关于AH—24机翼延寿实验的疲劳寿命分散系数

本文介绍了疲劳分散系数;并指出对于飞机疲劳寿命,在考虑分散系数时,应将两机翼看成是串联结构以确定其可靠度。文中还依据实验数据计算了AH-24飞机的延寿寿命。     

MATLAB与VC++混合编程进行混沌时间序列分析

应用MATLAB与VC++混合编程进行混沌时间序列分析是一种快速有效的方法。本文介绍了混合编程的优点和实现结合的三种方法,重点介绍了应用MATLAB的API接口调用C++语言MEX文件的方法。对Lorenz系统进行的混沌特性分析表明,在混沌时间序列分析中采用混合编程效果明显。     

红外探测器时间常数测试系统(一)

介绍了红外探测器时间常数测量装置的建立,关键技术的解决,并进行了不确定度的验证。     

基于地面测量的卫星导航系统时间同步技术研究

根据卫星导航系统地面观测数据的特点,建立了站间和星地时间同步的状态空间方程和量测方程,设计了序列Kalman滤波算法,综合利用时间同步观测数据及伪距观测数据,求解出监测站及导航卫星钟差。通过仿真计算表明,本文所建立的模型及设计的序列Kalman滤波算法,提高了卫星导航系统站间和星地时间同步的精度,具有一定的应用价值。     

基于响应面方法的风力机叶片多目标优化设计研究

运用基于响应面方法的优化设计技术,于径向使用NPU-WA-风力机专用翼型族的某1.5MW水平轴风力机叶片的多目标、多约束优化设计研究中。风力机气动性能使用基于叶素-动量理论的风力机性能分析和设计软件PROPID51。设计变量为叶片径向外形参数,包括弦长和扭转角分布,但是相对厚度保持不变;设计目标为年发电量和功率系数的最大化;在多目标优化中,使用"统一目标函数"法将多个设计目标函数通过加权求和统一到一个目标函数中。为减小计算量,响应面模型使用不含二阶交叉项的二阶多项式模型;构建模型中试验点的选择满足D-优化准则。以某1.5MW变速变矩型风力机叶片为例,进行了优化设计研究。叶片径向使用西北工业大学翼型研究中心设计的NPU-WA-风力机专用翼型族,使用CFD计算的气动性能数据作为输入进行了设计,分析了目标函数的权值分配对设计结果的影响;使用风洞测量自由转捩的气动性能数据进行了设计并分析了表面光滑条件对气动性能的影响。     

基于时间序列分析的装备可用度预测方法

阐述了装备可用度预测的重要性,并以此为需求牵引,构建了具有非线性、非平稳的装备可用度时间序列。基于奇异值分解滤波算法,将原始序列分解为趋势成分和随机成分,分别应用粒子群训练的径向基神经网络模型和函数系数自回归模型进行组合预测,充分体现了2类模型的各自的优势。实例分析,验证了模型和算法的有效性。实验与应用结果表明,该组合方法的预测性能和效果比单一使用RBF和FAR进行预测更好。     

Advanced receiver autonomous integrity monitoring (ARAIM) schemes with GNSS time offsets

Within the current Advanced Receiver Integrity Monitoring (ARAIM) scheme, the time offsets between different Global Navigation Satellite System (GNSS) constellations are estimated along with a position solution and the GNSS receiver clock error. This scheme is called the Time-offsets Estimated ARAIM, or the TOE ARAIM. In order to enhance the interoperability and compatibility between different constellations, the time offsets are expected to be broadcast to users in future multi-GNSS positioning and navigation applications. This paper describes two new ARAIM schemes to make use of the Broadcast Time Offsets (BTOs): Time Offset Observed ARAIM (TOO ARAIM) and Time Offset Synchronized ARAIM (TOS ARAIM). It has been shown that the VPL performances of these two new ARAIM schemes rely strongly on the accuracy of BTOs. By varying the error model of the BTOs, the simulation results also demonstrate that the proposed new TOO ARAIM scheme can outperform the existing TOE ARAIM scheme-even if the accuracy of BTOs for integrity is degraded to 4.5 m and the probability of a BTO fault is relaxed to 10⁻² h⁻¹. In addition, the new Time Offset Synchronized ARAIM scheme (TOS ARAIM) can also perform better than the existing TOE ARAIM scheme if the accuracy of BTOs for integrity can reach 0.75 m. As the TOO ARAIM also has a very relaxed requirement on BTOs and better VPL performance, the TOO ARAIM is regarded as a superior ARAIM scheme for multi-GNSS with BTOs available.     

基于SCSO-BP神经网络的卫星姿态控制系统故障预测

近年来,随着人工智能的迅速发展,基于人工神经网络的卫星姿态控制系统故障预测方法得到了越来越多的重视。在反向传播(Back Propagation ,BP)神经网络中,权重和偏置是重要的可调节参数,与神经网络的预测性能密切相关。BP神经网络的初始权重和偏置为随机生成,设置不当容易导致网络在训练过程中陷入局部极值,进而影响预测性能。为了提高BP神经网络的预测性能,提出了一种将沙猫群优化(Sand Cat Swarm Optimization ,SCSO)算法与BP神经网络相结合的预测方法。在训练过程中,首先通过SCSO 算法对BP神经网络权重和偏置进行预训练,在此基础上,利用精调后的BP神经网络对卫星姿态控制系统周期渐变故障数据的未来趋势进行预测。实验结果表明,与原始BP神经网络预测方法相比,SCSO-BP预测方法能够有效减小预测误差,具有更好的预测精度。     

On the ability of sliding mode and LQR controllers optimized with PSO in attitude control of a flexible 4-DOF satellite with time-varying payload

Precise pointing of the satellite and its payload is essential in the accurate accomplishment of a space mission. In this study, the system of a satellite and its payload are considered as 4-DOF equations of motion. The time-varying payload can observe one direction of the Earth independently, and the satellite can point to the Earth station by its 3-DOF motions simultaneously. Sliding mode and LQR controllers are designed for damping disturbances, and consequently high pointing accuracy. Environmental disturbances and the associated time delay of Low Earth Orbit (LEO) are applied to the system. An algorithm based on Particle Swarm Optimization (PSO) is proposed to find the optimum values of variables and Normalized Integral Square Error (NISE) of the two aforementioned controllers. Numerical simulations indicate the optimized magnitudes of target detection errors and control efforts in four directions. The results revealed that PSO-SMC can finely track the time-varying payload and has better efficiency in comparison with PSO-LQR.     

Time delay of ionospheric TEC storms to geomagnetic storms and pre-storm disturbance events in East Asia

Using the TEC data at Beijing (39.61°N, 115.89°E)/Yakutsk (62.03°N, 129.68°E) stations of East Asia regions and relevant geomagnetic data from 2010 to 2017, we have studied the time delay of ionospheric storms to geomagnetic storms and compare it with our previous results of Taoyuan (25.02°N, 121.21°E) station (Zhang et al., 2020). The data shows a well-known local time dependence of the time delay, and seasonal dependences are different at these stations. In addition, there is no correlation between the time delay and the magnetic storm intensity /solar activity, except the time delay of negative storms has weakly negative dependence on the solar activity. Comparing with the results of Taoyuan station which is located at EIA region in East Asia, we find that the time delay increases nonlinearly as the latitude decreases due to different ionospheric backgrounds at these places. Moreover, the pre-storm disturbance events are found to have similar statistical characteristics as the pre-storm enhancement in Europe middle latitudes (Bure?ová and La?tovi?ka, 2007). By subtracting the common features of the pre-storm disturbance events, we preliminarily infer that auroral activity might be main driver of the pre-storm disturbance events.