基于AADL的航电构型控制系统的建模分析

针对航电系统的不同构型仿真、系统加改装的验证,为了使构型控制系统可以根据应用需求可靠转换,以满足系统结构能够可靠重构的需求,采用先进的建模语言AADL(结构化分析设计语言)完成了对航电构型控制系统的建模设计。结合AADL对航电构型控制系统进行了详细的分析,展示了该系统的特征与关键技术,体现了此系统的工作原理与内部结构。该模型可以表达系统的功能与非功能约束,实现了系统级的组件建模策略,层次化地描述了系统的架构。     

基于反步法与动态控制分配的航天器姿态机动控制

针对存在未知转动惯量与外部干扰的航天器姿态机动控制问题,提出了一类基于反步法的鲁棒自适应控制器,并利用Lyapunov方法分析了系统的稳定性;考虑到作为执行机构的反作用飞轮存在冗余性,进一步提出了一种基于约束最优二次规划的动态控制分配算法来实现指令到期望飞轮的指令分配,克服传统伪逆法难以考虑飞轮动态特性、最大力矩等物理约束,并能有效的抑制姿态敏感器的测量噪声和测量异常值,实现控制力矩的平稳性.最后,将本文提出的控制方案应用于某型轮控刚体航天器的姿态机动任务中,仿真结果验证了本文提出方法的可行性、有效性.     

机场跑道异物定位算法研究

跑道异物的存在给机场安全造成了很大的危险隐患,为了减小异物存在导致的经济和人身安全的影响,利用三维坐标定位技术,将Hough变换改进后用于确定跑道位置,归一化算法实现以机场跑道灯为特征点的匹配,同时为了提高匹配效果,采用特征点旋转整合,有效获取特征点位置。结合传感器逐区域扫描时的方位改变与像机初始坐标系换算关系,确定跑道异物的相对空间位置,实现对跑道异物的定位。该算法利用坐标变换方法,理论基础完善,实际应用时,所需传感器数目较少,成本较低,定位准确,有很好的应用价值。     

A cam-quadrilateral mechanism for power transmission of a twin-rotor piston engine

A quadrilateral with four invariable lengths of sides has the characteristic of transforming the variation of the diagonal length to the variation of its interior angle. Thus, the combination of two quadrilaterals with a cam forms the differential velocity drive mechanism (DVDM) of a novel twin-rotor piston engine (TRPE). The DVDM restricts the two coaxial rotors to rotate with periodical but nonuniform velocity, and the volume of working chambers created by the adjacent vane pistons of the two rotors alternately expands and then contracts. The volumetric change of working chambers is used to generate the four-stroke engine cycle. The kinematic model and the detailed position, velocity, and acceleration analysis results of the TRPE are presented. The results show that this novel engine, associated with the advantages of higher uniformity of torque and power density due to multiple power strokes per revolution of the output shaft, has a compact and totally balanced design.     

Load transfer of graphene/carbon nanotube/polyethylene hybrid nanocomposite by molecular dynamics simulation

Load transfer of the graphene/carbon nanotube (CNT)/polyethylene hybrid nanocomposite is studied here from molecular dynamics (MD) simulations. Simulations of this composite material under uniaxial tension were conducted by varying CNT’s position and diameter in the polymer matrix. The obtained results show that: (1) The peak strength of stress and strain evolution in the polymer matrix is lower than the peak strength of the graphene/graphene and graphene/polymer interfaces. Hence, the damage zone is always located in the polymer matrix. (2) Agglomerated two-layer graphenes do not possess an increased value in the peak strength compared with single-layer graphene-reinforced polymer nanocomposite (PNC), while two separate layers of graphene show slightly higher peak strength. (3) The largest peak strength is observed before CNT moves to the center of the polymer matrix. The damage location moves from the upper to the lower part of CNT when the CNT is located at the centre of polymer matrix. (4) The influence of the CNT diameter on the peak strength is not obvious, while the damage location and shape in the polymer matrix changes with respect to varying CNT diameters. In addition, the damage zone always falls outside the interphase zone.     

A robust adaptive weighted constant modulus algorithm for blind equalization of wireless communications systems under impulsive noise environment

A robust adaptive weighted constant modulus algorithm is proposed for blind equalization of wireless communication systems under impulsive noise environment. The influence of the impulsive noise is analyzed based on numerical analysis method. Then an adaptive weighted constant modulus algorithm is constructed to adaptively suppress impulsive noise. Theoretical analysis is provided to illustrate that the proposed algorithm has a robust equalization performance since the impulsive noise is adaptively suppressed. Moreover, the proposed algorithm has stable and quick convergence due to avoidance of large misadjuntment and adoption of large step size. Simulation results are presented to show the robust equalization performance and the fast convergence speed of the proposed algorithm under both impulsive noise and Gaussian noise environments.     

Erosion resistance of CO2 corrosion scales formed on API P110 carbon steel

The erosion resistance of CO₂ corrosion scales formed on carbon steel was investigated in water–sand two-phase flow utilizing weight loss test, scanning electron microscopy, and X-ray diffraction. The effects of CO₂ partial pressure, stirring speed, test time, and grain size on the erosion resistance of the scales were analysed. Results show that several characteristics of CO₂ corrosion scales are key factors affecting erosion resistance. Cubic polynomials are used to fit the erosion rate data, and effectively evaluate the ability of CO₂ corrosion scales to resist erosion. An erosion mechanism, based on fluid dynamics and CO₂ corrosion scales characteristics, is discussed.     

磁性磨粒辅助磁针磁力研磨的应用研究

目的解决磁针磁力研磨工艺中磁针对工件表面碰撞损伤及存在研磨盲区的问题。方法在磁针中加入磁性磨粒增加磁针束的柔性,同时磁针为磁性磨粒提供研磨压力和切削力。将三相正弦交流电接入定子线圈,利用交流电的相位差产生旋转磁场,驱动混合磨料对微小复杂工件进行研磨。在混合磨料总质量不变的条件下,依次采用磁针、磁性磨粒和不同质量混合比的混合磨料进行对比试验。结果相较于单一磨料,使用混合磨料加工40 min后的工件表面形貌较好,表面粗糙度值下降幅度大,且有较大的材料去除量。当磁针与磁性磨粒的质量混合比为1∶2时,加工后的工件表面形貌最佳,无明显加工纹理和磁针碰撞痕迹,工件表面粗糙度值由原始的1.0μm下降到0.54μm左右,材料去除量为2.8 mg左右,微小沟槽内无研磨盲区。结论在电磁研磨工艺中,使用磁针和磁性磨粒质量比为1∶2的混合磨料可提高研磨效果,避免磁针的碰撞对工件表面造成损伤,磁针可将磁性磨粒挤入工件微小沟槽,无研磨盲区。     

时频分析在轴承故障诊断中的应用研究

在齿轮与滚动轴承的故障诊断中,由于振动信号的不平稳性,时频分析得到越来越广泛的重视.时频分析着重于研究信号能量在某一特定时间和频率处的分布.研究了一种新的时频分布,利用时频分布的新核来分析滚动轴承故障.通过对比证明,新核的能量集中度优于WVD.     

基于LXI的飞机音频管理系统检测系统研究

飞机音频管理系统检测中一方面要模拟、测量与之存在交联的来自机载导航和通信设备的信号,且测试项目、信号种类和数量繁多;另一方面,还要控制和监视专用试验平台模拟机载运行环境以便音频管理系统故障复现,因此基于LXI总线的自动测试系统构建方案成为最佳选择。在软件开发中,通过分析被测对象的测试需求和测试过程,提出面向对象的模块化软件开发方法,大大提高了软件复用性和开发效率。实践证明,采用LXI总线提高了自动测试系统的可靠性,缩短了航修公司的维修时问,降低了维修成本,提高了维修效率。