横风向旋涡脱落共振响应分极及在规范上的应用

结构在风作用下,不但顺风向产生风振响应,而且横风向必然产生旋涡脱落风振．当横风向旋涡脱落频率与结构某阶自振频率一致时,结构产生极大的横风向共振,如不注意,结构将产生损坏或破坏,国内外有很多这类指导。本文基于国内外研究和规范资料,对本规范横风向共振依据的原理予以介绍,并对有关条文加以说明。     

大高宽比方形截面高层建筑的横风向风荷载及风致响应研究

基于一栋高层建筑的刚性模型表面压力测量风洞试验数据,分析了高宽比较大且截面为方形的高层建筑横风向风效应的共同特征。得到如下结论:高层建筑横截面为方形时,其横风向风荷载主要由规则性旋涡脱落导致的尾流激励构成,为窄带随机激励;当高层建筑的高宽比较大时,基阶固有频率相对较低;当高层建筑兼具方形截面和大高宽比这两个特征时,其基阶固有频率可能接近其尾流的旋涡脱落频率,从而发生剧烈的横风向涡激共振。建筑结构截面的小幅增大可使这种剧烈的横风向涡激共振得到有效控制。上部外形的适当处理,也可能有效降低高层建筑的横风向等效风荷载。低矮群楼的出现将在一定程度上影响高层建筑的风荷载。     

三边形桅杆风荷载谱模型试验研究

对三边形格构式桅杆进行了均匀流和两种紊流下的高频测力天平风洞试验,得到了顺风向、横风向和扭转向的气动力系数以及脉动风荷载谱。采用基于风速谱的数学模型对顺风向脉动风荷载谱进行拟合,验证了该经验公式在不同流场下的适用性。根据试验所得横风向和扭转向脉动风荷载功率谱曲线的特点,建立由紊流激励和旋涡脱落激励两部分组成的谱函数数学模型,最小二乘法拟合结果与风洞试验结果吻合良好。横风向脉动风荷载谱以紊流激励为主,紊流强度15%时旋涡脱落激励贡献仅占10%,扭转向脉动风荷载谱中旋涡脱落激励贡献明显增大,达到40%。     

结构风振控制综合方程及简化实用方法研究

结构在风作用下可产生强烈的振动 ,振动可以是顺风向的 ,也可以是横风向的。为了减少振动 ,可采用振动控制方法来满足要求。本文对顺风向随机振动写出了结构振动控制统一的综合方程 ,对有关非线性问题作出了研讨 ,并提出一个简化实用方法。对横风向涡流脱落共振控制也作了分析     

利用人工模拟脉动风压计算高层建筑横风向风振动力反应时程

根据日本规范中提出的横风向脉动风力谱系数函数,利用人工模拟横风向脉动风压时程的方法,提出了一个矩形平面高层建筑横风向风振反应时程的计算方法.在计算过程由横风向脉动风压谱系数公式模拟了建筑结构横风向脉动风压过程,采用N ewm ark法计算了两幢建筑物顶部的横风向风振反应.计算结果表明:在横风向脉动风压的作用下,结构的风振反应以共振响应为主,非共振响应仅为次要的部分,这与谱分析法得出的结论是一致的,从而说明了计算结果的正确性.这对于正确估算结构的风振反应值,为高层建筑风振控制措施设计提供参考依据具有一定的意义.     

矩形超高层建筑归一化横风向脉动风荷载谱模型

为研究超高层建筑横风向脉动风荷载谱特性，在B、D两类紊流风场中开展了不同长宽比矩形刚性模型测压试验。结果表明：横风向脉动风荷载特性主要受紊流风场、气动外形和旋涡脱落等因素影响，矩形柱截面的长宽比变化将影响功率谱幅值及能量分布。当矩形柱截面长宽比小于3时，横风向脉动风荷载谱特性主要受旋涡脱落控制，但当长宽比超过3后，矩形柱侧面分离再附流动的影响逐渐加强，具体表现在：功率谱峰值减小、带宽增大及高频区出现较小谱峰。根据风洞试验结果和矩形柱横风向脉动风荷载谱特性，提出了归一化横风向脉动风荷载谱模型，该经验公式物理意义明确、形式简洁，有一定的工程参考意义。     

利用人工模拟脉动风压计算高层建筑横风向风振动力反应时程

根据日本规范中提出的横风向脉动风力谱系数函数，利用人工模拟横风向脉动风压时程的方法，提出了一个矩形高层建筑横风向风振反应时程的计算方法供参考。采用Newmark法与Wilson-θ法计算了2栋建筑物顶部的横风向风振反应。计算结果表明，在横风向脉动风压的作用下，结构的风振反应以共振响应为主，非共振响应仅为次要的部分；这与谱分析法得出的结论是一致的；从而说明了计算结果的正确性。这对于正确估算结构的风振反应值，为高层建筑风振控制措施设计提供参考依据是有一定意义的。     

索膜屋盖结构横风向共振响应的时程分析方法

索膜屋盖结构的横风向共振问题与以往研究的高层 /高耸结构的横风向共振问题有较大区别。本文根据索膜屋盖结构的受力特点 ,发展了一种适合大跨索膜结构非线性横风向风振响应计算分析的方法 ,利用Newmark法和Newton Raphson法的思想推导了索膜结构在横风向风荷载作用下 ,结构的非线性动力增量平衡方程 ,并提出如何判别结构发生横风向共振的方法。文中还对有关参数的取值进行了讨论。最后本文利用ANSYS程序对某算例进行分析 ,得到其发生横风向共振时的风速     

国内外规范圆截面高耸结构横风向等效风荷载取值对比研究

圆截面高耸结构（烟囱）因涡激共振而发生破坏或损坏的例子屡见不鲜,显示现存各种荷载规范对圆截面高耸结构横风向设计荷载考虑不足。本文简要介绍了中国、日本、加拿大、欧洲等四种规范关于圆截面高耸结构横风向等效风荷载的计算方法,并结合-200m的高烟囱实例分析了四种规范计算结果的差异。研究表明,比较四种规范,中国规范偏不安全,我国圆截面高耸结构横风向涡振等效风荷载规范方法亟待完善。     

基于大涡模拟的三维高层建筑结构气弹响应数值模拟

以宽高比为1∶6的方形截面高层建筑为研究对象,采用弱耦合分区交错算法,流体域采用大涡模拟方法,进行了紊流边界层风场内三维高层建筑结构多自由度模型的气弹数值模拟,计算中考虑了来流紊流,以及结构的顺、横风向响应。将结构静止时大涡模拟结果与刚性模型测压风洞试验进行比较,验证了该方法在准确预测结构风荷载方面的可行性。通过与气弹模型风洞试验结果的比较表明,本文数值分析方法可用于求解风与结构的相互作用,且具有较高的精度。进行了高折减风速下的气弹数值模拟,研究了结构顶部顺、横风向位移响应随折减风速的变化规律。结果表明：结构风振气弹响应主要为来流紊流引起的顺风向抖振和旋涡脱落引起的横风向涡激振动;折减风速较小时,结构顺、横风向位移振幅相当,且位移响应均相对较小;随着折减风速的增加,结构位移响应增大,横风向涡激振动逐渐占据主导地位,并经历了从“拍”到“涡激共振”的转化。     

深圳京基金融中心气动抗风措施试验研究

深圳京基金融中心高439m,风荷载是该超高层建筑的控制荷载。采用高频底座力天平方法对该建筑模型进行了风洞试验,考察了利用其顶部设备和避难层进行开敞形成不同的风走廊(气动措施)对结构风荷载和风致响应的影响。试验结果表明：在重现期100a敏感风向作用下结构漩涡脱落频率明显低于结构基阶固有频率;气动措施可显著抑制和削弱脱落漩涡的强度,当没有受到明显干扰影响时,气动措施显示出良好的抗风效果。不同气动措施可使重现期100a结构基底弯矩减少8.2%~21.2%,使重现期10a峰值加速度减少5.3%~16.0%;受到来自于地王大厦的干扰效应的影响,在所关注重现期风速范围内的结构风振响应为上游地王大厦的尾流所控制,影响了气动措施的控制效果,但在发生涡激共振的临界风速时气动控制措施效果显著。     

Investigation of vortex-induced vibration of a suspension bridge with two separated steel box girders based on field measurements

This paper investigates the vortex-induced vibration of a twin steel box girder suspension bridge with a centre span of 1650 m based on field measurements. Two ultrasonic anemometers, two tri-axial accelerometers and 52 wind pressure sensors are installed at the quarter span section. The other 20 pressure sensors are installed in another 5 sections, and each section has 4 pressure sensors. Four vortex-induced oscillation events are measured. The analytical results indicate that the vortex-induced vibration more likely occurs in a low wind speed range of 6-10 m/s, with the wind direction nearly perpendicular to the bridge line, and low turbulence intensity. The mean pressure distribution on the surface of the bridge deck is obtained and the characteristics of fluctuant pressures are analysed by proper orthogonal decomposition (POD) method. Moreover, the spatial-temporal evolution of flow around the bridge deck is investigated. The results indicate that in the beginning stage of vortex-induced resonance, the regular vortex shedding phenomena occur only in the gap of the deck and at tailing region of downstream deck; however, when in the lock-in stage, the vortex shedding is strengthened due to the dramatic vibration, and the regular vortex shedding phenomena extend to the entire lower surface of downstream deck and the tail of upstream deck, the vortex shedding regions in the gap and lower surface link together. In the lock-in range, the span-wise correlation of the wind pressure is analysed, and the correlations of wind pressure along the bridge line are very high and do not decrease with the increase in distance.     

封闭式单向张拉膜结构气弹失稳机理研究

在均匀流场中进行了封闭式单向张拉膜结构气弹模型风洞试验,考察了膜预张力和来流风速对结构振幅、振动模态和总阻尼比的影响,以及膜面位移与膜上方流场的频谱相关性,分析了封闭式膜结构的气弹失稳机理,给出了气弹失稳无量纲临界风速。研究结果表明：低风速下(无量纲风速小于1.2时),流场中的旋涡主频远低于结构基频,结构以受迫振动为主;随着风速增大,流场中出现与结构2阶反对称模态频率接近的旋涡,导致结构发生以2阶模态大幅振动为特征的涡激共振,且在无量纲风速不小于1.2 的风速范围内出现振动锁定现象,结构总阻尼比迅速衰减接近0。由此可认为,封闭式膜结构的气弹失稳由涡激共振引起,结构振幅的突然增大、主导振动模态的突然改变以及总阻尼比的突然减小为其主要特征;气弹失稳无量纲临界风速约为1.2。     

基于表面风压分析的分离式双箱梁流场特性研究

为研究分离式双箱梁流场特性,以某分离式双箱梁断面斜拉桥为研究对象,采用节段模型测振与测压试验的方法得到分离式双箱梁不同状态下的表面风压,通过对风压进行分析处理得到不同状态下风压脉动主频分布及平均风压系数分布.在振动状态下,对扭转涡振锁定区间内及超出扭转涡振锁定区间后分离式双箱梁模型表面风的压力脉动主频分布区域的变化进行...     

Wind induced dynamic response of the Wye bridge

As part of the research effort to improve the understanding of the effect of wind on bridges, the Transport and Road Research Laboratory (TRRL) has measured the wind-induced dynamic response of the 235 m span cable stayed box girder bridge that carries the M4 motorway over the River Wye. Measurements are presented which were made during the winter months of 1977 and 1978, using automatic recording equipment developed at TRRL.

The main wind-induced vibration frequency measured was at 0.46 Hz, which corresponds to the first bending mode. The response occurs mainly when the wind speed is in the range 7–8 m/s and the direction is close to normal to the bridge. This agrees with wind tunnel section tests but the maximum amplitudes predicted in the laboratory have not been attained to date. The strong dependence of vibration amplitude on wind speed, showing a peak in the range 7–8 m/s is characteristic of vortex shedding excitation. The problem of predicting the likelihood of the bridge response from wind speed data is discussed.

Finally, the effect on the fatigue life of the structure is discussed. It is shown that it is most unlikely that wind-induced oscillations will contribute to a significant shortening of the fatigue life of the bridge.     

Vortex-induced vibration of stay cable under profile velocity using CFD numerical simulation method

Vortex-induced vibration (VIV) of a stay cable subjected to a wind profile is numerically simulated through combining computational fluid dynamics (CFD) code CFX 10.0 and computational structural dynamics (CSD) code ANSYS 10.0. A stay cable with the inclined angle of 30° is used as the numerical model. Under a profile of mean wind speed, unsteady aerodynamic lift coefficients of the cable have been analyzed in both time domain and frequency domain when VIV occurs. The results indicate that the lift coefficient wave response of the stay cable under a wind profile is different from that of an infinitely long cable under a uniform flow in water (i.e., without consideration of profile) obtained by direct numerical simulation. Cable oscillations can severely affect the unsteady aerodynamic frequencies, change flow field distribution near the cable and affect the vortex shedding in the wake.     

On the vortex shedding forcing on suspension bridge deck

Vortex-induced vibrations are not negligible while evaluating the aerodynamic and aeroelastic behavior of a long-span suspension bridge. This kind of forcing, that can produce high vibration levels, occurs at very low reduced velocities concerning low wind speed and high-frequency modes. This work presents results of experimental tests performed on the multibox deck shape of the Messina Strait bridge investigating vortex shedding phenomena and developing a numerical model to reproduce the vortex shedding forcing. The experimental tests, focused on low reduced velocities, highlight the typical non-linear pattern of the vortex shedding.     

Vortex-induced vibration of stay cable under profile velocity using CFD numerical simulation method

Vortex-induced vibration (VIV) of a stay cable subjected to a wind profile is numerically simulated through combining computational fluid dynamics (CFD) code CFX 10.0 and computational structural dynamics (CSD) code ANSYS 10.0. A stay cable with the inclined angle of 30° is used as the numerical model. Under a profile of mean wind speed, unsteady aerodynamic lift coefficients of the cable have been analyzed in both time domain and frequency domain when VIV occurs. The results indicate that the lift coefficient wave response of the stay cable under a wind profile is different from that of an infinitely long cable under a uniform flow in water (i.e., without consideration of profile) obtained by direct numerical simulation. Cable oscillations can severely affect the unsteady aerodynamic frequencies, change flow field distribution near the cable and affect the vortex shedding in the wake.     

Estimation of the vortex shedding frequency of a 2-D building using correlation and the POD methods

A method was developed to estimate the frequency of vortex shedding in turbulent flow. In this method, a Particle Image Velocimetry (PIV) system was used to acquire the original complex turbulent flow field. Proper orthogonal decomposition (POD) analysis was applied to the PIV data in order to extract the main structure of the overall physical characteristics from the measured wind velocity field. A bivariate correlation was introduced to the POD results to determine the correlation of the vortex structures. Fast Fourier Transform (FFT) was employed to perform a power spectra analysis of these correlation coefficients to obtain the frequency of vortex shedding from the power peak. A PIV experiment was carried out within a wind tunnel simulated atmospheric surface layer, which involved a two-dimensional building problem with wind from two directions. The developed method was applied to the PIV experimental data and the frequency of vortex shedding was successfully extracted. The results show that the frequency of vortex shedding increases with increase in incoming flow velocity for both wind directions.