高雷诺数下双圆柱绕流诱发振动的数值模拟

基于表面涡方法研究了不同间隙比及归一化阻尼参数下,串列和并列双圆柱的流体诱导振动问题,并计算了圆柱的振动响应、流体力、振动频率等.结果表明:圆柱为刚性时的计算模拟结果与相关文献的实验结果吻合良好;在文中的研究条件下,串列双弹性圆柱具有屏蔽流的特征,涡脱落频率比刚性圆柱的大,其值主要取决于归一化阻尼而非间隙比;流体从并列双弹性圆柱分离的涡是对称的,与并列双刚性圆柱相比其平均力系数略小,但由于流体诱导振动造成的脉动力系数较大,故流体诱导振动对并列圆柱的动态响应有重要的影响.研究结果为亚临界雷诺数范围内热交换器管束的复杂流体诱导振动等问题提供了一种可能的计算方法.     

单列圆柱流体诱导振动数值模拟研究

基于表面涡方法和流固耦合模型,研究了雷诺数为2.67×104时的单列圆柱流体诱导振动问题,并计算了涡云图、流体力、振动响应、涡脱落频率等.计算模拟结果很好地重现了刚性单列圆柱在小间隙比(1.5)下以宽、窄尾涡交替和多频为特征的非均匀流态,以及间隙比为2.0时的涡脱落现象.此外,还研究了单列自由振动的弹性圆柱在间隙比为2.0时的流体诱导振动问题,结果表明:在大振幅条件下,流体诱导力在x方向和y方向有较强烈的耦合;随着振幅的减小,x方向振动对y方向振动的影响可以忽略,可采用单自由度的动力学模型假设进行计算.     

水流作用下圆柱体的涡激振动分析

以弹性支承的刚性圆柱体为研究对象,把流体对结构的作用力分成升力FL和流体反力FR两部分,建立了一种分析圆柱体涡激振动的方法。该方法把结构振动的微分方程转化为振幅与频率的代数方程,并给出了流体力系数的经验公式。实例计算表明,圆柱体的涡激振动主要受无量纲参数折算速度的控制,一般在折算速度Vr为4.0—9.0时,发生频率的锁定现象。该方法是预测圆柱体涡激振动的一种实用方法。     

汽车悬架减振器绕流涡旋动态特性分析

为了麦弗逊悬架运动造成其翼子板内流场特性多变的问题。通过将该问题简化为绕流圆柱平面流场,首先利用 SST方程对静态的圆柱绕流体模型进行理论计算和仿真,获得了稳定涡旋下的升力、阻力系数及斯特劳哈尔数等特征值。在此基础上,分析空气流速、减振器直径、横向振动频率和振幅等结构和动力学参数对涡旋动态特性的影响,获得了平均升力系数和瞬时阻力系数曲线的拟合方程。结果表明,斯特劳哈尔数的最大误差为5%,简化模型忽略减振器结构的三维效应是可以接受的;脱涡频率与减振器直径的倒数成二次关系;横向振动频率则对动态脱涡频率起到了关键作用,且对流场的压力分布影响显著,而横向振幅对无边界流场条件下的涡旋特性及压力场分布影响不大。     

流体横掠波状圆柱的动特性研究

提出了一种可减小流体诱导振动的波状圆柱,并对3种不同表面倾斜度的波状圆柱进行了实验研究.实验在一低速风洞进行,工作段的横截面尺寸为0.6 m×0.6 m,湍流度小于0.2%,雷诺数在2.0×104到5.0×104范围内.实验结果表明:波状圆柱与普通圆柱相比其脉动升力系数较小,具有减小流体诱导振动的作用;流体绕波状圆柱流动的斯德鲁哈尔数等于绕普通圆柱流动的斯德鲁哈尔数,说明波状圆柱的减振并不是通过改变其斯德鲁哈尔周期来实现的.     

剪切来流作用下圆柱体结构物的双自由度流致振动

基于四步半隐式特征线分裂算子稳定化流体有限元方法,对二维线性剪切来流作用下弹性支撑圆柱体结构物双自由度流致振动问题进行了数值计算,着重研究雷诺数Re=150时,不同参数(频率比、剪切率与折减速度)对圆柱体结构物振动响应及其流场的影响.计算分析表明,随剪切率的增加,圆柱体结构物2个方向的频率锁定区间扩大,结构发生共振现象的范围亦增大;折减速度对圆柱钝体最大振动幅度的影响较大,在锁定区间内,圆柱振动位移较大,否则较小;在高频率比工况下圆柱运动轨迹呈‘8’字形;当频率较低时,圆柱运动轨迹随剪切率的增大由‘8’字形渐变为‘雨滴’形;在剪切来流作用下圆柱尾流模态为双单涡(2S)与涡对(P)+单涡(S)两种泄涡模式.     

基于梁刚体元模型的圆柱风致响应耦合分析

基于梁刚体元方法提出了圆柱风致响应分析的近似模型,通过计算流体动力学(CFD)求解器FLUENT及其动网格方法求解流体方程,实现了结构与流体的流固弱耦合分析,并利用精细积分法提高了结构的动力分析效率.针对梁刚体元近似模型、刚性模型与弹性模型,比较了不同风速下三维圆柱结构的顶部位移与加速度响应.结果表明,随着风速的增大,结构横向振动幅值呈非线性增加;不考虑耦合作用的刚性模型计算结果误差较大.     

基于本征正交分解和动态模态分解的尾涡激振现象瞬态过程的模态分析

尾涡激振是气动弹性领域的一种常见现象,在上游尾迹的气动激励下会导致流场中结构的强迫振动,该现象会危及被激励结构的完整性和疲劳寿命.本文使用圆柱/叶片的近似模型研究尾涡激振问题.该模型中的圆柱位于上游均匀来流,能够产生特定频率的卡门涡街;叶片位于流场下游,受到圆柱尾迹所施加的持续脉动激励,产生强迫振动.针对尾涡激励的近似模型,通过基于Fluent的二维数值计算,模拟了上游圆柱的脱落涡以及叶片从固定到以本身自然频率振动的瞬态过程,从而提供了流场变化过程的详细信息.基于非定常瞬态结果,采用本征正交分解(POD)和动态模态分解(DMD)分析方法,通过分解与重构叶片附近流场的压力场,提取模态频率及其变化过程,得到了尾涡激振现象的主要流动特征.通过对比两种模态分析结果发现,POD重构在残差处理方面有较大的优势,而DMD在单一频率模态的提取以及变化情况的分析方面更有优势.     

运用修正剪应力输运湍流模型模拟双自由度涡激振动

针对低质量比圆柱双自由度涡激振动振幅响应的数值模拟结果小于实验值的问题,基于OpenFOAM开源软件,对标准剪应力输运(SST)湍流模型以及数值模拟方法进行了修正,并通过圆柱绕流算例进行验证.运用扫频法,对约化速度为2~14,质量比m~*=2.6的圆柱双自由度涡激振动进行了数值模拟,并对结果进行了详细的分析与对比.结果表明,与标准SST模型的结果相比,采用修正SST模型的数值模拟结果与实验数据更为接近,运用扫频法能更好地体现涡激振动的非线性特性.文中提出的修正模型可以应用于海洋立管涡激振动的预报.     

脉动流条件下的圆柱绕流特性研究

为探究脉动流对流体绕流结构物产生的影响,采用数值方法研究了脉动流条件下圆柱绕流场特性,对涡量分布、升阻力系数、升力系数频谱特性等进行分析。结果表明:脉动流作用会使圆柱尾涡剪切层变薄,提高脉动频率使尾涡长度变短、脱离加快,提高无量纲脉动振幅使主导涡的脱落速度降低,使旋涡生成区域更靠近圆柱表面;脉动频率与无量纲脉动振幅的增大使升力系数、阻力系数的振幅均增大,而且与升力系数相比,阻力系数的振幅更大,变化更快;升力系数频谱图存在多个主频,包括旋涡脱落频率和相位叠加频率,其中旋涡脱落频率的振幅随着脉动频率的增加而减小,随着无量纲脉动振幅的增加而增加。在流场中加入脉动流,可以增强流体振动促进流动混合。     

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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