中空夹层钢管混凝土风力机塔架风振性能研究

传统风力发电机组塔架大多为锥形单管钢薄壁细长结构,此类结构在叶片转动及风荷载作用下易发生大的变形和振动。为克服传统风电塔自身发展的局限性并发挥中空夹层钢管混凝土(CFDST)结构优良的力学性能,基于某锥形钢塔筒,通过承载力等效提出CFDST塔筒结构形式,利用ABAQUS软件建立其风振性能有限元模型,对比了两种塔筒的振动模态。从时域和频域对二者在不同荷载工况下的动力响应特征进行对比分析,并对塔筒与叶片是否共振及瞬态冲击荷载下的振动进行了研究。结果表明:CFDST塔筒在保证原有钢塔筒抗弯承载力和刚度的同时,底部截面尺寸减小了25.6%,且不会与叶轮转动产生的谐波激励发生共振; 阻尼对风机塔筒位移、速度、加速度及应力响应幅值影响显著; 与钢塔筒相比,CFDST塔筒在正常运行荷载工况下峰值位移、加速度幅值和最大等效应力分别降低21.1%、30.2%和41.6%,而在暴风荷载工况下,分别减小14.4%、32.2%和36.3%; 研究成果可为相关塔筒的设计优化提供参考。     

Numerical Modeling of Dynamic Behavior of Annular Tuned Liquid Dampers for Applications in Wind Towers

Abstract: In this study, the performance of annular liquid tanks as a tuned liquid damper (TLD) in mitigating the vibration of wind turbines was investigated using a numerical model. A proposed hybrid wind tower model composed of a concrete shaft and a steel mast with a height of 150 m was simulated using a single‐degree‐of‐freedom system. The structural domain including the tank wall and a rigid mass was modeled using finite element method, while the fluid domain was simulated by finite volume method using CFX software. A parametric study was carried out to investigate the behavior of annular TLD under harmonic loads for different mass and frequency ratios as well as displacement amplitudes. The damping characteristics of the annular TLD model were derived by comparing the numerical results with an equivalent linear model. In addition, the effectiveness of annular TLD was estimated by comparing the numerically calculated damping ratios with those corresponding to the optimum damping ratio values derived for a particular mass ratio based on the concept of tuned mass damper. It was found that that the annular TLD is effective when the amplitude of excitation is small. Moreover, the response of TLD in terms of nonlinear free surface sloshing and the energy dissipated by the system was discussed. Finally, the effectiveness of annular TLD in reducing the structural response of wind turbine towers under random vibrations was evaluated and discussed.     

Comparison of wind‐induced dynamic property of super‐large cooling tower considering different four‐tower interferences

Dynamic amplification effects caused by tower‐group interference is the most critical causes of wind‐induced destructions of super‐large cooling tower (SLCT), and four‐tower combinations are the most common tower‐group combining form. However, the dynamic amplification effects of SLCT of different four‐tower arrangements have not been studied systematically so far. The highest (220 m) SLCT in the world was taken as the target to conduct SLCT wind pressure measurement under 320 wind tunnel test conditions. Firstly, the stability performance under the design wind loads was analyzed. Then, the dynamic time‐history analysis was carried out, and the distribution characteristics of peak factors and values of extreme response were discussed. Furthermore, with a new concept parameter “tower‐group wind vibration coefficient” for the wind‐resistance design of SLCT, the distribution laws of two‐dimensional (2D), one‐dimensional (1D), and global tower‐group wind vibration coefficient were revealed under different four‐tower interferences. On these bases, we recommend the design parameters for wind‐resistance study of SLCT and the priority of four‐tower combination forms. The study showed that the dynamic effects of SLCT under different four‐tower arrangements were significantly different from each other and the tower‐group wind vibration coefficients proposed in this paper can reflect the interference effects of tower‐group more efficient than traditional design method. The results may become a useful database for the wind‐resistance design of SLCT and provide clues for the optimization of four‐tower arrangements in power plants.     

Non‐Gaussian characteristics and extreme distribution of fluctuating wind pressures on large cylindrical–conical steel cooling towers

Large cylindrical–conical steel cooling tower (SCT) represents a new configuration of cooling tower, and its wind load distribution pattern and forming mechanism are very different from those of the traditional hyperbolic cooling towers. Large eddy simulation was used for the numerical simulation on a superlarge cylindrical–conical SCT that exceeds the specification limit, which is also the highest (189 m) SCT under construction in Asia. The surface flow field and time history of 3‐D aerodynamic force were obtained for the cylindrical and conical parts, respectively. Comparison with the measurements of other large cooling towers and the results of wind tunnel test confirmed the validity of the numerical simulation. Then, based on the probability density distribution and spatial correlation of representative measuring points, regions of non‐Gaussian distribution were identified. The forming mechanism of non‐Gaussian wind pressure distribution was revealed from the perspective of the correlation of non‐Gaussian distribution versus flow separation and eddy motion. The criteria for classifying the region of non‐Gaussian distribution for the cylindrical and conical parts were analyzed, respectively. Research shows that the wind pressures in the windward regions of conical and cylindrical parts obey Gaussian distribution; however, the wind pressures from the region of extreme negative pressure to the region of flow separation are largely non‐Gaussian and the wind pressures of the conical part are generally non‐Gaussian in the leeward region. Finally, the three algorithms for calculating the extreme values of wind pressure were used, namely, peak factor method, improved peak factor method, and Sadek–Simiu method. The distribution patterns of peak factors and extreme values of wind pressure in SCT towers were analyzed comparatively. The 2‐D formulae for fitting the extreme values of wind values for the cylindrical and conical parts were derived by nonlinear least square method. Moreover, strategy for value determination was also presented. The present research aimed to strengthen the understanding of the fluctuating wind pressure distribution and its forming mechanism for large cylindrical–conical SCT towers.     

应县木塔动力特性原位试验及有限元分析

为研究现有变形状态下应县木塔的动力特性,采用941B型传感器和INV3060S型采集仪对木塔各层明层柱头、柱脚东西方向和南北方向的脉动信号进行原位测试试验和数据采集.通过峰值拾取法与随机子空间法相结合的方式,分析得到了木塔前7阶的自振频率、振型及阻尼比.考虑到木塔的变形较为严重,利用大型有限元分析软件ANSYS建立损伤...     

Aerodynamic damping properties of two transmission towers estimated by combining several identification methods

Based on full-scale measurement data, we report on several aerodynamic damping properties of two transmission towers under conditions of strong winds. In estimating the damping ratio from data that contain many components of close frequencies of tower and conductor vibrations, we cannot estimate the damping ratio of each component if we use an estimation method available for only a single-degree-of-freedom system. Therefore, we combined several identification methods and are introducing a new method of estimating damping properties. This method is applicable to the response record of a multi-degree-of-freedom system such as the coupled structure of a transmission tower-and-conductors. Using the new estimation procedure, we were able to extract the component of every vibration mode of the towers from a measured time history and estimate the accurate damping ratios individually; and, our results revealed that the wind speed dependency of the aerodynamic damping property of the coupled tower-and-conductors system had wide differing characteristics depending on the vibration mode. Moreover, using a three-dimensional nonlinear analysis, we discuss, in detail, the effects of the progressive deformation of a transmission-conductor-plane due to an increase in wind speed on the development of the aerodynamic damping of the coupled tower-and-conductors system.     

随机地震激励下柔性连接双塔连体结构位移参数分析

以3-DOF力学模型推导了柔性连接双塔连体结构在随机地震激励下各位移传递函数和均方值,采用数值计算进行参数分析,变量包括连体与塔楼以及塔楼与塔楼的质量比,连体对塔楼的频率比,连体支座阻尼比.随机地震激励包括白噪声和金井清谱.对于对称塔楼结构,其基本规律和TMD结构相同,但为控制支座位移需采取不同于TMD结构的策略,即连体的固有频率需避开塔楼自振频率以免共振,且宜增加连体支座的阻尼比及连体对塔楼的质量比.对于不对称塔楼结构,双塔对连体部分异步驱动,连体在两支座约束下的固有频率需避开两个塔楼自振频率,并且可通过调整两支座刚度的比例使两支座的相对位移趋于均匀.     

Experimental study of across‐wind aerodynamic damping of super high‐rise buildings with aerodynamically modified square cross‐sections

Across‐wind aerodynamic damping ratios are determined from the wind‐induced acceleration responses of 10 aeroelastic models of square super high‐rise buildings in an urban flow condition (exposure category C in the Chinese code) using the random decrement technique. Moreover, the influences of amplitude‐dependent structural damping ratio on the estimation of aerodynamic damping ratio are discussed. The validity of estimated damping is examined through a comparison with previous research achievements. On the basis of the estimated results, the characteristics of the across‐wind aerodynamic damping ratios of modified square high‐rise buildings are studied. The effects of aerodynamically modified cross‐sections, such as chamfered, slotted and tapered cross‐section, on the across‐wind aerodynamic damping ratio are investigated. The results indicate that modifications of cross‐sections are not always effective in suppressing the aeroelastic effects of super high‐rise buildings. Low corner‐cut ratios (chamfer ratios from 5% to 20% and slot ratios from 5% to 10%) and low taper ratio (1%) significantly decrease the magnitudes of absolute aerodynamic damping ratios. However, large modifications of cross‐sections (slot ratio of 20% and taper ratios from 3% to 5%) increase wind‐induced responses by changing the aerodynamic damping ratios. According to the database, empirical aerodynamic damping function parameters are fitted for high‐rise buildings with aerodynamically modified square cross‐sections. Copyright © 2013 John Wiley & Sons, Ltd.     

基于配筋量准则的冷却塔结构抗风设计

通过风洞试验、结构有限元分析和结构配筋设计计算,对某八塔组合冷却塔工程进行系统分析,通过内力加权的方法整合荷载模式多样性的影响,提出以内力加权为准则的冷却塔结构安全评定准则。获得了冷却塔结构空间和时间尺度动态配筋及其包络配筋结果,并与现行规范基于单塔配筋结果进行对比。研究表明,风的脉动效应不可忽略,在配筋层面可以看出其影响不只存在于迎风面,对侧风面与背风面也有显著影响。群塔干扰对塔下部的影响大于对上部的影响,在冷却塔的设计中全塔选择统一的群塔干扰系数与风振系数是不合理的。     

基于分层壳单元模型超大型冷却塔风致倒塌机制与失效准则

历史上超大型冷却塔风毁事件多次发生,国内外现行规范中缺乏超大型冷却塔风致倒塌机制与失效判别准则。以我国西北地区某在建高228 m的冷却塔为背景,建立分层壳单元模型,考虑塔筒的多尺度壁厚及配筋率变化,通过刚体测压风洞试验获取了冷却塔表面风荷载,结合增量动力分析法分析了典型风速下塔筒位移和内力响应,确定临界倒塌风速为83 m/s;基于节点失效前后von Mises应力变化规律提炼了冷却塔倒塌过程中3种内力重分布机制,结合塔筒喉部位移构建了结构变形失效准则。研究表明：采用分层壳单元模型可以有效模拟超大型冷却塔倒塌全过程,中心破坏区域扩散形成裂隙网,直至完全倒塌破坏;塔筒首个单元失效首先引发滑动面机制,随后以转动铰机制和滑移面机制为主进行内力重分布;当结构变形失效指标(喉部迎风面与背风面的相对水平位移与喉部直径之比)不小于1.5%时,超大型冷却塔失效倒塌。     

Collapse mechanism and failure criteria based on layered shell element model for super-large cooling tower under wind action

历史上超大型冷却塔风毁事件多次发生，国内外现行规范中缺乏超大型冷却塔风致倒塌机制与失效判别准则。以我国西北地区某在建高228 m的冷却塔为背景，建立分层壳单元模型，考虑塔筒的多尺度壁厚及配筋率变化，通过刚体测压风洞试验获取了冷却塔表面风荷载，结合增量动力分析法分析了典型风速下塔筒位移和内力响应，确定临界倒塌风速为83 m/s；基于节点失效前后von Mises应力变化规律提炼了冷却塔倒塌过程中3种内力重分布机制，结合塔筒喉部位移构建了结构变形失效准则。研究表明：采用分层壳单元模型可以有效模拟超大型冷却塔倒塌全过程，中心破坏区域扩散形成裂隙网，直至完全倒塌破坏；塔筒首个单元失效首先引发滑动面机制，随后以转动铰机制和滑移面机制为主进行内力重分布；当结构变形失效指标(喉部迎风面与背风面的相对水平位移与喉部直径之比)不小于1.5%时，超大型冷却塔失效倒塌。     

地铁上盖层间隔震结构竖向地震响应

为了考察地铁上盖大底盘-层间隔震塔楼在竖向地震作用下的响应,对大底盘-层间隔震塔楼竖向振型的特点、周期和振型质量参与系数进行了分析。在设防烈度竖向地震作用下,通过振型分解反应谱法和时程分析法考察大底盘-层间隔震塔楼结构的基底剪力、隔震垫反力和转换梁内力,研究塔楼高度、隔震层竖向刚度等参数对大底盘-层间隔震塔楼竖向地震响应的影响。结果表明:大底盘-层间隔震塔楼结构存在塔楼竖向主振型,随着塔楼高度增高,竖向主振型的周期和振型质量参与系数逐渐加大; 在设防烈度竖向地震作用下,塔楼底部竖向地震力与重力荷载代表值之比(垂重比)的平均值为0.35,比非隔震塔楼平均增大4.6%; 隔震垫竖向地震反力与重力荷载代表值下反力之比(反力比)的平均值为0.30; 大底盘转换梁竖向地震下弯矩与重力荷载代表值下弯矩之比(弯矩比)的平均值为0.31; 随着塔楼高度增大,垂重比、隔震垫竖向反力比以及转换梁弯矩比均相应减小。     

Influence of soil‐structure interaction on performance of a super tall building using a new eddy‐current tuned mass damper

Tuned mass dampers (TMDs) can be used as vibration control devices to improve the vibration performance of high‐rise buildings. The Shanghai Tower (SHT) is a 632‐m high landmark building in China, featuring a new eddy‐current TMD. Special protective mechanisms have been adopted to prevent excessively large amplitude of the TMD under extreme wind or earthquake loading scenarios. This paper presents a methodology for simulating behavior of the new eddy‐current TMD that features displacement‐dependent damping behavior. The TMD model was built into the SHT finite element model to perform frequency analysis and detailed response analyses under wind and earthquake loads. Furthermore, soil‐structure interaction (SSI) effects on wind and seismic load responses of the SHT model were investigated, as SSI has a significant impact on the vibration performance of high‐rise buildings. It was found that SSI has more significant effects on acceleration response for wind loads with a short return period than for wind loads with a long return period. Some of the acceleration responses with SSI effects exceed design limits of human comfort for wind loads with shorter return periods. As to the seismic analyses, it was found that SSI slightly reduces the displacement amplitude, the damping force, and the impact force of the TMD.     

Improving the wind‐induced human comfort of the Beijing Olympic Tower by a double‐stage pendulum tuned mass damper

With five sub towers and a maximum height of 246.8 m, the Beijing Olympic Tower (BOT) is a landmark of Beijing. The complex structural properties and slenderness of the BOT render it prone to wind loading. As far as the wind‐induced performance of this structure is concerned, this paper thus aims at a tuned mass damper‐based mitigation system for controlling the wind‐induced acceleration response of the BOT. To this end, the three‐dimensional wind loading of various wind directions are simulated based on the fluctuating wind force obtained by the wind tunnel test, by which the wind‐induced vibration is evaluated in the time domain by using the finite element model. A double‐stage pendulum tuned mass damper (DPTMD), which is capable of controlling the long period dynamic response and requires only a limited space of installation, is optimally designed at the upper part of the tower. Finally, the wind‐induced response of the structure with and without DPTMD is compared with respect to various wind directions and in both the time and frequency domains. The comparative results show that the wind‐induced accelerations atop the tower with the wind directions of 45, 135, 225, and 315° are larger than those with the other directions. The DPTMD significantly reduces the wind‐induced response by the maximum acceleration reduction ratio of 30.05%. Moreover, it is revealed that the control effect varies noticeably for the five sub towers, depending on the connection rigidity between Tower1 and each sub tower.     

Estimation of damping ratio of TV towers based on ambient vibration monitoring

Damping ratio is an important component in the dynamic analysis and plays a key role in design of supertall buildings. It is necessary to have reliable field measurement records for estimation of structural dynamic characteristics. The main objective of this paper is to estimate eigen mode damping ratio of TV towers as a kind of supertall buildings with the height of more than 250 m. In this regard, field measurements were performed on Milad TV tower, located in Tehran, which has a height of 435 m by ambient vibration monitoring. Damping ratio of this tower is determined using random decrement technique and compared with available data of a few other TV towers. For proposing eigen mode damping ratio of TV towers, it is shown that Rayleigh damping coefficients could not be calibrated properly for tall slender TV towers. A damping estimation chart of TV tower that is a function of natural frequency and structural aspect ratio is proposed, and the chart validity has been checked with field measurement results of other TV towers. The chart shows that structural damping for wind analysis proposed in design codes and standards is overestimated for tall slender TV towers. Copyright © 2011 John Wiley & Sons, Ltd.     

Natural draft steel hyperbolic cooling towers: Optimization and performance evaluation

Demand for efficient and economical hyperbolic cooling towers has driven engineers toward designing tall and lightweight towers, specially, in regions with high‐seismic ground motions. An effective way to achieve this goal is using steel cooling towers. Also, by using tubular diagonal grid (Diagrid) system as the structural system, the weight of cooling tower will reduce, significantly. Therefore, in this investigation, a steel hyperbolic cooling tower is modeled with Diagrid system. A linear analysis, under dead and wind load, is performed on several systems with different angles of Diagrids to reach the optimal angle of grids. Furthermore, the effect of stiffening rings on the cooling tower is examined, and it is observed that the use of stiffening rings makes the tower lighter. And, by performing nonlinear time history and stability analyses, the behavior of the cooling tower is investigated under strong earthquakes, and it is represented that the system shows very good performance during strong earthquakes. Copyright © 2013 John Wiley & Sons, Ltd.     

Vorgespannte Betontürme für Windenergieanlagen: Einflüsse nichtlinearer Materialeigenschaften auf die Eigenfrequenzen als Entwurfskriterium

Pre‐stressed Concrete Towers for Wind Energy Turbines: Influences of non‐linear Material Properties on the Eigenfrequencies as a Design criterion The fast increase of the wind energy market in Germany promoted a dynamic development of wind turbine technology in the last decades. New concepts in the fields of construction, control and generation resulted in improved quality and efficiency of the wind turbines. With the growing rotor size and tower height new questions arise for the structural engineers and the building companies. In order to distribute the large forces at the tower‐head down to the soil and to balance the eigenfrequency of the structure with the excitation of the wind‐turbine, in general pre‐stressed concrete towers are necessary in case of tower heights beyond 100 m. The present paper will summarize the main design criteria for such towers and will explore the influences which are relevant for a reliable dynamic design.     

Wind field simulation and wind‐induced responses of large wind turbine tower‐blade coupled structure

Herein, by a case study on a 5‐MW wind turbine system developed by Nanjing University of Aeronautics and Astronautics, the wind field simulation and wind‐induced vibration characteristics of wind turbine tower‐blade coupled systems is analyzed. First, the blade‐nacelle‐tower‐basis integrated finite element model with centrifugal forces induced by rotational blades is established. Then, based on a harmony superposition method and the modified blade element‐momentum theory, the fluctuating wind field of tower‐blade coupled systems is simulated, which considers wind shear effect, tower shadow effect, rotational effect, blade‐tower dynamic and model interaction effects. Finally, the wind‐induced dynamic responses and wind vibration coefficients of the wind turbine tower‐blade coupled structure are discussed through the ‘consistent coupled method’ previously proposed by us. The results indicate that the wind‐induced responses of a large wind turbine tower‐blade coupled structure present complicated modal responses and multimode coupling effect. Additionally, the rotational effect would amplify aerodynamic loads on blades with high frequency, wind‐induced dynamic responses and wind vibration coefficients of wind turbine tower. The centrifugal force effect could also amplify natural vibration frequency of the tower‐blade coupled system and reduce the wind‐induced dynamic responses and wind vibration coefficients of wind turbine tower. The research could contribute to wind‐resistant design of structure for a large‐scale wind turbine tower‐blade system. Copyright © 2014 John Wiley & Sons, Ltd.     

基于ANSYS的大跨斜拉桥地震响应分析及性能评估

为研究西部高烈度地区大跨度斜拉桥的地震响应特点,以兰州市南绕城高速公路上一座跨径为177 m+360 m+177 m的结合梁斜拉桥为研究对象,利用有限元软件ANSYS建立其空间计算模型,分析了该桥的动力特性。运用非线性时程分析法计算桥梁结构在50年超越概率10%和2%两种地震水平作用下的地震响应,并以构件的能力需求比评估了该桥的抗震性能。结果表明:地震作用下主梁纵向振动与横向振动基本不耦合,其竖向位移受纵向地震作用影响较大;由于结构的非对称性,5#塔（南桥塔）的塔顶位移及塔底弯矩均大于4#塔（北桥塔）;在E1和E2两种水平地震作用下,各桥墩和桥塔关键截面以及斜拉索最小能力需求比均大于1,满足抗震性能要求;各桥墩纵桥向能力需求比小于横桥向,而桥塔纵桥向能力需求比大于横桥向,建议在过渡墩和辅助墩上安装减隔震装置,加强其纵桥向抗震性能。     

考虑百叶窗透风率超大型冷却塔内吸力风振系数研究

为研究不同百叶窗透风率下超大型冷却塔内吸力风振系数的分布特性和取值,以国内某在建210m高超大型冷却塔为工程背景,首先通过同步刚体测压风洞试验,得到了不同透风率（0%、15%、30%及100%）下冷却塔结构内表面平均与脉动风荷载。在此基础上,对比分析不同透风率平均和脉动风压分布特性,并采用有限元方法建立了塔筒-支柱-环基一体化仿真分析模型,对该超大型冷却塔进行四种内吸力作用工况下完全瞬态时域动力计算。对比了四种透风率下内吸力风振系数的一维、二维和三维分布特征,分析了以塔筒径向位移、子午向轴力、von Mises应力和环向弯矩四种典型目标响应下的风振系数取值标准,分别给出了此类超大型冷却塔不同透风率下内吸力风振系数的取值建议,即0%、15%、30%及100%透风率下内吸力风振系数分别取为1.69、1.79、1.69和1.57。