武理工结构防灾技术课件03结构抗风-10脉动风的概率特性.pptx

第十第十章章 脉动风的概率特性脉动风的概率特性Chapter 10 Probabilistic Characteristic offluctuating wind10.110.1 脉动风的概率脉动风的概率分分布布1 0.11 0.1 ProbabilisticProbabilistic distributiondistribution ofof fluctuatingfluctuating windwind1脉动风反映了大气边界层中自然风的湍流特性 Fluctuating wind reflects the fluctuating characteristics of natural wind turbulence in the atmospheric boundary layer1风速的脉动特性对工程结构的作用十分重要 The fluctuation characteristic of wind is very important to engineering structures1刚性结构要受到脉动风速所产生的阵风荷载 Rigid structures are subject to gust loading generated by fluctuating wind1柔性结构在脉动风速作用下会发生动力响应 Flexible structures produce dynamic response under fluctuating windChapter 10 Probabilistic Characteristic of fluctuating wind10.110.1 ProbabilisticProbabilistic distributiondistribution ofof fluctuatingfluctuating windwind1柔性结构的空气动力特征的参数可以分为能量特征参数和空间 特征参数The aerodynamic characteristic parameters of flexiblestructures can be described by energy characteristic parameters and spatial characteristic parameters.1能量参数：湍流度、脉动风功率谱Energy parameters:turbulence intensity,wind power spectrum 1空间参数：湍流积分尺寸、空间相关性。

Space parameters:turbulence integral dimension,spatialcorrelation.10.110.1 ProbabilisticProbabilistic distributiondistribution ofof fluctuatingfluctuating windwind1对风速记录的分析表明，如果忽略初始阶段的严重非平稳对风速记录的分析表明，如果忽略初始阶段的严重非平稳区区域域，脉动风十分接近于平稳随机过程，它的概率密度很接近，脉动风十分接近于平稳随机过程，它的概率密度很接近于于正正 态分态分布布1 WindWind speedspeed recordrecord analysisanalysis showsshows thatthat if if thethe serious non-stationary parts is ignoredgnored inin thethe initialinitial phasephase，thethe fluctuatingfluctuating windwind is is veryvery closeclose toto stationarystationary randomrandom processprocess,thethe probabilityprobability distributiondistribution is is veryvery closeclose toto normalnormal distributiondistribution10.110.1 脉动风的概率脉动风的概率分分布布1 0.11 0.1 ProbabilisticProbabilistic distributiondistribution ofof fluctuatingfluctuating windwind10.110.1 脉动风的概率脉动风的概率分分布布1 0.11 0.1 ProbabilisticProbabilistic distributiondistribution ofof fluctuatingfluctuating windwindChapter 10 Probabilistic Characteristic of fluctuating wind10.110.1 脉动风的概率脉动风的概率分分布布1 0.11 0.1 ProbabilisticProbabilistic distributiondistribution ofof fluctuatingfluctuating windwind10.110.1 脉动风的概率脉动风的概率分分布布1 0.11 0.1 ProbabilisticProbabilistic distributiondistribution ofof fluctuatingfluctuating windwind1湍流积分长度(Turbulence integral length)通过某一点气流中的速度脉动可以认为是由平均风所运输 的一些理想涡旋叠加而引起的，若定义涡旋的波长就是涡旋 大小的量度，紊流积分尺度则是气流中湍流涡旋平均尺寸的 量度。

The velocity fluctuation passing through a point canbe recognized as the Superposition of the ideal vortex transported by mean wind.If the wavelength is defined as the measurement of vertex size,Turbulence integral length is the measurement of average size of the turbulent vortex in the airflow.函数C分别表示两个脉动风速的互协方差函数 Function C respectively represents covariance functions of two pieces of fluctuating wind.如果互协方差函数是相隔距离的快速递减函数，则湍流积分长度很小，紊流影响也很 小反之如果互协方差函数随相隔距离的增大递减很慢，则湍流积分长度很大，紊流 的影响也大If the covariance function is a fast decreasing function of the distance,then the interval of turbulence integral is small,coLLe2bouq!uaI入 the effect of turbulence is small.Conversely,If the covariance function decreases slowly with distance,the interval of turbulence integral is large,the effect of turbulence is also large.10.110.1 脉动风的概率脉动风的概率分分布布1 0.11 0.1 ProbabilisticProbabilistic distributiondistribution ofof fluctuatingfluctuating windwind湍流积分长度从数学上可定义为湍流积分长度从数学上可定义为 TheThe mathematicalmathematical definitiondefinition ofof turbulenceturbulence integralintegral cancan bebe defineddefined asas followfollow:10.210.2 脉动风脉动风的的功率谱功率谱10.210.2 PowerPower spectraspectra ofof fluctuatingfluctuating windwind脉动风功率谱(Power Spectra)表现了脉动风能量在整个频率范围内的分布特征It describes the energy distribution of fluctuating wind over full frequency range.脉动风功率谱需由强风观测记录得出，一般有两种方法：Power spectra is obtained by observing strong winds.Generally there are two methods:把强风记录通过超低频率滤波器，直接测出风速的功率谱曲线；Directly measure the power spectrum of wind speed by letting strong wind records go through ultra-low frequency filter.把强风记录经过相关性分析，获得风速的相关曲线，建立相关函数的 数学表达式，然后通过傅里叶变换得到功率谱。

Obtain the correlation curve by analyzing strong wind records and establish expressions of correlation function.And finally,the power spectrum is obtained through Fourier transformation(1)在中心频率为0.01(1/小时)出现第一个峰值，对应于天气系统整个运 转的变化周期4天通常称为宏观气象峰值；The first peak corresponding to the whole period of the weather system appears at where the center frequency is 0.01(1/h),which is usually called macro meteorological peak (2)第二个峰值出现在12小时周期处，相当于昼夜间的温度变化 The second peak occurs at the period of 12 hours,which is equivalent to the change in temperature between day and night.(3)第三个峰值出现在1分钟周期处，反映了大气湍流的脉动，即不边界层 湍流作用有关的从十分钟到小于3秒周期的高频作用，通常称为微观气象峰值 The third peak occurs at the period of 1 minute,reflecting the fluctuation of atmospheric turbulence,which is the high frequency action of a period of 3 seconds to 10 minutes and is usually called micro meteorological peak.10.210.2 脉动风脉动风的的功率谱功率谱10.210.2 PowerPower spectraspectra ofof fluctuating。