充有弹性介质多层复合材料圆筒壳稳定性

本文分析了充有弹性介质的多层复合材料圆筒壳在轴压、侧压与水压作用下的稳定性。所采用的方法是用Galerkin—差分法求介改型的Donnell方程,再根据稳定准则确定临界值。若干算例已在文中列出。计算结果表明:内部介质材料性能和壳体的边界条件对临界载荷有较大影响。本文采用的分析方法和结论可供固体火箭发动机壳体设计工作者参考。     

微波带通滤波器的时域分析法研究

文章介绍了一种利用微波带通滤波器的时域反射损耗(即S11)曲线分析和调试滤波器的方法,运用此法在调试滤波器时可以快速地分析出具体是哪一个谐振电路或耦合器需要调试,以便对其进行专门的修正和调试,从而节省调试时间,简化调试过程。同时也介绍了3种方法作为把频域数据转换为时域数据的理论基础,即傅里叶级数法、快速傅里叶变换法和Chirp-z变换法,并对这3种方法作了相应的评价。     

Ultrastructural and geochemical characterization of Archean-Paleoproterozoic graphite particles: implications for recognizing traces of life in highly metamorphosed rocks

Abundant graphite particles occur in amphibolite-grade quartzite of the Archean-Paleoproterozoic Wutai Metamorphic Complex in the Wutaishan area of North China. Petrographic thin section observations suggest that the graphite particles occur within and between quartzite clasts and are heterogeneous in origin. Using HF maceration techniques, the Wutai graphite particles were extracted for further investigation. Laser Raman spectroscopic analysis of a population of extracted graphite discs indicated that they experienced a maximum metamorphic temperature of 513 +/- 50 degrees C, which is consistent with the metamorphic grade of the host rock and supports their indigenicity. Scanning and transmission electron microscopy revealed that the particles bear morphological features (such as hexagonal sheets of graphite crystals) related to metamorphism and crystal growth, but a small fraction of them (graphite discs) are characterized by a circular morphology, distinct marginal concentric folds, surficial wrinkles, and complex nanostructures. Ion microprobe analysis of individual graphite discs showed that their carbon isotope compositions range from -7.4 per thousand to -35.9 per thousand V-PDB (Vienna Pee Dee Belemnite), with an average of -20.3 per thousand, which is comparable to bulk analysis of extracted carbonaceous material. The range of their size, ultrastructures, and isotopic signatures suggests that the morphology and geochemistry of the Wutai graphite discs were overprinted by metamorphism and their ultimate carbon source probably had diverse origins that included abiotic processes. We considered both biotic and abiotic origins of the carbon source and graphite disc morphologies and cannot falsify the possibility that some circular graphite discs characterized by marginal folds and surficial wrinkles represent deflated, compressed, and subsequently graphitized organic-walled vesicles. Together with reports by other authors of acanthomorphic acritarchs from greenschist-amphibolite-grade metamorphic rocks, this study suggests that it is worthwhile to examine carbonaceous materials preserved in highly metamorphosed rocks for possible evidence of ancient life.     

整体离心叶轮的形状优化设计

本文对离心叶轮的形状优化设计过程进行了研究。提出了整体叶轮结构分析的一种有效的方法, 探讨了其优化数学模型的建立方法, 包括设计变量的选择、目标函数的确定及约束条件的选取。并对某压气机离心叶轮进行了优化, 有效地减轻了叶轮的重量。      

一种六杆并联机器人的控制问题和控制器研究

针对一种六杆并联结构工业机器人,研究了其运动学逆解和正解算法,以及它们在开放式数控系统中的具体实现技术,解决了基于逆解算法的实时坐标变换问题和基于正解算法的系统初始化问题,并给出了相应模块与数控系统内核的接口,最后在一种开放式数控系统平台上实际开发成功针对这种并联结构机器人的控制系统,从而得出结论,采用正确的实现技术,并联结构机器人的实时控制问题可以在开放式数控系统中很好地得到解决.      

起落架缓冲器静压曲线符合性偏差问题分析

依据起落架缓冲器静压缩曲线图对确保飞机起落架质量的重要性,对绘制起落架静压缩曲线图时出现的符合性偏差问题进行了分析,并提出了相应工艺措施。     

Experiment on a Double-Foot Stepping Piezoelectric Linear Motor

A novel double-foot piezoelectric linear motor is proposed.The kinematic model of the motor under stepping motion is presented.The motor mainly consists of a stator with four piezoelectric stacks,a mover,a holding mechanism,and a preloading mechanism to achieve large stroke with high resolution.Finite element simulations are carried out to analyze the motion characteristics of the motor.A prototype is fabricated and a serial experiments are conducted to validate the feasibility of the motor principle.Experimental results indicate that the motor can move at a speed of 670.22μm/s with a driving frequency of 120 Hz and a voltage of 120 V.The resolution of the proposed motor is 3.6μm while the resolution of the single-step motion is 0.1μm.     

基于分岔理论的起落架撑杆式锁机构设计

提出了运用分岔理论研究锁机构性能问题的分析方法，以前起落架上下位一体式锁机构为对象，基于分岔理论，通过数值延拓，研究了收放作动筒和解锁作动筒对该机构稳定性能的影响，阐释了锁机构运动分岔图中分岔点与上锁、解锁行为的对应关系，并分别针对上、下位解锁过程按照不同解锁力共划分了5种锁机构解锁状态。论述了延拓解锁、上锁分岔点得到的轨迹曲线，并根据曲线临界尖点定义了临界解锁力和临界解锁角度2个状态变量，随后分析了弹簧刚度、原长和安装点位置对以上变量的影响趋势。基于影响分析结果，在锁机构上锁能力一定的前提下，改变参数，优化了下位临界解锁力。研究表明，分岔分析能够快速全面地把握锁机构动力学特性随不同参数的变化趋势，在分析锁机构性能、指导参数初步设计方面有一定优势。     

基于支持向量回归代理模型的气动力优化设计

目前,气动力优化设计中通常基于经验风险最小化原则构建代理模型,预测精度的提高需要更多的训练样本,计算代价较大,同时盲目降低代理模型的训练误差难以避免过学习问题。针对上述问题,首先提出采用支持向量回归(SVR)方法基于结构风险最小化原则构建代理模型的思路,然后对测试函数和翼型阻力进行预测,最后对某型运输机机翼进行优化设计试验。结果表明:与其他代理模型对比,基于SVR的代理模型在小样本情况下具有较好的泛化能力,并且能够快速准确地预测气动特性,在飞机优化设计中,可以提高工作效率,优化结果可靠、可控。     

精密同轴回转式测量机构模态分析及优化

在完成对某同轴回转式测量系统中回转装置的初期设计基础上,对其中回转装置进行模态分析,结果显示回转装置第一阶模态频率偏低,为避免其与检测现场激振频率发生共振,并提高检测精度,提出采用 Workbench 中灵敏度分析的方法,对回转装置结构进行优化,得到了回转装置的最佳设计方案。研究结果对提高系统精度,防止共振的发生等方面具有重要意义,为进一步的设计改进工作提供很好的理论支持。