Prediction Model for Vortex-Induced Vibration of Circular Cylinder with Data of Forced Vibration

A model based on the data from forced vibration experiments is developed for predicting the vortex-induced vibra- tions （VIV） of elastically mounted circular cylinders in flow. The assumptions for free and forced vibration tests are explored briefly. Energy equilibrium is taken into account to set up the relationship between the dynamic response of selfexcited oscillations and the force coemcients from forced vibration experiments. The gap between these two cases is bridged straightforwardly with careful treatment of key parameters. Given reduced mass m^# and material damping ratio of an elastically mounted circular cylinder in flow, the response characteristics such as amplitude, frequency, lock-in range, added mass coefficient, cross-flow fluid force and the corresponding phase angle can be predicted all at once. In- stances with different combination of reduced mass and material damping ratio are compared to investigate their effects on VIV. The hysteresis phenomenon can be interpreted reasonably. The predictions and the results from recent experiments carried out by Wifliamson＇ s group are in rather good agreement.

The Interface Stress Field in the Elastic System Consisting of the Hollow Cylinder and Surrounding Elastic Medium Under 3D Non-Axisymmetric Forced Vibration

The paper develops and employs analytical-numerical solution method for the study of the time-harmonic dynamic stress field in the system consisting of the hollow cylinder and surrounding elastic medium under the non-axisymmetric forced vibration of this system.It is assumed that in the interior of the hollow cylinder the point-located with respect to the cylinder axis,non-axisymmetric with respect to the circumferential direction and uniformly distributed time-harmonic forces act.Corresponding boundary value problem is solved by employing of the exponential Fourier transformation with respect to the axial coordinate and by employing of the Fourier series expansion of these transformations.Numerical results on the frequency response of the interface normal stresses are presented and discussed.

Asymptotic analysis on weakly forced vibration of axially moving viscoelastic beam constituted by standard linear solid model

The weakly forced vibration of an axially moving viscoelastic beam is inves- tigated. The viscoelastic material of the beam is constituted by the standard linear solid model with the material time derivative involved. The nonlinear equations governing the transverse vibration are derived from the dynamical, constitutive, and geometrical relations. The method of multiple scales is used to determine the steady-state response. The modulation equation is derived from the solvability condition of eliminating secular terms. Closed-form expressions of the amplitude and existence condition of nontrivial steady-state response are derived from the modulation equation. The stability of non- trivial steady-state response is examined via the Routh-Hurwitz criterion.

A vertical coupling dynamic analysis method and engineering application of vehicle–track–substructure based on forced vibration

Purpose–This study aims to propose a vertical coupling dynamic analysis method of vehicle–track–substructure based on forced vibration and use this method to analyze the influence on the dynamic response of track and vehicle caused by local fastener failure.Design/methodology/approach–The track and substructure are decomposed into the rail subsystem and substructure subsystem,in which the rail subsystem is composed of two layers of nodes corresponding to the upper rail and the lower fastener.The rail is treated as a continuous beam with elastic discrete point supports,and spring-damping elements are used to simulate the constraints between rail and fastener.Forced displacement and forced velocity are used to deal with the effect of the substructure on the rail system,while the external load is used to deal with the reverse effect.The fastener failure is simulated with the methods that cancel the forced vibration transmission,namely take no account of the substructure–rail interaction at that position.Findings–The dynamic characteristics of the infrastructure with local diseases can be accurately calculated by using the proposed method.Local fastener failure will slightly affect the vibration of substructure and carbody,but it will significantly intensify the vibration response between wheel and rail.The maximum vertical displacement and the maximum vertical vibration acceleration of rail is 2.94 times and 2.97 times the normal value,respectively,under the train speed of 350 km$h
1.At the same time,the maximum wheel–rail force and wheel load reduction rate increase by 22.0 and 50.2%,respectively,from the normal value.Originality/value–This method can better reveal the local vibration conditions of the rail and easily simulate the influence of various defects on the dynamic response of the coupling system.

Simple and fast prediction of train-induced track forces,ground and building vibrations

A simple and fast prediction scheme is presented for train-induced ground and building vibrations.Simple models such as(one-dimensional)transfer matrices are used for the vehicle–track–soil interaction and for the building–soil interaction.The wave propagation through layered soils is approximated by a frequency-dependent homogeneous half-space.The prediction is divided into the parts“emission”(excitation by railway traffic),“transmission”(wave propagation through the soil)and“immission”(transfer into a building).The link between the modules is made by the excitation force between emission and transmission,and by the free-field vibration between transmission and immission.All formula for the simple vehicle–track,soil and building models are given in this article.The behaviour of the models is demonstrated by typical examples,including the mitigation of train vibrations by elastic track elements,the low-and high-frequency cut-offs characteristic for layered soils,and the interacting soil,wall and floor resonances of multi-storey buildings.It is shown that the results of the simple prediction models can well represent the behaviour of the more time-consuming detailed models,the finite-element boundary-element models of the track,the wavenumber integrals for the soil and the three-dimensional finite-element models of the building.In addition,measurement examples are given for each part of the prediction,confirming that the methods provide reasonable results.As the prediction models are fast in calculation,many predictions can be done,for example to assess the environmental effect along a new railway line.The simple models have the additional advantage that the user needs to know only a minimum of parameters.So,the prediction is fast and user-friendly,but also theoretically and experimentally well-founded.

VIBRATIONS OF STEPPED ONE-WAY THIN RECTANGULAR PLATES SUBJECTED TO IN-PLANE TENSILE/ COMPRESSIVE FORCE IN Y-DIRECTION ON WINKLER'S FOUNDATION

Differential equations of free/forced vibrations of n_step one_way thin rectangular plates subjected to in_plane tensile/compressive force in y_direction on Winkler's foundation are established by using singular functions, their general solutions solved for, expression of vibration mode function and frequency equation on usual supports derived with W operator. Influence functions for various cases deduced here may also be used to solve problems of static buckling or stability for beams and plates in relevant circumstances.

RADIAL VIBRATIONS OF AXISYMMETRICALLY LOADED STEPPED PRESSURE VESSELS

Differential equations of free/forced radial vibrations of axisymmetrically loaded stepped pressure vessels are established by using singular functions. Furthermore, their general solutions are solved, the expression of vibration mode function and frequency equations on usual supports are derived with W operator and the forced response of such vessels are calculated.

A study of ice response spectra

Some problems concerning the ice forces and ice response spectra are studied from both theoretical and practical points of view. On the basis of structural analysis,the analysis method of ice response spectra is proposed, since it plays an important role in the prediction of maximum structural response in cold regions. And it is illustrated that it is easy to study the structural response to ice using the ice response spectra.

VIBRATIONS OF STEPPED RECTANGULAR THIN PLATES ON WINKLER’S FOUNDATION

Differential equations of free/forc ed vibrations of stepped rectangular thin plates on Winkler's foundation are estab lished by using singular functions, and their general solutions are also solved for expression of vibration mode function and frequency equations on usual suppo rts derived with W operator, as well as forced responses of such plates unde r different_type loads disc ussed with Fourier expansion of generalized functions.

VIBRATIONS OF ONE-WAY RECTANGULAR STEPPEDTHIN PLATES ON WINKLER'S FOUNDATION

Differential equations of free forced vibrations of one -way rectangular stepped thin plated on Winkler 's foundation are established by using singular functions ,their general solutions are solved :exprssion of vibration mode function and frequency equations on usual supports are derived from W operator :forced responses of such plates under different -type loads are discussed with generalized functions .

Experimental and Analytical Study of Torsional Vibration under Multiaxial Loading in Time Domain

The torsional vibration of power transmission shaft is a phenomenon whose analytical modeling can be represented by a differential equation of motion proposed by technical literature. The solutions of these equations need coefficients and parameters that, usually, must be experimentally estimated. This work uses a resistive electric SG （strain gage） to dynamically determine strains produced in the shaft due to harmonic oscillatory motion under multiaxial loading. This movement is simulated on a prototype specially developed for this purpose. It comprises a pulley attached to the end of a stepped cantilevered shaft, which is clamped at the opposite end. In this configuration, a cam generates a torque to the system, springs regulate the stiffness and the damping coefficient of the assembly, as well as they can be suitably adjusted to produce an underdamped condition. The main advantage, highlighted in this study, refers to a major simplification. Although the system under study shows multiple degrees of freedom （torsion and bending）, the shape and the positioning of linking SGs with the resistor bridge （Wheatstone Bridge）, allow ＂to evaluate the loading effects independently, as if only one degree of freedom of the system exists at a time domain. Strains graphs for two forms of cyclic torsional oscillation, analytical and experimental, were successfully generated.

大型发电机端部绕组电磁力物理数字孪生建模

为了在“智慧汽轮机”中更好地结合物理信息模型先验知识与数据驱动模型,并向真实机组模型迁移试验模型,进一步实现可靠的实验室数值仿真数据和真实运行数据互相印证与混和建模驱动,以600 MW大型汽轮发电机为研究对象,建立融合演进因素的汽轮发电机定子绕组本体模型,提出集成数字孪生智能绕组研究框架,并提出智能绕组内涵的形式化定义。基于镜像法、气隙回转电流应用叠加法、毕奥-萨伐尔定律和安培力定律建立定子端部绕组电磁力的数学机理物理信息模型。对有限元电磁力和数字化电磁力进行了分析对比,验证了所建立电磁力数字化物理信息模型的合理性。对比分析振动响应结果,进一步验证了数字化电磁力物理信息建模的正确性以及有限元电磁力对比验证的正确性。研究将对“智慧汽轮机”运维的振动动态基于物理机理与数据驱动混和建模的数字孪生故障诊断与预测提供有力的支撑。

基于谐响应的大型异步电机电磁振动分析

大型异步电机的电磁振动是电机振动的主要构成部分,对电机振动等级的评估需要进行准确的电磁振动分析,本文以一台10 kV兆瓦级大型异步电机为对象进行电磁振动分析。首先对完整的电机模型进行模态分析,求解固有频率及对应振型,并实验测量了电机实际运行时的固有频率;然后将电磁场二维有限元计算得到的径向电磁力作为载荷,对该电机进行谐响应分析,最后与实验测得的振动速率对比。结果表明,基于电机整机模型的模态分析和谐响应分析可以较为准确地分析大型异步电机电磁振动,能够为电机的优化设计或电磁振动抑制提供理论依据。

双向恢复力模型对基础隔震建筑风振响应的影响

为明确MSS、Casciati和Harvey and Gavin这3种常用双向恢复力模型计算基础隔震建筑风振响应的差异,采用3种模型模拟铅芯橡胶支座在水平单向和双向位移下的恢复力,对比试验或有限元结果的差异,采用3种模型对一算例在双向风荷载下隔震层位移、顶点位移和顶点加速度3个指标的差异进行了分析。研究表明:3种模型模拟铅芯橡胶支座在单向循环位移、方形和偏置方形位移下恢复力的趋势基本一致;而模拟圆形和偏置圆形位移时,MSS模型双向恢复力形状与有限元结果不同,不能较为准确地模拟支座双向耦合行为,Casciati模型误差稍小于Harvey and Gavin模型。Casciati模型和Harvey and Gavin模型计算风振响应基本一致;对于横风向响应均方根,3种模型差距不大;对于顺风向隔震层位移、顶点位移和顶点加速度均方根,MSS模型稍小,而对于顺、横风向隔震层位移峰值因子,MSS模型稍大;对于顺、横风向顶点加速度峰值因子和双向与单向模型顶点加速度最值比值随风速变化规律,MSS模型与其他模型差异较大。基于双向耦合效应模拟及风振响应指标的差异,建议采用Casciati模型考虑双向恢复力模型对基础隔震建筑风振响应的影响。

附加阻尼环的航空齿轮强迫响应分析方法

为了避免航空齿轮振动过大导致齿轮辐板破裂,在齿轮外缘安装阻尼环是一种有效减振方法。针对工程中阻尼环设计时缺乏有效便捷的设计方法问题,基于能量法建立了航空齿轮节径型振动下阻尼环的等效参数模型。在给定模态振型下,将阻尼环的影响效果简化为依赖于齿轮振幅(振动应力)的等效阻尼、等效刚度和等效质量,实现了齿轮-阻尼环系统幅频响应快速求解。以某航空齿轮为例,分析了激励载荷、摩擦系数、转速以及结构固有阻尼对强迫响应的影响,结合许用振动应力进行了阻尼环优化设计。结果表明:阻尼环减振效果与振动应力具有强非线性,在本文给定的激励载荷及100 MPa许用振动应力下,阻尼环质量比不应大于5%,最佳摩擦系数为0.1,设计得当的阻尼环能够降低50%以上的振动应力。

带限位隔振系统的主共振响应及隔振性能研究

针对舰船设备带限位隔振系统中普遍存在的非线性特性,文中建立包含分段线性刚度和分段线性阻尼的限位隔振系统数学模型,采用平均法对主共振响应进行解析求解,推导出系统力传递率方程,综合分析了限位器各参数对系统幅频特性和隔振性能的影响规律,通过扫频试验进行验证。结果表明:限位器阻尼对系统振动性能具有积极意义,大阻尼限位有效减小了幅频响应峰值,降低了力传递率,减小甚至避免了跳跃和滞后现象的产生;对于任意一组系统参数都存在一个最优刚度比,使得相对位移幅值最小、隔振性能最好,同时保证了跳跃区间相对较小;适当增大限位间隙可以减小跳跃区间,进一步改善系统的振动性能。

考虑液体晃荡的部分充液圆柱壳受迫振动分析

充液圆柱壳结构广泛存在于在工程中,在外部激励作用下,圆柱壳会与流体产生耦合振动,且未充满的液面也会产生晃荡,这种耦合振动响应分析在工程中具有重要意义。提出了一种求解考虑内部液体小幅晃荡的弹性圆柱壳振动响应的半解析法。首先分别在壳体建立结构坐标系、在自由液面建立液体坐标系,各自用来描述结构及内部液体的运动。基于Flügge壳体理论建立了圆柱壳的运动控制方程。将液体视为无黏、不可压缩的理想流体,根据线性水波理论和液体自由表面运动边界条件,得出了内部液体的速度势函数。通过流固耦合界面的连续性条件,结合坐标变换推导得到流固耦合系统的运动控制方程。研究了壳体在径向点力激励下振动响应,并得出了对应的液面晃荡响应。和有限元法对比验证了方法的正确性,然后改变相关参数讨论了考虑内部液体晃荡的弹性圆柱壳振动响应特性。

基于不同桩基模拟方式的大块式基础动力数值分析

为了更合理预测采用桩基的大块式基础的动力特性,建立桩基仿真模型并与桩-土动力试验相互验证,对组合桩基模型与大块式基础模型进行有限元数值分析,同时参考设计院所使用以弹簧单元模拟桩基的方式,建立数值模型并进行分析,探讨不同的桩基模拟方式对大块式基础动力特性的影响。研究结果表明:使用弹簧单元模拟桩基的方式忽略桩土质量、阻尼的影响,会造成大块式基础振型缺失、自振频率整体偏大、强迫振动响应被放大;使用桩基仿真模型更能反映大块式基础动力特性但计算成本增加。上述结论可为采用桩基的大块式基础动力特性研究提供参考。

波浪作用下高速列车-轨道-桥梁系统耦合振动研究

为研究波浪作用对高速铁路跨海桥梁车-轨-桥系统耦合振动的影响,基于线性波浪理论和Morison方程模拟波浪荷载,采用分布力模式输入既有车-轨-桥系统耦合振动分析程序,提出波浪作用下的车-轨-桥系统耦合振动分析方法。以某高速铁路跨海斜拉桥为背景,研究波坡面效应、波浪重现期、车速对车-轨-桥系统动力响应的影响,并评估不同重现期波浪作用下过桥列车的走行性。结果表明:波坡面效应会使作用于不同单桩的波浪荷载初始相位不同,从而导致作用于群桩基础的波浪荷载合力不同;随着波浪重现期的增大,车-轨-桥系统的横向动力响应均增大,而竖向动力响应几乎不变;考虑波浪作用后,列车的行车安全性指标均随车速的增大而增大,波浪荷载会显著降低桥上列车的乘坐舒适性并增加桥上列车的脱轨风险。常遇波浪(10年重现期)和极端波浪(100年重现期)作用下列车的安全车速阈值分别为325 km/h和275 km/h。

人车路耦合系统的非线性振动特性及试验研究

为了解决车辆行驶中产生的复杂非线性振动响应问题,建立三自由度人车路耦合非线性动力学模型。基于扭转几何变形非线性特征,利用拉格朗日方程推导出三自由度人车路耦合非线性振动方程,该方程中的正弦和余弦函数项来源于几何非线性扭转变形。针对自由振动,给出非线性恢复力曲面、势能曲面及固有频率解析表达式。针对强迫振动,运用数值仿真方法分析车辆质量、转动惯量、乘客质量、座椅刚度/阻尼、悬架刚度/阻尼、阻尼、质心位置、路面波长及波幅等系统参数对振幅速度响应曲线的影响。搭建人车路耦合振动系统的实验平台,通过振动实验结果验证理论分析与数值结果的可靠性。研究结果表明:该三自由度非线性动力学耦合系统可精确描述人车路耦合系统的响应特性,合理选择系统参数能够有效减小振动响应幅值和提升乘坐舒适性。