高速凸轮NURBS廓线改进人工鱼群多目标动力学优化

为改善高速凸轮机构动力学性能,首先采用非均匀有理B样条（NURBS）重构凸轮廓线,建立高速凸轮单自由度弹性动力学模型,进行高速凸轮机构多目标动力学优化设计。然后利用改进人工鱼群算法求解该模型,获取系统Pareto最优解从而得到优化后的NURBS廓线。最后,分析和比较高速凸轮机构在NURBS和修正正弦两种廓线下的动力学响应。结果表明：改进人工鱼群算法可以有效解决多目标优化问题,优化后NURBS廓线运动学特性与修正正弦廓线相差不大,在一定程度上降低了高速凸轮机构的残余振动幅值,提高了高速凸轮机构的定位精度和动力性能,减少了振动和冲击的噪声。     

高速取纸机构设计与仿真分析

目的 利用机构实现取纸机在高速取纸时无纸间摩擦的目的。方法 明确无纸间摩擦情况下取纸吸头的姿态和动作要求。利用凸轮连杆机构的运动特点,并考虑高速运动中凸轮机构运动规律要求,设计凸轮五杆机构取纸机构。利用Adams仿真验证机构运动情况。结果 通过分析凸轮五杆机构连杆上两点的位移变化,获取作为吸头的凸轮五杆机构的连杆运动情况。通过机构的运动仿真分析可知,吸头在取纸时以垂直于纸面的姿态作间歇平动,实现了预定目标要求。结论 利用凸轮五杆机构能够很好地实现高速、无纸间摩擦取纸。     

弹性连杆复合机构的灵敏度分析

本文针对一种凸轮连杆复合机构,在运动弹性动力学分析的基础上运用直接微分法得到该机构的稳态动力学响应灵敏度的计算方法。     

滚珠型弧面凸轮分度机构动力学模型的建立及模态分析

应用拉格朗日方程对一种新型的滚珠型弧面凸轮分度机构进行了动力学建模。忽略滚珠的质量,将滚珠与凸轮之间的接触刚度以及滚珠与分度盘之间的接触刚度近似看作为两个接触刚度的串联,得到等效接触刚度。在建模过程中,利用回转变换张量法对机构中广义坐标几何位移关系进行了分析,建立了考虑扭转弹性模量的滚珠型弧面凸轮分度机构的动力学方程。由动力学方程得到了机构固有频率及其相对应的振型。结果表明,固有频率在分度时期随凸轮转角变化,在停歇时期为恒定值,并且不同阶的固有频率变化趋势也不相同。     

凸轮符合“最小条件”误差值的求解

1.概述 凸轮轮廓的形状误差,是通过凸轮机构从动件（挺柱）的运动误差（升程误差）来反映的。根据形状误差的定义,凸轮的升程误差是指被测实际凸轮对其理想凸轮的变动量。因为处于不同方位理想凸轮下的实际凸轮会得到不同的升程误差值,所以应按最小区域法并考虑凸轮升程公差大小、公差带形状的影响,     

探析凸轮机构设计中应注意的问题

一、压力角与自锁现象 图1所示为尖顶直动从功件凸轮机构。苦不考虑摩擦,凸轮作用于从动件上的力Fn是沿接触点的法线n—n方向。     

基于Matlab和ADAMS的共轭凸轮下摆式递纸机构的设计

本文根据共轭凸轮下摆式递纸机构的工作原理,选择符合的从动件运动规律进行递纸机构的设计。基于Matlab软件得到了共轭凸轮和开闭牙凸轮的理论轮廓和实际轮廓,以及对共轭凸轮组的安装角进行了计算。运用UG软件对共轭凸轮下摆式递纸机构进行了建模和装配,并运用ADAMS软件对设计的机构进行了运动学仿真,通过运动学仿真验证了机构的可行性。     

直动从动件凸轮机构的计算机辅助设计

本文论述了直动从动件凸轮机构的计算机辅助设计方法，可用于凸轮机构的设计和凸轮机构的教学。     

等径共轭调焦凸轮机构的精度分析及优化设计

为保证航空遥感器的成像质量,对遥感器偏移的焦平面进行校正,设计了等径共轭凸轮调焦机构.研究了影响凸轮机构精度的因素,分析了滚子径向跳动误差、凸轮加工误差、基圆半径对机构位移正确度的影响,并提出了一种基于最小二乘法,保证凸轮共轭等径、消除机构空回误差及防止机构卡死的优化方法.优化设计了某等径共轭调焦凸轮机构并对其进行了精度分析.结果表明,等径共轭凸轮机构的最大位移误差为主±4.7μm,最大空回误差为4.8μm,机构运行稳定可靠.     

热成型机开合模机构的设计及运动仿真

通过对热成型机开合模机构工作原理的分析,设计了一种新的凸轮曲柄连杆开合模机构,同时对凸轮曲柄连杆开合模机构进行了运动学及动力学分析,给出了凸轮曲柄连杆开合模机构的位移、速度及加速度的设计方程和仿真曲线,验证了该凸轮曲柄连杆机构设计的合理性。     

Effect of the Elastic Modulus of a Coating on the Serviceability of the Substrate–Coating System

We study the effect of the elastic modulus of a coating on its strength and strain characteristics, as well as on the residual stresses in it. The tangential and normal stresses that occur in the substrate and coating depend on the elastic modulus of the latter. It has been concluded that when designing substrate–coating systems, one should try to seek the optimum ratio of their elastic properties. An original approach has been proposed to the deposition of protective structurally inhomogeneous coatings, in which, unlike functionally gradient materials, not the composition but the structure is varied continuously.     

Convergence problems in the theory of random elastic media

A main result of the rigorous theory of random, linearly elastic media consists in the representation of the tensor of effective elastic moduli as a Neumann type infinite series which contains the infinite set of correlation functions of the distribution of the local elastic moduli. Under the restriction to statistically homogeneous and isotropic finite media it is proved that convergent series can always be obtained provided the local elastic moduli remain finite everywhere in the medium. This means that the mentioned theory cannot be applied in the above mentioned form to media with pores and/or rigid inclusions. It also means that the theory is not restricted to media with small fluctuations of the elastic parameter.     

Neutrality of the elliptic inhomogeneity in the case of non-uniform loading

In this paper, we consider the problem of a single elliptic elastic inhomogeneity embedded within an infinite elastic matrix in antiplane shear. In particular, we examine the (stress) neutrality of this inhomogeneity when a non-uniform stress field is prescribed in the surrounding matrix. Since it is known that neutral elastic inhomogeneities do not exist when the inhomogeneity is assumed to be perfectly bonded to the matrix, the method presented here is based on the assumption of imperfect interface and the appropriate choice of the (single) interface parameter (characterizing the imperfect interface) to achieve the desired neutrality. Specifically, neutrality is established for specific (polynomial) classes of prescribed states of stress in the surrounding matrix. The results in this paper affirm the feasibility of designing a neutral elastic inhomogeneity by controlling the (imperfect) interface parameter describing the inhomogeneity-matrix interface.     

A new method for calculating the elastic component of the crack opening displacement (COD)

A criticism is made in the method of calculating the elastic component of the Crack Opening Displacement (COD) following the British standard. The problem with this standard is the criterion for selecting the value of force, from a force-displacement curve, to be used for calculating the elastic component of COD. A theoretical discussion is made showing the impropriety of the criterion with the standard; experimental evidence also points to this fact. A new method for calculating the elastic component of COD is proposed. It is also shown that for the materials and conditions of the present work the values of the elastic component do not depend upon the geometry and orientation of the COD specimens.     

Universal theorems for total energy of the dynamics of linearly elastic heterogeneous solids

In this paper we consider a sample of a linearly elastic heterogeneous composite in elastodynamic equilibrium and present universal theorems which provide lower bounds for the total elastic strain energy plus the kinetic energy, and the total complementary elastic energy plus the kinetic energy. For a general heterogeneous sample which undergoes harmonic motion at a single frequency, we show that, among all consistent boundary data which produce the same average strain, the uniform-stress boundary data render the total elastic strain energy plus the kinetic energy an absolute minimum. We also show that, among all consistent boundary data which produce the same average momentum in the sample, the uniform velocity boundary data render the total complementary elastic energy plus the kinetic energy an absolute minimum. We do not assume statistical homogeneity or material isotropy in our treatment, although they are not excluded. These universal theorems are the dynamic equivalent of the universal theorems already known for the static case [Nemat-Nasser and Hori, 1993] and [Nemat-Nasser and Hori, 1995]. It is envisaged that the bounds on the total energy presented in this paper will be used to formulate computable bounds on the overall dynamic properties of linearly elastic heterogeneous composites with arbitrary microstructures.     

配合关系对弹性环式挤压油膜阻尼器减振特性的影响

为了研究配合关系对弹性环式挤压油膜阻尼器减振特性的影响,搭建了带弹性环式挤压油膜阻尼器的转子实验系统,设计了两套弹性环组件。通过改变弹性环凸台的配合关系及转子的不平衡质量,实验研究了弹性环式挤压油膜阻尼器的减振特性。实验结果表明:弹性环的内凸台为过盈配合时可能导致阻尼器减振失效,为间隙配合时减振效果更好;外凸台配合关系的变化不会导致阻尼器减振失效;凸台为间隙配合时,弹性环的减振效果及转子的响应与不平衡质量的关系线性度更高。提出了设计与应用弹性环式挤压油膜阻尼器时,应保证内凸台为间隙配合的设计建议。     

A dynamic oscillatory test that fulfills the objective of the elastic recovery test for asphalt binders

The ductilometer is currently being used by the asphalt pavement community for determination of elastic recovery of asphalt materials. Briquet specimens are pulled apart at 5 cm/min, held after a specified elongation, then severed at the center and allowed to recover undisturbed for 1 h with the idea of getting a measure of the ability of the asphalt material to recover after imposing a deformation. Materials with poor ability to recover are known to lend themselves to permanent deformation resulting in rutting of pavements. The Superpave specification parameter |G*|/sinδ recommended by the Strategic Highway Research Program was found not to relate well with observed rutting of mixtures that used polymer-modified asphalts with increased elastic behavior. This led researchers to seek methods to refine this parameter. While refinement efforts have been ongoing, there has been an inclination on the part of a number of State Departments of Transportation to use the elastic recovery test to complement the Superpave specification tests. However, the elastic recovery test is truly not very elegant and accurate, and often fails to discriminate between the behaviors of differently modified binders. The present work suggests a dynamic oscillatory test using the dynamic shear rheometer DSR that would fulfill the objectives of the elastic recovery test. The elastic recovery term and the condition under which it is determined from DSR data are selected by observation of master plots of a wide variety of asphalt binders. The criterion is developed by observing the ability of the selected term in best discriminating asphalt binders for their elastic recovery behavior. It is recommended that the term cosδ determined at a temperature T = 82°C and frequency ω = 1 radian/s be used to assess the elastic recovery of asphalt materials. Cosδ (T = 82°C, ω = 1) > 0.04 is recommended as the criterion for acceptance of required elastic recovery behavior. The opinions, findings, and conclusions expressed in this document are those of the author only and not necessarily of the Federal Highway Administration or any other researcher at the Turner-Fairbank Highway Research Center.     

山区台地框架建筑抗震性能研究

建于山区台地上的多台阶爬山式横向错层框架是多见的一种结构形式，但以往对其抗震性能的研究还很少。利用二次开发后的ANSYS对台地框架在E1-Centro波作用下的抗震性能进行了上下部共同作用分析，对台地框架与普通框架的自振频率进行了对比，探讨了台地框架最大加速度及最大层间位移角沿高度分布规律。有两个因素对台地框架的频率变化产生影响：一个是徒坎本身随着高度的增加而自振频率降低的趋势；另一个因素是由于位于徒坎上部的那部分框架层数减少，框架本身变刚而产生的自振频率增加的变化趋势。当徒坎弹性模量较大时，第二个影响因素占主导地位，当徒坎弹性模量较小时，第一个影响因素占主导地位。徒坎高度越高、位于徒坎下部的框架跨数越少，则台地框架与对应普通框架的地震反应差异越大。但这种差异既可能是台地框架的地震反应大于对应的普通框架，也可能小于对应的普通框架。当输入的地震动高频成分较多、徒坎弹性模量较小时，则趋向增大地震反应，而输入地震动的高频成分较小、徒坎弹性模量较大时，则趋向减小地震反应。     

Towards the resolution of the Smith-Herrmann paradox

Summary. The counterintuitive behaviors associated with Smith-Herrmanns columns under follower force and on elastic foundation, as well as the Bernoulli-Euler pipe conveying fluid on a partial elastic foundation, are re-examined. It is shown that treating the pipe as a Timoshenko beam removes, albeit not always, the paradoxical patterns of stability loss.     

On evolution equations for elastic deformation and the notion of hyperelasticity

For elastic-plastic and elastic-viscoplastic materials it is possible to introduce an evolution equation for an elastic deformation measure. Also, it is possible to develop constitutive equations for which the stress and strain energy are functions of elastic deformation only, the stress is determined by a derivative of the strain energy function and the associated material response is rate-independent and non-dissipative in the absence of the rate of inelasticity. Yet, these equations do not necessarily exhibit hyperelastic response in the elastic range. The objective of this paper is to emphasize the importance of satisfying an additional condition that requires the work done between two configurations to be insensitive to the history and rate of total deformation. This work condition places restrictions on the evolution equation which ensure that the integrated elastic deformation measure is a function of total deformation only. Also, it is argued that there is no need to complicate the evolution equation for elastic deformation to accommodate alternative strain measures since the nonlinearities of these strain measures can be absorbed into the form of the strain energy function.