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.     

膜结构风振响应的二维数值模拟研究

结合膜结构的风振响应特点,采用流固耦合问题数值计算方法,实现了二维情况下膜结构风场的数值模拟。阐述了膜结构流固耦合计算中的结构域与流体域的网格关系和流固耦合边界的控制条件。选择大涡模拟作为湍流模型,并采用隐式时间积分TR-BDF法对流体域的Navier-Stokes方程进行时间域的离散。对耦合系统的有限元方程组采用Newton-Raphson法进行求解。计算结果表明,湍流模型选择大涡模拟可以较好模拟二维情况下膜结构在流场中的脉动反应。对于一般性的算例,瞬态流场中膜的应力增加较为明显。合理选择膜结构体型可以减小膜结构风振响应的脉动幅度。     

考虑流固耦合作用的索膜结构开洞与封闭条件下的风压风振模拟

在任意拉格朗日-欧拉(Arbitrary Lagrangian-Eulerian,简称ALE)描述下,引入Menter SST湍流模式和非线性有限元方法,建立了耦合方程迭代求解策略,进而研究考虑流固耦合作用的索膜结构风振响应.数值模拟了结构膜帽开洞和封闭等工况下的伞形索膜结构风致动力响应,揭示和总结出某些规律.     

膜结构风振分析的数值风洞方法

本在考虑膜结构与风荷载动力耦合作用的基础上,建立了一种适用于大跨度张拉结构风振分析的CFD数值模拟方法．计算采用分区迭代算法,包含流体域、结构域和网格域三个计算模块．流体域采用Taylor—Galerkin有限元法和大涡模拟技术来求解不可压缩粘性流动;结构域的计算采用Update Lagrangian有限元列式和Newmark逐步积分技术,并考虑了几何非线性的影响;网格域采用拟弹性介质法来计算动态网格的更新．算例分析表明,数值风洞方法是求解流固耦合问题的一种有效方法．     

TLD结构减震控制的数值分析

TLD作为一种有效的被动耗能减震控制方法,其减震规律及其分析设计方法一直较受关注。以往的研究较多依赖于试验,并在试验的基础上发展了简化分析方法。但由于模型受限于有限的试验结果,其应用具有一定的局限性。近年来,随着计算机技术的发展,开展考虑流固耦合的TLD数值模拟分析研究成为可能。首先采用流固耦合分析方法对设置屋顶水箱TLD控制的高层框架结构进行地震反应分析,并与已有试验规律及简化方法进行了对比验证;初步探讨了流固耦合问题的计算及建模,并对其进行了验证,实现了考虑流固耦合的TLD数值模拟,总结了高层框架结构的减震规律;并对太原钢铁集团150t不锈钢炼钢主厂房进行了TLD减震效应分析和设计。结果表明,采用考虑流固耦合的FSI分析方法符合试验规律,物理意义更加明确、直观,用于TLD减震效应分析将是一种趋势,也是对现有分析方法的有益补充。     

Drag coefficients and Strouhal numbers of a port crane boom girder section

This work reports the drag coefficients (C_d) for three wind directions measured in low turbulence flow and in turbulent flow with characteristics of the atmospheric boundary layer wind, and the Strouhal numbers (St) of an approximately trapezoidal flanged section, used in the boom girder of a 100 m high port crane. These experimental results were obtained at the Boundary Layer Wind Tunnel of the Dept. Aeronautica at the Universidad Nacional de La Plata, in the range of Reynolds numbers between 30,000 and 180,000. The drag coefficients in the three studied directions showed a reduction for turbulent flow. Further measurements were carried out for the model with an inclination of 80° relative to the flow direction, the position of the crane boom when out of service, giving practically the same drag coefficients.     

TLD减小钢桥塔涡激振动的原理及应用研究

讨论了TLD（Tuned Liquid Damper）的减振机理，并用解析形式给出了TLD对结构控制的减振力，求出了TLD与结构相互作用时结构的位移响应，推导了结构安装TLD后结构的等效阻尼比，给出了结构的减振效率，验证了TLD减振效果非常好，可以保证桥塔建设过程中的施工安全。     

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。     

桩土耦合的桥梁管桩涡激振动数值模拟

采用有限元软件对跨海桥梁管桩涡激振动进行了数值模拟,分析了流速,土体刚度对管桩振动幅值的影响,结果表明:流速越大,桩体振动幅值越大,振动越剧烈,在相同流速下,土刚度对管桩振动幅值有着明显抑制作用,是一项不可忽略的参数。     

基于非线性涡激力广义模型的涡振幅值换算

节段模型测振风洞试验是研究涡激共振风速锁定区间和振动幅值的主要手段之一,但节段模型涡振振幅并不能由几何缩尺比直接换算至实桥,需要对测试结果进行修正.已有研究表明,涡激力具有强烈的非线性特性,因此基于线性涡激力模型的换算方法不再适用.此外,由于采用的非线性涡激力模型不准确,基于非线性涡激力模型的已有换算方法也不一定适用,...     

流固耦合界面信息传递理论和方法研究进展

合理有效的界面信息传递方法是实现流固耦合(FSI)分析的关键环节,本文研究了流固耦合界面信息传递理论和方法.归纳了流固耦合界面信息传递所遵循的基本原理:运动学连续条件、动力学连续条件及能量原理等.将信息传递方法总结为局部插值法和整体插值法两大类.局部插值法中研究了映射点插值法、加权余量法、常体积转换法等方法,并给出了主单元及映射点搜寻算法;整体插值法研究了样条函数法、Shepard方法、径向基函数法.最后对瞬态问题给出了CSD、CFD间的时间插值模式.本文从理论和方法上为解决流固耦合界面数据传递问题提供了指导.     

尺寸效应对节段模型涡激振动参数的影响

通过对西堠门大桥主梁截面分别采用两种缩尺比进行节段模型涡激振动风洞试验,探讨了不同尺寸下涡激振动性能的变化.试验结果表明,在进行节段模型涡激振动试验时,不同的缩尺比对试验结果具有一定影响.     

Vibration characteristics identification of ultra-long cables of a cable-stayed bridge in normal operation based on half-year monitoring data

Abstract

The Sutong Bridge with a span of 1088?m is supported by 272 cables, whose lengths range from 152.85?m to 576.77?m (the longest in the world). The half-year vibration acceleration data of two cables from structural health monitoring system (SHMS) is analysed, in conjunction with the wind field data, weather data and vehicle data to explore and three types of cable vibrations. The large-scale cable vibration is mainly rain-wind-induced vibrations (RWIV) when the wind direction lies in an angular range of 40°–80° relative to the cable axis, and the bridge-deck wind velocity is 4–20?m/s. The ultra-long cable also experiences in-plane vibrations, which satisfy many characteristics of vortex-induced vibrations (VIVs). Cable VIV occurs only when the bridge-deck wind velocity 4–8?m/s, with the frequency ranging from 9.5?Hz to 10?Hz. The daily small-amplitude vibration of the cables and steel girder is mainly induced by the passage of heavy trucks. There exists a positive correlation between the number of heavy trucks and the vibration level. Based on the characteristics and occurrence probabilities of these three types of cable vibrations, corresponding measures are suggested for the maintenance of ultra-long cables.     

Large-eddy simulation of flows past complex truss structures

Numerical simulation of turbulent flows past typical truss structures that are common in bridges and towers has been conducted. Large-eddy simulation (LES) method is used that has been verified in computing flows past simple bodies at moderate Reynolds numbers. Truss structures consist of thin members that are too small to be accurately resolved by numerical grids that can be handled by most computer systems. It has been found that when the individual members are long angular bars, the overall flow can be reproduced fairly well by approximating the members with rectangular cylinders whose cross sections are resolved by more than 2×2 computational cells and by taking computational regions extending at least four structure heights downstream and about three heights across the vertical and spanwise directions. The drag coefficient and the vortex shedding characteristics along with the complex wake structures associated with the truss structures are reproduced reasonably well.     

分离双箱主梁涡激振动性能研究

通过节段模型风洞试验,并对某长江大桥初设方案的涡激振动抗风性能进行了定量分析,试验结果表明:该方案主梁涡激振动问题比较严重,并基于数值模拟方法模拟了气流流过桥梁断面的绕流变化,提出了改善主梁涡振性能的措施,优化后主梁断面的风洞试验结果表明:优化后的主梁具有较好的抗风稳定性。     

Re-examination of the effect of a plane boundary on force and vortex shedding of a circular cylinder

The hydrodynamic forces and vortex shedding of a smooth circular cylinder immersed in different boundary layers were experimentally investigated at Reynolds numbers from 1.30×10⁴ to 1.45×10⁴. The effects of the bed proximity, the thickness of the boundary layer, and the velocity gradient in the boundary layer on the pressure distribution, the hydrodynamic forces and the vortex shedding behavior were examined. The experimental results show that both the drag and lift coefficients strongly depend on the gap ratio, and are affected by the boundary layer. A downward lift is observed at certain gap ratios in rod-generated boundary layers, and an explanation of this downward lift is given. Two different criteria for calculating the Strouhal number in the literature are discussed in this paper. It is found that the variation of the root-mean-square (RMS) lift coefficient reveals the onset or suppression of the vortex shedding. A quantitative method for identifying the vortex shedding suppression point is proposed. The observations show that the vortex shedding is suppressed at a gap ratio of about 0.2–0.3, depending on the thickness of the boundary layer. This critical gap ratio decreases as the thickness of the boundary layer increases.     

大攻角及桥面粗糙度对扁平钢箱梁涡振性能的影响

为探究大攻角及桥面粗糙度对扁平钢箱梁涡振性能的影响,对寸滩长江大桥主梁进行了风洞试验。应用Matlab软件模拟桥面粗糙度变化范围,根据模拟结果选取对应的砂纸在试验中模拟桥面粗糙度,分析了攻角及桥面粗糙度对扁平钢箱梁涡振区间及幅值的影响。试验研究表明:在大攻角下扁平钢箱梁的涡振振幅和范围明显增大,对桥址位于山区等容易发生大风攻角的地区的桥梁应进行大攻角试验。扁平钢箱梁的涡振响应随着桥面粗糙度增大而减小。正攻角范围内,桥面粗糙度对涡振响应的影响随着攻角减小而增大。桥面粗糙度发生变化时,扭转涡振响应更加敏感,变化幅度大于竖向涡振响应变化幅度。     

近海单桩式风机地震响应分区耦合分析方法

海上风机是低碳可持续能源的重要战略选择之一,其地震安全性问题是急需解决的重要课题。将近海单桩式风机三维地震响应问题看作波动散射问题,结合人工边界条件实现海域场地的波动输入,并基于广义饱和多孔介质统一计算框架,发展了一套海水-饱和海床-风机耦合作用高效分区分析方法,实现了综合考虑土-结构相互作用效应和流固耦合效应的近海单桩式风机三维地震响应分析,并分析了海水深度、海床波速和地震波入射角度对近海单桩式风机地震响应的影响。分析结果表明,海水深度和海床剪切波速的变化,一方面会改变自由场,另一方面会改变海域场地-风机体系的自振特性,从而影响风机结构的地震反应。当海水增加到某深度时,体系自振频率与地震波输入频率接近时,风机的地震响应会急剧增大;海床剪切波速对塔底弯矩的影响要比对位移的影响大;当入射角度增大时,塔顶水平向位移和加速度以及塔底弯矩均有不同程度的减小,塔顶竖向位移和加速度均有不同程度的增大。本文没有考虑海床和风机的非线性,考虑非线性时的影响规律需进一步研究。