流线型单脊膜结构表面风压特性数值模拟分析

风荷载是大跨度空间结构及膜结构设计的控制荷载。以流线型单脊膜结构的实际工程为例,基于Reynolds时均方程,选取剪切应力传输湍流模型(SST k-ω模型),采用ANSYS-CFX14.0流体分析软件对膜表面的风压分布进行数值模拟。通过对比分析不同风向角下膜表面风压分布规律、平均风压系数及湍流特征,得出该结构最不利风向角取值范围以及膜表面不同分区平均风压系数、风荷载体型系数值。结果表明:60°～90°为此结构的最不利风向角,在此风向角区间内,膜结构表面的湍流特性复杂多变。迎风面屋檐形成较高的正压,背风面屋脊形成较高的负压,该部位更易遭受破坏;整个背风面形成较大的负压区,在结构中部产生明显的漩涡,主要表现为吸力。     

基于多相流理论的风雨共同作用下鞍形膜结构响应分析

膜结构重量轻、跨度大、自振频率低,对风敏感,因此膜结构抗风设计是一个必须考虑的因素。但在实际中,大风暴雨往往相携而来,仅考虑风荷载对设计已经不足,由此而出现的事故也有发生,因此风雨共同作用下膜结构的设计成为一个现实问题。以此为背景研究风雨共同作用下鞍形膜结构的响应,基于多相流理论的欧拉-欧拉模型,考虑降雨强度、雨滴直径、体积分数和末速度等对风荷载的影响,取4种风向角,3种不同降雨强度和3种不同风速,对比风速变化、雨强变化等对鞍形膜结构响应的影响。结果表明:风雨共同作用时鞍形膜结构位移、应力显著增加;45°风向角下结构稳定性较差。     

伞形组合膜结构风荷载分布特性分析

膜结构对风荷载极为敏感,抗风设计在膜结构设计中成为至关重要的环节.本文针对常见的双伞和四伞组合膜结构进行风压分布特性分析,研究组合膜结构的风压分布规律.首先对某实际膜结构罩棚进行数值模拟和风洞试验,通过对比所得数据,验证了数值模拟方法是可靠的;其次采用SSTk-ω模型,对伞形组合膜结构周围绕流风场做数值分析,探究在风荷载作用下伞形组合膜结构表面风压分布特性.研究发现,组合膜结构的正压区位置在风向角不同时有差别,在设计时应注意风向角对组合膜结构膜面风压正负分区的影响及角点部位的膜面处理,并给出风荷载体型系数取值建议.     

典型张拉膜结构风压分布特性数值分析

为研究典型张拉膜结构在风荷载作用下的受力特点,对鞍形、伞形、双跨脊谷式及拱支式4种张拉膜结构进行了系统的数值分析。基于雷诺时均法的k-kl-ω湍流模型对某一鞍形膜结构进行了数值分析,并将其结果与试验结果进行对比分析,验证了采用数值方法的准确性。对4种张拉膜结构进行数值模拟,分析了风向角、矢跨比、跨高比及跨度对结构平均风压分布的影响规律。结果表明:风向角对风压分布的影响最大,不同风向角下膜面最大风吸力出现的位置也不同,说明气流在屋盖前缘产生的漩涡脱落作用是影响屋面风荷载特性的主要因素;矢跨比的影响次之,迎风前缘的风压变化明显,其余区域变化较小。根据4种张拉膜结构的结构型式及风压分布特点将屋面分区,并依据本文的数值模拟结果给出了屋面各区域的风载体型系数,以期为工程设计提供参考。     

青岛颐中体育场膜结构风洞试验研究

通过风洞试验研究了在B类场地条件下 ,青岛颐中体育场膜结构挑篷建筑的风荷载特性 ,探讨了挑篷上各处膜面平均风荷载随来流风向角的变化规律 ,及其在各风向角下的表面风荷载的分布规律 ,确定了该设计方案随膜顶形状变化的风载体形系数 ,为进一步的结构计算提供了科学依据。     

体育场上凸和下凹膜结构罩篷风荷载特性比较

以分别具有下凹和上凸形状膜结构罩篷的山东招远和四川达州体育场为例,通过风洞试验模拟的方法对比研究了这两种体育场罩篷的风荷载特性。试验结果表明,两种膜结构在各个风向角下,上风向罩蓬的风压分布都比较均匀,并且负压峰值都位于下风向罩篷的前檐附近;下凹形膜结构受到风荷载作用时的下压力要比上凸形膜结构的大,而上吸力要比上凸结构的小。     

盐城体育馆风荷载体型系数及风振系数的试验分析

为分析风荷载对盐城体育馆网壳结构的影响,提出了测压模型风洞试验的方法。将体育馆整体结构分为典型特征12块,通过试验得到不同风向角下各结构分块的体型系数,并采用风振响应数值分析得到了各分块各风向角下的风振系数。结合建筑结构荷载规范,考虑风振系数后的风荷载可用于建筑结构设计。     

大跨悬挑屋盖风振系数研究

针对荷载规范中对大跨悬挑屋盖结构风振系数计算的不足,利用时程分析法,在有限元建模的基础上,直接采用风洞试验数据,计算了某大跨悬挑屋盖结构的荷载风振系数和位移风振系数,研究了其随风向角的变化规律,并讨论了不同风向角下结构参数的影响。     

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     

椭球面屋盖与圆锥面玻璃幕墙的风压分布特征

结合杭州大剧院主体结构风压分布的风洞试验研究 ,详细介绍了风洞试验及数据处理方法 ,讨论了在不同风向角下椭球面屋盖和圆锥面玻璃幕墙的风压分布 ,并与荷载规范中类似结构的风压分布进行了比较。为了便于整体结构设计 ,根据结构的实际情况对椭球面和圆锥面进行分块并给出相应的分块风压数据 ,根据各风向角下的风压分布特征给出了整体结构抗风设计的最不利风向角。     

Extreme wind speeds in mixed wind climates

In this paper, a technique is discussed which enables extreme wind speed probabilities in mixed wind climates to be determined. It is shown that in such wind climates the method is likely to yield more accurate probability estimates than the traditional Gumbel analysis of annual wind speed maxima, particularly for annual probabilities of less than 2% (i.e. return periods greater than 50 years). The technique requires a separate analysis of each significant wind-producing meteorological phenomenon and practical methods of achieving this are presented. Extreme wind speed parameters obtained from each analysis may then be combined to yield a “composite extreme wind speed diagram” and several examples illustrating this procedure are shown. By means of a numerical simulation of a typical mixed wind climate, a detailed study is made of the distribution of extreme wind gusts from different meteorological phenomena. This study indicates that a Gumbel analysis of 20 annual maxima may severely underestimate low annual probability (i.e. long return period) gust speeds.     

Compensation of high-frequency components of wind load by wind tunnel testing

To analyze the wind-induced response of structures, wind tunnel tests are often carried out to determine the wind loads on structures. However, due to the influence of similarity requirements in wind tunnel tests, the resulting data from the model test still needs to be translated by similarity rules for predicting the real loads on prototype structures. During this process, an inevitable result is that the high-frequency components of fluctuating wind loads get lost, which leads to some unexpected errors in the subsequent wind-induced response analysis. To solve this problem, a frequency compensation method is put forward. The purpose of this method is to reconstruct the high-frequency part of fluctuating wind loads based on experimental data and some basic principles of the aerodynamics of bluff bodies. The causes and effects of the frequency compensation problem are discussed first, then a practical method of frequency compensation is proposed by combining the fluctuating wind energy spectrum theory and the Proper Orthogonal Decomposition technique. Based on this method, the wind-induced response of a single-layer reticulated shell is analyzed to show the validity and necessity of this method.     

Small wind turbine power control in intermittent wind gusts

This paper analyzes control strategies for a small scale wind turbine in intermittent winds using a computer model based on wind data collected on-site and computer simulation data. Standard generator control with a lowered gain was found to produce the greatest power capture by biasing the rotational speed towards high energy wind gusts. Optimal gain was able to be determined by calculating an estimated wind speed using physical and measured quantities. An augmentation to the standard control provides a method for capturing power safely beyond the rated wind speed.     

Specification of the design wind load based on wind tunnel experiments

Once a high-quality wind tunnel experiment with no major flaws on the experimental side has been performed and the data have been processed/translated appropriately to the design-decisive variable, the final step is to estimate the appropriate load or load effect coefficient for the specification of the design wind load. Four questions arise: what is the appropriate length of a single run in the wind tunnel, what is the appropriate fractile of the observed extreme coefficients, how many independent experiments are required to estimate this fractile and what should be the target confidence interval. The paper tries to give some answers to these questions and discusses the findings in regard to some wind load codes.     

广州塔风荷载及风洞试验研究

广州塔总高600m,塔体外形复杂,基本周期长,对风荷载的响应比较敏感,风荷载成为结构设计的主要控制荷载。针对广州塔的特点,分两阶段进行了风工程研究,第一阶段解决外界风的输入问题,第二阶段解决结构在风荷载作用下的响应问题。风荷载及风洞试验的主要成果可作为类似工程结构设计的参考资料。     

北京当代MOMA风载及风环境数值模拟研究

根据计算流体动力学(CFD)的基本原理,基于计算流体力学软件Fluent平台,对当代MOMA工程的建筑群进行数值风洞模拟.获得12个不同风向下建筑物表面风压分布参数和建筑群区域不同高度的风环境参数.结果表明,建筑群的互相干扰既会影响建筑物表面的风压分布,又对不同区域的风向和风速有重要影响.来流上游建筑物的阻挡,会造成下游建筑物迎风表面压力值的减少,局部的风速加剧又会加大周围建筑物表面压力值;在产生流动分离和涡脱落的区域风速较高,而背风区域的风向与来流风向有较大差异.数值模拟获得的结果为建筑群的优化设计提供了重要参考.     

Measurements of wind drag on people standing in a wind tunnel

This report describes an experiment in which measurements were made of the wind drag on 331 people standing in turn in a wind tunnel. The results were analysed in terms of projected areas and drag coefficients, as is customary with wind tunnel measurements. Areas were then expressed as ratios to a person's total body surface area, calculated from weight and height. It was found that these area ratios and the drag coefficients could be related to the type of clothing, and eight categories were selected. The results thus provide a simple way of estimating the wind drag on a person for a known windspeed if his weight, height and type of cloting are known.     

A study of wind and buoyancy driven flows through commercial wind towers

Commercial wind towers have been the focus of intensive research in terms of their design and performance. There are two main forces which drive the flow through these devices, external wind and buoyancy due to temperature difference. This study examines the relationship between these two forces and the indoor ventilation rate achieved. The work uses computational fluid dynamics (CFD) modeling to isolate and investigate the two forces and draw comparisons. The study found that as expected the external driving wind is the primary driving force providing 76% more internal ventilation than buoyancy driven flow, which is deemed secondary. Moreover the study found that the effect of buoyancy is insignificant without an external airflow passage other than the wind tower itself. The addition of an external airflow passage such as a window in combination with buoyancy force increased the indoor ventilation by 47%. Therefore the careful positioning of windows in conjunction with internal heat source has the potential to overcome the lack of external wind driven forces in dense urban environments.     

数值风洞在大跨屋盖结构风荷载确定中的应用

运用计算流体力学数值模拟技术对大跨屋盖结构表面风荷载进行了研究。对平屋面和曲面屋面表面风压分布进行了数值模拟。在此基础上,对大庆石油学院体育馆屋盖表面进行了风洞试验和数值模拟的对比研究,并对大射电望远镜FAST反射面的风压分布及其周围流场进行了数值模拟,为该工程的结构抗风设计提供了参考。     

山地风电场风力发电机组安装安全技术研究

从当前山地风电场的发展情况出发,结合山地风电场风电机组的各种类型以及所发挥的作用,探讨了风电机组的吊装注意事项,分析了风力发电机组安装安全技术措施。