Sliding mode control design for oblique wing aircraft in wing skewing process

When the wing of Oblique Wing Aircraft (OWA) is skewed, the center of gravity, inertia and aerodynamic characteristics of the aircraft all significantly change, causing an undesirable flight dynamic response, affecting the flying qualities, and even endangering the flight safety. In this study, the dynamic response of an OWA in the wing skewing process is simulated, showing that the three-axis movements of the OWA are highly coupled and present nonlinear characteristics during the wing skewing. As the roll control efficiency of the aileron decreases due to the shortened control arm in an oblique configuration, the all-moving horizontal tail is used for additional roll and the control allocation is performed based on minimum control energy. Given the properties of pitch-roll-yaw coupling and control input and state coupling, and the difficulty of establishing an accurate aerodynamic model in the wing skewing process due to unsteady aerodynamic force, a multi-loop sliding mode controller is formulated by the time-scale separation method. The closed-loop simulation results show that the asymmetric aerodynamics can be balanced and that the velocity and altitude of the aircraft maintain stable, which means that a smooth transition is obtained during the OWA’s wing skewing.     

Initiation characteristics of oblique detonation waves from a finite wedge under argon dilution

In this paper, the flow field characteristics of Oblique Detonation Waves (ODWs) induced by a finite wedge under argon dilution are studied by solving the Euler equations with a detailed chemical model of hydrogen and air. First, the effects of the expansion waves, argon concentration, geometric parameters, and Mach number on the ODW are discussed. The results show that the changes of these parameters may make the oblique detonation not be initiated. Then, the ODW initiation criterion of the finite wedge is summarized, as the characteristic length of the induction zone L_C and the characteristic length of the oblique wedge L_W meet the condition L_C/L_W < 1, the initiation of the ODW occurs; otherwise, it does not occur. What’s more, the Constant Volume Combustion (CVC) theory is applied to study the characteristic length of induction zone. It is found that CVC theory is more suitable for the “smooth transition” type of ODW flow field, the theoretical and numerical characteristic length in induction regions are in good agreement. This work is of great significance for the design of oblique detonation engines for hypersonic vehicles.     

W波段UAV MISAR实时成像运动补偿方法

建立了实时成像正侧视合成孔径雷达(SAR)运动误差模型,采用了一种基于惯导和相位梯度自聚焦(PGA)运动误差估计的中心波束平面运动补偿算法。该算法对回波包络和相位进行分开补偿,利用惯导数据把带有运动误差的回波包络拉直,再利用相位梯度自聚焦算法对回波进行相位误差估计并补偿。针对实时成像的时间少、运算量大、运算资源受限等特点,该算法取消了距离徙动校正的步骤,将运动误差矢量在斜距平面投影并完成包络校正和相位误差估计。该方法运算量小,同时能满足分辨率要求。仿真结果表明:该方法能够得到质量较高的SAR图像。     

SiC/CVD SiC复合涂层的抗氧化及抗热震性能研究

为了提高C/SiC复合材料耐高温性能,采用泥浆浸渍裂解与真空化学气相沉积(CVD)在材料表面制备了SiC/CVD SiC复合涂层,通过XRD、SEM分析了涂层组成与结构;研究了复合涂层的高温抗氧化(700～1 500℃)和抗热震性能。结果表明,泥浆浸渍法制备的SiC涂层具有一定的封孔效果,可使材料开孔率下降,但高温抗氧化效果并不佳,1 200℃氧化10 min后材料弯曲强度保留率下降明显仅有86%。CVD SiC涂层结构致密,与SiC封孔涂层结合较好,在700～1 500℃具有较好的抗氧化效果,随着氧化温度的升高,氧化后涂层完好,表面O元素逐渐增加,材料失重率缓慢增加但不大于0.5%,且材料性能并未下降。涂层材料在1 200℃-10 min短时热震5次后材料弯曲强度保留率仍有95%以上,且未出现开裂、剥落等热震损伤。在1 200℃-30 min长时热震10次后,涂层材料基本被完全氧化,材料失去保护作用,弯曲强度下降至90%左右。     

多种工质下螺旋波等离子体源波场结构数值模拟

针对螺旋波等离子体放电机理，开展了多种工质条件下的螺旋波放电等离子体内波场结构数值模拟研究。计算发现:氦气等离子体的Er分量在径向边界处的峰值更为突出，有利于等离子体在径向的输运，波电场径向分量决定了电流密度径向分量在内部的表现。在0.266 Pa和1.064 Pa两种气体压强条件下，通过波场结构验证了气压对于波阻尼影响的结论。波场结构是螺旋波在等离子体内传播以及能量沉积的微观体现，研究螺旋波波场结构是揭示其高电离效率的重要途径。初步探索了功率耦合机制，为实验系统优化及实验方案设定奠定理论基础。     

Satellite launch vehicle effect on the Earth’s lower ionosphere: A case study

The effect of the rocket exhaust products on the D-region of the ionosphere is investigated with the help of Very low frequency (VLF) electromagnetic wave propagation characteristics within the Earth-ionosphere waveguide. The changes in the electron density profile are computed from the observed VLF signal amplitude perturbations about 3 dB during the rocket launch. We find a localized electron depletion in the lower ionosphere at an altitude of around 58 km, that is thought to be originated by the attachment of ionospheric ion and molecular hydrogen along with water molecule in the exhaust product of first stage burn of Geosynchronous Launch Vehicle (GSLV) rocket at the time of GSLV launched from Sriharikota, India, on 27 August 2015 at 11:22 UT (16:52 IST). The ionospheric depletion perturbed the navigational VLF signal (VTX = 17 kHz) 134 s after the launch of the GSLV rocket.     

航天器AIT中心典型霉菌形态及其消杀效果研究

航天器总装厂房是航天器携带微生物的重要环境来源之一，厂房内的微生物检测与鉴定及其杀菌方法研究对于航天器的微生物安全与防控技术研究具有重要意义。本文报道了航天器AIT中心分离的青霉属、曲霉属和枝孢霉属等8个种属的典型霉菌菌落和孢子形态，为航天器霉菌鉴定和菌种库的构建提供了参考；同时研究了消毒剂、UVC辐照和热处理对这些霉菌的消杀效果，以期为航天器的霉菌防控技术研究提供科学依据。研究结果表明不同种属霉菌对3种消杀方法的敏感性具有较大的差异性。结合我国不同地区AIT中心霉菌种属的多样性，在进行我国AIT中心霉菌的消杀工作时应有针对性地科学选择不同消杀方法或综合应用多种消杀方法。     

弹丸速度对超爆轰冲压加速器性能影响

为研究超爆轰模态冲压加速器的推进性能，采用混合的Roe/HLL（Harten, Lax, Van Leer）格式，结合自适应网格加密技术(AMR )与沉浸边界法(IBM )，数值模拟了弹丸速度高于预混可燃气体C-J爆速的冲压加速器流场，揭示了弹丸速度对流场结构与推力的影响。结果表明当弹丸速度在一定范围时，斜爆轰波可驻定在弹丸肩部或头部，在弹丸尾部形成高压区加速弹丸，并且，斜爆轰波驻定在弹丸头部推力更高，稳定工作的速度范围 更宽 。     

Application of Wuhan Ionospheric Oblique Backscattering Sounding System (WIOBSS) for the investigation of midlatitude ionospheric irregularities

An upgrade of Wuhan Ionospheric Backscattering Sounding System (WIOBSS) was developed in 2015. Based on the Universal Serial Bus (USB), and a high performance FPGA, the newly designed WIOBSS has a completely digital structure, which makes it portable and flexible. Two identical WIOBSSs, which were situated at Mile (24.31°N, 103.39°E) and Puer (22.74°N, 101.05°E) respectively, were used to investigate the ionospheric irregularities. The comparisons of group distance, Doppler shift and width between Mile-Puer and Puer-Mile VHF ionospheric propagation paths indicate that the reciprocity of the irregularities is satisfied at midlatitude region. The WIOBSS is robust in the detection of ionospheric irregularities.     

Case study of inclined sporadic E layers in the Earth’s ionosphere observed by CHAMP/GPS radio occultations: Coupling between the tilted plasma layers and internal waves

We have used the radio occultation (RO) satellite data CHAMP/GPS (Challenging Minisatellite Payload/Global Positioning System) for studying the ionosphere of the Earth. A method for deriving the parameters of ionospheric structures is based upon an analysis of the RO signal variations in the phase path and intensity. This method allows one to estimate the spatial displacement of a plasma layer with respect to the ray perigee, and to determine the layer inclination and height correction values. In this paper, we focus on the case study of inclined sporadic E (E_s) layers in the high-latitude ionosphere based on available CHAMP RO data. Assuming that the internal gravity waves (IGWs) with the phase-fronts parallel to the ionization layer surfaces are responsible for the tilt angles of sporadic plasma layers, we have developed a new technique for determining the parameters of IGWs linked with the inclined E_s structures. A small-scale internal wave may be modulating initially horizontal E_s layer in height and causing a direction of the plasma density gradient to be rotated and aligned with that of the wave propagation vector k. The results of determination of the intrinsic wave frequency and period, vertical and horizontal wavelengths, intrinsic vertical and horizontal phase speeds, and other characteristics of IGWs under study are presented and discussed.