Heat transfer analysis for particle–fluid suspension thermomagnetohydrodynamic peristaltic flow with Darcy–Forchheimer medium

This theoretical analysis explores the effect of heat and mass transfer on particle–fluid suspension for the Rabinowitsch fluid model with the stiffness and dynamic damping effects through Darcy–Brinkman–Forchheimer porous medium. In this study, we also incorporate slip and transverse magnetic field effects. Using low Reynolds number, to neglect inertial forces and to keep the pressure constant during the flow, channel height is used largely as compared with the ratio of length of the wave. A numerical technique is used to solve flow governing system of differential equations. Particular attention is paid to viscous damping force parameter, stiffness parameter, and rigidity parameter; also, the numerical data for thermal profile, momentum, and concentration distribution are presented graphically. Outcomes are deliberated in detail for different fluid models (thinning, thickening, and viscous models). It is found that velocity profile increases for greater values of viscous damping effect and stiffness and rigidity parameter for shear thinning, but conflicting comportment is showed for thickening nature model. Viscous dissipation effects increases the thermal profile for all cases of fluid models. The scope of the present article is valuable in explaining the blood transport dynamics in small vessels while considering the important wall features with chemical reaction characteristics. The current analysis has extensive applications in biomedical engineering field, that is, peristaltic pumps.     

基于柔性装配偏差模型的汽车车身薄板零件公差设计

基于汽车车身柔性薄板零件装配建模方法,建立柔性薄板零件公差优化设计方法。根据柔性薄板零件测点装配偏差与各偏差源间的确定性模型,综合得到测点装配偏差的方差与零件制造方差和夹具定位方差之间的模型,以零件测点平均方差为公差设计函数,工序能力指数和零件制造方差比为约束函数进行零件公差优化设计,并采用车身后地板装配进行应用分析。结果表明,搭接焊接结构的零件公差设计需同步进行,对接焊接结构零件公差设计各自独立进行,而角接焊接结构的零件公差设计则先进行其中对接零件公差设计,然后进行搭接零件公差设计;搭接焊接结构中零件间刚度差异比较大时,刚度小的零件公差可以取相对更大的公差。     

A new level set method for topology optimization of distributed compliant mechanisms

A new level set method for topology optimization of distributed compliant mechanism is presented in this study. By taking two types of mean compliance into consideration, several new objective functions are developed and built in the conventional level set method to avoid generating the de facto hinges in the created mechanisms. Aimed at eliminating the costly reinitialization procedure during the evolution of the level set function, an accelerated level set evolution algorithm is developed by adding an extra energy function, which can force the level set function to close to a signed distance function during the evolution. Two widely studied numerical examples in topology optimization of compliant mechanisms are studied to demonstrate the effectiveness of the proposed method. Copyright © 2012 John Wiley & Sons, Ltd.     

刚性机构与柔性机构性质的探讨

简单介绍了柔性机构及其性质,分析和研究了由拓扑优化得到的力和位移反向器的典型模型,发现在模型构件为刚体条件下,模型的几何增益和机械增益能达到极大即力和位移的输出效率最大。以桁架机构的位移反向器作为基本模型,分析得到有关模型的几何增益的优化目标函数,对目标函数进行了数值优化计算,得到模型的尺寸参数,用结构力学的方法对得到的机构模型进行计算分析。     

用无网格法进行大变形柔性机构拓扑优化设

基于连续体结构的拓扑优化理论,将无网格伽辽金数值方法引入分布式大变形柔性机构拓扑优化设计,并解决了优化中的几何非线性问题。在优化问题中,基于各向同性固体材料惩罚模型（solidisotropic material with penalization,SIMP)和折衷规划法,同时考虑结构的柔性和刚度要求,建立了柔性机构拓扑优化的多准则优化模型,并利用优化准则法求解。采用无网格伽辽金法将求解域离散成节点,避免了有限元方法在处理大变形问题时由于使用网格而产生网格畸变等问题。求解经典算例,与基于线性理论的优化结果相比较分析,说明了该方法的正确性和有效性。     

全柔性机构与MEMS

柔性机构是一种新型机构。首先描述了柔性机构和全柔性机构的概念及特点,论述了它们与MEMS之间的关系。然后详细介绍了全柔性机构在MEMS领域内包括微装配、微操作等应用背景下的状况及前景。最后就对全柔性机构研究中的几个关键技术问题如机构的分析、设计及加工,柔性铰链的选择与设计,驱动器的选择及设计等进行了探讨。     

全适应性双稳态微机构及其假刚体模型

概述了双稳态微机构的定义、优点及分类。介绍了全适应性双稳态微机构的特征及其建模技术，重点分析了假刚体模型的思想及其在适应性机构设计中的应用，并对全适应性双稳态微机构假刚体模型的优化方法进行了一定的研究。     

压电位移放大机构的力学解析模型及有限元分析

研究了压电位移放大机构的运动学和动力学建模问题。基于能量守恒原理和弹性梁弯曲理论推导了桥式位移放大机构的位移放大比等静力学解析模型;在此基础上,通过拉格朗日方程建立了桥式位移放大机构的固有频率解析模型。通过有限元计算验证和分析了提出的解析模型的可行性和优越性,并与国内外典型的位移放大比数学模型进行了比较。结果表明:由于本文提出的模型考虑了位移放大机构的拉伸和弯曲变形,并且摒弃了国内外普遍采用近似几何关系进行数学推导的思路,因此所建立的位移放大比解析模型精度更高;固有频率解析计算结果与有限元模态分析结果的相对误差约为5%。得到的结果显示:本文给出的建模方法以及位移放大比、固有频率等解析模型可为柔性机构的优化设计和研制提供依据和参考。     

弹性箔片动压气体推力轴承承载性能研究

气弹耦合解是准确预测弹性箔片动压气体轴承承载性能的有效方法。通过引入箔片的弹性变形以及联立求解动压气体润滑Reynolds方程和弹性箔片的变形方程,给出了弹性箔片动压气体推力轴承的气弹耦合解。应用气弹耦合解理论,将顶层箔片的局部弹性变形纳入考虑范围,对弹性箔片动压气体推力轴承的承载性能进行了计算和分析。有限元数值仿真结果表明:顶层箔片在气膜压力作用下的局部弹性变形直接导致弹性箔片动压气体推力轴承承载能力的降低;根据轴承瓦块上气膜压力分布的特点合理设计支承拱箔的结构形式,可以减小顶层箔片的局部弹性变形,有效提高轴承的承载能力。得到了一种承载能力较高的弹性箔片动压气体推力轴承支承拱箔结构设计方案。     

Design of deployable bistable structures for morphing skin and its structural optimization

The morphing skin is the surface of a deployable frame which can change its shape to present optimal performance in all stages of a task for an aerospace vehicle. This article proposes a deployable frame with low kinematic error and high stability. Mechanical design and optimization of the deployable mechanism are developed, and specifically the analysis model of the deployable mechanism is established by the use of extendable units. The genetic algorithm is employed to find the optimal geometric parameters of the foldable structure. Furthermore, the design method of a bistable compliant mechanism is investigated to achieve the bistability. An example of a morphing leading edge (MLE) is analysed using the proposed method. The results show that the position errors converge to the optimal solution which supplies the minimum value. Numerical analysis indicates that the mechanism can provide two bistable positions for the actual use of the MLE.