跨介质冲压发动机理论性能与工作参数分析

针对空水一体跨介质导弹应用需求，提出了一种采用同一金属基固体推进剂，能够实现在空中和水中工作的跨介质冲压发动机方案。分析了空中和水中典型工况下，金属基固体推进剂配方、空/水燃比、金属种类等对跨介质冲压发动机理论性能的影响。针对给定的跨介质导弹飞行弹道和金属基固体推进剂配方，对发动机设计参数进行了选取，并完成了空中和水中工作条件下发动机工作参数计算，从理论上验证了该跨介质冲压发动机方案的可行性。     

Monitoring of maize lodging using multi-temporal Sentinel-1 SAR data

Lodging is a common phenomenon in maize production, which seriously affects its yield, quality, and mechanical harvesting capacity. With good penetrating power, satellite radar can monitor crop growth even under cloudy weather conditions. In this study, a method based on the change in plant height before and after lodging in maize is proposed to calculate the lodging angle and monitor the lodging degree by using dual-polarization Sentinel-1A data. The results show that the optimal sensitive polarization combinations of maize plant height before and after lodging are VH/VV and VV, respectively. The lodging angle is calculated using the plant height inversion results before and after lodging. The overall accuracy of classifying lodging grade of maize is 67%. The proposed model based on lodging angle could effectively mapped the maize lodging range on a regional scale and classify the lodging grades.     

Highly efficient computation method for hazard quantification of uncontained rotor failure

Uncontained Engine Rotor Failure (UERF) can cause a catastrophic failure of an aircraft, and the quantitative assessment of the hazards related to UERF is a very important part of safety analysis. However, the procedure for hazard quantification of UERF recommended by the Federal Aviation Administration in advisory circular AC20-128A is cumbersome, as it involves building auxiliary lines and curve projections. To improve the efficiency and general applicability of the risk angle calculation, a boundary discretization method is developed that involves discretizing the geometry of the target part/structure into node points and calculating the risk angles numerically by iterating a particular algorithm over each node point. The improved efficiency and excellent accuracy for the developed algorithm was validated through a comparison with manual solutions for the hazard quantification of the engine nacelle structures of a passenger aircraft using the guidance in AC20-128A. To further demonstrate the applicability of the boundary discretization method, the proposed algorithm was used to examine the influence of the target size and the distance between the target and rotor on the hazard probability.     

Prediction of clear-sky biologically effective erythematic radiation (EER) From global solar radiation (250–2800 nm) at Cairo,Egypt

The hourly and daily measured clear-sky global solar radiation (G) and biologically important effective erythematic radiation (EER) incident on a horizontal surface at Cairo, Egypt (latitude 30° 05′ N & Longitude 31° 15′ E), during the period from January 1995 to December 2005 are used in this paper. The relationship between daily integrated totals of EER and the daily totals of broadband global solar radiation (250–2800 nm) is established. The temporal variability of the percentage ratio of the total daily erythema to total daily broadband solar global irradiation (EER/G) is determined. The monthly and the seasonal averages of the extraterrestrial UVB solar radiation, Mesurad and estímated UVB solar radiation and clearness index K_tUVB of UVB radiation are discussed. The average monthly mean variation of slant ozone (Z) and UVB transmission (K_tUVB) at the present work are found. The two variables show an opposite seasonal behavior, and the average monthly of slant ozone column and UVB transmission values shows the relationship between them in a clearer way than those of daily values. The estimated values of UVB solar radiation a good agreement with the measured values of the UVB solar radiation, the difference between the estimated and measured values of UVB solar radiation varies from 1.2% to 2.8%. The effect of the annual cycles of solar zenith angle (SZA) and total column ozone (TCO) on the ratios (EER/G) are presented and the correction factors are determined for removal of the ozone cycle. The seasonal variability of EER/G is also discussed. The effect of the annual cycles of solar zenith angle (SZA) and total column ozone (TCO) on the ratios (EER/G) is presented and the correction factors are determined for removal of the ozone cycle.     

Characterisation of residual ionospheric errors in bending angles using GNSS RO end-to-end simulations

Global Navigation Satellite System (GNSS) radio occultation (RO) is an innovative meteorological remote sensing technique for measuring atmospheric parameters such as refractivity, temperature, water vapour and pressure for the improvement of numerical weather prediction (NWP) and global climate monitoring (GCM). GNSS RO has many unique characteristics including global coverage, long-term stability of observations, as well as high accuracy and high vertical resolution of the derived atmospheric profiles. One of the main error sources in GNSS RO observations that significantly affect the accuracy of the derived atmospheric parameters in the stratosphere is the ionospheric error. In order to mitigate the effect of this error, the linear ionospheric correction approach for dual-frequency GNSS RO observations is commonly used. However, the residual ionospheric errors (RIEs) can be still significant, especially when large ionospheric disturbances occur and prevail such as during the periods of active space weather. In this study, the RIEs were investigated under different local time, propagation direction and solar activity conditions and their effects on RO bending angles are characterised using end-to-end simulations. A three-step simulation study was designed to investigate the characteristics of the RIEs through comparing the bending angles with and without the effects of the RIEs. This research forms an important step forward in improving the accuracy of the atmospheric profiles derived from the GNSS RO technique.     

光电编码器模拟测速机在转台控制系统中的应用

在转台的可靠性设计中, 常用测速机输出作为转台限速报警的触发信号, 但传统的测速机在安装、成本及精度上都不具有优势。利用美国AD 公司生产的AD650 芯片,对被广泛用于转台测角系统中的Heidenhain 公司的RON886C 型增量式旋转编码器 信号进行电压频率(V/ F) 和频率电压(F/V) 转换, 实现利用编码器输出模拟测速机电路, 不仅可以满足限速保护要求,并且较测速机具有成本低,安装使用方便,且精度较高的 优点,在实际应用中效果良好。     

Bifurcation analysis of polynomial models for longitudinal motion at high angle of attack

To investigate the longitudinal motion stability of aircraft maneuvers conveniently, a new stability analysis approach is presented in this paper. Based on describing longitudinal aerodynamics at high angle-of-attack (a < 50 ) motion by polynomials, a union structure of two-order differential equation is suggested. By means of nonlinear theory and method, analytical and global bifurcation analyses of the polynomial differential systems are provided for the study of the nonlinear phenomena of high angle-of-attack flight. Applying the theories of bifurcations, many kinds of bifurcations, such as equilibrium, Hopf, homoclinic (heteroclinic) orbit and double limit cycle bifurcations are discussed and the existence conditions for these bifurcations as well as formulas for calculating bifurcation curves are derived. The bifurcation curves divide the parameter plane into several regions; moreover, the complete bifurcation diagrams and phase portraits in different regions are obtained. Finally, our conclusions are applied to analyzing the stability and bifurcations of a practical example of a high angle-of-attack flight as well as the effects of elevator deflection on the asymptotic stability regions of equilibrium. The model and analytical methods presented in this paper can be used to study the nonlinear flight dynamic of longitudinal stall at high angle of attack.     

Delaying stall of morphing wing by periodic trailing-edge deflection

Morphing wings can improve aircraft performance during different flight phases. Recently research has focused on steady aerodynamic characteristics of the morphing wing with a flexible trailing-edge, and the unsteady aerodynamic and stall characteristics in the deflection process of the morphing wing are worthy further investigation. The effects of the angle of attack and deflection rate on aerodynamic characteristics were examined, and based on the aerodynamic characteristics of the morphing wing, a method was developed to delay stall by using the flexible periodic trailing-edge deflection. The numerical results show that the lift coefficients in the deflection process are smaller than those in the static situation at small angles of attack, and that the higher the deflection rate is, the smaller the lift coefficients will be. On the contrary, at large angles of attack, the lift coefficients are higher than those in the static case, and they become larger with the increase of the deflection rate. Further, the periodic deflection of the flexible trailing-edge with a small deflection amplitude and high deflection rate can increase lift coefficients at the critical stall angle.     

圆锥曲线上三点构成直角三角形的充要条件

研究椭圆、双曲线、抛物线上三点构成直角三角形的充要条件,得到若干有益的结果。     

三维机器鸟自主飞行的涡动力学分析与控制

鸟类通过翅膀的拍动和旋转运动提供飞行的驱动力和升力.本文研究了机器鸟翅膀的旋转幅度和旋转时间对飞行的状态影响,发现适当地选取这两个参数可以控制机器鸟在水平方向和竖直方向上的速度.本研究主要使用了两个工具:在不可压粘性流体中自主飞行的三维机器鸟和一个三维计算流体力学软件包,后者包含了浸入边界法(IBM)、体积函数法(VOF)、自适应多重网格有限体积法和游动与飞行的控制机制.