Detection in correlated Gaussian plus impulsive noise

A detector which is designed to operate in a correlated Gaussian-plus-impulsive-noise environment is presented. The detector whitens the data robustly and then uses a two-sided threshold test to determine the presence of impulsive samples. The impulsive samples are discarded, and the remaining samples are used to detect the presence or absence of a signal using a matched filter. An approximate analysis is presented, and simulations are used to demonstrate the effectiveness of this approach     

斜齿轮齿根动应力数值计算与实验研究

运用三维有限元和齿根局部网格密化技术提出了一套计算斜齿轮啮合过程齿根弯曲应力的方法。根据齿轮系统动态特性分析, 求得作用在轮齿上的动载历程, 计算了在动态载荷作用下的齿根应力分布。通过斜齿轮齿根动应力实验, 说明了本文方法的有效性。给出了啮合过程中齿宽不同截面上的动应力分布形态, 讨论了转速和扭矩对齿根动应力的影响。      

中值滤波方法在燃气涡轮传感器数据校正中的应用研究

分析了发动机测量信号滤波需求,设计了针对传感器数据校正的中值滤波器和快速算法,给出了模拟发动机故障和变工况试验情况下的传感器输出,给出了滤波比较研究结果。数值实验和实际应用于涡轮试验测量数据滤波的结果表明,中值滤波器对于脉冲噪声可以完全剔除,对随机噪声也具有较好的抑制效果,并能够较好保持信号中的陡峭边沿等趋势成份。      

Laboratory and Numerical Simulations of the Impulsive Penetration Mechanism

Plasma interaction at the interface between the magnetosheath and magnetosphere has been extensively studied during recent years. As a consequence various theoretical models have emerged. The impulsive penetration mechanism initially proposed by Lemaire and Roth as an alternative approach to the steady state reconnection, is a non-stationary model describing the processes which take place when a 3-D solar wind plasma irregularity interacts with the outer regions of the Earth's magnetosphere. In this paper we are reviewing the main features of the impulsive penetration mechanism and the role of the electric field in driving impulsive events. An alternative point of view and the controversy it has raised are discussed. We also review the numerical codes developed to simulate the impulsive transport of plasma across the magnetopause. They have illustrated the relationship between the magnetic field distribution and the convection of solar-wind plasma inside the magnetosphere and brought into perspective non-stationary phenomena (like instabilities and waves) which were not explicitly integrated in the early models of impulsive penetration. Numerical simulations devoted to these processes cover a broad range of approximations, from ideal MHD to hybrid and kinetic codes. The results show the limitation of these theories in describing the full range of phenomena observed at the magnetopause and magnetospheric boundary layers.     

基于FW-Hpds方法的直升机旋翼气动噪声指向性分析

本文使用基于可穿透数据面的Ffowcs Williams-Hawkings方程(FW-Hpds)的预测方法分析了跨声速直升机悬停旋翼气动噪声的指向性。通过求解三维非定常欧拉方程计算了近场噪声,通过延迟时积分方法和求解FW-Hpds方程计算远场噪声。预测了跨声速UH-1H悬停旋翼的高速脉冲噪声(HSI),然后计算了不同观测点处的声压级,并通过声压级在不同方向上的分布分析了HSI噪声的方向性。根据本文研究发现HSI噪声在桨盘平面上最大,在转轴方向上最小,和其它研究者的结论一致。     

基于解析梯度的微推进转移轨道优化方法

 研究基于离散脉冲策略的行星际微推进转移轨道优化问题,为改善收敛性和计算效率,提出了一种解析的梯度矩阵计算方法。首先,基于离散脉冲思想建立了行星际微推进转移轨道优化模型,通过对速度脉冲矢量进行参数变换,避免了传统优化模型初值猜测和搜索域难以界定的缺点;然后,基于变分原理分析了离散脉冲模型中轨道状态转移矩阵与状态变分之间的关系,并给出了多种轨道特征条件下状态变分的计算方法,该方法可扩展到多次状态不连续情况;在此基础上,推导了离散脉冲轨道优化模型中性能指标与轨道约束对寻优参数梯度矩阵的解析表达式。以地球-火星的燃料最省微推进转移为例对所提解析梯度方法进行了仿真验证。数值结果表明：本文推导的解析梯度矩阵是正确的,与传统数值梯度计算方法相比,解析梯度矩阵可有效改善寻优算法的收敛特性,并能够提高计算效率约47%。     

点火药量对微型脉冲推力器内弹道性能的影响

研究了用于高速动能导弹和超高速火箭弹道修正的微型脉冲推力器的三种推力—时间(F-t)曲线,发现由于脉冲推力器点火药量与主装药量之比明显高于常规固体火箭发动机该两者的比值,点火药量的多少会对推力器F-t曲线的形状和内弹道性能产生明显影响。必须严格控制点火药量,特别是引燃药剂的量,才能获得较为满意的内弹道性能。      

Digital Communication Systems in Impulsive Atmospheric Radio Noise

Analyses are presented of the performance of binary and M-ary coherent and noncoherent communication systems operating in the impulsive atmospheric radio noise environment. The receiver is usually a maximum likelihood detector for white Gaussian interference and therefore has the form of a parallel bank of matched filters followed by decision circuitry. By employing a Poisson or generalized Shot noise model for the impulsive noise with a suitable probability density function (pdf), closed-form expressions and bounds of error probabilities for M-ary noncoherent and coherent amplitude-shift keying (ASK), phase-shift keying (PSK), and frequency-shift keying (FSK) systems are obtained and the results discussed.     

在冲击噪声环境中基于子空间的测向算法研究

 首先分析了冲击噪声的性质以及它对传统的基于二阶或高阶统计量的子空间测向技术的影响, 然后提出了一种新的在冲击噪声环境中基于子空间的阵列测向算法。该算法利用TLS-ESPRIT 算法的基本思想, 通过对阵列输出信号的协变异系数矩阵进行奇异值分解来估计来波方位, 最后进行了计算机仿真试验, 验证了该算法的可行性和有效性。     

旋翼BVI噪声的理论模拟与分析

ＢＶＩ噪声是旋翼产生的一种非常强烈的脉冲式噪声,本文应用理论模拟的方法分析了ＢＶＩ噪声的规律。对叶片表面非定常力的计算采用了有限翼展叶片对倾斜正弦式阵风的响应函数,声场计算应用了基于Ｌｉｇｈｔｈｉｌｌ声类比理论的频域方法。应用本文方法计算的ＢＶＩ噪声声压信号与实验结果比较吻合较好。     

脉冲推力矢量控制方法及对导弹弹道的影响

针对固定倾角发射的防空导弹,建立了发射段纵平面内弹道数学模型;研究了脉冲推力矢量控制对弹道转弯特性的影响,并结合实际作战过程,利用数值方法给出了一种控制参数确定算法,该算法具有较好的工程可实现性。最后分析了脉冲推力矢量控制对导弹弹道的影响。仿真结果表明,该控制方法能扩大导弹的作战空域,减小中段飞行侧向过载,较好地消除中、末交班目标视线转率,对提高拦截精度有重要意义。     

人体冲撞耐受性分析中的数值模型

 对人体在驾驶椅上臀部和头部受冲击载荷作用时的动力响应做了有限元计算分析,工况参照直升机垂直坠毁过程的人员生存性评估标准,材料选用可描述人体生物本构特性的参数,载荷分为定速垂直冲撞型和外力作用型,包括：阶跃载荷、矩形脉冲载荷和三角形脉冲载荷。结果显示,对于各种工况,颈部均出现较高应力,为危险区域。对于头部受不同形式冲击载荷作用的情况,颅骨的动力响应基本保持一致,说明颅骨的响应对载荷形状不敏感。     

航天器燃耗最优轨道直接/间接混合法延拓求解

针对转移时间和始末状态固定的航天器燃耗最优轨道的求解,给出了一种延拓方法:以双脉冲轨道为初值,首先求解全程推进轨道,然后逐步增加推力幅值,应用直接/间接混合法依次求解所有推力幅值下的、满足包括开关函数在内的所有必要条件的转移轨道,包括连续和脉冲推力轨道。通过基于开关函数曲线变化趋势的开关序列预设方法,以及基于已有优化结果的延拓步长自适应方案,实现了延拓方法的自动运行。为实现该延拓方法,给出了适用于改进春分点根数模型的脉冲最优转移轨道主矢量必要条件,推导了无推力轨道段改进春分点根数协态变量状态转移矩阵。通过3个算例对延拓求解会遇到的不同情况进行了具体说明。延拓方法可以看作现有直接/间接混合法的进一步完善与拓展,延拓过程和结果有助于对燃耗最优轨道与系统参数之间的关联获得更为深刻的认识。     

Abundances,Ionization States,Temperatures, and FIP in Solar Energetic Particles

The relative abundances of chemical elements and isotopes have been our most effective tool in identifying and understanding the physical processes that control populations of energetic particles. The early surprise in solar energetic particles (SEPs) was 1000-fold enhancements in \({}^{3}\mbox{He}/{}^{4}\mbox{He}\) from resonant wave-particle interactions in the small “impulsive” SEP events that emit electron beams that produce type III radio bursts. Further studies found enhancements in Fe/O, then extreme enhancements in element abundances that increase with mass-to-charge ratio \(A/Q\), rising by a factor of 1000 from He to Au or Pb arising in magnetic reconnection regions on open field lines in solar jets. In contrast, in the largest SEP events, the “gradual” events, acceleration occurs at shock waves driven out from the Sun by fast, wide coronal mass ejections (CMEs). Averaging many events provides a measure of solar coronal abundances, but \(A/Q\)-dependent scattering during transport causes variations with time; thus if Fe scatters less than O, Fe/O is enhanced early and depleted later. To complicate matters, shock waves often reaccelerate impulsive suprathermal ions left over or trapped above active regions that have spawned many impulsive events. Direct measurements of ionization states \(Q\) show coronal temperatures of 1–2 MK for most gradual events, but impulsive events often show stripping by matter traversal after acceleration. Direct measurements of \(Q\) are difficult and often unavailable. Since both impulsive and gradual SEP events have abundance enhancements that vary as powers of \(A/Q\), we can use abundances to deduce the probable \(Q\)-values and the source plasma temperatures during acceleration, ≈3 MK for impulsive SEPs. This new technique also allows multiple spacecraft to measure temperature variations across the face of a shock wave, measurements otherwise unavailable and provides a new understanding of abundance variations in the element He. Comparing coronal abundances from SEPs and from the slow solar wind as a function of the first ionization potential (FIP) of the elements, remaining differences are for the elements C, P, and S. The theory of the fractionation of ions by Alfvén waves shows that C, P, and S are suppressed because of wave resonances during chromospheric transport on closed magnetic loops but not on open magnetic fields that supply the solar wind. Shock waves can accelerate ions from closed coronal loops that easily escape as SEPs, while the solar wind must emerge on open fields.     

高超声速主流中横向喷流干扰非定常特性研究

脉冲发动机产生的横向喷流往往伴随着非定常效应,由于其持续时间非常短,给流场模拟和测量带来很大的困难.目前在地面设备中难以进行精确的试验,本文采用数值模拟方法对横向喷流的非定常效应进行了研究.重点对发动机启动和关车过程中典型时刻的流场进行了细致的刻画,分析了流动参数和模型气动力系数的动态变化过程,并给出了喷流压比和攻角变化所带来的影响.研究表明,喷流启动和关闭过程中,飞行器所呈现出的动态气动特性与稳态喷流时有着明显的差异,尤其是压心位置和法向力系数将发生显著的变化.在飞行器设计中,必须从安全控制的角度出发,考虑这一非定常效应的影响.     

低信噪比情况下识别模态参数的时域平均方法

 <正> 1.引官 模态参数识别方法在应用中需要解决的一个重要问题是观测噪声的干扰问题。为了有效地抑制观测噪声的影响,各种时域参数识别方法普遍引入了估计方法,以ITDM为代表的利用脉冲响应包括对脉冲激励的响应和脉冲响应函数)识别模态参数的识别方法还引入了噪声模态     

冲击噪声环境下基于任意阵列流形的空时二维DOA估计方法

 针对冲击噪声环境中信号源的高分辨二维波达方向(DOA)估计问题,提出了一种适合任意阵形的基于联合对角化分数低阶空时(ST)相关矩阵的二维DOA估计方法。该方法先对分数低阶空时矩进行采样构建伪快拍数据矩阵,然后对两个时延分数低阶空时矩阵进行联合对角化处理。其无需二维谱峰搜索和参数配对,在低信噪比下对强冲击噪声具有更好的抑制作用,适合存在一维角度兼并的情况。仿真结果证明了该方法的有效性。     

Narrowband interference suppression in impulsive channels

Suppression algorithms are developed first for a channel containing only impulsive background noise and then for a channel containing a spread-spectrum signal as well. These algorithms are based on nonlinear filters that produce predictions of the interfering signals that are then subtracted from the received signal to suppress the interference. Several such filters, including both fixed and adaptive ones, are proposed and compared using extensive computer simulations. The independence of the filtering procedures from the noise distribution shape, given constant second-order statistics, is shown     

TARANIS—A Satellite Project Dedicated to the Physics of TLEs and TGFs

TARANIS “Tool for the Analysis of RAdiations from lightNIngs and Sprites” is a CNES satellite project dedicated to the study of impulsive transfers of energy between the Earth atmosphere and the space environment. Such impulsive transfers of energy, identified by the observation at ground and in space (rocket, balloons, FORMOSAT 2 satellite) of Transient Luminous Events (TLEs) and the detection on satellites (CGRO, RHESSI) of Terrestrial Gamma ray Flashes (TGFs), are likely to occur in other astrophysical environments as well. The TARANIS mission and instrumentation is presented. The way the TARANIS programme (associated ground-based and balloon-based measurements included) may answer questions about the physics of TLEs and TGFs is examined. The questions addressed include: TLEs and TGFs source regions, associated phenomena, transfers of energy between the radiation belts and the atmosphere, TLEs and TGFs generation mechanisms, input parameters to the modelling of the variation of the atmosphere and the electric circuit.