利用改进牛顿-拉夫逊法的高速圆柱滚子轴承打滑分析

在考虑油气阻力和保持架与滚子之间的摩擦力的基础上,推导了圆柱滚子轴承拟动力学分析模型。提出采用改进的牛顿拉夫逊法求解大规模非线性方程组,可以克服传统算法对初值要求较高、方程组规模较大时迭代很难收敛的问题,在分析高速滚子轴承打滑时具有较好的效果。通过与已有的分析和实验结果进行对比后发现:滚动轴承保持架打滑与轴承所受径向载荷有关,在一定范围内增大径向载荷,可明显抑制打滑现象;在高速滚动轴承非承载区,滚子转速与保持架转速相关,且随保持架转速的增加而增加,而当保持架转速接近理论转速时,滚子打滑程度与径向载荷无关。     

加速工况下圆柱滚子轴承运动特性

为了准确分析加速过程中圆柱滚子轴承的运动特性,建立圆柱滚子轴承动力学模型,模型中考虑加速度、运行工况、结构参数以及润滑剂流变特性等参数,对轴承运动特性进行瞬态以及时变分析。研究结果表明:考虑润滑剂的黏弹性可以提高动力学模型的预测精度。加速度对轴承打滑影响较大,尤其对非承载区滚子的转速影响较大;加速度越大,轴承滚子和保持架打滑越严重;轴承在加速过程中,滚子转速随时间呈阶梯上升,而保持架转速呈线性增大;滚子由承载区进入非承载区时,滚子转速先略微减小,由非承载区进入承载区时,滚子转速骤然增大;滚子与内滚道间相对滑动速度vij大于滚子与外滚道间的相对滑动速度voj,由于加速度的影响,相对滑动速度voj的方向在最大承载区附近发生变化;在非承载区,滚子与内滚道相对滑动速度较大,大载荷以及小轴承游隙可以有效减小相对滑动速度。     

转盘轴承对数修形滚子的特性分析

基于ABAQUS建立转盘轴承对数修形滚子与滚道接触的局部有限元模型,分析对数修形滚子在滚动和滑动工况下转盘轴承的应力分布。结果表明:随滚动和滑动的速度增加,应力分布趋势相同,但应力值变化不大,可以忽略速度对应力分布的影响。载荷较小时,滚道上应力分布均匀。载荷较大时,滚子端部与滚道接触位置应力明显增加。随载荷增加,模型整体应力值变大。摩擦因数增加,滚道上应力分布均匀,等效应力和接触应力变化不大,交变应力变大,且最大交变应力向滚道表面移动。     

双列圆锥滚子轴承动力学分析

基于滚动轴承动力学理论,建立了双列圆锥滚子轴承动力学分析模型。采用精细积分法和预估-校正Adams-Bashforth-Moulton多步法相结合的方法,对轴承非线性动力学微分方程进行求解。研究了双列圆锥滚子轴承的最大接触压力、滚子打滑率、滚子歪斜角以及轴承疲劳寿命等动态性能。分析结果表明:轴承的最大接触压力随轴向预紧量的增加呈先减小后增大的趋势,最佳预紧量随外载荷的增加而变大;滚子歪斜角随径向载荷的增加而变大,"压紧"侧的滚子歪斜角略微大于"放松"侧;轴承疲劳寿命随轴向预紧量的增加而增大直至最大值,随后迅速下降。     

考虑润滑碰撞的精密轴承保持架动态特性

保持架作为轴承中的浮动组件,在套圈引导和滚动体撞击作用下随机运动,其动态特性直接影响精密轴承的服役性能。为了准确分析保持架的动态特性,考虑轴承保持架和滚动体之间真实润滑状态和碰撞过程建立了滚动体和保持架润滑碰撞模型及精确的保持架动力学模型,分析了轴承预紧力、径向载荷、内圈转速及引导-兜孔间隙比对精密轴承保持架动态特性的影响规律。实验结果表明,相比于传统的保持架兜孔-滚动体干摩擦模型,考虑润滑的保持架动态特性分析与实验现象更吻合。相同转速下,增大预紧力或径向载荷可以降低保持架打滑率,相比径向载荷,预紧力对保持架打滑的影响更大。保持架在低速和高速下呈现不同的打滑形式,低速下外载荷对保持架打滑影响不大;高速下外载荷对保持架打滑影响较大。相同预紧时保持架打滑率随轴承内圈转速增加而增加,中预紧时转速对保持架打滑影响最小。随着引导间隙-兜孔间隙比的增加,保持架打滑率降低。研究工作可为精密轴承保持架的设计提供一定的依据。     

高速列车轴箱轴承典型故障特征的数值仿真分析

基于Adams建立考虑摩擦打滑和保持架效应的高速列车轴箱轴承完全动力学模型,分析高速列车轴箱轴承4种典型缺陷下滚子与保持架的故障动力学响应;通过EMD-包络谱抓取4种典型缺陷下的微弱故障信号特征频率,分析现有故障理论特征频率评估方法的局限性,并将EMD-包络谱方法抓取的特征频率与理论计算故障特征频率结果进行对比。研究结果表明：无论轴承是否存在缺陷,滚子的打滑率均在非承载区有所增大;外圈缺陷会导致保持架角速度比率呈正弦半波周期性变化;内圈缺陷会导致滚子角速度波动较大,保持架角速度偏高于理论角速度,保持架角速度比率呈非周期性激励波动变化,且波动频率较高;滚子缺陷仅对该缺陷的滚子的动力学特性影响较大;保持架缺陷对滚子与保持架的动力学特性的影响较小;理论特征频率计算公式需要充分考虑滚子-滚道摩擦打滑与滚子-保持架兜孔碰撞效应的影响。     

双列球面滚子轴承力学分析及滚子受载计算方法

以球面滚子轴承为研究对象,运用切片法,综合考虑了滚子-滚道凸度以及轴承内圈倾斜角的影响,建立了滚子并排和滚子错排的球面滚子轴承滚子载荷的计算模型。数值计算了内圈倾斜角、径向游隙、滚子错排角、以及外载荷等参数对球面滚子轴承滚子载荷和轴承内圈径向位移量的影响。计算结果表明,在一定的外载荷作用下,轴承内圈倾斜角度与滚子最大载荷呈线性变化规律;错排滚子的球面滚子轴承最大滚子载荷比并排略小,内圈径向位移量也略小。     

基坑开挖对围护墙竖向变形的影响机理

采用数值分析方法,研究开挖卸荷引起的基坑围护墙竖向变形机理.在有限差分软件中建立考虑土与结构共同作用的分析模型,采用理想弹塑性接触模型模拟墙土接触力学特性,对比分析了3种土体参数下墙体和墙底土体竖向位移、墙土相对位移和墙体两侧摩阻力分布特性.结果表明:墙体的竖向位移主要由墙底土体竖向隆起和墙土相对滑动共同决定;坑底土体位移主要受到土体卸荷回弹的影响,与土层参数关系较大;当黏聚力增大时,墙体的下沉量减小;砂土的摩擦角越大,墙体的竖向隆起量也越大;墙土相对滑动则受墙体两侧的摩阻力共同作用,而摩阻力受参数取值的影响;当接触属性变强时,坑内摩阻力上升的趋势将增强,墙体发生的竖向隆起量也显著增加.     

锥孔双列短圆柱滚子轴承的动态特性分析

建立了锥孔双列短圆柱滚子轴承动态特性分析理论,用Matlab工具开发了具有自主知识产权的分析软件.以3182120型锥孔双列短圆柱滚子轴承为对象,在0～15 000 r/min的范围内分析了径向刚度与转速、径向预紧及外加径向载荷等因素之间的非线性关系.研究表明:由于离心力的存在,锥孔双列短圆柱滚子轴承的径向刚度随着转速的提高呈非线性软化现象;随着径向预紧量的增加,轴承的径向刚度有所增大;在确定的预紧量下,轴承达到某一转速时,滚子将脱离内圈而导致轴承无法正常工作;径向载荷的变化对轴承径向刚度的影响可以忽略.锥孔双列短圆柱滚子轴承动特性参数分析理论、方法与软件为高速机床主轴部件的动态设计提供了有力的工具.     

双金属复合内圈滚动轴承接触特性分析

为解决圆柱滚子轴承在大载荷条件下易磨损的问题,设计了一种双层金属复合材料内圈圆柱滚子轴承.以复合内圈与滚子的接触为例,基于赫兹接触理论和波西涅斯克理论,给出了单个滚子与轴承内圈的最大接触应力.结合层复合材料力学模型,计算双层金属复合材料内圈等效弹性模量.建立内圈与单个滚子间接触模型,采用有限元仿真方法,探究不同材料厚度下的接触应力和弹性变形.通过接触摩擦试验,验证复合材料内圈在不同材料厚度下的接触宽度.结果表明:双层金属复合材料内圈轴承滚子与内圈接触变形增大,接触应力减小,可以有助于减少圆柱滚子轴承的磨损.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

正~~