确有效.合成花瓶图像的实验结果表明,与基于正交投影的算法相比,新算法恢复三维形状高度的平均误差和均方根误差均有较大幅度减少.