同温层气球平台反向定位系统的研究

反向定位系统是针对驻留型同温层气球平台的一种新型定位系统 ,该系统的基本原理是由接收站的位置计算得出发射机的位置。文章采用卡尔曼滤波的方法 ,建立了反向定位系统的模型 ,给出其滤波算法 ;鉴于地面接收站的位置选择对该系统的定位精度有较大的影响 ,给出地面站选址依据 ,并通过计算、仿真获得一组较为理想的布站方式。此外 ,钟差是系统的一个主要误差源 ,文中对其引起的定位误差进行了分析 ,并给出估算的方法 ;对系统中的传播误差、设备误差也进行了分析。最后 ,对系统建立了仿真模型进行仿真。结果表明 ,该定位系统具有较好的定位精度     

涡轮泵转子的临界转速研究(Ⅳ)分布质量轴的传递矩阵法

根据旋转的 Timoskenko梁的运动微分方程式 ,导出分布质量轴段的 4× 4阶精确传递矩阵 ,计入轴分布质量的平动惯量、转动惯量、陀螺力矩和剪切变形的影响 ,并计算了三个转子的临界转速。算例的计算结果表明 ,轴模型是否按分布质量考虑、是否计入平动惯量、转动惯量、陀螺力矩和剪切变形 ,对临界转速有明显的差别 ;同时在等截面轴不分段情况下 ,传递矩阵的计算结果和精确解一致性很好 ,表明计算实际转轴临界转速时 ,只需按截面不同划分轴段 ,即所取的轴分段数量少 ,就可以达到很高的计算精度     

速度调整在空中交通管制中的应用

介绍了航空器有关速度调整（简称调速）的部分性能原理－－调速的基础,又以中国民航、国际民航组织、美国联帮航空局所颁布的规章条例为依据,对目前中国空中交通管制员在提供管制服务时所采用的调速方法及原因的合理性进行了分析,并以Ｂ７３７－３００为例具体说明各种情况下调速范围的选择,最后,提出了笔者的一些观点。     

GPS速度法确定飞机空速系统位置误差

飞机空速系统位置误差的测定,飞行试验中有多种常规方法,但期精度只能满足常规型号空速系统的验证要求。针对这一问题提出了ＧＰＳ速度法,叙述了该方法的原理、实施过程和数据处理方法,讨论了方法的系统精度并给出了误差估算结果。通过对某型飞机的验证试飞,表明该方法简便易行,可满足气动补偿型空速系统的试飞验证要求。     

Time delay compensation in lateral-directional flight control systems at high angles of attack

The previous studies of time delay compensation in flight control systems are all based on the conventional aerodynamic derivative model and conducted in longitudinal motions at low angles of attack. In this investigation, the effects of time delay on the lateral-directional stability augmentation system in high-α regime are discussed based on the $\dot{\beta }$ model, which is proposed in our previous work and proved as a more accurate aerodynamic model to reveal the lateral-directional unsteady aerodynamic characteristics at high angles of attack. Both the $\dot{\beta }$ model and the quasi-steady model are used for simulating the effects of time delay on the flying qualities in high-α maneuvers. The comparison between the simulation results shows that the flying qualities are much more sensitive to the mismatch of feedback gains than the state errors caused by time delay. Then a typical adaptive controller based on the conventional dynamic derivative model and a gain-prediction compensator based on $\dot{\beta }$ model are designed to address the time delay in different maneuvers. The simulation results show that the gain-prediction compensator is much simpler and more efficient at high angles of attack. Finally, the gain-prediction compensator is combined with a linearized $\dot{\beta }$ model reference adaptive controller to compensate the adverse effects of very large time delay, which exhibits excellent performance when addressing the extreme conditions at high angles of attack.     

超大口径环形天线包带展开过程动力学仿真

中间柔性包带是环形可展开天线的重要组成部分.中间包带拔销器解锁后,复材包带与环形桁架同步展开.因复材包带柔性较强,它会绕根部固定端进行回弹,因此展开过程存在金属接头和桁架上复材薄壁管件碰撞风险.随着天线口径增大,该风险会持续增大.基于柔性多体动力学理论对超大型口径环形可展开天线包带展开过程进行动力学建模仿真,并在此基础...     

发动机高速动平衡的振动相位分析

针对发动机转子高速动平衡转速波动、无法保证振动信号同步整周期采样的特点,提出了一种基于转速脉冲的振动信号重构技术,大大提高了相量测量的准确度和稳定性。经试验验证,这项技术是有效、可行的。     

氧化镍电致变色薄膜及其器件的制备与性能研究

以氧化铟锡(ITO)玻璃为基底,采用直流反应磁控溅射法在室温环境下制备了高透过率调制的NiO_x薄膜,利用X射线衍射仪(XRD)、扫描电子电镜(SEM)、紫外可见分光光度计(UV 3600)对薄膜进行分析和表征,研究溅射过程中氩氧比、气压、功率对薄膜结构、形貌及电致变色性能的影响。结果表明：制备的NiO_x薄膜表面有明显的结晶颗粒及孔隙,并沿(200)晶面择优生长;随着气压、功率、氧分压的增大,透过率调制先增大后减小,在时间为45 min、溅射气压4.9 Pa、氩氧比113∶7、功率215 W时最高可达58.3%,着褪色响应时间分别为9和19s,相应的着褪色效率分别为77.56和40.39 cm²/C;以最优工艺的NiO_x薄膜组装了结构为Glass/ITO/NiO_x/Li-electrolyte/WO₃/ITO/Glass的电致变色器件,器件在550 nm处的光调制幅度为46.5%,着褪色时间分别为27和45 s,相应的着褪色速率为1.5和0.9%/s,在循环...     

Laser-induced oxidation assisted micro milling of high aspect ratio microgroove on WC-Co cemented carbide

Severe tool wear and poor surface quality are the main problems during micro machining of cemented carbide. In this work, an innovative hybrid process of laser-induced oxidation assisted micro milling (LOMM) was proposed to solve the problems. A nanosecond laser was utilized to induce oxidation of the WC-20%Co material, producing loose oxide which was easy to remove. The micro machinability of the material was improved by laser-induced oxidation. The oxidation mechanisms of cemented carbide were studied. A microgroove with a depth of 2.5 mm and aspect ratio of 5 was fabricated successfully. The milling force, surface quality and tool wear mechanisms were investigated. For comparison, a microgroove was also fabricated with conventional micro milling (COMM) using identical milling parameters. Results revealed that in LOMM the milling force and tool wear rate were extremely low during removing the oxide. The machined surface quality and dimensional accuracy achieved by LOMM were superior to those obtained by COMM. The surface roughness S_a of the microgroove bottom reached 88 nm in LOMM, while the cross-sectional geometry of the microgroove was a trapezoid. Perpendicularity of the microgroove sidewall machined by LOMM was better than that by COMM. The tool wear forms in LOMM were coating spalling and slight tool nose breakage. Compared with COMM, the tool life in LOMM was prolonged significantly. It indicates that the proposed hybrid process is an effective and efficient way to fabricate high aspect ratio micro-features with high dimensional accuracy.     

基于云贝叶斯网络的运输飞机超轮速风险评估

起飞超轮速严重威胁飞行安全,为了有效评估运输飞机起飞时在不确定性因素影响下的超轮速风险水平,提出一种基于云模型和贝叶斯网络的评估模型。选取抬轮速度、总重、低压转子转速、抬轮率、抬轮时机、升降舵控制量、风的分量、总温8个指标,建立超轮速风险指标体系;运用基于启发式高斯云变换算法和正向高斯云算法的云模型,实现超轮速风险等级软划分和指标离散化,并确定各指标的先验概率;构建超轮速风险的贝叶斯网络,基于所建网络和节点信息计算节点后验概率,通过网络反向诊断得到超轮速的主要诱因。结合实际运行数据进行仿真验证,结果表明：评估结果符合实际情况,验证了模型的有效性。研究结果可为超轮速事件分析、民航运行安全风险管理提供理论依据。