H2O污染对超燃冲压发动机燃烧室性能影响的三维数值模拟

为了解来流污染对超燃冲压发动机性能的影响,需要大量的实验和CFD模拟。基于纯净空气和污染空气(H2O)来流下燃烧对比实验,采用较为详细的化学反应动力学模型(13组分33方程),对三个试验条件的燃烧室反应流场进行了三维大规模并行CFD模拟。模拟结果与对比试验测得的壁面压强比较接近,能"分辨"试验气体中H2O的污染影响。模拟结果显示,从燃烧室整体性能看,7.4%H2O和18.3%H2O污染导致燃烧室单位流量的空气对应推力分别下降4.1%和10.7%,而燃烧室燃烧效率分别下降5.5%和9.5%。     

星载天线指向精度建模与分析

随着天线定位机构运动日趋复杂以及对定位机构任务要求的不断提高,提高指向精度已成为星载天线机构能力提升的核心。综合考虑卫星姿态控制误差、展开机构误差、双轴驱动机构误差和反射面误差等因素,利用齐次变换矩阵得到天线指向运动学误差等式,从而得到天线指向精度分析的一般方法。以某星载点波束定位机构为例,对各误差源的影响进行了分析,...     

An efficient large-scale mesh deformation method based on MPI/OpenMP hybrid parallel radial basis function interpolation

An efficient MPI/OpenMP hybrid parallel Radial Basis Function (RBF) strategy for both continuous and discontinuous large-scale mesh deformation is proposed to reduce the computational cost and memory consumption. Unlike the conventional parallel methods in which all processors use the same surface displacement and implement the same operation, the present method employs different surface points sets and influence radius for each volume point movement, accompanied with efficient geometry searching strategy. The deformed surface points, also called Control Points (CPs), are stored in each processor. The displacement of spatial points is interpolated by using only 20–50 nearest control points, and the local influence radius is set to 5–20 times the maximum displacement of control points. To shorten the searching time for the nearest control point clouds, an Alternating Digital Tree (ADT) algorithm for 3D complex geometry is designed based on an iterative bisection technique. Besides, an MPI/OpenMP hybrid parallel approach is developed to reduce the memory cost in each High-Performance Computing (HPC) node for large-scale applications. Three 3D cases, including the ONERA-M6 wing and a commercial transport airplane standard model with up to 2.5 billion hybrid elements, are used to test the present mesh deformation method. The robustness and high parallel efficiency are demonstrated by a wing deflection case with a maximum bending angle of 45° and more than 80% parallel efficiency with 1024 MPI processors. In addition, the availability for both continuous and discontinuous surface deformation is verified by interpolating the projecting displacement with opposite directions surface points to the spatial points.     

美国共同基金费率变化趋势研究

基于ICI各年有关基金费率的研究，从美国共同基金的费率水平和组成结构、费率水平下降的动因，以及费率设计创新趋势三方面总结了美国共同基金费率体系自1980年以来的变化。在市场竞争机制约束下，美国共同基金的整体费率水平下降，免费基金大量崛起，其中传统的前端费用逐渐被后端费用替代，12b-1服务营销费用比重上升。同时，美国共同基金的收费方式和费用补偿机制的创新也正在向组合灵活、适应投资者多样化需求的目标发展。     

基于并联机构的轻型自主爬行钻铆系统法向调姿算法

法向调姿是飞机部件自动化钻铆的技术基础,是提高制孔质量的技术保证。根据飞机装配自主爬行钻铆系统的功能需求分析,设计了一套基于并联机构法向调姿的轻型自主爬行钻铆系统,采用改进的Grubler-Kutzbach算法对其进行自由度分析,论证该系统符合法向调姿时所需的5自由度运动。搭建了法向检测及法向调姿数学模型,提出了在保证虚拟刀尖点位置不变的情况下末端执行器由初始状态调姿到期望的姿态时并联机构所需调整量的位置逆解算法和算例,并运用Matlab对算法进行算例验证。结果表明:法向调姿位置逆解算法正确,计算过程简单。     

倾转旋翼机转动机构运动学仿真分析

转动机构在倾转旋翼机过渡飞行阶段起着重要作用。为了研究倾转旋翼机转动机构在发动机短舱与旋翼向前倾转90°过程中的运动特征,寻找较为适用的转动模式,以倾转旋翼机转动机构为研究对象,简化机构模型,采用MATLAB软件计算两种转动方案机构的运动学特征,采用LMS软件仿真两种方案机构的转动过程。通过对比分析两种方案的运动学特征图,发现MATLAB和LMS软件得出的两种方案的角速度、速度、角加速度和加速度曲线是一致的,两种方案各有其优势。     

Strategic flight assignment approach based on multi-objective parallel evolution algorithm with dynamic migration interval

The continuous growth of air traffic has led to acute airspace congestion and severe delays, which threatens operation safety and cause enormous economic loss. Flight assignment is an economical and effective strategic plan to reduce the flight delay and airspace congestion by reasonably regulating the air traffic flow of China. However, it is a large-scale combinatorial optimization problem which is difficult to solve. In order to improve the quality of solutions, an effective multi-objective parallel evolution algorithm(MPEA) framework with dynamic migration interval strategy is presented in this work. Firstly, multiple evolution populations are constructed to solve the problem simultaneously to enhance the optimization capability. Then a new strategy is proposed to dynamically change the migration interval among different evolution populations to improve the efficiency of the cooperation of populations. Finally, the cooperative co-evolution(CC) algorithm combined with non-dominated sorting genetic algorithm II(NSGA-II) is introduced for each population. Empirical studies using the real air traffic data of the Chinese air route network and daily flight plans show that our method outperforms the existing approaches, multiobjective genetic algorithm(MOGA), multi-objective evolutionary algorithm based on decomposition(MOEA/D), CC-based multi-objective algorithm(CCMA) as well as other two MPEAs with different migration interval strategies.     

An inertial parameter identification method of eliminating system damping effect for a six-degree-of-freedom parallel manipulator

A new simple and effective inertial parameter identification method based on sinusoidal vibrations of a six-degree-of-freedom parallel manipulator is proposed. Compared with previously known identification algorithms, the advantages of the new approach are there is no need to design the excitation trajectory to consider the condition number of the observation matrix and the inertial matrix can be accurately defined regardless of the effect of viscous friction. In addition, the use of a sinusoidal exciting trajectory allows calculation of the velocities and accelerations from the measured position response. Simulations show that the new approach has acceptable tolerance of dry friction when using a simple coupling parameter modified formula. The experimental application to the hydraulically driven Stewart platform demonstrates the capability and efficiency of the proposed identification method.     

An Investigation of Near-Equatorial Geomagnetic Pi2 Pulsations

There is understanding to date that Pi2 pulsations have two sources. One source is a high-latitude one and is due to fluctuations of electrojet parameters. The other source is a mid-latitude one and is driven by a global mode excited in the Earths plasmasphere. There is experimental evidence that in the near-equatorial regions the character of Pi2 excitation is different from high and mid-latitudes. In this connection, we investigated the amplitude-spectral-polarization characteristics of Pi2 pulsations using the date from near-equatorial Chinese stations. The detected regularities in the excitation of near-equatorial Pi2 pulsations are used in the discussion of the possible physical mechanism that is responsible for the generation of these pulsations.