GPS伪卫星组合定位方法及在变形监测中的应用

针对GPS在城市高楼密集区、深山峡谷等区域所跟踪的可见星数目少且分布不佳导致定位精度下降,以及GPS系统本身在垂直方向定位精度较差的问题,提出GPS伪卫星组合定位新方法,利用伪卫星增强GPS技术提高定位精度。建立了GPS和伪卫星组合定位的观测模型,分析了伪卫星多路径效应的特点,给出了减弱伪卫星多路径误差的有效方法。对某大坝坝区的实测数据进行处理的结果表明,文中所提出的方法能有效地减弱伪卫星多路径效应产生的误差,GPS和伪卫星组合定位方法提高了系统的定位精度,特别是垂直方向的精度。     

Separation control on NACA23012 using synthetic jet

A numerical study of separation control has been made to investigate aerodynamic characteristics of NACA23012 airfoil with synthetic jets. Computed results demonstrated that stall characteristics and control surface performance could be substantially improved by resizing separation vortices. The maximum lift was obtained when the separation point coincides with the synthetic jet location and the non-dimensional frequency is about 1. In addition, separation control effect was proportional to the peak velocity of the synthetic jet. It was observed that the actual flow control mechanism and flow structure is fundamentally different depending on the range of synthetic jet frequency. For low frequency range, small vortices due to synthetic jet penetrated to the large leading edge separation vortex, and as a result, the size of the leading edge vortex was remarkably reduced. For high frequency range, however, small vortex did not grow up enough to penetrate into the leading edge separation vortex. Instead, synthetic jet firmly attached the local flow and influenced the circulation of the virtual airfoil shape which is the combined shape of the main airfoil with the separation vortex. As a way to reduce the jet peak velocity, performance of a multi-array synthetic jet was investigated. Moreover, a high frequency multi-location synthetic jet was exploited to efficiently eliminate the unstable flow structure which was observed in low frequency range. Finally, by changing the phase angle in multi-location synthetic jets, highly controlled flow characteristics could be obtained with multi-array/multi-location synthetic jets. This shows efficiency of the current approach in separation control using synthetic jet.     

Enhancing the efectiveness of film cooling

Advanced gas turbine stages are designed to operate at increasingly higher inlet temperatures to increase thermal efficiency and specific power output.To maintain durability and reasonable life,film cooling is needed in addition to internal cooling,especially for the first stage.Film cooling lowers material temperature by forced convection inside film-cooling holes and by forming a layer of coolant about component surfaces to insulate them from the hot gases.Unfortunately,each cooling jet forms a pair of counter-rotating vortices that entrains hot gas and causes the film-cooling jet to lift off from the surface that it is intended to protect.This paper gives an overview of efforts to enhance the effectiveness of film-cooling.This paper also describes two new design concepts.One design concept seeks to minimize the entrainment of hot gases underneath of film-cooling jets by using flow-aligned blockers.The other design concept shifts the interaction between the approaching hot gas and the cooling jet to occur further above the surface by using an upstream ramp.For both design concepts,computational fluid dynamics results are presented to examine their usefulness in enhancing film-cooling effectiveness.      

低RCS飞行器表面弱散射源研究

飞行器表面不同宽度缝隙、不同高度台阶、不同结构形式对缝（主要包括横向对缝、锯齿对缝两种）等弱散射源对前方雷达截面（RCS）有着比较重要的影响,为了说明控制弱散射源的重要性,介绍了常规飞行器表面结构的缝隙、台阶等弱散射源的分布情况及特点,采用理论方法分析了缝隙的雷达后向散射强度,设计了低RCS载体和实验模型,开展了不同宽度缝隙、不同高度台阶、不同结构形式对缝的RCS实验。结果表明：减小缝隙宽度、台阶高度,采用锯齿缝隙代替直缝隙等方法,是控制隐身飞行器表面电磁缺陷的有效技术途径。     

空间目标轨道信息软件平台的建设

空间目标轨道信息是空间态势感知的重要要素,是空间碰撞预警、空间碎片环境模型和许多空间应用的基础。因而,空间目标轨道确定成为空间态势感知的主要任务之一。文章介绍武汉大学测绘学院正在开发建设的空间目标轨道信息服务软件平台,该平台拥有的主要功能有:利用多源数据的卫星/空间碎片轨道确定(包括初轨确定)与预报、大气质量密度模型精化、空间碰撞预警和半解析法快速精密轨道传播等。文章还针对软件平台功能的研究进展进行了综述,介绍了软件平台发展规划。     

管道机器人动力学分析

在分析了开链式拓扑结构的多节蠕动机器人结构和运动特点的基础上,利用空间算子代数(Spatial operator algebra,SOA)方法,建立了适用于这类机器人系统的通用动力学模型,为验证所建立的动力学模型的正确性,将原理样机运行试验和与动力学仿真分析结果进行了对比.在此基础上,利用该动力学模型,对样机结构的改进与优化,并对机器人运动学和动力学性能的影响进行了分析和评估,为机器人运动控制策略的拟定提供了重要的依据.     

Solar Wind Electron Observations Near Solar Maximum at High Latitudes From Thermal Noise Spectroscopy

The Ulysses spacecraft is reaching high heliolatitudes during the approach to solar maximum. We show preliminary in situ electron observations from the URAP experiment, using thermal noise spectroscopy. This method is especially suited to measure accurately the electron density and thermal temperature. The data acquired in the period June–September 2000 are compared to those obtained at similar heliolatitudes near solar activity minimum and in the ecliptic plane near both solar maximum and minimum. This revised version was published online in August 2006 with corrections to the Cover Date.     

一种喷气推进系统的进气压力畸变测控系统

介绍了一种基于VXI总线的航空发动机进气压力畸变测控系统。在高速采集的同时，实现了数据的不间断存储，多种实时显示，综合畸变指数W的实时计算。并通过实验验证了系统的功能。     

SolidWorks软件在机械加工工艺中的应用

用实例介绍了SolidWorks软件的三维草图、焊件切割清单、钣金等模块、相应功能以及它们在机械加工工艺中的广泛运用;研究了SolidWorks软件在机械设计中的实用性和先进性。详细介绍了该软件的使用方法和具体特点,对推广SolidWorks在机械设计中的应用具有重要的指导作用。     

横侧静稳定性的一种分析方法

通过对迎角、侧滑角、后掠角等概念的几何意义进行确认,从几何上确定了各迎角间的关系,在不改变几何意义的基础上对有侧滑和无侧滑时的迎角关系式进行近似处理,并运用目前通行的方法推导了由侧滑导致的后掠翼飞机的滚转力矩公式,对后掠翼飞机横侧静稳定性的分析提出一种较准确的方法。这个方法几何意义明确,采用类比的方法后,避免了复杂的几何证明,因而公式的推导过程也比较简捷。 由于对基本概念的认识不同和近似处理的方法不同,所得滚转力矩的变化规律也是不同的。但在精度不高的情况下,各种方法所得的简化结果则相同。