基于有限元--离散元耦合的粒子阻尼减振研究

在侧挂构型发射任务中，中心承力筒与卫星直接连接，其动力学特性对卫星的振动响应有直接影响。首先分析中心承力筒的模态特性，据此完成粒子阻尼器的结构参数设计。随后，使用有限元--离散元耦合仿真方法，确定了阻尼器填充粒子的最佳直径和阻尼器最佳安装位置。仿真结果表明，该方案下星箭界面减振效果可达40%。最后，使用最优粒子阻尼参数开展水平激励实验。实验结果表明，与未安装粒子阻尼器相比，中心承力筒+粒子阻尼器组合体的减振效果可达35%以上，与仿真结果一致。     

溶胶-凝胶法制备纳米TiO2 及粒径控制工艺

采用溶胶-凝胶法,以钛酸丁酯为前驱体,乙二醇作为螯合剂制备纳米TiO2 粒子。考察钛的乙二

醇盐的浓度、pH 值、温度等因素对TiO2 粒径的影响,并用红外光谱和SEM 对纳米TiO2 粒子进行结构和形貌表

征。结果表明,采用溶胶凝胶法可以制备出呈椭圆形且粒径分布均匀的TiO2 纳米粒子。使用硝酸铵可以有效

阻止TiO2 纳米粒子团聚。当pH 值为2 ~3、温度为20 ~40℃,钛的乙二醇盐在丙酮中的浓度为0. 03、0. 05 及

0. 07 M 时,粒径分别为150、240 及600 nm。

     

Particle filter-based real-time phase line bias estimation for GNSS-based attitude determination with common-clock receivers

Global navigation satellite system (GNSS)-based attitude determination has been widely adopted in a wide variety of terrestrial, sea, air, and space applications. Recently, the emergence of commercial multi-GNSS common-clock receivers has brought new opportunities for high-precision GNSS-based attitude determination with single-differenced (SD) model. However, the key requirement of using this approach is the accurate estimation of the troublesome line bias (LB) in real-time. In this contribution, we propose a particle filter-based real-time phase LB estimation approach that apply to SD model with single-system single-frequency observations from common-clock receiver. We first analyzed the relationship between the integer ambiguity ratio value and the phase LB. It is proved that the accuracy of a given phase LB value can be qualified by the related ambiguity resolution ratio value, and the normalized ratio value can therefore be used to represent the likelihood function of observations. Then, we presented the particle filter-based real-time phase LB estimation procedure, and assessed its performance using GPS L1/BDS B1I observations from two datasets collected with different types of common-clock receivers in terms of the accuracy and convergence time of phase LB estimation, the computation load, and the positioning and attitude determination accuracy with respect to the double-differenced (DD) model. Experimental results demonstrated that the phase LB could be accurately estimated with short convergence time (generally within 15 epochs). Moreover, compared with the classical DD approach, the particle filter-based SD approach delivers comparable positioning root-mean-square (RMS) errors in the North and East components but significantly smaller RMS errors in the Up component. Accordingly, the achievable yaw accuracy is comparable whereas the pitch accuracy is remarkably improved. The improvements of positioning accuracy in the Up component and pitch accuracy are approximately 35.7 % to 63.7 %, and 33.3 % to 63.1 %, respectively. Additionally, the single-epoch computation time with our particle filter-based SD approach is generally 0.08 s, which is obviously larger than the DD approach but could still meet the requirements of real-time applications below 10 Hz sampling.     

基于轨迹拐点滤波的激光雷达里程计定位算法研究

在GPS拒止环境下，激光雷达里程计可以利用帧间匹配跟踪车辆实现定位，但是定位误差随时间累积的特性造成激光雷达里程计(LO)缺乏持续性。为解决LO的误差累积问题，引入轻量级地图OSM。基于粒子滤波框架，以LO作为运动模型的输入，通过两次筛选提取拐点，利用拐点匹配完成与地图的对齐，并以粒子的均值作为车辆校正后的位置，实现对定位误差的校正。提出了一种新的粒子权重模型，利用不同节点的相似度模型及测量值作为粒子权重的更新依据，避免拐点与路网节点的错误关联导致定位误差加大。经由KITTI数据集上的实验验证，该算法可以有效克服LO误差漂移问题，相较于原始LO定位精度至少提高了49.22%，且具有较好的实时性。     

Numerical study on combustion efficiency of aluminum particles in solid rocket motor

The combustion of aluminum particles in solid rocket motor plays an important role in energy release of propellants. However, due to the limited residence time, aluminum particles may not be burned completely, thus hindering the improvement of specific impulse. This study aims to explore the characteristics of aluminum combustion efficiency and its influencing factors by experiments and numerical simulations, providing a guideline for engine performance improvement. As an input of simulation, the initial agglomerate size was measured by a high pressure system. Meanwhile, the size distribution of the particles in plume was measured by ground firing test to validate the numerical model. Then, a two-phase flow model coupling combustion of micro aluminum particle was developed, by which the detailed effects of particle size, detaching position and nozzle convergent section structure on aluminum combustion efficiency were explored. The results suggest that the average combustion temperature in the chamber drops with increasing initial particle size, while the maximum temperature increases slightly. In the tested motors, the aluminum particle burns completely as its diameter is smaller than 50 μm, and beyond 50 μm the combustion efficiency decreases obviously with the increase of initial size. As the diameter approaches to 75 μm, the combustion efficiency becomes more sensitive to particle size. The combustion efficiency of aluminum particle escaping from end-burning surfaces is significantly higher than that from internal burning surface, where the particle combustion efficiency decreases during approaching the convergent section. Furthermore, the combustion efficiency decreases slightly with increasing nozzle convergent section angle. And theoretically it is feasible to improve combustion efficiency of aluminum particles by designing the convergent profile of nozzle.     

改进的Chan-粒子滤波算法超宽带室内三维定位

针对超宽带室内定位时容易受到非视距误差的影响，导致定位精度大大下降，甚至无法准确定位的问题，提出了一种融合粒子滤波的改进Chan定位新方法。首先，在Chan定位方法中引入模拟退火算法，对到达时间差（TDOA）算法的测量值进行优化，获得初步定位的最优解；然后，采用粒子滤波对测量值进行再次优化，粒子重采样后得到的中心位置即为目标节点的精确位置。仿真和实验结果均表明，该算法能有效提高在非视距环境下超宽带室内定位的精度，较好地消除非视距误差的干扰。