Autonomous fault detection and removal using GPS carrier phase

This paper is focused on the use of carrier phase measurements and parity space methodology to investigate the limits of high-integrity and high-continuity satellite-based navigation performance. In this regard, a new algorithm for receiver autonomous fault detection and removal is developed with the specific goal of attaining the high levels of integrity and continuity required for aircraft precision approach and landing applications. Fault detection and removal algorithm performance is demonstrated through analysis and simulation, and the results of tests using deliberately induced failures in raw night data are presented     

高温合金过滤中的界面问题研究

  过滤器吸附固态夹杂须满足两个条件:一是控制熔体的流动状态,使固态夹杂与过滤器相接触;二是熔体、过滤器及固态夹杂之间满足一定的界面能条件,使固态夹杂被过滤器吸附捕获,然后在高温下依靠热能将固态夹杂与过滤器烧结在一起。因此过滤器去除固态夹杂存在着三种机制;机械拦截机制、流体动力学机制及热力学机制。     

材料切除对机匣铣削动力学与稳定性的影响

在薄壁零件加工过程中,工件材料的连续切除会造成工艺系统动力学特性的不断变化,并对工艺系统的颤振稳定性产生显著影响。以航空发动机机匣为对象,研究了其铣削过程中工件材料切除以及切削位置变化对工件动力学特性与颤振稳定性的影响规律。首先,根据机匣的几何结构与铣削工艺特点,提出了按切削行及切削段进行材料切除过程细分的方法。其次,建立了工艺系统动力学特性演化的快速计算方法和颤振稳定性极限的频域预测方法,并在单个切削行内和不同切削行间分析了材料切除过程对工艺系统的影响。结果显示,在单个切削行内工艺系统的动力学特性会小幅度减小,稳定性极限图会向左下方小幅度偏移;在不同切削行间工艺系统的动力学特性变化幅度较大,稳定性极限图呈现出交错排列现象,难以针对整个铣削过程进行切削参数优选,因此提出了基于单行刀位轨迹的切削参数优选方法,保证了整个材料切除过程的稳定切削。最后,进行了机匣铣削与模态试验,验证了所提方法的正确性与有效性。     

一种保持图像纹理的去噪方法

总变分去噪方法自提出以来得到了广泛的发展,该方法处理的数字图像收敛于一个分段光滑的函数,这导致图像纹理特征的大量丢失。将图像视为结构和纹理的组合,定义能够分辨纹理特征的局部方差,并利用定义的局部方差限制总变差保真项,进而在去除噪声的同时很好地保持了图像的纹理特征。针对各类图像进行了仿真试验,结果表明提出的方法是有效可行的。     

铝合金阀门壳体交叉孔数控去毛刺的工艺优化与应用

随着火箭增压输送系统的阀门制造任务日益繁重，阀门零件交叉孔毛刺的去除急需稳定有效的工艺方法。为实现运载火箭铝合金阀门壳体交叉孔相贯线毛刺稳定高效的去除，提出了一种使用过孔刀数控加工去除交叉孔毛刺的工艺方法。设计了过孔刀数控加工去毛刺试验方案，研究了交叉孔相贯线毛刺去除原理，分析了工艺参数对毛刺去除质量的影响规律，得出了铝合金阀门壳体的交叉孔毛刺去除的最优工艺参数。研究表明，该方法能在交叉孔相贯线位置形成过渡圆角，实现了铝合金交叉孔毛刺稳定高效的去除，在航天阀门产品应用中取得了良好的加工效果。     

基于工效分析与过程仿真模型的机载设备拆装时间评估方法

机载设备拆装时间是重要的维修性设计指标,是选择或优化设计方案的重要参数。提出一种以过程 仿真模型为基础,综合考虑维修作业复杂度和维修工效评估结果的拆装时间综合评估方法。首先,将机载设备 拆装过程分解为基础维修活动单元,规划仿真过程并建立仿真模型;然后,使用模特分析法分析基础维修活动 时间,并根据维修作业复杂度与维修工效综合评估结果确定维修时间修正系数,修正基础维修活动时间;最后, 根据基础维修活动时间和工作流程评估机载设备拆装时间,并以飞机发动机拆卸时间分析为例进行应用验证。 结果表明:该方法可对机载设备拆装时间进行准确评估,能够满足飞机研制的需要。     

某型涡扇发动机使用可靠性评估

对某型发动机进行使用故障统计分析,得到故障随使用时间、故障类型的分布和平均故障间隔时间、返修率等可靠性参数。对该型发动机使用返修记录进行统计分析,得到发动机返修、提前换发与发动机返修后使用寿命的关系,以对该型发动机寿命控制提供借鉴或依据。     

基于均匀圆阵的信号二维方向角高精度估计

基于均匀圆阵(UCA),提出一种信号二维方向角的高精度估计方法。首先,充分利用了信号的空、时域信息,构造时空旋转矩阵,从而达到多个信源分离的目的。其次,直接利用UCA的阵列流形,采用最小二乘法估计信号二维方向角。最后,给出解相位整周期性模糊的方法。计算机仿真表明了此方法具有估计精度高,对阵元的幅相误差鲁棒性强等特点。     

分层去除微细电火花铣削加工的NC程序生成

利用简单电极,基于分层制造原理的微细电火花铣削加工技术是实现微三维结构加工的有效手段之一。本文研究了用该方法进行三维曲面加工时的NC程序生成方法,并给出了加工实例。     

Laser Doppler Velocimeter Development

A new two-channel laser Doppler velocimeter developed for the Ames High Reynolds Channel No. II is described. Design features required for the satisfactory operation of the optical system in the channel environment are discussed. Fiber optics are used to transmit the megahertz Doppler signal to the photodetectors located outside the channel pressure vessel, and provision is made to isolate the optical system from pressure and thermal strain effects. Computer-controlled scanning mirrors are used to psoition the laser beams in the channel flow. Techniques used to seed the flow with 0.5-?-diam polystyrene spheres avoiding deposition on the test-section windows and porous boundary-layer removal panels are described. Preliminary results are presented with a discussion of several of the factors affecting accuracy.     

基于测量数据的雕塑曲面数控粗加工

提出一种新的雕塑曲面数控粗加工刀位规划方法。被加工曲面用多面体模型来描述 ,采用分层切削方法加工。在各切削层分别用一个参考平面与毛坯和曲面模型求交 ,根据各相交环之间的拓扑关系 ,求出有效加工区域 ,利用数控编程自动生成粗加工刀具轨迹 ,并进行干涉检查和修正。该方法成功地解决了层切法加工雕塑曲面时不能处理岛中岛的难题。     

Effects of surface topography and specimen thickness on high-speed raindrop impact damage of CFRP laminates

Raindrop impact erosion has been observed since early days of aviation, and can be catastrophic for exposed materials during supersonic flight. A single impact waterjet apparatus is established for mimicking drop impacts at the velocities between 350 m/s and 620 m/s. Carbon Fiber Reinforced Polymer(CFRP) laminates with three different surface morphologies and specimen thicknesses are tested here. A central region with no visible damage has been noticed, surrounded by a “failure ring” with common...     

Shock wave/turbulent boundary layer interaction and its control

The interaction between a shock wave and a boundary layer often leads to extremely detrimental effects, especially if the shock is strong enough to separate the boundary layer. When this happens, there occurs a rapid growth of the dissipative region along with a dramatic intensifying of turbulent fluctuations with the frequent occurrence of buffeting. In the present review some fundamental properties of the interaction are first considered for a two-dimensional, adiabatic flow developing on a flat surface. The following features are first examined: upstream interaction length, incipient shock-induced separation and evolution of the boundary layer properties during the interaction process. Supersonic and transonic flows are both considered. In a second part, the means envisaged to control shock/boundary layer interactions are presented, with emphasis on the physics of phenomena involved in this process. Control methods can be classified into two categories: those acting on the boundary layer properties before it enters the shock region (e.g. wall cooling, wall mass transfer, upstream blowing) and those having a local action in the shock foot region itself (e.g. suction or injection, boundary layer removal, passive control). The most appropriate technique depends on the specific application under consideration. Finally, some calculation methods are briefly presented, most of them being restricted to laminar interactions.     

基于约束序贯M估计的时空域融合红外杂波抑制

针对红外弱小目标检测中的强背景杂波干扰抑制问题进行研究,提出了一种基于参数约束序贯M估计的时空域融合自适应杂波抑制算法.该算法首先在分析序列图像帧间失配的基础上建立了一种改进的时空域融合背景预测模型,结合二维离散傅里叶快速变换图像配准和双线性插值方法进行灰度值估计;然后,基于约束序贯M估计方法进行模型参数的自适应估计,...     

Flank milling optimization - the flamingo project

An approach to increase the material removal rate, to lower the cutting forces, to eliminate necessary hand finish and to assure an improved component accuracy, is to implement the high speed flank milling technology for manufacturing processes. The presented paper analyses the flank milling process. A special consideration is given to the issue of tool deflection and its dependency on the applied process parameters. Further subject is the development of advanced tool path generation for optimised tool positions minimising gauges and stock material as well as reducing the risk of collisions.     

航空电液伺服系统阀套珩磨材料去除体积预测研究

针对珩磨加工阀套孔生产率低、加工精度难控制等问题,开展了内孔珩磨技术研究,通过分析9Cr18不锈钢珩磨过程中材料去除率的变化规律,提出一套适用于珩磨加工的材料去除体积理论公式.同时为使珩后孔不同轴向位置处的孔径趋近一致,需要在上下越程处增设停留时间,以此改进初始模型.基于初始模型与优化模型分别开展单因素珩磨试验,结果表...     

Theory of formation of the ionosphere

Current knowledge about the solar radiation and absorption and ionization cross sections of atmospheric gases is reviewed. Next the main observed features of ionospheric layers are summarized. Using CIRA 1965 model atmospheres the heights of the peak of the ionization rate are calculated for a number of solar emission lines and it is made clear which of these lines are responsible for the formation of E and F1 layers. The mechanism of electron removal in the F and upper E regions as well as in the lower regions is considered, and the mechanism of formation and some behaviours of each ionospheric layer is discussed. In particular, the equatorial F2 layer is briefly considered. Discrepancies are pointed out between the values of the recombination coefficient and the rate constant for ion-atom interchange reaction obtained from ionospheric observations and from laboratory experiments. Inconsistency of the values of the intensity of solar radiation measured by rocket techniques and inferred from ionospheric considerations is also noted. Some evidence is presented suggesting that corpuscular radiation may be responsible for part of the ionization in the ionosphere even in temperate latitudes.     

Energy principle and material removal sequence optimization method in machining of aircraft monolithic parts

In the machining process of aircraft monolithic parts, the initial residual stress redistribution and structural stiffness evolution often lead to unexpected distortions. On the other hand, the stress redistribution and stiffness reduction during the machining process depend on the material removal sequence. The essence of the stress redistribution is releasing the initial elastic strain energy. In the present study, the influence of the material removal sequence on the energy release is studied. Moreover, a novel optimization method is proposed for the material removal sequence. In order to evaluate the performance of the proposed method, the mechanism of the machining distortion is firstly analyzed based on the energy principle. Then a calculative model for the machining distortion of long beam parts is established accordingly. Moreover, an energy parameter related to the bending distortion and the procedure of the material removal sequence optimization is defined. Finally, the bending distortion analysis and material removal sequence optimization are performed on a long beam with a Z-shaped cross-section. Furthermore, simulation and experiments are carried out. The obtained results indicate that the optimized sequence results in a low distortion fluctuation and decreases the bending distortion.     

基于启发强化学习的大规模ADR任务优化方法

随着航天事业的蓬勃发展,空间碎片尤其是低轨碎片已成为航天任务不可忽视的威胁。考虑到碎片清除的紧迫性和成本,低轨多碎片主动清除（ADR）技术成为缓解现状的必要手段。针对大规模多碎片主动清除任务规划问题,首先,基于任务规划的最大收益模型,提出一种强化学习（RL）优化方法,并依照强化学习框架定义了该问题的状态、动作以及收益函数;其次,基于高效启发因子,提出一种专用的改进蒙特卡罗树搜索（MCTS）算法,该算法使用MCTS算法作为内核,加入高效启发算子以及强化学习迭代过程;最后,在铱星33碎片云的全数据集中检验了所提算法有效性。与相关MCTS变体方法以及贪婪启发算法对比,所提方法能在测试数据集上更高效地获得较优规划结果,较好地平衡了探索与利用。     

ASPeCT: Unambiguous sine-BOC(n,n) acquisition/tracking technique for navigation applications

This article presents a new tracking technique for sine-BOC(n,n) (or Manchester encoded) ranging signals, which is most likely to be a part of the new European Global Navigation Satellite System (GNSS), Galileo, signal plan. When traditional sine-BOC(n,n) tracking is considered, although offering excellent performance compared with current signals, it has the main drawback of potentially giving biased measurements. The new method presented herein allows the removal of this threat while maintaining the same level of performance. An adapted version of this technique can also be used for acquisition purposes