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101.
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103.
基于旋转坐标系转轴振动信号的滚动轴承故障诊断方法 总被引:2,自引:0,他引:2
实验验证了基于旋转坐标系转轴振动信号的滚动轴承局部故障诊断方法.建立起滚动轴承故障实验台, 采用压电晶体加速度传感器测取转轴的振动.通过滚动轴承内环、外环、滚动体和保持架四种典型故障的实验分析结果, 证明了该方法的可行性, 并发现转轴振动信号的传递路径相对简单, 对轴承内环、滚动体和保持架早期微小故障的发现与诊断可能是有利的. 相似文献
104.
多压电膜式零质量射流激励器的设计与性能研究 总被引:1,自引:0,他引:1
设计了一种多压电膜式零质量射流激励器,并利用热线风速仪,得到了对应于射流中心线上固定位置处速度最大时的最佳频率.在该频率下,测量了零质量射流在不同孔径时沿中心线的速度分布;测量、分析和比较了不同激励膜数目对射流出口速度分布的影响.表明:在其他条件完全相同的情况下,一片振动膜时的激励器出口中心线上的平均速度和峰值速度,都较5片膜的情况小一半左右,而3片和5片压电膜时的激励器性能差别却不大.也就是说,虽然压电膜的数目增加能使激励器出口射流的能量增加,但这两者之间并非呈线性关系.此外还用PIV测量方法,直观地显示了射流出口的涡结构. 相似文献
105.
DU Xin-kang WANG Tian-min WANG Cong CHEN Bu-liang ZHOU Long 《中国航空学报》2007,20(2):140-144
Some fundamental studies on the preparation, structure and optical properties of NbN films were carried out. NbN thin films were deposited by DC reactive magnetron sputtering at different N2 partial pressures and different substrate temperatures ranging from –50 ℃ to 600 ℃. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) were employed to characterize their phase com- ponents, microstructures, grain sizes and surface morphology. Optical properties inclusive of refractive indexes, extinction coefficients and transmittance of the NbN films under different sputtering conditions were measured. With the increase in the N2 partial pressure, δ-NbN phase structure gets forming and the grain size and lattice constant of the cubic NbN increasing. The deposited NbN film has relatively high values of refractive index and extinction coefficient in the wavelength ranging from 240 nm to 830 nm. Substrate tem- perature exerts notable influences on the microstructure and optical transmittance of the NbN films. The grain sizes of the δ-NbN film remarkably increase with the rise of the substrate temperature, while the transmittance of the films with the same thickness decreases. Ultra-fine granular film with particle size of several nanometers forms when the substrate is cooled to –50 ℃, and a remarkable aug- mentation of transmittance could be noticed under so low a temperature. 相似文献
106.
薄膜太阳帆(FSS)是集推进、发电和姿轨控功能于一体化的超大型挠性太阳帆式航天器,通过调整薄膜反射率产生可变推力和力矩,实现其姿态和轨道运动控制。结合薄膜太阳帆在地球同步轨道运行时的受力特性进行了轨道漂移分析。通过建立薄膜太阳帆动力学模型及受力模型,提出了调整帆面角度轨道修正方法以及基于薄膜光压力矩角动量卸载的长期在轨对日定向面内双轴动量轮稳定控制方法。通过系统仿真验证表明所提的轨道修正和对日定向控制方法是合理有效的,可使薄膜太阳帆长期在定点位置维持对日定向。 相似文献
107.
X. Wang J.K. ShiG.J. Wang Y. Gong 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
Monthly median values of foF2, hmF2 and M(3000)F2 parameters, with quarter-hourly time interval resolution for the diurnal variation, obtained with DPS4 digisonde at Hainan (19.5°N, 109.1°E; Geomagnetic coordinates: 178.95°E, 8.1°N) are used to investigate the low-latitude ionospheric variations and comparisons with the International Reference Ionosphere (IRI) model predictions. The data used for the present study covers the period from February 2002 to April 2007, which is characterized by a wide range of solar activity, ranging from high solar activity (2002) to low solar activity (2007). The results show that (1) Generally, IRI predictions follow well the diurnal and seasonal variation patterns of the experimental values of foF2, especially in the summer of 2002. However, there are systematic deviation between experimental values and IRI predictions with either CCIR or URSI coefficients. Generally IRI model greatly underestimate the values of foF2 from about noon to sunrise of next day, especially in the afternoon, and slightly overestimate them from sunrise to about noon. It seems that there are bigger deviations between IRI Model predictions and the experimental observations for the moderate solar activity. (2) Generally the IRI-predicted hmF2 values using CCIR M(3000)F2 option shows a poor agreement with the experimental results, but there is a relatively good agreement in summer at low solar activity. The deviation between the IRI-predicted hmF2 using CCIR M(3000)F2 and observed hmF2 is bigger from noon to sunset and around sunrise especially at high solar activity. The occurrence time of hmF2 peak (about 1200 LT) of the IRI model predictions is earlier than that of observations (around 1500 LT). The agreement between the IRI hmF2 obtained with the measured M(3000)F2 and the observed hmF2 is very good except that IRI overestimates slightly hmF2 in the daytime in summer at high solar activity and underestimates it in the nighttime with lower values near sunrise at low solar activity. 相似文献
108.
S. Narendranath P.S. Athiray P. Sreekumar V. Radhakrishna A. Tyagi B.J. Kellett the CLASS team 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Surface chemistry of airless bodies in the solar system can be derived from remote X-ray spectral measurements from an orbiting spacecraft. X-rays from planetary surfaces are excited primarily by solar X-rays. Several experiments in the past have used this technique of X-ray fluorescence for deriving abundances of the major rock forming elements. The Chandrayaan-2 orbiter carries an X-ray fluorescence experiment named CLASS that is designed based on results from its predecessor C1XS flown on Chandrayaan-1. We discuss the new aspects of lunar science that can be potentially achieved with CLASS. 相似文献
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110.
Anand K. Singh A.K. Sinha Rahul Rawat Bulusu Jayashree B.M. Pathan Ajay Dhar 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2012
Magnetic data from a newly commissioned Indian Antarctic station Bharati (corrected geomagnetic (CGM) coordinates 74.7°S, 97.2°E) and closely-spaced IMAGE chain observatories (∼100° magnetic meridian in Northern hemisphere) has been analyzed to study the climatology of substorms which were localized poleward of the standard auroral oval. We considered four austral summers (year 2007–2010) when data from Bharati was available. Several very high latitude substorms were observed in this duration when the solar activity remained unexpectedly low for a long time. Various features of very high latitude substorms, e.g., local time dependence, interplanetary state, hemispherical asymmetry and their nightside low latitude signatures are examined. Events studied here, suggested the following properties of substorms occurring at very high latitudes: (1) maximum occurrence was observed near magnetic midnight (21:00–02:00 MLT). (2) In contradiction to earlier reports, many substorms were observed even during negative IMF Bz condition. In addition, majority of substorms occurred during low or moderate solar wind streams. (3) Magnetic signatures were often pronounced in the winter hemisphere. (4) Even if widely used standard AE indices fail to monitor very high latitude substorms, their low latitude signatures are often evident. 相似文献