天基轻气炮发射清除低轨碎片方案及关键技术分析

文章分析了现有的空间碎片清除方式,并以800~1200 km低地球轨道高度上1~10 cm量级的空间碎片为清除目标,提出了天基轻气炮清除碎片的新方法。首先分析了轻气炮有效载荷在典型参数下的弹丸加速能力;之后根据将碎片降轨使其坠入大气层烧毁的设想,提出天基轻气炮共面清除碎片的方式,并选择轨道高度800 km的圆轨道作为碎片运行轨道进行可行性分析。计算表明,对半径10 cm、厚度1 cm的铝合金圆板碎片(质量211.95 g),使用初速1 km/s、重10 g的黏性弹丸可按任务方案达到清除效果。此外,计算出该参数弹丸对轨道高度800~1200 km的圆轨道上可清除的最大碎片质量为500~825 g,证明轻气炮弹丸对1~10 cm的碎片具有较强的清除能力。最后,分析了以轻气炮为有效载荷的航天器在完成清除碎片任务时的关键技术。     

飞机液压系统柱塞泵热分析

随着飞机液压系统向高压化、大功率化方向发展，液压系统的发热及温升问题受到了广泛关注。柱塞泵作为液压系统中重要的能量转换装置，对液压系统的功率损失和温度有重大的影响，良好的柱塞泵的热分析对液压系统的热设计和温度控制有重要的意义。然而传统的柱塞泵热分析方法，如平均油温法、软件仿真法和热节点网络法，因不够准确、高效和简洁而不能满足现代飞机液压系统热分析和热设计的相关需求。本文针对飞机液压系统柱塞泵发热的相关问题，采用基于集总参数的热网络分析方法，建立了柱塞泵热网络模型，通过对柱塞泵不同工况下的仿真，验证了模型的有效性和准确性，为柱塞泵及液压系统的热分析提供了参考。     

Comparison of vertical E × B drift velocities and ground-based magnetometer observations of DELTA H in the low latitude under geomagnetically disturbed conditions

In the present work, we analyzed the daytime vertical E × B drift velocities obtained from Jicamarca Unattended Long-term Ionosphere Atmosphere (JULIA) radar and ΔH component of geomagnetic field measured as the difference between the magnitudes of the horizontal (H) components between two magnetometers deployed at two different locations Jicamarca, and Piura in Peru for 22 geomagnetically disturbed events in which either SC has occurred or Dst_max < ?50 nT during the period 2006–2011. The ΔH component of geomagnetic field is measured as the differences in the magnitudes of horizontal H component between magnetometer placed directly on the magnetic equator and one displaced 6–9° away. It will provide a direct measure of the daytime electrojet current, due to the eastward electric field. This will in turn gives the magnitude of vertical E × B drift velocity in the F region. A positive correlation exists between peak values of daytime vertical E × B drift velocity and peak value of ΔH for the three consecutive days of the events. It was observed that 45% of the events have daytime vertical E × B drift velocity peak in the magnitude range 10–20 m/s and 20–30 m/s and 20% have peak ΔH in the magnitude range 50–60 nT and 80–90 nT. It was observed that the time of occurrence of the peak value of both the vertical E × B drift velocity and the ΔH have a maximum (40%) probability in the same time range 11:00–13:00 LT. We also investigated the correlation between E × B drift velocity and D_st index and the correlation between delta H and D_st index. A strong positive correlation is found between E × B drift and D_st index as well as between delta H and D_st Index. Three different techniques of data analysis – linear, polynomial (order 2), and polynomial (order 3) regression analysis were considered. The regression parameters in all the three cases were calculated using the Least Square Method (LSM), using the daytime vertical E × B drift velocity and ΔH. A formula was developed which indicates the relationship between daytime vertical E × B drift velocity and ΔH, for the disturbed periods. The E × B drift velocity was then evaluated using the formulae thus found for the three regression analysis and validated for the ‘disturbed periods’ of 3 selected events. The E × B drift velocities estimated by the three regression analysis have a fairly good agreement with JULIA radar observed values under different seasons and solar activity conditions. Root Mean Square (RMS) errors calculated for each case suggest that polynomial (order 3) regression analysis provides a better agreement with the observations from among the three.     

Multi-mode optimal fuzzy active vibration control of composite beams laminated with photostrictive actuators

Firstly, a multi-field coupling finite element formulation of composited beam laminated with the photostrictive actuators is developed in this paper. Moreover, an optimal fuzzy active control algorithm is also proposed on the basis of the combination of optimal control and fuzzy one.This method opens a new avenue to resolve the contradiction between the linear system control method and nonlinear actuating characteristics of photostrictive actuators. The desired control for suppressing multi-modal vibration of photoelectric laminated beam is firstly obtained through optimal control and then the fuzzy control is used to approach the desired mechanical strain induced by photostrictive actuators. Thus, the multi-mode vibration control of beam is realized.In the design process of optimal fuzzy controller, the design of fuzzy control is independent of optimal control. The simulation results demonstrate that the proposed control method can effectively realize multi-modal vibration control of photoelectric laminated beams, and the control effect of optimal fuzzy control is better than that of optimal state feedback control.     

Geometric error analysis of an over-constrained parallel tracking mechanism using the screw theory

This paper deals with geometric error modeling and sensitivity analysis of an overconstrained parallel tracking mechanism. The main contribution is the consideration of overconstrained features that are usually ignored in previous research. The reciprocal property between a motion and a force is applied to tackle this problem in the framework of the screw theory. First of all, a nominal kinematic model of the parallel tracking mechanism is formulated. On this basis, the actual twist of the moving platform is computed through the superposition of the joint twist and geometric errors. The actuation and constrained wrenches of each limb are applied to exclude the joint displacement. After eliminating repeated errors brought by the multiplication of wrenches, a geometric error model of the parallel tracking mechanism is built. Furthermore,two sensitivity indices are defined to select essential geometric errors for future kinematic calibration. Finally, the geometric error model with minimum geometric errors is verified by simulation with SolidWorks software. Two typical poses of the parallel tracking mechanism are selected, and the differences between simulation and calculation results are very small. The results confirm the correctness and accuracy of the geometric error modeling method for over-constrained parallel mechanisms.     

飞秒激光系统图像调焦装置以及方法

飞秒激光直写技术在复杂三维微结构加工领域具有显著优势，而调焦是否精准直接影响了所加工结构的完整度.提出了在光路中临时置入调焦光源和物的图像调焦技术，通过调节物的位置使其成像面与激光聚焦面一致，从而通过清晰可分辨的成像状态间接反映激光聚焦状态.利用Zemax软件模拟分析了原飞秒激光光路与加入调焦光源和物的调焦光路，二者可实现相同加工物镜后工作距离与良好成像质量，证明了该方法的可行性.通过分析得到该过程的成像误差主要由成像镜头焦深(3.9 μm)引起，我们获得的理想调焦精度可达到1/2焦深以内.设计了单层高度为5 μm的二层圆柱结构，通过多次实验验证了所加工元件高度误差在1.5 μm范围以内，与理论分析一致，满足飞秒激光系统的调焦要求.     

高温铝合金电磁超声检测回波特性及因素分析

针对高温铝合金在线检测条件下，温度对铝合金电磁超声检测回波特性的影响规律尚不明确、高温检测时缺陷定量/定位补偿困难这一难题，以螺旋线圈电磁超声换能器（EMAT）为例，建立了高温铝合金EMAT检测过程的场路耦合有限元模型；研究了温度对EMAT激励/接收换能效率、EMAT激励/接收电路的功率分配特性、超声传播过程中的扩散/介质衰减特性、回波幅值和超声声速等因素的影响规律；研制了耐高温EMAT探头，对20~500℃高温铝合金试样进行了检测实验，并测定了高温铝合金的超声介质衰减系数和超声声速。在仿真和实验相结合的基础上，分析了高温检测时超声回波幅值变化特性及其影响因素。结果表明：对于铝合金这类非铁磁性金属材料，导致高温时超声回波幅值下降的主要原因是超声介质衰减系数随着温度的升高而增大，其次为高温时EMAT激励/接收电路的功率分配特性的改变。在激励EMAT在试样表面形成的洛伦兹力不变的条件下，其所激励的超声波回波幅值具有随着温度的增加而增加的特点，可以有效减缓超声回波幅值下降的趋势。     

基于有限Fourier级数的航天器转移轨迹设计

针对航天器小推力转移轨迹的初始设计问题，利用基于三阶Fourier级数的设计方法实现了航天器小推力的多圈转移。同时，基于有限Fourier级数的形状法，对具有多个约束条件的小推力多圈转移轨迹进行了优化设计。选取了共面同轴同偏心率的初始和末端轨道位置，对所提出的方法进行了仿真验证。结果表明：与改进逆五阶多项式形状法相比，所提出的方法虽然增加了转移时间，但当转移圈数为5圈、有限Fourier级数的项数为10时，可减少将近75%的转移速度增量，同时大大减小了所需的最大推力加速度的值。     

直升机新型旋翼翼型气动特性与布局分析

利用结构网格计算流体力学(Computational fluid dynamics ,CFD)的翼型气动特性分析方法开展旋翼翼型气动特性计算。通过RAE282，NACA0012，OA212，OA207等翼型压力分布、升力和阻力等特性计算结果与试验结果的对比分析，验证了计算方法的准确性，并进一步完成了HF系列旋翼翼型的气动特性计算。基于翼型的气动特性，采用时间步进自由尾迹的旋翼气动性能分析方法开展旋翼桨叶翼型的气动布局优化设计，对悬停和前飞条件下的旋翼开展计算分析，得到两种条件下的旋翼气动特性。而后通过本文建立的优化方法开展旋翼翼型布局优化设计。     

某型装备能源电池异常爆破故障分析

对一起因电池设计缺陷引发装备战训失利的故障进行分析,重点对电池工作机理和设计缺陷展开解析,明确故障定位,并对国内外装备弹上不同体系电池的优缺点进行比较,旨在为产品维护保障、国产化科研等工作提供参考。