微纳聚合体卫星的对称式重构规划算法

为解决微纳聚合体卫星变构过程中，聚合体各部分之间的动力学耦合导致的卫星整体姿态翻转或紊乱，提出了一种对称式变构规划算法。首先建立了铰链约束下的漂浮基多刚体系统动力学模型，研究了重构过程中各运动模块对本体姿态的影响，提出当每两个运动模块位置与转动方向满足对称性条件时，两者对本体姿态的影响可在一定程度上相互抵消。基于上述理论，在A*算法中引入最优分配度量和对称性判定，设计了并行对称重构规划算法。仿真结果表明，该规划算法可实现重构过程中多模块并行、对称运动，重构过程总步数较少，运动模块对本体姿态的影响小。     

Plasma transport process in the equatorial/low-latitude ionosphere

The behaviour of the equatorial/low-latitude ionosphere and the transport processes during magnetic disturbed and quiet periods of a high solar activity year, 2014, in the American sector are investigated. Parameters used include vertical drift (Vz), transport term (W), NmF2, hmF2 and scale-height (H). The F2 plasma variations followed the diurnal local solar pattern, being higher at daytime. The sunset maximum and sunrise minimum peaks of hmF2 were directly opposite to the scale height (H) pattern. The plasma distribution was basically controlled by combined actions of the electrodynamic convection/thermospheric composition, which is geomagnetic activity dependent. The annual, semi-annual and winter-anomalies of the F2 parameters were higher at the dip equator in comparison with the low-latitude. The Vz pre-reversal peak magnitude coincided with hmF2 peak and the effects are more pronounced during geomagnetic disturbed conditions. The transport term pattern was similar to that of the scale height and it is suggested as a proxy parameter for quantifying low-latitude plasma irregularities and distribution of thermospheric composition.     

航天器表面电荷激发空间静电场规律研究

从带电表面微元出发，通过求解泊松方程，得到带电介质平板表面邻近空间静电势的解析表达式，建立介质表面电位-介电常数模型，求得了带电介质平板表面电位、表面带电量和介质介电常数三者之间的关系式。结合典型的航天器表面介质材料带电案例，对此类圆盘结构介质平板带电问题进行了仿真分析，结果表明，在介质材料表面电位一定的情况下，表面电荷激发的空间静电势值随距离的增大而减小，并且距离介质表面越近，电势的空间变化率越大；在介质材料带电量相等的情况下，介质表面电位随着介质介电常数的增大而减小，并逐渐趋于一个稳定值，所以在一定范围内选择介电常数较大的介质材料可以降低介质的表面电位，减小介质间发生静电放电的几率。     

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.     

The Kumtag meteorite strewn field

The Kumtag meteorite strewn field was found in the Kumtag desert, 132 km south of Hami city in the Xinjiang province, China. It is an ellipse of 2.5 × 7.9 km, with a long axis extending along the northeast-southwest direction. The largest individual meteorite of the strewn field weighs about 10 kg; the smallest individual has a mass of only 27 g. In total, more than 100 individuals with a total mass of more than 180 kg were collected. The location and the distribution of the fragments suggest that the Kumtag meteoroid entered the atmosphere in the direction Northeast-Southwest. All meteorites collected in this strewn field are samples from the same unique meteorite shower. The Kumtag meteorite is an H5 ordinary chondrite with a shock stage S2, and a weathering grade W2. The cosmic ray exposure age of Kumtag is 6.7 ± 0.8 Ma, which is rather typical for H chondrites and which indicates that Kumtag was derived from the massive impact event on its parent body ~7 Ma ago. A significant amount of He has been lost during certain unknown processe(s) before the Kumtag meteorite was ejected from its parent body.     

基于Mecanum轮配送车的视觉与磁带双重导引技术研究

针对卫星总装过程中提出的物料配送需求,设计并实现了以Mecanum轮全方位移动平台为基础,可在狭窄配送通道内快速、灵活移动的智能物料配送车。结合总装现场实际环境条件,配送车采用了视觉导引与磁带导引相结合的智能导引策略,有效消除了光照强度变化、地面裂纹、电磁信号干扰等环境因素对车道线采集的影响,最终实现总装物料从库房至多工位的自动配送。     

A boundary vector cell model of place field repetition

Hippocampal place cells are thought to form the neural substrate of a global cognitive map. However, in multicompartment mazes, these cells exhibit locally repeating representations, undermining the global cognitive map view of place cells. This phenomenon appears to be related to the repetitive layout of these mazes, but still no hypothesis adequately explains it. Here, we use a boundary vector cell (BVC) model of place cell firing to model the activity of place cells in numerous multicompartment environments. The activity of modeled place cells bears a striking resemblance to experimental data, replicating virtually every major experimental result. Our results support the BVC model and indicate that locally repeating place cell firing could result purely from local geometry.     

基于动网格技术的飞机舱弹分离过程 CFD/ RBD耦合数值仿真

飞机舱弹分离瞬间特性严重影响导弹/炸弹的打击精度。采用计算流体动力学(CFD)和刚体动力学(RBD)模型耦合求解的数值仿真方法,应用网格弹性光顺和局部重构相结合的动网格技术,有效地避免了刚体运动而引起的网格畸变,仿真计算了炸弹舱弹分离后俯仰角度变化过程 .仿真结果表明,舱弹分离时向炸弹施加 1个合适的抛 射力矩,有助于炸弹在下降过程中快速地调整其打击姿态。     

水下超声速过膨胀燃气射流的流场特性

为研究水下超声速过膨胀燃气射流的流场特性,在压力水筒中开展了大扩张比锥形喷管的固体火箭发动机水下点火实验,并基于雷诺时均Navier-Stokes（RANS）方法和流体体积（VOF）模型进行数值求解,分析了过膨胀燃气射流与水介质的相互作用过程。研究表明：超声速过膨胀燃气建立射流通道后,射流核心区长度随喷管落压比的减少而减少;射流核心区剧烈振荡,表现为高频的膨胀和收缩,振荡频率随喷管落压比的减小而增加,范围为100~200 Hz;射流边界不断振荡,并伴随波系结构变化,当过膨胀程度较大时,激波进入喷管使其发生流动分离现象,流动分离点周期性往复移动;分离区内压力脉动没有显著的特征频率,主要集中在100~600 Hz的宽频带,锥形喷管水下流动分离的简易判据为喷管出口压力不低于环境背压的0.44倍。     

高超声速风洞流场非均匀性对气动力试验影响研究

高超声速风洞流场品质是气动力试验主要误差的决定因素,常规高超声速风洞流场均匀性虽然满足国军标GJB4399-2002《高超声速风洞气动力试验方法》对风洞流场品质的要求,但其风洞流场严格意义上说是“非均匀”的,这种流场非均匀性会对模型气动力特性存在不同程度的影响。为此,在CARDC常规高超声速风洞中开展了某升力体模型和某通气模型“多位置试验”,验证了风洞流场的非均匀性对飞行器气动力(特别是力矩特性)试验结果有显著影响,这种影响量已远超过常规的风洞重复性试验误差,甚至大于国内现有的在AIAA-S071A-1999标准上建立的不确定度评估方法所获取的“不确定度”。