箔片动压止推气体轴承流固耦合数值模拟

针对鼓泡弹性箔片动压止推气体轴承的结构,在假设内部流体为层流、沿气膜厚度方向压力不变、忽略流体体积力和惯性力的基础上,建立了可压缩性流体Reynolds方程;采用有限差分法,在考虑流场为等温过程的条件下,对Reynolds方程进行了数值求解,得出轴承内部的压力分布。充分考虑鼓泡结构在压力作用下的弯曲变形,采用双向流固耦合模型,分析了顶层箔片的变形与压力场之间的相互作用,结合薄板弯曲模型得出的轴承顶层箔片的变形和气膜间隙分布,分析了轴承数、箔片结构对轴承性能的影响。研究结果表明:支承结构位置不当会直接影响气膜压力的分布,造成承载能力下降;提高轴承数、增大进出口气膜间隙比和轴承内外径之比,可以提高轴承的承载性能;节距比为0.5时承载性能最佳。该结果可为鼓泡弹性箔片动压止推气体轴承的结构设计提供参考。     

推力空气箔片轴承新型结构构建及其动力学性能

提出一种新型推力箔片轴承，该轴承的优点是通过波箔和平箔的组合来改变箔片轴承的轴向刚度等动态特性。以新型推力箔片轴承为对象，运用弹性力学理论分析推力箔片轴承顶箔和波箔的变形，联立黏温方程、气膜三维能量方程和等温Reynolds方程得到非等温Reynolds方程。利用小扰动法处理非等温Reynolds方程得到气膜压力的定常控制方程和微分控制方程。运用有限差分法和逐点松弛迭代法对其进行数值求解得到推力箔片轴承的气膜压力分布、气膜厚度分布、箔片变形量分布、气膜温度分布、轴向刚度、轴向阻尼等特性参数。结果表明，箔片轴承的轴向刚度和轴向阻尼随着波拱半长、楔形间隙高度差、波拱半径的增加而减小；轴向刚度和轴向阻尼随着涡动频率比、转速、波箔厚度、顶箔厚度、轴承外径的增加而增大。     

箔片安装位置对气体轴承性能影响的仿真分析

为研究弹性箔片气体轴承中箔片安装位置对轴承静、动态性能的影响,对具有不同箔片安装位置角的弹性箔片气体轴承进行了静、动态性能的计算。采用有限差分法耦合气体轴承压力控制方程及箔片柔度方程,获得了气膜压力、厚度分布及轴承承载力;基于小扰动法,计算了轴承的动力学系数。结果表明:弹性箔片气体轴承安装箔片时存在一个"敏感"位置区间,会对轴承静、动态性能构成显著影响;在这一区间内,气膜平均气压及承载力显著下降,主刚度系数下降,交叉刚度系数会在数值上接近主刚度系数,严重影响轴承稳定性,阻尼系数变化相对较小;这一"敏感"位置区间在数值上与轴承偏位角形成近似互补关系;在进行弹性箔片气体轴承实际安装操作时,可以先进行360°整周箔片轴承的偏位角计算,将安装狭槽布置在偏位角的对侧,即远离主要承载区位置。     

平箔式箔片径向气体轴承的理论研究

分析了平箔式箔片径向轴承的结构刚度和结构阻尼 ,对箔片在气膜发散区脱离弹性基础的情况进行了具体讨论 .求解了箔片轴承静态特性 ,重点讨论了箔片轴承与刚性轴承的不同之处 .     

新型三瓣式径向气体箔片动压轴承热特性分析

为研究新型三瓣式径向气体箔片动压轴承的温度特性，提出了考虑热特性的润滑理论计算模型. 通过耦合求解非等温Reynolds方程和气膜能量方程，并计入转子的离心效应和热膨胀量对轴承间隙的影响，运用数值模拟的方法求解出轴承内气膜温度分布，研究轴承载荷、转速和冷却气流量等因素对轴承温度的影响. 计算结果表明：气膜温度峰值位于压力峰值的下游位置；气膜温度随轴承载荷和转子转速的增加而递增，相较于转速对气膜温度的影响，轴承载荷的影响并不明显；往轴承箔片结构内通入冷却气流可以起到明显的降温效果，且轴承温度随冷却气流的上升先迅速下降后逐渐平缓.     

箔片非线性结构刚度对转子瞬态冲击的影响

弹性箔片轴承支承的转子在高速旋转时,转子可能会和轴承发生碰摩。为了揭示当转子采用不同结构刚度箔片支承时,该冲击对转子振动的影响机理,针对2个径向GFBs支承的刚性转子系统模型,应用龙格库塔法求解转子动力学状态方程,获得3种结构刚度箔片(均匀刚度箔片、软箔片、硬箔片)下的轴颈位移。推导出箔片轴承的等效刚度和等效阻尼系数,发现当轴颈无涡动时,箔片轴承的等效刚度正好是气膜刚度和箔片结构刚度的串联;而当轴颈有涡动时,箔片轴承的等效刚度和等效阻尼均是结构刚度、结构阻尼和涡动频率的函数,且当轴颈涡动频率趋于无穷大时,上述等效刚度和等效阻尼趋于无涡动时的值。计算表明,当采用恒定刚度箔片时,转子稳态振幅最小,但是瞬态响应时间较长;当采用非线性软箔片时,转子稳态振幅最大,但是瞬态响应时间最短。当增大非线性箔片的结构刚度时,转子稳态振幅会减小,瞬态响应时间会增加。因此,箔片的设计需要辅以轴承-转子动力学特性的考量,以获得箔片结构刚度和结构阻尼的合理匹配。     

新型弹性箔片动压气体止推轴承的理论研究

对新开发的弹性箔片动压气体止推轴承进行了理论分析,采用等温气体模型,导出求解该轴承静态特性的弹性流体动力润滑方程,利用有限元方法对方程进行求解,得到了该轴承在流固耦合下的压力分布和间隙分布,以及结构参数对轴承性能的影响.数值计算结果表明:节距比和瓦块张角存在最佳取值,节距比取0.5,瓦块张角为70°~90°时,可得到理论上的最大无量纲承载力;弹性模量越大,无量纲承载力随着间隙比和轴承数的增加而增大的趋势就越明显;选择合适的结构和材料,可以得到较高的承载力,这将进一步扩大该轴承的应用范围.     

弹性箔片轴承的气弹润滑解

通过引入柔性箔片的静、动变形以及联立求解气体润滑Reynolds方程和弹性箔片轴承的静、动变形方程，给出了弹性箔片空气动压轴承的完全气弹润滑耦合解，完全气弹润滑解不仅适用于箔片轴承的静态性能分析，同样也适用于动态刚度和阻尼的计算，从而为弹性箔片空气动压轴承静、动态性能分析和相应转子系统动力学行为预测提供了系统的理论与分析方法．     

多层弹性支承箔片动压气体径向轴承稳定性的实验研究

为了保证轴承支承高速转子的稳定运行,提出了一种具有多层弹性支承结构的新型箔片动压气体轴承。该轴承采用两层或多层具有鼓泡状凸起阵列的金属箔片作为弹性支承结构,通过调整鼓泡阵列的周向和轴向截距或调整上下层弹性箔片布置,可以实现轴承支承刚度特性和阻尼特性的调节。在直径为25mm主轴的高速(10万r/min)透平膨胀机上,实验研究了这种箔片轴承支承高速转子的运转特性,详细分析了3种典型排列方式下转速与压力的关系,以及高速转子升速及降速特性。结果表明:采用不同的多层结构排列方式,可以有效调整和改善弹性箔片轴承支承高速透平转子的刚度和阻尼特性,抑制高速转子的不稳定涡动;多层弹性箔片轴承能够产生多重刚度及多重阻尼,从而改进了传统箔片轴承刚度和阻尼的影响,改善了弹性箔片动压气体轴承的稳定性和可靠性。     

拱箔成型工艺对箔片轴承性能影响的仿真分析

为研究不同拱箔成型工艺对弹性箔片气体轴承静、动态性能的影响,对理想拱箔及3种不同成型工艺加工出的拱箔支承的箔片轴承进行了静、动态性能的计算,3种工艺重点对比箔片固定方式及加载卸载速度。采用有限元方法,获得了不同成型工艺下拱箔的型线及厚度分布;采用有限差分法,耦合箔片轴承结构变形方程与压力控制方程,通过积分得到了轴承承载力;使用小扰动法计算了箔片轴承刚度系数及阻尼系数。分析结果表明:拱箔的成型工艺会对箔片轴承静、动态性能构成一定影响,相比于理想拱箔,各种拱箔成型工艺均会造成箔片性能的下降;厚度与型线更为均匀的拱箔支承的箔片轴承承载力更高、稳定性更强;在拱箔冷压成型过程中,箔片固定方式对拱箔性能的影响较大,加载及卸载速度对拱箔性能的影响较小;在实际生产过程中,建议的拱箔冷压成型工艺为箔片一端压边固定一端自由,采用适中的加载及卸载速度。     

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

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