具有负折射的二维光子晶体设计

提出一种具有负折射特性的二维光子晶体设计。对其色散关系的分析表明,该设计对归一化频率为0.5263的TE极化光波具有负折射特性。时域有限差分(FDTD)数值计算模拟结果证明了分析的正确性;并且负折射对光子晶体层数没有依赖关系;很薄的光子晶体就能表现出明显的负折射,且便于实验制作和探测;在一定入射角范围内,光子晶体平板表现出奇异的负折射导引现象。给出了光子晶体模型参数。     

Prediction of Vibration Characteristics in Beam Structure Using Sub-Scale Modeling with Experimental Validation

Geometric or sub-scale modeling techniques are used for the evaluation of large and complex dynamic structures to ensure accurate reproduction of load path and thus leading to true dynamic characteristics of such structures. The sub-scale modeling technique is very effective in the prediction of vibration characteristics of original large structure when the experimental testing is not feasible due to the absence of a large testing facility. Previous researches were more focused on free and harmonic vibration case with little or no consideration for readily encountered random vibration. A sub-scale modeling technique is proposed for estimating the vibration characteristics of any large scale structure such as Launch vehicles, Mega structures, etc., under various vibration load cases by utilizing precise scaled-down model of that dynamic structure. In order to establish an analytical correlation between the original structure and its scaled models, different scale models of isotropic cantilever beam are selected and analyzed under various vibration conditions( i.e. free, harmonic and random) using finite element package ANSYS. The developed correlations are also validated through experimental testing. The prediction made from the vibratory response of the scaled-down beam through the established sets of correlation are found similar to the response measured from the testing of original beam structure. The established correlations are equally applicable in the prediction of dynamic characteristics of any complex structure through its scaled-down models. This paper presents modified sub-scale modeling technique that enables accurate prediction of vibration characteristics of large and complex structure under not only sinusoidal but also for random vibrations.     

基于产品结构与配置管理报价系统的设计开发

本文从改善电力电气行业相对落后的报价方法入手,研究了配电设备的产品结构与产品配置特点,阐述了基于产品结构和配置管理的产品报价系统的原理、关键技术、模型及应用。     

跨座式单轨车辆转向架构架模态分析

以跨座式单轨车辆转向架构架为研究对象,建立了构架的几何模型和有限元模型。介绍了构架结构模型的建模技巧、建模过程、建模单元特性以及有限元模型的创建技巧。根据模态分析的理论基础对构架的有限元模型进行了自由模态分析,通过计算得出了构架前16阶模态的固有振动频率和振型模态,确定了构架结构的动态特性,指出构架中振动的薄弱环节。为构架动态特性的改进设计和有效地避免共振现象的发生提供了参考,对进一步构架的动力学分析也有重要的意义。     

基于EBSD技术构建弹性各向异性粗晶材料超声仿真模型的研究

针对弹性各向异性粗晶材料晶粒结构和取向定量描述困难,导致超声检测仿真结果与试验符合程度较差的问题,提出基于电子背散射衍射(Electron back-scatter diffraction,EBSD)技术确定晶粒形态及晶体取向的建模思路。利用EBSD技术实测得到了尺寸为96 mm×12 mm的离心铸造奥氏体不锈钢(Centrifugally cast austenitic stainless steel,CCASS)轴-径向截面的晶体取向图谱,选择15°取向相(差)角定义EBSD图谱的晶粒结构,并对晶体取向进行归一化处理。在此基础上借助Bond变换法赋以晶粒在对应晶体取向下的刚度矩阵,对模型中晶粒的弹性特征进行量化表征,建立CCASS超声检测模型。采用时域有限差分法进行数值计算,结果表明:利用该方法能够较好地重现CCASS超声检测特有的结构噪声和主频降低等现象,为揭示超声波在弹性各向异性粗晶结构中的散射机理提供了解决思路。     

Identification of external forces in mechanical systems by using LifeCycle model and stress-stiffening effect

This paper presents an optimization-based inverse procedure for the determination of external loads applied to a given mechanical structure, by using information concerning the dynamic behavior of the system and its corresponding finite element model. The influence of the stress-stiffening effect on the dynamic characteristics of structural systems is used to establish a relation between the dynamic responses and the applied external forces. An optimization problem is formulated in which the objective function represents the difference between the measured modal characteristics of the loaded structure and their finite element counterparts. The loading parameters (magnitude, position and direction) assumed as being unknown, are considered as design variables. The identification procedure is illustrated by means of numerical simulations and experimental tests, in which a heuristic technique known as LifeCycle model was used.     

基于神经网络和遗传算法的卫星结构参数优化

针对卫星结构要求总质量轻小、一阶固有频率较高的特点,建立了卫星结构多目标优化的数学模型,通过BP神经网络和遗传算法相结合进行参数优化,并编制了相应的计算程序,既利用了神经网络的非线性映射、网络推理和预测功能,又发挥了遗传算法的全局优化特性,得出了合理的优化结果,与传统的结构优化方法相比,此方法效率较高,精度良好.     

联邦数据库系统协商机制的设计和实现

联邦分布数据库系统支持异构自治和多库共享,为此,系统要解决的一个主要问题是协商机制的实现.本文论述了协商机制的结构、访问权限协商模型以及实现的主要步骤和技术,该机制具有灵活可扩充的联邦特点,可以方便地对系统进行剪裁.     

光纤机敏结构振动形态感知及其SMA致动控制

以模拟太空帆板结构为试验模型,针对振动状态监测与主动控制技术需求,着重进行柔性光纤机敏结构振动形态感知及其形状记忆合金(SMA)致动控制研究。技术方法上基于分布植入式FBG传感网络的信息感知特性与结构形态曲面拟合算法,实现结构分布多点曲率检测与形态重构,并为基于SMA致动的结构振动主动控制提供判决依据;基于结构表面分布配置的SMA驱动网络,采用分组交替驱动方式实现结构低阶模态大幅振动主动控制;设计试验模型结构与构建完整试验测控平台,并综合阐述了试验方案与试验过程。试验结果验证了结构振动形态感知的有效性,以及结构振动SMA致动控制的可行性和高效性,为航天柔性结构低阶模态振动主动监控提供了较好的技术探索思路。     

A study on large mass method for dynamic problem of multiple degree-of-freedom system excited by ground acceleration time history?

We considered a numerical modeling technique called ‘large mass method’ or large mass model, which is used for a dynamic problem of a structure that is subjected to support or ground acceleration time history. Since its analytic background has not been extensively verified yet, this paper extends the previous analysis for a single degree-of-freedom system to that for the multi-degree-of-freedom springmass system to present theoretical effectiveness or rigorous comprehension of the technique. The theorems are discussed and checked by using the concept of quasi-static decomposition with simple examples. The analysis shows that the characteristics of LM model for single DOF system are conserved consistently even in multi-DOF system and that the response of LM model for spring-mass system is also composed of quasi-static part and dynamic part like the response of an original spring-mass model. Numerical tests for multi-degree-offreedom spring-mass systems show that they match well with the present analysis.     

基于动网格技术的减振器流通阀片仿真分析

液力减振器流通阀片与减振液间的微观、高频的流固耦合作用机理非常复杂,决定着液力减振器的阻尼特性和异响发生。为深入分析这种流固耦合作用机理,文章建立了液力减振器流通阀片的力学模型,采用ANSYSCFX软件并结合其动网格技术,对液力减振器流通阀片在正弦进口速度载荷条件下的动力学特性进行仿真分析,得到了减振器流通阀片的振动特性,并进行了减振器噪声台架试验。结果表明,采用动网格技术能够较好地实现液力减振器流通阀片的仿真分析和计算。     

控加工过程的建模与仿真

面向对象技术强调模型的层次化和模块化 ,有利于提高模型的封装性、重用性、可扩展性和可维护性。本文在对仿真对象进行面向对象分析的基础上 ,提出了以装配树为基础 ,采用面向对象技术建立数控加工仿真系统的几何模型和运动模型的新方法 ,统一了运动模型和几何模型 ,解决了数控加工仿真系统中的模型复杂和重用性差的问题     

基于VOF模型与动网格技术的油气悬架气液两相流数值模拟

针对某型大吨位矿用自卸车油气悬架为油气两相相互接触的特点,拟从多相流数值仿真的角度对其非线性刚度阻尼特性进行分析。首先,在探讨了现有多相流建模方法适用性、湍流模型适用性的基础上,结合VOF模型和动网格技术,在Fluent软件中建立悬架的气液两相流模型,并采用UDF方法对两相流模型的边界运动形式进行预定义。其次,模拟了悬架拉伸和压缩状态下的内部瞬态流场特性,得到不同时刻相应流道中的速度和压力云图,提取出气室内压力的变化以及悬架内因阀系结构而产生的压力差的变化,进而计算得到其刚度和阻尼特性曲线。再次,将所求力学特性曲线通过Spline函数导入ADAMS/View中,建立了某型矿用自卸车的多体动力学模型,开展了随机道路平顺性仿真分析,并借助实车道路振动测试验证了仿真结果的准确性。最后,通过两相流仿真分析了阻尼孔倒圆大小、开孔角度、不同单向阀开度对悬架阻尼特性的影响。     

基于非线性振动调制超声导波的悬臂梁结构的非线性损伤定位

提出了一种利用非线性振动调制超声导波的方法,实现了悬臂梁结构中非线性损伤定位（疲劳裂纹）。在该技术中,损坏的金属梁设计为悬臂梁结构,引入的磁铁系统用来控制悬臂结构的动力学响应,使模型呈现出非线性振动。结合非线性振动声调制技术和同步锁相解调技术,提取出由于疲劳裂纹引起的非线性响应,实现疲劳裂纹的定位。     

Application of the standard-layer method to determine thermal characteristics of materials constituting multilayered structures

A method for determining thermal characteristics of materials in multilayered objects is proposed. The method is based on the use of an additional layered structure with present thermal characteristics that is named the standard layer (SL). The error associated with a finite size of the SL is assessed. A technique that considerably simplifies the procedure of determining the thermal resistance of multilayered objects is proposed. This technique is simpler than the state-of-the-art methods that are based on numerical integration of the heat-conduction equation and used for solving inverse problems. A possible structure of the SL is presented.     

产品装配结构技术的实现及应用

计算机信息集成技术应用于产品设计领域，一个关键问题是将零件几何信息与物理信息的集成。首先研究了Pro／Engineer内部装配图树状结构的实现方法，利用模型内部零部件路径标识唯一的特点，通过Pro／E的二次开发，建立了新的装配结构，实现了零件的几何模型与零件设计过程信息的集成。通过数据库统一管理的方式，能方便地实现模型的自动生成，以厦设计历史信息的查看，实现了设计参数和设计结果的版本管理。有利于缩短产品研发周期，提高研发效率，并方便企业积累宝贵的知识财富。     

龙门起重机金属结构的多目标动态优化

针对龙门起重机金属结构动态特性的复杂性和非线性,综合考虑龙门起重机金属结构设计中尺寸参数及起升载荷的不确定性,利用参数化有限元模型和试验设计方法,在龙门起重机金属结构动态系统中,建立了设计变量和动态参数间的关系。通过运用非支配排序遗传算法(NSGA-Ⅱ),寻求桁架梁尺寸及节间布置最优化方案,并满足低应力、高固有频率及轻量化的要求,在构建高精度的响应面近似模型的基础上,运用Monte-Carlo模拟技术对优化方案的鲁棒性进行了评价。结果表明,该优化方法有效地实现了龙门起重机的动态结构优化,显著提高了其设计质量和效率。     

圆柱曲界面对垂直入射法超声检测的影响分析

用垂直入射法检测圆柱曲界面工件时,工件的曲界面对超声检测的可靠性带来一定的影响。针对直探头纵波检测,从理论上分析圆柱曲界面对超声波耦合、声场结构、探头特征参数、缺陷定位与定量等诸多方面的影响,并针对性地加工了曲表面对比试样进行试验研究,对理论模型进行验证,提出了改善曲界面影响的对策措施,在实践中取得了较好效果。     

高速数控铣削的机床刀具及编程技术

分析了高速数控铣削的机床、刀具及编程中的特点及技术要点,提出了高速数控铣削机床结构、刀具系统及基于CAM的高速数控铣削编程技术的策略,实践证明,效果良好.