纳秒激光脉冲宽度对2024铝合金损伤特性的影响

飞机激光除漆对2024铝合金蒙皮可能造成潜在的损伤,需探究激光参数变化对基体材料表面的作用规律,其中脉冲宽度对激光-材料作用与材料损伤特性具有重要影响。本文采用COMSOL Multiphysics软件模拟分析了不同脉冲宽度时激光作用铝合金表面的温升特性,并借鉴ISO 11254 1-on-1激光损伤阈值测试方法研究了脉冲宽度对铝合金损伤阈值的影响,进一步分析了不同脉冲宽度下的烧蚀凹坑微观形貌、直径与深度变化规律。结果表明：铝合金表面峰值温度随脉冲宽度增加而降低;脉冲宽度从150 ns增加到240和330 ns时,铝合金损伤阈值从9.96 J/cm²分别增加到11.24和12.66 J/cm²,当激光能量密度达到损伤阈值时,3μm厚氧化膜被完全损伤,破坏了铝合金表面完整性;烧蚀凹坑直径和深度随脉冲宽度增加而增加,深度受影响程度更大。该研究可为激光与材料作用的脉冲宽度选择提供一定的参考。     

一种改善防渗碳性能的脉冲镀铜工艺优化

为了实现对航空发动机零件非渗碳区域的有效防护,需要进行局部镀铜工艺的优化。通过脉冲镀铜正交试验和镀层孔隙率极差分析,确定了脉冲镀铜的主要和次要影响参数,优化了脉冲镀铜工艺参数。优化工艺脉冲制备的铜镀层结合力良好,表面形貌、孔隙率、防渗效果均优于直流镀铜层,将镀铜厚度由50~70μm降低到20μm,节约镀铜成本,且提高了工作效率。     

X射线脉冲星导航技术研究进展

X射线脉冲星能够为近地轨道、深空和星际空间飞行航天器提供位置、速度、时间和姿态等丰富的导航信息,实现航天器高精度自主导航和运行管理,有着巨大的发展潜力.本文论述了X射线脉冲星导航技术研究历程;重点研究了X射线脉冲星导航的基本原理、信息处理流程和自主导航算法,进而提出了脉冲星导航的关键技术;分析了国内脉冲星观测研究的基础条件,以及开展X射线脉冲星导航技术研究的必要性和可行性.      

基于薄膜铌酸锂的微波光子雷达芯片

微波光子雷达拥有分辨率高、处理速度快、同时多波段、多功能等优势,在航天系统中具有广阔的应用前景。为了满足航天应用对雷达系统体积、质量和功耗的严格要求,集成化已经成为微波光子雷达的重要发展方向。介绍了一款基于薄膜铌酸锂的微波光子雷达芯片,利用该芯片实现了雷达发射信号倍频产生和回波信号去斜接收,并对距离天线不同位置的目标进行了测距实验,得到的测量距离与实际距离基本相同,两者之间的误差小于4 mm。     

Acceleration of DDT by non-thermal plasma in a single-trial detonation tube

This paper compares the flame acceleration in single-trial dual-detonation tubes triggered by a spark plug and non-thermal plasma igniter. The low-temperature plasma was generated by an in-house novel AC-driven dielectric barrier discharge igniter, which reduces the power supply requirements and was applied in the quiescent ignition of a single-trial detonation tube. Three different types of detonation mixtures were tested with flame propagation tracked by ion probes and pressure waves recorded by high-frequency pressure transducers. The flame propagation speeds were calculated and compared based on signals from the ion probes. The detonation combustion succeeded in the dual tubes, but the deflagration-to-detonation transition could be significantly accelerated by the plasma for all mixtures, as it was shortened by more than 50% compared to that of the spark plug. The present study provides a suitable technological approach for igniters of PDEs.     

动能拦截器运动伪装末制导律设计

针对动能拦截器末制导问题，基于运动伪装理论设计了末制导律和相应的脉冲宽度脉冲频率(PWPF)调节器。根据拦截器和目标在视线旋转坐标系下的相对运动关系建立了动力学模型。通过运动伪装特性得出的拦截条件推导出作用在视线法向上的制导指令表达式。在动能拦截器制导推力受限情况下，利用PWPF调节器调节制导指令。考虑系统的可控条件和拦截条件，对调节器参数进行了理论设计。运动伪装末制导律保证动能拦截器在制导过程起到伪装作用，具有较高的制导精度和较小的命中过载，同时经过参数设计后的PWPF调节器可以节省燃料。最后，通过数值仿真校验了所设计末制导律的正确性和有效性。     

Fast approximate maximum likelihood period estimation from incomplete timing data

 To estimate the period of a periodic point process from noisy and incomplete observations, the classical periodogram algorithm is modified. The original periodogram algorithm yields an estimate by performing grid search of the peak of a spectrum, which is equivalent to the periodogram of the periodic point process, thus its performance is found to be sensitive to the chosen grid spacing. This paper derives a novel grid spacing formula, after finding a lower bound of the width of the spectral mainlobe. By employing this formula, the proposed new estimator can determine an appropriate grid spacing adaptively, and is able to yield approximate maximum likelihood estimate (MLE) with a computational complexity of O(n²). Experimental results prove that the proposed estimator can achieve better trade-off between statistical accuracy and complexity, as compared to existing methods. Simulations also show that the derived grid spacing formula is also applicable to other estimators that operate similarly by grid search.     

基于旋转阀的脉冲爆震火箭发动机实验

针对现有条件下电磁阀高频与大流量不可兼得的矛盾,设计了一种凸轮式旋转阀,以此来控制脉冲爆震火箭发动机氧化剂、燃料和隔离气体的间歇式供给.基于该旋转阀,以汽油和富氧空气为推进剂,进行了不同频率下的实验.实验结果表明,推进剂和隔离气供给压力与点火相位直接影响到能否稳定起爆.随着频率的增加,在1～ 10 Hz范围内,降低隔离氮气压力、调整点火相位可实现发动机的稳定工作;10Hz以上时,仅需要提高油气的供给压力.基于该旋转阀控制技术,脉冲爆震火箭发动机实现了工作频率30 Hz的稳定工作.     

电磁铆接放电过程仿真分析

目前,电磁铆接的放电回路主要有两种形式,一种是电容直接对线圈进行放电;另一种是电容对脉冲变压器放电,然后脉冲变压器作用于线圈.