从竞争到合作

大约4年前,加拿大航空技术公司(ACTS)与铬合金公司结为战略合作伙伴,在CF34发动机的维修中采用由铬合金公司生产的PMA件,以减少大修成本.     

Simulating clefts in pumpkin balloons

The geometry of a large axisymmetric balloon with positive differential pressure, such as a sphere, leads to very high film stresses. These stresses can be significantly reduced by using a tendon re-enforced lobed pumpkin-like shape. A number of schemes have been proposed to achieve a cyclically symmetric pumpkin shape, including the constant bulge angle (CBA) design, the constant bulge radius (CBR) design, CBA/CBR hybrids, and NASA’s recent constant stress (CS) design. Utilizing a hybrid CBA/CBR pumpkin design, Flight 555-NT in June 2006 formed an S-cleft and was unable to fully deploy. In order to better understand the S-cleft phenomenon, a series of inflation tests involving four 27-m diameter 200-gore pumpkin balloons were conducted in 2007. One of the test vehicles was a 1/3-scale mockup of the Flight 555-NT balloon. Using an inflation procedure intended to mimic ascent, the 1/3-scale mockup developed an S-cleft feature strikingly similar to the one observed in Flight 555-NT. Our analysis of the 1/3-scale mockup found it to be unstable. We compute asymmetric equilibrium configurations of this balloon, including shapes with an S-cleft feature.     

Impact of Jason-2/T2L2 Ultra-Stable-Oscillator Frequency Model on DORIS stations coordinates and Earth Orientation Parameters

Doppler Orbitography and Radiopositioning Integrated by Satellite (DORIS) is a tracking technique based on a one-way ground to space Doppler link. For Low Earth Orbit (LEO) satellites, DORIS shows a robust capability in terms of data coverage and availability, due to a wide and well-distributed ground network, where data are made available by the International Doris Service (IDS). However, systematic errors remain in the DORIS data, such as instabilities of the on-board clock due to radiation encountered in space, which limit the accurate determination of station positions.The DORIS on-board clock frequency stability is degraded by the increased radiation found in the region of the South Atlantic Anomaly (SAA) and has been shown to degrade station position estimation. This paper introduces a new model correction to the DORIS data for the frequency of the Jason-2 Ultra Stable Oscillator (USO), derived from the Time Transfer by Laser Link (T2L2) experiment (Belli and Exertier, 2018). We show that a multi-satellite DORIS solution including this T2L2-corrected data applied to the frequency modelling for The DORIS data, improves the estimation of station coordinates. We show the tie residuals with respect to collocated GPS stations are improved by several millimeters. We also demonstrate that the 117-day (Jason-2) draconitic signal in the geophysical parameters is reduced, implying that the origin of this signal is not just solar radiation pressure mis-modeling, but also radiation-induced clock perturbations on the Jason-2 DORIS Ultra-Stable-Oscillator (USO). Finally we demonstrate through comparisons with the International Earth Rotations and Reference Systems Service (IERS) C04 series for Earth Orientation Parameters (EOP), that the estimation of EOP is improved in both a Jason-2 DORIS-only and a multi-satellite DORIS solution for EOP.     

A study of acoustic halos in active region NOAA 11330 using multi-height SDO observations

We analyze data from the Helioseismic Magnetic Imager (HMI) and the Atmospheric Imaging Assembly (AIA) instruments on board the Solar Dynamics Observatory (SDO) to characterize the spatio-temporal acoustic power distribution in active regions as a function of the height in the solar atmosphere. For this, we use Doppler velocity and continuum intensity observed using the magnetically sensitive line at 6173?Å as well as intensity at 1600?Å and 1700?Å. We focus on the power enhancements seen around AR 11330 as a function of wave frequency, magnetic field strength, field inclination and observation height. We find that acoustic halos occur above the acoustic cutoff frequency and extends up to 10?mHz in HMI Doppler and AIA 1700?Å observations. Halos are also found to be strong functions of magnetic field and their inclination angle. We further calculate and examine the spatially averaged relative phases and cross-coherence spectra and find different wave characteristics at different heights.     

拟合激光陀螺数学模型的方法研究…

在分析激光陀螺的数学模型和三欠样条函数拟合原理的基础上,针对俄罗斯某型低精度激光陀螺实际输入－输出特性曲线的数据,应用三次样条合方法进行分析处理,推导出了适用于非线性工作范围误差补偿且实际陀螺特性的数学模型。本文所提方法可用于工作区线性化较差,工作精度低的激光陀螺的精度补偿。     

Impact of ITRS 2014 realizations on altimeter satellite precise orbit determination

This paper evaluates orbit accuracy and systematic error for altimeter satellite precise orbit determination on TOPEX, Jason-1, Jason-2 and Jason-3 by comparing the use of four SLR/DORIS station complements from the International Terrestrial Reference System (ITRS) 2014 realizations with those based on ITRF2008. The new Terrestrial Reference Frame 2014 (TRF2014) station complements include ITRS realizations from the Institut National de l’Information Géographique et Forestière (IGN) ITRF2014, the Jet Propulsion Laboratory (JPL) JTRF2014, the Deutsche Geodätisches Forschungsinstitut (DGFI) DTRF2014, and the DORIS extension to ITRF2014 for Precise Orbit Determination, DPOD2014. The largest source of error stems from ITRF2008 station position extrapolation past the 2009 solution end time. The TRF2014 SLR/DORIS complement impact on the ITRF2008 orbit is only 1–2 mm RMS radial difference between 1992–2009, and increases after 2009, up to 5 mm RMS radial difference in 2016. Residual analysis shows that station position extrapolation error past the solution span becomes evident even after two years, and will contribute to about 3–4 mm radial orbit error after seven years. Crossover data show the DTRF2014 orbits are the most accurate for the TOPEX and Jason-2 test periods, and the JTRF2014 orbits for the Jason-1 period. However for the 2016 Jason-3 test period only the DPOD2014-based orbits show a strong and statistically significant margin of improvement. The positive results with DTRF2014 suggest the new approach to correct station positions or normal equations for non-tidal loading before combination is beneficial. We did not find any compelling POD advantage in using non-linear over linear station velocity models in our SLR & DORIS orbit tests on the Jason satellites. The JTRF2014 proof-of-concept ITRS realization demonstrates the need for improved SLR+DORIS orbit centering when compared to the Ries (2013) CM annual model. Orbit centering error is seen as an annual radial signal of 0.4 mm amplitude with the CM model. The unmodeled CM signals show roughly a 1.8 mm peak-to-peak annual variation in the orbit radial component. We find the TRF network stability pertinent to POD can be defined only by examination of the orbit-specific tracking network time series. Drift stability between the ITRF2008 and the other TRF2014-based orbits is very high, the relative mean radial drift error over water is no larger than 0.04 mm/year over 1993–2015. Analyses also show TRF induced orbit error meets current altimeter rate accuracy goals for global and regional sea level estimation.     

遥操作机器人神经网络Smith预估控制(英文)

针对遥操作机器人通讯通道中存在的时延 ,提出了一种神经网络 Smith预估控制方法。控制系统适合于时延不变但未知的情况。控制系统包括主控制器和从系统两部分。从系统采用动态神经网络辨识机器人的动态模型 ,神经网络权重在线学习 ,用神经网络的输出对非线性系统进行局部非线性补偿 ,将非线性系统线性化。主系统针对线性化的从系统 ,采用 Smith预估控制解决时延问题并保证系统的性能品质。通过李雅普诺夫稳定理论保证了时延控制系统的稳定性。对两关节机器人的仿真结果说明了该方法的有效性。     

客改货市场的前景预测

尽管航空货运市场出现了强烈反弹,但客改货市场的前景却并不明朗。尽管航空货运市场开始升温,预计在未来20年,70%的货运飞机需要由客机改装完成,客改货市场的前景十分可观,但近期客改货市场的发展路线图还不够清晰,尤其是对中型宽体货机,可供改装的客机资源缺乏和新货机的冲击将是影响客改货市场发展的重要因素。