【作者】 赵杨；

【导师】 段忠东； Tamura Yukio； 武岳；

【作者基本信息】 哈尔滨工业大学 ， 工程力学， 2010， 博士

【摘要】 现行结构抗风设计方法主要是以对良态风气候(如季风)的观测为基础,平稳来流和拟定常气动力是这类方法的基本假定。而实际建筑风灾害绝大多数是由极端风气候引起的,包括台风、雷暴和龙卷风等。这些极端风气候有一个共同特点,即风速和风向会产生瞬时急剧改变(本文称之为突变)。显然,平稳来流和拟定常气动力假定已不适用于描述突变风作用,基于现行规范的结构抗风设计也不能够有效地防范这类风灾害的发生。对于极端风气候及其作用的研究是近年来国内外风工程领域的热点问题之一,但是由于一些客观因素的制约,进展较为缓慢。这些困难主要表现在:由于极端风的发生具有偶然性,作用范围具有区域性,作用时间又通常较短,因此实测资料较少;不仅如此,对于极端风的风洞实验和数值模拟技术也均不成熟,这就使得研究人员很难获得实验资料;此外,由于极端风的非平稳非高斯特性,也给相关的数据分析和处理带来困难。针对以上问题,本文首先建立了一种概念化的阶跃型突变气流模型,并且研究了这种气流的风洞实验实现方法;然后通过一系列模型风洞实验,对突变风作用下的结构风荷载特性进行研究,揭示了相关作用机理,建立了一种突变风荷载模型;最后,对建筑物的抗突变风设计方法进行探讨,给出了一些设计建议。本文主要研究内容包括以下几方面:针对极端风气候的突变特点,提出一种阶跃气流模型,除了可改变气流加速度外,还可以改变加速后的流场形态,从而得到“下击暴流型阶跃流”和“平滑流型阶跃流”两种可能的形式。在此基础上,以日本宫崎大学的多风扇主动控制风洞为实验平台,通过对不同位置风扇的转速及相位进行反复调试,获得了与目标气流功率谱一致的风洞流场,实现了对上述气流形式的模拟。为探究突变气流作用下的结构风荷载特性,设计了一系列风洞实验。具体考察的参数包括:二维圆柱体和方柱体,三维高层建筑、多层建筑和低矮建筑模型,不同来流加速度以及流场形态,不同来流风向等,实验工况共计190余种。通过以上试验,为揭示突变气流荷载的作用机理提供基本数据。根据风洞实验结果,采用“先二维后三维、先局部后整体、先静力后动力、先均匀流后阶跃流”的分析步骤,分别从时域和频域两方面对结构表面的突变气流荷载进行了细致研究。具体参数包括:点风压系数、面风压系数、阻力系数、侧力系数,脉动风压的空间相关性、滑动相关性和频谱特性等。在此基础上,重点探讨了在气流加速段结构表面气动力所出现的“峰值”现象,得到了突变气流作用下结构荷载整体和局部特征的定量描述。针对突变气流荷载的非平稳特点,引入希尔伯特-黄变换(HHT)时频分析方法,研究了突变气流风荷载的时变特点,得到加速全过程的时频能量分布图,揭示了突变气流荷载的作用机理。在此基础上,利用经验模(EMD)方法提取了突变气流作用下结构风荷载的趋势项,作为风荷载的时变平均分量;并对利用斜度和峰度的概念对突变气流荷载脉动分量的非高斯特征进行了研究,建立了突变气流作用下的结构风荷载模型。在以上研究的基础上,对建筑物抗突变风设计方法进行了初步探讨。在风荷载部分,将突变气流荷载分为时变平均风荷载和脉动风荷载两部分,通过引入非平稳风压系数来表示时变平均风荷载,并利用脉动风压谱的经验式并结合谐波合成法得到了非高斯脉动风荷载。结合一算例,探讨了在突变风作用和在规范风荷载作用下的结构风荷载及风响应差别,说明按照规范方法不能够保证结构在突变风作用下的安全性。通过这些探讨,希望能够为进一步研究建筑物抵御极端风气候下的抗风设计方法提供有益的参考。更多还原

【Abstract】 Current structure wind-resistant design methods are based on observation of normal climate condition (e.g. monsoon), steady inflow and quasi-steady aerodynamics are the basic hypotheses of these methods. Building disasters are actually caused by extreme wind climate, including typhoon, thunderstorm and tornado etc. These extreme wind climates share a common feature that wind velocity and direction could transform rapidly. (It is called transient in this paper.) Obviously, steady inflow and quasi-steady aerodynamics assumption cannot be applied to the study on wind loading with transient characteristics, and current wind-resistant design could not effectively prevent structures from disasters. The research on extreme wind climate and its effect become one of the cutting edge issues in wind engineering field in both domestic and overseas, but its development is slow because of some object factors. The major difficulty is shown as following: observed data are scarcely available because of contingency, regional characteristics and short acting time; moreover, the technology of both wind tunnel experiment and numerical simulation are quite immature so that experimental data are difficult to obtain by researchers; non-stationary and non-Gaussian characteristics of extreme winds also pose great difficulty for data analyzing and processing.Focusing on these problems, firstly, a conceptualized model of step transient flow is proposed, and wind tunnel experiment and its implementation method are studied in this paper; secondly, related mechanism of transient flow is revealed by studying the characteristics of wind load of construction under transient flow; finally, wind-resistant design methods are researched, and some design suggestions are presented.The main content includes the parts as follows:According to transient characteristic of extreme wind climate, a conceptualized model of step transient flow is proposed. Both the acceleration of air flow and flow field form after accelerating could be changed so that down-burst step flow and slipping stream step flow can be obtained. On this basis, by applying the multiple fans active control system in the turbulent wind tunnel in Miyazaki University, the above mentioned flow forms are successfully simulated through repeating debugging of fan rotational speed and phase in different positions to obtain flow field in wind tunnel with same power spectrum density as target flow.A series of wind tunnel experiments are designed in order to investigate the characteristics of wind loading of structure under transient flow. Specific investigated parameters includes: 2-D cylinder section and square section, 3-D high-structure, middle-structure and low-structure models, different acceleration and flow field form of inflow, different wind direction of inflow and etc. The number of experimental scenarios is about 190. Based on the above work, it is intended to accumulate the experimental data, on which the mechanism of transient flow is studied.According to the experimental results, adopting the analysis procedure of " from two-dimension to three-dimension, partial to integral, static to dynamic, stationary flow to step flow", wind loading of structure surface under transient flow is studied in both time domain and frequency domain in detail. The specific parameters include: point wind pressure coefficient, surface wind pressure coefficient, drag coefficient, side force coefficient, spatial correlation and running correlation of fluctuating wind pressure, spectrum characteristics of fluctuating wind pressure and etc. On the base of which, this paper mainly discusses the phenomena of Peak-Value of aerodynamics on structure surface during flow accelerating, and quantitative description of integral and local features of wind load of structure under transient flow.According to its non-stationary characteristics of transient flow, by introducing Hibert-Huang Transform (HHT) spectral analysis, the time-varying characteristic of wind load of transient flow is studied, and the time-frequency scalogram during the whole process of acceleration is obtained, thus the mechanism of wind load of transient flow is revealed. Based on this, trend in the wind load of structure under transient flow is extracted by applying theempirical mode decomposition (EMD), and this extraction is regarded as time-varying average component of wind load; by adopting the concept of skewness and kurtosis to study the non-Gaussian characteristics of fluctuation component of transient flow loading, the model of wind load of structure under transient flow is build.Based on the above studies, preliminary study on structural design methods against transient flow is carried out. In wind load, wind load of transient flow are composed of two parts, which are mean wind load with time varying and fluctuant wind load. Mean wind load with time varying can be expressed by coefficient of non-stationary wind pressure, and non-Gaussian fluctuating wind load is obtained by applying empirical formula of spectrum density of fluctuating winds combined with harmonic component representation. Based on an example, the difference of wind load and wind response under transient flow and normal wind in codes is discussed, and it demonstrates that structural safety under transient flow cannot be guaranteed using the methods in design code. The study could be valuable reference for further research on wind resistant design method of structure against extreme wind climate condition.更多还原