基于灵敏度分析方法的光学镜架动力学模型修正

论述了理论建模与实验建模的特点,介绍了模型修正方法的相关理论,采用灵敏度分析方法,分析了光学镜架的设计参数: 材料的弹性模量、密度、内径、镜框厚度、镜架底部厚度、筋板厚度的灵敏度系数,通过镜架有限元仿真与模态实验结果的对比,建立一个以固有频率为修正目标的多变量动力学修正问题,对包含非线性连接关系的镜架动力学模型进行了修正,修正结果表明前四阶固有频率的平均误差为2.5%,满足工程要求,同时模态阶次也得到了修正。     

基于实验模态的某结构动力学模型修正

目前，动力学建模主要有3种方法：理论建模、实验建模、理论与实验综合建模。理论建模的主要方法是有限单元法，它所建立的有限元模型往往不能完全真实反映结构实际情况，计算结果与实验结果可能不一致。实验建模主要是基于实验模态分析方法。它可以识别结构动力学模型，能够用来修正有限元模型，使其模态参数与实验结果一致或基本一致。第3种方法也被广泛采用，通过大型有限元分析软件建立结构的有限元模型，计算理论模态参数，再结合实验识别出的模态参数对有限元模型进行动力学修正。     

考虑结合部特征的?150 mm口径反射镜模型修正

针对?150 mm口径反射镜受结合部的非线性因素影响导致结构分析模型精度较差的问题,提出了线性的动力学等效建模与参数修正方法。首先,在实际装配和约束环境下测试并获得了反射镜结构的试验模态参数。然后,根据界面结合部的动力学特征,对反射镜结构按照镜框固定连接模型、镜面螺钉夹持模型以及间隙等效模型进行了等效建模。最后,以试验模态参数为修正目标,采用优化方法对反射镜结构的动力学等效模型进行了参数修正,并采用模型分层和分步修正的思路,依据结合部特征将修正模型细分为两部分,提高模型参数的修正效率。结果表明,参数修正后的固有频率平均误差为1.5%,模态置信度均大于0.8,提升了反射镜结构的动力学模型精度,验证了线性化等效建模方法的正确性。     

星载光电跟瞄转台动态特性分析EI北大核心CSCD

针对目前利用有限元方法分析星载光电跟瞄转台动态特性时存在的建模失真问题,提出使用广义弹簧单元对轴承和锁紧机构等效建模,并通过定义模态阻尼比,精确模拟转台的固有频率及响应特性。通过理论计算和基于模态试验数据的参数辨识,确定各等效单元刚度;通过基于扫频试验数据的参数辨识,确定结构模态阻尼。基于建立的等效有限元模型进行仿真分析,模态分析中前6阶固有频率与试验结果的最大偏差为5.1%,谐响应分析中X、Y、Z三个主方向的最大响应与试验结果的最大偏差为3.2%,固有频率与响应一致性良好,均在允许的误差范围内。说明使用广义弹簧单元对轴承和锁紧机构进行等效建模,通过模态和扫频试验数据确定转台刚度和阻尼特性是可行的,对同类型转台的建模仿真有一定借鉴作用。     

基于动力学性能的超高速摄影仪转镜的设计

为探索超高速摄影仪转镜的设计,提出了系统性的转镜动力学性能设计理论和方法。结合静力学和动力学理论,利用有限元分析软件对初始设计的转镜进行静强度、模态、谐响应、固有频率灵敏度进行数值分析,并对数值分析结果进行试验验证,根据分析结果反复修改相应的转镜的结构尺寸并设计新的转镜,对新设计的转镜进行交变力疲劳分析和试验。结果发现,初始设计转镜的最大应力小于转镜材料的屈服强度,转镜不会出现静强度失效;转镜一阶临界转速落在工作转速以内,其动力学特性不满足要求;镜体外接圆半径与转镜的固有频率负相关且相关程度最高;新转镜的一阶固有频率从459.4 Hz增大到713.6 Hz,变化率55.3%,转镜的一阶临界转速达到42 816 r/min,成功地避开了共振点,且疲劳强度满足设计要求。     

反射镜架系统运动学支撑连接的有限元建模

 根据反射镜架系统中运动学支撑连接的物理接触形式,采用相应的位移协调方式来模拟其连接,建立了一个镜架结构的有限元模型,并分析了该镜架系统的模态及结构在地脉动载荷下的微振动分析。得到前三阶模态固有频率的最大误差小于5%,各测点的位移响应均方根的计算值与试验值吻合较好,多数点位移均方根误差控制在30%以内,且各支撑连接部位的传递特性的计算结果与试验结果比较一致,验证了所采用的运动学支撑连接的建模方法的可行性。     

反射镜架系统运动学支撑连接的有限元建模

根据反射镜架系统中运动学支撑连接的物理接触形式,采用相应的位移协调方式来模拟其连接,建立了一个镜架结构的有限元模型,并分析了该镜架系统的模态及结构在地脉动载荷下的微振动分析。得到前三阶模态固有频率的最大误差小于5%,各测点的位移响应均方根的计算值与试验值吻合较好,多数点位移均方根误差控制在30%以内,且各支撑连接部位的传递特性的计算结果与试验结果比较一致,验证了所采用的运动学支撑连接的建模方法的可行性。     

超高速摄影仪转镜动力学性能的研究

对超高速摄影仪转镜动力学特性提出了系统的数值分析方法,包括对转镜分别进行模态、谐响应、灵敏度数值分析和试验研究.首先利用数值方法提取出转镜前5阶固有频率、振型及转镜幅频特性曲线,发现转镜的1阶和2阶共振带出现了叠加现象,在1阶弯曲振动处幅频特性曲线上的峰值远大于其它各阶的峰值,最大应力出现在转轴上,说明转轴的损伤是转镜...     

某稳瞄转塔结构的有限元模态分析与试验验证

结构动态效应是影响稳瞄系统稳定精度的关键因素。目前有限元模态分析与试验模态分析结合的方法是分析结构动力学特性的最有效途径之一。以某型稳瞄具两轴四框架结构为研究对象,首先利用有限元方法进行了模态预分析。根据仿真结果获取的振型特征,对两轴四框架的外环进行模态测试,给出了前8阶模态的固有频率、振型和模态阻尼比。模态仿真与测试的结果相互验证表明:有限元仿真可实现两轴四框架结构固有频率相对误差小于15%的精度要求,在测点密度足够的条件下振型相关性良好。     

航空侦察相机镜头模态分析与结构优化

针对某型航空侦查相机镜头仿真的工程需求,根据其结构建立三维几何模型,将模型导入到Patran/Nas-tran分析软件中,对其进行模态分析.在初次分析中得出,第1阶和第2阶模态的固有频率(573Hz、576Hz)过低(低于军方要求的600Hz以上),所以需要在提高刚度方面对结构进行优化.为了提高固有频率,对其结构进行了...     

Preserving synchronization under matrix product modifications

In this article we present a methodology under which stability and synchronization of a dynamical master/slave system configuration are preserved under modification through matrix multiplication. The objective is to show that under a defined multiplicative group, hyperbolic critical points are preserved along the stable and unstable manifolds. The properties of this multiplicative group were determined through the use of simultaneous Jordan decomposition. It is also shown that a consequence of this approach is the preservation of the signature of the Jacobian matrix associated with the dynamical system. To illustrate the results we present several examples of different modified systems.     

Quantum Kinetic Theory for Laser Plasmas. Dynamical Screening in Strong Fields

A quantum kinetic theory for correlated charged-particle systems in strong time-dependent electromagnetic fields is developed. Our approach is based on a systematic gauge-invariant nonequilibrium Green's functions formulation. Extending our previous analysis [1] we concentrate on the selfconsistent treatment of dynamical screening and electromagnetic fields which is applicable to arbitrary nonequilibrium situations. The resulting kinetic equation generalizes previous results to quantum plasmas with full dynamical screening and includes many-body effects. It is, in particular, applicable to the interaction of dense plasmas with strong electromagnetic fields, including laser fields and x-rays. Furthermore, results for the modification of the plasma screening and the longitudinal field fluctuations due to the electromagnetic field are presented.     

A nonstandard dynamical theory of x-ray scattering in crystals

A new version of the X-ray diffraction dynamical th eory in perfect crystals is presented. The theory is based on direct analysis of Maxwell equations taking into account the model approximations of the character of X-ray-crystal interaction corresponding to the Evald—Laue theory. The method modification of many scales is used as a mathematical method for approximate solution of the diffraction equation. The obtained results correspond to the known conclusions of the diffraction dynamical theory beyond the area of full external reflection. The expressions for the reflection amplitude factors of diffracted and specular waves for arbitrary angles including the area of full external reflection have been obtained.     

忆阻电路降维建模与特性分析

通过对蔡氏忆阻电路的数学建模分析,提出了忆阻电路动力学建模的降维问题.以包含两个磁控忆阻器的忆阻电路为例,进行了忆阻电路降维建模,由此建立了一个三维系统模型.基于该模型,分析了忆阻电路的平衡点和稳定性,研究了电路参数变化时忆阻电路的动力学特性.进一步,对包含两个磁控忆阻器的忆阻电路常规模型的分析结果和其降维模型的分析结果进行了比较.结果表明:忆阻电路降维模型的维数只与电容器的数量和电感器的数量有关,而与忆阻器的数量无关;当电路参数变化时忆阻电路存在分岔模式共存等非线性现象;降维建模降低了系统建模复杂度,有利于系统的动力学特性分析,但消除了忆阻器内部状态变量的初始条件对忆阻电路动力学特性的影响.     

Photoelectron spectroscopy of localized levels near surfaces: Scattering effects and relaxation shifts

We calculate the spectrum of photoelectrons excited from localized levels in solids far into the continuum (XPS situation), in a model that takes into account exactly their interaction with a boson-like spatially non-uniform field. The general results are applied to discuss the spectra of photoelectrons in metals, where the dominant interaction is the coupling to bulk and surface plasmons. In particular, we study the modification of spectral sum rules connecting the strength of inelastic processes with the energy shifts in the spectrum, showing that the electron (“extrinsic”) scattering changes the average position of the spectrum with respect to the pure “intrinsic” result in the “sudden approximation”, which leads also to its dependence on the excitation energy and position of localized level. We estimate these deviations in a simple model which nevertheless reproduces correctly the dynamical aspects of the problem.     

三维磁共振电阻抗成像的改进分层灵敏度算法

针对人体组织电导率的三维成像问题,提出一种改进的分层灵敏度磁共振电阻抗重建算法.利用单方向磁感应强度信息,对三维电导率图像实行分层重建,每层重建仅利用该层磁通密度分量测量数据,然后对单层重建结果进行修正以获得三维电导率重建图像.三介质长方体模型上的仿真实验证明,改进的分层重建算法改善了层间串扰现象,可以获得比一般分层算法甚至整体算法更高的图像分辨率,而且重建时间较整体算法显著减少;基于人体腿模型的仿真实验表明该算法对复杂模型三维重构的可行性;最后通过仿体实验验证算法的重建效果.改进的分层灵敏度重建算法降低了灵敏度矩阵法的计算机硬件需求,减少了重建时间,对MREIT的三维重建具有较高的成像精度和求解效率.     

Nucleon-nucleon correlations with quark degrees of freedom

A dynamical equation of two nucleons in a nucleus is formulated in the nonrelativistic quark model including Pauli blocking due to the other nucleons. This equation is solved with a model wave function containing the possiblity of six-quark bags with different radii. It is shown that the Pauli blocking effect is emphasized by the non-nucleonic degrees of freedom represented by six-quark bags. The modification of the quark momentum distribution for correlated nucleons is calculated and probabilities of non-NN components in nuclei are estimated.     

Cooperative motions in a finite size model of liquid silica: an anomalous behavior

Finite size effects on dynamical heterogeneity are studied in liquid silica with Molecular Dynamics simulations using the BKS potential model. When the system size decreases relaxation times are found to increase in accordance with previous results in finite-size simulations and confined liquids. It has been suggested that this increase may be related to a modification of the spatially heterogeneous dynamics in confined liquids. In agreement with this hypothesis we observe a decrease of the spatially heterogeneous dynamics when the size decreases. The spatially heterogeneous dynamics is usually characterized by the dynamical aggregation of the most or the least mobile atoms. However we find that the decrease of the dynamical aggregation associated to the least mobile atoms is much more important than the decrease associated to the most mobile atoms when the size decreases. This result associated with a slowing down of the liquid is surprising as it is expected that the dynamical aggregation of the least mobile atoms should increase the slowing down of the liquid dynamics. The decrease of the heterogeneous behaviour is also in contradiction with the increase of the spatially heterogeneous dynamics observed in liquids confined inside nanopores. However, an increase of the non-Gaussian parameter appears both for the confinement inside nanopores and for the finite size simulations. As the non-Gaussian parameter is usually associated with the heterogeneous dynamics, the increase of the non-Gaussian parameter together with a decrease of the spatially heterogeneous dynamics is also surprising.     

修正屏蔽库仑势下二维尘埃等离子体的动力学和结构特性

本文考虑等离子体密度分布变化, 得到了修正屏蔽库仑势的解析解. 数值分析以及分子动力学模拟表明, 在常见实验室参数情况下, 等离子体密度分布变化引起的屏蔽库仑势修正对二维尘埃等离 子体系统的动力学和结构特性影响很小. 在极限参数情况下, 本模型的计算结果表明二维尘埃等离子体系统的扩散能力明显降低, 并且系统组态呈圆形分布. 此外, 本文还研究了实验室常见大小磁场对二维尘埃等离子体系统的影响. 关键词： 修正屏蔽库仑势 二维尘埃等离子体 分子动力学模拟