部分埋入水中椭圆柱体弯曲自由振动

本文研究了部分埋入水中椭圆柱体弯曲自由振动.首次给出柱水耦联体系振型函数的精确解和以有限阶行列式表示的频率方程.指出水的效应等价于一个附加的分布质量,因此,水中柱体的振动频率低于无水时柱体的振动频率.     

计及液面波动和液体可压缩性时部分潜入水中椭圆柱体的扭转振动

本文研究部分潜入水中椭圆柱体的扭转振动问题,同时计及了液面波动和液体可压缩性对椭圆柱体扭转振动的影响。利用马休(Mathieu)级数以及一组广义三角级数的正交完备性,导出了柱水耦联扭振振型函数和频率方程的精确解析解,可利用非线性代数方程的求根方法,数值解出各阶频率参数。     

部分潜入水中椭圆柱体振动分析*

本文在文献[1]的基础上,提出一种研究部分潜入水中椭圆柱体弯曲振动的解析法,并指出文献[2]的不足之处.作为特例,本文计算了考虑水体可压缩影响时的水中圆柱体的自振频率,给出了可压缩性影响范围.     

气-液横向流动下悬臂柱体结构涡激振动机理研究北大核心CSCD

针对潜艇侦查望远镜举升水面时产生的涡激振动现象,该文建立了悬臂柱体结构受气-液两种不同横向流作用下的涡激振动理论模型.研究了两种流体不同的分布比和密度比对柱体结构涡激振动行为的影响规律.基于Galerkin法和Runge-Kutta法,得到了柱体结构涡激振动响应的数值结果.研究表明,柱体结构的涡激振动锁频区随着流体分布比的增大而增大,自由端最大幅值随着流体分布比的增大先增大后减小.当分布比为0.5附近时,振幅出现极大值,该极大值随着流体密度比的减小呈现明显的增大趋势.此外,柱体的动力学行为随着流体分布比的变化呈现出周期和多周期等振动模式.该研究可为潜艇侦查望远镜结构的设计与分析提供理论指导意义.     

贮液圆筒在水中的弯曲自由振动

本文研究了贮液圆筒在水中的弯曲自由振动问题,液体和水的深度均可任意,导出了水中贮液圆筒的振型函数及固有频率的精确计算公式,结果可由计算机解出.分析表明,液体和水对简体振动的影响各自等效一附着于筒体的广义分布质量.     

一类非线性偏差分方程组的频率振动性

应用频率测度法,讨论了一类非线性偏差分方程组的频率振动性,得到了此类方程组频率振动的全新判别准则.最后给出例子对主要结果进行说明.     

Stokes流动中的Phragmén-Lindelf型及其连续相关性的结果

就三维半无限柱体上的Stokes流动,研究边端效应的渐近性质.柱体水平面上的速度满足均匀的Dirichlet条件时,发现问题的解,随柱体有限端的距离,或呈指数增长,或呈指数衰减.最后讨论了方程参数的摄动影响.     

Stokes 流动中的 Phragmén-Lindel(o)f型及其连续相关性的结果

就三维半无限柱体上的Stokes流动,研究边端效应的渐近性质.柱体水平面上的速度满足均匀的Dirichlet条件时,发现问题的解,随柱体有限端的距离,或呈指数增长,或呈指数衰减.最后讨论了方程参数的摄动影响.     

流体力学中的Kelvin-Voigt流体在柱体上的距离效应

考虑了通过半无穷柱体的Kelvin-Voigt流体,其中Kelvin-Voigt流体在柱体的侧面上满足齐次边界条件.利用能量估计和先验估计的方法,证明了应变能随距柱体有限端的距离指数式衰减性质.这种类型的结果可看作Saint-Venant原理型的“距离效应”.     

Experimental Study on the Vortex-Induced Vibration of Fixed-Hinged Flexible Risers北大核心CSCD

海洋立管顶部常铰接于浮式平台下方,在海流激励下存在涡激振动响应,潜在疲劳失效的风险.该文采用非介入光学测试方法（高速摄像）,对布置于循环水槽中顶部铰接-底部固定的悬链线柔性立管进行了振动响应研究.实验结果表明,立管三个方向被激发的振动模态阶数与主导振动频率均随约化速度的增加而逐渐升高,平面外的最大均方根振幅在模态过渡时有先降后升的变化,与振动模态分支相呼应.流体与立管之间能量传递在不同方向的分布存在一定差异,导致不同步的模态过渡现象.平面内振动存在与平面外振动主导频率吻合的频率,根据其是否主导对应管段的平面内振动,将其分为强耦合和弱耦合两种模式.     

Nonlinear low frequency water waves in a cylindrical shell subjected to high frequency excitations – Part I: Experimental study

This paper presents an experimental investigation on nonlinear low frequency gravity water waves in a partially filled cylindrical shell subjected to high frequency horizontal excitations. The characteristics of natural frequencies and mode shapes of the water–shell coupled system are discussed. The boundaries for onset of gravity waves are measured and plotted by curves of critical excitation force magnitude with respect to excitation frequency. For nonlinear water waves, the time history signals and their spectrums of motion on both water surface and shell are recorded. The shapes of water surface are also measured using scanning laser vibrometer. In particular, the phenomenon of transitions between different gravity wave patterns is observed and expressed by the waterfall graphs. These results exhibit pronounced nonlinear properties of shell–fluid coupled system.     

Free vibration of the fluid-filled single-walled carbon nanotube based on a double shell-potential flow model

A double shell-potential flow model is developed to study the free vibration of single-walled carbon nanotube (SWCNT) conveying water. Water is divided into the absorbed layer of water molecules and the water flow in the center of the SWCNT. The SWCNT and the internally absorbed layer of water are modelled as two-layer thin shells coupled via the interlayer van der Waals (vdW) interaction. It is shown that the vdW interaction is responsible for an upshift in the frequency of the SWCNT and an improvement of the system stability. Results also reveal that the internal moving water plays an important role in the instability of system whereas it has very little influence on the dynamic characteristics of the SWCNT. It is hoped that the paper can provide a new and efficient approach for the study of the general dynamic behavior of fluid-filled nanodevices.     

基于数值分析的动水效应对连续刚构桥抗震性能影响

为了研究不同水深下,动水效应对连续刚构桥抗震性能的影响,基于一实际工程,利用有限元软件Midas建立全桥模型,采用反应谱数值分析法,并考虑桩土的相互作用,研究了动水效应对连续刚构桥抗震性能的影响.结果表明:考虑动水效应将会减小结构的频率,且高阶频率对动水效应更加敏感;另外,动水效应将会放大结构的地震响应,随着水深的增加,地震响应的增大幅度也越大.当水深达到20m以上时,动水效应将使结构的内力增大约10%,此时在抗震设计中应重点考虑动水效应的影响.     

天津高村井水位主要周期成分的干扰因素及特征分析

以天津高村井水位与气压观测数据及理论固体潮为研究对象,首先利用别尔采夫滤波滤除其日波、半日波;其次利用一般多项式分段曲线拟合(按月分段),将周期在1-2个月内的月波滤除;再次利用小波分析研究高村井水位分钟值与气压、理论固体潮的关系,结果表明:1)高村井水位观测主要周期有日波、半日波、1-2月的月波及年周期;2)高村井水位的日波、半日波主要的影响因素为固体潮,它们之间为线性关系;3)高村井水位1-2月的月波频段受气压影响较显著,井水位与气压呈线性关系;4)小波分析结果表明,在64-256min频段高村井水位与气压线性相关程度较高,受气压影响显著.     

Finite element method to fluid–solid interaction problems with unbounded periodic interfaces

Consider a time‐harmonic acoustic plane wave incident onto a doubly periodic (biperiodic) surface from above. The medium above the surface is supposed to be filled with a homogeneous compressible inviscid fluid of constant mass density, whereas the region below is occupied by an isotropic and linearly elastic solid body characterized by its Lamé constants. This article is concerned with a variational approach to the fluid–solid interaction problems with unbounded biperiodic Lipschitz interfaces between the domains of the acoustic and elastic waves. The existence of quasiperiodic solutions in Sobolev spaces is established at arbitrary frequency of incidence, while uniqueness is proved only for small frequencies or for all frequencies excluding a discrete set. A finite element scheme coupled with Dirichlet‐to‐Neumann mappings is proposed and the convergence analysis is performed. The Dirichlet‐to‐Neumann mappings are approximated by truncated Rayleigh series expansions. Finally, numerical tests in 2D are presented to confirm the convergence of solutions and the energy balance formula. In particular, the frequency spectrum of normally reflected signals is plotted for water–brass and water–brass–water interfaces. © 2015 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 32: 5–35, 2016     

明渠层流失稳与沙纹成因机理研究

动床水流中,泥沙起动之后,往往要出现沙纹,沙纹成因各家的解释不一。白玉川,罗纪生的观点是:沙纹的尺度较小,主要是由于明渠层流不稳定性波或床面近壁流层中小尺度拟序结构发展演化所致。当床面边界附近扰动波或拟序结构以及水流自身所产生的床面底部切应力大于Shields切应力后,床面即产生响应,形成沙纹;如果扰动所产生的扰动切应力频率接近床面泥沙固有频率,则产生与泥沙颗粒的共振,这种现象也称之为“泥沙的检波性质”,此时床面发生最大响应,沙纹发展速度也最快。     

Evolution of Nonlinear Sloshing in a Tank Near Half the Fundamental Resonance

This article describes the evolution of shallow water waves in a tank that is closed at one end and is periodically forced at half the fundamental frequency at the other end. The nonlinear response occurs at the same order as the linear response and is governed by a forced Korteweg–de Vries ( K dV ) equation. Unlike the corresponding problem for a gas (or the hydraulic limit), there may be nonperiodic (beating) solutions and multiple steady solutions for the same frequency. The addition of a component at the fundamental frequency to the piston input can be used to cancel the nonlinear effects and leave only the linear response in the steady state.