输电线路导线阵风响应系数研究

采用阵风荷载因子法推导了不同档数、影响线函数下输电线路导线阵风响应系数的计算公式,研究了湍流积分尺度、风速、档距、共振响应分量、分离系数和峰值因子等因素对导线阵风响应系数的影响规律,并将其与现行ASCE规范和中国规范的导线阵风响应系数进行了比较分析。分析结果表明,计算导线跨中位移和输电塔风致响应时,应分别考虑单档和相邻两档导线上的风场不完全相关性。影响线函数采用线性函数或正弦函数时,其差异对导线阵风响应的影响可以忽略。与风速和湍流积分尺度相比,档距对导线阵风响应系数的影响更为显著,档距由100 m增至1000 m时,导线阵风响应系数至少降低了20%。忽略导线共振响应分量影响,导线阵风响应系数会偏小5%以上。峰值因子对导线阵风响应的影响较为显著,峰值因子按照ASCE规范取3.6比按照DL/T 5551—2018规范取2.5计算得到的导线阵风响应系数高8.6%。     

圆形线状结构风致响应的分析方法

获得不同风向、风速下结构的风致响应是进行风致疲劳寿命可靠性分析的基础。考虑顺风向脉动力、横风向脉动力以及由结构振动引起的自激力,对不同风向角不同风速下圆形线状结构风振响应进行估算。根据ESDU(En-gineering Sciences Data Unit)工程科学数据库的资料,在对结构进行风振响应估算的过程中,一定程度上记入雷诺数效应、结构表面粗糙度等重要因素对结构风力及风致振动响应的影响。最后,计算了一实际钢质圆形截面天线的风振响应,并与该天线的气动弹性模型风洞试验结果进行了比较。结果表明计算得到的结果与气动弹性模型试验结果吻合较好。     

Reliability analysis of composite wing subjected to gust loads

An aerospace vehicle in atmospheric flight can be exposed to random air turbulence which may cause critical structural failure. Especially, for high aspect ratio wing, the effect of gust becomes more significant and its response to random gust need to be analyzed precisely. In this paper, the reliability analysis is conducted for composite wing subject to gust loads. For this, the probability distribution function of bending moment from random gust is calculated by power spectral analysis and the material properties of composite skin are assumed to be normal random variables to consider uncertainty. With these distributions of random variables, the probability of failure of the wing structure is calculated by Monte Carlo simulation.     

基于高频天平测力试验的500kV单回路输电塔风致响应研究

基于高频测力天平风洞试验的结果,采用平稳激励下随机振动的模态叠加法,计算了典型500kV单回路酒杯型输电塔的风致响应。结果表明：输电塔结构顺风向和横风向脉动位移响应、加速度和基底弯矩值都较大,横风向响应值甚至大于顺风向。各个方向一阶振型在响应中起主导作用。位移阵风响应因子和基底弯矩响应因子随风向变化趋势相近,顺风向关键节点位移响应因子最大值不超过1.8,弯矩响应因子约为1.5。     

台风致窗户破坏时大跨度屋面风振响应研究

通过大跨度屋盖建筑刚性模型风洞试验和气动弹性模型风洞试验,得到屋面节点风压时程和加速度时程。采用试验所得的脉动风压时程数据利用有限元法对屋面进行风振瞬态响应分析得到了屋面位移和加速度响应,并与气动弹性模型风洞试验结果相比较,验证瞬态分析的正确性。详细阐述了台风致窗户破坏时大跨度屋盖结构的风振响应机理和特点,计算并比较了四周封闭和突然开孔两种情况的荷载风振系数和位移风振系数。这些结论为大跨度屋盖结构的抗风设计提供了指导和参考。     

A stochastic approach for modeling incident gust effects on flow quantities

The uncertainty in gust loads on a rigid, flat-plate airfoil at zero angle-of-attack due to imprecise knowledge of the gust parameters is quantified. The loads are computed using the unsteady vortex lattice model, which includes temporal variations in wake vorticity and the associated downwash on the airfoil. The non-intrusive formulation of the polynomial chaos expansion in terms of the multivariate Hermite polynomials is employed to quantify the uncertainty in the predicted unsteady lift. The expansion coefficients were estimated through Latin hypercube sampling of the parameters in the vertical and streamwise gust spectra. The first-order chaos expansion in terms of the uncertain spectral parameters was found to be sufficient for representing the stochastic aerodynamic lift, which was found to be most sensitive to imprecision in the standard deviation of the vertical component of the gust. These conclusions were found to be unaffected by ignoring the effects of gusts on the locations of the shed vortices in the airfoil’s wake.     

张拉式膜结构抗风设计

抗风设计一直是膜结构设计中的核心问题和难点问题。以Davenport提出的阵风荷载因子法为基础,结合张拉式膜结构的风振响应特点,提出一系列改进措施,初步建立了一种适用于张拉式膜结构抗风设计的实用化方法。采用随机模拟时程分析方法对几种典型形状的张拉式膜结构进行了较为系统的风致动力响应参数分析,总结了结构风振响应的规律。并在此基础上,依据提出的抗风设计方法给出了可供设计人员参考的风振系数取值。     

柱面网壳结构风致抖振响应研究

基于刚性模型风洞试验,在时域上对一柱面网壳结构进行风振响应计算,并细致分析了网壳结构在风荷载作用下的节点位移、单元应力、阵风响应因子和响应谱。结果表明,对于柱面网壳结构,受斜风作用时的工况为最不利工况,并且迎风侧端部的位移及单元应力最大;多个高阶振型参与振动;共振响应一般不可忽略,但对于起控制作用的响应,背景分量的贡献大于共振分量。     

非线性振型结构HFFB试验模态力计算方法及不确定性分析

基于高频测力天平风洞试验对非线性振型结构的风致响应提出了改进的评估方法。假设结构风荷载沿高度的分布与阵风风压分布相同,采用结构真实振型计算风荷载模态力。推导了高耸结构风荷载模态力及风致响应计算公式,可以考虑结构多阶真实振型,从而使高频测力天平方法可更为准确地评估非线性振型结构的风致响应及等效静力风荷载。对某一质量、刚度有突变的高耸结构进行了高频测力天平风洞试验,与现有的线性化振型法进行对比,结果表明在弱非线性振型下,线性化振型法得到的加速度响应较层荷载假设方法偏大约40%。研究了层荷载分布的不确定性对计算加速度响应结果的影响,结果表明在阵风剖面层荷载的假设下,荷载分布的不确定性对结构最大加速度响应的影响很小,验证了本文方法的适用性。     

基于扭转强迫振动风洞试验的矩形截面高层建筑三维风荷载研究

为了研究扭转振动对高层建筑三维气动力的影响,利用扭转强迫振动装置,通过多点测压风洞试验测试了三个矩形截面高层建筑模型在不同试验风速和不同扭转振幅情况的表面风压时程。进而讨论了结构顺风向、横风向和扭转向均方根风力系数及功率谱的变化规律,研究结果表明：结构顺风向、横风向和扭转向均方根风力系数均随着试验风速和扭转振幅的变化而变化;结构顺风向阻力系数随着扭转振动振幅的变化主要是由于结构顺风向气动力的变化引起,而其横风向和扭转向风力系数随着扭转振动的变化包含了气动力变化与结构气动弹性效应两部分。对于高层建筑来说,应考虑扭转振动引起的结构三维气动力的变化以及结构横风向和扭转向气弹效应。     

输电杆塔阵风响应实测与准静态设计研究

为分析输电塔的动力特性和阵风响应因子的变化规律,在现场风荷载条件下,对作用于新建输电塔的脉动风速及其各部位加速度和基底动应变响应进行了同步实测。采用模态识别法和有限元法对输电塔的动力特性进行了对比分析;采用实测数据直接分析法和不同的准静态法分别计算了基于塔顶位移和基底弯矩的阵风响应因子。结果表明,实测数据的模态识别法与有限元法得到的输电塔动力特性相吻合,有限元数值分析正确有效;实测数据分析法与准静态法得到的阵风响应因子的变化规律相同,且与脉动风速的均值和湍流强度相关;基于弯矩的阵风响应因子吻合较好,各种方法的计算值相差在5%以内;基于实测位移的阵风响应因子与准静态法差异较大,其原因有待于进一步试验研究的检验与识别。     

Dynamic Response Analysis of Fuzzy Stochastic Truss Structures under Fuzzy Stochastic Excitation

A novel method (Fuzzy factor method) is presented, which is used in the dynamic response analysis of fuzzy stochastic truss structures under fuzzy stochastic step loads. Considering the fuzzy randomness of structural physical parameters, geometric dimensions and the amplitudes of step loads simultaneously, fuzzy stochastic dynamic response of the truss structures is developed using the mode superposition method and fuzzy factor method. The fuzzy numerical characteristics of dynamic response are then obtained by using the random variable’s moment method and the algebra synthesis method. The influences of the fuzzy randomness of structural physical parameters, geometric dimensions and step load on the fuzzy randomness of the dynamic response are demonstrated via an engineering example, and Monte-Carlo method is used to simulate this example, verifying the feasibility and validity of the modeling and method given in this paper.     

结构基频对冷却塔风振效应的影响

为明确结构基频f₀对冷却塔风振效应的影响,以某大型冷却塔为例,在风振响应时程计算和风振效应特征分析的基础上,通过调整材料弹性模量E实现对f₀的改变,以单独分析f₀对风振效应尤其是共振分量σ_R的影响,并阐述了该方法的优点。结果表明,根据共振与背景分量σ_R、σ_B在时域内的分离方法,不管f₀如何变化,σ_R与σ_B之间的耦合分量始终可以忽略。各响应σ_R随f₀的降低而增加,并在f₀小于0.7 Hz以后急剧增加,但因σ_B在总脉动响应σ_T中贡献较高,故σ_T和阵风响应因子GRF仅在f₀小于0.5 Hz以后才有较明显的增加。各响应σ_R随f₀的降低而增加的原因在于风谱能量随频率的降低而增加,且结构f₀越小其共振参与模态越多。为方便评价共振响应σ_R随f₀的变化,提出参数RP=（1/f₀×（1/f₀-1/2））综合考虑以上两种因素作为σ_R的评价指标,且各响应的σ_R与RP均呈线性变化。     

Alongwind dynamic effects on bluff bodies

The dynamic alongwind coefficient has been evaluated by means of a single-degree-of-freedom rectangular cylindrical model in a partial boundary layer wind tunnel. Experimental results show a tendency that the ratio of dynamic alongwind force coefficient to the static one is considerably greater than unity in a low reduced velocity range and increases when the reduced velocity decreases, while it converges to a fairly constant value less than unity when the reduced velocity increases. This tendency can be explained by pressure correlation effects. Although the turbulence intensity and scale were found to have a significant effect on the static coefficient value the ratio of dynamic to static coefficient appears to be insensitive to those turbulence parameters.     

Probabilistic 3-D turbulence modeling for gust buffeting of structures

Literature on turbulence modeling is rich in empirical, semi-empirical and theoretical spectral equations whose parameters assume deterministic values. Starting from a critical review of the state of the art, this paper proposes a unified model of atmospheric turbulence especially suited to determine the 3-D gust-excited response of structures. Unlike classical models, all parameters are assigned through first and second order statistical moments derived from a wide set of selected experimental measurements. A general discussion is also provided about model errors and other sources of randomness. Due to these properties the model proposed is suitable for carrying out reliability analyses which take into account the propagation of the uncertainties.     

大跨度屋盖结构等效静力风荷载背景分量的确定方法探讨

重点对结构等效静力风荷载背景分量的确定方法进行了系统分析。并结合风洞试验,分别采用阵风荷载因子法、风压轮廓面法和荷载响应相关系数法,分析一鞍形索网屋盖结构不同风向角、不同极值响应对应的等效静力风荷载背景分量,并与风洞试验方法确定的极值响应对应的瞬态脉动风压进行对比,结果表明荷载响应相关系数法在确定该类结构等效静力风荷载背景分量有很好的适用性,而其它几种方法计算偏差较大,这为大跨度屋盖结构等效静力风荷载的研究奠定了一定的基础。     

Gust severity effects on fatigue crack propagation in aluminium alloy sheet materials

Flight simulation fatigue tests were carried out on specimens of two aluminium alloys to investigate the effect of differing gust load experiences on fatigue crack propagation in 7075-T6 and the effect of gust load alleviation on 2024-T3. Two gust spectra were used: the Fokker F-27 spectrum for 7075-T6; and the reference spectrum TWIST for 2024-T3. There was a large systematic effect of gust severity on crack propagation rates in 7075-T6, and this effect correlated with the stress intensity factor for the root mean square of the gust amplitudes. Gust alleviation increased the crack initiation and total lives for 2024-T3, but decreased the crack propagation lives owing to a lessening of crack growth retardation following severe flights.     

Three-dimensional finite element for analysing thin plate/shell structures

A three-dimensional (3-D) hexahedron finite element is presented for the analysis of thin plate/shell structures. The element employs an explicit algebraic definition of six uniform (continuum) strains, six rigid body modes and classical Lagrange-Germain-Kirchhoff thin plate bending modes. Nine additional stiffness factors are used to control higher-order hourglass modes. The element may be used for plate/shell analyses where the flat plate assumptions are appropriate. Also it can easily be adapted to form transition elements to lower order 2-D elements, or to higher-order 3-D continuum elements. The stiffness matrix satisfies the geometric isotropy requirement, passes the patch test, and gives essentially identical response to either applied transverse corner forces or to twisting moments applied on the corner, a requirement of Kirchhoff's corner conditions for a classical thin plate. Several examples are presented to demonstrate the performance of this finite element.     

屋盖结构背景响应等效风荷载的一种简化算法

屋盖结构以非共振响应为主,因此适用于共振响应的阵风荷载因子法已不再适用,而LRC法由于具有计算繁琐、与响应位置和类型有关等不足而难于应用。提出以最大(小)升力为目标的荷载升力相关(LLC)法,分析其原理,并给出具体的计算步骤。当风压为全相关时,LLC法得到的等效风荷载即为屋面的脉动风压,因而LLC法将用于结构整体计算和围护结构计算的风荷载公式相统一。通过两个实例检验LLC法计算低层房屋屋盖结构等效风荷载时的合理性。     

拟负刚度与粘滞阻尼混合减振结构的动力特性与减振效果分析

对拟负刚度与粘滞阻尼混合减振结构的动力特性与减振效果进行了研究。首先,通过加速度放大系数和位移放大系数对拟负刚度与粘滞阻尼混合减振结构的动力特性进行分析。其次,通过反应谱对地震作用下拟负刚度与粘滞阻尼混合减振结构的减振效果进行分析,并与粘滞阻尼减振结构的减振效果进行比较。研究结果表明：拟负刚度控制能够延长结构的等效周期;当结构周期较长时,拟负刚度与粘滞阻尼混合减振结构对绝对加速度和相对位移的减振效果好于粘滞阻尼减振结构。