无阻尼高速列车板结构声辐射特性研究

基于有限元方法结合声学分析软件Virtual.Lab Acoustic建立高速列车铝型材外地板加筋板结构分析模型,完成了外地板结构模态振动特性和板结构声辐射特性分析。重点研究无阻尼条件下边界条件、面板厚度和激励位置对外地板结构模态振动特性和声辐射特性的影响。研究结果表明:板结构加筋后其刚性显著增强;外地板结构边界条件变化对板结构振动声辐射特性影响较小,后续计算采取两端面简支约束;面板厚度增加,刚性增强,使结构截止频率向高频移动,使得外地板结构声辐射能力减弱;激励位置远离板结构中心时,也能够有效减弱外地板结构声辐射能力,可考虑实行区域化划分安装。     

加筋位置对铝型材板振动声辐射特性的影响分析

以高速列车的内部带三角形空腔的四边固支铝型材外地板为研究对象,采用有限元方法对其进行结构振动特性和声辐射特性研究。重点探究了结构在20 Hz~800 Hz的中低频区域内,不同加筋位置对板结构振动声辐射特性和隔声量的影响。研究结果表明:在中低频范围内,铝型材板加筋后,其辐射声压和声功率能得到很好的抑制效果,在下底板加筋时的抑制效果最为明显,其声学性能最;加筋对铝型材板结构隔声量的影响不明显。     

湍流激励下橡胶贴敷声呐罩自噪声抑制机制

基于湍流边界层脉动压力功率谱模型、正交周期加筋板弯曲运动、声波和固体波动及随机振动理论,建立了湍流边界层激励下声呐罩壳板自噪声的计算模型.研究发现:橡胶层主要依靠横波传播截止效应抑制湍流脉动压力水动力学成分所致的壳板自噪声,降噪量高低与厚度模态有关,同时可以保持声波高透射.随着声呐罩外贴的橡胶横波波速减小或阻尼因子增大,橡胶贴敷声呐罩对湍流脉动压力的降噪效果明显.正交周期加筋板的板格尺寸改变,比如流向肋骨或展向肋骨间距较小,会使壳板振动加速度自功率谱共振峰频率向高频移动,但是壳板振动加速度或壳板内侧声压自功率谱整体幅值基本不变.     

敷设阻尼层的有限长加筋板声振性能研究

以有限长加筋板和敷设阻尼加筋板为对象,通过模型试验分析了单频激励和白噪声激励下的加筋板在空气中、水中的振动和声辐射,针对计算模型开展相应的数值分析.结果表明：加筋板敷设阻尼层后,结构的振速级峰值左移.阻尼层在整个频带体现出较好的抑振降噪效果,但在低频区降噪效果不明显,甚至在局部频点出现失效区.在同等激励条件下,其辐射声压级普遍降低.数值分析进一步验证阻尼层对抑制振动与声辐射非常有效.     

非阻塞性颗粒阻尼器内部的颗粒莱顿弗罗斯特现象

为了更好地揭示非阻塞性颗粒阻尼器(NOPD)的减振机理,基于振动颗粒物质的流变特性,研究了NOPD的阻尼效果和其内部阻尼颗粒运动形态之间的关系,通过实验确定了NOPD发挥最优阻尼效果时其内部颗粒的运动形态,使用离散元仿真分析了最优阻尼颗粒的耗散特性。研究表明:实验设计参数下的NOPD发挥最优阻尼效果时(激振强度Γ=3.3,f=21 Hz),其内部出现稳定的颗粒莱顿弗罗斯特现象;这种状态下的NOPD最优阻尼效果主要来自两方面,一方面是主系统的部分振动动能通过颗粒间或颗粒与容器壁间发生的碰撞和摩擦以热能的形式散发,是颗粒对主系统振动能量的直接耗散;另一方面是主系统的部分振动动能转化为浮动颗粒的势能以维持颗粒莱顿弗罗斯特效应的稳定,这可看作是颗粒对主系统振动能量的间接耗散。     

梁-阶梯板耦合结构的功率流

当板的厚度较大和变化时，如厚板或阶梯类的板，这时板的剪切、转动惯量及板的面内运动，将对板结构的振动功率流产生影响。基于功率流的分析方法和梁、板动力学的原理，推导了梁一阶梯板耦合结构的功率流表达式。计算和测量结果表明：振动频率较低时，板厚比增大使得从梁传递到阶梯板的功率流减小；振动频率较高时，梁－阶梯板结构的传递功率流小于梁－薄板结构的传递功率流。在这类板结构功率流估计中应注意这些差异，否则将引起功率流估计的误差。     

基于面内充气筋的悬臂结构振动控制实验研究

提出一种基于充气加筋技术的振动半主动控制方法。充气筋易于折叠,其刚度随充气压力变化,为空间可展开柔性结构的振动控制提供了一种新的变结构控制手段。设计制作了2块板厚分别为5 mm和1 mm的柔性悬臂板作为被控主结构。针对每1个柔性悬臂板模型,分别设计制作了面内充气加筋装置,开展了相应的振动试验研究。试验结果验证了利用充气加筋方案进行柔性结构振动控制可行性。面内充气筋对悬臂板结构的高阶振动模态影响大于低阶模态,在附加刚度匹配适当的条件下,可有效抑制正弦激励所激发的高频模态振动,但难以抑制悬臂板结构受瞬态激励所激起的自由衰减振动。     

正交异性薄板的振动能量传递特性

为了解决正交异性薄板的中高频振动问题,引入结构声强概念研究其振动能量传递特性。首先,对正交异性薄板能量密度控制方程进行有限元离散处理,推导出能量有限元方程,并且通过数值算例将其与经典模态法对比,计算结果验证了方程的正确性;然后,求解能量有限元方程得到结构声强场,同时以流线可视化方式更直观地呈现结构振动能量传递特性;最后,应用该方法分析了不同局部阻尼分布位置对正交异性薄板的振动能量传递特性的影响。分析结果表明:正交异性材料属性使振动能量优先沿着弯曲刚度较小方向流动;值得注意的是,局部阻尼分布在很大程度上决定了振动能量分布以及流向,研究对工程振动特性分析以及阻尼位置优化有一定的指导意义。     

带框架肋骨圆柱壳振动特性分析

基于Flügge壳体理论,采用波动法建立带框架肋骨加筋圆柱壳数学模型,对其自由振动特性和频响特性进行研究.相比于传统的采用梁模型或平摊法处理环肋,采用圆环板模型研究任意尺寸的环肋.根据肋骨、激励力位置对圆柱壳离散并将激励力作为边界条件处理,对离散子构件运用不同理论分析后通过连续条件组装所有子构件得到运动方程.与有限元结果对比验证本文方法的正确性,在此基础上分析不同惯性矩的框架肋骨对圆柱壳振动特性影响.结果表明:框架肋骨惯性矩高于普通肋骨2倍便影响圆柱壳振动特性,高于512倍时则与舱壁作用相同.     

基于声辐射模态的板加筋位置优化

为了降低筋板结构振动辐射噪声,提出了两种加筋位置优化模型。一种采用遗传算法直接搜索辐射声功率最小时的加筋分布;另一种取声辐射模态的辐射效率作为优化各阶声功率的加筋数权重,然后采用遗传算法逐阶搜索声辐射模态的声功率最小时的加筋分布。对一典型板结构,使用这两种优化模型进行加筋位置优化的数值计算。计算结果表明了两种优化模型的有效性;并分析了加筋位置对各阶声辐射模态的声功率的影响。在加筋位置优化的基础上,采用声功率灵敏度进一步优化了筋的结构参数。     

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.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

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     

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