运载火箭圆柱形贮箱中推进剂大幅晃动的数值模拟

运载火箭飞行过程中,贮箱内推进剂晃动及波面破碎现象会对燃料贮箱产生较大的干扰力,控制不当会影响飞行稳定性.为了研究推进剂大幅晃动对贮箱结构的影响,建立了圆柱形贮箱内液体晃动非线性动力学模型,利用流体体积函数与水平集法解决了大幅晃动过程中产生的破碎波的描述及自由液面的追踪问题,并对三维圆柱形贮箱在多种含液状态下,由俯仰运...     

燃油初温对两相爆震性能影响的实验研究

为研究燃油初温对两相爆震性能的影响,在24mm内径爆震管中,以30~200℃的不同初温煤油为燃料,氧气为氧化剂,成功进行了10Hz的两相爆震实验。实验发现,随着燃油初温的升高,火焰锋面的稳态传播速度逐渐增大,爆震燃烧的稳定性逐渐提升,两相爆震峰值压力增大,起爆距离缩短。此外对不同燃油初温下的爆震燃烧尾焰观测表明,油温升高后,非稳态排气总压增大,发动机可获取的推力增大。     

基于外辐射源直达波的对消及仿真研究

利用外辐射源（如调频广播、电视、GPS等的发射信号）的无源雷达探测技术一直是国内外研究的热点。在目标检测上,直达波信号的干扰不但对通道的动态范围提出了极高的要求,同时对微弱目标回波的检测构成了限制。文中利用二元阵的方法对直达波的干扰进行抑制,并对其对消性能进行了仿真分析和研究。     

一种航空噪声背景下的语音增强方法

依据航空噪声的频谱特性,提出将自适应滤波算法与改进的谱减法相级联的方法来增强语音。在强航空噪声背景下,处理后的语音不仅信噪比得到了很大提高,而且在有效抑制背景噪声和音乐噪声的同时,其清晰度和可懂度也得到了很大的改善。     

Enhanced wave and finite element method for wave propagation and forced response prediction in periodic piezoelectric structures

As a promising numerical tool of structural dynamics in mid-and high frequencies, the wave and finite element method (WFEM) is receiving increasingly attention and applications. In this paper, an enhanced WFEM has been developed with a reduced model and a new eigenvalue scheme. The reduced model is applicable for structures with piezoelectric shunts or local dampers;the new eigenvalue scheme can mitigate the ill-conditioning when the wave basis is calculated. The enhanced WFEM is applied to a thin-wall structure with periodically distributed piezoelectric mate-rials (PZT). Both free wave characteristics and forced response are analyzed and the influences of the suggested enhancements are presented. It is shown that if the control factors are properly cho-sen, these enhancements can improve the accuracy while accelerating the calculation. Resulting from the complexity of the application, these enhancements are not optional but imperative.     

内重力波传播的3维传输函数模式研究

在考虑背景风场及大气耗散的条件下,建立了3维内重力波传输函数数值模式.分析了300 km高度3维传输函数在频率波数域的特性,并以近地面单位脉冲点源为激发源,得到了内重力波在3维空间中的时空分布.讨论了不同时空尺度地面方波源激发的内重力波在电离层高度的能量分布特征.结果表明,(1)对内重力波而言,背景大气相当于一个带通滤波器,只有波动周期和波长分别在15～30 min和200～400 km之间的重力波扰动最容易上传到300km高度;(2)在背景风场的作用下水平面上以同心圆扩散的波阵面以及垂直方向上成漏斗状的波阵面发生了变形,并且逆风方向比顺风方向更有利于声重力波由对流层向电离层高度传播;(3)300km高度对时间尺度和空间尺度分别在20～30 min和150～250 km之间的地面方波源响应的总能量最强.      

波动方程差分解法及其对矩形波导双T形接头的分析

对波动方程差分解法进行了研究 ,给出了电场的计算公式 ,将上述方法应用于矩形波导双T形接头的分析 ,得到了与实测相吻合的各端口反射系数值。     

相控阵雷达长时跟踪波束调度与波形优化策略

针对相控阵雷达多目标跟踪波束调度和波形参数优化控制的问题，本文提出了一种基于马尔可夫决策过程（MDP）的相控阵雷达跟踪波束调度与波形参数优化策略，该方法以无迹卡尔曼滤波（UKF）算法为基础来估计目标的状态。首先将本文的序列决策问题建模为马尔可夫决策过程，定义了资源的效费比和长期回报率，然后与当前实际跟踪误差综合考虑作为MDP的回报函数，进而给出了调度的优化模型，最后将长时决策问题转化为动态规划算法结构进行求解，并且提出了一种并行混合遗传粒子群优化算法来求解各决策时刻的最优策略。仿真结果表明了长时策略的先进性以及寻优算法的优越性，与传统的短时策略相比，跟踪精度可提高11.17%。     

The attitude inversion method of geostationary satellites based on unscented particle filter

The attitude information of geostationary satellites is difficult to be obtained since they are presented in non-resolved images on the ground observation equipment in space object surveillance. In this paper, an attitude inversion method for geostationary satellite based on Unscented Particle Filter (UPF) and ground photometric data is presented. The inversion algorithm based on UPF is proposed aiming at the strong non-linear feature in the photometric data inversion for satellite attitude, which combines the advantage of Unscented Kalman Filter (UKF) and Particle Filter (PF). This update method improves the particle selection based on the idea of UKF to redesign the importance density function. Moreover, it uses the RMS-UKF to partially correct the prediction covariance matrix, which improves the applicability of the attitude inversion method in view of UKF and the particle degradation and dilution of the attitude inversion method based on PF. This paper describes the main principles and steps of algorithm in detail, correctness, accuracy, stability and applicability of the method are verified by simulation experiment and scaling experiment in the end. The results show that the proposed method can effectively solve the problem of particle degradation and depletion in the attitude inversion method on account of PF, and the problem that UKF is not suitable for the strong non-linear attitude inversion. However, the inversion accuracy is obviously superior to UKF and PF, in addition, in the case of the inversion with large attitude error that can inverse the attitude with small particles and high precision.     

First observation of upper mesospheric semi annual oscillations using ground based airglow measurements from Indian low latitudes

We summarize two years of Mesosphere Lower Thermosphere Photometer (MLTP) operation of mesospheric OH and O₂ emission monitoring. The deduced mesospheric OH and O₂ temperatures show large variability. Nightly temperature variations over Gadanki (13.5°N, 79.2°E) are dominated by the short period wave features, while tidal amplitudes are relatively small. Our measurements are the first to report a long period seasonal variation at two upper mesospheric altitudes simultaneously over the Indian sector. Our observations reveal the presence of a dominant semi-annual oscillation (∼6 months periodicity) together with a shorter period (∼2.5  months periodicity) oscillation in both OH and O₂ data.