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21.
星型齿轮传动非线性动力学建模与动载荷研究 总被引:8,自引:3,他引:8
本文建立了星型齿轮传动的弯扭耦合非线性动力学计算模型,模型中考虑了原动机和负载惯性,齿轮副的啮合综合误差,齿轮的偏心误差,时变啮合刚度以及齿轮的啮合间隙。采用适当的广义坐标变换,将线性恢复力和非线性恢复力共存的动力学方程组统一成矩阵形式,用数值解法获得了在有间隙非线性的情况下受强参数激励和多频激励的系统的动态响应和动载荷历程。最后给出了一个算例,讨论了间隙、齿频误差和偏心误差对齿轮系统的响应、动载荷以及各星轮的载荷分配均匀性的影响。并研究了刚度和误差激励和间隙的相互耦合关系,得出了对星型齿轮传动设计和制造有意义的结论。 相似文献
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The energy state of a planet depends fundamentally on its radiation budget. Measurements made from space over past decades
have led to significant revisions of ground-based estimates, both of the reflected fraction (the Bond albedo) of solar radiative
flux and of the emitted thermal infrared radiation flux, for the Earth as well as for the other planets. After a brief survey
of methods and difficulties in accurately determining planetary radiation budgets, we note contradictions in existing tabulations
of global parameters, in particular Bond albedo. For the Earth, such contradictions are unjustified, considering that global
and annual means as well as the seasonal cycle of Earth Radiation Budget components have now been determined with high accuracy.
The Earth's Bond albedo is close to 0.3. Net storage of energy in the Earth-ocean system is close to zero, with a well-established
annual cycle of amplitude close to ±12 Wm−2. Some contradictions remain for the other terrestrial planets. For the giant planets, modern reduced values of the Bond albedo
imply reduced but still significant internal energy generation. 相似文献
24.
J.S. Mandeep 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2009
The 0 °C isotherm height is an important parameter for prediction of rain attenuation of microwave and millimeter wave for Earth-space communication. The variations of 0 °C isotherm heights for two monsoon seasons have been studied based on an analysis of radiosonde over three stations. The exceedence probability statistics of rain height are compared between the two seasons. The results on the 0 °C isotherm height can be utilized for the estimation of attenuation of microwave and millimeter wave due to rain over Earth-space paths. Attenuations of radio wave due to rain at frequencies above 10 GHz and above have also been estimated using the 0 °C isotherm height so derived. 相似文献
25.
V.V. Guryanov A.N. Fahrutdinova 《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2014
Daily UK Met Office stratospheric assimilated data for the Northern and Southern Hemispheres, accumulated for the period from 2004 to 2012 and pressure range of 1000–0.1 hPa, are used in this paper. The paper presents and thoroughly discusses spatial–temporal distributions of stationary planetary wave (SPW) amplitudes and phases, calculated on the basis of geopotential height, temperature, zonal and meridional wind data for zonal wave numbers 1 and 2 (SPW1 and SPW2). The climatological planetary wave amplitudes and phases are calculated by extracting waves from three types of data: daily, monthly mean and climatological monthly mean. It has been established that magnitude of amplitudes and height-latitude distribution of amplitudes of SPW1 and SPW2 depend on data processing method for all parameters. It has also been established that height-latitude distribution amplitudes and phases significantly differ for geopotential height, temperature, zonal and meridional wind and depend on wave number and hemisphere. However, height-latitude distributions of phases are little different from each other for the used methods of data processing. 相似文献
26.
《中国航空学报》2020,33(5):1549-1561
Planetary gear train is a prominent component of helicopter transmission system and its health is of great significance for the flight safety of the helicopter. During health condition monitoring, the selection of a fault sensitive feature subset is meaningful for fault diagnosis of helicopter planetary gear train. According to actual situation, this paper proposed a multi-criteria fusion feature selection algorithm (MCFFSA) to identify an optimal feature subset from the high-dimensional original feature space. In MCFFSA, a fault feature set of multiple domains, including time domain, frequency domain and wavelet domain, is first extracted from the raw vibration dataset. Four targeted criteria are then fused by multi-objective evolutionary algorithm based on decomposition (MOEA/D) to find Proto-efficient subsets, wherein two criteria for measuring diagnostic performance are assessed by sparse Bayesian extreme learning machine (SBELM). Further, F-measure is adopted to identify the optimal feature subset, which was employed for subsequent fault diagnosis. The effectiveness of MCFFSA is validated through six fault recognition datasets from a real helicopter transmission platform. The experimental results illustrate the superiority of combination of MOEA/D and SBELM in MCFFSA, and comparative analysis demonstrates that the optimal feature subset provided by MCFFSA can achieve a better diagnosis performance than other algorithms. 相似文献
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29.
Marie Jourdain De Muizon 《Space Science Reviews》2005,119(1-4):201-214
Debris discs around stars were first discovered by the Infrared Astronomical Satellite (IRAS) in 1983. For the first time
material orbiting another star than the Sun, but distinct from a circumstellar envelope, was observed through its far infrared
emission. This major discovery motivated astronomers to investigate those discs by further analyzing the IRAS data, using
ground-based telescopes for the hunting of exoplanets, developing several projects using the Infrared Space Observatory (ISO),
and now exploiting the ISO Data Archive (IDA). This review presents the main ISO results, statistical as well as individual,
on debris discs in orbit around pre-main-sequence and main-sequence stars.
Based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries:
France, Germany, The Netherlands, and the United Kingdom), and with the participation of ISAS and NASA. 相似文献
30.
We use a simplified atmospheric general circulation model (AGCM) to investigate the response of the lower atmosphere to thermal
perturbations in the lower stratosphere. The results show that generic heating of the lower stratosphere tends to weaken the
sub-tropical jets and the tropospheric mean meridional circulations. The positions of the jets, and the extent of the Hadley
cells, respond to the distribution of the stratospheric heating, with low latitude heating displacing them poleward, and uniform
heating displacing them equatorward. The patterns of response to the low latitude heating are similar to those found to be
associated with solar variability in previous observational data analysis, and to the effects of varying solar UV radiation
in sophisticated AGCMs. In order to investigate the chain of causality involved in converting the stratospheric thermal forcing
to a tropospheric climate signal we conduct an experiment which uses an ensemble of model spin-ups to analyse the time development
of the response to an applied stratospheric perturbation. We find that the initial effect of the change in static stability
at the tropopause is to reduce the eddy momentum flux convergence in this region. This is followed by a vertical transfer
of the momentum forcing anomaly by an anomalous mean circulation to the surface, where it is partly balanced by surface stress
anomalies. The unbalanced part drives the evolution of the vertically integrated zonal flow. We conclude that solar heating
of the stratosphere may produce changes in the circulation of the troposphere even without any direct forcing below the tropopause.
We suggest that the impact of the stratospheric changes on wave propagation is key to the mechanisms involved. 相似文献