弹性地基输流管道的耦合模态颤振分析

推导出了弹性地基输流管道的固-液耦合振动微分方程,用幂级数法计算了Winkler模型地基和双参数模型地基输流管道的临界流速和复频率,分析了弹性地基对输流管道静力稳定性与动力稳定性的影响.结果表明,与不考虑弹性地基的情况相比较,弹性地基的作用可使管道发生静力失稳和动力失稳的临界流速增大,并且增大弹性地基参数可提高静力失稳和动力失稳的临界流速,从而推迟发散与颤振的发生.当质量比β较大时,管道会在某个地基参数组合下,在发生静力失稳后,会在较高流速下出现再稳定和再发散现象,然后发生耦合模态颤振.     

简支Mexwell模型粘弹性输流管道的稳定性分析

在弹性输流管道研究的基础上,采用递推格式的有限差分法,对简支Maxwell模型粘弹性输流管道（回转守恒系统）,探讨了其动力特性和稳定性问题,具体分析了材料的松弛时间对无量纲流速与前三阶模态的无量纲频率的实部及虚部之间的变化曲线的影响。发现发散临界流速随松弛时间的减小而降低,随后发生的耦合模态颤振临界流速随松弛时间的减小而增大;甚至在质量比较大时,随着松弛时间的减小,可推迟乃至不发生耦合模态颤振。当无量纲松弛时间达到10^3量级以上时,即可将其按弹性管道处理。甚至在H为10^2量级时,按弹性管道处理也不会带来太大的误差。     

输流粘弹性曲管的稳定性分析

根据变质量弹性系统Hamilton原理,用变分法建立了输流粘弹性曲管的运动微分方程,并用归一化幂级数法导出了输流粘弹性曲管的复特征方程组．以两端固支Kelvin-Voigt模型粘弹性输流圆管为例,分析了无量纲延滞时间和质量比对输流管道无量纲复频率和无量纲流速之间的变化关系的影响．在无量纲延滞时间较大时,粘弹性输流圆管的特点是它的第1、2、3阶模态不再耦合,而是在第1、第2阶上先发散失稳,然后在1阶模态上再发生单一模态颤振．     

柔性输流管泄流效应实验研究

基于模型试验研究了柔性输流管在恒定内流速度下由泄漏孔引入的泄流效应.研究发现:泄流效应可改变临界值,使得形变随流速增大近似线性增大;增加管道失稳时的形变幅值,可激发不同输流管的系统模态,引起管道多个频率的振动响应.研究结果为管道运输泄漏点定位提供了支撑,为数值模拟提供了实验参照.     

超临界输流管道3:1内共振下参激振动响应

研究了3:1内共振下输流管道在超临界领域的参激稳态响应.基于输流管道的非平凡静平衡位形,通过坐标代换得到超临界输流管道非线性振动的偏微分-积分控制方程.运用直接多尺度法,分析得到3:1内共振下输流管道参激振动响应的近似解析解,并用Galerkin截断法数值验证近似解析结果的可靠性.数值算例表明,内共振条件下输流管道系统不同模态间存在能量转移.通过近似解析结果预测了参激幅值对内共振条件下幅频响应曲线的影响.     

周期激励浅拱1∶2内共振参数平面定常运动分布

本文研究了已具有静变形的受周期激励作用下浅拱在１：２内共振条件下的分岔特性，进而按系统的运动形式将整个参数平面分成不同的区域，得到了物理参数平面上浅拱的定常运动分布情况，结合数值分析方法详细分析了系统在各个区域内特别是Ｈｏｐｆ分岔区域内系统的动力学特性，指出系统模态相互作用的规律及其通向混沌的过程·     

两自由度非对称三次系统非线性模态的奇异性质

利用非线性模态子空间的不变性和摄动技术,研究两自由度非对称三次系统在奇异条件下系统的性质.重点考虑子系统之间线性耦合退化时的奇异性质.对于非共振情形,所得到的解析结果表明,系统出现单模态运动以及振动局部化现象,这种现象的强弱不但与非线性耦合刚度有关,而且与非对称参数有关.并解析地得到了参数的门槛值;对于1:1共振情形,模态随非线性耦合刚度和非对称参数的变化会出现分岔,得到了参数分岔集以及模态的分岔曲线.     

非线性系统动力分析的模态综合技术

各种模态综合方法已广泛应用于线性结构的动力分析,但是,一般都不适用于非线性系统. 本文基于[20][21]提出的方法,将一种模态综合技术推广到非线性系统的动力分析.该法应用于具有连接件耦合的复杂结构系统,以往把连接件简化为线性弹簧和阻尼器.事实上,这些连接件通常具有非线性弹性和非线性阻尼特性.例如,分段线性弹簧、软特性或硬特性弹簧、库伦阻尼、弹塑性滞后阻尼等.但就各部件而言,仍属线性系统.可以通过计算或试验或兼由两者得到一组各部件的独立的自由界面主模态信息,且只保留低阶主模态.通过连接件的非线性耦合力,集合各部件运动方程而建立成总体的非线性振动方程.这样问题就成为缩减了自由度的非线性求解方程,可以达到节省计算机的存贮和运行时间的目的.对于阶次很高的非线性系统,若能缩减足够的自由度,那么问题就可在普通的计算机上得以解决. 由于一般多自由度非线性振动系统的复杂性,一般而言,这种非线性方程很难找到精确解.因此,对于任意激励下系统的瞬态响应,可以采用数值计算方法求解缩减的非线性方程.     

无锚固储液罐提离的流-固多种非线性耦合的三维移动边界问题统一分析格式*

本文建立了在地震作用下无锚固储液罐提离的流-固多种非线性耦合的移动边界问题的统一格式的三维分析方法,其中建立了任意四边形标薄板壳拟协调非线性有限元的列式和分析移动边界问题的线性互补方程;提出了在ALE标架下用带压力项的时间分裂步法求解储液罐内含自由液面大幅晃动(移动边界问题)的非定常的三维粘性流体(N-S)问题的方法;其中没有利用轴称性和梁式模态假定等条件及未曾利用势函数理论;该方法适用于一般板壳-流体多种非线性耦合的多种移动边界问题.     

微极流体蠕动泵经由滑移边界管道输送的Stokes流动

计及管道边界条件滑移的影响,研究微极流体蠕动泵,经由圆柱形管道输运的Stokes流动.壁面运动的控制方程为正弦波方程.使用润滑理论,得到了轴向速度、微转动向量、流函数、压力梯度、摩擦力和机械效率的解析数值解.用图形表示出构成参数,如像耦合参数、微极参数和表征蠕流泵特性的滑移参数、摩擦力和俘获现象的影响.数值计算表明,当耦合参数较大时,需要蠕动泵的压力更大,而微极参数和滑移参数正相反.俘获团块的大小随耦合参数和微极参数的减小而缩小,而随滑移参数的增大而缩小.     

Dynamical analysis of spinning functionally graded pipes conveying fluid with multiple spans

In this paper, a dynamical model of spinning multi-span pipes conveying fluid is proposed and the transverse natural and resonant frequencies and mode characteristics of such system are explored. The pipe body is considered to be composed of functionally graded materials (FGMs), in which a power law is used to govern the distribution of material properties along the pipe wall thickness. The partial differential equations (PDEs) governing two transverse motions of the pipe are derived by the extended Hamilton principle, in which the contributions of the FGM and intermediate supports are highlighted. The PDEs are discretized by the Galerkin procedure and the eigensystem theorem is applied to find the numerical solutions. The results show that various frequency characteristics can be attainable by use of different materials and mixing patterns. Attachments of intermediate supports can heighten the rigidity and improve the stability of spinning FG pipes conveying fluid, which are consequently used as “stabilizers” for the slender drill strings. Also, the mode characteristics of different spans will determine the locations of vibration amplitude of the pipes.     

Dynamic analysis, controlling chaos and chaotification of a SMIB power system

The dynamic behaviors of a SMIB power system are studied in this paper. A single modal equation is used to analyze the qualitative behaviors of the system. The famous equation of motion is called “swing equation”. The Lyapunov direct method is applied to obtain conditions of stability of the equilibrium points of the system. The bifurcation of the parameter dependent system is studied numerically. Besides, the phase portraits, the Poincaré maps, and the Lyapunov exponents are presented to observe periodic and chaotic motions. Further, the addition of periodic force and the feedback control are used to control chaos effectively. Finally, the chaotification problem of the SMIB power system is also issued.     

Forced oscillations with a sliding regime range of a two-mass system interacting with a fixed stop : PMM vol. 37, n6, 1973, pp. 999–1006

We investigate, by the method developed in [1]. the forced oscillations with a sliding regime range of a two-mass system with elastic connection between the elements, impacting a fixed stop. The system being considered is a dynamic model for a number of vibrational mechanisms. Forced oscillations with a sliding regime range of a system with shock interactions are periodic motions accompanied by a period of an infinite succession of instantaneous collisions of two fixed elements of the model [2]. Within the framework of conditions of roughness of the parameter space [3], in this paper we study by the method of [1] periodic motions with a sliding regime range of a two-mass system with a stop. This problem was posed because in real systems the velocity recovery factor R changes from shock to shock, mainly taking small values (0, 0.2). At the same time, the regions of realizability of one-impact oscillations, in practice the most essential ones among motions with a finite number of interactions over a period, narrow down sharply as R decreases and becomes very small even for R < 0.6 [4]. Thus, the stability of the given operation can be ensured by a law of motion which is independent or weakly dependent on R (^*) (see footnote on the next page). By virtue of what has been said above, finite-impact periodic modes are little suitable for this purpose. Regions, delineated in the parameter space of the model being considered, of existence of stable periodic motions with a sliding regime range have proved to be sufficiently broad. By virtue of the adopted approximation of the sliding regime, the dynamic characteristics of these motions do not depend upon R. The circumstances mentioned confirm the practical value of motions with a sliding regime range in dynamic systems with impact interactions.     

Modal analysis reduction of multi-body systems with generic damping

Modal analysis of multi-body systems is broadly used to study the behavior and controller design of dynamic systems. In both cases, model reduction that does not degrade accuracy is necessary for the efficient use of these models. Previous work by the author addressed the reduction of modal representations by eliminating entire modes or individual modal elements (inertial, compliant, resistive). In that work, the bond graph formulation was used to model the system and the modal decomposition was limited to systems with proportional damping. The objective of the current work is to develop a new methodology such that model reduction can be implemented to modal analysis of multi-body systems with non-proportional damping that were not modeled using bond graphs. This extension also makes the methodology applicable to realistic systems where the importance of modal coupling terms is quantified and potentially eliminated. The new methodology is demonstrated through an illustrative example.     

输送流体管道的固——液耦合动力学研究

根据Ｈａｍｉｌｔｏｎ原理推导输送流体管道固—液耦合振动方程，得到反对称的固—液耦合阻尼矩阵和对称的固—液耦合刚度矩阵；用ＱＲ法计算管道固有频率，给出了管道前４阶固有频率—流速曲线；讨论了流体的流速、压强变化以及固—液耦合阻尼和固—液耦合刚度对管道固有频率的影响；用Ｎｅｗｍａｒｋ法计算不同流速时管道对阶跃载荷的动力响应；发现了各阶固有频率都有随流速的提高而降低、再提高、再降低的周而复始现象·     

Stochastic stability of coupled linear systems: a survey of methods and results

The analysis of dynamic systems subject to stochastic parametric excitation is important in a variety of branches of engineering and physics. For example, models of this type frequently occur in the analysis of linear continuous systems using modal decomposition. The random coupling or parametric excitation can, for example, model the influence of externally applied loads on the system parameters. In this paper we investigate the almost–sure stability properties of the sample trajectories of linear stochastic systems with parametric excitation.     

Modeling and modal analysis of non-uniform multi-span oil-conveying pipes with elastic foundations and attachments

This paper studies the parametric modal characteristics of non-uniform multi-span oil-conveying pipes, considering many combined factors such as the various foundations that pipes rest on, the accessary masses attached to the pipes, and the flow moving inside the pipes. A new modified lumped-mass transfer matrix method (LTMM) is proposed to derive the governing equation of the system, where we simplified and modeled all the combined factors as lumped masses and springs that can be treated in uniform ways. The boundary is also modeled in a similar lumped-spring strategy. In such a way, the system with combined factors and various boundary conditions is eventually modeled as a “Free-Free” pipe with only lumped masses and springs. Numerical results are illustrated to testify the accuracy and efficiency of the proposed method, and a general case with combined factors affecting the modal characteristics is discussed. It can be presented that rotary inertia and concentrated mass can affect different order mode shapes; under different foundation parameters, the differences between mode shapes are remarkable while the positions of the nodes do not change much, even under classical boundary condition. The results through modal analysis can afford the basis for the vibration analysis, fault diagnosis and prediction, and the optimization design of the dynamic characteristics of the structure.     

微曲输流管道振动固有频率分析与仿真北大核心CSCD

首次建立了基于Timoshenko梁理论的微曲输流管道横向振动的动力学模型,并分析了流体流动影响下微曲管道横向自由振动的固有特征.采用广义Hamilton原理,导出了考虑流体影响的微曲管道横向振动的控制方程,通过Galerkin截断对控制方程离散化,再由广义本征值问题得到管道横向振动的固有频率,并研究了液体流速和弯曲幅度对管道横向固有振动特征的影响.发展了基于等效刚度和等效阻尼方法的考虑流体影响的微曲管道振动分析的有限元仿真计算方法,并通过有限元软件实现数值仿真,验证了Galerkin截断的分析结果以及所建立的Timoshenko微曲管道动力学模型的有效性.研究表明,流体的流速以及管道的弯曲幅度对管道横向振动固有频率均有显著影响.     

非线性系统动态响应的数值计算方法

文[9]曾将一种模态综合技术推广到非线性系统的动态响应分析,应用于线性子结构具有非线性连接件耦合系统的振动分析.本文进一步把模态综合技术推广到各子结构具有非线性特性大型复杂结构的动态分析.文末给出的算例表明本方法具有良好的精确度和很高的计算效率.     

The dynamic stability and nonlinear vibration analysis of stiffened functionally graded cylindrical shells

A theoretical model is developed to study the dynamic stability and nonlinear vibrations of the stiffened functionally graded (FG) cylindrical shell in thermal environment. Von Kármán nonlinear theory, first-order shear deformation theory, smearing stiffener approach and Bolotin method are used to model stiffened FG cylindrical shells. Galerkin method and modal analysis technique is utilized to obtain the discrete nonlinear ordinary differential equations. Based on the static condensation method, a reduction model is presented. The effects of thermal environment, stiffeners number, material characteristics on the dynamic stability, transient responses and primary resonance responses are examined.