移动荷载列作用下多层梁系统的动力响应分析

为研究多层梁系统在任意移动荷载列作用下的动力响应,基于有限傅里叶变换,提出一种求解移动荷载列作用下多层梁系统动力响应的解析计算方法.利用本研究的解析计算方法分析了梁的抗弯刚度、层间阻尼及层间刚度对一跨长32 m的梁-轨系统动力响应的影响,分析结果表明:改变轨道抗弯刚度、层间刚度或层间阻尼对主梁跨中动力响应的影响可以忽略;随着轨道抗弯刚度、层间刚度或层间阻尼的增大,轨道的跨中动力响应都缓慢减小;随着主梁抗弯刚度的增大,轨道及主梁的跨中动力响应均显著减小.     

双层弹性支承梁的有限元分析

用有限单元法分析了双层弹性支承梁的静力响应.双层弹性支承梁结构由二种平行的梁(上层梁和下层梁)、上层梁和下层梁之间的离散弹簧和下层梁下部的Winkler基础组成.上层长梁、下层短梁、离散弹簧、Winkler基础和作用在上层梁上的荷载视为一个系统,并将该系统进行有限单元离散,梁单元的弯曲形函数采用Hermitian 3次方插值函数,利用变分原理及形成矩阵的"对号入座"法则建立该系统有限单元形式的平衡方程.阐明了单元刚度矩阵以及在上层梁单元作用竖向集中荷载或分布荷载下单元节点荷载列阵的形成.举例说明了该方法的应用,为类似结构的力学分析提供了一种数值方法.图5,参13.     

简谐移动荷载作用下饱和土地基上无限长梁的动力响应

根据Biot理论及Euler-Bernoulli理论,建立饱和土体地基上的无限长梁受简谐移动荷载作用模型;由梁-土体系的变形协调条件,推导梁-土体系的等效刚度;由Fourier变换得到时间-空间域的梁-土体动力响应;分析荷载速度、频率、饱和土体的参数对梁-土体系的影响。研究结果表明:当荷载在某一低频时,随着荷载速度增大,梁的最大竖向变形、弯矩也增大,而当移动荷载的频率较高时,荷载速度对梁的变形及内力的影响较小;对于饱和土体地基上的无限长梁,当荷载速度超过土体剪切波速时,梁仍然存在一系列其他模态所对应的关键速度,此时,梁有最大变形出现。     

轨下基础参数对钢轨动力响应的影响

以钢轨动力响应周期解析法为理论基础,采用双层弹簧阻尼支承的Timoshenko梁为轨道的力学模型,从时域和频域两方面计算分析了钢轨垫层刚度、轨枕质量、轨枕垫层刚度、钢轨垫层阻尼、轨枕垫层阻尼及轨枕间距对钢轨点动力响应的影响.随着钢轨垫层刚度和轨枕垫层刚度的减小,钢轨的振动响应增大;随着轨枕质量的增大,钢轨的振动响应减小;随着轨枕间距的减小,大部分频段内的振动响应减小,小频段内的振动响应值增加;钢轨垫层阻尼、轨枕垫层阻尼对钢轨的振动响应基本不产生影响.     

直逆向过岔列车与桥上道岔耦合振动影响因素分析

针对桥上无缝道岔,运用有限单元法,建立钢轨一岔枕一桥梁弹簧一阻尼空间振动模型;运用弹性系统动力学总势能不变值原理及形成矩阵的"对号入座"法则建立列车一道岔一桥梁空间振动方程组;以温福客运专线田螺大桥为例,拟定桥上铺设了由2组38号道岔组成的单渡线,分析直逆向过岔时,列车运行速度、轨下垂向刚度、枕下垂向均布刚度、岔区垂向不平顺幅值及梁体高度等参数对列车一道岔一桥梁系统耦合振动的影响.研究结果表明:系统响应随列车速度和岔区垂向不平顺幅值增大、梁体高度减小而增加;轨下垂向刚度对系统不同的响应有不同的影响;道岔响应随枕下垂向均布刚度增大而降低.     

考虑支座失效的基础隔震结构振动台试验研究

为研究隔震结构在多向动力耦合激励下的动力响应和荷载传递路径,进行了一个缩尺比例为1∶4的三层平面不规则RC隔震框架结构振动台试验. 通过研究结构的加速度响应、位移响应、隔震支座内力响应、损伤跨梁混凝土和钢筋应变等,揭示了多向动力耦合激励下的抗倒塌性能. 进一步利用OpenSees有限元软件,分析了损伤跨梁内力和支座损伤指数分布规律. 研究结果表明：在双向水平地震和单个隔震支座突然失效引起的竖向不平衡荷载耦合激励下,失效点位置处结构的竖向动力响应显著增大,并发生明显的竖向变形;支座瞬时失效产生的动力效应对各支座内力均有影响,特别是对相邻支座的内力影响更加明显;支座瞬时失效产生的竖向不平衡荷载由空腹效应和梁端弯矩共同抵抗;支座瞬时失效对相邻支座损伤指数影响最大;在多向动力耦合激励下失效区域的动力响应比仅考虑竖向不平衡荷载下更显著,隔震层损伤指数分布相比地震单独作用下更加离散.     

考虑水平摩阻效应的交通荷载下路面沉降分析

为分析计算高速公路水泥混凝土路面承载结构在交通荷载作用下的沉降,将路面结构视为黏弹性地基梁.在Kelvin地基梁模型的基础上,考虑路面结构与路基土界面摩阻效应的影响,进而分析交通荷载下黏弹性地基有限长梁的瞬态问题,通过三角级数展开法和Laplace-Fourier积分变换以及逆变换得到黏弹性地基梁在半正弦波荷载作用下的位移解析解.并研究分析了路基路面摩阻效应、荷载移动速度、路面结构刚度、路基竖向反力系数、路基阻尼等因素对路面沉降的影响.分析结果表明:路面沉降随车辆移动速度的增大而减小,随路基黏滞阻力系数及路基刚度的增大而减小,随路面结构刚度及结构层高度的增大而减小,与此同时增大路面结构刚度还可减小路面的波动.     

混凝土折板式拟球面网壳的弹性稳定分析

混凝土折板式拟球面网壳是通过在球面上切割平面后再网格化而成,结构由密肋平板在脊线处交汇组成,本文采用有限元方法分析其弹性稳定性能,并讨论主脊线、副脊线、密肋梁、支座环梁等的抗弯刚度以及矢跨比、屋面板厚度等因素对其临界荷载的影响。结果表明:结构的低阶失稳模态关于主脊线对称,靠近支座环梁的密肋平板刚度相对较弱;矢跨比是影响结构临界荷载的重要因素,且不宜低于1/8;主脊线是结构低阶失稳模态的节线,其抗弯刚度对结构临界荷载的影响较小;提高副脊线的抗弯刚度可以有效增大结构的临界荷载;支座环梁抗弯刚度的增加对临界荷载的影响较小,其截面高度可按自身跨度的1/12;密肋梁的抗弯刚度对结构临界荷载的影响较大,提高密肋梁的截面高度有利于增强结构抵抗失稳的能力;屋面板的厚度改变对结构临界荷载的影响较小。     

双向隔震铁路桥梁与列车的耦合振动响应研究

为了研究铅芯橡胶双向隔震铁路桥梁在列车荷载作用下的动力性能,本文首先建立一座三跨隔震桥梁三维模型,然后对双向隔震铁路桥梁和列车组成的车桥系统耦合振动进行分析,研究其机理.结果表明,隔震桥梁在横桥向的隔震周期越大,桥梁梁体在列车荷载作用下横桥向位移越大,支座阻尼对桥梁梁体横桥向水平振动的衰减作用更加明显,对桥梁上部结构扭转角和竖向位移的影响可以忽略不计.桥梁横桥向的隔震周期的增大,使车体横摆、侧滚振动位移响应更加剧烈,对车体各个自由度的加速度响应影响可以忽略不计;隔震支座阻尼的增大对车体横摆、侧滚角、摇头角、沉浮和点头角位移响应以及对车体各自由度的加速度响应影响较小.     

下肋U型钢-混凝土组合空腹夹层板的动力特性分析

为了解下肋为混凝土外包U型钢的组合空腹夹层板的动力特性,将下肋U型钢按轴向刚度等效为混凝土,采用8节点弹性块体单元应用子空间迭代法求解自振方程计算了50个算例。结果表明:组合空腹夹层板的频率具有密集分布特点,振型与相同支承条件的实心平板类似;支承梁刚度增大有利于提高结构基频,但梁截面高度不宜大于跨度的1/14;基频随楼盖高跨比的提高而增大,结构高跨比可采用1/25~1/20;过大的肋刚度将使结构基频降低,因此肋截面高度可按网格尺寸的1/14~1/8采用;增大下肋U型钢的厚度对提高结构基频是有利的;过小的网格划分频数将降低结构整体刚度,网格长度不宜超过2.5 m;支承条件明显影响楼盖的动力特性,振动舒适度分析时应计及支座刚度影响,提高支座刚度是增大楼盖基频的有效措施。     

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     

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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Brief Introduction to “Journal of Jilin University( Science Edition) ”

<正>"Journal of Jilin University(Science Edition)"is a comprehensive academic journal in the fields of science sponsored by Jilin University and administrated by the Ministry of Education of the Peoples Republic of China.The journal started publication in 1955.The original name at starting publication was"Journal of Natural Science of Northeast People University",which was changed into"Acta Scientiarum Naturalium Universitatis Jilinensis"in 1958 owing to the name change of the university.The present journal name has