基于变刚度变阻尼的柔性喷管动态模型

针对柔性接头动态迟滞曲线受控制系统控制位置精度和动态响应速度影响较大的问题,基于电液伺服机构和柔性接头变刚度变阻尼模型,构建了柔性喷管的电液伺服机构-变刚度变阻尼模型,将其和电液伺服机构-定刚度定阻尼模型进行了对比。分析了电液伺服机构主要参数、柔性接头工作参数等对电液伺服机构-柔性接头系统动态特性的影响。分析结果表明:电液伺服机构-变刚度变阻尼模型所构造的迟滞曲线可更准确地与实验结果相吻合,并符合迟滞曲线随频率变化的规律,反馈系数、放大器静态放大系数、电液伺服机构增益、滑阀流量增益等参数对系统动态特性的影响更为明显。该模型为固体火箭发动机电液伺服机构-柔性接头系统动态特性的调整提供理论依据。     

基于轨道角动量的电磁涡旋SAR成像新方法

为研究电磁涡旋波在合成孔径雷达(SAR)领域的应用潜力,验证电磁涡旋SAR成像的可行性,将电磁涡旋与合成孔径雷达模型结合,通过使用单一模式的轨道角动量,用合成孔径原理实现方位聚焦。给出了基于电磁涡旋的SAR几何模型和回波信号模型,并提出了适用于电磁涡旋SAR的改进chirp-scaling(CS)成像算法。通过点目标仿真分析,验证了所提成像算法的有效性。该方法可为SAR系统新体制设计及雷达的研究提供参考。     

Stability of relative equilibria of the full spacecraft dynamics around an asteroid with orbit–attitude coupling

The full dynamics of spacecraft around an asteroid, in which the spacecraft is considered as a rigid body and the gravitational orbit–attitude coupling is taken into account, is of great value and interest in the precise theories of the motion. The spectral stability of the classical relative equilibria of the full spacecraft dynamics around an asteroid is studied with the method of geometric mechanics. The stability conditions are given explicitly based on the characteristic equation of the linear system matrix. It is found that the linearized system decouples into two entirely independent subsystems, which correspond to the motions within and outside the equatorial plane of the asteroid respectively. The system parameters are divided into three groups that describe the traditional stationary orbit stability, the significance of the orbit–attitude coupling and the mass distribution of the spacecraft respectively. The spectral stability of the relative equilibria is investigated numerically with respect to the three groups of system parameters. The relations between the full spacecraft dynamics and the traditional spacecraft dynamics, as well as the effect of the orbit–attitude coupling, are assessed. We find that when the orbit–attitude coupling is strong, the mass distribution of the spacecraft dominates the stability of the relative equilibria; whereas when the orbit–attitude coupling is weak, both the mass distribution and the traditional stationary orbit stability have significant effects on the stability. We also give a criterion to determine whether the orbit–attitude coupling needs to be considered.     

Characterization of ionospheric amplitude scintillations using wavelet entropy detrended GNSS data

The extensive monitoring networks of Global Navigation Satellite System (GNSS) ionospheric scintillation have been established to continuously log observation data. Further, the amplitude scintillation index and the phase scintillation index, which are derived from scintillation observations, are anticipated to accommodate the accuracy requirement of both the user level and the monitoring station level. However, raw scintillation observations essentially measure superposed waveform impairments of GNSS signals propagating through ionosphere and troposphere. It implies that fluctuations of raw scintillation observations are caused by multiple factors from the entire radio propagation environment. Hence, it is crucial to characterize ionospheric scintillations from GNSS observation data. And the characterization is implemented through extracting fluctuations of raw observations merely induced by ionospheric scintillations. Designed to address this problem by means of Fourier filtering detrending, the present work investigates the influence of varying detrending cutoff frequencies on wavelet statistical energy and wavelet entropy distributions of scintillation data. It consequently derives criteria on the optimum detrending cutoff frequency for three types of raw amplitude scintillation data, which are classified by their wavelet energy distributions. Results of the present work verify that detrending with specific optimum cutoff frequencies rather than the fixed and universally applicable one renders the validity and credibility of characterizing ionospheric scintillations as the part of GNSS observation fluctuations purely induced by ionosphere electron density irregularities whose scale sizes are comparable with or smaller than the Fresnel scale.     

越肩发射反导拦截弹复合制导律研究

研究了优化反导拦截弹的越肩发射制导律,实现了对尾追目标的拦截,采用伪谱法和滑膜变结构理论设计了全弹道复合制导规律。利用Radau伪谱法求解以转弯时间最优为指标泛函的最佳转弯规律,通过曲线拟合给出了初制导转弯段的过载指令。选择零控脱靶量作为滑动模态对末制导律进行设计;利用这两种制导律的加速度指令构造了交接班导引律实现弹道的平滑。最后,对载机越肩发射反导拦截弹拦截来袭导弹的反导场景进行了数字仿真,结果表明所设计的复合制导律能够完成反导拦截任务。     

侧板边界层对正激波/边界层干扰特性影响的数值模拟研究

为了研究外压式进气道处于临界工况时结尾正激波同时与压缩面和侧板上边界层的相互干扰,专门设计了三组具有不同前伸长度侧板的简化构型作为研究对象,利用数值模拟手段评估了侧板边界层厚度对正激波/边界层干扰特性的影响。仿真结果表明,当没有侧板边界层参与干扰时流动呈现较好的准二维特性,但当侧板边界层参与干扰后将形成较强的角区干扰结构,该角区三维干扰结构与对称面上的准二维干扰结构存在此消彼长的关系。此外,波系的空间形态也将由“准二维λ波”结构变为“双λ波+角区压缩波”结构,波系形态的改变则进一步导致壁面回流区分布以及摩擦力线拓扑结构变得更加复杂。     

H2/H∞组合方法及其对导弹纵向运动的控制分析

在对Ｈ２／Ｈ∞组合控制问题描述和分析的基础上,总结了此类问题的一种求解算法,即转换为双线性矩阵不等式问题,通过迭代运算加以求解。以某型导弹纵向运动的控制为例,对Ｈ２／Ｈ∞组合算法进行了仿真计算,结果表明,该方法在一定程度上协调了系统的Ｈ２及Ｈ∞设计任务间的矛盾,使得所设计控制系统不但有着要求的噪声抑制能力,而且具有良好的鲁棒稳定性。     

基于延误油耗优化的平行跑道运行方式

在比较现有平行跑道运行方式的基础上,制定了基于延误油耗优化原则的跑道选择策略。同时根据航班时刻表及起降间隔标准,建立了数学模型,提出了基于油耗优化原则的跑道选择和排序方法。算例表明该方法提高了混合运行方式下跑道的运行效率,减少了航空器的滑行时间和等待时间,降低了航空公司的运营成本。     

军用飞机跳伞供氧系统改进

介绍三种跳伞供氧分系统改进方法,可用在现役主战飞机的跳伞供氧分系统中增加快速、可靠的分离机构,配合手动或自动解脱机构,使飞行员弹射救生后下降着陆或着水之前,能自动或手动解脱跳伞供氧分系统的大部分成件,使之脱离与人体的连接,减轻入水重量,减少对救生过程的不利影响,以提高水上救生的成功率。经过试验检验提出了一种较优改进方案。     

高稳定性电弧等离子体超声速喷管流动装置

笔者在已研制的壁稳电弧等离子体发生器基础上,改进了阳极结构、加置Laval喷管,建立了一套可长期连续运行的高稳定性电弧等离子体超声速喷管流动装置,超声速电弧射流的不稳定度为1％(纯氩)和3％(氮氩),电弧射流具有很好的稳定性、再现性和对称性。测量表明：超声速电弧射流的电子温度沿流动方向呈现出波浪形周期升降的变化规律。