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CONTENTS
Volume 15, Number 4, July 2012
 

Abstract
This paper describes the development and calibration of a structural monitoring system installed in a 80 meters high steel wind tower supporting a 2.1 MW turbine Wind Class III IEC2a erected in the central part of Portugal. The several signals are measured at four different levels and include accelerations, strains on the tower wall and inside the connection bolts, inclinations and temperature. In order to correlate measurements with the wind velocity and direction and with the turbine operational parameters the corresponding signals are obtained directly from the turbine own monitoring system and are incorporated in the developed system. Results from the system calibration, the structural identification and the initial period of data acquisition are presented in this paper.

Key Words
Wind tower; steel; monitoring; wind loading; modal identification; stresses; dynamic response

Address
C. Rebelo, L. Simoes da Silva, R. Simoes and J. Henriques :
ISISE, Civil Engineering Department, University of Coimbra, Rua Luis Reis Santos, Coimbra, Portugal
M. Veljkovic :Lulea University of Technology, SE-97187 Lulea, Sweden

Abstract
This paper presents results from the structural monitoring of a steel wind tower characterized and presented in Part I of the paper. Monitoring period corresponds to about fifteen months of measurements. Results presented refer to stress distribution on shell and in bolts at different heights, stress fatigue spectra, section forces along height evaluated from the stress measurements and comparison with design forces, dynamic response in terms of accelerations, stresses, deflections and rotations.

Key Words
Wind tower; steel; monitoring; wind loading; fatigue; dynamic response

Address
C. Rebelo, R. Matos and L. Simoes da Silva : ISISE, Civil Engineering Department, University of Coimbra, Rua Luis Reis Santos, Coimbra, Portugal
M. Veljkovic,: Lulea University of Technology, SE-97187 Lulea, Sweden

Abstract
There have existed for a number of years good practice guidelines for the use of Computational Fluid Dynamics (CFD) in the field of wind engineering. As part of those guidelines, details are given for the size of flow domain that should be used around a building of height, H. For low-rise buildings, the domain sizes produced by following the guidelines are reasonable and produce results that are largely free from blockage effects. However, when high-rise or tall buildings are considered, the domain size based solely on the building height produces very large domains. A large domain, in most cases, leads to a large cell count, with many of the cells in the grid being used up in regions far from the building/wake region. This paper challenges this domain size guidance by looking at the effects of changing the domain size around a tall building. The RNG k-e turbulence model is used in a series of steady-state solutions where the only parameter varied is the domain size, with the mesh resolution in the building/wake region left unchanged. Comparisons between the velocity fields in the near-field of the building and pressure coefficients on the building are used to inform the assessment. The findings of the work for this case suggest that a domain of approximately 10% the volume of that suggested by the existing guidelines could be used with a loss in accuracy of less than 10%.

Key Words
tall buildings; CFD; domain

Address
J. Revuz: Ansys France, Montigny le Bretonneux, France
D.M. Hargreaves and J.S. Owen: Faculty of Engineering, The University of Nottingham, Nottingham, UK

Abstract
Thunderstorm downbursts are responsible for numerous structural failures around the world. The wind characteristics in thunderstorm downbursts containing vortex rings differ with those in \'traditional\' boundary layer winds (BLW). This paper initially performs an unsteady-state simulation of the flow structure in a downburst (modelled as a impinging jet with its diameter being Djet) using a computational fluid dynamics (CFD) method, and then analyses the pressure distribution on a solar updraft tower (SUT) in the downburst. The pressure field shows agreement with other previous studies. An additional pair of low-pressure region and high-pressure region is observed due to a second vortex ring, besides a foregoing pair caused by a primary vortex ring. The evolutions of pressure coefficients at five orientations of two representative heights of the SUT in the downburst with time are investigated. Results show that pressure distribution changes over a wide range when the vortices are close to the SUT. Furthermore, the fluctuations of external static pressure distribution for the SUT case 1 (i.e., radial distance from a location to jet center x=Djet) with height are more intense due to the down striking of the vortex flow compared to those for the SUT case 2 (x=2Djet). The static wind loads at heights z/H higher than 0.3 will be negligible when the vortex ring is far away from the SUT. The inverted wind load cases will occur when vortex is passing through the SUT except on the side faces. This can induce complex dynamic response of the SUT.

Key Words
wind pressure; solar updraft tower; thunderstorm downburst; vortex

Address
Xinping Zhou :Department of Mechanics, School of Civil Engineering and Mechanics, Huazhong University of Science
and Technology, Luoyu Road 1037, Wuhan, Hubei 430074, PR China, Technical Center, Maanshan Iron and Steel Co. Ltd., Maanshan, Anhui 243000, PR China
Fang Wang and Chi Liu : Department of Mechanics, School of Civil Engineering and Mechanics, Huazhong University of Science and Technology, Luoyu Road 1037, Wuhan, Hubei 430074, PR China

Abstract
This work discusses the wind stability requirements specified by UN Reg. 27 on emergency car warning triangles, which are of mandatory use in many countries. Wind tunnel experiments have been carried out in order to determine aerodynamic coefficients of commercial warning triangles and the friction coefficients between the triangle legs and an asphalt base that fulfils the roughness requirements stated by Reg. 27 for wind stability certification. The wind stability specifications for warning triangles are reviewed, compared with pressure field measurements and discussed. Results of wind tunnel tests and comparison with field measurements reported in the literature show that the requirements could be excessively conservative.

Key Words
warning triangles; drag coefficient; wind stability; UN regulations

Address
A. Scarabino : Laboratorio de Capa Limite y Fluidodinamica Ambiental, LaCLyFA, Universidad Nacional de La Plata,
Calle 116 e/ 47 y 48, 1900 La Plata, Argentina
J.S. Delnero and M. Camocardi: Laboratorio de Capa Limite y Fluidodinamica Ambiental, LaCLyFA, Universidad Nacional de La Plata, Calle 116 e/ 47 y 48, 1900 La Plata, Argentina
, Consejo Nacional de Investigaciones Cientificas y Tecnicas, Avda. Rivadavia 1917, CP C1033AAJ, Cdad. de Buenos Aires, Argentina


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