Single photon laser altimeter simulator and statistical signal processing

Spaceborne altimeters are common instruments onboard the deep space rendezvous spacecrafts. They provide range and topographic measurements critical in spacecraft navigation. Simultaneously, the receiver part may be utilized for Earth-to-satellite link, one way time transfer, and precise optical radiometry. The main advantage of single photon counting approach is the ability of processing signals with very low signal-to-noise ratio eliminating the need of large telescopes and high power laser source. Extremely small, rugged and compact microchip lasers can be employed. The major limiting factor, on the other hand, is the acquisition time needed to gather sufficient volume of data in repetitive measurements in order to process and evaluate the data appropriately. Statistical signal processing is adopted to detect signals with average strength much lower than one photon per measurement. A comprehensive simulator design and range signal processing algorithm are presented to identify a mission specific altimeter configuration. Typical mission scenarios (celestial body surface landing and topographical mapping) are simulated and evaluated. The high interest and promising single photon altimeter applications are low-orbit (∼10 km) and low-radial velocity (several m/s) topographical mapping (asteroids, Phobos and Deimos) and landing altimetry (∼10 km) where range evaluation repetition rates of ∼100 Hz and 0.1 m precision may be achieved. Moon landing and asteroid Itokawa topographical mapping scenario simulations are discussed in more detail.     

卫星变轨初探

为了推算卫星变轨时刻和研究变轨过程中轨道变化规律,在仿真计算检验方案可行性的基础上,对有实际背景的某类卫星变轨进行了计算,大致复现了整个变轨过程。仿真和实例结果可为研究非合作目标的卫星轨道改变和变轨后再次捕获提供相关信息和参考依据。     

飞机航炮后固定座支座裂纹故障分析

针对某型飞机航炮后固定座支座裂纹故障频发的情况，对该支座的裂纹故障进行了研究分析，查找出裂纹发生的原因，提出了相应的解决办法，供相关工作人员参考。     

Experimental study of flow field distribution over a generic cranked double delta wing

The flow fields over a generic cranked double delta wing were investigated. Pressure and velocity distributions were obtained using a Pitot tube and a hot wire anemometer. Two different leading edge shapes, namely ‘‘sharp" and ‘‘round", were applied to the wing. The wing had two sweep angles of 55° and 30°. The experiments were conducted in a closed circuit wind tunnel at velocity 20 m/s and angles of attack of 5°–20° with the step of 5°. The Reynolds number of the model was about 2 ×10~5 according to the root chord. A dual vortex structure was formed above the wing surface. A pressure drop occurred at the vortex core and the root mean square of the measured velocity increased at the core of the vortices, reflecting the instability of the flow in that region. The magnitude of power spectral density increased strongly in spanwise direction and had the maximum value at the vortex core. By increasing the angle of attack, the pressure drop increased and the vortices became wider; the vortices moved inboard along the wing, and away from the surface; the flow separation was initiated from the outer portion of the wing and developed to its inner part. The vortices of the wing of the sharp leading edge were stronger than those of the round one.     

Validation of space-born Moderate Resolution Imaging Spectroradiometer remote sensors aerosol products using application of ground-based Multi-wavelength Radiometer

The measurements of aerosol optical properties were carried out during April 2006 to March 2011 over Mohal (31.9°N, 77.12°E) in the northwestern Indian Himalaya, using the application of ground-based Multi-wavelength Radiometer (MWR) and space-born Moderate Resolution Imaging Spectroradiometer (MODIS) remote sensors. The average (±standard deviation) values of aerosol optical depth (AOD) at 500 nm, Ångström exponent and turbidity coefficient during the entire measurement period were 0.25 ± 0.09, 1.15 ± 0.42 and 0.12 ± 0.06 respectively. About 86% AOD values retrieved from MODIS remote sensor were found within an uncertainty limit (Δτ_pλ = ±0.05 ± 0.15τ_pλ). In general, the MWR derived AOD values were higher than that of MODIS retrieval with absolute difference ∼0.02. During the entire period of measurement space-born MODIS remote sensor and ground-based MWR observation showed good correspondence with significant correlation coefficient ∼0.78 and root mean square difference ∼0.06. For daily observations the relative difference between these two estimates stood less than 9%. However, satellite-based and ground-based observation showed good correspondence, but further efforts still needed to eliminate systematic errors in the existing MODIS algorithm.     

2边连通3正则平面图的边着色

对具有正常３边着色的２边连通３正则平面图的顶点定义了方向，并且在这样的图上建立了路径上的积分，进一步给出了２边连通３正则平面图是３边可着色的等价条件。     

MCS—51单片机计数器／定时器在测控系统中的应用

介绍了MCS－51单片机内部计数器／定时器的基本结构及其基本功能，并在此基础上讨论了其功能的扩展应用及需注意的问题。     

Individual influence of pitching and plunging motions on flow structures over an airfoil during dynamic stall

The individual influence of pitching and plunging motions on flow structures is studied experimentally by changing the phase lag between the geometrical angle of attack and the plunging angle of attack. Five phase lags are chosen as the experimental parameters, while the Strouhal number, the reduced frequency and the Reynolds number are fixed. During the motion of the airfoil, the leading edge vortex, the reattached vortex and the secondary vortex are observed in the flow field. The leading edge vortex is found to be the main flow structure through the proper orthogonal decomposition. The increase of phase lag results in the increase of the leading edge velocity, which strongly influences the leading edge shear layer and the leading edge vortex. The plunging motion contributes to the development of the leading edge shear layer, while the pitching motion is the key reason for instability of the leading edge shear layer. It is also found that a certain increase of phase lag, around 34.15° in this research, can increase the airfoil lift.     

某型发动机压气机叶片对性能的影响分析

采用CFD数值模拟方法和厂内试车方法,对某型发动机压气机叶片设计状态(A状态)和产品实际情况(B状态,转接半径、叶型厚度偏离较大)下,叶片前缘形状对发动机性能的影响进行了分析和试车验证,结果表明:B状态叶片,气流沿叶型整个型面附面层厚度呈迅速增大趋势,在较大区域较早出现气流分离,易导致压气机处于非稳定性状态工作;试车结果表明其导致整机推力性能降低。     

基于FPGA的自适应陷波器研究和设计

对基于FPGA的自适应滤波器进行了研究.首先,分析了最小均方根(LMS)算法原理,并介绍了陷波器的稳定性问题.然后,提出了一种基于FPGA的自适应滤波器的实现方法,并进行了仿真验证.最后搭建了试验平台验证了陷波器的功能.仿真和试验结果表明,该自适应陷波器有良好的滤波功能.