磁层压缩ULF湍流对电子的加速

在准线性理论下,磁层压缩 ULF(超低频)湍流可以通过“渡越时间加速”机制使电子增加能量．典型的压缩 ULF 湍流的频率为2—15mHz,被加速的源电子为同步轨道附近的背景电子(E＜30keV)和亚暴注入电子(30—300 keV)．当发生波粒共振时,低能电子数减少,而高能尾部分的相对论(E≥1 MeV)电子数增加,这说明电子得到了压缩湍流的有效加速,且亚暴注入的电子数越多,其加速产生的相对论电子数也越多．在亚暴注入率ε=0.5的情况下,这种加速机制只要约12h 就可以造成同步轨道附近相对论电子数量的显著增加．     

弹载SAR大斜视改进CS成像算法

针对弹载SAR在成像过程中复杂的运动状态,以及大斜视所造成的频谱混叠问题,建立了大斜视加速运动模型.引入新的CS因子,有效解决了距离频谱混叠问题并补偿了导弹在三方向速度和加速度的影响;引入方位deramp处理方法,有效解决了方位多普勒频谱混叠问题.仿真结果表明该方法优于现有算法.     

Structural topology optimization under stationary random base acceleration excitations

Structural topology optimization subjected to stationary random base acceleration excitations is investigated in this paper. In the random response analysis, the Large Mass Method(LMM) which attributes artificial large mass values at each driven nodal Degree Of Freedom(DOF) to transforming the base acceleration excitations into force excitations is proposed. The Complete Quadratic Combination(CQC) which is commonly used to calculate the random responses in previous optimization has been proven to be computationally expensive especially for large-scale problems. In order to conquer this difficulty, the Pseudo Excitation Method(PEM) and the combined method of PEM and Mode Acceleration Method(MAM) are adopted into the dynamic topology optimization, and random responses are calculated using these two methods to ascertain a high efficiency over the CQC. A density-based topology optimization method minimizing dynamic responses is then formulated based on the integration of LMM and PEM or the combined method of PEM and MAM. Numerical examples are presented to verify the accuracy of the proposed schemes in dynamic response analysis and the quality of the optimized design in improving dynamic performance.     

高速平台下动目标高分辨成像方法研究

高速平台对地面强散射移动目标或者海面舰船目标进行合成孔径雷达成像（SAR）时，存在两方面问题：一是传统SAR匀速直线模型已不适应高速平台自身高动态运动特征；二是目标的非合作运动一方面会引起图像散焦，另一方面动目标在地距图中的位置会产生较大偏移。针对这两个问题，首先在匀加速度模型频域相位滤波算法下，推导出了精确的斜地投影关系以及近似的反投影关系，同时给出了基于惯性组合导航（INS）的平台运动补偿方法，最后结合自聚焦技术，完成对舰船目标的聚焦并得到以目标为图像中心的地距图。     

A Lamb wave signal reconstruction method for high-resolution damage imaging

In Lamb wave-based Structural Health Monitoring(SHM), a high-enough spatial resolution is highly required for Lamb wave signals to ensure the resolution and accuracy of damage detection. However, besides the dispersion characteristic, the signal spatial resolution is also largely restricted by the space duration of excitation waveforms, i.e., the Initial Spatial Resolution(ISR)for the signals before travelling. To resolve the problem of inferior signal spatial resolution of Lamb waves, a Lamb Wave Signal Reconstruction(LWSR) method is presented and applied for highresolution damage imaging in this paper. In LWSR, not only a new linearly-dispersive signal is reconstructed from an original Lamb wave signal, but also the group velocity at the central frequency is sufficiently decreased. Then, both dispersion compensation and ISR improvement can be realized to achieve a satisfying signal spatial resolution. After the frequency domain sensing model and spatial resolution of Lamb wave signals are firstly analyzed, the basic idea and numerical realization of LWSR are discussed. Numerical simulations are also implemented to preliminarily validate LWSR. Subsequently, LWSR-based high-resolution damage imaging is developed. An experiment of adjacent multiple damage identification is finally conducted to demonstrate the efficiency of LWSR and LWSR-based imaging methods.     

Validation of IRI-2012 TEC model over Ethiopia during solar minimum (2009) and solar maximum (2013) phases

This paper investigates the capacity of the latest version of the International Reference Ionosphere (IRI-2012) model in predicting the vertical Total Electron Content (vTEC) over Ethiopian regions during solar minimum (2009) and solar maximum (2013) phases. This has been carried out by comparing the IRI-2012 modeled and experimental vTEC inferred from eight ground based dual frequency GPS (Global Positioning System) receivers installed recently at different regions of the country. In this work, the diurnal, monthly and seasonal variation in the measured vTEC have been analyzed and compared with the IRI-2012 modeled vTEC. During the solar minimum phase, the lowest and highest diurnal peak of the experimental vTEC are observed in July and October, respectively. In general, the diurnal variability of vTEC has shown minimum values around 0300 UT (0600 LT) and maximum values between around 1000 and 1300 UT (1300 and 1600 LT) during both solar activity phases. Moreover, the maximum and minimum monthly and seasonal mean hourly vTEC values are observed in October and July and in the March equinox and June solstice, respectively. It is also shown that the IRI-2012-model better predicts the diurnal vTEC in the time interval of about 0000–0300 UT (0300–0600 LT) during the solar minimum phase. However, the model generally overestimates the diurnal vTEC except in the time interval of about 0900–1500 UT (1200–1800 LT) during the solar maximum phase. The overall result of this work shows that the diurnal vTEC prediction performance of the model is generally better during the solar minimum phase than during solar maximum phase. Regarding the monthly and seasonal prediction capacity of the model, there is a good agreement between the modeled and measured monthly and seasonal mean hourly vTEC values in January and December solstice, respectively. Another result of the work depicts that unlike the GPS–TEC the IRI-2012 TEC does not respond to the effect resulted from geomagnetic storms.     

电传飞机加速度传感器安装位置对飞行品质的影响

从飞行控制系统原理出发,以某型电传飞机为例,通过六自由度仿真对比,分析加速度传感器安装位置对飞行品质的影响,并从飞行品质的角度出发,对采用电传飞控系统飞机的加速度传感器安装位置提出建议.     

An adaptive attitude algorithm based on a current statistical model for maneuvering acceleration

A current statistical model for maneuvering acceleration using an adaptive extended Kalman filter(CS-MAEKF) algorithm is proposed to solve problems existing in conventional extended Kalman filters such as large estimation error and divergent tendencies in the presence of continuous maneuvering acceleration. A membership function is introduced in this algorithm to adaptively modify the upper and lower limits of loitering vehicles' maneuvering acceleration and for realtime adjustment of maneuvering acceleration variance. This allows the algorithm to have superior static and dynamic performance for loitering vehicles undergoing different maneuvers. Digital simulations and dynamic flight testing show that the yaw angle accuracy of the algorithm is 30% better than conventional algorithms, and pitch and roll angle calculation precision is improved by 60%.The mean square deviation of heading and attitude angle error during dynamic flight is less than3.05°. Experimental results show that CS-MAEKF meets the application requirements of miniature loitering vehicles.     

飞机自动钻铆技术研究现状及其关键技术

飞机自动钻铆技术能够实现飞机机身、机翼等处壁板的自动钻铆装配,极大地提高飞机装配质量与装配效率。经过几十年的发展,自动钻铆技术在国外已广泛运用于航空航天制造领域,而国内在这一方面正处于起步阶段,技术水平普遍较低。为此调研国外先进自动钻铆技术的研究应用现状,以GEMCOR、Electroimpact、BROETJE三大国外自动钻铆设备供应商为代表,介绍各自技术特点及在自动钻铆技术方面最新的进展。同时,对国内自动钻铆技术的发展进行简要介绍,指出国内在这一技术发展中存在的问题。此外,对自动钻铆技术中包括高精度定位技术、制孔质量在线检测技术、自动送钉技术、离线编程与仿真技术在内的四大关键技术进行详细分析,总结其研究难点,为国内自动钻铆技术的发展提供参考。     

基于频响函数的复合材料空间分布模量场识别

针对纤维编织复合材料宏观力学性能的非均匀特性,提出了基于频响函数(FRF)的复合材料梁空间分布弹性模量场的识别方法。采用基于灵敏度分析的方法构造优化问题,以实测和计算加速度频响残差范数最小为目标函数,进而通过迭代求解识别出复合材料梁弹性模量的空间分布。首先,以悬臂梁模型为研究对象进行数值仿真分析,验证识别方法的正确性。进一步开展复合材料梁模态试验研究,将复合材料三点弯曲试验获取的近似均质化弹性模量作为优化问题的初值;利用非接触测量方法获取模态试验中梁上各测点处的动位移响应,并计算得到各测点的加速度频响函数作为优化问题的输入值。结果表明:采用所提出的识别方法获取的模量场计算得到的梁上各处频响函数与试验获取值吻合,且所提方法在实测动响应存在噪声污染工况下是可行的。该方法能够为复合材料等效建模提供更加准确的弹性模量场。