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CONTENTS
Volume 25, Number 1, July 2017
 

Abstract
This paper presents a 1:25 multi-freedom aero-elastic model for a high lighting pole at the Zhoushan stadium. To validate the similarity characteristics of the model, a free vibration test was performed before the formal test. Beat phenomenon was found and eliminated by synthesis of vibration in the X and Y directions, and the damping ratio of the model was identified by the free decay method. The dynamic characteristics of the model were examined and compared with the real structure; the similarity results were favorable. From the test results, the major along-wind dynamic response was the first vibration component. The along-wind wind vibration coefficient was calculated by the China code and Eurocode. When the peak factor equaled 3.5, the coefficient calculated by the China code was close to the experimental result while Eurocode had a slight overestimation of the coefficient. The wind vibration coefficient during typhoon flow was analyzed, and a magnification factor was suggested in typhoon-prone areas. By analyzing the power spectrum of the dynamic cross-wind base shear force, it was found that a second-order vortex-excited resonance existed. The cross-wind response in the test was smaller than Eurocode estimation. The aerodynamic damping ratio was calculated by random decrement technique and the results showed that aerodynamic damping ratios were mostly positive at the design wind speed, which means that the wind-induced galloping phenomenon is predicted not to occur at design wind speeds.

Key Words
high lighting pole; aero-elastic model; wind tunnel experiment; high-rise structure; aerodynamic damping ratios

Address
Yaozhi Luo, Yucheng Wang, Jiming Xie, Chao Yang and Yanfeng Zheng: College of Civil Engineering and Architecture, Zhejiang University, 866# Yuhangtang Road, Hangzhou, Zhejiang, China


Abstract
This study investigates the dynamic analysis of a transversely isotropic thin plate. The plate is made of hyperelastic John\'s material and its constitutive law is obtained by taken the Frechect derivative of the highlighted energy function with respect to the geometry of deformation. The three-dimensional equation governing the motion of the plate is expressed in terms of first Piola-Kirchhoff\'s stress tensor. In the reduction to an equivalent two-dimensional plate equation, the obtained model generalizes the classical plate equation of motion. It is obtained that the plate under consideration exhibits harmonic force within its planes whereas this force varnishes in the classical plate model. The presence of harmonic forces within the planes of the considered plate increases the natural and resonance frequencies of the plate in free and forced vibrations respectively. Further, the parameter characterizing the transversely isotropic structure of the plate is observed to increase the plate flexural rigidity which in turn increases both the natural and resonance frequencies. Finally, this study reinforces the view that non-classical models of problems in elasticity provide ample opportunity to reveal important phenomena which classical models often fail to apprehend.

Key Words
dynamic analysis; thin plate; transversely isotropic

Address
Odunayo O. Fadodun, Olawanle P. Layeni and Adegbola P. Akinola: Department of Mathematics, Obafemi Awolowo University, Ile-Ife, 220005, Nigeria
Adebowale S. Borokinni: Distance Learning Institute, University of Lagos, Nigeria

Abstract
Buffeting induced resonance (BIR) of hangers on long-suspension bridges is briefly reviewed, including mechanism and experimental verification. Taken the Xihoumen suspension bridge as a numerical example, sensitivities of the BIR of hangers to wind properties are investigated, including types of wind spectrum, turbulence intensity, and spacial coherence of wind fluctuations. Numerical simulations indicate that the BIR of hangers occur to both cases of different wind spectra, showing that it is insensitive to types of wind spectrum. On the other hand, it is found that the turbulence intensity affects buffeting of main cables almost in a linear manner, and so it does to the BIR of the hangers; however, the resonance factors, namely the ratio of the response of the hanger to that of the main cable, are little affected by the turbulence intensity. The spacial coherence of the wind fluctuations, although plays an important role on the buffeting responses of the main structure, has no substantial effects on the BIR of the hangers. Finally, replacement of steel strand with CFRP material has been verified as a very effective countermeasure against the BIR of hangers.

Key Words
bridge; hanger; buffeting; resonance; wind property; countermeasure

Address
Zhitian Zhang: Wind Engineering Research Center, Hunan University, Changsha, 410082, China;
Hunan Provincial Key Laboratory for Wind Engineering and Bridge Engineering, Changsha, 410082, China
Weifeng Zhang: Wind Engineering Research Center, Hunan University, Changsha, 410082, China


Abstract
When railway vehicles run by towers of long span bridges, the railway vehicles might experience a sudden load-off and load-on phenomenon in crosswind conditions. To ensure the running safety of the railway vehicles and the running comfort of the passengers, some studies were carried out to investigate the impacts of sudden changes of aerodynamic loads on moving railway vehicles. In the present study, the aerodynamic coefficients which were measured in wind tunnel tests using a moving train model are converted into the aerodynamic coefficients in the actual scale. The three-component aerodynamic loads are calculated based on the aerodynamic coefficients with consideration of the vehicle movement. A three-dimensional railway vehicle model is set up using the multibody dynamic theory, and the aerodynamic loads are treated as the inputs of excitation varied with time for kinetic simulations of the railway vehicle. Thus the dynamic responses of the railway vehicle passing by the bridge tower can be obtained from the kinetic simulations in the time domain. The effects of the mean wind speeds and the rail track positions on the running performance of the railway vehicle are discussed. The three-component aerodynamic loads on the railway vehicle are found to experience significant sudden changes when the vehicle passes by the bridge tower. Correspondingly, such sudden changes of aerodynamic loads have a large impact on the dynamic performance of the running railway vehicle. The dynamic responses of the railway vehicle have great fluctuations and significant sudden changes, which is adverse to the running safety and comfort of the railway vehicle passing by the bridge tower in crosswind conditions.

Key Words
wind shielding effects of bridge tower; sudden changes of aerodynamic loads; crosswind condition; railway vehicle; running performance; multibody dynamic theory

Address
Mengxue Wu: School of Civil Engineering and Architecture, Southwest Petroleum University, Chengdu, Sichuan 610500, P.R. China
Yongle Li: Department of Bridge Engineering, Southwest Jiaotong University, Chengdu, Sichuan 610031, P.R. China
Wei Zhang: Department of Civil and Environmental Engineering, University of Connecticut, Storrs, CT 06269-3037, USA




Abstract
The use of wind energy resources is developing rapidly in recent decades. There is an increasing number of wind farms in high wind-velocity areas such as the Pacific Rim regions. Wind turbine towers are vulnerable to tropical cyclones and tower failures have been reported in an increasing number in these regions. Existing post-disaster failure case studies were mostly performed through forensic investigations and there are few numerical studies that address the collapse mode simulation of wind turbine towers under strong wind loads. In this paper, the wind-induced failure analysis of a conventional 65 m hub high 1.5-MW wind turbine was carried out by means of nonlinear response time-history analyses in a detailed finite element model of the structure. The wind loading was generated based on the wind field parameters adapted from the cyclone boundary layer flow. The analysis results indicate that this particular tower fails due to the formation of a full-section plastic hinge at locations that are consistent with those reported from field investigations, which suggests the validity of the proposed numerical analysis in the assessment of the performance of wind-farms under cyclonic winds. Furthermore, the numerical simulation allows to distinguish different failure stages before the dynamic collapse occurs in the proposed wind turbine tower, opening the door to future research on the control of these intermediate collapse phases.

Key Words
wind turbine tower; tropical cyclone; wind load; buckling analysis; structural collapse; failure mode

Address
Kaoshan Dai: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China;
Key Laboratory of Energy Engineering Safety and Disaster Mechanics, Ministry of Education (Sichuan University) Chengdu, China
Chao Sheng, Zhi Zhao, Zhengxiang Yi: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai, China
Alfredo Camara: Department of Civil Engineering, City University London, UK
Girma Bitsuamlak: Department of Civil and Environmental Engineering, University of Western Ontario, Canada




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