Field measurement and aeroelastic wind tunnel test of wind‐induced vibrations of lattice tower

Lattice towers are among the most vulnerable structures during typhoons. In this study, the wind engineering research field base near Shanghai Pudong International Airport was used to measure the mean wind speeds and directions at a height of 10 m, as well as the accelerations atop a 40‐m high lattice tower during Typhoons Neoguri and Nakri to investigate the characteristics of the near‐ground wind and the responses of the lattice tower. Moreover, an aeroelastic model of the lattice tower was generated by the discrete stiffness method. Using the wind tunnel test of the aeroelastic model, the root mean square accelerations of the tower were studied with different wind speeds and directions. The responses of the tower in the across‐wind direction were found always higher than those in the along‐wind direction, which meant the vortex shedding of each single cylinder had an impact on the responses of the tower in the across‐wind direction. The test results were compared with those of field measurements to evaluate the accuracy of the aeroelastic model, and the two were generally in a good agreement. Thus, the aeroelastic model could precisely simulate the dynamic characteristics of a prototypical lattice tower using the discrete stiffness method.     

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.     

Mitigation of wind‐induced motion of Milad Tower by tuned mass damper

With a height of 435 m, Milad Tower, situated in north‐west of Tehran, Iran, would be the fourth highest telecommunication tower of the world. This tower has the largest head structure among its counterparts. Preliminary studies demonstrate that the upper part of the tower has excessive wind‐induced acceleration‐related vibrations beyond human comfort limit during wind events. In this paper, the effectiveness of tuned mass damper (TMD) on the suppression of wind‐induced motion of Milad Tower is examined through mathematical analyses. The tower is modelled as a vertical linear cantilever beam, with 57 degrees of freedom. The fluctuating wind speed is assumed to be a stochastic process which is identified by an appropriate power spectral density function. Random vibration analyses were carried out to determine response statistics. The possible application of TMDs in suppressing wind‐induced motions of the tower was investigated, and a TMD was designed to be installed at the sky dome. The results clearly show that the designed TMD has a considerable influence on the suppression of the structural response of the tower below human comfort limits. The authors believe that Milad Tower can be considered as a benchmark control problem for television and telecommunication towers by the structural control community. Copyright © 2008 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‐induced internal pressure effect within a novel super‐large cylindrical–conical steel cooling tower

A cylindrical–conical steel cooling tower (SCT) is a new type of very large thin‐walled, flexible structure. This study focused on the wind loads on the internal and outer surfaces of this structure and its wind‐induced responses. First, using the computational fluid dynamics method, the numerical wind tunnel was conducted to simulate a 189‐m‐high cylindrical–conical SCT, Asia's highest cooling tower that is still under construction. This numerical method was validated by comparing the wind pressures across typical cross sections of the tower model's cylindrical and conical segments with known standard curves. Based on this, the features of the airflow around the typical cross sections and its wake were extracted, and the distribution of mean wind loads along the internal and outer surfaces of the cylindrical and conical sections was obtained. Then functions for estimating the internal and outer surfaces shape factors of the cylindrical and conical segments were obtained by fitting to the simulated data. Furthermore, finite element method was used to analyze the static wind‐induced response of the cylindrical–conical SCT under internal pressure, external pressure, or both internal and external pressure. The effect patterns of internal pressures on the wind‐induced responses of the main tube, stiffening trusses, and auxiliary trusses of the tower were derived from the analysis results. Main findings of the research can provide a reference for design of very large cylindrical–conical SCTs for wind resistance in the future.     

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.     

大型冷却塔表面脉动风压原型实测与分布准则

我国冷却塔规范风荷载条款仍源自20世纪80年代原型冷却塔（约90m高）实测资料,且仅规定了塔筒表面静态风压分布。事实上,超大型冷却塔（高度≥165m）风振问题与风荷载脉动作用关系更加密切,由此导致了冷却塔数学和物理试验模型雷诺数效应模拟准则的不完整性,难于准确再现冷却塔表面动态风荷载与来流条件、塔群组合状况等参数间的合理关系,已成为制约大型冷却塔抗风性能研究和结构设计的瓶颈。为此,采用全天候动态风压采集设备,对某电厂冷却塔（约166m高）进行通风筒表面动、静态风压长期现场观测,量化表面脉动压力与来流紊流度之间的影响关系,提出具有原创性的冷却塔超高雷诺数条件（Re≥6E7）脉动风压雷诺数效应模拟准则。     

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.     

配有高耸塔结构的大射电望远镜馈源支撑系统的风振分析

通过时域法分析配有高耸塔结构的大射电望远镜馈源支撑系统的风振响应。首先,由非线性静力分析确定结构初始静态参考位形和初应力;其次,模拟作用在悬索、馈源舱和高耸塔上的随机风荷;最后,对比分析考虑索塔和不考虑索塔两种情况下的馈源支撑系统50m模型的风响应。结果验证了高耸塔变形对舱体定位精度有一定的影响。     

Design optimization of wind turbine tower with lattice‐tubular hybrid structure using particle swarm algorithm

As the size of wind turbine grows, the cost of the commonest tubular structural system will also increase because of the increasing cost of transportation, assembly, erection and servicing. A lattice‐tubular hybrid structural system, which is composed of a four‐angle cross‐shaped lattice structure at the bottom and a tubular structure at the top, is proposed for large wind turbine systems. The welding processes can be totally avoided and the fatigue strengths effectively improved because all members can be assembled by bolts in site after cutting and drilling in the factory. The ultimate bearing capacities of combined cross‐shaped members subjected to axial compressions are obtained by a series of numerical analyses. The column curve of four‐angle‐combined cross‐shaped members is obtained by fitting numerical results with a piecewise function. The particle swarm optimization algorithm is adopted to optimize the shape and size of the lattice partition in this study. The constraints including stress, slenderness ratio and frequency are applied to find the minimum weight of the lattice partition in the hybrid tower. The optimal results show that the proposed structural system is feasible and can resolve the disadvantages of the traditional tubular system in the fabricating, mounting and transporting. Copyright © 2016 John Wiley & Sons, Ltd.     

Design optimization of steel–concrete hybrid wind turbine tower based on improved genetic algorithm

The steel–concrete hybrid wind turbine tower is characterized by the lower part of the traditional steel tubular tower replaced with the concrete segment. The lateral stiffness will be improved obviously, and then, the excessive vibration of the steel tower can be solved effectively. Based on the improved genetic algorithm, an optimization program is built to consider the influence of materials, labor, machinery, and transportation on the construction cost of a steel–concrete hybrid tower for a 2.0‐MW wind turbine with a hub height of 120 m, in which the initial height of the concrete segment is 32 m. During the optimization process, design requirements of relevant specifications and industry standards are used as the constraints. The optimization variables include the bottom and top diameters of the tower, the wall thickness of each segment, the height of the concrete segment, and the area of the prestressed steel strand. By comparing the results of construction cost and structural capacity before and after optimization, it can be found that the steel–concrete hybrid wind turbine tower after optimization has the better structural stiffness and lower construction cost. The proposed optimization program can meet the design requirements and significantly improve the economic performance of the tower.     

Das große Viadukt von Millau – Stahlbau und Montage mit hochfesten Feinkornbaustählen

The Millau Viaduct – Steel construction, fabrication and erection with high‐strength fine grain steel. 16^th of December 2004 the Millau Viaduct, a 2460 m long multi cable‐stayed bridge, was opened of traffic in the Southern part of the French Massif Centrale mountains. This bridge comprises 6 main spans of 342 m length respectively and two side spans of 204 m length respectively. The steel superstructure consists of an orthotropic box deck of 27.75 m width and a maximum height of 4.20 m aerodynamically optimised due to the enormous wind loads in the valley. The deck is fixed to the 7 steel pylons via 22 stay cables per pylon in a height of up to 270 m above the river Tarn. Thus this viaduct represents the highest bridge in world with a total height of 343 m, even more than the Eiffel Tower in Paris.     

Zum Trag‐ und Verformungsverhalten großformatiger geschoßhoher Sanierungs‐Dämmelemente unter statischer Mitwirkung der außenseitigen Putzdeckschicht

Load‐bearing capacity and deformation property of largesized heat‐insulating redevelopment elements by static participation of the outside rendering coat. Because the low heat insulation level of our old buildings (here: before 1982 erected buildings) on the one hand and the high share of old buildings relating to the total existing buildings on the other hand, the totality of the old buildings (about 77 % of the total existing buildings) uses about 95 % of the annually nationwide required heating energy [1], [2]. Today the heat‐insulating redevelopment of the outside walls of old buildings represents an important contribution to the energy saving, to the environmental protection and to the sustainable management with the restricted energy. Many existing buildings are apartment houses with more than 4 residential units and large facade surfaces with repetition factor. If homeowners interest about an effective heat‐insulating redevelopment, facts like time and expense, restrictions of occupancy during redevelopment and quality assurance are very important. A solution for this can be given by the application of prefabricated heat‐insulating elements. This elements should be large‐size as possible for reasons of rationalization and effectiveness. Because of the prefabrication and the application with only few fixing points, such large‐size elements must be self‐supporting. Besides aspects of architecture and design and physics relating to construction also structural aspects must be considerate. When using established surface materials, for example rendering, for prefabricated self‐supporting heat‐insulating redevelopment elements, new constructions were create, whose load‐bearing capacity, physical suitability, durability and serviceability must be guaranteed for the range of application.     

Wind tunnel test and field measurement study of wind effects on a 600‐m‐high super‐tall building

Ping An Finance Center with a height of 600 m and 118 storeys, located in Shenzhen, is currently the second tallest building in China. This paper presents a comprehensive study of wind effects on the supertall building through wind tunnel testing and field measurement. The wind‐induced loads and pressures on the skyscraper were measured by high‐frequency force balance technique and synchronous multipressure sensing system, respectively. In the wind tunnel study, a whole range of characteristic properties, including mean and r.m.s force coefficients, power spectral densities, coherences, correlations, and phase‐plane trajectories, wind‐induced displacement, and acceleration responses were presented and discussed. In addition, a field measurement study of the dynamic responses of Ping An Finance Center was conducted during a tropical cyclone, which aimed to verify the design assumptions and further the understanding of the dynamic properties and performance of the 600‐m‐high supertall building, including natural frequencies, damping ratios, and wind‐induced structural responses. Then, the serviceability of the skyscraper is assessed on the basis of the experimental results and field measurements. The outcomes of this combined model test and field measurement study are expected to be useful for the wind‐resistant design of future supertall buildings.     

Continuous monitoring of the dynamic behavior of a high‐rise telecommunications tower

This article describes the experimental evaluation of the dynamic effects induced by wind on a high‐rise telecommunications tower based on a permanent monitoring system. Monte da Virgem telecommunications tower is located near the city of Porto (Portugal), and its structure consists in a reinforced concrete shaft and a steel mast, with a total height of 177 m. The monitoring system includes accelerometers, anemometers, and a meteorological station, allowing the characterization of the maximum accelerations of the structure and wind regimes during a period of 6 months. The analysis of the results enabled identifying specific events, denominated as critical events, for which the dynamic response of the tower under wind actions appears significantly amplified due to wind aeroelastic instability phenomena in the steel mast. The automatic identification of the critical events was based on the application to the acceleration's records of an autoregressive model and estimation of its optimal order number based on a singular value decomposition. The results proved the robustness and efficiency of the proposed technique in identifying the number, duration, and maximum amplitude of accelerations associated to the critical events, envisaging its potential integration in structural health monitoring systems.     

Wind field simulation of large horizontal‐axis wind turbine system under different operating conditions

This paper proposes a technique of generating turbulent wind velocities on large horizontal‐axis wind turbine systems under different operating conditions. The rotational sampling effect, vertical wind shear and coherence between wind velocities at blades and on the tower were taken into account. Coordinate system of wind time series at certain discrete sampling points on the vertical plane of the wind turbine is generated by the hybrid weighted amplitude wave superposition and proper orthogonal decomposition (POD) methods. The POD eigenmodes on the blades after updating locations were calculated subsequently using B‐spline surface interpolation method, and the rotationally sampled wind velocities are reconstructed by taking advantage of POD method again. Examples are subsequently presented to validate this proposed technique and demonstrate the generation of wind velocities under different operating conditions. The results show that the simulated spectrum of turbulent wind velocities at blades corresponds well to the measured data and that on the tower agrees well with the fixed point Kaimal spectrum. The reasonable sampling points spacing is suggested to be about 10 m for the wind field simulation of wind turbine system. The proposed method is of great advantage in accuracy and efficiency, which is greatly significant for the fine analysis of multi‐megawatt wind turbines. Copyright © 2015 John Wiley & Sons, Ltd.     

Tragstruktur und Installation der Offshore‐Windenergieanlage Repower 5M

Design, fabrication and installation of the offshore wind turbine REpower5M. In summer 2006 the first 5 MW offshore wind turbine has been installed in 45 m water depth in Scotland. The large water depth and other difficult site conditions, like harsh wave climate and unfavourable soil conditions, made numerous innovations for the support structures and installation necessary. This paper describes design, fabrication and installation of the jacket structures which have been developed. Furthermore the installation methodology for the turbine for which a floating crane instead of a fixed platform was used, is described. The knowledge gained from this project will enable realization of offshore windfarms in water depth beyond 20 m.     

Schädigungsberechnung an einem Spannbetonschaft für eine Windenergieanlage unter mehrstufiger Ermüdung

Damage calculation at a prestressed concrete tower for a Wind Energy Converter subjected to multi‐stage fatigue loading The application of a linear damage accumulation law devised by Palmgren and Miner for dimensioning constructions of Wind Energy Converters could lead to very unsafe or uneconomical calculation results. The real high non‐linear fatigue behaviour of concrete is not considered sufficiently by a simplified linear damage model. Additionally effects of different orders of load cycles to the resulting fatigue life are not represented as well. Based on a mechanical damage model available in literature a proceeding is established to determine the stiffness and damage evolution in concrete under multi‐stage fatigue loading. This extended damage approach is associated with the elastic‐plastic material model for concrete providing in the FE‐Program ABAQUS and subsequently a numerical investigation at a prestressed concrete tower for a multi‐megawatt wind turbine is performed. The results of the numerical simulation indicate obviously the influence of the order of load cycles to the fatigue life and that due to alterations of stress distributions a significant lower fatigue damage state occurs compared with calculation results without stress alterations.     

Study on wind characteristics of a strong typhoon in near‐ground boundary layer

In order to solve the problems existing in predicting typhoon design wind speeds used for tall and special buildings, a 40‐m‐high meteorological tower, which is located near the coast of the East China Sea in Shanghai, was built to observe the strong winds. Based on the measurement data during Typhoon Muifa (2011), the characteristics of strong wind such as wind speeds and directions, turbulence integral scales, probability densities, power spectra, spatial correlation coefficients, and coherence coefficients were analyzed. The results revealed that the turbulence integral scales increased with height and averaging time interval. All three fluctuating wind components follow the Gaussian distribution, regardless of the measurement height and the time interval of the segment. The power spectra of longitudinal fluctuating wind velocity agreed with the von Karman spectrum. However, the power spectra of lateral and vertical fluctuating wind velocity are deviated from the von Karman model in high‐frequency region. The decay rate of the autocorrelation coefficients of the longitudinal and lateral fluctuating wind velocity decreased with height. The variations of cross‐correlation coefficients among three fluctuating wind display no clear regulation. The spatial cohesion coefficients follow the predictions made according to Davenport's empirical formula.     

Parametric study of the use and optimization of tuned mass dampers to control the wind‐ and seismic‐induced responses of a slender monument

Passive energy dissipation devices have been used around the world to mitigate the response of structures under dynamic excitations, such as wind or seismic loading. The use of tuned mass dampers (TMD) in tall and slender buildings to reduce unwanted responses has proved to be very effective. The main purpose of this work is to study the structural behavior of a 115‐m‐height slender monument fitted with TMDs subjected to simulated wind and seismic loading. Turbulent wind forces were calculated based on samples of turbulent wind speed simulated with an auto regressive and moving average (ARMA) model. Ground motions compatible with a seismic site spectrum were also simulated. An optimization approach is suggested to determine the parameters of the TMDs that reduce the structural response to the maximum. The effectiveness of the TMDs for reducing the structural response of the monument is discussed in detail, and the use of optimally tuned TMDs is emphasized.