DAB系统中一种低复杂度的整偏算法

文章以欧洲尤里卡-147数字音频广播接收系统为研究重点,提出了一种基于OFDM的通信系统的低复杂度粗偏估计算法。仿真结果显示此算法具有较好的鲁棒性来对抗较大范围的符号定时偏移,且具有较低的实现复杂度。     

基于灰色系统理论的软件可靠性综合评价框架

从系统工程的角度出发,提出一套完整的基于灰色系统理论的软件可靠性综合评价框架.首先,在ISO/IEC 9126软件质量模型的基础上,建立起软件可靠性综合评价体系,并利用灰关联分析方法计算每个度量元与软件可靠性之间的相关程度,由此确定度量元在评价体系中的权重值.在此基础上,提出基于灰色聚类的软件可靠性综合评价方法.初步的实验结果表明,基于灰色系统理论的软件可靠性综合评价框架具有方便实用、全寿命周期评价、数据来源广泛、且可准确反映当前软件可靠性指标水平等优点,适合于软件可靠性工程决策活动.      

电磁阀动态响应特性的有限元仿真与优化设计

 利用有限元分析软件Maxwell 2D/3D计算电磁阀的动态响应特性,仿真出其工作电流曲线和磁化曲线,并进行变参数化设计,由此可实现对电磁阀设计方案的评估和优化。通过对比仿真结果和产品实测数据,证明了这种有限元设计方法行之有效。     

一种高距离分辨低截获概率雷达信号性能分析

首先分析步进频率雷达信号实现高分辨率的优缺点,在此基础上设计了一种改进的步进频率信号-参差脉冲重复间隔步进频率信号,然后分析了该信号的处理过程.与步进频率信号在高速目标下成像失真相比,参差脉冲重复间隔步进频率信号的多普勒性能有了很明显的改善.最后分析了参差脉冲重复间隔步进频率信号的低截获概率特性.     

A Cosmic Microscope to Probe the Universe from Present to Cosmic Dawn:Dual-element Lowfrequency Space VLBI Observatory

A space-based Very Long Baseline Interferometry (VLBI) program, named as the Cosmic Microscope, is proposed to involve dual VLBI telescopes in the space working together with giant ground-based telescopes (e.g., Square Kilometre Array, FAST, Arecibo) to image the low radio frequency Universe with the purpose of unraveling the compact structure of cosmic constituents including supermassive black holes and binaries, pulsars, astronomical masers and the underlying source, and exoplanets amongst others. The operational frequency bands are 30, 74, 330 and 1670 MHz, supporting broad science areas. The mission plans to launch two 30-m-diameter radio telescopes into 2 000 km×90 000 km elliptical orbits. The two telescopes can work in flexibly diverse modes. (i) Space-ground VLBI. The maximum space-ground baseline length is about 100 000 km; it provides a high-dynamic-range imaging capacity with unprecedented high resolutions at low frequencies (0.3 mas at 1.67 GHz and 20 mas at 30 MHz) enabling studies of exoplanets and supermassive black hole binaries (which emit nanoHz gravitational waves). (ii) Space-space single-baseline VLBI. This unique baseline enables the detection of flaring hydroxyl masers, and more precise position measurement of pulsars and radio transients at mas level. (iii) Single dish mode, where each telescope can be used to monitor transient bursts and rapidly trigger follow-up VLBI observations. The large space telescope will also contribute in measuring and constraining the total angular power spectrum from the Epoch of Reionization. In short, the Cosmic Microscope offers astronomers the opportunity to conduct novel, frontier science.      

高室压脉冲推力器冷流实验

为了检验高室压脉冲推力器的设计并了解其工作特性,进行了冷流实验.可移动喷注器的动态密封采用O型圈结构,推进剂的流动通道既能保证充填时推进剂的流通,又能保证挤压时不会有回流.实验表明密封效果良好,摩擦力大小符合设计要求,冷流下推力器仍可脉冲工作,可移动喷注器能够实现增压的目的.      

微阵列射流冲击肋化表面传热特性研究

本文以去离子水为工质,对微阵列射流冲击光滑和肋化表面的传热特性进行了实验研究,并以光滑表面传热性能为基准,讨论了肋化表面强化因子(ε)变化规律。实验结果表明：(1) 浸没和自由射流的传热系数均受无量纲射流距离(H/d)影响;提高射流Re数和减小无量纲孔间距(S/d)都能够增强换热。(2)浸没射流ε受H/d影响大,而自由射流ε基本不受H/d影响;两种射流方式的ε都随Re数增大,且渐趋于一个常数。(3)对流热阻在各种射流情况下均随流量不断下降,但下降趋势逐渐平缓,当流量大到一定时,热阻基本不再降低。     

一种自由曲面视觉测量三维数据拼接方法

提出一种利用标志点构建全局测量控制点的视觉测量三维数据拼接方法.在被测自由曲面上粘贴标志点,并在被测区域放置基线尺,采用1台数码相机在不同视点拍摄标记点和基线尺图像,由此求解数码相机在不同视点的坐标系变换关系.在此基础上,根据立体视觉模型确定标志点三维坐标,转换到全局坐标系下,形成全局测量控制点.视觉传感器在不同位置对各局部区域进行三维扫描,获得局部区域内标志点在局部测量坐标系下的坐标,通过至少3个非共线标志点解算局部坐标系到全局坐标系的变换,从而将实现局部三维数据的拼接.该方法操作简便,适合现场使用.实验结果表明, x,y,z 坐标的拼接误差分别为0.03mm,0.02mm,0.07mm.     

Exponential Time-varying Sliding Mode Control for Large Angle Attitude Eigenaxis Maneuver of Rigid Spacecraft

An eigenaxis maneuver strategy with global robustness is studied for large angle attitude maneuver of rigid spacecraft. A sliding mode attitude control algorithm with an exponential time-varying sliding surface is designed, which guarantees the sliding mode occurrence at the beginning and eliminates the reaching phase of time-invariant sliding mode control. The proposed control law is global robust against matched external disturbances and system uncertainties, and ensures the eigenaxis rotation in the presence of disturbances and parametric uncertainties. The stability of the control law and the existence of global siding mode are proved by Lyapunov method. Furthermore, the system states can be fully predicted by the analytical solution of state equations, which indicates that the attitude error does not exhibit any overshoots and the system has a good dynamic response. A control torque command regulator is introduced to ensure the eigenaxis rotation under the actuator saturation. Finally, a numerical simulation is employed to illustrate the advantages of the proposed control law.     

压电纤维复合材料铺层用于翼面设计的驱动特性与刚度影响

压电纤维复合材料驱动器在形状控制、振动控制、颤振抑制与抖振控制等方面有广泛的应用前景。首先简单介绍了压电应变驱动的比拟载荷方法,并采用该方法讨论了压电陶瓷片状驱动器与压电纤维复合材料驱动器在驱动特性上的主要差异。在此基础上,对压电纤维复合材料在不同铺设方式、铺设角度与铺设层数下的驱动特性进行了分析,在刚度影响方面展示了不同铺设角度下模型刚轴的移动。分析结果表明:对称铺设反向电场可以同时获得弯曲与扭转变形,而反对称铺设同向电场主要获得扭转变形;两种铺设方式下45°铺设角均获得最大弦向转角,而0°铺设角将获得最大挠度;多铺层可以增加驱动载荷,但总体变形效果还取决于结构系统的刚度比例;对称铺设方式下铺设角对结构刚轴移动的影响非常明显,在气动弹性控制中应着重关注。