Experimental and semi-analytical studies on the aerodynamic forces acting on a vehicle passing through the wake of a bridge tower in cross wind

In a strong cross wind, sudden change of wind velocity in the wake of a bridge tower causes rapid change of the aerodynamic forces acting on a passing vehicle, which may result in an accident due to driver’s miss-steering. This paper discusses and clarifies the transient characteristics of the aerodynamic forces acting on a ground vehicle in high cross winds when the vehicle is passing through the wake of a bridge tower using a scale model in a wind tunnel experiment. Various parameters, such as wind speed and direction, type of vehicle and tower, were considered in the study.The side force and yawing moment acting on the vehicle model were measured using strain gauges on the model-supporting system that was designed as two cantilever beams with high stiffness. Characteristics of the aerodynamic forces acting on the vehicle model were described and the prediction methods that considered the wind non-uniformity acting on the vehicle were proposed and their applicability was studied.For the side force, the quasi-steady forces based on the relative wind velocity acting at the c.g. of the vehicle model generally agreed with the measured results. Changes in side force were found to be more or less proportional to the wind speed distribution. For the yawing moment, however, the quasi-steady prediction did not agree well with the measured results due to the wind non-uniformity. Therefore, a modified prediction method was proposed that included the effects of wind non-uniformity in a simple manner. Depending on the case, the agreement of prediction and measured results was still not good quantitatively, but from the qualitative point of view, the proposed prediction method could reproduce the yawing moment peak that was similar to the experimental results.     

Effects of grid curtains on the wind loads of a high‐rise building

The effects of grid curtains on the local and overall wind loads of a high‐rise building are investigated in detail according to a series of wind pressure and wind force tests on rigid model in a wind tunnel. The effects of grid curtains on the mean and fluctuating wind pressures on windward and sideward walls when the wind direction is parallel to the geometrical axes are investigated, along with the effects of the most unfavorable wind pressures for all wind directions. Furthermore, the effects of grid curtains on the mean and fluctuating aerodynamic forces on the entire building are also analyzed for various wind directions, along with the effects of grid curtains on the aerodynamic force spectra when the wind direction is parallel to the geometric axes. The test results indicate that grid curtains affect the mean and fluctuating windward pressure slightly but greatly influence the large sideward negative pressures. Grid curtains increase the mean and fluctuating windward aerodynamic forces and reduce the fluctuating aerodynamic torsions. According to the aerodynamic force spectra, grid curtains can mainly affect the wind forces in the low‐frequency range. Copyright © 2015 John Wiley & Sons, Ltd.     

东莞第一国际项目连体双塔高层建筑的风荷载

通过风洞试验研究了截面为切角曲边三角形的连体双塔高层建筑的风荷载特性,并作单塔试验比较。将风压沿截面进行积分求出沿坐标轴方向的合力,然后反算为沿坐标轴方向的整体体型系数。结果显示:风压沿高度变化不大,整体体型系数沿高度递减。单塔最大体型系数对应风向角比坐标轴偏15°。双塔连线方向(x向)体型系数上游塔略小于单塔情形,下游塔基本为零,y向的体型系数略小于单塔y向的,连体部分体型系数达2.2。根据规范和试验结果,提出了类似工程合理的取值建议。     

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.     

基于完全气弹模型风洞试验输电塔风荷载识别

按照基本缩尺律,设计、制作了输电塔完全气弹模型,并通过大气边界层风洞试验,测试了多种风速、风向条件下输电塔的位移与加速度响应。通过加速度响应功率谱识别出结构的固有频率,并采用Hilbert-Huang变换结合随机减量法识别出包含结构阻尼和气动阻尼的结构总阻尼。利用虚拟激励法建立了由测点位移响应来识别结构顺风向、横风向风荷载的方法。由识别出的风荷载谱曲线,利用非线性最小二乘法拟合得到输电塔顺风向、横风向风荷载经验公式。研究结果表明：风洞试验设计、制作的输电塔气弹模型,测试得到的模型第1阶自振频率与有限元计算结果吻合较好;横风向荷载谱形态与顺风向的相比有较大的区别,其能量分布在一个更宽的频带上,其峰值频率是顺风向的3～4倍。     

Wind field simulation and wind‐induced responses of large wind turbine tower‐blade coupled structure

Herein, by a case study on a 5‐MW wind turbine system developed by Nanjing University of Aeronautics and Astronautics, the wind field simulation and wind‐induced vibration characteristics of wind turbine tower‐blade coupled systems is analyzed. First, the blade‐nacelle‐tower‐basis integrated finite element model with centrifugal forces induced by rotational blades is established. Then, based on a harmony superposition method and the modified blade element‐momentum theory, the fluctuating wind field of tower‐blade coupled systems is simulated, which considers wind shear effect, tower shadow effect, rotational effect, blade‐tower dynamic and model interaction effects. Finally, the wind‐induced dynamic responses and wind vibration coefficients of the wind turbine tower‐blade coupled structure are discussed through the ‘consistent coupled method’ previously proposed by us. The results indicate that the wind‐induced responses of a large wind turbine tower‐blade coupled structure present complicated modal responses and multimode coupling effect. Additionally, the rotational effect would amplify aerodynamic loads on blades with high frequency, wind‐induced dynamic responses and wind vibration coefficients of wind turbine tower. The centrifugal force effect could also amplify natural vibration frequency of the tower‐blade coupled system and reduce the wind‐induced dynamic responses and wind vibration coefficients of wind turbine tower. The research could contribute to wind‐resistant design of structure for a large‐scale wind turbine tower‐blade system. Copyright © 2014 John Wiley & Sons, Ltd.     

基于风洞试验的苏通大跨越输电塔风振系数研究

苏通大跨越输电塔的结构形式有别于普通的钢结构杆塔,其塔身下部结构采用钢管混凝土、上部结构采用钢管,质量突变大,主要受风荷载控制,并且塔高超出GB 50009—2012《建筑结构荷载规范》的梯度风高度限制。为此,采用气动弹性模型和刚性模型的边界层风洞试验确定苏通大跨越输电塔的风致响应和气动力,基于试验数据计算不同风向角下的惯性力风振系数、位移风振系数和有效荷载风振系数,并进行对比。并通过有限元分析梯度风高度对惯性力风振系数的影响,同时将有限元分析得到的风振系数分布和加权值与DL/T 5154的风振系数规定作比较。结果表明：上述3种风振系数分布规律并不相同,由其分别确定的等效位移接近于试验值;考虑梯度风高度后,风振系数变小,分布形状影响小;苏通大跨越输电塔的惯性力风振系数加权值小于1.6,且风振系数由下到上不是单调增大。     

不同风载作用下单管塔的设计

单管塔因其结构轻巧、造型美观,越来越多地被应用于城市及对环境有美观要求的地方.通信单管塔属于高耸结构,其受力特点是风荷载起决定作用,高度越高,风荷载的响应越明显.由于通信基站的密度较集中,对于同一地区的风压及地貌相差不大、对通信工艺要求相同的基站,可以规格化塔身主材.针对2类经常建造落地单管塔的地貌,通过对目前运营商常用天线挂高的单管塔结构进行不同风压下的受力分析,给出各参数的选择建议,为工程设计提供一定参考.     

Effects of wind barrier on a vehicle passing in the wake of a bridge tower in cross wind and its response

Vehicles passing behind a bridge tower in strong cross winds are affected by sudden change of wind forces acting on them, which may cause accidents due to miss-steering of the drivers. As a countermeasure, wind barrier has sometimes been applied. However, the efficiencies of wind barrier are not known quantitatively, because the characteristics of the aerodynamic forces acting on a vehicle and the response of the vehicle due to those forces are not clear.In this paper, aerodynamic forces acting on a vehicle passing in the wake of a bridge tower with wind barrier are measured and their characteristics are presented first. Then, using the prediction procedures proposed in a previous study by the authors (J. Wind Eng. Ind. Aerodyn., submitted for publication), a vehicle response simulation was conducted and the effects of the wind barrier on the vehicle response were examined.In the experiment, the change of wind speed is confirmed to become moderate and the magnitude of the aerodynamic forces variation is found to reduce with the installation of wind barrier.Based on simulation results without wind barrier, the vehicle response becomes larger due to increased wind and vehicle speed, and reaches maximum when the wind direction is skewed 30° from the axis normal to the bridge axis and against the vehicle heading direction. The effects of the wind barrier were studied with a fixed steering simulation, and the responses such as side acceleration and yaw angular acceleration are found to be reduced effectively.     

塔冠对方形超高层建筑顺风向基底弯矩的影响研究

高层建筑顶部塔冠形状多样,其对建筑整体气动力的影响目前尚不明确。为此,利用高频测力天平技术,在大气边界层风场下对19种不同顶部塔冠的方形截面超高层建筑进行了风洞试验,分析塔冠形状对超高层建筑顺风向基底弯矩系数值及顺风向基底弯矩功率谱的影响。讨论坡面变化、顶部开洞、阶梯变化和锥形变化等四大类塔冠形状对结构整体顺风向气动力的影响规律。试验结果表明：将坡面置于迎风侧能够降低顺风向基底弯矩系数值;相同开洞形状和面积时,顶部敞口开洞对降低顺风向基底弯矩平均值的效果优于闭口开洞;斜坡面阶梯塔冠对降低顺风向弯矩系数值的效果优于直坡面阶梯塔冠;上棱椎下棱台的棱椎式塔冠能够大幅减小顺风向基底弯矩系数平均值。塔冠能够改变顺风向基底弯矩功率谱峰值大小,棱锥形塔冠对降低顺风向弯矩功率谱峰值最为明显。     

On the aerodynamic and aeroelastic response of a bridge tower

This work is concerned with the aerodynamic characterization of a cable-stayed bridge tower in free-standing configuration; experimental tests were performed at Politecnico di Milano Wind Tunnel under smooth and turbulent flow conditions. The aerodynamic behavior of the tower was investigated through static and dynamic tests on a 1:30 scale sectional model; the whole structure response has been studied using a 1:100 scale full aeroelastic model in stand-alone configuration. Aim of this paper is to compare wind tunnel test results obtained on the two models for different wind exposures, discussing the problems related to scale effects in scale model testing. Some inconsistencies found during the experimental campaign confirm that scale effects in wind tunnel testing represent a serious issue especially for bluff body structures whose vortex shedding response is strongly affected by Reynolds number.     

Quasi-static computational approach to wind load on cooling towers in conditions of aerodynamic interference

A quasi-static computational approach is proposed to predict the wind load in conditions of aerodynamic interference of a cooling tower with other cooling towers and neighbouring objects. The proposed approach is a modification of the coefficient of exposure and coefficient of outer wind pressure concepts; it aims at considering the possible asymmetry of load and local overloads. Examples of static calculations of cooling towers for four combinations of wind load and dead load have been given. Solutions can be used for standardization of wind load on cooling towers.     

无锡蠡湖科技大厦表面风荷载研究

无锡蠡湖科技大厦刚性模型的风洞试验测量了模型表面的平均和脉动风压,给出了不同风向角下各测点的平均风压系数和体型系数。讨论了风场和风向角对平均风压系数和体型系数的影响,以及两个正方形截面塔楼的相互气动干扰影响特点,得到双塔高层建筑中各单塔楼的总体体型系数大于单体建筑的结论。     

Wind‐induced fatigue of large HAWT coupled tower–blade structures considering aeroelastic and yaw effects

An efficient approach for predicting wind‐induced fatigue in large horizontal axis wind turbine coupled tower–blade structures subject to aeroelastic and yaw effects is presented. First, aerodynamic loads under yaw conditions are simulated based on the harmonic superposition method and modified blade element momentum theory, in which wind shear, tower shadow, tower–blade interactions, aeroelastic, and rotational effects are taken into account. Then, a nonlinear time‐history of wind‐induced responses under simulated aerodynamic loads is obtained. Finally, based on these results, wind‐induced fatigue damage and lifespan are predicted according to linear cumulative damage theory. For completeness, the influences of mean wind speed, aeroelasticity, and yaw angle on horizontal axis wind turbine fatigue life are discussed. The results indicate that the aerodynamic loads and residual fatigue life can be estimated accurately by the proposed model, which can be used to simulate the 3D wind fields of wind turbines under given wind conditions. The wind energy of the wind turbine blade is mainly concentrated at its edge and is weaker at the hub. Estimation of wind turbine fatigue life is therefore suggested to be based on the component with the shortest life, being the blade root. Furthermore, yaw conditions significantly shorten fatigue life and should not be ignored. Fatigue life is also rather sensitive to mean wind speed.     

组合结构发电塔架灌浆连接段接触压分析

钢-混组合结构发电塔中的连接段对于整个结构来说至关重要,采用灌浆连接可以有效减小应力集中和疲劳破坏,但目前关于钢-混组合结构风电塔中灌浆连接方式的研究和应用都较少.本文以某150m大型风力发电塔架为研究对象,利用有限元分析软件ABAQUS分析了在外力作用下,钢-混凝土组合结构风电塔架灌浆连接段的接触压,并探究了外侧混凝...     

Effect of cross winds on high-speed trains: development of a new experimental methodology

Optimising the running performance and increasing the stability and comfort of high-speed trains require the knowledge of aerodynamic behaviours with cross winds. The rolling moment and the side force are determined by the leading vehicle design, especially by the head shape of the first car. In this paper, a new methodology based on pressure field measurements has been developed in order to know the local and instantaneous aerodynamic loads. Complementary calculations can also give the density of aerodynamic forces along each vehicle. Therefore, thanks to this method, the loads associated to each part of the vehicle can be defined. Mean aerodynamic forces measured by a classical dynamometer balance fit the pressure measurements. The method presented in this paper provides a reliable way to assess the aerodynamic forces due to side wind, source of discomfort and risk of overturning.     

Non‐Gaussian characteristics and extreme distribution of fluctuating wind pressures on large cylindrical–conical steel cooling towers

Large cylindrical–conical steel cooling tower (SCT) represents a new configuration of cooling tower, and its wind load distribution pattern and forming mechanism are very different from those of the traditional hyperbolic cooling towers. Large eddy simulation was used for the numerical simulation on a superlarge cylindrical–conical SCT that exceeds the specification limit, which is also the highest (189 m) SCT under construction in Asia. The surface flow field and time history of 3‐D aerodynamic force were obtained for the cylindrical and conical parts, respectively. Comparison with the measurements of other large cooling towers and the results of wind tunnel test confirmed the validity of the numerical simulation. Then, based on the probability density distribution and spatial correlation of representative measuring points, regions of non‐Gaussian distribution were identified. The forming mechanism of non‐Gaussian wind pressure distribution was revealed from the perspective of the correlation of non‐Gaussian distribution versus flow separation and eddy motion. The criteria for classifying the region of non‐Gaussian distribution for the cylindrical and conical parts were analyzed, respectively. Research shows that the wind pressures in the windward regions of conical and cylindrical parts obey Gaussian distribution; however, the wind pressures from the region of extreme negative pressure to the region of flow separation are largely non‐Gaussian and the wind pressures of the conical part are generally non‐Gaussian in the leeward region. Finally, the three algorithms for calculating the extreme values of wind pressure were used, namely, peak factor method, improved peak factor method, and Sadek–Simiu method. The distribution patterns of peak factors and extreme values of wind pressure in SCT towers were analyzed comparatively. The 2‐D formulae for fitting the extreme values of wind values for the cylindrical and conical parts were derived by nonlinear least square method. Moreover, strategy for value determination was also presented. The present research aimed to strengthen the understanding of the fluctuating wind pressure distribution and its forming mechanism for large cylindrical–conical SCT towers.     

《高耸结构设计规范》修编对钢塔设计的影响

国家对《高耸结构设计规范》进行了修编,规范的修编使钢塔设计更为合理、方便.本文根据规范修编改动的部分内容,通过实例计算比较钢塔按新、旧规范计算的差异,分析规范修编对钢塔内力、位移以及基底作用力的影响.文章还针对规范修编在基本风压定义上的修改,对全国31个省市241个地区的30年一遇、50年一遇和100年一遇的基本风压按全国各地人口数进行加权统计分析,得出结论.     

大型冷却塔表面脉动风压原型实测与分布准则

我国冷却塔规范风荷载条款仍源自20世纪80年代原型冷却塔（约90m高）实测资料,且仅规定了塔筒表面静态风压分布。事实上,超大型冷却塔（高度≥165m）风振问题与风荷载脉动作用关系更加密切,由此导致了冷却塔数学和物理试验模型雷诺数效应模拟准则的不完整性,难于准确再现冷却塔表面动态风荷载与来流条件、塔群组合状况等参数间的合理关系,已成为制约大型冷却塔抗风性能研究和结构设计的瓶颈。为此,采用全天候动态风压采集设备,对某电厂冷却塔（约166m高）进行通风筒表面动、静态风压长期现场观测,量化表面脉动压力与来流紊流度之间的影响关系,提出具有原创性的冷却塔超高雷诺数条件（Re≥6E7）脉动风压雷诺数效应模拟准则。     

基于数值模拟的某通信塔风荷载体型系数研究

基于Fluent软件平台,采用混合网格进行划分,选用Realizable k-ε湍流模型对某移动通信塔的风场进行三维数值模拟研究,考虑风向角的变化,每隔15°模拟一次,得到通信塔各风向表面平均风压的分布结果:以此为基础,在塔体表面沿高度计算分段风压体型系数,将结果与现行规范进行比较分析并讨论模拟结果的合理性.研究分析表明,数值模拟得到风压系数随风向角的变化而变化,与规范取值吻合且略大于规范取值,为移动通信塔类结构风振计算提供合理的风压体型系数.