大型氦制冷机的净化系统

氦制冷机是我国大型空间环境模拟器的重要组成部分,是完成红外相机定标试验、航天器运动部件超高真空冷焊试验的关键部件.文章介绍了氦制冷机净化系统的组成及设备性能.化系统在定标试验中的有效运转保证了氦制冷机可靠运行.     

固体火箭喷管颗粒尺寸分级两相跨音速流场计算

本文中对固体火箭喷管颗粒尺寸分级的两相跨音速流场作了计算.气相控制方程采用隐式近似因子分解法求解,尺寸分级的颗粒控制方程采用特征线求解,然后,二者进行充分的耦合,可以获得固体火箭发动机含有任意颗粒质量分数和不同颗粒尺寸时轴对称喷管跨音速流场的参数分布.文中讨论了不同颗粒半径和质量分数对流场的影响,对单一颗粒尺寸和颗粒尺寸分级的参数进行了比较.两相耦合计算的迭代收敛速度取决于气相,本文中气相方程求解的格式除部分边界外是隐式的,CFL数可取至6左右,收敛速度快.特别是对颗粒尺寸分级的计算,得益更大,其得益的倍数为颗粒的分级数.     

Plume aerodynamic effects of cushion engine in lunar landing

 During the second period of China "Tanyue" Project, the explorer will softland on the moon. The cushion engines are used to decelerate the explorer and reduce the impact on the lunar ground. It is necessary to study its plume effects on the explorer component. The self-developed PWS (Plume WorkStation) software based on direct simulation Monte Carlo (DSMC) method is used to simulate the plume effects of two 150 N engines. Due to the complex structure of the explorer, PWS uses a decoupling method to treat the boundary mesh, which mainly interacts with simulation particles, and has no relation with the computational grids. After the analytical expressions of plane surfaces and curved surfaces of each boundary block are given, the particle position within or without the boundary blocks can be easily determined. Finally the 3D plume field of two 150 N engines is simulated. The pressure, temperature and velocity distributions of plume field are clearly presented by three characteristic slices. The aerodynamic effects on the explorer bottom, the landfall legs and antenna are separately shown. The compression influence on the plume flow of four landfall legs can be observed.     

A new method to predict fatigue crack growth rate of materials based on average cyclic plasticity strain damage accumulation

By introducing a fatigue blunting factor, the cyclic elasto-plastic Hutchinson-Rice-Rosengren (HRR) field near the crack tip under the cyclic loading is modified. And, an average damage per loading-cycle in the cyclic plastic deformation region is defined due to Manson-Coffin law. Then, according to the linear damage accumulation theory-Miner law, a new model for predicting the fatigue crack growth (FCG) of the opening mode crack based on the low cycle fatigue (LCF) damage is set up. The step length of crack propagation is assumed to be the size of cyclic plastic zone. It is clear that every parameter of the new model has clearly physical meaning which does not need any human debugging. Based on the LCF test data, the FCG predictions given by the new model are consistent with the FCG test results of Cr2Ni2MoV and X12CrMoWVNbN 10-1-1. What’s more, referring to the relative researches, the good predictability of the new model is also proved on six kinds of materials.     

Design and analysis of spiral bevel gears with seventh-order function of transmission error

This paper proposes a new approach to mial function of transmission error （TE） for spiral design and implement a seventh-order polyno- bevel gears with an aim to reduce the running vibration and noise of gear drive and improve the loaded distribution of the tooth. Based on the constraint conditions of predesigned seventh-order polynomial function curve and the theory of linear algebra, the polynomial coefficients of the seventh-order polynomial function of transmission error can be obtained. By applying a method named reverse tooth contact analysis, the modified roll coefficients as well as parts of machine-tool settings for the face-milling of spiral bevel gears can be individually determined. Therefore, a predesigned seventh-order polynomial function of transmission error for spiral bevel gears can be obtained by the modified roll with high-order coef- ficients, and comparisons of the seventh-order polynomial and parabolic functions of transmission error are also performed. The achievement of spiral bevel gears with the seventh-order function of transmission error can be accomplished on a universal Cartesian-type hypoid gear generator or a numerically controlled cradle-style hypoid gear generator due to its simple generating motion of axes of the cradle and the work piece. The results of a numerical example show that the bending stresses of the tooth of seventh-order are less than those of a parabolic one, while the contact stresses remain almost eouivalent.     

数据挖掘技术在图书馆中的应用展望

近十几年来,随着数据库技术的迅速发展,尤其是分布式数据库技术的发展,数据库管理系统被广泛应用于商业管理、政府办公、教学科研和工程开发等众多领域。这一方面极大的改善了人们对信息的管理与利用,另一方面积累的数据越来越多,激增的数据背后隐藏着许多重要信息,人们渴望能对这些隐藏的信息进行更高层次的利用。现有的数据库可以实现诸如录入、查询、统计等功能,但无法发现数据之间存在的规则与关联,无法根据现有的数据预测未来的发展趋势,缺乏挖掘数据背后隐藏的知识的功能。数据挖掘技术就是为解决这样一种矛盾而出现的,它是一种新的数…     

智能便携式三表数据处理器

介绍一种智能型的便携式三表数据处理器，解决了三表检定数据处理繁琐的问题。     

智能自治体及其在敏捷制造中的应用

介绍了智能自治体及多智能自治体系统（ＭＡＳ）理论，在分析敏捷制造单元特点的基础上，提出基于ＭＡＳ的敏捷制造单元框架结构，用协商机制实现了敏捷制造单元的分布式动态调度和控制。     

直升机划代

直升机划代对于人们认识直升机技术的发展规律的制订直升机发展规划有重要意义。本文在对直升机技术发展深入研究的基础上提出了直升机划代的“六大要素”,并以此六要素为判别标准,将直升机分为四代,提出了世界直升机发展划代的建议。     

航空发动机振动传递特性研究进展

航空发动机振动传递规律是业内研究热点之一。为了控制整个机械系统振动传递,通过找到振动能量的传递主要路 径,进行了结构优化和参数设计。介绍了航空发动机振源机理及研究进展,分别对航空发动机规律性激振源与非规律性激振源进 行了系统地论述,总结了国内外关于转子系统故障的研究情况;详细分析了传递路径分析方法及其衍生方法相关技术的优点以及 近年来传递路径分析法（TPA）、工况传递路径分析法（OTPA）、扩展工况传递路径分析法(OPAX)等传递路径分析方法在汽车、地 铁、船舶、航空领域中的应用,指出了不同传递路径分析方法存在的问题;对航空发动机整机振动传递特性研究的发展趋势进行了 展望。由于振动传递路径分析方法在航空发动机领域并未系统开展,分类综述了航空发动机整机振动传递特性研究成果,搜集整 理了应用于转子-轴承-机匣-吊挂系统振动传递分析方法,可为航空发动机整机振动传递特性研究提供参考。