Automatic target recognition for hyperspectral imagery using high-order statistics

Due to recent advances in hyperspectral imaging sensors many subtle unknown signal sources that cannot be resolved by multispectral sensors can be now uncovered for target detection, discrimination, and identification. Because the information about such sources is generally not available, automatic target recognition (ATR) presents a great challenge to hyperspectral image analysts. Many approaches developed for ATR are based on second-order statistics in the past years. This paper investigates ATR techniques using high order statistics. For ATR in hyperspectral imagery, most interesting targets usually occur with low probabilities and small population and they generally cannot be described by second-order statistics. Under such circumstances, using high-order statistics to perform target detection have been shown by experiments in this paper to be more effective than using second order statistics. In order to further address a challenging issue in determining the number of signal sources needed to be detected, a recently developed concept of virtual dimensionality (VD) is used to estimate this number. The experiments demonstrate that using high-order statistics-based techniques in conjunction with the VD to perform ATR are indeed very effective     

Dynamic modeling and beating phenomenon analysis of space robots with continuum manipulators

Space robotics has been used extensively in complex space missions. Rigid-manipulator space robots may suffer from rigid-body collisions with targets. This collision is likely to cause damage to the space robot and the target. To overcome such a problem, a novel Continuum-Manipulator Space Robot (CMSR) for performing on-orbit servicing missions is proposed in this paper. Compared with rigid-manipulator space robots, CMSRs are able to perform compliant operations and avoid rigid-body collisions with a target. The CMSR consists of two kinds of flexible components, including solar arrays and continuum manipulators. The elastic vibrations of these flexible components disturb the position and attitude of CMSRs. The beating phenomenon introduced by the energy transfer among these flexible components can cause damage to solar arrays. The complicated dynamic coupling poses enormous challenges in dynamic modeling and vibration analysis. The dynamic model for CMSRs is derived and the mechanism of the beating phenomenon is analyzed in this paper. Simulation results show that an obvious beating phenomenon occurs and the amplitude of the solar arrays increases significantly when the natural frequencies of two kinds of flexible components are close. A method is provided to avoid the beating phenomenon.     

Acceleration sensors based modal identification and active vibration control of flexible smart cantilever plate

Some flexible appendages of spacecrafts, such as solar panels, are cantilever plate structures. Thus, vibration problem is unavoidable when there is slewing maneuver or external disturbance excitation. Vibration of such cantilever plate structures includes coupled bending and torsional motion. Furthermore, the low amplitude vibration near the equilibrium point is very difficult to be quickly suppressed due to nonlinear factors of the hardware in the system, which is harmful to stability and attitude control accuracy. To solve these problems, acceleration sensor-based modal identification and active vibration control methods are presented for the first two bending and the first two torsional modes vibration of the cantilever plate. Optimal placements of three acceleration sensors and PZT patches actuators are performed to decouple the bending and torsional vibration of such cantilever plate for sensing and actuating, and identifications are achieved by experiments. A nonlinear control method is presented to suppress both high and low amplitude vibrations of flexible smart cantilever plate significantly. Experimental comparison researches are conducted by using acceleration proportional feedback and the presented nonlinear control algorithms. The experimental results demonstrate that the presented acceleration sensor-based methods can suppress the vibration of cantilever plate effectively.     

浮环轴承非线性耦合动力润滑特性

针对浮环轴承-柔性转子结构的某型微型燃机实验结果的分析,结合浮环轴承非线性耦合动力润滑的机理研究,进一步研究与探讨了浮环轴承流固耦合润滑的非线性行为.给出了浮环轴承存在的五种典型非线性振动的频率特征,阐明了转子临界区域工频振动特征与转子涡动频率谐波振动特征的区别与联系,同时也明确了相应的振动抑制或消除的措施及方法.根据单膜润滑油膜承载能力及涡动速度的解析表达式,论证了浮环轴承半速涡动的频率特征及其稳定性.试验证明,浮环内、外油膜半速涡动与油膜振荡现象的涡动比接近于0.5与0.3,并且理论与实验具有很好的一致性.这为浮环轴承的设计及性能研究提供了相应理论与实验的依据.      

An Optical Technique for Simultaneous Beamforming and Cross-Correlation

This paper presents a method of greatly simplifying the processing of received signals from antenna arrays through the use of a coherent optical system for signal processing. It is shown that a coherent optical system is ideally suited for carrying out beamforming operations. Several other advantages of coherent optics for this application are also discussed. A major result is a technique for forming several unambiguous beams simultaneously by correlating the signals from two linear arrays. The coherent optics technique permits this operation to be carried out with extreme simplicity.     

Sensor/actuator placement for flexible space structures

A new approach for the placement of sensors and actuators in the active control of flexible space structures is developed. The approach converts the discrete nature of sensor and actuator positioning problems to a nonlinear programming optimization through approximation of the control forces and output measurements by spatially continuous functions. The locations of the sensors and actuators are optimized in order to move the transmission zeros of the system further to the left of the imaginary axis. This criterion for sensor/actuator placement can be useful for optimal regulation and tracking problems, as well as for low authority controller designs. Two performance metrics are considered for the optimization and are applied to the sensor/actuator positioning of a large-order flexible space structure     

变截面梁式压电智能板振动控制的小波模式

基于 Daubechies小波理论的尺度函数变换 ,对于变截面悬臂板结构的弯曲建立了由压电片感应器的观测电量识别挠曲变形构形的显式关系式。此基础上 ,采用具有位移与速度信号负反馈控制律后 ,建立了抑制振动的压电动力控制程序。由于小波尺度函数逼近具有低带通性质 ,即具有自动滤除高频分量的能力 ,该控制程序将不会出现由观测溢出与控制溢出耦合而造成的控制失稳 (即在抑制低频 (阶 )扰动时系统激发出高频 (阶 )扰动的现象 )。数值仿真结果表明 :该控制方法所能控制的模态阶数与压电片数相同 ,而且其控制程序在抑制外界干扰方面是有效的。     

Variable structure control and active vibration suppression of flexible spacecraft during attitude maneuver

This paper presents a new approach to vibration reduction of flexible spacecraft during attitude maneuver by using the theory of variable structure control (VSC) to design switching logic for thruster firing and lead zirconate titanate (PZT) as sensor and actuator for active vibration suppression. The spacecraft to be investigated is a hub with a cantilever flexible beam appendage, which can undergo a single axis rotation. The proposed control system includes the attitude controller acting on the rigid hub, designed by variable structure control technique, and the surface-bonded PZT patches for active vibration suppression of flexible appendages, designed by the positive position feedback (PPF) control technique. To avoid chattering, pulse-width pulse-frequency (PWPF) modulation is adopted for the thruster control, which makes the thrusters to be operated in a close to linear manner and also can suppress the relatively large amplitude vibrations excited by, for example, rapid maneuver. However, some residual micro-vibrations still exist due to the switching actions. Upon that, the technique of active vibration control using PZT is turned on to provide further vibration suppression of the residual micro-vibrations and fine tuning of the system performance. By combining the advantages of both these control strategies, an improved performance for vibration control in both the macro-and micro-senses can result. Both analytical and numerical results are presented to show the theoretical and practical merit of this approach.     

常规闭口风洞相阵列气动声学试验

传统气动声学研究观点认为,精确的声学测量要求风洞背景噪声和洞壁反射足够低,传声器测量结果有足够高的信噪比,这是大多数风洞无法达到的要求。近些年,基于声纳和雷达技术发展起来的麦克风相阵列技术可以通过增加阵列的传声器数目从而大幅提高声学测量的信噪比,具有噪声源研究和定位能力,并被成功地应用于非声学固壁风洞噪声源测量和噪声物理机制研究。作者基于相阵列波束生成频域算法研制出常规闭口风洞相阵列系统及相关技术,在FD-09风洞尝试进行了相阵列校准试验和某民机噪声测量试验。结果表明：相阵列技术能够准确捕捉到真实的校准声源,并从技术上验证了相阵列系统在常规闭口风洞测量气动噪声是有效的。     

Advanced measurement of rotor vibration in electric drives

The combination of microelectronic acceleration transducers and an RF telemetry link can provide a reliable means of measuring shaft vibrations of electric drives. Clear advantages include the possibility of installing the instrumentation into currently existing motor systems without any need to use flexible couplings or mounts. The proposed system covers frequencies up to several kilohertz and can handle torque transients of 20 Nm with a typical uncertainty of 1%. The preliminary system is extendable to cover adaptive control of dynamic drive performance and can be customized to specific speed and torque ranges     

Ultra-lightweight space power from hybrid thin-film solar cells

The development of hybrid inorganic/organic thin-film solar cells on flexible, lightweight, space-qualified, durable substrates provides an attractive solution for space power generation with high mass specific power (W/kg). The high-volume, low-cost fabrication potential of organic cells will allow for square miles of solar cell production at one-tenth the cost of conventional inorganic materials. Plastic solar cells take a minimum of storage space and can be inflated or unrolled for deployment. We explore a cross-section of NASA in-house and sponsored research efforts that aim to provide new hybrid technologies that include both inorganic and polymer materials as active and substrate materials. For NASA applications, any solar cell or array technology must not only meet weight and AMO efficiency goals, but also must be durable enough to survive launch and space environments. Also, balance of system technologies must be developed to take advantage of ultra-lightweight solar arrays in power generation systems.     

风洞模型-支撑系统涡激振动测量与分析

以0.55m×0.4m低湍流航空声学风洞某模型及其支撑系统为研究对象,采用基于加速度传感器直接测量支撑系统和热线间接测量模型尾流相结合的方法,测量并分析了风洞模型-支撑系统的涡激振动模态,给出了测量方案和数据处理方法。采用基于加速度传感器的功率谱分析方法,获得了模型-支撑系统的三阶振动频率分别为31.1、120.9和221.4Hz;采用基于加速度传感器的频域滤波和频域积分方法,提高了有效信号的信噪比,获得了模型-支撑系统振动的振型和振动节点位置;采用热线测量模型尾流分离涡脱落频率的方法,获得了模型一阶和二阶振动的尾流涡激频率分别为31.1和124.1Hz,并从测量尾流速度脉动量获得了模型振幅变化和抖振边界信息。实验结果表明,采用热线测量模型尾流从而分析模型振动的方法,有利于小尺度的模型振动测量,而且相对于加速度传感器装于模型表面的直接测量方法而言,对试验模型的绕流流场干扰较小,为测量风洞试验模型的涡激振动模态提供了一种方法。     

An intelligent algorithm for coherent sound source localization based on a strong tracking filter

Background noise is inevitable when sensor arrays are used for aeroacoustic measurements in wind tunnels. The direct removal of background noise, however, would affect the measurement accuracy. In particular, the existing array signal processing algorithms are either invalid or inefficient for removing the noise that is coherent with the signal of interest. In this paper, an intelligent algorithm is developed to localize the coherent sound sources and background noise in real time by iteratively checking the collected data from the array. The proposed method can automatically adjust the suboptimal fading factor to extract useful information as much as possible in residual sequence. This algorithm is tested in simulations and then demonstrated in an experiment.Compared to the two existing methods, the results indicate that the new method has a good phase-shift tracking ability and rapid estimation-error convergence speed, and can achieve an acceptable performance even for low-cost acoustic sensors. Overall, the proposed method should assist array beamforming and hence benefit aeroacoustic measurement.     

针对SF6分解气的多参数综合监测平台设计

设计了SF6分解气多参数综合监测平台,选择多频正弦调制方法研发了基于FPGA的多通道锁相放大电路,并对多通道锁相放大原理进行了理论推导,提出一种多频调制信号的频率分配原则.搭建针对多组分气体的多参数综合监测平台,给出温度、压强、微水、SF6纯度等传感器的集成方案.实验结果表明,本系统平台能够从较低浓度的H2S、HF、CO混合气体中正确解调出二次谐波信号,不同气体的二次谐波之间干扰性较小,对弱吸收的CO气体信号提高2个数量级,实现了多组分微量气体的同时监测.     

裂纹转子非线性振动特征的谐波小波与分形识别

通过对谐波小波的分析研究,指出了谐波小波对振动信号局部频段分析的优良特性。采用谐波小波对裂纹转子的非线性振动信号在低频段进行了分析。理论分析与实验结果表明:对实际裂纹转子信号,经谐波小波的频段分析后,能够得到通常难以由理论分析与实验结果获得的非整数倍周期分叉的非线性特征频谱。计算了裂纹转子的分形维数,发现裂纹转子的振动信号比理论结果要复杂、可以用多重分形作为判断实际转子是否有裂纹的一个特征。提出了用谐波小波变换后的奇异谱来识别裂纹转子非整数倍周期分叉的非线性特征频谱的方法,并对实际转子信号进行分析,得到了明显的非整数倍周期分叉的奇异谱。      

柔性转子振动的计算机控制

本文从理论和实验证明了柔性转子的振动可以进行控制。并介绍了一种控制方案,它是利用一套液压系统来改变支承的刚度,支承刚度大小随油压的变化而变化,支承刚度的变化可以控制转子系统的振动。本文还介绍了计算机控制系统,此系统接收振动和转速信号,并根据这些信号改变油压,使得转子系统和支承系统达到最佳的匹配关系,从而达到对柔性转子振动的自动控制。      

Reducing geometric dilution of precision using ridge regression

A signal processing technique is proposed for improving position-fix navigation system accuracy performance when the geometry of the navigation landmarks (e.g. sensors) are nearly collinear. In the navigation literature, the accuracy degradation associated with a nearly collinear measure geometry is termed the geometric dilution of precision (GDOP). Its presence causes not only the variance of the position estimates to be highly inflated but also any bias terms which may be present in the model. Since a nearly collinear predictor matrix is mathematically equivalent to GDOP, it is proposed to use the ridge regression technique in a navigation signal processor. A position-fix algorithm based on ridge regression reduces the bias and variance inflation caused by GDOP and the overall mean-squared position error as well. Ridge regression contains the GDOP-sensitive least-mean-square (LMS) estimator as a special case. Even with a matched model, GDOP can inflate the mean-square error (MSE) of the ordinary least-squares estimator, whereas the ridge regression technique chooses a suitable biased estimator that will reduce the MSE, which is the main goal. The ridge concept is extended to include GDOP-amplified bias errors. A simple range/range navigation system is analyzed to illustrate the underlying principles of ridge regression     

压电作动器用于振动主动控制技术的研究

 从理论和实验两方面分析了利用压电作动器进行柔性结构振动主动控制的机理，从能量的角度对施加控制时悬臂梁自由衰减振动的阻尼比进行了理论计算，得出了主动阻尼比与反馈增益之间的关系。建立相应的实验系统，对上述关系式进行了实验验证。     

Phase Compensation for Widely-Spaced Antenna Systems Employing Coherent Signal Combinations

This paper describes a technique for providing phase compensation to signals received at widely-spaced antennas and processed at a central location. Self-compensation is provided for pathlength variations in reference-signal distribution systems. The technique may be adapted to include the measurement and compensation of signal-channel phase variations. Practical systems which require this type of compensation include interferometric systems used for position and position-rate measurements of missiles and spacecraft, interferometers and arrays of antennas used for radio and radar astronomy, and arrays of large-aperture antennas used for deep-space communications.     

基于机敏材料的冗余度柔性机器人复模态主动控制

研究了基于机敏材料的冗余度柔性机器人的振动主动控制问题。应用复模态理论对机器人的动力学方程进行解耦 ,建立了受控系统的状态空间表达式。利用极小值原理设计了连续LQR状态反馈控制器 ,并根据对偶原理设计了具有指定稳定度的Luenberger全维状态观测器。平面 3R冗余度柔性机器人的仿真算例表明 ,该方法可以显著改善受控系统的动力学性能。