小样本下维修性评估方法

小子样维修性评估在装备评估中频繁出现,需要建立一种有效的评估方法.针对小子样维修性评估,分析了自助法、随机加权法,并建立一种具有更好评估效果的改进自助法.首先以设定定参数产生一组小样本的随机数据,然后依据自助法、改进自助法和随机加权法的计算模型,分别对产生的随机数据进行分析计算,得出模型下随机数据的参数的估计值.将估计的参数与设定参数进行比较,模型较优则估计的参数误差较小.     

基于跑道灯光的计算机视觉辅助无人机着陆

针对夜间无人机着陆时标准跑道的灯光会加重图像处理的难度问题,提出一种利用跑道灯光辅助着陆的机器视觉方法。该方法参考标准跑道灯光设置,提取跑道灯光直线特征,对EPnP方法进行扩展,将直线特征表示成跑道平面上3个控制点的加权形式,利用奇异值分解的方法求出控制点在相机坐标系中的坐标,最后使用正交化方法解算出无人机相对于跑道的位置和姿态,为无人机着陆提供了引导信息。仿真结果表明:在距机场距离较远时,该方法能有效地引导其自主着陆。     

基于信号预处理的杜芬振子弱信号检测方法

杜芬振子对周期信号极其敏感,对噪声具有较强免疫力,被研究用于强噪声背景下弱周期信号的检测及其各项参数的测量。为进一步提高杜芬振子检测含噪信号的性能,本文提出了先对待测信号预处理再送入杜芬振子的弱信号检测算法,并在理论上进行了证明。该方法先将待测信号分割、叠加、延拓再送入杜芬振子进行检测,仿真表明该方法在将信号分割成多段、叠加、延拓时可获得较大的信噪比增益,其中分割数目为3时,检测信噪比下限降低约为2 dB,分割数目为5时,检测信噪比下限降低约为3 dB。     

双星定位系统中星历误差的分析与研究

为了研究星历误差对双星定位系统定位精度的影响,根据双星定位系统定位的数学模型,分析各种测量误差对系统定位精度的影响,推导出了差分定位体制下系统的定位误差模型.重点研究了星历误差对其定位精度的影响,并推导出了其数学误差模型,得出系统经过差分修正后较大的星历误差可等效于一个较小的测距误差的结论,并在一定条件下给出了其仿真结果,从而揭示了星历误差影响系统定位精度的规律.研究结果为分析其他误差因素对其定位精度的影响奠定了基础.     

航天器刚性基板太阳电池阵在轨热分析

针对周期性热交变环境引起的航天器上刚性太阳电池阵温度变化对其性能和可靠性有着较大影响的问题.以4块电池板组成的太阳电池阵作为研究对象,将其内部传热过程看成无内热源三维各向异性的非稳态导热问题,全面考虑光电转换效率、布片效率和外热流等各种影响因素,进行刚性太阳电池阵在轨热分析.首先进行网格划分,计算节点为5 060个,然后运用有限差分法,考虑节点的不同位置特点,建立全隐式离散方程,最后采用AD I算法求解离散方程,得到太阳电池阵周期温度变化及各方向上温度分布规律,并与太阳电池阵的遥测数据进行比对,验证了热分析的正确性.该研究为太阳电池阵可靠设计提供参考.     

基于图像处理的Wigner-Ville分布交叉项抑制

将图像处理技术同Wigner-Ville分布相结合得到一种新的交叉项抑制方法。先对信号做伪Wigner-Ville变换,然后对时频图旋转一定角度,再逆方向旋转相同的角度,则此时信号的时频分布在交叉项地方存在明显的偏差;利用这种偏差检测到交叉项,最后设计二值滤波将交叉项滤去,得到没有交叉项的信号时频表示。仿真结果表明了该方法的有效性。     

Nonlinear transient analysis of FGM and FML plates under blast loads by experimental and mixed FE methods

Nonlinear transient behavior of fiber-metal laminated (FML) composite plates under non-ideal blast loads are investigated by both experimental and numerical techniques. In the experiments three plates with different aspect ratios are tested under blast loads and their response is also simulated and compared with both the developed mixed finite element method and the commercial software ANSYS. Furthermore parametric numerical analyses are conducted for nonlinear transient behavior of functionally graded (FGM) thin plates under blast loads with mixed FEM. In these parametric analyses the effect of aspect ratio, load distribution and impulse function in time domain are investigated. In the developed mixed FE formulation, the von Kármán plate theory is used. Nonlinear functional is developed using the Hellinger-Reissner principle and linearized with the incremental formulation. Dynamic analyses are carried using the Newmark method with the Newton-Raphson iterations. Condensation is not performed hence time derivative of internal forces are also calculated during the solutions. Damping is incorporated to the analysis in the sense of the Rayleigh damping. As a result of conducted analyses, there is a good and reliable agreement between the numerical and the experimental results. Moreover, the developed mixed FEM results are almost identical to the ANSYS results.     

Damage propagation mechanism in low-cycle creep fatigue of Cu–Cr–Zr alloy

This paper describes a characteristic damage propagation mechanism in low-cycle creep–fatigue of Cu–0.7Cr–0.09Zr (mass%), as investigated by creep–fatigue tests including strain controlled fatigue and stress-holding type creep, and following microstructural observations by scanning electron microscopy (SEM). The total stress-holding time until rupture in the creep–fatigue test was shorter than one-tenth of the rupture life in the simple creep test, and the rupture life of the specimen in the creep–fatigue test was shorter than half of that in the simple fatigue test. The SEM images suggest that the connection between fatigue crack propagating along grain boundaries and intergranular creep voids rapidly accelerates crack propagation.     

A comparative study of the improvement of performance using a PSO modified by ACO applied to TSP

Swarm-inspired optimization has become very popular in recent years. Particle swarm optimization (PSO) and Ant colony optimization (ACO) algorithms have attracted the interest of researchers due to their simplicity, effectiveness and efficiency in solving complex optimization problems. Both ACO and PSO were successfully applied for solving the traveling salesman problem (TSP). Performance of the conventional PSO algorithm for small problems with moderate dimensions and search space is very satisfactory. As the search, space gets more complex, conventional approaches tend to offer poor solutions. This paper presents a novel approach by introducing a PSO, which is modified by the ACO algorithm to improve the performance. The new hybrid method (PSO–ACO) is validated using the TSP benchmarks and the empirical results considering the completion time and the best length, illustrate that the proposed method is efficient.     

Transient Heat Transfer Analysis of Blast Furnace Cooling Staves

The capability of cooling staves is crucial for a long campaign life of blast furnaces (BF). Transient heat transfer analysis of blast furnace cooling staves made of copper, cast steel, and ductile cast iron are performed. Moreover, the temperature field variations of cooling staves according to different distributions of gas flow temperature are studied. A discussion of cooling staves made of the three different materials is given based on their performance during the transient heat transfer process. The results indicate that copper staves are suited for a long campaign life, as their performance is much better compared to cast steel and ductile cast iron staves especially during unsteady heat transfer. Moreover, the capacity of staves made of cast steel is better than that of ductile cast iron.