新型敏感器有限元动力学分析

介绍了一种超大口径、长焦距、折反式光学系统的新型敏感器。为验证其结构设计的可靠性和稳定性,使用大型通用有限元软件MSC Patran建立了整机有限元分析模型,用MSC Nastran对其进行了模态分析和随机振动分析。分析结果表明,星敏感器性能稳定可靠,可对一些关键部件的设计提供理论依据。     

空间相机反射镜组件的随机振动疲劳分析

针对空间相机反射镜组件在随机振动试验中出现的疲劳破坏问题,为了保证结构的安全,应用有限元方法预测结构随机振动疲劳寿命。首先建立了反射镜组件有限元模型,然后进行了模态和频率响应分析,最后利用MSC.Fatigue软件结合材料S-N曲线和载荷谱进行了随机振动疲劳分析。通过分析得到反射镜组件的疲劳寿命最小为80235s,其位置在柔性支撑结构的十字筋处。结果表明,反射镜组件的疲劳寿命远大于试验的所需时间,满足设计要求,可以对材料的选取和结构的优化设计做出快速响应,为结构随机振动疲劳寿命的研究提供参考和依据。     

微小非球面玻璃透镜超精密模压成型数值模拟

利用非线性有限元软件MSC.Marc,建立了微小非球面玻璃透镜超精密模压的有限元模型,并进行了微小非球面玻璃透镜模压数值模拟分析.通过对比模拟出的不同加工参量下的成型透镜和模具的残余应力分布结果,得出最优的超精密模压成型的模压速率和模压温度范围,并解释了模压速率和模压温度影响微小非球面玻璃透镜成型质量的原因.模拟可以对实际的大批量生产微小非球面玻璃透镜提供有力的帮助.     

微小非球面玻璃透镜超精密模压成型数值模拟

利用非线性有限元软件MSC.Marc,建立了微小非球面玻璃透镜超精密模压的有限元模型,并进行了微小非球面玻璃透镜模压数值模拟分析.通过对比模拟出的不同加工参量下的成型透镜和模具的残余应力分布结果,得出最优的超精密模压成型的模压速率和模压温度范围,并解释了模压速率和模压温度影响微小非球面玻璃透镜成型质量的原因.模拟可以对实际的大批量生产微小非球面玻璃透镜提供有力的帮助.     

基于SiC材料的大长宽比长条型反射镜轻量化结构设计

介绍了一种大长宽比长条型反射镜的轻量化结构设计方法.讨论了反射镜的材料选择和轻量化结构形式,同时在轻量化设计过程中引入拓扑优化方法,以反射镜柔性变形为设计约束,以最小体积为设计目标,经过迭代计算得到最优结果.根据优化结果,建立反射镜的三维实体模型,并利用MSC.Patran软件建立反射镜的有限元模型,对影响反射镜自重变...     

热致梯度折射率对非球面光学系统成像质量的影响

机载相机在上升过程中,由于温度降低和镜头各部分材料的导热率大小不同,镜头部分会产生温度梯度,从而导致非球面光学系统产生梯度折射率.利用有限元分析软件对镜头部分进行瞬态热分析以模拟机载相机上升过程中温度的变化情况,将有限元分析不同时间节点温度分布结果导入编写的折射率梯度系数拟合程序,将所求解的梯度折射率系数通过镜面类型接口在光学软件中建立光学系统模型,利用点列图的弥散斑半径评价不同时间节点梯度折射率对成像质量的影响.结果表明,机载相机刚升入工作高度时温度梯度最大,对成像质量影响也最严重,梯度折射率系数随着温度梯度系数的降低而降低,同时成像质量提高,该结果对光学系统的设计具有指导意义.     

长焦距空间光学遥感器支撑结构有限元分析

为了提高长焦距空间光学遥感器主支撑结构的刚度,实现结构的轻量化,分析了几种常用的空间支撑结构材料,并结合三反离轴光学系统的特点,用有限元分析软件MSC．PATRAN建立了几种不同支撑结构的有限元模型。对其进行了模态分析,并对支撑结构在温度场和重力场影响下的变化进行了研究,从而对实际工程中光学遥感器结构的材料及构型选择提供了参考,对大型离轴三反空间光学遥感器主支撑结构的设计具有一定指导意义。     

基于Tahoe框架的某夹具并行计算

在开源软件Tahoe框架基础上,结合有限元前后处理程序MSC.Patran及Tecplot,对某复杂夹具进行建模.通过区域分解、编制接口和采用PHG中提供的PCG(preconditioned conjugate gradient,预处理共轭梯度法)迭代解法成功实现262×10⁴自由度模型的串、并行计算.结果表明,并行计算收敛速度更快,4进程并行计算时间不到串行计算时间的1/4.通过与商用程序MSC.Nastran比较,验证计算结果的正确性.利用大型并行计算机对该模型并行计算性能进行研究,获得最高32进程的并行计算加速比.研究表明,改进后的Tahoe计算框架对于开展大规模自由度下的结构并行计算分析研究是可行的,并且随计算节点增加,并行计算过程基本呈线性加速.     

小挠度碳纤维复合材料镜筒设计

碳纤维复合材料目前广泛应用于航天结构高强度要求的场合，对复合材料满足小变形使用要求的刚度设计仍然是航天相机结构设计的难题。通过对共轴三反光学系统公差的分析，给出变形量小于2μm的复合材料的刚度设计要求。根据结构的受力状况建立了物理模型。结合复合材料层压板理论，对碳纤维铺层设计进行了合理的简化，并通过有限元分析软件MSC.Nastran对设计进行了完善和验证。结果表明：设计的碳纤维复合材料镜筒满足了结构端面变形量小于2μm的刚度使用要求。     

航空光谱相机反射镜部件的有限元分析

反射镜是光谱相机的关键元件,为保证在复杂环境下的成像质量,有必要对其进行研究分析以验证结构设计的可靠性。针对反射镜在工作中的面形变化及结构的动力学性能,应用有限元分析软件MSC.Nastran对反射镜部件进行了静力分析及随机振动分析。计算结果表明,装配时压紧力对反射镜面形变化影响明显,可根据计算结果指导装调;随机振动分析结果表明,反射镜部件结构设计可靠,符合结构破坏的3σ原则,能够满足成像对反射镜位置精度和面形精度的要求。     

Modeling multi-jet mode electrostatic atomization using boundary element methods

A two-dimensional, nonlinear model has been developed to assess the dynamics of charged liquid columns. The model, which is based on the boundary element method (BEM), has been used to investigate oscillations and instabilities of single and multi-column configurations. For the single-column configuration, oscillation frequencies have been determined for a range of charge and initial distortion levels. In addition, simulations of unstable jets have been conducted; these results show a “spiked” behavior at the pinching event. An energy-based analysis has been used to determine maximum voltages for stable configurations with a given number of ligaments. These results are compared against experimental data.     

并联管内两相流密度波脉动线性均相模型

两相流不稳定性理论分析方法可以分为两大类:一类是数值解析法,另一类是近似分析法。数值分析法已经有很多学者进行了大量研究,而近似分析法研究相对少一些。本文提出了描述并联沸腾管内两相流密度波型脉动的线性均相模型。根据线性均相模型运用系统控制原理的方法导出了描述系统稳定性的无因次参数ε。运用参数ε判断系统的稳定性,计算值和实验值基本吻合。     

Fractals in DNA sequence analysis

Fractal methods have been successfully used to study many problems in physics,mathematics,engineering,finance,and even in biology,There has been an increasing interest in unravelling the mysteries of DNA;for example,how can we distinguish coding and noncoding sequences,and the problems of classification and evolution relationship of organisms are key problems in bioinformatics,Although much research has been carried out by taking into consideration the long-range correlations in DNA sequences,and the global fractal dimension has been used in these works by other people,the models and methods are somewhat rough and the results are not satisfactory.In recent years,our group has introduced a time series model(statistical point of view)and a visual representation (geometrical point of view) to DNA sequence analysis.We have also used fractal dimension,correlation dimension,the Hurst exponent and the dimension spectrum (multifractal analysis)to discuss problems in this field.In this paper,we introduce these fractal models and methods and the results of DNA sequence analysis.     

On mean square displacement behaviors of anomalous diffusions with variable and random orders

Mean square displacement (MSD) is used to characterize anomalous diffusion. Recently, models of anomalous diffusion with variable-order and random-order were proposed, but no MSD analysis has been given so far. The purpose of this Letter is to offer a concise derivation of MSD functions for the variable-order model and the random-order model. Numerical results are presented to illustrate the analytical results. In addition, we show how to establish a variable-random-order model for a given MSD function which has clear application potentials.     

Simulation of a High Harmonic Gyrotron with Axis-Encircling Electron Beam and Permanent Magnet

A computer code for simulation of beam-field interaction in a resonant cavity of a gyrotron has been developed. It is based on a self-consistent, time-independent, single-mode physical model. The code has been applied to the analysis of the electrodynamical system of a novel high-harmonic gyrotron with axis-encircling beam and a permanent magnet. In this paper both the physical model and numerical techniques used are outlined. Some results of the numerical experiments are presented and discussed.     

The structure of pure tertiary butanol

The technique of second-order difference neutron scattering with hydrogen/deuterium isotopic substitution has been used to measure the intermolecular structural correlations in pure liquid tertiary butanol. The newly developed technique of empirical potential structure refinement has been used to perform a detailed structural analysis of the resulting partial distribution functions, providing a means by which a full set of interatomic partial distribution functions consistent with the experimental data can be extracted. A comparison with our experimental results is made for a Monte Carlo model produced using fixed potentials as in earlier simulations of this alcohol system, and for the model which results from our procedure. The results suggest that the extent of intermolecular hydrogen bonding, although significant, is less dominant than generally accepted.     

采用BP神经网络研究C-F键核自旋偶合常数

通常理论研究核自旋偶合常数的方法是基于线性模型进行拟合和预测，该方法在拟合和预测中仍有较大误差. 本文在前面工作的基础上，提出了基于非线性模型对C-F键核自旋偶合常数进行研究的观点，采用BP神经网络方法对C-F键核自旋偶合常数的函数关系式进行拟合，并用拟合结果对4种化合物的偶合常数进行预测. 结果表明，采用非线性的BP神经网络方法其训练效果与预测效果均优于线性模型方法；其预测误差对文中的4种化合物不超过0.40%.     

Measurement and study of the embedding impedance presented by the whisker antenna of a schottky diode corner cube mixer

A 250× scale model of a Schottky diode corner cube mixer designed for operation in the terahertz region has been built and tested. It has been successfully used to measure the embedding impedance presented to the diode at the whisker tip and also determine the impedance of the whisker antenna itself. The results have been input into a computer analysis to determine as to how the performance may be improved. With regards to improving the physical ruggedness of such mixers, a simple equivalent whisker structure has been determined and a new technique that may be used to fabricate a space qualifiable corner cube mixer intended for terahertz operation is disclosed.     

支持向量回归在葡萄酒红外定量分析中的应用

近年来,基于朗伯-比尔定律和化学计量学的红外光谱定量分析方法发展十分迅速。其中,选择合适的预处理方法和有效的校正模型是定量分析成功的关键。选取30个葡萄酒样品,运用红外光谱结合向量回归算法SVR,对葡萄酒乳酸、酒石酸、乙酸异戊酯、3-甲基-1-丁醇进行了红外含量预测。选用标准归一化、基线校正以及异常样本点剔除三种谱图预处理方法,结合支持向量回归算法。实验结果表明该方法行之有效,计算值与标准值间的相对误差可被控制在5%以内。该方法可应用于葡萄酒中代表性物质含量的定量分析检测。