Pre-storm behaviour of NmF2 and TEC (GPS) over equatorial and low latitude stations in the Indian sector

The pre-storm behavior of NmF₂ and TEC over an equatorial station, Trivandrum (8.47°N, 76.91°E, dip 0.6°S) and a low latitude station, Waltair (17.7°N,83.3°E, dip 20°N) has been studied for a total of 18 strong geomagnetic storms with DST ? −100 nT. The simultaneous measurements of GPS-TEC and NmF₂ over Trivandrum and Waltair during the period 2000–2005 have been considered for the present study. It is found that there is a substantial increase in NmF₂ and TEC before the onset of the storm over Waltair, while the increase is not present at Trivandrum. The origin of pre-storm enhancements in electron density still remains unresolved owing to several conditions in their potential sources and occurrence mechanisms. In the present study an attempt is made to identify the possible mechanisms responsible for such enhancements in electron density of the F-region.     

Study on the lift and propulsive force shares to improve the flight performance of a compound helicopter

To investigate the effects of lift and propulsive force shares on flight performance, a compound helicopter model is derived. The model consists of a helicopter model, a wing model and a propeller model. At a low speed of 100 km/h, the Lift-to-Drag ratio(L/D) of the compound helicopter is improved when the wing provides 20.2% of the take-off weight. At high speeds, the L/D can be improved when the propeller provides the total propulsive force. Lowering the main rotor speed increases the wing lif...     

竖直平板自然对流强化换热的实验

研究各种强化换热结构对竖直平板自然对流换热的强化作用.通过比较圆柱扰流、圆锥扰流、三棱柱扰流、三棱锥扰流、四棱柱扰流、四棱锥扰流和直角三角翼纵向涡发生器LVG(Longitudinal vortex gener-ator)等对自然对流换热的强化效果,发现:单种换热结构中直角三角翼纵向涡发生器的强化换热效果最好,组合结构中直角三角翼叉排与圆柱扰流的混合排列换热效果最好,其能将竖直平板自然对流换热效果提高24.%.      

Ground and satellite-based observations of ionospheric plasma bubbles and blobs at 5.65° latitude in the Brazilian sector

This investigation uses simultaneous observations from all-sky imager system and an ionosonde collocated at Araguatins (5.65° S, 48.07° W and dip-latitude of 4.17° S), a near-equatorial region in Brazil. These simultaneous observations were used to investigate the occurrence of plasma bubbles and blobs in the field of the imaging system and their association with atypical range Spread-F signature in ionograms. Also, in-situ observation of plasma density from Swarm satellites were used to support the ground-based observations. Using a few cases, a methodology will be established to identify in the plasma blobs (atypical ESF) in the ionograms when there is the simultaneous observation of plasma bubbles and blobs in the field of view of the ionosonde. For this purpose, simultaneous sequence of OI 630.0 nm nightglow images and ionograms are presented for different case studies; 1. when there is the absence of a plasma bubble or blob, 2. when there is only the occurrence of plasma bubbles and 3. when there is the occurrence of plasma bubbles and blobs, in order to compare traces in the ionogram in all these case studies. With these we can cover all kinds of signatures in the ionograms corresponding to no irregularities, plasma bubbles only and plasma bubbles-blobs. These OI 630.0 nm nightglow and ionograms recorded simultaneously make it possible to establish a novel methodology to recognize in ionograms cases when there is the occurrence of Spread-F signature associated with bubble-blob in the FOV of the ionosonde.     

Mini-TED跨声速气动特性及其增升机理

通过求解二维可压Navier-Stokes方程,研究了NACA0012翼型加装微型后缘增升装置（mini-TED）后的跨声速流场特性,与Gurney flap （GF）对比分析了几何参数对mini-TED后方涡系及翼型气动特性的影响.将mini-TED的几何细节参数定义为弦向长度和有效高度,两者方向正交.在相同迎角下仅改变mini-TED的弦向长度,后缘涡系结构虽发生变化,但翼型气动力几乎没有影响;反之仅改变有效高度则后缘涡系和翼型气动力系数同时发生明显改变,且与同等高度下的GF气动系数相近.结果表明：有效高度是影响翼型气动特性的决定因素.有效高度改变了mini-TED后涡系的发生范围,而相对于整个翼型绕流,后缘涡系的大小是影响翼型流场最重要的因素,而涡系的微观结构和形态的改变影响相对很小.加装mini-TED后上表面激波位置后移、下表面激波强度削弱,从而翼型表面压力分布特性发生了改变.随有效高度增大,mini-TED诱导的涡系发生区域随之增大,引流作用增强,翼型升力系数、阻力系数和低头力矩系数提高,同时相同迎角下翼型的升阻比明显提高.     

Prediction of aerodynamic characteristics of an aircraft model with and without winglet using fuzzy logic technique

This paper describes the potentials of an aircraft model without and with winglet attached with NACA wing No. 65-3-218. Based on the longitudinal aerodynamic characteristics analyzing for the aircraft model tested in low subsonic wind tunnel, the lift coefficient (CL) and drag coefficient (CD) were investigated respectively. Wind tunnel test results were obtained for CL and CD versus the angle of attack α for three Reynolds numbers Re (1.7×¹⁰⁵, 2.1×¹⁰⁵, and 2.5×¹⁰⁵) and three configurations (configuration 1: without winglet, configuration 2: winglet at 0° and configuration 3: winglet at 60°). Compared with conventional technique, fuzzy logic technique is more efficient for the representation, manipulation and utilization. Therefore, the primary purpose of this work was to investigate the relationship between lift coefficients and drag coefficients with free-stream velocities and angle of attacks, and to illustrate how fuzzy expert system (FES) might play an important role in prediction of aerodynamic characteristics of an aircraft model with the addition of winglet. In this paper, an FES model was developed to predict the lift and drag coefficients of the aircraft model with winglet at 60°. The mean relative error of measured and predicted values (from FES model) were 6.52% for lift coefficient and 4.74% for drag coefficient. For all parameters, the relative error of predicted values was found to be less than the acceptable limits (10%). The goodness of fit of prediction (from FES model) values were found as 0.94 for lift coefficient and 0.98 for drag coefficient which were close to 1.0 as expected.     

面向导航增强的低轨星座设计与应用

随着传统产业升级和新兴技术的发展,社会生产和生活对分米级、厘米级的实时精准定位需求日益凸显。低轨卫星轨道高度低、信号强度大、短时间内几何构型变化快,因此应用低轨卫星开展导航增强服务成为研究热点。低轨卫星的增强服务性能依赖于星座的快速组网和设计,低轨卫星星座构型、轨道高度、轨道倾角等是影响其覆盖性能和增强性能的关键因素。全面分析了低轨星座设计的关键要素,包括轨道高度、轨道倾角和单星覆盖性、地面人口密度、空间环境等,在此基础上设计了单构型和复合构型低轨导航增强星座,并进一步分析低轨星座的覆盖性能。结果显示:复合低轨导航增强星座可以实现对全球的连续覆盖,同时满足极地高密度覆盖和低纬度的连续覆盖需求,对北斗导航系统的增强效果明显。     

颗粒传热增强对微型脉冲推力器点火过程的影响

为了分析点火药产物中炽热颗粒对固体脉冲推力器点火过程的影响,采用了颗粒对壁面的冲击热增强模型来模拟炽热颗粒对推进剂表面的传热增强效应,进行了微型脉冲推力器点火过程的数值分析。结果表明,颗粒热增强效应显著影响脉冲推力器的点火启动过程,颗粒的热增强效应显著缩短了点火延迟时间,并使点火启动过程的压强增大,点火过程对颗粒含量较少的点火药更敏感;设计微型脉冲推力器点火器时要严格匹配产物颗粒含量,并严格控制点火药量范围。     

遥感图像去雾算法研究

针对现有的去雾算法对彩色图像处理后会出现色彩畸变的问题,提出了基于Retinex算法和色度比的去雾算法,该算法在用Retinex算法进行图像恢复的过程中引入了原图像的色彩信息,改善了处理后的图像的色彩。     

合成孔径雷达弹射式干扰增强方法

分析了弹射式干扰的信号特点和它对SAR图像的干扰效果,根据其特殊性,给出了一种弹射式干扰增强方法,分析了弹射式干扰增强的关键问题.以机载SAR为例进行了仿真实验,结果表明,通过干扰增强可改善对SAR的干扰效果,降低干扰功率需求.