斜拉索的参数振动

对斜拉桥拉索的参数振动问题建立了非线性力学模型 ,并进行了数值计算分析。指出了拉索参数振动的可能性 ,并对其特征进行了研究。对桥面振动而导致的拉索振动提出了一种新的抑振装置 ,计算结果表明具有较好的减振效果     

斜拉桥拉索的振动控制

基于对拉索风致振动机理的认识,提出了一系列相应的振动控制方法,主要分为空气动力学措施和机械措施。前者主要通过改变拉索的断面形状,使其空气动力学性能得到改善;后者通过在拉索上附加阻尼器或辅助索等机械(结构)装置,增加拉索的阻尼或形成有干扰效应的索组,达到减小振动的目的。     

斜拉桥拉索参数振动研究进展

介绍了拉索振动的危害、拉索参数振动的原理和研究意义,概述了国内外对斜拉桥拉索参数振动的研究进展,通过分析现有研究存在的不足,对进一步研究的方向提出了建议。     

剪切来流作用下的拉索流致振动分析

基于计算流体动力学(CFD),对二维线性变化的剪切来流作用下拉索横向流致振动响应进行数值计算,分析了不同剪切率与不同折减速度对拉索横向振动响应及其绕流的影响.结果表明:折减速度较大时,来流的剪切率对拉索最大振幅影响明显;折减速度的变化显著影响拉索最大振幅,来流的剪切率、折减速度对拉索流致位移、升力的相位关系及其尾流模态影响较大.     

用磁流变阻尼器实现对桥梁拉索的振动控制

介绍一种新型的半主动控制装置——磁流变阻尼嚣的工作原理及控制算法，简明阐述该阻尼器实现对桥梁拉索进行振动控制的过程，从而显示出这种阻尼器进行拉索振动控制的优越性及其发展前景．     

斜拉索风致振动减震措施分析

斜拉索是斜拉桥的关键部位和主要承重部件。索的大柔度、小质量和小阻尼等特点,极易在风、雨、地震及交通等荷载作用下发生振动。文章对斜拉索的风致振动形态进行了分析,并介绍了一些常用的减震措施,为今后进一步的研究提供了基础。     

考虑脉动风影响的斜拉索在支点激励下的非线性振动

应用柔性拉索的非线性振动响应计算理论,提出考虑横向脉动风荷载作用及支点激励的拉索非线性振动计算方法。以力学特性不同的两种斜拉索为对象,通过数值方法分析横风作用和支点激励下的钢索、CFRP拉索非线性振动响应,比较支点激励频率、风速、阻尼器对参数振动响应的影响。结果表明,在拉索基频f1以及两倍基频2f1的支点位移激励下,脉动风虽然导致拉索出现不规则的竖向和横向水平振动轨迹,但不会改变拉索的参数振动特性;横向风荷载对参数振动具有空气阻尼力的效应;总体上CFRP拉索的参数振动振幅小于钢索,特别当拉索跨度比较大时,CFRP拉索的振幅将明显低于同跨度的钢索;黏性阻尼装置的减振效果与拉索的结构条件有关,当拉索的无量纲参数λ(Irvine参数)较大时,阻尼器的减振效果不明显,反之当λ较小时阻尼器有一定的减振效果。     

磁流变阻尼器对斜拉索的振动控制

利用有限元软件建立了拉索振动控制系统的力学模型,对深圳湾公路大桥上的最长斜拉索和MR阻尼器组成的系统进行了动力分析。在振动控制系统中分别模拟了正弦简谐力作用下的谐波共振和参数共振这两种最危险的振动情况,研究了阻尼器的减振效果,并通过拉索位移幅值衰减率分析了各种参数对磁流变阻尼器振动控制效果的影响,从而得出最优减振方式。     

斜拉桥拉索参数振动的研究

为探讨桥面激励对斜拉索非线性的影响,研究了斜拉桥中拉索的参数振动,得出了拉索与全桥振动的频率匹配关系,并指出了抑制拉索参数振动的有效措施。结果表明,增大阻尼比并不能有效地抑制拉索的参数振动,但当阻尼比大于某一值时,拉索将不会发生参数振动;激励幅值越大,拉索发生参数振动时瞬态振幅和稳态振幅也越大,当激励幅值小于某一值时,拉索不会发生参数振动;为了抑制拉索的参数振动,可以通过拉索的阻尼比及拉索的激励幅值来综合控制。     

来流湍流度对斜拉索风雨激振影响的理论研究

斜拉索风雨激振严重地影响斜拉桥的安全运营,而来流湍流度是影响风雨激振的一个重要因素。采用理论分析方法,研究来流湍流对斜拉索风雨激振响应的影响。引入2种类型的风场,首先,假设来流为简谐脉动风场,然后,采用谐波合成方法,将Kaimal风谱作为目标谱,模拟来流随机脉动风场。采用上述2种来流风场,在已建立的两质量三自由度理论模型的基础上,研究各种湍流度下拉索和水线的风雨激振振动规律。计算结果表明,当湍流度达到15%时,水线不能在拉索表面稳定地存在,风雨激振能得到有效的抑制;水线运动的脉动成分主要受来流风脉动成分的影响,拉索运动对水线运动有一定的影响,但影响较小;随着紊流度的增加,起振风速也增大。     

磁流变阻尼器对支座简谐运动下拉索参数振动的智能控制

以斜拉索为研究对象,忽略索桥之间的耦合作用,研究支座简谐运动下,磁流变阻尼器对拉索参数振动的智能半主动控制。首先建立斜拉索-阻尼器系统的三维运动方程,并采用有限差分法进行离散化。针对磁流变阻尼器的力学特点,提出简单适用的基于平衡逻辑算法的半主动控制策略,该控制策略的实现仅需测量阻尼器的位移和速度反应。重点考察支座简谐运动频率与拉索面内基本频率之比为2,1,2/3和1/2这4种工况。仿真分析表明,采用半主动控制策略,大多数情况下磁流变阻尼器能显著地降低拉索的面外位移,可以认为磁流变阻尼器能有效避免拉索平面外参数振动的发生;另一方面,仅在少数情况下磁流变阻尼器才对拉索的面内振动产生明显的减振效果。此外,提出的控制算法会导致拉索振动的混沌性。     

Computational study on aerodynamic mitigation of wind-induced, large-amplitude vibrations of stay cables with strakes

Modifications of circular cylinder surfaces, such as strakes and helical wires, effectively mitigate Kármán vortex-induced vibrations normal to flow and have been applied to the reduction of large-amplitude vibrations of stay cables in bridges, which occur under wind oblique to a cable with or without rainfall. This aerodynamic control method cannot be fully effective without understanding the behavior of the flow around and the associated forces on oblique cables. To address this issue, flow around a yawed cylinder with various strake patterns was studied using three-dimensional detached eddy simulation (DES) at Reynolds number of 1.4×10⁵. Results demonstrated that strake patterns strongly influence the development of flow structures around a yawed cylinder and therefore the associated forces on the cylinder. The results suggest that particular strake patterns can mitigate large-amplitude and low-frequency vibrations of stay cables induced by oblique wind.     

斜拉索风雨振现场观测与振动控制

介绍了斜拉索风雨振现场观测与振动控制研究的情况。在湖南岳阳洞庭湖大桥上建立了风雨振观测系统，并连续4年进行了长时间现场观测，在风速、风向、雨量等参数对风雨振的影响规律与拉索风雨振振动形态方面有了新的发现。提出了一种多模态振动控制的参数优化方法。进行了拉索一磁流变阻尼器系统的减振性能仿真研究与现场试验研究，全面评估了磁流变阻尼器的实际减振性能。开发了一套磁流变式拉索减振系统，并于2002年在该大桥全桥实施，3年来显示了良好的减振效果。同时针对城市桥梁磁流变减振系统的低压供电线路最易受到人为破坏的问题，设计开发了一种永磁可调式磁流变阻尼器（PMAA—MR），并将其成功应用于湖南长沙洪山庙大桥的拉索减振。     

Solution for large amplitude vibrations of circular plates via modified Berger's approximation

Complex mathematical formulations for the geometrically nonlinear analysis of structural members have been presented by many researchers using the von-Karman strain-displacement relations. Berger proposed a simplifying approximation to take care of the geometric nonlinearity by neglecting the second strain invariant. Although it is a reasonable approximation, it poses problems when applied to circular plates. This is mainly due to the coupling between the radial and circumferential inplane strains, by the radial displacement. In this article, a modification to the Berger's approximation, applicable to the circular plates, is proposed. The main motivation of the present study is to examine how the modified Berger's approximation works in the case of the large amplitude vibrations of circular plates. It is shown that the modified Berger's approximation gives consistently accurate results, for both the simply supported and clamped circular plates, when compared to the classical results.     

Control of vibrations induced by people walking on large span composite floor decks

The low damping properties of lightweight large span floor decks composed of a reinforced concrete slab on top of a steel space frame structure may lead to undesirable dynamic responses, even to ordinary human actions such as walking.This problem was investigated through laboratory tests performed on a 1:1 scale prototype of a composite floor deck structure. Experimental measurements were taken for the structure subjected to several dynamic human loads, especially those produced by the random walking of people.To compensate for the lack of damping, a passive control system was designed and installed in the composite structure prototype.The performance of the mechanical control devices was evaluated by means of straight comparisons between the experimental acceleration amplitudes obtained for the controlled and uncontrolled structure subjected to similar dynamic forces produced by one or more persons walking. The most relevant results for both time and frequency responses are presented and used to argue that small and low cost passive control devices can already be included in the design stage of a smart structure as effective accessories to substantially reduce vibrations induced by people in low damped large span composite floor decks.     

Simple model of rain-wind-induced vibrations of stayed cables

This paper proposes a single-degree-of-freedom model of rain-wind-induced vibrations in stayed cables. It is assumed that the frequency of the circumferential motion of the upper rivulet is equal to that of cable and the rivulet amplitude is set constant for a given wind speed. The obtained results are verified with the existing experimental data showing that these assumptions capture the qualitative properties of the phenomenon. The explicit, analytical expressions are derived for the aerodynamic damping and exciting force. Finally, a linear SDOF model is derived for simple estimation of the amplitude of cable vibrations induced by wind and rain.     

高精度风雨模拟环境下拉索风雨激振试验研究新发现

拉索风雨激振是一种在风雨共同作用下发生的拉索大幅低频振动,现有人工降雨风雨激振试验无法准确模拟自然降雨的多种特性,难于实时再现风雨介质耦合环境拉索气动失稳现象。开发高精度人工降雨模拟装置,可对降雨强度进行精细连续调节,较为准确模拟雨滴大小、能量、均匀度等自然降雨的特性,合理地再现风雨联合作用条件下拉索风雨激振过程;系统研究风速、雨量以及风雨联合作用对拉索风雨激振的影响,揭示了拉索在低风速大雨量、高风速小雨量时,风雨激振发生规律和特点。     

斜拉桥拉索风雨激振的两质量三自由度理论模型

斜拉索的风雨激振严重地影响到斜拉索以至于斜拉桥的安全,其机理至今仍无定论。同时考虑拉索面内和面外两个自由度,并假设拉索和水线之间的作用力为库仑阻尼力和线性阻尼力,建立斜拉桥拉索风雨激振的两质量三自由度理论模型。采用Runge-Kutta法对拉索和水线的耦合方程进行数值求解,得到拉索和水线的运动规律。与仅考虑拉索面内自由度的两质量两自由度理论模型相比,考虑拉索面内面外自由度的两质量三自由度理论模型的起振风速区更多,这主要是因为拉索的水平气动力系数也存在突降,且拉索面内面外运动是相互耦合的。水线上的气动力和重力为水线提供总体的平衡;阻尼力则消耗水线的能量;至少一个方向的拉索运动引起的附加惯性力(竖向或水平)一直对水线做正功。