星载ScanSAR天线指向稳定度对辐射校正的影响

基于均匀加权天线模型,推导星载ScanSAR天线指向不稳定引起的多普勒中心频率估计误差,建立多普勒中心频率估计误差与图像辐射校正精度之间的数学模型,进而提出星载ScanSAR辐射校正对天线指向稳定度的要求。最后,通过计算机仿真,验证了理论分析的正确性。     

Switching and performance variations of on-orbit BDS satellite clocks

The information of the satellite clock switching and performance variations on-orbit of Chinese BeiDou-2 Navigation System (BDS) is not available for the public. In order to detect the BDS satellite clock switching and performances variation, we analyzed the precise clock offset products with a total duration of 5?years every BDS satellite equipped four atomic clocks from four different manufactures from January 2013 to October 2017. Three important contributions are concluded as follows. (1) It is found that the average time of on-orbit operation for BDS satellite clocks is about 1–2?years. There have been 22 times of clock switching for BDS satellites, of which the C05 and C08 satellites have been switched to the fourth (last) atomic clock. (2) There are frequent phase adjustments for BDS on-orbit satellite clocks, and the frequency series is relatively stable. Furthermore, there are semi-annual sinusoid cycles in the frequency drift series of C06 and C09 satellites. (3) The performances of MEO satellite clocks perform better than the IGSO and GEO satellite clocks. The average ten-thousand frequency stability of BDS satellite clocks is about 1E-13, which is worse than that of GPS and Galileo but better than that of GLONASS.     

Modified unscented Kalman filtering and its application in autonomous satellite navigation

In this paper, a modified unscented Kalman filter (UKF) for nonlinear stochastic systems is proposed, and it is applied to autonomous orbit determination for Earth satellites. Based on some standard results about the boundedness of stochastic processes and a new formulation of the unscented transformation (UT), it is demonstrated that the design of the noise covariance matrix plays an important role in enhancing the filter stability. Furthermore, a particular design of the noise covariance matrix is proposed as a modification of the UKF. The modified UKF is less sensitive to the initial error than the usual one. High performance of the modified UKF is illustrated in comparison with the usual one by using the real data obtained from an Earth sensor.     

Convection of liquid with internal heat release in a rotating container

The convection of heat-generating fluid in a rotating horizontal cylinder is experimentally investigated. The threshold of convection excitation, the structure of convective flows and the heat transfer in the cylinder depending on the heat release capacity, liquid viscosity and aspect ratio of the cavity are studied. It is found that the average convection is excited by the thermovibrational mechanism —the gravity force, rotating in the cavity frame, produces the oscillations of non-isothermal fluid relative to the wall, which in turn result in excitation of mean convective flows. It is shown that the structure of convective flows depends on the dimensionless velocity of rotation. At relatively low rotation velocity the convection develops in the form of a periodic system of vortices regularly distributed along the cylinder axis. The threshold of excitation (critical value of vibration parameter) of three-dimensional vortex structures grows with rotation velocity. Above some definite rotation velocity the convection develops as two-dimensional rolls parallel to the axis of rotation. The threshold of two-dimensional structures excitation does not depend on the rotation velocity. Besides the structure of thermal convective flows the analysis of the relatively weak currents generated by the inertial waves below the threshold of convection is performed.     

系统不确定性边界未知的变结构控制器设计方案

在设计变结构控制器的过程中，确定对象不确定性的范围是一个重要的前提步聚。但是，在某些情况下要确定其边界是相当困难的，或者存在不能精确描述的外部扰动不可能得到其变化的准确范围。针对上述问题，在传统的变结构控制器中加入了对应不确定因素的自适应环节，并证明了该方法设计之控制器的稳定性。仿真结果表明了该法的有效性。     

一种高效稳定的LDO线性稳压器设计

设计了一种准确输出的低压差（LDO）线性电压稳压器。通过采用改进型密勒补偿技术和高电流效率缓冲电路来改善传统LDO线性电压稳压器的稳定性,并采用了一种低噪声的带隙基准电压源的拓扑架构,有效解决了稳压器的噪声问题。在Cadence Virtuoso IC平台下采用TSMC-0．35μm-2P3M的CMOS混合信号工艺进行了仿真和版图设计,仿真结果表明该电压稳压器达到设计目的。     

Stability analysis of explicit guidance laws for space launch vehicles with varying thrust integrals

In this study, a stability analysis of the explicit guidance laws for space launch vehicles is performed with consideration of varying thrust integrals. Among various forms of explicit guidance, linear tangent guidance in its general form is selected and six different acceleration profiles are considered for this numerical experiment. A linear system modeling which includes all of the significant dynamic elements of a space launcher is performed to analyze the effect of the characteristics of thrust integrals on stability margins. Numerical results show that in an aspect of guidance stability, it is advantageous to have thrust integrals derived from increasing acceleration profiles, such as constant thrust case, which may be considered in the development of propulsion systems. Finally, time-domain simulation with the original nonlinear models is performed to verify the approach and the result shows that the nonlinear dynamics of the system is conserved well in the linear model.     

一类多变量MRAC算法的研究

本文应用超稳定性理论证明了由Sobel和Bar—kana等提出的多变量模型参考自适应算法。直接得到了自适应控制信号u_p并且推出了一种δ——校正算法。     

一种简易而精确测试计算机时钟精度的方法

利用８２５３芯片的计时／计数功能，精确而简易地测试计算机时钟精度，误差在十万分之一以内     

混凝土结构中模板高支撑的计算和应用

文章介绍了钢筋混凝土施工中高支撑模板系统的计算及应用情况，解决了施工中模板高支撑的稳定和安全问题，对于实际操作具有一定的指导意义。