等离子-物理气相沉积硅/莫来石/硅酸镱环境障涂层的高温防护和耐热冲击性能研究

通过SiCf/SiC复合材料表面等离子喷涂(APS)硅黏结层和莫来石中间层,等离子-物理气相沉积(PS-PVD)制备硅酸镱面层,喷涂的整个环境障涂层体系组织致密,PS-PVD工艺制备的硅酸镱为层状结构,孔隙率＜1％.研究了 SiCf/SiC复合材料环境障涂层的抗静态氧化、循环氧化、水汽腐蚀和热冲击性能,发现复合材料表面...     

地面实验室模拟空间等离子体环境的初步测试

空间等离子体和航天器的相互作用对航天器的安全有重要影响，利用空间实验来研究这些作用的代价很大，可以通过在地面实验室中模拟空间等离子体环境来低成本地研究这些相互作用。本研究通过使用ECR等离子体源期望在地面实验室来近似模拟空间等离子体环境。通过初步测量，我们得到了一个比较均匀的等离子体环境。     

CO2气体保护焊的波形模糊逻辑控制的方法

针对CO2气体保护焊恒流特性控制中弧长稳定性差问题,提出了弧长的波形模糊逻辑控制方案,介绍了波形控制系统工作原理和模糊逻辑控制器设计方法,并进行了试验研究.研究结果表明,此波形模糊逻辑控制系统完全实现了弧长恒定控制,得到焊接过程稳定,飞溅小和焊缝成形好等优良的工艺性能.     

In situ measurements of ionospheric plasma turbulence over five frequency decades: Heritage flight of the Plasma Local Anomalous Noise Experiment (PLANE)

Observations of ionospheric plasma density and frequency-dependent broadband plasma turbulence made during the heritage flight of the Plasma Local Anomalous Noise Experiment (PLANE) are presented. Rather than record high frequency time series data, the experiment was designed to record Power Spectral Distributions (PSDs) in five decadal frequency bins with upper limits ranging from 1.0 Hz to 10 kHz. Additionally, PLANE was designed distinguish turbulence in the ambient plasma from that local to the spacecraft. The instrument consists of two retarding potential analyzers (RPAs) connected together via a feedback loop to force one analyzer into the I–V trace retardation region at all times. Fluctuations in this measurement are believed to be ambient only as the RPA’s voltage would be too high for locally turbulent plasma to surmount the potential barrier, which is nominally at ram energy. The instrument requires pointing along the spacecraft’s ram velocity vector to make this measurement, thus requiring stabilization in pitch and yaw. During PLANE’s heritage flight, though the satellite’s attitude control system failed early in the mission, plasma data were collected during opportune times in which the instrument rotated into and out of the ram. Observations of plasma density and PSDs of high frequency plasma turbulence were recorded on several occasions. Additionally, a plasma source onboard the satellite was used to generate artificial plasma turbulence, and the PLANE data observed periodic structure presumably associated with the rotation of the spacecraft during these source firings. A brief comparison with other high frequency in situ plasma instruments is presented.     

Comparative anatomy of the day- and night-time radar echoes from the 130–170 km region of the low latitude ionosphere

Recent observations of daytime 150 km echoes made from Gadanki have revealed ‘descending layer type’ echoing pattern, which are remarkably different from their well known ‘necklace’ pattern. These descending layer type echoing pattern have close resemblance to those of the nighttime valley region echoes that are presumably linked with the intermediate layer formed by the meridional wind shear associated with the semidiurnal/terdiurnal tidal winds. The observed close resemblance between the two echoing patterns reminds the plausible role of the semidiurnal/terdiurnal tidal wind and metallic ions in the governing physical processes. We present a comparative anatomy of these two echoing phenomena by making a close examination of the radar observations from Gadanki. Importantly, we bring out the similarities and dissimilarities in their characteristics and discuss the results in the light of currently available theoretical frameworks in an effort to further our understanding on the origin of these echoing phenomena, which have been addressed so far in isolation.     

高速流前端磁场B_z分量的变化

等离子体片高速流在磁层活动中起着重要作用,其形成机制以及与背景等离子体的相互作用日益引起关注.本文利用搭载于Cluster四颗卫星上的磁场和等离子体观测仪器,对2001和2002两年发生在磁尾等离子体片中高速流事件期间的磁场变化进行了统计研究.结果表明,在高速流前端,伴随着等离子体整体速度的增加,绝大多数高速流前端磁场的B_z分量经常出现先短暂减小然后剧烈增大的现象,符合以往利用Geotail卫星观测数据获得的统计特性.然而个例研究发现B_z的下降与上升常常是不对称的,且B_z分量下降的程度并不是总能达到反向的程度,说明这种变化特征并不一定是存在磁结构的表现.我们认为更多时候这种磁场的变化特征是高速流挤压背景等离子体磁场造成的,是相互作用的结果.当偶极化锋面形成后,由类似间断面的磁场界面反射的热离子产生抗磁效应,可能对B_z下降形成部分贡献,而B_z增加则是高速流携带磁通量堆积的效果.     

圆柱绕流脱落旋涡相关长度的测量

本文探讨了圆柱绕流脱落旋涡空间相关长度的测量技术。除应用硬件系统外,还发展了一种测量用的软件系统,并对测量结果进行了分析和讨论。     

等离子弧穿孔熔池的数值模拟

根据流体力学理论和传热学机理,采用有限元法建立了运动等离子弧作用下穿孔焊接熔池流场、温度场的三维瞬态数值分析模型,根据计算出的温度场,模拟并图形显示了熔池形状和穿孔熔池的形成过程。计算表明,所建立的数值分析模型可用于等离子弧穿孔焊接熔池流场和温度场的有限元计算、熔池形状和穿孔熔池形成过程的模拟,为等离子弧穿孔焊接在工程实际中的应用提供理论依据。     

矢量喷管静推力特性风洞实验研究

给出了轴对称收扩喷管和实施矢量偏转后的收扩喷管模型在FL 8风洞中的动力模拟静特性实验结果。对于轴对称喷管模型主要进行了喷管的推力特性测量,对于实施矢量偏转后的喷管模型除了给出了喷管推力特性外,还给出了喷管的偏转效率。实验结果表明:在FL 8风洞中进行单喷管的推力静特性测量实验结果可靠,与理论规律相一致。     

铝合金点蚀对应力集中系数影响的分析

采用有限单元法建立铝合金点蚀三维圆锥体模型,对拉伸载荷下不同径深比和深度的点蚀应力场进行分析,得到点蚀有效应力集中系数巧：并在定性分析点蚀群蟛影响因素的基础上,采用分区随机数定位分布的方法,引入点蚀系数定量分析点蚀群巧。最后采用回归方法分析得到点蚀径深比、深度和点蚀系数与巧的经验公式。