拉索端部弹性约束振动控制研究(Ⅰ)——理论模型

本文建立了拉索振动的轴向被动控制理论模型。在拉索端部沿轴向设置弹性约束,通过影响索端支座的移动,从而改变拉索的振动特性,最终达到减振效果。通过D’Alembert原理建立拉索-弹性约束系统振动方程,通过Galerkin方法将偏微分方程转化为常微分方程,应用龙格-库塔积分法求解方程;经过仿真分析,验证了该振动控制具有明显的减振效果,并且讨论了初始拉力、支座质量、振动频率及弹簧刚度对减振效果的影响;最后给出了计算最优阻尼参数的近似解析式,为工程师提供了简便有效的参考依据及设计方法。     

拉索端部弹性约束振动控制研究(Ⅱ)——试验验证

在索端沿轴向设置弹性约束,对拉索振动轴向被动控制进行了试验研究。研究了支座移动对拉索振动频率的影响;验证了弹性约束对拉索振动的减振效果,讨论了阻尼系数和弹簧刚度对减振效果的影响;最后验证文献[10]中理论研究的正确性。     

防振锤抑制拉索振动的仿真分析与试验研究

针对目前斜拉桥拉索减振方法的不足,提出利用防振锤抑制拉索振动的思路。为验证该方法的有效性,本文分别建立了拉索和防振锤的运动方程,并采用振型叠加法建立与其对应的广义坐标方程,采用状态空间法建立与其对应的状态方程,运用SIMULINK仿真系统对拉索进行了动力仿真分析。设计了相应的室内试验,进行了拉索-防振锤组合系统试验,并利用SIMULINK对试验进行了相同参数的仿真分析,对比验证了防振锤减振的有效性。仿真结果与试验结果对比发现,作为拉索减振装置防振锤减振效果较为显著,对于防振锤的设计应使其振动频率与拉索振动频率相一致、安装质量不宜过小、阻尼不宜太大、且宜安装在拉索振幅较大处。研究结果表明:防振锤抑制拉索的振动是有效的,利用防振锤装置抑制超长拉索振动是可行的。     

具有弹性转动约束的斜拉桥多索-浅拱模型及其面内自由振动分析

考虑斜拉桥的初始构型,建立具有弹性转动约束的多索-浅拱模型。首先,采用Hamilton变分原理得到了索和浅拱的控制微分方程。为了保证浅拱在索-浅拱连接处满足连续条件,将浅拱分段考虑,通过索-浅拱连接处的位移连续条件和力的平衡条件以及两端支座处的边界条件,推导了求解该系统自由振动问题的基本方法。然后,以弹性转动约束双索-浅拱模型为例,对其面内特征值问题进行求解,同时,建立相应的ANSYS模型,得到该模型频率和振型的有限元解。通过与有限元方法计算结果的对比,表明本文方法的正确性和有效性。最后,选取了斜拉索的倾角、垂度,浅拱的抗弯刚度、矢跨比,以及支座的转动刚度等参数,对模型的前5阶频率进行了参数化分析。     

面内端部激励下斜拉索振动方程推导与求解

为精确描述面内端部激励下拉索非线性振动机制,构建抽象端部激励下的拉索力学描述模型,分别推导了拉索拟静态振动和模态振动控制方程,基于有限差分法给出了拉索模态振动的数值求解方法。由于垂度效应的影响,在轴向、竖向以及轴向和竖向共同激励下拉索的拟静态索力与端部位移采用一个非线性方程予以表征。拉索拟静态振动可视作外部激励施加在拉索上,引起拉索的非线性模态振动,通过理论推导分别求得模态振动的控制方程和变形协调方程。在模态振动过程中,拉索的动力特性(如刚度和周期)不断变化,索力和拉索变形相互耦合,使得其求解非常复杂。采用有限差分法进行数值求解,并基于有限元方法验证了数值求解方法的准确性。重点讨论了拉索模态振动共振机制,结果表明,在轴向、竖向以及轴向和竖向激励下,拉索模态振动存在多个共振区域,包括小周期、0.5T₁、T₁和2T₁等(T₁为成桥状态下拉索基本振动周期);在共振区域内,拉索振动索力幅度较大,模态振动对总索力的贡献系数较高,超过0.4,在实际工程中不容忽视;拉索阻尼对模态振动的影响较大,增加拉索阻尼比将改...     

黏滞阻尼器对拉索参数振动的控制分析

提出采用黏滞阻尼器对拉索参数振动进行控制,建立了黏滞阻尼器控制拉索参数振动的运动方程。从频域和时域以及起振幅值等角度,研究了最优黏滞阻尼器对不同垂度拉索参数振动的控制效果;此外,还研究了最优黏滞阻尼器安装位置对拉索参数振动控制效果的影响。研究表明,黏滞阻尼器可以有效控制拉索的参数振动,控制效果与拉索的激励幅值、最优阻尼器的安装位置和斜拉索的垂度有关。激励幅值越大,控制效果一般越差;最优阻尼器的安装位置越靠近跨中,则控制效果越好;黏滞阻尼器对大垂度拉索的控制效果不及对小垂度拉索的控制效果。     

圆球减振装置对风力发电高塔的振动控制研究

本文提出了圆球减振装置对风力发电高塔振动控制的工作原理和计算方法,并对其控制效果进行了理论研究。首先利用拉格朗日方程推导得到圆球减振装置的自振频率及其对单自由度系统的被动控制力,并推广至多自由度系统。进而将风力发电高塔等效为集中质点模型,建立了风塔-减振装置体系的运动微分方程。用谐波叠加法模拟得到脉动风速时程,分析比较了风力发电高塔在无控及有控状态下的动力响应及疲劳寿命。计算结果表明,圆球减振装置是一种简单、经济和实用的减振装置,能够有效减小风塔的动力响应,延长其疲劳寿命。     

纵向剪切波作用下长型地下结构与地基动力相互作用研究

为了研究在剪切波沿地下长型结构纵向传播情况下,惯性力对地下结构与地基动力相互作用的影响,基于Winkler地基模型和Euler-Bernoulli梁模型,分别建立了长型地下结构的静力平衡方程、自由振动方程和强迫振动方程。通过振型叠加法将偏微分方程简化为常微分方程;利用微分算子法分别求得静力平衡方程;自由振动方程和强迫振动方程的解析解。通过算例计算,比较并分析了静力平衡方程解与强迫振动方程解的差别。结果表明在算例取值情况下,惯性力对结构振动的影响较小;而在地基基床系数k很小或轴向力N很大时,惯性力的影响才较为显著。     

考虑斜拉索刚度、垂度、阻尼的非线性运动方程研究

随着斜拉桥跨径的快速增长,斜拉索的长度也大大增加,斜拉索是斜拉桥的主要受力构件,其在外荷载作用下经常引发大幅振动,这样就降低了斜拉索的寿命或造成拉索的破坏,因此研究斜拉索的非线性运动方程对解决振动问题具有实际工程的意义。本文在考虑斜拉索非线性静平衡曲线、抗弯刚度、粘滞阻尼影响的斜拉索平面内非线性振动的基础上,建立了斜拉索非线性运动方程。采用Galerkin法解耦了斜拉索非线性运动方程,并运用Runge-Kutta法对其自由振动和周期强迫振动两种情形进行了求解,最后,通过对该索的理论计算数据与原型仿真数据的对比分析,可知上述非线性方程比传统的线性方程更精确。本文的研究为今后斜拉索的非线性分析及其振动控制奠定了一定的理论基础。     

大型储液罐摩擦摆基底隔震控制分析

针对弹性钢制圆柱储液罐,基于Haroun-Housner模型,将连续流体质量等效为3种集中质量,分别为:对流质量、脉冲质量和刚性质量,与这些集中质量连接的相应刚度取值依赖于储罐壁和流体质量.在水平地震激励下,在储罐底部加摩擦单摆支座,给出了简化的液体 - 储罐-隔震支座的力学分析模型,建立了摩擦摆支座基底隔震体系的振动控制方程,并利用Newmark逐步积分法对控制方程进行了数值求解,研究了摩擦摆支座基底隔震的储液罐地震反应,验证了FPB隔震的有效性.     

Semiactive variable stiffness control for parametric vibration of cables

In this paper, a semiactive variable stiffness （SVS） device is used to decrease cable oscillations caused by parametric excitation, and the equation of motion of the parametric vibration of the cable with this SVS device is presented. The ON/OFF control algorithm is used to operate the SVS control device. The vibration response of the cable with the SVS device is numerically studied for a variety of additional stiffness combinations in both the frequency and time domains and for both parametric and classical resonance vibration conditions. The numerical studies further consider the cable sag effect. From the numerical results, it is shown that the SVS device effectively suppresses the cable resonance vibration response, and as the stiffness of the device increases, the device achieves greater suppression of vibration. Moreover, it was shown that the SVS device increases the critical axial displacement of the excitation under cable parametric vibration conditions.     

ACTIVE TENDON CONTROL OF CABLE-STAYED BRIDGES

This paper considers the active vibration control of cables and cable/structure systems with an active tendon controlling the axial displacement of the cable anchor point. It is demonstrated that a force feedback based on a collocated force sensor measuring the tension in the cable is feasible and that this control configuration can be associated with control laws with guaranteed stability properties. Experimental results are presented on a cable with small sag and on a cable/structure system. They show that the control algorithm can provide the structure with several percent of active damping and that the parametric resonance does not occur when the natural frequency of the structure is twice that of the cable.     

An experimental study on active control of in-plane cable vibration by axial support motion

Active control of slightly sagged cables using the axial motion at the cable support is studied experimentally and analytically. Non-linear modal equations of a cable are presented, and two control schemes are identified, i.e. active stiffness control and active sag-induced force control. In this study, emphasis is placed on the active sag-induced force control. Additional damping is analytically expressed when a velocity feedback control is used. Although the active sag-induced force control can be applicable only for in-plane symmetric modes, it is shown that it is very efficient for the first mode. An experiment is conducted using a scaled cable model of 2 m length. First, it is shown by the experiment that the analytical model can predict well the non-linear cable motion. Next, sag-induced force control is examined using free vibration and harmonic excitations. The results agree well with the analytical predictions and confirm that additional damping can be obtained efficiently from the axial support motion.     

Analysis of the earth resistivity response of buried cables

Current flow in homogeneous and layered conducting media is analyzed for the case where an axial conductor or cable is present. The cable is characterized by a specified axial impedance and is assumed to be infinite in length. Various configurations are chosen such as a current point source in an infinite, semi-infinite, and layered region where the cable is taken parallel to the interface(s). The resulting formulas for the potentials reduce to known cases in the absence of the cable. Using these formulations, we present some concrete calculated examples that are relevant to resistivity probing of perturbed homogeneous and layered structures. Only the two-electrode array is treated, but various cable orientations are considered. In general, it is found that a long axial conductor such as a bare cable will distort the potential distribution of the current in a major way. This leads to profound departures from the apparent resistivity curves calculated for idealized homogeneous and layered structures.U.S. Government Work not subject to U.S. copyright.     

Modeling of cable vibration effects of cable-stayed bridges

The analysis of dynamic responses of cable-stayed bridges subjected to wind and earthquake loads generally considers only the motions of the bridge deck and pylons. The influence of the stay cable vibration on the responses of the bridge is either ignored or considered by approximate procedures. The transverse vibration of the stay cables, which can be significant in some cases, are usually neglected in previous research. In the present study, a new three-node cable element has been developed to model the transverse motions of the cables. The interactions between the cable behavior and the other parts of the bridge superstructure are considered by the concept of dynamic stiffness. The nonlinear effect of the cable caused by its self-weight is included in the formulation. Numerical examples are presented to demonstrate the accuracy and efficiency of the proposed model. The impact of cable vibration behavior on the dynamic characteristics of cable-stayed bridges is discussed. Supported by: Natural Science and Engineering Research Council of Canada     

An experimental study on active tendon control of cable-stayed bridges

Active tendon control of cable-stayed bridges subject to a vertical sinusoidal force is experimentally and analytically studied. Emphasis is placed on the effects of linear and non-linear internal resonances on the control (due to the presence of the cable vibration). A simple cable-supported cantilever beam is used as a model. It is found that active tendon control is very effective in vertical girder motion with small cable vibration (girder dominated motion), whereas it is not effective in vertical girder motion with large cable vibration (cable dominated motion). Analytical prediction is very satisfactory except for the latter case.     

基于弹性拉索的超高墩三塔斜拉桥减震效果研究

为探究超高墩三塔斜拉桥在弹性拉索装置下的减震效果,首先利用SAP2000建立了考虑支座非线性和拉索几何非线性的三维有限元模型;其次基于弹性拉索装置,研究了弹性拉索刚度对三塔斜拉桥地震响应的影响;最后基于数值分析结果并结合某三塔斜拉桥实际工程提出3种减震方案。研究表明:在两边塔塔梁结合处设置弹性拉索可显著减小桥梁在地震作用下的内力和位移响应;提出的方案1(两边塔单根弹性索均为50股,单股刚度均为12000kN/m)、方案2(两边塔单根弹性索均为100股,单股刚度均为10000kN/m)和方案3(15#主塔单根弹性拉索100股,单股刚度10000kN/m;17#主塔单根弹性拉索100股,单股刚度为16000kN/m)相较于无弹性索状态,均可有效降低主塔塔底弯矩、塔底剪力、塔顶位移及主梁纵向位移;相较于方案1,方案2和方案3是更优方案。     

基于环境振动的斜拉桥拉索基频识别

斜拉索是现代斜拉桥最重要的结构构件，索力在斜拉桥的施工控制和长期监测中起着重要作用。振动测试法是斜拉桥索力测定、监测和状态评估中应用最广泛的一种方法。振动法测索力的关键在于准确地识别出索的基频。本文使用自功率谱和倒频谱方法，基于MATLAB平台，开发出了斜拉桥拉索环境振动模态分析图形用户交互(GUI)工具箱，实现了斜拉索基频的快速自动识别。应用本文的方法，对福州青洲闽江主跨605m斜拉桥拉索的环境振动实测加速度数据进行了分析处理，斜拉索基频识别方便直观，结果可靠。