Investigation on the Thermal Conductivity of 3-Dimensional and 4-Directional Braided Composites

It is vital to choose a factual and reasonable micro-structural model of braided composites for improving the calculating precision of thermal property of 3-D braided composites by finite element method (FEM). On the basis of new microstructure model of braided composites proposed recently, the model of FEM calculation for thermal conductivity of 3-dimennsional and 4-directional braided composites is set up in this paper. The curves of coefficient of effective thermal conductivity versus fiber volume ratio and interior braiding angle are obtained. Furthermore, comparing the results of FEM with the available experimental data,the reasonability and veracity of calculation are confirmed at the same time.     

基于遗传算法的H∞混合灵敏度导弹解耦控制器设计及加权函数选择方法研究

导弹在大攻角再入飞行过程中,偏航通道和滚动通道存在着气动交连耦合,当耦合影响较大时,采用传统的把耦合项当作随机干扰的办法来处理,容易造成系统失稳。因此采用基于H∞混合灵敏度解耦控制的方法对通道间进行解耦,对于H∞混合灵敏度加权函数,通过遗传算法优化获得,并推导了H∞混合灵敏度标准型的建立过程和遗传算法优化加权函数的步骤。应用该方法,对导弹大攻角飞行过程中通道间的解耦控制进行设计。仿真表明,对参数不确定性的耦合系统,该方法具有良好的解耦性和鲁棒稳定性。     

基于数据库技术的故障诊断知识库管理系统设计

为解决传统大型复杂系统故障诊断专家系统中存在的知识库庞大、难于维护管理的问题,结合数据库技术设计了一套基于Windows平台的知识表示和知识库管理系统。该系统充分利用了数据库技术,实现了对知识库中知识的存储、添加、删除、修改和查询以及编辑过程中的一致性、完备性和冗余性要求,通过将该系统应用到运载火箭测试发射中的故障诊断专家系统中,一定程度上实现了知识处理的自动化,为运载火箭故障诊断专家系统的开发和运用奠定了重要基础。     

单通道DRFM的数字多普勒产生技术

根据脉冲多普勒雷达信号处理的相参性要求,提出以相位控制为基础的多普勒干扰信号产生方法.针对单通道采样结构的数字射频存储器,给出利用希尔伯特变换产生多普勒信号的数字算法.在Matlab中对多普勒干扰效果进行了仿真,对其FPGA实现方式进行了优化设计,结果表明了该算法的有效性和可实现性,最后对利用数字射频存储器实施多种多普勒干扰进行了研究.     

锻造LF6法兰阳极化后表面深灰色原因分析

锻造LF6材料法兰硫酸阳极化后表面产生深灰色物质,影响产品质量和性能。分析认为这种现象与材料、机械加工和表面腐蚀有关,为此设计了一系列工艺验证试验,探寻深灰色物质产生的原因。试验结果表明,锻造LF6材料自身所含有的金属元素、机械加工和生产周期过长是阳极化封闭后零件表面产生深灰色的主要原因。     

桂南平话山摄、臻摄入声韵的演变

以选点和计量统计方式,对桂南平话山摄和臻摄入声韵的今读情况进行描述,分析探讨其演变类型、规律,试图揭示桂南平话固有层次语音的演变。     

抑制恒压变量柱塞泵压力低频振荡方法的研究

为解决恒压变量柱塞泵出口压力出现低频振动的问题,阐述了恒压变量机构的原理,从理论上分析了影响出口压力的因素,并指出产生振荡的原因,提出在泵装配过程中,采用工艺关键要点控制的方法可抑制压力低频振荡。试验表明,该方法有效地减小了泵出口压力的低频振荡,使产品装调合格率大大提高。     

Using the radial basis function neural network to predict ionospheric critical frequency of F2 layer over Wuhan

Neural networks (NNs) have been applied to ionospheric predictions recently. This paper uses radial basis function neural network (RBF-NN) to forecast hourly values of the ionospheric F₂ layer critical frequency(f_oF₂), over Wuhan (30.5N, 114.3E), China. The false nearest neighbor method is used to determine the embedding dimension, and the principal component analysis (PCA) is used to reduce noise and dimension. The whole study is based on a sample of about 26,000 observations of f_oF₂ with 1-h time resolution, derived during the period from January 1981 to December 1983. The performance of RBF-NN is estimated by calculating the normalized root-mean-squared (NRMSE) error, and its results show that short-term predictions of f_oF₂ are improved.     

A high-performance ground-based prototype of horn-type sequential vegetable production facility for life support system in space

Vegetable cultivation plays a crucial role in dietary supplements and psychosocial benefits of the crew during manned space flight. Here we developed a ground-based prototype of horn-type sequential vegetable production facility, named Horn-type Producer (HTP), which was capable of simulating the microgravity effect and the continuous cultivation of leaf–vegetables on root modules. The growth chamber of the facility had a volume of 0.12 m³, characterized by a three-stage space expansion with plant growth. The planting surface of 0.154 m² was comprised of six ring-shaped root modules with a fibrous ion-exchange resin substrate. Root modules were fastened to a central porous tube supplying water, and moved forward with plant growth. The total illuminated crop area of 0.567 m² was provided by a combination of red and white light emitting diodes on the internal surfaces. In tests with a 24-h photoperiod, the productivity of the HTP at 0.3 kW for lettuce achieved 254.3 g eatable biomass per week. Long-term operation of the HTP did not alter vegetable nutrition composition to any great extent. Furthermore, the efficiency of the HTP, based on the Q-criterion, was 7 × 10⁻⁴ g² m⁻³ J⁻¹. These results show that the HTP exhibited high productivity, stable quality, and good efficiency in the process of planting lettuce, indicative of an interesting design for space vegetable production.     

机翼结构布局优化的并行子空间方法

机翼内部构件的布局优劣在很大程度上影响着机翼结构质量,因此进行布局优化设计尤为重要。采用并行子空间方法求解机翼结构布局优化的问题,将机翼结构布局设计问题分为梁站位优化、桁条优化和厚度优化三个并行的子空间,设计变量在各自的子空间内单独优化;各子空间优化结束后,在系统级中协调三个子空间的设计变量,保持最小质量的子空间的优化变量不变;采用近似一维搜索的方法协调其他子空间的设计变量,然后进行变量迭代直至收敛。结果表明:该方法具有较高的优化效率,能够取得较好的优化结果,具有实际工程应用价值。