Comparison of computational and experimental results in vibroacoustic active control using piezoelectric film technology

The present investigation concerns control of far-field acoustic radiation generated by a thin plate in a broad frequency band using piezoelectric films. System dynamics is of modal nature.This paper describes a comparison of numerical and experimental results for a closed loop type control. This comes from Optimal Control Theory via radiation filter causal transformation based on a dissipative criterion.     

Impact of the orbital eccentricity on the attitude performance before and after the deorbiting phase for Alsat-1

Due to the presence of periodic forcing terms in the gravity gradient torque, orbit eccentricity may produce large response for the roll, yaw and pitch angles. This paper investigates the influence of the orbit eccentricity on the performance of the attitude determination and control subsystem (ADCS) pointing of passive Low Earth Orbit (LEO) satellites stabilized by a gravity gradient boom or having long appendages before and after the deorbiting operation. The contribution of this work is twofold. First, the satellite attitude dynamics and kinematics are modeled by introducing the orbit eccentricity in the equations of motion of a LEO satellite in order to provide the best scenario in which satellite operators can keep the nominal functionality of LEO satellites with a gravity gradient boom after the deorbiting operation. Second, a Quaternion-based Extended Kalman Filter (EKF) is analyzed when the orbit eccentricity is considered in order to determine the influence of this disturbance on the convergence and stability of the filter. The simulations in this work are based on the true parameters of Alsat-1 which is a typical LEO satellite stabilized by a gravity gradient boom. The results show that the orbit eccentricity has a big influence on the pointing system accuracy causing micro-vibrations that affect the geocentric pointing particularly after the deorbiting phase. In this case, satellites have no orbital correction option. The Quaternion-based Extended Kalman Filter analyzed in this paper, achieved satisfactory results for eccentricity values less than 0.4 with respect to pointing system accuracy. However, singularities were observed for eccentricity values greater than 0.4.     

Multi-rover navigation on the lunar surface

The paper presents a method of determination an accurate position of a target (rover, immobile sensor, astronaut) on surface of the Moon or other celestial body devoid of navigation infrastructure (like Global Positioning System), by using a group of self-calibrating rovers, which serves as mobile reference points. The rovers are equipped with low-precision clocks synchronized by external broadcasting signal, to measure the moments of receiving radio signals sent by localized target. Based on the registered times, distances between transmitter and receivers installed on beacons are calculated. Each rover determines and corrects its own absolute position and orientation by using odometry navigation and measurements of relative distances and angles to other mobile reference points. Accuracy of navigation has been improved by the use of a calibration algorithm based on the extended Kalman filter, which uses internal encoder readings as inputs and relative measurements of distances and orientations between beacons as feedback information. The key idea in obtaining reliable values of absolute position and orientation of beacons is to first calibrate one of the rovers, using the remaining ones as reference points and then allow the whole group to move together and calibrate all the rovers in-motion. We consider a number of cases, in which basic modeling parameters such as terrain roughness, formation size and shape as well as availability of distance and angle measurements are varied.     

某控制组合电磁发射超标分析及解决方案

本文针对电磁兼容测试中,传导发射和辐射发射超过标准限值要求问题,首先介绍了发射超标主要原因,继而梳理超标定位方法和常用电磁兼容加固措施。并以某控制组合为例,应用上述方法制定排查方案,完成电磁发射测试超标问题的干扰定位;并针对干扰源,使用线缆添加屏蔽层、电源端口添加滤波器等加固措施,经验证,措施有效,发射明显降低。同时,本文所述排查方法和加固措施,可为后续电子产品电磁兼容性设计和通过测试提供参考。     

空间机动目标的跟踪和定位

轨道机动控制过程中，推力加速度的不确定性是机动目标运动的主项摄动。通过对推力加速度和机动目标运动建模，在地心惯性系建立了增广系统状态动力学模型，在地平测量坐标系建立了离散量测模型，同时讨论了机动目标增广状态非线性动力学模型的线性化问题。给出了扩展卡尔曼滤波实时估计增广状态向量的算法，仿真分析证明所述算法稳定、收敛，对机动目标具有较高的定位精度。     

基于激光反射层析法的换能器声场测量技术及仿真研究

换能器的辐射声场分布能够直接反映出换能器声学性能的好坏,若不能精确测量出换能器的辐射声场,则会对换能器的诊断和评估造成严重影响。从理论仿真的角度出发,推导了运用激光反射层析法重建换能器辐射声场的理论公式,着重利用推导出的理论公式对激光反射层析法进行了仿真计算。结果表明激光反射层析法能够精确地重建出换能器的辐射声场分布及声场中的声压量值,这为换能器的声场重建及声压测量提供了一种可行的方法。     

某控制组合电磁发射超标分析及解决方案

本文针对电磁兼容测试中,传导发射和辐射发射超过标准限值要求问题,首先介绍了发射超标主要原因,继而梳理超标定位方法和常用电磁兼容加固措施。并以某控制组合为例,应用上述方法制定排查方案,完成电磁发射测试超标问题的干扰定位;并针对干扰源,使用线缆添加屏蔽层、电源端口添加滤波器等加固措施,经验证,措施有效,发射明显降低。同时,本文所述排查方法和加固措施,可为后续电子产品电磁兼容性设计和通过测试提供参考。     

基于半参数建模的弹道目标实时滤波

设计弹道目标的实时跟踪滤波器时,精确的动态建模和测量系统误差自校准是提高滤波精度的重要手段。基于补偿最小二乘原理和Tikhonov正则化定理,将难于参数化的复杂运动成分和测量系统误差表示为非参数分量,建立了基于半参数化建模的弹道递推模型和实时滤波算法,并详细设计了半参数建模时所需的光滑因子、正则化矩阵和窗口宽度等建模参数的在线选取方法。仿真实验和实际数据的计算结果表明,非参数成分可以有效地补偿状态模型误差,且可在线校准测量系统误差,显著改善弹道估计精度。算法已初步应用于实际飞行任务,其中的递推建模方法和参数选择策略对其它实时滤波器的设计同样有参考价值。     

卫星编队飞行相对轨道的确定

卫星之间相对轨道的确定对于多颗卫星编队飞行的控制和任务是十分重要的。结合空间圆形的编队飞行星座，本文给出了描述卫星近距离运动的C-W方程，讨论了空间圆形的编队卫星星座的构成，进而设定了利用激光仪测量星间位置矢量，并设计了Kalman滤波器来实现相对轨道的确定，分析和仿真结果表明，Kalman滤波器能够有效提高相对位置确定精度并给出相对速度的高精度估计。     

旋转目标微波成象中的旁瓣抑制研究

本文首先引出了微波成象中的旁瓣抑制问题,介绍了这领域中前人已得到的结论。接着阐述了传统傅里叶谱分析中的窗函数不能用于旋转目标成象的原因,提出了变迹滤波器的求解方法。最后通过计算机仿真给出了不同相对带宽条件下低旁瓣特性和再现图象,结果是满意的。