基于北斗导航卫星信号的低轨卫星自主定轨（英文）

利用北斗卫星导航信号对低轨卫星自主定轨进行了研究。首先对卫星轨道动力学方程进行了推导,建立一个考虑地球J2摄动下的卫星动力学模型,并利用4阶龙格-库塔数值积分法进行轨道传播。选用北斗卫星导航信号的伪距和伪距率作为定轨的测量方程。然后,对北斗卫星可见星的个数进行了分析。最后,采用SRUKF算法对低轨CHAMP卫星轨道状态进行估计,并通过STK8.1生成仿真数据对SRUKF、UKF和EKF算法的跟踪性能进行对比分析。仿真结果表明,在跟踪过程中最少能接收到18颗北斗卫星信号,能够满足定轨要求。在相同条件下,SRUKF算法的跟踪精度优于UKF、EKF算法,SRUKF算法能减少89%的位置误差和90%的速度误差。     

一种基于自适应去偏转换滤波的机动目标跟踪（英文）

针对于机动目标的跟踪问题,提出了一种基于交互式多模型的自适应去偏转换卡尔曼滤波器。该算法利用交互多模型算法来完成不同跟踪模型的相互切换;根据自适应去偏转换测量卡尔曼滤波算法来推导跟踪目标状态,同时自适应因子可以确保不正常测量时的鲁棒性。与传统的去偏转换卡尔曼滤波算法对比,该算法可以很好地改善所获量测信息在雷达被干扰时的目标跟踪精度。仿真结果表明了算法的有效性和可行性,且跟踪精度相对传统的去偏转换卡尔曼滤波算法减少9.38%的位置误差。     

基于平方根无迹卡尔曼滤波平滑算法的水下纯方位目标跟踪（英文）

为了避免被动跟踪中非线性带来的计算复杂化及跟踪精度的下降,提出将平方根无迹卡尔曼滤波平滑算法(SR-UKFS)应用到水下纯方位目标跟踪。SR-UKFS利用Rauch-Tung-Striebel(RTS)平滑算法将平方根无迹卡尔曼滤波(SR-UKF)作为前向滤波算法得到的目标状态估计向后平滑,得到前一时刻目标状态估计,再利用该状态估计值进行再次滤波得到当前时刻目标状态估计。该算法得到的前一时刻的目标状态估计更加精确,从而进一步提高了目标跟踪的精度。最后,通过对SR-UKFS算法和SR-UKF算法的跟踪性能进行了对比分析和验证,仿真结果表明在相同条件下,SR-UKFS算法能减少59%的位置误差和54%的速度误差,SR-UKFS算法应用于水下纯方位目标跟踪系统是有效的,为水下纯方位目标跟踪系统的工程实现提供了非常有价值的参考。     

一种基于双IMU框架的室内个人导航方法（英文）

为了实现低成本的室内行人导航,提出了一种双惯性测量单元(IMU)框架。在这种模式下,一个IMU固定于足部,另一个IMU固定于肩部。当行人在行走过程中处于静止状态时,卡尔曼滤波器利用测量得到的速度和角速度误差对足部IMU的解算误差进行预估,与此同时,通过对足部IMU和肩部IMU测量得到的航向角做差完成对航向角误差的观测。在此基础上,双IMU框架结构采用了闭环模式。实验结果显示,采用该方法能够提供行人导航信息,平均位置误差与采用开环模式的方法相比降低了14.93%左右。     

一种基于快速反射镜的星敏感器图像稳定系统（英文）

在机载星敏感器工作过程中,大气抖动和载体晃动将会导致星图模糊产生拖尾,影响测量精度,降低观测效率。基于快速反射镜的星敏感器图像稳定系统通过补偿图像位移保持光路的稳定性。首先利用改进的质心提取算法对星敏感器获取的星图进行开窗搜索,然后在窗口内计算星点质心坐标,以获得星点相对于图像中心的脱靶量。控制系统根据脱靶量驱动音圈电机,带动快速倾斜镜反向位移,补偿外界运动,将星点控制在图像中心,以达到稳定图像的目的。研究结果表明,当系统的校正频率为100Hz,曝光时间为8ms时,图像晃动的幅度可减小约3个像素。载体运动对成像的影响基本消除,同时大气抖动导致的图像抖动也被大大改善,系统的观测效率得以显著提升。     

A low-complexity tracker design for uncertain nonholonomic wheeled mobile robots with time-varying input delay at nonlinear dynamic level

A low-complexity design problem of tracking scheme for uncertain nonholonomic mobile robots is investigated in the presence of unknown time-varying input delay. It is assumed that nonlinearities and parameters of robots and their bounds are unknown. Based on a nonlinear error transformation, a tracking control scheme ensuring preassigned bounds of overshoot, convergence rate, and steady-state values of a tracking error is firstly presented in the absence of input delay, without using any adaptive and function approximation mechanism to estimate unknown nonlinearities and model parameters and computing repeated time derivatives of certain signals. Then, we develop a low-complexity tracking scheme to deal with unknown time-varying input delay of mobile robots where some auxiliary signals and design conditions are derived for the design and stability analysis of the proposed tracking scheme. The boundedness of all signals in the closed-loop system and the guarantee of tracking performance with preassigned bounds are established through Lyapunov stability analysis. The validity of the proposed theoretical result is shown by a simulation example.     

Ultrasound calibration with ladder phantom at multiple depths for breast biopsy navigation system

Ultrasound guided breast biopsy navigation system with a graphical user interface and a passive robotic needle holder is developed to increase the performance and reliability of the radiologist. Ultrasound calibration and tool tip calibration are required before using the system. A ladder phantom is developed to be used for ultrasound calibration in real time system with only one ultrasound image required. The passive robotic needle holder structure results in an identity matrix for the makes the rotation matrix; therefore, only translation and scaling are required in the system. This method can be applied to multiple ultrasound depths, which has a relationship at each depth and a relationship to the ultrasound image on the display. The results show high accuracy (<1 mm.) and rapid calibration (5–10 minutes) which is suitable for a real time system like a breast biopsy navigation system based on tests with a breast phantom.     

Green's function of a point dislocation for the bending of a composite infinite plate with an elliptical hole at interface

Summary  The problem of a hole at bimaterial interface is of practical importance in providing a good understanding of the debonding phenomenon and for determining factors that affect the mechanical properties of composite elements of structures. The problem of a point dislocation in bending bonded dissimilar semi-infinite plates with an elliptical hole at interface is tackled in this paper. Based on the method of analytic continuation and the rational mapping function technique, the problem of obtaining the stress functions in the upper and lower plates is decoupled, and reduced to two Riemann–Hilbert problems. The closed-form solution is obtained. The stress distributions at the bimaterial interface, as well as the debonding at both vertices of the elliptical hole are studied. The stress intensities of debonding are depicted for various parameters. Received 16 March 2000; accepted for publication 12 July 2000     

L2-decay for Navier-Stokes flows in unbounded domains,with application to exterior stationary flows

Communicated by C. Dafermos     

{L}_{2}-gain analysis and output feedback control for continuous-time switched systems with actuator saturation

This paper is concerned with the problem of \(L_2\) -gain analysis for a class of continuous-time switched systems with actuator saturation. Different from the existing results using the state-dependent switching approach, a linear parameter-varying output feedback controller with the time-dependent switching mechanism is designed such that the overall system is exponentially stable and with disturbance tolerance capacity and \(L_2\) gain. Further, the proposed controller is insured by introducing the slack matrices to have less conservatism, which maximizes the ellipsoid where the state trajectories starting from the origin will remain. Sufficient conditions for the existence of the switching and output feedback control law are derived in terms of linear matrix inequalities. Finally, a practical example is given to show the effectiveness of the proposed method.     

Adaptive finite element method for an optimal control problem of Stokes flow with L2‐norm state constraint

An adaptive finite element approximation for an optimal control problem of the Stokes flow with an L²‐norm state constraint is proposed. To produce good adaptive meshes, the a posteriori error estimates are discussed. The equivalent residual‐type a posteriori error estimators of the H ¹‐error of state and L²‐error of control are given, which are suitable to carry out the adaptive multi‐mesh finite element approximation. Some numerical experiments are performed to illustrate the efficiency of the a posteriori estimators. Copyright © 2011 John Wiley & Sons, Ltd.