三种典型子午线型大型冷却塔风致响应分析

为研究大型双曲冷却塔不同子午线型对其在风荷载作用下强度和稳定的影响,根据某实际工程建立有限元模型,分析了不同子午线型对冷却塔动力特性的影响,比较了规范静风载荷作用下不同线型冷却塔塔筒和支柱风致响应的差异,探讨了线型变化对冷却塔稳定性的影响.结果表明:子午线型的优化在冷却塔结构设计中是十分必要的, "矮胖"型冷却塔基频更高,但其抗风承载性能和稳定性比"高瘦"型塔弱,风致内力和位移响应也较大.     

自然通风冷却塔的实验及有限元分析

本文以宁海电厂二期冷却塔为例简要介绍了冷却塔进行刚性模型及气弹模型试验的情况,用通用有限元软件ANSYS及专用冷却塔抗震分析软件LBSD进行冷却塔内力分析、稳定性分析、抗震分析,用刚性模型试验结果计算风振系数,并将计算结果与气弹模型试验的结果进行比较,所得结果对相关冷却塔设计与安全评估有重要工程意义.     

烟塔合一自然通风冷却塔的有限元分析

应用ANSYS有限元软件对浙江省拟建最高烟塔合一冷却塔的内力及线性稳定性进行了分析．计算表明,在72°风向角风压作用下在孔口附近产生局部屈曲,使临界风速急剧下降,而在孔口附近经局部加厚处理可消除局部屈曲现象．     

Nonlinear buckling analysis of hyperbolic cooling tower shell with ring-stiffeners

This paper is concerned with a numerical solution of hyperbolic cooling tower shell, a class of full nonlinear problems in solid mechanics of considerable interest in engineering applications. In this analysis, the post-buckling analysis of cooling tower shell with discrete fixed support and under the action of wind loads and dead load is studied. The influences of ring-stiffener on instability load are also discussed. In addition, a new solution procedure for nonlinear problems which is the combination of load increment iteration with modified R-C are- length method is suggested. Finally, some conclusions having important significance for practice engineering are given.The Project Supported by National Natural Science Foundation of China.     

加劲环和加劲肋对冷却塔动力特性的影响简

为提高冷却塔的自振频率和抗风性能,以某大型冷却塔为例,通过增设环向加劲环或子午向加劲肋,分析了各自的尺寸、位置、数量等参数对动力特性的影响. 冷却塔的动力特性主要受环向刚度控制,在适当的位置布置加劲环可以有效提高结构的频率,而子午向加劲肋则无此效果. 加劲环对结构频率的提高源自结构整体振型所激发的加劲环刚度参与程度,加劲环的模态变形幅值越大,环向谐波越多,其参与度就越高,对结构频率的提高效果也越明显. 实际应用中,可在塔筒中部等间距布置3~5 道加劲环,这样就可以使结构频率有显著提高.     

Stress analysis of hyperbolic shells of revolution with non-axisymmetrical geometric imperfections

In analyzing hyperbolic shells of revolution with non-axisymmeteric imperfections, an approximate method based on simulating the effect of imperfections by the application of fictitious normal pressure loading on the perfect shell is investigated. In the analysis of a shell of revolution with a bulge-type imperfection under non-axisymmetric loads, an efficient algorithm of applying the method is developed: the effect of individual curvature errors on stress resultants and couples are separately considered, while the interactions among various curvature errors are properly treated in the analysis by an iterative procedure. This algorithm avoids repeated analyses for non-axisymmetric loads and may be implemented with a purely axisymmetric analysis capability.A hyperbolic cooling tower shell with a bulge-type imperfection is analyzed under dead load and wind load conditions by the equivalent load method. A direct analysis of the imperfect shell is also made by a specialized finite element program. Through numerical studies, the accuracy and applicability of the equivalent load method are examined.     

基于立体打印自然通风冷却塔模型稳定性试验研究

为研究自然通风冷却塔在风载荷下的屈曲模式及临界风速,用立体打印技术打印了三个不同壁厚的缩尺模型,在风洞中完成了稳定性试验,并将实验结果与有限元计算结果进行对比分析.研究表明,模型失稳发生在弹性阶段,其壁厚与喉部半径之比是确定临界载荷的一个关键参数.实验得到的临界风压值同现有规范的设计相接近,约为有限元计算的1/4,说明我国现有规范中基于冷却塔整体稳定性得到的最小壁厚是偏保守的.     

大型冷却塔的风致振动响应数值分析

风荷载是大型冷却塔建筑设计的主要荷载之一,通过风振时域分析可以全面地了解塔身的风振响应特性。本文探讨了采用线性滤波法中的自回归模型(auto-regressive,AR)模拟大型冷却塔风致振动响应的数值方法。首先根据AR模型,基于随机模拟方法,计算冷却塔表面不同高度的随机脉动风压。通过将随机脉动风压和平均风压作为冷却塔表面的外载,采用有限元分析软件计算某冷却塔的风致振动响应。结果表明,基于随机脉动风荷载模拟的数值计算方法,能正确反映冷却塔塔身的风振响应。该方法特别适用于冷却塔高度超出规范要求的情况下,评估冷却塔的风振响应。     

基于压力迭代修正的大型冷却塔抗风性能分析

目前,大型冷却塔的抗风性能分析主要把得到的风压分布施加到结构上进行结构计算,没有考虑风载引起的结构变形对风压分布的影响,会产生较大的误差。本文结合计算流体力学与有限元分析的特点,建立了考虑结构变形影响的风压迭代修正模型,进行平均风压下大型冷却塔的抗风性能分析,并讨论了内部空气流动及淋水层的影响。计算结果与规范分析结果进...     

钢筋凝混土壳体的非线性分析

本文采用有限元数值方法,分析计算了大型钢筋混凝土壳的几何、物理非线性静力问题。对非线性方程组的求解,文中提出了一种将载荷增量和位移增量相结合的合理方法,保证了在临界点附近迭代法的收敛性。最后,文中通过对实际双曲冷却塔壳的分析,得到了一些对实际工程设计具有指导意义的有益结论。     

基于概率密度演化的输电塔-线体系抗风可靠性分析

以三线两塔直线段输电塔-线体系为工程对象,应用有限元数值模拟,建立了基于概率密度演化的输电塔-线体系抗风可靠性分析方法。首先,应用谱表示-降维方法模拟结构脉动风场,生成风荷载的代表性样本集合。然后,结合概率密度演化理论,分析了输电塔-线体系考虑气弹效应的随机动力反应。最后,应用等价极值思想构建了风荷载作用下输电塔-线体系失效准则,进而对输电塔-线体系的抗风可靠性进行精细化分析。本文结合谱表示-降维方法与概率密度演化理论,实现了仅用较少数量的代表性样本来精细地分析结构的抗风可靠性,为工程实践提供参考。     

Normal and typhoon wind loadings on a large cooling tower: A comparative study

Large cooling towers are sensitive to wind effects with their increasing heights and flexibilities. Unlike traditional approaches, which employed Code-defined normal winds to check the loading characteristics, this paper developed a framework for checking the typhoon-induced wind loading on a large cooling tower using Monte Carlo simulations and multi-fan wind tunnel tests. Some distinct characteristics of typhoon winds were compared with those of Code-defined normal winds. Furthermore, wind characteristics of incoming normal and typhoon winds in terms of vertical profile of mean wind speed, turbulence intensity, turbulence integral length scale and power spectrum density of fluctuating winds were well reproduced by a feedback control process of a multi-fan actively controlled wind tunnel. The surface wind pressure distributions of a large cooling tower under these conditions were then investigated by testing a 1:600 reduced scale model. Mean and fluctuating external wind pressures along the circumferential direction under various incoming winds were discussed and quantitatively formulated with eight-term trigonometric equations. Moreover, the cross correlations of wind pressures in the circumferential and meridian directions and correlations with structure base forces, i.e. integral drag and lift forces, were investigated. Non-Gaussian characteristics in terms of skewness and kurtosis of fluctuating wind pressures were also analyzed under two wind climates. Peak factors for modeling extreme wind pressures were examined and compared with those of various models. Finally, the extreme wind loads on a large cooling tower obtained from different wind pressure combinations were compared with peak-factor-theory-based results to identify an appropriate combination for structural design.     

ASYMPTOTIC ANALYSES OF DYNAMIC RESPONSE OF HYPERBOLIC COOLING TOWER SHELLS WITH RING-STIFFENERS—PERTURBATION FINITE ELEMENT SOLUTION

In this paper, a new analysing method called perturbational finite element is suggested, by means of which we calculate the dynamic behaviour and response to turbulent wind of hyperbolic cooling tower shell with ring-stiffeners. The results are compared with those of finite element numerical method and show that the method has the advantages of clear physical idea and convenience of calculation and the accuracy of results is assured. This paper was published in the second computational mechanics conference in Shanghai, China, Aug., 1986.     

一类梁系结构线性稳定性分析的简化处理

本文给出了旋转壳与支承支柱系统组合结构线性稳定性分析的简化处理方案,即将空间梁系结构每根梁的单元刚度阵及几何阵按离散富氏系数变量叠加得等效刚度阵及几何阵。从所给算例知,这一简化处理是成功的,也说明稳定性分析反映的是结构的总体效应,局部区域的简化处理对整体结构临界载荷影响不大,但可使计算量大大减少。本文的计算方案及程序已应用于实际的冷却塔设计。     

某电厂自然通风冷却塔塔群风载荷研究

自然通风冷却塔属高耸的薄壳结构,在风载荷作用下冷却塔顶部的位移可超 过壁厚的数倍,对风载荷极为敏感,特别是在塔群情况下,风速、风压分布和塔间气流十分复 杂. 根据某电厂不规则塔群风洞试验结果,提出塔群条件下自然通风冷却塔设计风荷 载取值的几点意见,可供工程参考.     

Dynamic analysis of wind turbine tower structures in complex ocean environment

Studying and analyzing the dynamic behavior of offshore wind turbines are of great importance to ensure the safety and improve the efficiency of such expensive equipments. In this work, a tapered beam model is proposed to investigate the dynamic response of an offshore wind turbine tower on the monopile foundation assembled with rotating blades in the complex ocean environment. Several environment factors like wind,wave, current, and soil resistance are taken into account. The proposed model is analytically solved with the Galerkin method. Based on the numerical results, the effects of various structure parameters including the taper angle, the height and thickness of the tower, the depth, and the diameter and the cement filler of the monopile on the fundamental natural frequency of the wind turbine tower system are investigated in detail. It is found that the fundamental natural frequency decreases with the increase in the taper angle and the height and thickness of the tower, and increases with the increase in the diameter of the monopile. Moreover, filling cement into the monopile can effectively improve the fundamental natural frequency of the wind turbine tower system, but there is a critical value of the amount of cement maximizing the property of the monopile. This research may be helpful in the design and safety evaluation of offshore wind turbines.     

Influence of axisymmetric dents in ribbed shells on minimum critical loads

The effect of axisymmetric dents in ribbed shells on the minimum critical loads is studied analytically. The upper and lower bounds for the critical stresses in imperfect cylindrical shells reinforced with stringers, rings, and both are estimated. The upper bounds are compared with those obtained from the known solutions for perfect ribbed momentless shells and with experimental data. The effect of the amplitude of initial dents and their number on the upper and lower bounds of critical stresses is examined. The procedure used is the most efficient to determine the load-bearing capacity of ring-reinforced and ribbed shells __________ Translated from Prikladnaya Mekhanika, Vol. 43, No. 5, pp. 73–79, May 2007.     

On Stability Analysis of Ribbed Cylindrical and Conical Shells under Axial Compressive Forces

An experimental study into the stability of ribbed cylindrical and conical shells is described. It is shown that when the equivalent rigidity introduced earlier is chosen as an argument in the formula for calculation of the critical stresses at the stage of shell design, this formula has the form of a linear function.     

Critical loads of shells with high-modulus reinforcement

The analytical method developed to determine the upper and lower critical stresses is applied to cylindrical shells reinforced with stringers and rings. Buckling modes typical of shells reinforced with discrete ribs are considered. The minimum critical loads are determined and compared with available experimental data. Perfect and imperfect ribbed shells with high-modulus reinforcement are studied. It is proved that the effect of small axisymmetric imperfections in such shells is not so drastic as in isotropic shells. Ribs made of a high-modulus material can enhance the stability of shells by a factor of tens     

Model equations for the Eiffel Tower profile: historical perspective and new results

Model equations for the shape of the Eiffel Tower are investigated. One model purported to be based on Eiffel's writing does not give a tower with the correct curvature. A second popular model not connected with Eiffel's writings provides a fair approximation to the tower's skyline profile of 29 contiguous panels. Reported here is a third model derived from Eiffel's concern about wind loads on the tower, as documented in his communication to the French Civil Engineering Society on 30 March 1885. The result is a nonlinear, integro-differential equation which is solved to yield an exponential tower profile. It is further verified that, as Eiffel wrote, “in reality the curve exterior of the tower reproduces, at a determined scale, the same curve of the moments produced by the wind”. An analysis of the actual tower profile shows that it is composed of two piecewise continuous exponentials with different growth rates. This is explained by specific safety factors for wind loading that Eiffel & Company incorporated in the design of the free-standing tower. To cite this article: P. Weidman, I. Pinelis, C. R. Mecanique 332 (2004).