逆金字塔式安全着陆点选择方法

针对现有地外天体软着陆安全着陆点选择方法的不足,设计了逆金字塔式安全着陆点选择方法,结合着陆器的落点精度和自主避障及地形坡度适应能力,建立了基于平整点、安全着陆点、可靠避障点和标称着陆点的地形安全性分析与定量搜索模型,该模型呈四层逆金字塔结构,每一层搜索的结果作为下一层搜索的输入,从弱约束到强约束逐步收敛至100%地形安全着陆区,嫦娥五号探测器飞行结果表明该方法能够快速确定安全着陆区及标称着陆点,并有效指导着陆下降过程的标称航迹设计和轨道控制策略制定。     

基于CFD高精度算法的雷电电磁场研究

雷电空间电磁场一直是电磁领域研究的热门，成熟的算法例如有限时域差分法（FDTD），传输线矩阵法（TLM）以及频域的矩量法（MoM）在计算雷电问题方面都有广泛的应用。由于计算流体力学（CFD）中的Euler方程与电磁学中的Maxwell方程有着相同的守恒形式，而且采用间断伽辽金方法（DG）已经在流场问题上得到广泛的尝试，因此引入了基于计算流体力学的DG方法来离散时域Maxwell方程，并采用网格分区并行技术加速计算，使用基于DG的圆球雷达散射截面积（RCS）算例进行测试，数值结果一致表明DG算法在求解电磁场问题上的可行性，之后通过计算一段近场雷电通道的电场分布并与解析解、某算法仿真解对比，数据基本吻合，说明该方法适合于雷电电磁场的计算。     

Cutting path-dependent machinability of SiCp/Al composite under multi-step ultra-precision diamond cutting

Particle-tool interactions, which govern the synergetic deformation of SiC particle reinforced Al matrix composites under mechanical machining, strongly depend on the geometry of particle position residing on cutting path. In the present work, we investigate the influence of cutting path on the machinability of a SiCp/Al composite in multi-step ultra-precision diamond cutting by combining finite element simulations with experimental observations and characterization. Be consistent with experimentally characterized microstructures, the simulated SiCp/Al composite is considered to be composed of randomly distributed polygonally-shaped SiC particles with a volume fraction of 25vol%. A multi-step cutting strategy with depths of cut ranging from 2 to 10 μm is adopted to achieve an ultimate depth of cut of 10 μm. Intrinsic material parameters and extrinsic cutting conditions utilized in finite element simulations of SiCp/Al cutting are consistent with those used in corresponding experiments. Simulation results reveal different particle-tool interactions and failure modes of SiC particles, as well as their correlations with machining force evolution, residual stress distribution and machined surface topography. A detailed comparison between numerical simulation results and experimental data of multi-step diamond cutting of SiCp/Al composite reveals a substantial impact of the number of cutting steps on particle-tool interactions and machined surface quality. These findings provide guidelines for achieving high surface finish of SiCp/Al composites by ultra-precision diamond cutting.     

PMSM电流预测控制参数误差量化分析方法

交流永磁同步电机（PMSM）电流环控制性能是制约交流伺服系统性能的关键。电流预测控制拥有更快的动态响应、更低的电流谐波和优良的转矩响应，但该算法依赖精确的电机模型，参数失配会引发稳态电流误差，无法输出额定转矩，进而导致电机转矩输出效率降低。根据永磁同步电机电流预测模型，详细分析了d、q轴电流静差产生的原因，以及电流预测控制对电机参数误差的敏感性，提出了一种参数误差量化分析方法。该方法引入了电机参数偏差因子，量化描述了电机电感、磁链参数误差与电流静差之间的制约关系。通过仿真分析，验证了所提方法的合理性，为高性能永磁伺服电流预测数字控制技术打下了良好基础。     

航天嵌入式软件数组越界缺陷特征研究

根据统计,数组越界是航天嵌入式软件开发过程中出现最多且最容易被遗漏的缺陷类型之一.目前自动化检测数组越界多基于抽象解释、符号执行、程序模型检验等方法,这些方法在误报、漏报、可扩展性等方面的表现依赖于软件及缺陷特征.分析了近三年航天嵌入式软件第三方测试中发现的94个数组越界问题,从缺陷模式和缺陷表现形式两方面分析得出10项航天嵌入式软件数组越界缺陷特征,并提出对设计具体检测方法关键的若干启示.进一步基于这些特征和启示探讨了数组越界检测算法针对中断驱动型程序的改进方向.     

基于AFI混合聚类算法的轴承故障诊断方法

针对滚动轴承振动信号标记数据量小、故障模式多样的现状，提出了一种基于AFI混合聚类算法的半监督式轴承振动信号故障诊断方法。利用小波包分解方法提取了信号的能量特征谱，并通过主成分分析方法增强了信号的特征；参考迭代自组织数据分析的“分裂”和“合并”的思想，为人工鱼群算法中的个体鱼增加了“分裂进化”和“合并进化”行为；采用模糊C均值方法定义了隶属度矩阵和目标函数，并利用改进的人工鱼群算法，迭代搜寻了目标函数的全局最优解，得到了各故障模式的聚类中心；通过计算测试数据的最近邻聚类中心，实现了故障模式识别。结果表明，该方法无需指定聚类簇数，能在标记数据量小的情况下完成训练，较同类方法表现出了更优的故障模式识别性能。     

A progressive approach to predict shot peening process parameters for forming integral panel of Al7050-T7451

In this paper, a progressive approach to predict the multiple shot peening process parameters for complex integral panel is proposed. Firstly, the invariable parameters in the forming process including shot size, mass flow, peening distance and peening angle are determined according to the empirical and machine type. Then, the optimal value of air pressure for the whole shot peening is selected by the experimental data. Finally, the feeding speed for every shot peening path is predicted by regression equation. The integral panel part with thickness from 2 mm to 5 mm and curvature radius from 3200 mm to 16000 mm is taken as a research object, and four experiments are conducted. In order to design specimens for acquiring the forming data, one experiment is conducted to compare the curvature radius of the plate and stringer-structural specimens, which were peened along the middle of the two stringers. The most striking finding of this experiment is that the outer shape error range is below 3.9%, so the plate specimens can be used in predicting feeding speed of the integral panel. The second experiment is performed and results show that when the coverage reaches the limit of 80%, the minimum feeding speed is 50 mm/s. By this feeding speed, the forming curvature radius of the specimens with different thickness from the third experiment is measured and compared with the research object, and the optimal air pressure is 0.15 MPa. Then, the plate specimens with thickness from 2 mm to 5 mm are peened in the fourth experiment, and the measured curvature radius data are used to calculate the feeding speed of different shot peening path by regressive analysis method. The algorithm is validated by forming a test part and the average deviation is 0.496 mm. It is shown that the approach can realize the forming of the integral panel precisely.     

A novel framework for liquid propellant engine’s cooling system design by sensitivity analysis based on RSM and multi-objective optimization using PSO

One of the challenges of combustion chamber and nozzle design in a Liquid Propellant Engine (LPE) is to predict the behavior and performance of the cooling system. Therefore, while designing, the optimization of the cooling system is always of great importance. This paper presents the multi-objective optimization of the LPE’s cooling system. To this end, a novel framework has been developed, resulting from the application of the Response Surface Method (RSM) and the correlation coefficients matrix, sensitivity analysis and the The Particle Swarm Optimization (PSO). based on this method, the input variables, constraints, objective functions, and their surfaces were identified. In terms of multi-optimization algorithms, RSM and PSO are utilized to get global optimum. In conclusion, the methodology capability is to optimize the LPE’s cooling system, 6 percentage increase in total heat transfer and 7 bar decrease cooling system pressure loss, which resulted in a 1.2-seconds increase in the specific impulse of the engine.     

Solar sailing in realistic mode,based on a locally-optimal control laws

Ballistic design of solar sailing missions in the solar system is composed of defining the design parameters, the control programs, and the trajectories that provide performance goals of a flight. The use of a solar sail spacecraft imposes specific restrictions on mission parameters that include the degradation limit on the flight duration, the maximum temperature of solar sail's surface, the minimum distance from the Sun, the maximum angular velocity of the spacecraft's rotation and others.Many authors considered the impact of these restrictions on the design of the mission separately, but they used a sophisticated method of finding the exact optimal motion control or applied the most straightforward laws of motion control. This paper uses local-optimal control laws at the complete mathematical models of motion and functioning of solar sail spacecraft to describe a technique of designing interplanetary missions. The described method avoids the need to obtain an accurate optimal solution to the control problem and does not cause significant computational difficulties.     

详细化学反应机理对预混丙烷钝体熄火模拟影响

航空发动机熄火预测是重要关键问题之一，湍流和化学反应的非线性相互作用使预测非常困难。本文采用大涡模拟（LES）对湍流进行高精度模拟，采用概率密度函数输运方程湍流燃烧模型（TPDF）耦合JL4、Z66和H73三种化学反应机理，对预混丙烷钝体熄火现象和规律进行研究。JL4的反应机理最简单，反应释热快，局部放热高，火焰宽度大，火焰两侧温度梯度大，燃烧更加趋于稳定，无法模拟出熄火状态。H73机理绝热火焰温度低，火焰温度低，回流区中部OH含量高；在近熄火状态，大量CO被氧化，释放热量过高导致无法模拟出熄火现象。Z66机理可以模拟出火焰正常状态，在低当量比下也可以模拟出熄火状态。本文算例中，局部Da数大于1的区域超过35%则会发生熄火。