大型双反射紧缩场幅相特性校准技术研究

紧缩场是天线、目标RCS测试的关键设备,它能在近距离内把馈源发出的球面波校准为准平面波。为评定紧缩场静区产生的电磁波分布是否符合准平面波特性,需要现场搭建高性能微波幅相收发系统和大型多自由度高精度扫描系统。本文以大型双反射面紧缩场静区性能校准需求为例,从现场计量幅相系统构建、大型复杂扫描系统设计、现场计量实施等方面详细分析了紧缩场静区性能现场校准相关技术。实测结果表明现场搭建的校准系统满足远距离大型双反射面紧缩场静区性能计量需求,各项检测参数量值均满足该紧缩场设计指标要求。     

脉冲爆震发动机扩焰器试验研究

为使燃用液体燃料的大管径气动阀式脉冲爆震发动机点火及起爆成功,设计了多种结构的强化燃烧装置.包括半V型扩焰器、环型扩焰器和环型＋径向扩焰器.通过多种不同结构扩焰器在脉冲爆震发动机上的试验结果表明,采用各种强化燃烧装置后,能显著提高点火成功率,加速紊流火焰的传播,且带径向的扩焰器较之环型的扩焰器,更能有效缩短DDT距离,但带来的阻力损失增加.     

部分填充对脉冲爆震发动机冲量的影响

1引言脉冲爆震发动机是一种很有竞争力的新型发动机[1],在过去的几年里,研究者们就部分填充对于脉冲爆震发动机性能影响问题进行了大量的理论分析、数值模拟和试验研究[2~12]。Z itoun等人[2]测量了标况下带有等截面延伸段的爆震管中乙烯/氧气混合物的单次冲量。他们用约35焦耳     

EESS应用于舰面舱口盖除冰的可行性分析

现有的舰面露天甲板的除冰方法往往需要消耗大量的电力,有时还要用一些人工方法来辅助除冰。而排水孔和疏水管道都极易结冰,常用的融冰方法在甲板上很可能重复结冰,难以达到除冰效果。文中,作者借鉴美国成功应用于飞机机翼前缘除冰的一种设备EESS,该设备功率消耗小,除冰更有效,可靠性更高,改装更方便,生产及维护费用低。作者在文中对EESS应用于舰面舱口盖除冰的可行性进行了分析。     

直升机旋翼除冰系统加热垫试验研究

直升机旋翼桨叶结冰会导致其气动外形的破坏,严重影响飞行品质。为了提高直升机旋翼防除冰系统的柔韧性和抗疲劳性,以镍铬合金细丝编织的金属网作为加热元件,并将其以展向布置的方式设置于桨叶中;通过设计,确定金属丝的直径、网格的尺寸,结合现有的复合材料成型工艺,制备出电加热试验件;对所制备的加热垫分别进行电热性能测试、力学性能测试和实验室模拟除冰试验。结果表明:所制备的加热垫温升速度可达2.5℃/s,面内温度均匀性小于2℃,实验室模拟除冰效果良好。     

基于功率特征分组的空时自适应脉冲干扰抑制方法CSCD

脉冲干扰是一种常见的导航干扰类型,具有高带宽、突发性等特点,针对脉冲干扰的抑制具有较大难度。常规空时自适应处理不对接收信号类型进行区分,而是统一进行协方差矩阵估计及权值计算,存在抗脉冲干扰性能下降或失效的可能。针对以上问题,提出了一种基于功率特征分组的空时自适应处理方法。首先对接收数据进行功率检测,将信号采样数据分为有干扰数据组和无干扰数据组,然后对分组后的数据分别进行权值计算和滤波处理,最后将滤波后的数据按照采样顺序进行合并。该方法通过数据分组,提高了干噪比的统计计算准确度,增加了干扰零陷深度,实现了抗干扰能力的提升。理论分析和仿真实验均证明了该方法的有效性。     

无阀两相脉冲爆震发动机循环过程实验分析

在无阀式以汽油为燃料,空气为氧化剂的脉冲爆震发动机(PDE)模型机上进行了低点火能量多循环实验研究,分析了无阀两相脉冲爆震发动机多循环工作过程。模型机热态试验提供了10~66 Hz爆震循环特征时间分配和爆震管内不同位置压力的变化过程。由于在两相系统中存在较长的点火延迟时间和DDT时间,发现无阀PDE存在较长的点火后填充时间。通过对两相爆震波的形成过程和排出过程的实验研究和分析,以及点火后填充时间,提出了新的无阀PDE特征时间分布。不同频率实验结果表明,从火花塞放电到下一个循环新鲜混合气开始填充这段时间基本不变,称之为极限周期。在该模型中,点火延迟时间和DDT时间占据了极限周期时间的大部分时间,进一步分析了提高循环频率的关键因素。     

模拟冲压进气条件对PDE推力测量影响

研究了射流模拟冲压进气条件下,气源喷口尺寸和气源压头对脉冲爆震发动机(PDE)地面台架试验推力测量的影响,分析地面台架试验中阻力和测量推力随模拟进气条件变化的规律。研究结果表明,PDE充填速度随气源压头或气源喷口尺寸的增加而增加;PDE阻力随气源压头的增加线性增加,随喷口尺寸增加而增加;喷口尺寸在78~105 mm内,PDE台架测量推力随喷口尺寸增加而增加。     

Coherent optical array receiver for PPM signals under atmospheric turbulence

Adaptive combining of experimentally obtained heterodyned pulse position modulated (PPM) signals with pulse-to-pulse coherence, in the presence of simulated spatial distortions resembling atmospheric turbulence, is demonstrated. The adaptively combined PPM signals are phased up via an least-mean-square algorithm suitably optimized to operate with PPM in the presence of additive shot noise. A convergence analysis of the algorithm is presented, and results with both computer simulated and experimentally obtained PPM signals are analyzed.     

Locating Current Sheets in the Solar Corona

Current sheets are essential for energy dissipation in the solar corona, in particular by enabling magnetic reconnection. Unfortunately, sufficiently thin current sheets cannot be resolved observationally and the theory of their formation is an unresolved issue as well. We consider two predictors of coronal current concentrations, both based on geometrical or even topological properties of a force-free coronal magnetic field. First, there are separatrices related to magnetic nulls. Through separatrices the magnetic connectivity changes discontinuously. Coronal magnetic nulls are, however, very rare. Second, inspired by the concept of generalized magnetic reconnection without nulls, quasi-separatrix layers (QSL) were suggested. Through QSL the magnetic connectivity changes continuously, though strongly. The strength of the connectivity change can be quantified by measuring the squashing of the flux tubes which connect the magnetically conjugated photospheres. We verify the QSL and separatrix concepts by comparing the sites of magnetic nulls and enhanced squashing with the location of current concentrations in the corona. Due to the known difficulties of their direct observation, we simulated coronal current sheets by numerically calculating the response of the corona to energy input from the photosphere, heating a simultaneously observed Extreme Ultraviolet Bright Point. We did not find coronal current sheets at separatrices but at several QSL locations. The reason is that, although the geometrical properties of force-free extrapolated magnetic fields can indeed hint at possible current concentrations, a necessary condition for current sheet formation is the local energy input into the corona.