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CONTENTS
Volume 18, Number 5, May 2014
 

Abstract
Localized wind events, in the form of tornadoes and downbursts, are the main cause of the large number of failure incidents of electrical transmission line structures worldwide. In this study, a numerical model has been developed to study the behaviour of self-supported transmission lines under various tornado events. The tornado wind fields used were based on a full three-dimensional computational fluid dynamics analysis that was developed in an earlier study. A three-dimensional finite element model of an existing self-supported transmission line was developed. The tornado velocity wind fields were then used to predict the forces applied to the modelled transmission line system. A comprehensive parametric study was performed in order to assess the effects of the location of the tornado relative to the transmission line under F2 and F4 tornado wind fields. The study was used to identify critical tornado configurations which can be used when designing transmission line systems. The results were used to assess the sensitivity of the members\' axial forces to changes in the location of the tornado relative to the transmission line. The results were then used to explain the behaviour of the transmission line when subjected to the identified critical tornado configurations.

Key Words
transmission tower; transmission line; tornado; wind; high intensity wind; finite element

Address
A. Altalmas : AMEC plc, Alberta, Canada
A.A. El Damatty : Department of Civil and Environmental Engineering, Western University, London, Ontario, Canada

Abstract
Seismic and wind load performances of buildings are commonly improved by using bracing systems. In practice, standard bracing systems, such as X, Y, V, and K types are used. To determine the appropriate bracing type, the designer uses trial & error method among the standard bracings to obtain better results. However, using topology optimization yields more efficient bracing systems or new bracing can be developed depending on building and loading types. Determination of optimum bracing type for minimum deformation on a building under the effect of wind load is given in this study. A new bracing system is developed by using topology optimization. Element removal method is used to determine and remove the comparatively inefficient materials. Optimized bracing is compared with proposed bracing types available in the related literature. Maximum deformation value of building is used as performance indicator to compare effectiveness of different bracings to resist wind loads. The proposed bracing, yielded 99%, deformation reduction compared to the unbraced building.

Key Words
topology optimization; element removal; structural optimization; wind load; bracing

Address
M. Akif Kutuk and Ibrahim Gov: Department of Mechanical Engineering, University of Gaziantep, Gaziantep, Turkiye

Abstract
The characteristics of wake galloping phenomenon for two parallel/unparallel circular cylinders were investigated via wind tunnel tests. The two cylinders were initially deployed in parallel and wake galloping phenomena were observed by varying the center-to-center distance. The effect of an unparallel arrangement of two cylinders was next investigated by fixing the spacing ratio of one side of the cylinders at 5.0D and the other side at 3.0D, in which D represents the diameter of the cylinder. For the unparallel disposition, the 5.0D side showed a small, limited vibration while the 3.0D side produced much larger amplitude of vibration, resulting in a rolling motion. However, the overall amplitude appeared to decrease in unparallel disposition when compared with the amplitude of the 3.0D - 3.0D parallel case. This represents the mitigation effect of wake galloping due to the unparallel disposition between two cylinders. Flow visualization tests with particle image velocimetry were conducted to identify flow fields between two cylinders. The test results demonstrate the existence of a complex interaction of the downstream cylinder with the shear layer generated by the upstream cylinder. When the spacing ratio was large enough, the shear layer was not observed and the downstream cylinder showed only limited random vibration.

Key Words
flow visualization; particle image velocimetry (PIV); shear layer; stay cable; unparallel; wake galloping; wind tunnel test

Address
Sunjoong Kim and Ho-Kyung Kim : Department of Civil and Environmental Engineering, Seoul National University, Gwanak-ro, Gwanak-gu, Seoul 151-744, South Korea

Abstract
This article presents the unsteady aerodynamic performance of crosswind stability obtained numerically for the ATM train. Results of numerical investigations of airflow past a train under different yawing conditions are summarized. Variations of occurrence flow angle from parallel to normal with respect to the direction of forward train motion resulted in the development of different flow patterns. The numerical simulation addresses the ability to resolve the flow field around the train subjected to relatively large yaw angles with three-dimensional Reynolds-averaged Navier-Stokes equations (RANS). k-eturbulence model solved on a multi-block structured grid using a finite volume method. The massively separated flow for the higher yaw angles on the leeward side of the train justifies the use of RANS, where the results show good agreement with verification results. A method of solution is presented that can predict all aerodynamic coefficients and the wind characteristic curve at variety of angles at different speed.

Key Words
high speed train; aerodynamic performance; crosswind condition; numerical simulation

Address
Mohammad Ali Rezvani and Masoud Mohebbi : School of Railway Engineering, Iran University of Science and Technology,
Tehran, Iran, 16846-13114

Abstract
In spite of progress in the numerical simulation of typhoon wind field in atmospheric boundary layer (ABL), using typhoon wind field model in conjunction with Monte Carlo simulation method can only accurately evaluate typhoon wind field over a general terrain. This method is not enough for a reliable evaluation of typhoon wind field over the actual complex terrain with surface roughness and topography variations. To predict typhoon wind field over the actual complex terrain in ABL, a hybrid numerical simulation method combined typhoon simulation used the typhoon wind field model proposed by Meng et al. (1995) and CFD simulation in which the Reynolds averaged Navier-Stokes (RANS) equations and k-e turbulence model are used. Typhoon wind filed during typhoon Dujuan and Imbudo are simulated using the hybrid numerical simulation method, and compared with the results predicted by the typhoon wind field model and the wind field measurement data collected by Fugro Geotechnical Services (FGS) in Hong Kong at the bridge site from the field monitoring system of wind turbulence parameters (FMS-WTP) to validate the feasibility and accuracy of the hybrid numerical simulation method. The comparison demonstrates that the hybrid numerical simulation method gives more accurate prediction to typhoon wind speed and direction, because the effect of topography is taken into account in the hybrid numerical simulation method.

Key Words
typhoon wind field; complex terrain; CFD simulation; field measurement data; comparison

Address
Wenfeng Huang and Huanlin Zhou: School of Civil Engineering, Hefei University of Technology, Anhui, 230009, China

Abstract
In this paper, wind induced aerodynamic loads on a standard tall building have been evaluated through large-eddy simulation (LES) technique. The flow parameters of an open terrain were recorded from the downstream of an empty boundary layer wind tunnel (BLWT) and used to prescribe the transient inlet boundary of the LES simulations. Three different numerically generated inflow boundary conditions have been investigated to assess their suitability for LES. A high frequency pressure integration (HFPI) approach has been employed to obtain the wind load. A total of 280 pressure monitoring points have been systematically distributed on the surfaces of the LES model building. Similar BLWT experiments were also done to validate the numerical results. In addition, the effects of adjacent buildings were studied. Among the three wind field generation methods (synthetic, Simirnov\'s, and Lund\'s recycling method), LES with perturbation from the synthetic random flow approach showed better agreement with the BLWT data. In general, LES predicted peak wind loads comparable with the BLWT data, with a maximum difference of 15% and an average difference of 5%, for an isolated building case and however higher estimation errors were observed for cases where adjacent buildings were placed in the vicinity of the study building.

Key Words
LES; BLWT; inflow turbulence; wind force coefficients; power spectrum; tall building

Address
Agerneh K. Dagnew:Research and Modeling, AIR Worldwide, 131 Dartmouth Street, Boston, MA, USA
Girma T. Bitsuamlak: WindEEE Research Institute/Department of Civil and Environmental Engineering, University of Western Ontario in London, ON, Canada


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