Rotation and Shape of High Altitude Reflectors Controlled from the Ground

Passive, inverted-dish shaped communications mirrors made of a thin wire mesh may be maintained in a stationary position above most of the atmosphere by the pressure of reflected radiation beamed at the mirror from the ground. We show that by beaming at the mirror an appropriate mixture of linearly and circularly polarized radiation, and by inducing small periodic variations of the plane of polarization, one can monitor and sufficiently control wire orientation in the mirror, which allows one to reduce mirror weight and/or set the mirror in rotation. Mirror rotation in turn can modify mirror shape, open up flaps, and allow synchronized messages to be sent to prechosen locations.     

Dynamics of a cylindrical shell with a locally damaged protective coating

An approximate solution of a problem on the dynamic behavior of a thin elastic circular cylindrical shell with the damaged heat-protective layer section is presented. The influence of the fracture zone size and its mass on the frequencies of shell natural vibrations and its dynamic deflections is analyzed.     

复合材料层板的瞬态动响应分析

本文用混合杂交单元分析复合材料层板的瞬态动力响应。针对纤维增强复合材料层板的特点,综合考虑精确性和经济性,对于较薄的板采用Mindlin直线假设的位移模式;对于较厚的层板提出分段折线假设的位移模式,并讨论了其适用范围。对动响应分析采用振型叠加法和Wilson-θ积分法确定层板对突加载荷的动挠度和动应力。最后,通过各种数值算例考查本文方法的有效性。     

Aircraft system for measuring the angular deflections of control surfaces

We consider the aircraft system hardware and software to measure the angular deflections of control surfaces. The experimental studies of a photoelectric transducer for converting the control surface angular deflections into digital codes are performed. The mathematical models are obtained to describe a dependence of measuring errors on the coordinates of emitter arrangement. The optimal emitter arrangement is determined using the mathematical models and a pilot model of the aircraft system proposed has been developed.     

飞机蒙皮镜像铣加工稳定性分析

镜像铣技术是近年来提出的一种针对大尺寸薄壁件的加工方法,其加工环保、高效,具有逐步取代传统化铣加工的趋势。针对飞机蒙皮镜像铣加工过程中的颤振问题,首先,根据镜像铣加工特点,建立工艺系统颤振稳定性极限的预测模型;其次,通过有限元方法对蒙皮工件进行模态分析,分析蒙皮不同加工位置动力学特性变化导致的铣削稳定性变化,并通过实验测量获取工件动力学参数,对不同加工位置的稳定性做出预测;最后,开展加工实验,基于非接触测量方法,在线监测镜像铣加工区域的振动位移,通过时、频域信号对加工状态进行辨识,揭示了镜像铣加工过程的稳定性变化及失稳机制,验证了所提方法的准确性,在工程领域具有较高的实用价值。     

跨声速机翼操纵面非定常气动力Euler方程计算

采用代数法与椭圆型方程优化相结合的结构生成方法为带操纵面F5机翼生成面对接块结构网格;弹性变形技术生成动态网格;有限体积法、双时间推进法求解非定常Euler方程.给出一种适于面对接块结构网格计算的守恒量插值方法.数值计算了F5机翼操纵面作简谐运动时的非定常气动力,计算值与试验值吻合较好.     

Neural and fuzzy reconstructors for the virtual flight datarecorder

The results are presented of a comparative study evaluating the performance of neural network (NN) and fuzzy logic reconstructors (FLRs) for the development of a virtual flight data recorder (VFDK). Typical flight data recorders (FDRS) on commercial airliners do not record the aircraft control surface deflections. These dynamic parameters are critical in the investigation of an accident or an uncommanded maneuver. The results are shown relative to a VFDR based on a neural network simulator (NNS) along with a neural network reconstructor (NNR) or a FLR The NNS is trained off-line, using available flight data for the particular aircraft, for the purpose of simulating any desired dynamic output recorded in current FDRs. The NNS is then interfaced with the NNR or with the FLR. The output of the two reconstructors are the control surface deflections which minimize a performance index based on the differences between the available data from the FDR and the output from the NNS. The study tested with night data from a B737-300 shows that both schemes, the one with the NNR and the one with the FLR, provide accurate reconstructions of the control surface deflections time histories     

Dynamics investigation of the two-channel automatic system controlling the mirror of aircraft-based surveillance-search system

The mathematical model of the control system for the mirror having a cardan suspension, installed aboard an aircraft is investigated. Control algorithms that provide the required dynamic properties in scanning, guidance and tracking modes were synthesized. We analyze dynamics of the control system for a mirror with regard to nonlinearities in controllers using the computer-aided simulation.     

飞机平尾偏角引动量的自动检测

根据飞机纵向操纵系统工作原理和纵向平飞操纵原理，推导了平衡速度与平尾偏角的关系式，分析了操纵杆力、平衡速度、平尾偏角的相互关系及平衡速度的调整原理。结合平尾偏角检测现状，提出了一种利用机械臂自动检测飞机平尾偏角的方法，成功研制了平尾偏角自动检测仪，并用于平衡速度的调整。反复检测表明：该检测仪可取代目前广泛使用的人工检测方法，提高了飞机维修保障能力，具有较大的推广前景。     

考虑刷丝变形的刷式密封流场特性与力学特性流固耦合研究

应用双向流固耦合与动网格技术,建立了考虑刷丝变形的刷式密封流场与力学特性双向流固耦合瞬态三维求解模型.首先应用悬臂梁理论建立了刷丝的力学理论模型,将该流固耦合方法计算结果分别与理论模型和实验结果相互验证,在此基础上,分析了刷式密封的流场特性、刷丝的变形规律与应力特性以及刷式密封的滞后特性.研究结果表明:刷丝在气流力作用下会产生摆振运动,刷丝根部所受的应力也随着刷丝摆振运动而呈振荡变化;刷丝变形增大了刷丝与转子面间隙导致密封泄漏量增大,随着刷丝排数的增加,泄漏量先迅速下降,然后下降速度趋缓,最后趋于稳定;刷式密封随着末排刷丝与后挡板轴向间隙的增大,后挡板处相对压力系数逐渐降低,增加末排刷丝与后挡板的轴向间隙可有效降低滞后效应.      

Design and feedforward control of large-rotation two-axis scan mirror assembly with MEMS sensor integration

As a key component of electro-optical systems, a Two-axis Scan mirror AssemblY(TSAY) is usually used for Line-of-Sight(LOS) precision pointing, tracking, scanning, and stabilizing. Therefore, it is necessary for a TSAY to have a large angular range, high dynamic characteristics, and small mirror surface distortion. Furthermore, vibration from carriers of electro-optical systems, such as spacecraft and airplanes, is inevitable, so it is critical to guarantee the control accuracy of a TSAY under vibration. In this paper, a TSAY prototype is designed and developed. To increase the control bandwidth, structural topology optimization is applied to the TSAY's elliptical mirror to reduce the moment of inertia, meanwhile keeping surface flatness. A flexible hinge is adopted to achieve a large angular range. To suppress the angular perturbation caused by the base linear vibration, an adaptive feedforward loop with base-integrated Micro-Electro-Mechanical System(MEMS) accelerators is constructed to enhance the TSAY's feedback loop. Simulation and experimental results show that the TSAY prototype's two-axis mechanical angular ranges are more than ±3.2°, the mirror surface flatness Root Mean Square(RMS) value is better than 0.04 k, and the closed-loop bandwidth is beyond 330 Hz. These are suitable for most applications. Besides, the angular perturbation caused by the base vibration can be suppressed more than 37.7% with the addition of the adaptive feedforward loop.     

过驱动轮控卫星的动态控制分配方法

反作用飞轮在卫星姿态控制中具有重要作用,配置3个以上飞轮的卫星构成一类过驱动系统,能够提高姿态控制系统的可靠性.针对期望控制力矩到冗余飞轮的指令分配问题,提出了一种基于伪逆法的动态控制分配方法,并针对传统伪逆法难以考虑飞轮最大力矩等物理约束问题,采用零空间方法对传统伪逆法给出的分配结果进行了修正.基于稳定控制模式下姿态...     

跨声速机翼静气动弹性数值分析方法

本文给出一种以改进的跨声速守恒型全位势有限体积法为基础的机翼静气动弹性数值分析方法。改进发展了气动网格划分技术，使其对大后掠三角形机翼也能顺利适用。采用位移法计算机翼柔度影响矩阵。将非线性气动力与结构线化机翼弹性变形耦合迭代求解。当气动力和结构变形均收敛后，即求出弹性机翼的气动特性。通过算例计算，表明气动方法改进是成功的，弹性结果是合理的。跨声速范围弹性影响大，值得注意。     

滑模变结构飞行控制系统的设计

针对具有参数不确定性和外加干扰的飞机数学模型在控制执行机构受限的前提下，设计了带有积分项的滑动平面方程，通过选择适当的对角参数矩阵实现三通道的解耦控制。在分析Lyapunov函数的基础上，设计了变结构控制律，既满足滑动平面的到达条件，又保证了系统渐地稳定。对F－16战斗机俯仰角速度跟踪控制系统进行了设计，仿真结果表明，俯仰角速度以较高的精度跟踪给一值，系统性能良好。     

开裂式方向舵对某无尾飞翼布局飞机气动特性影响的实验研究

开裂式方向舵是无尾飞翼布局飞机一种重要的阻力式偏航装置。本文在不同马赫数和舵偏下,通过风洞实验,深入研究了开裂式方向舵的作动对某无尾飞翼布局飞机气动特性的影响。研究结果表明开裂式方向舵是一种合理的偏航式操纵装置,能够在升力、侧力和俯仰力矩变化较小的条件下提供较大的偏航力矩,但也与滚转力矩存在一定程度的耦合。本文的研究为开裂式方向舵的工程化应用提供了一定的基础。     

Electronically steerable plasma mirror based radar-concept andcharacteristics

An alternative to using a phased array to steer a radar beam is to electronically control the orientation of an inertialess broadband microwave reflector. Recent experiments have demonstrated that a planar plasma mirror immersed in a magnetic field can be formed with electron densities high enough to reflect X-band microwave beams. A plasma mirror performs like a metal mirror, but it is inertialess. Compared to high performance phased array systems, a plasma mirror based radar system is much simpler and is therefore more affordable. Electronic steering of microwave beams using a plasma mirror permits the use of wide instantaneous bandwidth waveforms. Potential areas of application for a plasma mirror based antenna system include ship self-defense, high-resolution radar imaging, target identification, electronic countermeasures, high data rate communications, spread spectrum links and remote sensing. As a reflector, the plasma mirror exhibits extremely low loss and the reflectivity is very nearly 100%. Since a perfectly reflecting object cannot radiate, the noise temperature contribution of the plasma mirror to the antenna temperature is likely to be small. The plasma sheet can be steered in elevation by tilting the magnetic field, and steering in azimuth may be accomplished by designating cathode initiation sites. Switching times between successive mirror orientations may be less than 20 μs     

一种快速有效的薄壁件加工表面误差预测算法

 在切削力作用下,刀具/工件的变形是影响薄壁弱刚度件加工精度与质量的关键因素,快速有效地进行表面误差的预测是实现工艺参数优化及在线刀具路径补偿的前提。针对立铣加工过程,提出了一种考虑刀具/工件变形位置的快速柔性迭代算法,基于此建立了薄壁件加工变形预测的有限元计算模型,并通过等效集中力作用位置的确定、模型分割及最小化网格重划方法进一步提高了模型的计算速度。通过刀具/工件的瞬时接触区域的限定算法、实际切深的修正算法、材料去除效应的模拟等关键技术更提高了模型的计算精度。以典型航空铝合金材料为对象,合理安排试验,并通过数值计算结果和试验数据的对比,表明该方法计算精度高,计算速度较文献方法提高了近2倍。     

多操纵面优化控制分配新方法

针对直接分配算法不具备优化能力的问题,提出了一种基于可达集的多操纵面控制量优化分配的新方法.简要描述了飞行控制中多操纵面的受限控制分配问题,以实际和期望的伪指令偏差最小为优化目标,将二次规划问题转化成空间中多维向量的简单运算,避免了二次规划在整个可达集中进行的复杂搜索.以某型飞机为仿真模型,对新方法与直接分配算法进行了对比仿真验证.仿真结果表明,该方法能使舵面在期望指令所指向的可达边界子集中得到最优的分配,且计算量小,实时性较好.     

非常规机动操纵要求的计算

首先推导了飞机运动的逆动力学模型，为使问题具有一般性，采用了刚体运动模型，其中力方程建立在风轴系中，力矩方程建立在体轴系中，并且已知气动力模型，其次，由于飞行轨变地标位置（ｘ，ｙ，ｚ）的形式给出，因此构造了一种基于坐标位置的算法，当给定坐标值后，即可据此对逆问题进行求解并得出相应的操纵要求，最后以一种非常规机动动作为例进行了逆仿真，得出了操纵要求。     

多块协调变形的网格变形技术及其应用

基于多块网格协调变形的理论,提出了适用于叶轮机内流多物边界的更具一般性的网格变形技术,先获得块边界处的变形量,然后插值得到块内网格各点的变形量。通过二维振荡叶栅和带叶尖间隙的三维跨音风扇叶片的非定常绕流算例,证明网格变形技术在叶轮机气弹稳定性数值模拟中的应用是有效的,能够在保证网格高精度的条件下,提高网格变形速度。