基于激光测距的月球探测重载六足机器人自主避障控制

月面未知环境下具有高承载力的六足移动机器人是月球探测中不可或缺的装备。六足机器人虽然可以借助足地接触信息和姿态信息在不平坦路面行走，在遇到较小障碍物时可以做出适当的反射动作，但当遇到无法逾越的障碍物时，基于视觉信息实现腿式机器人避障运动是非常重要的。针对电驱动六边形对称分布的六足机器人，基于激光测距仪的信息实现了模拟月壤地面的地形建模，提出基于虚拟机体模型的自主避障策略，获得最优可行方向和运动最短距离，规划了实时避障的机体和足端运动轨迹。实验结果表明,六足机器人可以实时、准确地跟踪避障策略得到实时偏航角度，实现了机器人在未知环境下的自主避障运动，为月球探测重载足式机器人研究奠定了基础。     

高温气体效应对高超声速磁流体控制的影响

高温气体效应会严重影响高温气体流场的流动特性，进而影响高超声速磁流体控制效率。基于低磁雷诺数假设，通过耦合求解带电磁源项的三维Navier-Stokes流场控制方程和电场泊松方程，开展完全气体模型、平衡气体模型、化学非平衡气体模型、热化学非平衡气体模型等条件下的高超声速磁流体控制数值模拟，分析气体模型对磁流体控制的影响，研究高温气体各种非平衡效应及焦耳热振动能量配比等对高超声速磁流体控制的影响规律。研究表明：化学非平衡效应对高超声速磁流体控制影响显著，采用化学非平衡气体模型模拟得到的磁控增阻特性介于完全气体模型和平衡气体模型之间，平衡气体和完全气体模型磁控热流变化的定性规律，与非平衡气体模型模拟结果差异很大；热力学非平衡效应对高超声速磁流体控制的影响，与焦耳热振动能量作用比率紧密相关，随该配比增大，磁场增阻效果由67%降到约12%；高温气体效应会极大地降低磁控增阻效果，会明显地增强部分表面区域的磁控热流减缓效果，要准确数值模拟高超声速磁流体控制，必须有效地考虑化学和热力学非平衡效应，同时选用接近实际情况的焦耳热振动能量配比。     

Research of flexible beam impact dynamics based on space probe-cone docking mechanism

The issue considered in this paper is the dynamic behavior of flexible probe based on space probe-cone docking mechanism in the docking process. The theoretical model of docking impact dynamics based on flexible beam is built according to the Lagrange Analytical Mechanics theory. The contact problem is solved by using Hertz point-surface contact model. Assumed Modes Method is introduced to describe the deformation of flexible beam. Runge–Kutta numerical method is used to solve this theoretical model. Results of the theoretical model show a good agreement with the experimental and MSC.Patran/Dytran simulation results. Moreover, the influence of flexible beam parameter on docking impact process is analyzed based on the theoretical model.     

内转式进气道自起动性能研究

为了研究内转式进气道的自起动性能以及下壁面泄流对自起动的影响规律,开展了数值计算和风洞实验,数值计算采用准定常的方法,风洞实验通过阴影录像以及下壁面丝线显示相结合的方法确定进气道的起动状态。结果表明Ma5、攻角0°时进气道不能自起动,下壁面存在大范围的三维流动分离,流动损失严重。为了提高进气道的自起动能力,在下壁面距前缘400mm位置开孔泄流,开孔区域约100mm×40mm,开孔率0.2,实验模型孔径3mm;研究表明,泄流后进气道顺利自起动,总压恢复系数提高了0.25,泄流量损失仅为捕获流量的1%。进一步数值研究表明,泄流构型在攻角0°时的自起动马赫数在4.3～4.4,泄流极大地拓宽了进气道的工作范围。     

A novel predictive algorithm for double difference observations of obstructed BeiDou geostationary earth orbit (GEO) satellites

Transmission link disturbances and device failure cause global navigation satellite system (GNSS) receivers to miss observations, leading to poor accuracy in real-time kinematic (RTK) positioning. Previously described solutions for this problem are influenced by the length of the prediction period, or are unable to account for changes in receiver state because they use information from previous epochs to make predictions. We propose an algorithm for predicting double difference (DD) observations of obstructed BeiDou navigation system (BDS) GEO satellites. Our approach adopts the first-degree polynomial function for predicting missing observations. We introduce a Douglas-Peucker algorithm to judge the state of the rover receiver to reduce the impact of predictive biases. Static and kinematic experiments were carried out on BDS observations to evaluate the proposed algorithm. The results of our navigation experiment demonstrate that RTK positioning accuracy is improved from meter to decimeter level with fixed ambiguity (horizontal?<?2?cm, vertical?<?18?cm). Horizontal accuracy is improved by over 50%, and the vertical accuracies of the results of the static and kinematic experiments are increased by 47% and 27% respectively, compared with the results produced by the classical approach. Though as the baseline becomes longer, the accuracy is weakened, our predictive algorithm is an improvement over existing approaches to overcome the issue of missing data.     

GNSS-R海面风速反演算法

针对目前GNSS-R海面风速反演方法观测量单一，精度较低的问题，提出一种基于时延多普勒相关功率图（Delay Doppler map，DDM）的分割多普勒波形匹配反演算法。该方法利用新的DDM观测量，经过训练后，可以反演海面风速。使用该算法根据给定条件建立风场反演模型，以CYGNSS数据作为仿真输入量。仿真结果表明，利用该方法在海面风速20 m/s以下，反演风速的均方根误差为2.01 m/s，结果优于传统GNSS-R风速反演使用的峰值功率法和前缘坡度匹配法（Leading edge slope matching method，LES）。     

火星探测器表面材料催化特性数值模拟研究

针对火星探测器高超声速进入过程中的表面材料催化作用及其对气动热环境影响这一问题，建立了变壁面温度的火星大气表面材料催化作用模型，并基于火星大气物理化学模型和求解三维热化学非平衡N-S方程的数值方法，对典型火星探测器防热大底进行了数值模拟，获得了不同催化特性下的高超声速非平衡流场和气动热数据，分析了表面材料催化特性对气动热环境影响的规律性。研究结果表明：表面催化特性对壁面附近组分分布影响很大，催化反应进程主要受O原子浓度限制；有限催化热流随催化效率增大而增大，完全催化峰值热流比催化效率为1的有限催化峰值热流高25%~64%；表面温度随催化特性的变化规律与热流变化规律类似。有限催化模型能根据表面材料的催化特性精细化预测表面热流和温度，为防热设计提供更精确合理的参考标准。     

VLBI observations to the APOD satellite

The APOD (Atmospheric density detection and Precise Orbit Determination) is the first LEO (Low Earth Orbit) satellite in orbit co-located with a dual-frequency GNSS (GPS/BD) receiver, an SLR reflector, and a VLBI X/S dual band beacon. From the overlap statistics between consecutive solution arcs and the independent validation by SLR measurements, the orbit position deviation was below 10?cm before the on-board GNSS receiver got partially operational. In this paper, the focus is on the VLBI observations to the LEO satellite from multiple geodetic VLBI radio telescopes, since this is the first implementation of a dedicated VLBI transmitter in low Earth orbit. The practical problems of tracking a fast moving spacecraft with current VLBI ground infrastructure were solved and strong interferometric fringes were obtained by cross-correlation of APOD carrier and DOR (Differential One-way Ranging) signals. The precision in X-band time delay derived from 0.1?s integration time of the correlator output is on the level of 0.1?ns. The APOD observations demonstrate encouraging prospects of co-location of multiple space geodetic techniques in space, as a first prototype.     

一种综合孔径微波辐射计成像处理算法

综合孔径成像是基于干涉仪成像原理实现的一种成像方式，其通过对干涉测量结果进行逆傅里叶变换得到场景的亮温分布，利用小波增强去噪算法在时域和频域同时对图像进行处理，增强需求信息抑制非必要信息，并附加特定的窗函数滤除杂波，提高重建的微波辐射计图像的清晰度和平滑感。采用盲解卷的Lorentzian超分辨率算法提高成像的分辨力，较好的解决了天线口面尺寸与分辨力矛盾的问题。     

Residual stresses of polycrystalline CBN abrasive grits brazed with a high-frequency induction heating technique

Residual stresses produced in polycrystalline CBN abrasive grits during a high-frequency induction brazing process are calculated by using ?nite element analysis, with a consideration of the nonuniform temperature distribution in the induction brazing model. The in?uences of induction brazing parameters on the residual stresses of polycrystalline CBN abrasive grits have been analyzed, including the embedding depth, grit side length, etc. Results obtained show that the tensile stress with a 40% embedding depth is 292 MPa, which is the minimum on the bonding interface compared with other embedding depths. Meanwhile, the maximum tensile stress is 575 MPa, with an increase of 59% compared with that of a grit side length of 50 mm. Finally, the simulation results of the brazing residual stress of polycrystalline CBN abrasive grits have been con?rmed valid based on the residual stress measurement of the brazed monocrystalline CBN grit.