钢管-钢管混凝土复合桥塔抗风性能试验研究

采用钢管-钢管混凝土复合桥塔可减轻桥塔自重,设计出更轻盈多样的结构造型,为分析桥塔抗风自立状态的抗风性能,采用MIDAS软件对该桥塔进行了抗风性能数值分析,并制作1:100的缩尺气弹模型进行风洞试验,研究桥塔的涡振、驰振和抖振响应.结果表明:在该桥塔自立状态风洞试验中未发现明显的涡振和驰振现象,紊流场中桥塔抖振响应也很...     

大跨度桥梁的抗风措施研究

目前,抗风问题已经成为决定大跨度桥梁结构安全性的控制因素。针对颤振、驰振、抖振和涡振这4种桥梁风致振动形式,分析了大跨度桥梁的风致振动情况,研究了此类问题的抗风措施。     

拉索间距及覆冰对双索尾流驰振的影响

利用FLUENT中的SST模型对不同索距的扇形覆冰双索和无覆冰双索绕流场进行三维数值模拟,得到下游索在0°~90°风攻角下的阻力系数、升力系数以及驰振力系数,进而研究两索之间的距离、风攻角及有无覆冰等条件对双索尾流驰振稳定性的影响。结果表明:覆冰双索三维数值模拟结果与无覆冰双索三维数值模拟结果差异较大;覆冰双索比无覆冰双索更易发生尾流驰振失稳;拉索间距越近,发生尾流驰振的可能性更大,当覆冰拉索间距超过一定范围时,不会发生尾流驰振失稳;双索发生尾流驰振的风攻角范围与拉索之间的距离有关,拉索间距越近,发生尾流驰振失稳的风攻角越小;不同间距双索的绕流场存在很大差异,当拉索间距较近时,类似于单钝体绕流。     

非线性屋盖结构的驰振分析

采用体型系数表达的空气动力模型,将 Newmark-β法和 Newton-Raphson 法相结合应用于风荷载作用下的非线性动力增量平衡方程中,形成大跨度非线性屋盖结构驰振分析的时程分析方法。验证了该方法计算驰振的可行性,通过工程算例进行分析。结果表明基于几何非线性特点,时程分析方法仍然行之有效,直观实用,为工程技术人员提供了参考。     

三维扇形覆冰单索及串列双索风致振动及尾流驰振分析

斜拉索偏心覆冰后,气动外形不再稳定,在风荷载作用下,可能诱发驰振。主要对三维扇形覆冰斜拉索以及串列双索尾流驰振进行研究。首先应用FLUENT中的SST k-ω模型对三维扇形覆冰斜拉索及串列双索的绕流场进行数值模拟,得到全向角下的阻力系数、升力系数及驰振力系数,然后依此判定覆冰斜拉索是否发生驰振,并得到某大跨斜拉桥部分斜拉索的驰振临界风速。数值分析结果表明,经过三维模拟计算的扇形覆冰直索及斜索的驰振力系数均大于零,表明在模拟的工况下,扇形覆冰单索在风荷载作用下不会发生驰振;而串列双索会在40°左右存在驰振力系数小于零的区域,会发生尾流驰振,但驰振临界风速很小。     

某单柱式斜拉桥桥塔的驰振稳定性分析

在桥塔模型风洞试验的基础上,根据结构驰振稳定性分析方法,对表面平均风压系数进行空间积分,得到侧弯模态广义气动力系数,通过对广义气动力系数随风向角变化的研究,计算得到横风向驰振失稳的各方向来流临界风速,从而确定桥塔的驰振稳定性.     

大跨柔性屋盖结构的空气动力失稳研究

张拉薄膜结构是风敏感结构，在风力作用下易导致空气动力失稳。这种索膜结构属于强几何非线性结构，计算分析中还存在很多问题。同时屋盖为多自由度结构，传统上用于节断模型分析的邓哈-托肯驰振临界风速判别式不再适用。鉴于此，本针对大跨索膜屋盖的结构特点，采用体型系数表示的平均风气动力模型，考虑风载竖向分量的影响及结构本身的非线性特性，用Newmark法和Newton Raphson法的思路，并借助ANSYS软件进行分析，得出屋盖结构发生横风向驰振时的临界风速，此方法可供实际工程进行空气动力失稳分析时参考。     

桥梁箱型吊杆涡振与驰振耦合振动的数值模拟

为研究桥梁箱型吊杆涡振与驰振耦合状态下的风致振动机理,基于某大跨度钢桁架拱桥大长细比箱型吊杆的节段模型风洞试验参数与试验结果,采用计算流体动力学（CFD）软件FLUENT对模型的耦合振动进行了数值模拟,通过FLUENT的后处理功能进一步研究分析了不同振动状态下的气动力和尾流旋涡特征信息。研究结果表明:数值计算得到的风振曲线与试验的实测结果吻合良好,在涡振与驰振的耦合振动过程中,随着振动幅值的不断增大,尾流旋涡脱落由小振幅阶段规则的卡门旋涡形态转化为大振幅阶段的复合模态特征,气动升力也由小振幅阶段的单频特征逐步转化为大振幅阶段的多频特征。     

双分裂导线尾流驰振的数值模拟

利用计算流体动力学(CFD)方法对双分裂导线在均匀来流作用下的气动力与流场特性进行数值模拟计算,研究得到各子导线的气动力系数,以及背风侧子导线气动力系数随其与迎风侧子导线相对位置的变化曲线。同时采用两节点索单元模拟导线,梁单元模拟间隔棒,建立双分裂导线的尾流驰振数值模拟的有限元模型,并基于CFD方法数值模拟得到的各子导线气动力参数建立双分裂导线的气动力模型;利用Ruange-Kutta显示积分法对其动力方程进行非线性数值求解,得到其尾流驰振的动力响应。最后以某实际工程中双分裂导线为例,研究间隔棒布置、分裂导线倾角以及风速对分裂导线尾流驰振的影响。上述结论可为双分裂导线的防振设计与研究提供参考。     

圆柱和带圆弧圆柱绕流的二维数值模拟

文章采用计算流体动力学软件Fluent中的SST k-ω湍流模型在雷诺数为6.8×10~4的条件下对圆柱和带圆弧圆柱的绕流情况进行二维数值模拟。首先计算了圆柱的阻力力系数与斯托罗哈数并与参考文献进行对比,以保证网格划分与边界条件的正确性。之后对不同角度下的带圆弧圆柱进行了数值计算,得到了绕流流线图、升力系数、阻力系数、斯托罗哈数、驰振力系数,并与圆柱的计算结果进行比较。研究结果表明:在不同角度下,带圆弧圆柱的模拟结果与圆柱相比差异明显;带圆弧圆柱的驰振力系数存在小于零的区域,有发生驰振的可能性。     

Design against wind-induced vibration of multi-flue chimney stacks

Experimental study based on flow visualization, model oscillation testing and power spectral measurement has revealed the complexity of flow passing a multi-flue arrangement. The occurence of instability due to various aerodynamic excitation is possible. In the case of the sectional configuration having flues and structural members in a pentagonal arrangement, the oscillation induced by wind was found to be due to galloping at reduced wind velocity greater than $\text{V}{}_{\mathrm{<mtext>r</mtext>}}\text{= 16}$ with the amplitude of oscillation increasing with increase in wind velocity. With the application of slat devices to the chimneys, galloping oscillation was suppressed completely. As it is not yet possible to predict the response of a multi-flue chimney stack in wind with any certainty, it is useful to consider means of reducing any oscillatory tendency by original design. The design of the new chimney stack for the Royal United Hospital in Bath against the possibility of wind-induced vibration is discussed as an example.     

Galloping stability of triangular cross-sectional bodies: A systematic approach

One of the classical aeroelastic instabilities of slender structures is galloping, which can be characterized as a low-frequency, large-amplitude normal to the flow oscillations phenomenon. In this paper, the transverse galloping stability of triangular cross-section bodies has been systematically analyzed (up to now, most of the effort in galloping oscillation research has been concentrated on bodies with square or rectangular cross-sections). To perform such analysis, first, the Glauert–Den Hartog criterion for galloping instability was used through wind tunnel static tests. Then, another series of wind tunnel dynamic tests was realized to determine the transversal cross-section displacements as a function of the incident wind velocity. The results from these dynamic tests are in very good agreement with the results obtained from the static ones. Finally, information on the flow morphology needed for the physical interpretation of the results was obtained by measuring the pressure distribution along the body surfaces.     

Three-dimensional behavior of galloping in telecommunication cables of figure-8 section

It has been reported that many telecommunication cables of figure-8 section suffered from operating problems and sometimes even failed because of wind-induced large-amplitude galloping oscillation. In this study three-dimensional figure-8 cable model was tested in the wind tunnel and aeroelastic behavior of the cable was observed in detail. It is found that wind-induced change in the angle of attack of the wind relative to the cable is significant and this is the fundamental cause of galloping. The critical wind speed that triggers galloping and the initial direction of the self-excited cable motion are explained by the Den Hartog's quasi-steady treatment of the aerodynamic force with some modifications. Applicability of 3-dimensional dynamic analysis with quasi-steady wind forces was also discussed.     

覆冰导线三自由度耦合舞动稳定性判定及气动阻尼研究

利用风洞内支架式三自由度频率可调的弹簧悬挂装置对D形覆冰六分裂导线节段气弹模型进行舞动试验,在不同气动力特性的风攻角下调整竖/扭自振频率比及风速,激发并记录纯竖向、纯扭转、竖扭耦合和扭转水平耦合等失稳舞动。分别基于实测响应和三自由度舞动响应非线性数值模拟结果识别导线的竖向和扭转气动阻尼并与Den Hartog或Nigol舞动理论计算值进行对比,研究导线气动阻尼与气动特性、自振特性及风速之间的关系。试验结果发现：由于Den Hartog或Nigol系数正负不同以及竖/扭频率比不同,导线气动负阻尼绝对值会随风速提高以指数形式增大或者是随风速提高先增大后减小至小于结构阻尼;用单自由度舞动理论来预测三自由度舞动存在较大缺陷且偏于不安全。基于特征值摄动法提出覆冰分裂导线竖向-水平-扭转三自由度耦合的舞动稳定性判断条件式,解释了无法用Den Hartog或Nigol单自由度稳定性判断条件式说明的舞动现象,并得到试验结果的验证。     

Identification and characterization of galloping of Tsuruga test line based on multi-channel modal analysis of field data

In spite of several signal processing and system identification techniques, discussion on field-observed galloping of overhead transmission lines is still based on primitive form of field data such as time series, Lissajous diagrams and power spectra. Any form of large amplitude vibration in ice storms is defined as galloping and an attempt has seldom made in identifying whether such vibrations are self-excited modal responses. In doing so, there are always possibilities of misinterpreting gust response as galloping. In this study, a method of multi-channel modal analysis consisting of random decrement method (RDM) and eigensystem realization algorithm (ERA) is proposed to identify galloping, which is self-excited modal response based on a typical field-monitored data of wind-induced vibration of the Tsuruga Test line. RDM was used to transform the field data into non-forced response component, which is similar to free vibration response, and ERA was used to extract modal parameters from the non-forced components. Based on these modal parameters, galloping events were identified, and characteristics of galloping such as coupled translational and rotational motions, and nature of full span vibration, oscillation envelopes and influence of geometry of the line section to its occurrence are discussed. Result of analysis has confirmed well-known mechanism of bundle conductor galloping, which is galloping of bundle transmission lines involves significant coupling of vertical and torsional motions. As for the characteristics of bundle conductor galloping, the most likely galloping mode in deadend span is found as first asymmetric mode and large amplitude of galloping occurs when torsion is in-phase with vertical velocity. Furthermore, it is found that deadend span line section is more prone to galloping than semi-suspension span line section. Finally, performance of proposed method was tested by introducing usual buffeting analysis, and it is confirmed that it has immense potential to identify and characterize galloping based on field data.     

On the galloping instability of two-dimensional bodies having elliptical cross-sections

Galloping, also known as Den Hartog instability, is the large amplitude, low frequency oscillation of a structure in the direction transverse to the mean wind direction. It normally appears in the case of bodies with small stiffness and structural damping, when they are placed in a flow provided the incident velocity is high enough. Galloping depends on the slope of the lift coefficient versus angle of attack curve, which must be negative. Generally speaking this implies that the body is stalled after boundary layer separation, which, as it is known in non-wedged bodies, is a Reynolds number dependent phenomenon. Wind tunnel experiments have been conducted aiming at establishing the characteristics of the galloping motion of elliptical cross-section bodies when subjected to a uniform flow, the angles of attack ranging from 0° to 90°. The results have been summarized in stability maps, both in the angle of attack versus relative thickness and in the angle of attack versus Reynolds number planes, where galloping instability regions are identified.     

Two-degree-of-freedom inclined cable galloping—Part 2: Analysis and prevention for arbitrary frequency ratio

It has previously been shown that inclined cables and other slender structures can experience galloping instabilities in the critical Reynolds number region, due to the changes in force coefficients, and that coupling of the vibrations in two orthogonal planes can significantly affect the behaviour. It is shown in this paper that for more than a few percent detuning of the natural frequencies, the structural damping required to prevent galloping vibrations tends towards solutions for uncoupled single-degree-of-freedom (DOF) systems. However, the coupling can cause the trajectory of cable motion to be elliptical. Using measured force coefficients for an inclined circular cylinder in the critical Reynolds number range, calculated results of the effective damping and the cable trajectory have been obtained in good agreement with a separate full-scale dynamic cable model test that exhibited galloping behaviour under certain conditions. The special case of sub-critical Reynolds numbers is also addressed. The 1DOF and perfectly tuned 2DOF solutions are considered for inclined circular cables in a horizontal wind from any direction, leading to simple guidelines for the structural damping required in practice to prevent dry inclined cable galloping, for any frequency ratio. Finally, other factors in the behaviour and similarity to rain-wind excitation are discussed.     

斜拉桥索的风振现象及天津慈海斜拉桥的抑振措施

斜拉桥的斜拉索对风荷载作用十分敏感,在风单独作用和风、雨共同作用下会发生振动。通过介绍世界几座著名桥梁斜拉索的风振实例及其抑振措施,对斜拉索的几种风致振动进行分析和总结。对斜拉桥拉索最可能发生的尾流驰振和风雨振的产生条件、振动特性、发生机理及抑振措施进行分析,最后对天津慈海桥进行分析,并论述慈海桥可能发生的三种风致振动现象,提出了三种抑振方法。     

小波分析在结构动力有限元结果处理中的应用

讨论了动力有限元求解瞬间波动过程中产生的高频振荡的原因以及常用的解决方法,采用小波分析的方法对结构的动力响应结果进行处理,主要讨论了利用小波分析降低减加速度频率振荡的问题,通过研究表明。小波分析方法能够将动力响应中的各种频率组分精细地分解出来,根据系统的截止频率对动力响应进行重组。经过重组后的动力响应信号较原始信号更加真实可靠,从而达到了消除高频振荡现象的目的。最后,通过一个具体的算例,验证了本文的方法。