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CONTENTS
Volume 17, Number 6, December 2013
 

Abstract
Obvious vortex induced vibration (VIV) was observed during section model wind tunnel tests for a single main cable suspension bridge. An optimized section configuration was found for mitigating excessive amplitude of vibration which is much larger than the one prescribed by Chinese code. In order to verify the maximum amplitude of VIV for optimized girder, a full bridge aeroelastic model wind tunnel test was carried out. The differences between section and full aeroelastic model testing results were discussed. The maximum amplitude derived from section model tests was first interpreted into prototype with a linear VIV approach by considering partial or imperfect correlation of vortex-induced aerodynamic force along span based on Scanlan\'s semi-empirical linear model. A good consistency between section model and full bridge model was found only by considering the correlation of vortex-induced force along span.

Key Words
vortex-induced vibration (VIV); partial correlation; countermeasure; wind tunnel tests; section model; long span bridge

Address
Yanguo Sun, Mingshui Li and Haili Liao : Research Centre for Wind Engineering, Southwest Jiaotong University,
Chengdu, Sichuan 610031, China

Abstract
A model is proposed to analyse the along-wind dynamic response of upwind turbines with horizontal axis under service wind conditions. The model takes into account the dynamic coupling effect between rotor blades and supporting tower. The wind speed field is decomposed into a mean component, accounting for the well-known wind shear effect, and a fluctuating component, treated through a spectral approach. Accordingly, the so-called rotationally sampled spectra are introduced for the blades to account for the effect of their rotating motion. Wind forces acting on the rotor blades are calculated according to the blade element momentum model. The tower shadow effect is also included in the present model. Two examples of a large and medium size wind turbines are modelled, and their dynamic response is analysed and compared with the results of a conventional static analysis.

Key Words
along-wind dynamic response; blade element momentum model; coherent wind speed field; rotationally sampled spectrum; tower shadow effect; upwind horizontal axis wind turbine

Address
Andrea Spagnoli and Lorenzo Montanari :Department of Civil-Environmental Engineering and Architecture, University of Parma, Viale Usberti 181/A, 43124 Parma, Italy

Abstract
The Yingxian wooden tower in China is currently the tallest wooden tower in the world. It was built in 1056 AD and is 65.86 m high. Field measurements of wind speed and wind-induced response of this tower are conducted. The wind characteristics, including the average wind speed, wind direction, turbulence intensity, gust factor, turbulence integral length scale and velocity spectrum are investigated. The power spectral density and the root-mean-square wind-induced acceleration are analyzed. The structural modal parameters of this tower are identified with two different methods, including the Empirical Mode Decomposition (EMD) combined with the Random Decrement Technique (RDT) and Hilbert transform technique, and the stochastic subspace identification (SSI) method. Results show that strong wind is coming predominantly from the West-South of the tower which is in the same direction as the inclination of the structure. The Von Karman spectrum can describe the spectrum of wind speed well. Wind-induced torsional vibration obviously occurs in this tower. The natural frequencies identified by EMD, RDT and Hilbert Transform are close to those identified by SSI method , but there is obvious difference between the identified damping ratios for the first two modes.

Key Words
wooden tower; full-scale measurement; wind speed; wind-induced response; modal parameter

Address
Bo Chen, Qingshan Yang and Ke Wang : School of Civil Engineering, Beijing Jiaotong University, Haidian District, Beijing, China
Linan Wang : Chinese Academy of Cultural Heritage, Chaoyang District, Beijing, China

Abstract
One of the most common solutions adopted to reduce vibrations of skyscrapers due to wind or earthquake action is to add external damping devices to these structures, such as a TMD (Tuned Mass Damper) or TLCD (Tuned Liquid Column Damper). It is well known that a TLCD device introduces on the structure a nonlinear damping force whose effect decreases when the amplitude of its motion increases. The main objective of this paper is to describe a Hardware-in-the-Loop test able to validate the effectiveness of the TLCD by simulating the real behavior of a tower subjected to the combined action of wind and a TLCD, considering also the nonlinear effects associated with the damping device behavior. Within this test procedure a scaled TLCD physical model represents the hardware component while the building dynamics are reproduced using a numerical model based on a modal approach. Thanks to the Politecnico di Milano wind tunnel, wind forces acting on the building were calculated from the pressure distributions measured on a scale model. In addition, in the first part of the paper, a new method for evaluating the dissipating characteristics of a TLCD based on an energy approach is presented. This new methodology allows direct linking of the TLCD to be directly linked to the increased damping acting on the structure, facilitating the preliminary design of these devices.

Key Words
TLCD; Hardware in the Loop; passive damping system; experimental tests; tall building

Address
Giorgio Diana, Ferruccio Resta, Diego Sabato and Gisella Tomasini: Department of Mechanical Engineering, Politecnico di Milano Via La Masa 1, 20156 Milano, Italy

Abstract
The paper presents a numerical approach to study of fluid flow characteristics and to predict performance of wind turbines. The numerical model is based on Finite-volume method (FVM) discretization of unsteady Reynolds-averaged Navier- Stokes (URANS) equations. The movement of turbine blades is modeled using moving mesh technique. The turbulence is modeled using commonly used turbulence models: Renormalization Group (RNG) k-eturbulence model and the standard k-eand k-wturbulence models. The model is validated with the experimental data over a large range of tip-speed to wind ratio (TSR) and blade pitch angles. In order to demonstrate the use of numerical method as a tool for designing wind turbines, two dimensional (2-D) and three-dimensional (3-D) simulations are carried out to study the flow through a small scale Darrieus type H-rotor Vertical Axis Wind Turbine (VAWT). The flows predictions are used to determine the performance of the turbine. The turbine consists of 3- symmetrical NACA0022 blades. A number of simulations are performed for a range of approaching angles and wind speeds. This numerical study highlights the concerns with the self-starting capabilities of the present VAWT turbine. However results also indicate that self-starting capabilities of the turbine can be increased when the mounted angle of attack of the blades is increased. The 2-D simulations using the presented model can successfully be used at preliminary stage of turbine design to compare performance of the turbine for different design and operating parameters, whereas 3-D studies are preferred for the final design.

Key Words
wind turbine; turbulence models; vertical axis wind turbine (VAWT); computational fluid dynamics (CFD)

Address
Lazaros Aresti and Yong Chen : 1School of Engineering and Technology, University of Hertfordshire, Collage Lane Campus, Hatfield, Hertfordshire AL10 9AB, UK
Mustafa Tutar: Mechanical and Manufacturing Department, MGEP, Mondragon Goi Eskola Politeknikoa, Loramendi 4 Apartado 23, 20500, Mondragon, Spain;
IKERBASQUE, Basque Foundation for Science, 48011,Bilbao, Spain
Rajnish K. Calay : Narvik University College, Lodve Langes Gate 2, 8505-Narvik, Norway

Abstract
Static aeroelastic is investigated in a wind turbine blade. Imposed to different loadings, the very long and flexible structures of blades experience some changes in its preliminary geometry. This results in variations of aerodynamic loadings. An iterative approach is developed to study the interactions between structure and aerodynamics evaluating variations in induced stresses in presence of aeroelasticity phenomenon for a specific wind turbine blade. A 3D finite element model of the blade is constructed. Aerodynamic loading is applied to the model and deflected shape is extracted. Then, aerodynamic loadings are updated in accordance with the new geometry of the deflected blade. This process is repeated till the convergence is met. Different operational conditions consisting of stand-by, start-up, power production and normal shut-down events are investigated. It is revealed that stress components vary significantly in the event of power production at the rated wind speed; while it is less pronounced for the events of normal shut-down and stand-by.

Key Words
composites; aeroelasticity; wind turbine blade; simulation

Address
Roham Rafiee and Mahdi Fakoor : Faculty of New Sciences and Technologies, University of Tehran, End of North Karegar St., Tehran, 1439955941, Iran


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