输电塔动力特性计算与模态试验研究

输电塔是国家电网的重要组成部分,具有结构高、跨度大、柔性强等特点,对风荷载反应灵敏。建立能反映输电塔动态特性的模型对风致振动控制至关重要。为研究输电塔理论模型的准确程度,分别建立3种输电塔实验模型,包括多质点模型、梁单元有限元模型和梁-杆混合单元有限元模型,并对其进行模态分析;同时采用锤击法,以单点激励多点响应(SIMO)的测试方法对输电塔实验模型进行模态测试。将各方案与测试结果进行比较分析,结果表明:梁-杆混合模型的求解精度高于另外两种计算模型的精度,能较好模拟输电塔的动力特性,是最优的输电塔模拟方案。     

Failure investigation of GFRP communication towers

The rapid growth in telecommunication system requires a large number of free-standing and guyed towers. Glass Fiber Reinforced Polymer (GFRP) material is corrosion resistant and light weight with specific gravity one-fourth of steel. In triangular based communication towers gusset plates can be avoided by using GFRP 60° angles for leg members. The failures encountered in the full-scale testing of a 24 m high triangular GFRP communication tower designed by the pultruded profile manufacturer purely based on the properties derived from tensile coupon test results is presented in this paper. The GFRP 60° angles as struts exhibited torsional-flexural buckling mode and the 90° angles failed by flexural buckling. ANSYS Shell 281 layered element used to model the GFRP struts predicted the failure loads closer to the experiments. The GFRP 60° angles as leg members have shown torsional-flexural buckling mode till failure but finally failed by de-bonding of layers in the case of angle sections made of stitched mat and by shearing of the cross section in angles with multi-axial technical fabrics. The 60° angles subjected to compression, exhibited higher strength at a component level compared to the leg member in tower restrained by secondary bracings. The strength and behaviour of GFRP angles with multi-axial technical fabrics (± 45°/90°) are superior compared to the angles with stitched mat.     

高压输电线路覆冰倒塔非线性屈曲分析

本文以湖南地区挂靖线220KV输电线路覆冰倒塔为例,按原工程资料建立精细化输电塔-线体系有限元模型。依据三峡地区覆冰资料建立覆冰增长曲线,考虑水平垂直档距、高差、不均匀覆冰和风荷载影响,对覆冰和风荷载作用下输电塔-线体系进行非线性屈曲分析,计算出覆冰荷载以及风荷载与覆冰共同作用下输电塔结构的极限承载能力,分析了倒塔的主要原因。研究表明,过载和不均匀覆冰引起的不平衡张力以及风荷载是倒塔的主要原因,重冰区覆冰架空输电线路技术设计规程的荷载水平需要进一步提高。     

Rubber covered rolls—the thermoviscoelastic problem. A finite element solution

The coupled thermomechanical behaviour of a layer of thermorheologically simple material bonded to a uniformly rotating rigid cylinder and indented by another rigid cylinder is studied by the finite element method. The various approximations necessary to reduce the problem to one of tractable size and the computational methods used are discussed in some detail. The complete thermal, deformation and stress fields may be computed. Some results, computed for a grid using ‘rectangular’ elements, presented graphically include the temperature distribution, the stress distribution near the bond surface, the contact pressure distribution and the asymmetric surface deformation of the rubberlike layer.     

超大型冷却塔风致倒塌全过程数值仿真与受力性能分析

历史上强风作用下大型冷却塔风毁事件多次发生,现有研究关注的重点大多为风致塔筒局部强度超限或失稳破坏,均忽略了由局部损坏引发的整体连续倒塌破坏的后续现象,且难以揭示大型冷却塔风致倒塌过程及作用机制。鉴于此,基于计算流体动力学（CFD）与显式动力分析算法（LS-DYNA）技术提出了大型冷却塔风致倒塌全过程数值仿真模拟方法,并以山西潞安电厂世界最高220 m超大型冷却塔为例,建立了考虑材料非线性塔筒-支柱三维有限元模型,并分析了结构动力特性;基于显示动力时程分析方法,加载基于CFD获得的塔筒三维平均风压进行拟动力分析,数值再现了超大型冷却塔风致倒塌全过程;研究了塔筒应力分布变化规律与倒塌全过程的扭曲变形姿态等特征,提炼出冷却塔风致倒塌的受力特点与作用机制,并讨论了单元失效参数的影响。结果验证了该文数值方法可以有效模拟超大型冷却塔风致倒塌全过程;其倒塌过程始于塔筒喉部迎风面大变形,并在两侧30°范围内呈现褶皱现象,最终因变形不协调而相互牵扯垮塌。研究表明,强风致超大型冷却塔倒塌受力机制可划分为弯拱机制与悬绞线机制,材料模型的单元失效参数对于超大型冷却塔风致倒塌的影响不可忽略。     

双曲冷却塔等效静力风荷载中国规范适应性研究

中国规范关于大型双曲冷却塔等效静力风荷载的条文仅适用于高度小于165m的冷却塔,在缺少系统研究的情况下,可借鉴国外规范的相关条文。首先,本文以单塔为例对德国规范等效静力风荷载计算公式进行适当变换,得到了与中国规范完全一致的表达形式,且公式中只有风振系数和平均风压分布系数取值有差异,对两国规范中上述二参数的取值进行了比较;然后,采用有限元计算方法,对3座不同高度的冷却塔在中、德规范等效静风荷载作用下的内力及变形分布进行计算分析,结果表明,即使对200m高的冷却塔,中国规范关于等效静力风荷载的条文规定也是适应的。     

基于向量式有限元的输电塔风致动力响应研究

该文以某大跨越格构式输电塔风致响应为例进行向量式有限元的应用分析,采用C++语言编写杆系结构向量式有限元的计算程序,获得输电塔的响应并与传统有限元结果进行比较,探讨阻尼处理方法和计算步长对计算结果的影响,最后针对输电塔进行风荷载作用下的倒塌分析。研究表明,两种方法算得的位移响应非常接近;向量式有限元法的计算效率比传统有限元高,该文算例中计算时间相差约20倍;计算步长对有限元计算结果有影响,建议计算时进行试算;向量式有限元可以用来求解输电塔的倒塌问题。     

大型塔式桁架组合结构分析的非经典能量法

本文针对工程上常见的各种塔式桁架系统组合结构的静力和动力分析,提出一种半连续半离散式基于非经典能变形理论的量法。文中,把整体桁架组合结构模拟成变截面的非经典梁,结构中任意结点的三向位移用其截面的四个广义位移(弯、剪、挤、拉)表示,由此导出每根杆件的两端位移,从而可仔细考虑每根杆件的应变、内力及相应的变形能、动能和外力功等。并由能量变分原理导出一组线性代数方程,方程阶次仅与所假定的四个广义位移试函数中待定系数的个数有关,与杆件数目,结点数目,层数等均无关,把大型塔架有限元分析的成百上千个自由度降为十几阶的数值计算问题,因此仅需求解阶次极低的代数方程组。同时,还可方便地考虑各种附加设施的影响。文中给出了实际电视塔结构和海洋平台导管架模型的静动力计算结果,并与其它方法计算结果和试验结果作了比较,表明本法是一种工程上较为通用有效的适于微机分析的简捷计算方法。本文方法也可称为非经典综合离散法,综合离散法     

超大型冷却塔风致干扰效应试验研究

设计加工了1:200缩尺比某超大型冷却塔气弹模型和刚体测压模型,对不同塔距双塔组合、四类典型工程场地单塔风振响应进行气弹模型测振风洞试验,比较了双塔塔距、来流方向角和流场条件对于冷却塔塔筒风振系数的影响;结合东南沿海某工程场地冷却塔群塔及周边建筑物组合形式,采用刚体模型测压试验和气弹模型测振试验比较了复杂场地条件多塔比例系数和风振系数,表明工程场地中与冷却塔同等尺寸其他建筑作为施扰物的重要影响。上述试验结论与我国冷却塔荷载规范进行了详细对比,指出现行规范在适用新建超大型冷却塔工程需要改进的方面。     

Dynamic Testing of Historic Towers Using an Interferometric Radar from an Unstable Measurement Position

Interferometric radar is a rather popular equipment able to remotely perform dynamic testing of large structures (towers, bridges, buildings?…) by detecting the relative displacement in the line of sight between the radar and geometric discontinuities in the engineering structure under test. This technique has been demonstrated effective when the radar is positioned at ground on a stable position. Unfortunately there are practical cases for which a suitable stable position is not available. This is the case of the towers of San Gimignano (Italy) that are embedded in the narrow streets of the old town. A solution to monitor the towers is to install the radar on the top of a tower, which is located in a central position of the town. The tower is not a stable arrangement for the radar and in this paper the authors propose and test the use of an accelerometer fixed to the radar head for detecting and removing its own movement.     

Discrete mesoscopic modeling for the simulation of woven-fabric reinforcement forming

A discrete modeling approach is proposed to simulate woven-fabric reinforcement forming via explicit finite element analysis. The tensile behaviour of the yarns is modeled by truss, beam or seatbelt elements, and the shearing behaviour of the fabric is incorporated within shell or membrane elements. This method is easy to set up using the user-defined material subroutine capabilities of explicit finite element programs. In addition, the determination of the material parameters is straightforward from conventional tensile and shear-frame tests. The proposed approach has been implemented in the ABAQUS and LS-DYNA explicit finite element programs. Two types of fabric, a plain-weave and a twill-weave Twintex® (commingled polypropylene and glass fibres) were characterized and used to validate the modeling approach. For this validation, shear-frame and bias-extension tests have been modeled, and the finite element results are compared to experimental data. The determination of experimental shear angle contours was possible via Digital Image Correlation (DIC). The finite element results from ABAQUS and LS-DYNA are similar and agree well with the experimental data. As an example of the capabilities of the method, the deep drawing of a hemisphere is simulated using both finite elements programs.     

风力机塔架在风-地震作用下的动力响应

为了获得水平轴风力机塔架在风-地震联合作用下的动力响应,首先推导了风力机塔架在风-地震联合作用下的动力学运动方程,并对塔架所受外部激励进行了详细的分析。通过对某3.0 MW风力机塔架动力响应进行计算,获得了风力机塔架在风-地震联合作用下的塔架顶部振动位移和塔架底部的载荷,分析了地震对塔架的影响程度,这些计算和分析对处于地震区域的风力机设计具有参考意义。     

模型表面粗糙度对冷却塔风荷载的影响

采用两种粗糙条数量和五种粗糙条厚度分析模型表面粗糙度对冷却塔风荷载的影响,应用本征正交分解法(POD)进行风压点的加密和重构,分析不同粗糙度下冷却塔的风压分布和总体受力,并将试验结果与规范、以往的实测和风洞试验结果进行比较.研究发现:冷却塔模型的表面越光滑,喉部附近B层测点最人负风压的绝对值越大;当模型表面粗糙条数量增...     

Static and dynamic characteristics of multi-cell jointed GFRP wind turbine towers

An extensive research project is currently being carried out at the University of Manitoba, Canada, involving the development of glass fiber-reinforced polymer (GFRP) wind turbine towers. The towers consist of multi-cell segments, each segment constructed from eight filament wound cells jointed together with resin applied over their interface. The present paper mainly addresses the static and dynamic characteristics, such as failure static loads, modes of failure, fundamental frequencies and periods of such segmented composite towers. Both experimental and numerical results are presented. The experimental investigation involved the testing of two jointed scaled towers. These specimens had a total height of 4.88-m (16-ft) and were tested as cantilevers under static and dynamic loading. The testing was conducted at the W.R. McQuade Structural Engineering Laboratory of the University of Manitoba. Finally, finite element models were developed to analyze the structural behavior, static and dynamic, of single and multi-cell composite segments and towers. The results from the finite element models under static loading were validated through comparison with the experimental results.     

Hybrid composites based on polyethylene and carbon fibres. Part 6: Tensile and fatigue behaviour

The tensile and fatigue behaviour of unidirectional carbon-high-performance polyethylene/epoxy hybrid composites has been studied, including the effect of hybrid design and surface treatment of the high-performance polyethylene (hp-pe) fibres. Results indicated that the tensile behaviour of carbon-hp-pe hybrids in both monotonic and fatigue testing can be interpreted, adopting the conventional ‘constant strain’ model for hybrid composites. Deviations from this constant strain model, so-called hybrid effects, were observed in monotonic tensile testing for those hybrid systems with the highest degree of fibre dispersion, incorporating either untreated or treated hp-pe fibres, whereas only the latter displayed synergistic fatigue performance. Hybrid effects under tensile loading conditions were in reasonable agreement with calculations accounting for statistical effects and stress concentrations as determined by finite element analyses.     

Reliability estimation by ALT when no analytical model holds

This paper presents an accelerated life testing method applicable to devices or systems when no analytical relationship with respect to the stress level can be defined. If a numerical approach remains possible, the numerical model can be fitted to the accelerated test results. Thus, long‐term failures can be predicted from short tests. This method is carried out in the case of fatigue, the evolution of the damage leading to the failure having to be modeled by a numerical finite element method. Copyright © 2010 John Wiley & Sons, Ltd.     

Numerical and experimental investigation of the strength of corrugated board packages

The buckling behaviour of corrugated paper packages was studied by means of an experimental and theoretical analysis. Mechanical behaviour of paperboard was first evaluated experimentally, then a local geometry FEM model, able to reproduce with a very good accuracy buckling loads obtained experimentally in the standard edge compression test, was developed. In order to investigate the buckling of a complete package, a finite element ‘corrugated board’ was introduced by means of a dedicated homogenization procedure. The FEM model of the package, assembled with this new element, can accurately predict the experimental data of incipient buckling observed during the standard box compression test, despite the few degrees of freedom and the minimal computational effort. Copyright © 2003 John Wiley & Sons, Ltd.     

Evaluation of ‘specia’ finite elements with non-conventional Gaussian quadratures

Finite elements with ‘Special’ basis functions have been proposed to develop better approximations for problems where the behaviour is known to be non-polynomial. This paper discusses extension of Gaussian quadrature integration procedures of non-conventional form to the evaluation of the finite element matrices for ‘Special’ elements. Algorithms for general ‘Special’ elements are discussed. The techniques are applied to ‘Special’ one- and two-dimensional elements for spherically symmetric potential flow. The accuracy of the new ‘Special’ element is shown to be superior to linear and quadratic elements for spherically symmetric potential flow problems.     

多高层建筑顶部塔楼的水平地震作用研究

研究了多、高层建筑顶部塔楼的水平地震作用,当采用底部剪力法简化计算时,对塔楼地震作用增大系数βn作了理论和计算分析,指出了βn的控制因素为主体结构基本周期T1、塔楼与主体的周期比Tn/T1和重力荷载比Gn/G,并对现行高层混凝土规范中的βn作了改进。分析中采用基于有限元理论的振型分解反应谱法建模计算,共计算了258种工况,根据这些结果给出了简化法中的修正系数βn值及实用表格,可供工程设计使用。     

环境激励下冷却塔结构模态测试与阻尼比特性研究

现行冷却塔结构阻尼比均借鉴荷载规范中钢筋混凝土的5%取值,考虑到冷却塔结构自身构型和材料属性,在理论上其真实阻尼比应小于规范值;阻尼比作为风与地震动力分析的重要输入参数,其取值大小将直接影响冷却塔抗风及抗震安全性,然而,现阶段国内外均缺乏大型冷却塔的现场实测和阻尼比取值研究。选取国内8座典型塔高和塔型的冷却塔进行现场测试,获取了环境激励下塔筒典型部位的加速度响应振动信号。首先采用随机减量法和自然激励技术对实测信号进行预处理,然后结合ARMA,ITD和STD三种模态识别方法获得冷却塔前10阶结构自振频率和阻尼比,并将实测值与有限元结果进行对比和误差分析,再借鉴振型组合的思路推荐了8座测试塔的等效综合阻尼比,最后给出了以基频为目标函数的前10阶模态阻尼比和等效综合阻尼比的估算公式。研究表明,8座冷却塔实测频率与有限元分析结果较为一致,基频最大相差为4.4%;阻尼比识别结果分布较为离散,前10阶模态阻尼比最大为2.86%;8座测试塔的综合等效阻尼比范围均在1.13%-2.16%,误差分析结果表明本文提出的阻尼比拟合公式精度高、稳定性好。