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Wind Tunnel Study on Bidirectional Vibration Control of Lattice Towers with Omnidirectional Cantilever-Type Eddy Current TMD

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Wind Tunnel Study on Bidirectional Vibration Control of Lattice Towers with Omnidirectional Cantilever-Type Eddy Current TMD applied sciences Article Wind Tunnel Study on Bidirectional Vibration Control of Lattice Towers with Omnidirectional Cantilever-Type Eddy Current TMD Wenjuan Lou, Zuopeng Wen , Yong Chen * and Mingfeng Huang College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China * Correspondence: [email protected] Received: 13 June 2019; Accepted: 21 July 2019; Published: 25 July 2019 Abstract: An omnidirectional cantilever-type eddy current tuned mass damper (ECTMD) for lattice towers is introduced to suppress bidirectional vibration of lattice towers, in a form of a cantilever beam with a tip magnet mass. The damping of the ECTMD can be easily changed by tuning the amount of the current. A typhoon-fashion wind environment is simulated for the wind tunnel test. Test results show that there exists an optimal damping of the ECTMD along with an optimal frequency ratio. The scaled aeroelastic model is tested under various wind conditions, and a good effectiveness of ECTMD is observed. The wind directions, perpendicular and parallel to the cross-arm, are the most critical for the design of ECTMD, as the vibration mitigation in either of these two cases is relatively weaker. Finally, a simplified model is established for theoretical analysis in the frequency domain, whereby the variance responses of the tower with and without ECTMD are computed. The numerical results agree well with the experimental results, which corroborates the feasibility of using the proposed omnidirectional cantilever-type ECTMD in suppressing the vibrations of the tower in both along-wind and across-wind directions. Keywords: omnidirectional cantilever-type ECTMD; lattice tower; wind tunnel test; frequency domain analysis; bidirectional vibration control 1. Introduction Lattice towers are widely used for power transmission, telecommunication, wind turbine, and observation towers, etc. Tall lattice towers usually have relatively low natural frequencies and small damping ratios, which may result in large amplitude vibration under dynamic excitation such as wind loads [1,2]. The excessive vibration may diminish the serviceability of the towers, and cause fatigue damage, joint bolt looseness and even structural failure [3–7]. The lattice transmission tower employed in transmission line systems is an important type of lattice tower. Many collapse accidents happened to transmission towers under strong winds [8–10], as shown in Figure1. The failure of the tower may cause massive blackouts, which results in a lot of economic loss and secondary disasters. With rapid development of power industry, many high-voltage transmission towers with greater height and span were constructed, especially in China. For example, the world’s highest transmission tower currently is located at Zhoushan in China, with a height of 380 m. These tall transmission towers, which are prone to large vibrations, pose new challenges to engineering design. Hence, improving the performance of wind resistance to ensure the structural safety of the tower has become an important issue, and has attracted great attention. Appl. Sci. 2019, 9, 2978; doi:10.3390/app9152978 www.mdpi.com/journal/applsci Appl. Sci. 2019, 9, 2978 2 of 23 Appl. Sci. 2019, 9, x 2 of 23 Figure 1. Collapse of a transmission tower in China caused by wind loading.loading. There areare twotwo mainmain countermeasurescountermeasures to to improve improve the the wind wind resistance resistance of of lattice lattice towers. towers. The The first first is tois to increase increase structural structural sti stiffnessffness by by enlarging enlarging the the size size of of the the members members oror addingadding secondarysecondary members. However, this maymay significantlysignificantly increaseincrease thethe materialmaterial consumptionconsumption and thethe projectproject cost,cost, whichwhich compromises the advantage of of the the low low self-weight self-weight of of lattice lattice towers. towers. The The second second countermeasure countermeasure is to is toinstall install vibration vibration control control devices devices to suppress to suppress the the vibration. vibration. In this In this way, way, the thedynamic dynamic response response of the of theinternal internal forces forces of the of the members members can can be be mitigated. mitigated. Consequently, Consequently, small small size size members members can can meet thethe requirement,requirement, whichwhich meansmeans aa lowerlower cost.cost. Various typestypes of of control control devices devices installed installed on structures on structures were studied,were studied, such as such tuned as mass tuned dampers mass (TMD)dampers [11 (TMD)–19], tuned [11–19] liquid, tuned dampers liquid (TLD) dampers [20], (TLD) liquid [20], column liquid vibration column absorbers vibration (LCVA) absorbers [5], (LCVA) friction dampers[5], friction [21 dampers], etc. Among [21], theseetc. Among control these devices, control using devices, TMD in using tower TMD vibration in tower control vibration seems control to be a promisingseems to be solution a promising due tosolution its efficiency, due to convenienceits efficiency, and convenience low cost [and14]. low A TMD cost typically[14]. A TMD consists typically of a mass,consists a springof a mass, and a a damper. spring Theand controla damper. effectiveness The control of a TMDeffectiveness depends of on a itsTMD parameters, depends such on its as mass,parameters, frequency such and as dampingmass, frequency ratio. Hence, and damping it is of great ratio. significance Hence, it tois of obtain great the significance optimal parameters to obtain forthe theoptimal TMD [parameters15–17]. For TMDsfor the on TMD lattice [15–17]. towers underFor TMDs wind on loads, lattice theoretical towers orunder numerical wind studiesloads, ontheoretical it were conducted.or numerical Pelc studies and Kolator on it were [18] performed conducted. a threePelc and dimensional Kolator (3D)[18] performed finite element a three (FE) analysisdimensional of a truss-type(3D) finite telecommunicationelement (FE) analysis tower of a withtruss-type a TMD te installed,lecommunication and the TMDtower ewithffectiveness a TMD wasinstalled, found and to bethe favorable TMD effectiveness in case of was wind found load. to Tian be favorable and Zeng in [19 case] conducted of wind load. a parametric Tian and studyZeng of[19] tuned conducted mass dampersa parametric fora study long spanof tuned transmission mass dampers tower-line for a long system span under transmission wind load, tower-line and the influencesystem under of TMD wind parameters load, and the on TMDinfluence effectiveness of TMD parameters was presented. on TMD effectiveness was presented. Though the eeffectivenessffectiveness ofof TMD can be evaluated theoretically or numerically, windwind tunnel test isis stillstill anan importantimportant methodmethod forfor physicalphysical verification.verification. For high-rise structures under wind loads, the eeffectivenessffectiveness ofof TMDTMD waswas experimentallyexperimentally examinedexamined [[22–25],22–25], whereaswhereas thethe experimentalexperimental studiesstudies onon latticelattice towerstowers with with TMD TMD installed installed are are scarce scarce [26 [26].]. Xu Xu et al.et [al.23 ][23] studied studied the along-windthe along-wind and across-windand across- performancewind performance of a TMD-installed of a TMD-installed building building under di unfferentder different wind speeds wind and speeds wind and directions, wind directions, and their resultsand their clearly results show clearly the eshowffectiveness the effectiveness of the TMD. of the Wang TMD. et al. Wang [26] performedet al. [26] performed wind tunnel wind tests tunnel for a transmissiontests for a transmission tower-line tower-line system with system TMDs with installed, TMDs and installed, the control and etheffectiveness control effectiveness in either along-wind in either oralong-wind across-wind or direction across-wind was favorable direction under was difavofferentrable wind under speeds. different In these wind experiments speeds. [22 In–26 these], the eexperimentsffectiveness of[22–26], TMD wasthe merelyeffectiveness verified of with TMD a limitedwas merely number verified of TMD with parameters, a limited asnumber the adjustment of TMD ofparameters, TMD parameters as the adjustment was inconvenient. of TMD The paramete optimalrs frequency was inconvenient. and damping The parametersoptimal frequency of the TMDs and aredamping thus hard parameters to obtain of experimentally. the TMDs are thus hard to obtain experimentally. For robustness, the vibration control device installed on a lattice tower needs to be capablecapable of controlling thethe vibration vibration of of the the structure structure under under diff erentdifferent wind wind directions. directions. In addition, In addition, the device the device needs toneeds mitigate to mitigate the along-wind the along-wind response response and across-wind and across-wind response response of the tower of the simultaneously. tower simultaneously. Hence, it isHence, of great it is significance of great significance to design an to omnidirectional design an omnidirectional device that is device able to that accommodate is able to diaccommodatefferent wind directionsdifferent wind and vibrationdirections directions. and vibration Eddy directions current tuned. Eddy mass current damper tuned (ECTMD) mass damper is a newly (ECTMD) developed is a andnewly promising developed device and forpromising vibration device
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