Source localization using a non-cocentered orthogonal loop and dipole （NCOLD） array

A uniform array of scalar-sensors with intersensor spacings over a large aperture size generally offers enhanced resolution and source localization accuracy,but it may also lead to cyclic ambiguity.By exploiting the polarization information of impinging waves,an electromagnetic vector-sensor array outperforms the unpolarized scalar-sensor array in resolving this cyclic ambiguity.However,the electromagnetic vector-sensor array usually consists of cocentered orthogonal loops and dipoles（COLD）,which is easily subjected to mutual coupling across these cocentered dipoles/loops.As a result,the source localization performance of the COLD array may substantially degrade rather than being improved.This paper proposes a new source localization method with a non-cocentered orthogonal loop and dipole（NCOLD）array.The NCOLD array contains only one dipole or loop on each array grid,and the intersensor spacings are larger than a half-wavelength.Therefore,unlike the COLD array,these well separated dipoles/loops minimize the mutual coupling effects and extend the spatial aperture as well.With the NCOLD array,the proposed method can effciently exploit the polarization information to offer high localization precision.     

Simulation of DC spacecraft power systems

A modular state-variable approach is presented for DC spacecraft power system modeling and simulation. Each modular component is treated as a multiport network, and a state model is written with the port voltages as the inputs. The state model of a component is solved independently of the other components, using its state transition matrix. The state variables of each component are updated, assuming that the inputs are constant. Network analysis principles are then utilized to calculate the component inputs     

Precision Stabilization Systems

This paper discusses the relationships that must be considered in analyzing the design and performance of typical precision stabilization systems. In particular, the disturbance inputs that are due to kinematic and geometrical coupling are examined in depth by considering systems implemented with either a conventional two-axis gimbal or a traditional half-angle mirror assembly. The disturbance coupling that is associated with the gimbal drive actuators and the effect of structural compliance on the stabilization control loops are also discussed in detail. Other aspects of stabilization system design that are considered include the potential improvements in performance that can be achieved by using appropriate multiaxis gimbal configurations and by utilizing the angular pointing characterisitics of beam expansion telescopes.     

非线性气动弹性模型参考自适应控制

 首先将含有前/后缘双控制面二元机翼的动态方程以状态空间形式描述,然后考虑俯仰方向的迟滞非线性模型存在参数不确定性的情况下,利用Lyapunov稳定性理论进行了结构化模型参考自适应控制律设计。仿真结果显示：所设计的控制律能够使开环不稳定的气动弹性系统快速地达到稳定状态。由于最大控制面偏转的存在,来流速度较高时闭环系统仍会发生颤振;根据控制面最大偏转的不同取值,文中给出了闭环临界颤振速度的变化曲线。     

Effects of yaw-roll coupling ratio on the lateral-directional departure prediction and restraint

The experimental data obtained from yaw-roll coupled wind tunnel tests are used for lateral-directional departure prediction, by linearizing the_b model to extract nominal dynamic derivatives at each coupling ratio.The prediction results are compared with those of the existing engineering methods which are based on the conventional aerodynamic derivatives.The comparison shows that the yaw-roll coupling ratio has a great influence on the departure susceptibility.The departure resistance will loss in partial region of the coupling ratio when the angle of attack is higher than a critical value.According to the stable and unstable regions of coupling ratio, a two-segment stability augmentation system with two different feedback gain matrices is obtained by pole-placement method.The two-segment stability augmentation system is used in the simulations of straight and level flight, steady turn, spin recovery and Herbst maneuver.The simulation results are also compared with the applications of a fixed-gain stability augmentation system designed by the conventional aerodynamic derivatives.When the yaw-roll coupling effects are fully considered, the two-segment stability augmentation system is more effective for departure restraint and can provide a better flying quality with less control energy.     

Multiplier Offset Voltages in Adaptive Arrays

The effects of multiplier offset voltages in adaptive arrays are examined. Multiplier offset voltages arise when active circuits are used to implement the error-by-signal multipliers required in an array based on the LMS algorithm. These offset voltages are known from experimental work to have a strong effect on array performance. It is first shown how multiplier offset voltages may be included in the differential equations for the array weights. Then their effect on weight behavior is studied. It is found that the offset voltages affect the final values of the weights, but not the time constants. Furthermore, the effect they have is influenced by the amount of element noise in the array. An adequate amount of noise is necessary to minimize weight errors due to offset voltages. An example is treated to show the effect of offset voltages on the final array weights and the output signal-to-noise ratio (SNR). With offset voltages present, it is found that there is a maximum SNR that can be obtained from the array. A specific input SNR is required to obtain this maximum output SNR. Finally, it is shown that a finite operating range for the weights places a further restriction on the acceptable values of offset voltages and noise.     

活性碳毡对称振子阵列／树脂复合吸波材料的研究

研究了含活性碳毡对称振子阵列吸波复合材料的微波吸收特性.结果表明:含振子阵列吸波材料的吸波性能与入射电场方向、振子两臂间的电阻、振子间的距离和阵列的位置密切相关.对称振子阵列对电磁波的吸收呈各向异性,振子与入射电场平行时,吸波性能较好;随振子两臂间电阻或振子间距的增大,材料的吸波性能先提高后降低,电阻和振子间距均存在最佳值;随振子阵列和试样下表面距离的减小,材料的吸波性能提高,振子与入射电场平行时,本实验条件下可获得有效带宽13GHz,最大吸收峰值-30.3dB的反射衰减.     

高超声速飞行器热环境与结构传热的多场耦合数值研究

为了准确预测高超声速飞行器面临的严峻气动热/力环境以及结构的热力响应,发展了高超声速流动与结构传热耦合框架。采用分区求解方法,通过耦合界面的实时数据传递,实现了基于Navier-Stokes方程的高超声速化学非平衡计算流体力学（CFD）求解器与结构的热力全耦合有限元法（FEM）求解器的多场耦合计算,建立了高超声速飞行器的多场耦合数值分析方法。首先对经典高超声速圆柱绕流实验进行了耦合计算,结果与实验值吻合良好。然后针对典型的超高温陶瓷（UHTC）材料的耦合传热问题进行了数值研究,考虑热传导效应对气动热环境和结构热响应预测的影响,结果表明对于复杂外形且热导率相对较高的UHTC材料,结构内部热传导对热环境和表面温度分布的影响不可忽略。最后针对UHTC材料热物性（比热和热导率）非线性对高超声速流动传热过程的影响进行了研究,结果表明当比热和热导率处于合理的误差范围内时,材料表面温度响应对其变化并不敏感。     

Wave dynamics in the thermosphere: I: Tidal motion

The atmospheric tides, their transmission and excitation in the thermosphere, are discussed in reviewing various investigations in this field. We are still fairly ignorant on the subjects and facing various unsolved problems although there is an established link between the theory and the observation in the dynamo region, the lower boundary of the thermosphere. As to the middle and upper thermosphere the observed data are scanty and only those obtained by satellite drag are available; the theoretical approach is very complicated because of viscosity, thermal conduction, hydromagnetic forces and non-linearity, all of which are effective above certain heights. Moreover, the thermosphere couples mainly with the lower atmosphere, this coupling having been considered only in a very simplified way. Another coupling is between thermal excitation and the resultant motion, the coupling of which has never been considered; thermal excitation has been discussed on a given input. International cooperation in the observations is of vital importance for future studies. New developments of observation techniques are desirable.     

耦合对风扇、压气机畸变传递特性的影响

本文从下游部件对具有畸变流动的压气机性能的影响机理出发, 着重分析了由于高压压气机的存在对具有进口压力畸变的风扇出口畸变强度的影响。采用一种新的快速收敛方法, 结合某型号发动机对耦合的影响进行了定量计算。      

C/C喉衬热化学烧蚀的高维不确定量化分析

为了定量化地评估SRM喷管喉衬烧蚀这一复杂物理化学过程中,不同因素相互制约或激励对喉衬烧蚀整体情况产生的耦合影响,并探寻影响喉衬烧蚀率的关键因素,应用自主研发的高维不确定量化算法,有效解决“维度灾难”问题,研究了燃烧室压强、燃气比热比等７个因素对烧蚀的耦合影响规律,并通过全局敏感度分析技术探究了不同关键因素对烧蚀率变化的贡献程度。研究发现:就烧蚀模型物理机制本身而言,影响烧蚀率的关键因素为燃气比热比、喉部马赫数和燃气温度;考虑实验实际中相关物理量的不确定性输入后,燃烧室压强由于自身较大的不确定度输入成为影响烧蚀率的首要因素。     

类乘波体防热壁板气动加热-温度场耦合特性分析

针对类乘波体防热壁板,采用松耦合算法推进气动热和传热迭代计算,研究气动加热-温度场的耦合特性.结果表明:在壁板达到辐射平衡前,冷壁热流和辐射平衡热流与真实气动加热的误差分别达+55.1%和-15.4%以上,必须将气动加热和温度场进行耦合分析;当地绝热壁面温度不随时间变化,表面传热系数是耦合效应的关键参数;采用平均表面传热系数进行瞬态气动加热-温度场耦合计算只进行2次气动加热计算,壁面温度预测误差在2.5%以内,可有效提高气动加热-温度场耦合计算的效率.      

转子-滚动轴承-机匣耦合系统的不平衡-碰摩耦合故障非线性动力学响应分析

建立了含转子不平衡-碰摩耦合故障的转子-滚动轴承-机匣耦合动力学模型.在模型中,充分考虑了转子系统的不平衡和碰摩故障的耦合.对滚动轴承模型,充分考虑了轴承间隙、滚珠与滚道的非线性赫兹接触以及由滚动轴承支撑刚度变化而产生的VC(Varying compliance)振动.运用数值积分方法获取了系统响应,研究了系统的分叉与混沌运动,分析了旋转速度、碰摩刚度、转子偏心量,轴承座-机匣刚度以及机匣-基础刚度对系统响应的影响,得到了在转子不平衡和碰摩故障耦合下的转子-滚动轴承-机匣耦合系统动力响应规律.      

Atmosphere-magnetosphere-ionosphere system mami

The effects on the terrestrial atmosphere and ionosphere of energy and momentum sources of magnetospheric origin are investigated theoretically. Parameters measured by instruments on board the GGS spacecraft and by the GGS ground-based networks are used as inputs to the models that quantify the magnetosphere-ionosphere-thermosphere coupling. Images of the aurora acquired at ultraviolet, visible and X-ray wavelengths by instruments on board the POLAR spacecraft are particularly useful in this investigation by yielding good spatial coverage and high time resolution of the aurora.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

Preparation of CF/Ni-Fe/CNT/silicone layered rubber for aircraft sealing and electromagnetic interference shielding applications

To meet the needs of preventing information leakage in space engineering and military industry, an efficient method was introduced to obtain layered electromagnetic shielding sealing rubber. The carbon fiber, Ni-Fe coating, and Carbon NanoTube (CNT) were combined by chemical plating and in-situ polymerization to obtain a lightweight (0.14 g/cm²) and thin (1 mm thick) Carbon fiber Fabric (CF)/Ni-Fe/CNT/silicone layered electromagnetic shielding composites. The layered material obtained by adjusting the electroless plating time exhibited a high Shielding Efficiency (SE) of 60.2–85.5 dB in the range of 0–4800 MHz, which can be used for aviation electromagnetic shielding. Carbon fibers and carbon nanotubes mainly attenuated electromagnetic waves through absorption loss, while the nickel-iron alloy coating through reflection loss interacted with the magnetic vector of incident ElectroMagnetic (EM) radiation and magnetic dipoles, therefore, the EM Interference (EMI) shielding composite attenuated EM waves with the “absorption-reflection-absorption” cooperative interaction. Moreover, the flexible fabric substrate adhered with silicone rubber possessed a breaking elongation of 52.3%, which can be utilized as a good sealing material. Simultaneously, the outstanding exothermicity (67.2 °C under the applied voltage of 5 V) makes it possible to be applied in electric heating area. The electromagnetic shielding composites prepared in this paper have good potential in the fields of precision electronic equipment and aviation systems.     

Coupling behavior between adhesive and abrasive wear mechanism of aero-hydraulic spool valves

Leakage due to wear is one of the main failure modes of aero-hydraulic spool valves. This paper established a practical coupling wear model for aero-hydraulic spool valves based on dynamic system modelling theory. Firstly, the experiment for wear mechanism verification proved that adhesive wear and abrasive wear did coexist during the working process of spool valves. Sec-ondly coupling behavior of each wear mechanism was characterized by analyzing actual time-variation of model parameters during wear evolution process. Meanwhile, Archard model and three-body abrasive wear model were utilized for adhesive wear and abrasive wear, respectively. Furthermore, their coupling wear model was established by calculating the actual wear volume. Finally, from the result of formal test, all the required parameters for our model were obtained. The relative error between model prediction and data of pre-test was also presented to verify the accuracy of model, which demonstrated that our model was useful for providing accurate prediction of spool valve’s wear life.     

An energy-based coupling degradation propagation model and its application to aviation actuation system

The degradation of components in complex mechatronic systems involves multiple physical processes which will cause coupling interactions among nodes in the system. The interaction of nodes may be carried out not only by physical connections but also by the environment which cannot be described by single network using the traditional methods. In order to give out a unified model to quantitatively describe the coupling degradation spreading by both physical connections and environment, a novel Energy-Flow-Field Network (EFFN) and a coupling degradation model based on EFFN are proposed in this paper. The EFFN is driven by energy flow and the state transition of spatially related nodes is triggered by the dissipation energy. An application is conducted on aviation actuation system in which the degradation spreading by fluid-thermal-solid interaction is considered. The degradation path and the most probable fault reason can be obtained by combining the state transition and energy output of nodes, which is consistent with the given scenario.     

转子支承不对中故障建模与机理分析

针对工程实际所出现的不对中现象,建立了一个转子支承不对中故障的通用模型。将任意形式的联轴器在径向刚度和角向刚度等效的前提下简化为1个等效模型,该模型与实际的总体径向刚度和角向刚度等效,依据实际联轴器刚度计算得到等效模型参数;根据等效联轴器模型推导出转子系统由于连接对角向位置的不均匀、连接刚度的差异性和非线性等不确定性因素所产生的不对中激励力,基于此建立含转子支承不对中故障的转子-支承耦合动力学模型。通过故障仿真分析得到转子支承不对中故障激励下的振动特征,通过数值仿真验证了平行不对中和角度不对中故障的2倍频和4倍频现象,以及由于角度不对中产生的1倍频轴向振动现象。利用含套齿联轴器的3支点转子故障模拟试验器进行了特征转速下多种不对中工况的振动响应试验,通过比较仿真结果的精度达到85%以上,表明所提出的转子支承不对中故障通用模型的正确有效性。     

Canonical transform for tracking with kinematic models

A canonical transform is presented that converts a coupled or uncoupled kinematic model for target tracking into a decoupled dimensionless canonical form. The coupling is due to non-zero off-diagonal terms in the covariance matrices of the process noise and/or the measurement noise, which can be used to model the coupling of motion and/or measurement between coordinates. The decoupled dimensionless canonical form is obtained by simultaneously diagonalizing the noise covariance matrices, followed by a spatial-temporal normalization procedure. This canonical form is independent of the physical specifications of an actual system. Each subsystem corresponding to a canonical coordinate is characterized by its process noise standard deviation, called the maneuver index as a generalization of the tracking index for target tracking, which characterizes completely the performance of a steady-state Kalman filter. A number of applications of this canonical form are discussed. The usefulness of the canonical transform is illustrated via an example of performance analysis of maneuvering target tracking in an air traffic control (ATC) system.     

基于卡尔曼滤波的星敏感器在轨校准方法

根据星敏感器光学镜头以径向畸变为主的特点,采用一阶径向畸变模型,利用摄像机标定中的径向排列约束(RAC),对其外部姿态和内参数进行在轨校准。以采集到的星点的图像坐标和对应导航星在天球坐标系下的赤经、赤纬信息作为滤波器的输入,外部姿态和内参数作为输出,构造相应的状态方程和观测方程,进行两次卡尔曼滤波迭代,结果作为校准参数的最优估计。仿真实验表明:本方法能消除内部参数与外部参数的耦合,校准过程不依赖外部姿态,且状态方程和观测方程均为线性方程,满足卡尔曼滤波迭代的最优条件,能够精确估计出星敏感器内外参数,在星点成像位置噪声标准差为0.05像素时,校准后x、y方向上的平均误差分别为0.044像素和0.049像素。